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Store-operated CRAC channels: Function in health and disease
Abstract
Elevation of cytosolic Ca(2+) levels through the activation of store-operated Ca(2+) release-activated Ca(2+) (CRAC) channels is involved in mediating a disparate array of cellular responses. These include secretion, metabolism and gene expression, as well as cell growth and proliferation. Moreover, emerging evidence points to the involvement of aberrant CRAC channel activity in human diseases, such as certain types of immunodeficiency and autoimmunity disorders, allergy, and inflammatory bowel disease. This article summarizes recent advances in understanding the gating and function of CRAC channels, their links to human disease and key issues for the development of channel blockers.
... The ubiquitous second messenger Ca 2+ regulates various cellular behaviors. Store-operated Ca 2+ entry (SOCE) is vital for the maintenance of endoplasmic reticulum (ER) Ca 2+ stores at precise levels for signaling in both nonexcitable and excitable tissues to regulate a variety of cellular functions [31,32]. The molecular components of SOCE are Orai1 and STIM1 (stromal interaction molecule 1), a pore-forming subunit, and an ER Ca 2+ sensor, respectively. ...
... The molecular components of SOCE are Orai1 and STIM1 (stromal interaction molecule 1), a pore-forming subunit, and an ER Ca 2+ sensor, respectively. STIM1 is oligomerized and translocated to the plasma membrane during ER Ca 2+ depletion that thereby triggers Ca 2+ entry via Orai1, a Ca 2+ -selective channel at the plasma membrane [31,32]. SOCE is a downstream effector of growth factor signaling. ...
... SOCE is essential for the maintenance of ER Ca 2+ stores at a precise level for cellular signaling and functions [31,32]. Disturbed SOCE-mediated Ca 2+ signaling and homeostasis of Ca 2+ store have been implicated in the pathogenesis of multiple diseases [31]. ...
αKlotho is a type 1 transmembrane anti-aging protein. αKlotho-deficient mice have premature aging phenotypes and an imbalance of ion homeostasis including Ca²⁺ and phosphate. Soluble αKlotho is known to regulate multiple ion channels and growth factor-mediated phosphoinositide-3-kinase (PI3K) signaling. Store-operated Ca²⁺ entry (SOCE) mediated by pore-forming subunit Orai1 and ER Ca²⁺ sensor STIM1 is a ubiquitous Ca²⁺ influx mechanism and has been implicated in multiple diseases. However, it is currently unknown whether soluble αKlotho regulates Orai1-mediated SOCE via PI3K-dependent signaling. Among the Klotho family, αKlotho downregulates SOCE while βKlotho or γKlotho does not affect SOCE. Soluble αKlotho suppresses serum-stimulated SOCE and Ca²⁺ release-activated Ca²⁺ (CRAC) channel currents. Serum increases the cell-surface abundance of Orai1 via stimulating vesicular exocytosis of the channel. The serum-stimulated SOCE and cell-surface abundance of Orai1 are inhibited by the preincubation of αKlotho protein or PI3K inhibitors. Moreover, the inhibition of SOCE and cell-surface abundance of Orai1 by pretreatment of brefeldin A or tetanus toxin or PI3K inhibitors prevents further inhibition by αKlotho. Functionally, we further show that soluble αKlotho ameliorates serum-stimulated SOCE and cell migration in breast and lung cancer cells. These results demonstrate that soluble αKlotho downregulates SOCE by inhibiting PI3K-driven vesicular exocytosis of the Orai1 channel and contributes to the suppression of SOCE-mediated tumor cell migration.
... dominant role (Parekh, 2010). By knocking down the ORAI gene, we show that ORAI1 plays an essential role in the generation of sEV PD-L1. ...
... However, other types of extracellular vesicles might contribute to some of our findings. We would like to point out, though, that intracellular calcium is a universal second messenger regulating many cellular functions, such as metabolism and gene expression, as well as cell growth, proliferation and exocytosis (Berridge et al., 2003;Parekh, 2010). Exocytosis, as well as fusion between endosome-like organelles involves the merging of two membranes in an environment of very low calcium (μmolar). ...
Blockade of immune checkpoints as a strategy of cancer cells to overcome the immune response has received ample attention in cancer research recently. In particular, expression of PD‐L1 by various cancer cells has become a paradigm in this respect. Delivery of PD‐L1 to its site of action occurs either by local diffusion, or else by transport via small extracellular vesicles (sEVs, commonly referred to as exosomes). Many steps of sEVs formation, their packaging with PD‐L1 and their release into the extracellular space have been studied in detail. The likely dependence of release on Ca2+‐signaling, however, has received little attention. This is surprising, since the intracellular Ca2+‐concentration is known as a prominent regulator of many secretory processes. Here, we report on the roles of three Ca2+‐dependent proteins in regulating release of PD‐L1‐containing sEVs, as well as on the growth of tumors in mouse models. We show that sEVs release in cancer cell lines is Ca2+‐dependent and the knockdown of the gene coding the Ca2+‐channel protein ORAI1 reduces Ca2+‐signals and release of sEVs. Consequently, the T cell response is reinvigorated and tumor progression in mouse models is retarded. Furthermore, analysis of protein expression patterns in samples from human cancer tissue shows that the ORAI1 gene is significantly upregulated. Such upregulation is identified as an unfavorable prognostic factor for survival of patients with non‐small‐cell lung cancer. We show that reduced Ca2+‐signaling after knockdown of ORAI1 gene also compromises the activity of melanophilin and Synaptotagmin‐like protein 2, two proteins, which are important for correct localization of secretory organelles within cancer cells and their transport to sites of exocytosis. Thus, the Ca2+‐channel ORAI1 and Ca2+‐dependent proteins of the secretion pathway emerge as important targets for understanding and manipulating immune checkpoint blockade by PD‐L1.
... Exposure to allergens causes hypersensitivity of the immune system to release immunoglobulin E (IgE), which binds to a high-affinity IgE receptor (FcεRI) on mast cells and basophils [1]. This binding increases intracellular Ca 2+ level, resulting in cell degranulation, activation of the calcium/nuclear factor of activated T-cells (NFAT) pathway, and, eventually, the release of β-hexosaminidase, histamine, and a variety of inflammatory mediators [2]. Histamine has a key pathological function in many allergic diseases, including atopic dermatitis, allergic rhinitis, and urticaria due to activation of its distinct receptors [3]. ...
... Mast cell activation results in a decrease of intracellular Ca 2+ level. The depletion of intracellular Ca 2+ level leads to the entry of extracellular Ca 2+ and subsequently causes the fusion of preformed granules and plasma membrane [2]. In the present study, camucamu fruit extract played important roles in immediate allergic reactions and calciumdependent mast cell degranulation. ...
Although Myrciaria dubia (camu-camu) has been shown to exert anti-oxidant and anti-inflammatory effects in both in vitro and in vivo studies, its use in allergic responses has not been elucidated. In the present study, the anti-allergic effect of 70% ethanol camu-camu fruit extract was tested on calcium ionophore (A23187)-induced allergies in RBL-2H3 cells. The RBL-2H3 cells were induced with 100 nM A23187 for 6 h, followed by a 1 h camu-camu fruit extract treatment. A23187 sanitization exacerbated mast cell degranulation; however, camu-camu fruit extract decreased the release of histamine and β-hexosaminidase, which are considered as key biomarkers in cell degranulation. Camu-camu fruit extract inhibited cell exocytosis by regulating the calcium/nuclear factor of activated T cell (NFAT) signaling. By downregulating the activation of mitogen-activated protein kinase (MAPK) signaling, camu-camu fruit extract hindered the activation of both histamine H1 and H4 receptors and inhibited histidine decarboxylase (HDC) expression by mediating its transcription factors KLF4/SP1 and GATA2/MITF. In A23187-induced ROS overproduction, camu-camu fruit extract activated nuclear factor erythroid-2-related factor 2 (Nrf2) to protect mast cells against A23187-induced oxidative stress. These findings indicate that camu-camu fruit extract can be developed to act as a mast cell stabilizer and an anti-histamine. This work also “opens the door” to new investigations using natural products to achieve breakthroughs in allergic disorder treatment.
... The outputs of calcium responses vary with cell type and stimuli and depend on the intensity, duration, frequency and spatiotemporal characteristics of the Ca 2+ signals. Two major calcium entry pathways exist in non-excitable cells: (i) the store-operated calcium entry (SOCE) or capacitative Ca 2+ entry and (ii) a Ca 2+ store depletion-independent receptor occupation-dependent calcium entry pathway [4,5]. Calcium channels play key roles in cell homeostasis by ensuring a low cytoplasmic Ca 2+ concentration at resting conditions, but an increase of Ca 2+ levels in response to a variety of stressors can ignite cell proliferation, differentiation and death. ...
... Upon depletion of the ER Ca 2+ store, Stromal Interaction Molecule 1 (STIM1) forms oligomers at the ER membrane and then translocates to the plasma membrane to activate ORAI calcium release-activated calcium modulator 1 (ORAI1), the pore-forming subunit of SOC channels [8]. As a consequence, Ca 2+ entry is activated, ensuring the replenishment of ER Ca 2+ store through the stimulation of SERCA [4]. ...
Calcium ions (Ca2+) play important and diverse roles in the regulation of autophagy, cell death and differentiation. Here, we investigated the impact of Ca2+ in regulating acute promyelocytic leukemia (APL) cell fate in response to the anti-cancer agent all-trans retinoic acid (ATRA). We observed that ATRA promotes calcium entry through store-operated calcium (SOC) channels into acute promyelocytic leukemia (APL) cells. This response is associated with changes in the expression profiles of ORAI1 and STIM1, two proteins involved in SOC channels activation, as well as with a significant upregulation of several key proteins associated to calcium signaling. Moreover, ATRA treatment of APL cells led to a significant activation of calcium/calmodulin-dependent protein kinase kinase 2 (CAMKK2) and its downstream effector AMP-activated protein kinase (AMPK), linking Ca2+ signaling to autophagy. Pharmacological inhibition of SOC channels and CAMKK2 enhanced ATRA-induced cell differentiation and death. Altogether, our results unravel an ATRA-elicited signaling pathway that involves SOC channels/CAMKK2 activation, induction of autophagy, inhibition of cellular differentiation and suppression of cell death. We suggest that SOC channels and CAMKK2 may constitute novel drug targets for potentiating the anti-cancer effect of ATRA in APL patients.
... The CRAC current was discovered by Hoth and Penner (141) in mast cells and has since been intensely studied in several different cell types (139,140,142). The CRAC channels are extremely Ca 21 selective, can only carry monovalent ions in the absence of divalent ions, have a very low single-channel conductance, and display an inwardly rectifying current-voltage relationship (139,140). ...
... It should therefore be possible to treat all forms of AP by blocking or markedly reducing the opening of Orai1 channels. The proof of principle, showing that this approach could work, was first provided in 2013, in a study on isolated acinar cells or small clusters of acinar cells in which it was shown that GSK-7975A, an agent that had been shown to block Orai1 channels in some immune cells (142), could markedly reduce the sustained global [Ca 21 ] i elevation evoked by FAEEs as well as the subsequent intracellular protease activation and necrosis (40). Two years later, this was confirmed in a study that also showed that GSK-7975A could be successfully used in vivo to treat experimental AP induced in mice by FAs and ethanol, bile acids, or hyperstimulation of CCK receptors (215). ...
This review deals with the roles of calcium and ATP in the control of the normal functions of the different cell types in the exocrine pancreas as well as the roles of these molecules in the pathophysiology of Acute Pancreatitis. Repetitive rises in the local cytosolic calcium ion concentration in the apical part of the acinar cells do not only activate exocytosis but also, via an increase in the intra-mitochondrial calcium ion concentration, stimulate the ATP formation that is needed to fuel the energy-requiring secretion process. However, intracellular calcium overload, resulting in a global sustained elevation of the cytosolic calcium ion concentration, has the opposite effect of decreasing mitochondrial ATP production and this initiates processes that lead to the necrotic destruction of the cells. In the last few years it has become possible to image calcium signalling events simultaneously in acinar, stellate and immune cells in intact lobules of the exocrine pancreas. This has disclosed processes by which these cells interact with each other, particularly in relation to the initiation and development of Acute Pancreatitis. By unravelling the molecular mechanisms underlying this disease, several promising therapeutic intervention sites have been identified. This provides hope that we may soon be able to effectively treat this often fatal disease.
... Lastly, as stated above, TRPC1 and TRPC3 are involved in SOCE, although their precise roles remain to be clarified [45,82]. In mice, TRPC5 is suspected to mediate the regulatory T cell-induced decrease of effector T cell activity [45]. ...
... Lastly, TRPC channels are activated after G protein-coupled receptor or receptor tyrosine kinase stimulation, but are also involved in SOCE [42,82]. Like in T cells, their exact roles here need further clarification, but TRPC5 seems to associate with STIM1 and Orai1, forming Ca 2+ -permeable SOC channels [89]. ...
Purpose of Review
Despite their high prevalence, the pathophysiology of allergic rhinitis (AR) and chronic rhinosinusitis (CRS) remains unclear. Recently, transient receptor potential (TRP) cation channels emerged as important players in type 2 upper airway inflammatory disorders. In this review, we aim to discuss known and yet to be explored roles of TRP channels in the pathophysiology of AR and CRS with nasal polyps.
Recent Findings
TRP channels participate in a plethora of cellular functions and are expressed on T cells, mast cells, respiratory epithelial cells, and sensory neurons of the upper airways. In chronic upper airway inflammation, TRP vanilloid 1 is mostly studied in relation to nasal hyperreactivity. Several other TRP channels such as TRP vanilloid 4, TRP ankyrin 1, TRP melastatin channels, and TRP canonical channels also have important functions, rendering them potential targets for therapy.
Summary
The role of TRP channels in type 2 inflammatory upper airway diseases is steadily being uncovered and increasingly recognized. Modulation of TRP channels may offer therapeutic perspectives.
... Upon endogenous depletion of Ca 2þ stores, activated STIM family proteins oligomerize and migrate to endoplasmic reticulum (ER)-plasma membrane junction where they activate and recruit ORAI family proteins through direct interactions (8,10). Together, they form Ca 2þ release-activated Ca 2þ (CRAC) channels and promote store-operated Ca 2þ entry (SOCE), engaging Ca 2þ release from the extracellular space (11). Such Ca 2þ influx with resultant elevated intracellular Ca 2þ level has long been known as a key in cellular cycles, and altered expressions of ORAIs are believed to regulate tumor metastasis in different cancer types (9)(10)(11)(12). ...
... Together, they form Ca 2þ release-activated Ca 2þ (CRAC) channels and promote store-operated Ca 2þ entry (SOCE), engaging Ca 2þ release from the extracellular space (11). Such Ca 2þ influx with resultant elevated intracellular Ca 2þ level has long been known as a key in cellular cycles, and altered expressions of ORAIs are believed to regulate tumor metastasis in different cancer types (9)(10)(11)(12). Evidences have shown that abnormal activation of SOCE leads to tumor cell migration and cancer metastasis, and local Ca 2þ influx is essential for building front-to-rear Ca 2þ gradient, which serves to maintain the morphologic polarity required by migrating cells (13)(14)(15). ...
The ubiquitous second messenger Ca2+ has long been recognized as a key regulator in cell migration. Locally confined Ca2+, in particular, is essential for building front-to-rear Ca2+ gradient, which serves to maintain the morphologic polarity required in directionally migrating cells. However, little is known about the source of the Ca2+ and the mechanism by which they crosstalk between different signaling pathways in cancer cells. Here, we report that calcium release–activated calcium modulator 2 (ORAI2), a poorly characterized store-operated calcium (SOC) channel subunit, predominantly upregulated in the lymph node metastasis of gastric cancer, supports cell proliferation and migration. Clinical data reveal that a high frequency of ORAI2-positive cells in gastric cancer tissues significantly correlated with poor differentiation, invasion, lymph node metastasis, and worse prognosis. Gain- and loss-of-function showed that ORAI2 promotes cell motility, tumor formation, and metastasis in both gastric cancer cell lines and mice. Mechanistically, ORAI2 mediated SOC activity and regulated tumorigenic properties through the activation of the PI3K/Akt signaling pathways. Moreover, ORAI2 enhanced the metastatic ability of gastric cancer cells by inducing FAK-mediated MAPK/ERK activation and promoted focal adhesion disassembly at rear-edge of the cell. Collectively, our results demonstrate that ORAI2 is a novel gene that plays an important role in the tumorigenicity and metastasis of gastric cancer.
Significance
These findings describe the critical role of ORAI2 in gastric cancer cell migration and tumor metastasis and uncover the translational potential to advance drug discovery along the ORAI2 signaling pathway.
... The frequency, duration, and volume of Ca 2+ concentrations in the cell, elicits a diverse cellular response, ranging from cell death to cell migration, activation of specific transcription factors and stimulating metabolism, processes that attribute to the aggressiveness of certain cancers [105,108]. There are many different types of Ca 2+ channels, transporters, and regulatory proteins involved in facilitating the movement of Ca 2+ in the extracellular and intracellular space, making their way through organelles such as the ER and mitochondria [97,[108][109][110]. Here we focus on mitochondrial Ca 2+ as it contributes to the regulation of metabolism and the invasiveness of TNBC. ...
Altered metabolism represents a fundamental difference between cancer cells and normal cells. Cancer cells have a unique ability to reprogram their metabolism by deviating their reliance from primarily oxidative phosphorylation (OXPHOS) to glycolysis, in order to support their survival. This metabolic phenotype is referred to as the “Warburg effect” and is associated with an increase in glucose uptake, and a diversion of glycolytic intermediates to alternative pathways that support anabolic processes. These processes include synthesis of nucleic acids, lipids, and proteins, necessary for the rapidly dividing cancer cells, sustaining their growth, proliferation, and capacity for successful metastasis. Triple-negative breast cancer (TNBC) is one of the most aggressive subtypes of breast cancer, with the poorest patient outcome due to its high rate of metastasis. TNBC is characterized by elevated glycolysis and in certain instances, low OXPHOS. This metabolic dysregulation is linked to chemotherapeutic resistance in TNBC research models and patient samples. There is more than a single mechanism by which this metabolic switch occurs and here, we review the current knowledge of relevant molecular mechanisms involved in advanced breast cancer metabolism, focusing on TNBC. These mechanisms include the Warburg effect, glycolytic adaptations, microRNA regulation, mitochondrial involvement, mitochondrial calcium signaling, and a more recent player in metabolic regulation, JAK/STAT signaling. In addition, we explore some of the drugs and compounds targeting cancer metabolic reprogramming. Research on these mechanisms is highly promising and could ultimately offer new opportunities for the development of innovative therapies to treat advanced breast cancer characterized by dysregulated metabolism.
... Disruption of this balance may be associated with various diseases such as cardiovascular diseases, immune deficiencies, and malignancies. When cells are stimulated externally, it causes changes in calcium ions, leading to apoptosis induced by the degradation of NO 2 into oligomers [6,7]. ...
Objective: This experiment explores the effect of calcium ion (Ca2+) on oxaliplatin-induced bladder cancer cell apoptosis and investigates the impact of blocking calcium channels on oxaliplatin-induced bladder cancer cell apoptosis.
... A direct comparison between the literature compounds using a single assay and a non-disease specific cell line is lacking. The existing SOCE inhibitors have been reviewed extensively and recently [36, [55][56][57][58][59]. Here we report a direct comparison of the published SOCE small molecule inhibitors (presented in S1 Fig) using a fluorescence based Ca 2+ recording system to measure thapsigargin (TG) induced SOCE in Human Embryonic Kidney 293 (HEK293) cells. ...
Calcium (Ca ²⁺ ) is a key second messenger in eukaryotes, with store-operated Ca ²⁺ entry (SOCE) being the main source of Ca ²⁺ influx into non-excitable cells. ORAI1 is a highly Ca ²⁺ -selective plasma membrane channel that encodes SOCE. It is ubiquitously expressed in mammals and has been implicated in numerous diseases, including cardiovascular disease and cancer. A number of small molecules have been identified as inhibitors of SOCE with a variety of potential therapeutic uses proposed and validated in vitro and in vivo . These encompass both nonselective Ca ²⁺ channel inhibitors and targeted selective inhibitors of SOCE. Inhibition of SOCE can be quantified both directly and indirectly with a variety of assay setups, making an accurate comparison of the activity of different SOCE inhibitors challenging. We have used a fluorescence based Ca ²⁺ addback assay in native HEK293 cells to generate dose-response data for many published SOCE inhibitors. We were able to directly compare potency. Most compounds were validated with only minor and expected variations in potency, but some were not. This could be due to differences in assay setup relating to the mechanism of action of the inhibitors and highlights the value of a singular approach to compare these compounds, as well as the general need for biorthogonal validation of novel bioactive compounds. The compounds observed to be the most potent against SOCE in our study were: 7-azaindole 14d (12), JPIII (17), Synta-66 (6), Pyr 3 (5), GSK5503A (8), CM4620 (14) and RO2959 (7). These represent the most promising candidates for future development of SOCE inhibitors for therapeutic use.
... After depletion of ER Ca 2+ , the stim1 and orai1 redistribute within their respective membrane and coaccumulate in clusters to activate SOCE [38]. The sites of coaccumulation are ER-PM junctions, where ER is held close enough but not fused to the PM, and the average ER-PM gap is reported to range from 10 to 17 nm [39]. So the observation of ER-PM junctions can partially reflect the relative positional relation between orai1 and stim1. ...
The exploration of cell response to nanotopography has attracted considerable attentions for years. This article focuses on the influence of nanotopography on the intracellular Ca²⁺ dynamics, the most ubiquitous but ignored second messenger. The classic titanium nanotubes (NT) were fabricated by anodization to formulate nanoporous surfaces. Firstly, the store operative calcium entry (SOCE) in endoplasmic reticulum (ER) and functional Ca²⁺ release-activated Ca²⁺ (CRAC) channels were significantly enhanced on NT surfaces that revealed by live-cell Ca²⁺ imaging and fluorescence resonance energy transfer (FRET) identification of orai1-stim1 connection. To investigate the potential implication of Ca²⁺ elevation, the dynamic cell migration trajectory was monitored by a self-made holder, which could not only be suitable for the opaque implant surface but also guarantee the focus fields identical during samples shifting. The cell migration on NT surface was more vigorous and rapid, which was correlated with higher focal adhesion proteins expression, Ca²⁺-dependent calpain activity and stim1 level. In conclusion, this study has confirmed the novel ER Ca²⁺ hemostasis pathway on nanosurfaces and its crucial role in cell migration regulation, which may help for more biofavorable implant surface design.
Graphical Abstract
... This, in turn, triggers the expression of various cytokines and promotes the activation and proliferation of T cells. Thus, manipulating the activities of the CRAC and K V 1.3 channels provides unique opportunities for regulating the immune response and could be used to treat diseases associated with uncontrolled inflammation [14]. In fact, pharmacologically inhibiting the CRAC channel has been passionately pursued for the treatment of acute pancreatitis(AP) [15,16], autoimmune disorders(ADs) [17], allergic asthma [18], brain injury [19], and several types of cancers [20]. ...
... SOCE'nin geleneksel olarak boşalmış hücre içi Ca 2+ depolarını yenilemek için ana yol olarak hizmet ettiği iyi bilinmektedir. Bu kadar önemli görevinin yanı sıra, SOCE'nin ekzositoz, mitokondriyal metabolizma, gen ekspresyonu, hücre büyümesi ve proliferasyonu gibi bazı daha spesifik biyolojik süreçleri düzenlemek için mekansal-zamansal olarak karmaşık Ca 2+ sinyalleri regüle edebileceğine dair kanıtlar ortaya çıkmaya devam etmektedir (28). Son yıllarda, ciddi kombine immün yetmezlik bozuklukları, alerji, tromboz, akut pankreatit, enflamatuar barsak hastalığı, romatoid artrit ve kanser dahil olmak üzere birçok insan hastalığında anormal Orai1 kanal aktivitesi kaydedilmiştir (29). ...
Amaç: Bu çalışmada statinlerin hücre içi Ca2+ regülasyonunda önemli bir role sahip olan SOCE mekanizması üzerine olan etkilerinin incelenmesi amaçlandı. Materyal ve metod: SOCE ölçümleri RBL-1 hücre hatları kullanılarak gerçekleştirildi. Fura-2 ile yüklenen hücreler thapsigargin ile inkübe edilerek hücre içi Ca2+ depolarının boşalması sağlandı ve sonrasında Ca2+ eklenerek SOCE ölçümleri floresan mikroskop kullanılarak gerçekleştirildi. Test grubu için hücreler, Ca2+ görüntülemenin başlamasından önce 15 dakika süreyle istenen bileşik konsantrasyonuyla ön işleme tabi tutuldu. Ca2+ görüntüleme oran-metrik (Fura-2 tabanlı) Ca2+ görüntüleme tekniği kullanılarak gerçekleştirildi. Bulgular: Pitavastatin haricinden diğer tüm statinlerin SOCE üzerinde istatistiksel olarak anlamlı ölçüde baskılayıcı rolü olduğu bulundu. Özellikle 3 µM konsantrasyonda mevastatin ve atorvastatinin diğer tüm statinlerden SOCE üzerinde daha etkin olduğu anlaşıldı. Yüksek konsantrasyonlarda ise metavastatinin %80 oranından fazla SOCE’yi baskıladığı bulundu. Mevastatin için IC50 değeri 4,76 µM olarak hesaplandı. Sonuç: Bu çalışmadan elde edilen bulgulara göre kardiyovasküler hastalıkların tedavisinde kolesterol düşürücü olarak kullanılan statinlerin sadece voltaj kapılı kanallar üzerinden değil ayrıca depo-bağımlı Ca2+ kanalları üzerinde etkin olduğu saptandı. Statinlerin SOCE üzerindeki bu etkileri, statinlerin Ca2+ regülasyonundaki rolünün anlaşılmasında ve yeni tedavi metotlarının geliştirilmesi açısından büyük faydalar sağlayabileceğine inanılmaktadır.
... surface receptors may promote dengue virus attachment and entry Wang et al., 2016). Orai is a receptor-operated calcium channel protein that is located in the cell membrane and that mediates the inward flow of calcium ions by regulating calcium ion influx; Orai can also regulate exocytosis (Cai, 2007;Parekh, 2010;Zeng et al., 2017;El Hachmane et al., 2018). We did not find that ApoD and Orai affected the acquisition and transmission of TSWV; a possible reason is that the ApoD and Orai protein turnover may be slow Control: 10% sucrose (wt/vol); dsEGFP, dsApoD, dsOrai, and dsObst: 100 μg of dsRNA, 10% sucrose (wt/vol). ...
Tomato spotted wilt orthotospovirus (TSWV) causes substantial economic losses to vegetables and other crops. TSWV is mainly transmitted by thrips in a persistent and proliferative manner, and its most efficient vector is the western flower thrips, Frankliniella occidentalis (Pergande). In moving from the thrips midgut to the sali-vary glands in preparation for transmission, the virions must overcome multiple barriers. Although several proteins that interact with TSWV in thrips have been characterized , we hypothesized that additional thrips proteins interact with TSWV and facilitate its transmission. In the current study, 67 F. occidentalis proteins that interact with G N (a structural glycoprotein) were identified using a split-ubiquitin membrane-based yeast 2-hybrid (MbY2H) system. Three proteins, apolipoprotein-D (ApoD), orai-2-like (Orai), and obstructor-E-like isoform X2 (Obst), were selected for further study based on their high abundance and interaction strength; their interactions with G N were confirmed by MbY2H, yeast β-galactosidase and luciferase complementation assays. The relative expressions of ApoD and Orai were significantly down-regulated but that of Obst was significantly up-regulated in viruliferous thrips. When interfering with Obst in larval stage, the TSWV acquisition rate in 3 independent experiments was significantly decreased by 26%, 40%, and 35%, respectively. In addition, when Obst was silenced in adults, the virus titer was significantly decreased, and the TSWV transmission rate decreased from 66.7% to 31.9% using the leaf disk method and from 86.67% to 43.33% using the living plant method. However, the TSWV acquisition and transmission rates were not affected by interference with the ApoD or Orai gene. The results indicate that Obst may play an important role in TSWV acquisition and transmission in Frankliniella occidentalis.
... Extracellular signals can trigger Ca 2+ release from the internal stores and therefore induce Ca 2+ influx into the cells. Store-operated calcium entry (SOCE) is the primary mechanism of Ca 2+ influx in non-excitable cells (Parekh 2010), wherein depletion of the intracellular stores stimulates Ca 2+ entry from the microenvironment. SOCE is highly complex mechanism that depends on the expression levels of stromal interacting molecule 1 (STIM1), Orai1 and other modulators. ...
Cervical cancer is a major cause of cancer-associated mortality among women in developing countries. Orai1-mediated store-operated Ca ²⁺ entry (SOCE) is the primary mechanism underlying most of the non-excitable calcium influx into cells. There is at present limited evidence showing that Orai1 can function as an oncogene or a tumor suppressor depending on the cancer type. Furthermore, the exact biological functions of Orai1 in cervical cancer and the underlying mechanisms are still poorly understood. In this study, we found that Orai1 was upregulated in cervical cancer tissues, and promoted the growth of human cervical cancer cells both in vitro and in vivo . Gene silencing of Orai1 in cervical cancer cells significantly decreased interleukin (IL)-6 secretion. Interestingly, exogenous IL-6 abrogated the effects of Orai1 silencing and restored the clonogenicity of cervical cancer cells. Furthermore, we also observed a positive correlation between Orai1 and IL-6 expression in human cervical cancer samples. Taken together, our findings indicate that Orai1 functions as an oncogene in cervical cancer and is a promising therapeutic target.
... Store-operated calcium entry (SOCE) through the CRAC channel is a central mechanism by which cells generate Ca 2+ signals and mediate Ca 2+ -dependent gene expression. The CRAC channel, composed of Ca 2+ release-activated Ca 2+ channel protein 1 (Orai1) and stromal interaction molecule (STIM), represents a prototypical example of SOCE to mediate Ca 2+ entry between the endoplasmic reticulum and the plasma membrane in most nonexcitable cells [59,60]. There is accumulating evidence to indicate that the CRAC channel can influence various processes associated with tumorigenesis [61,62]. ...
Intracellular calcium (Ca2+) concentration ([Ca2+]i) is implicated in proliferation, invasion, and metastasis in cancerous tissues. A variety of oncologic therapies and some candidate drugs induce their antitumor effects (in part or in whole) through the modulation of [Ca2+]i. Cervical cancer is one of most common cancers among women worldwide. Recently, major research advances relating to the Ca2+ signals in cervical cancer are emerging. In this review, we comprehensively describe the current progress concerning the roles of Ca2+ signals in the occurrence, development, and prognosis of cervical cancer. It will enhance our understanding of the causative mechanism of Ca2+ signals in cervical cancer and thus provide new sights for identifying potential therapeutic targets for drug discovery.
... Although this initial P2Y-IP3 pathway is initially neuroprotective and speaks to the beneficial role of microglia in neuronal recovery, as ischemic time progresses, extracellular calcium begins to enter the microglia via CRAC channels. After the intracellular Ca 2+ stores become depleted by the initial signaling processes, the CRAC channels in the plasma membrane open to mediate a major influx of extracellular Ca 2+ into the cell [68]. Within the hypoxic microglia, Ca 2+ affects an incompletely understood set of downstream processes, including the calcineurin pathway, which is involved in modulating gene expression in the immune cells [69][70][71]. ...
Cortical spreading depolarizations (CSDs) are characterized by waves of diminished electroencephalography activity that propagate across the cortex with subsequent loss of ionic homeostasis. CSDs have been found in many pathological conditions, including migraine, traumatic brain injury, and ischemic stroke. Because of CSD-associated ionic and metabolic disturbances at the peri-infarct area after ischemic stroke, it is thought that CSDs exacerbate tissue infarction and worsen clinical outcomes. Microglia, the main innate immune cells in the brain, are among the first responders to brain tissue damage. Recent studies demonstrated that microglia play a critical role in CSD initiation and propagation. In this article, we discuss the significance of CSD in the setting of ischemic stroke and how microglia may modulate peri-infarct CSDs, also known as iso-electric depolarizations. Finally, we discuss the significance of microglial Ca2+ and how it might be used as a potential therapeutic target for patients with ischemic stroke.
... It is well-documented that Stromal interaction molecule (STIM) proteins directly interact with ORAI1 to drive Ca 2+ refilling. 29,30 Mammalian cells express two STIM proteins, namely STIM1 and STIM2, which respond to the ER Ca 2+ depletion to activate Ca 2+ release-activated Ca 2+ (CRAC) channels including ORAI proteins. 29,31 We then examined the roles of STIM1/2 in SMO cholesterylation and Hh signaling. ...
Hedgehog (Hh) is a morphogen that binds to its receptor Patched 1 and activates Smoothened (SMO), thereby governing embryonic development and postnatal tissue homeostasis. Cholesterol can bind and covalently conjugate to the luminal cysteine-rich domain (CRD) of human SMO at the D95 residue (D99 in mouse). The reaction mechanism and biological function of SMO cholesterylation have not been elucidated. Here, we show that the SMO-CRD undergoes auto-cholesterylation which is boosted by calcium and involves an intramolecular ester intermediate. In cells, Hh stimulation elevates local calcium concentration in the SMO-localized endosomes through store-operated calcium entry. In addition, we identify the signaling-incompetent SMO D95E mutation, and the D95E mutant SMO can bind cholesterol but cannot be modified or activated by cholesterol. The homozygous SmoD99E/D99E knockin mice are embryonic lethal with severe developmental delay, demonstrating that cholesterylation of CRD is required for full-length SMO activation. Our work reveals the unique autocatalytic mechanism of SMO cholesterylation and an unprecedented role of calcium in Hh signaling.
... More investigations are required to answer this question. Although the development of drugs targeting SOCE is in full swing, most of them lack the specificity of the target, and the mechanism is still unclear [133,139,140]. The further description of the relationship between TMEM family proteins and SOCE may provide another direction for the development of targeted drugs, which will have considerable clinical significance. ...
Store-operated Ca²⁺ entry (SOCE) is a major pathway for calcium signaling, which regulates almost every biological process, involving cell proliferation, differentiation, movement and death. Stromal interaction molecule (STIM) and ORAI calcium release-activated calcium modulator (ORAI) are the two major proteins involved in SOCE. With the deepening of studies, more and more proteins are found to be able to regulate SOCE, among which the transmembrane (TMEM) family proteins are worth paying more attention. In addition, the ORAI proteins belong to the TMEM family themselves. As the name suggests, TMEM family is a type of proteins that spans biological membranes including plasma membrane and membrane of organelles. TMEM proteins are in a large family with more than 300 proteins that have been already identified, while the functional knowledge about the proteins is preliminary. In this review, we mainly summarized the TMEM proteins that are involved in SOCE, to better describe a picture of the interaction between STIM and ORAI proteins during SOCE and its downstream signaling pathways, as well as to provide an idea for the study of the TMEM family proteins.
... Ca 2+ entry is activated by the depletion of Ca 2+ from the ER and mediated by STIM1, which moves close to the plasma membrane and forms highly Ca 2+ selective pores with ORAI1. This leads to Ca 2+ influx from the extracellular space directly into the ER through the Ca 2+ release-activated Ca 2+ current (I CRAC ) [48,49]. Even though ER Ca 2+ depletion represents an undisputed factor of neuronal cell injury, the modulation of the STIM1/ORAI1 complex during ischemia is still under scrutiny. ...
The two crucial cellular insults that take place during cerebral ischemia are the loss of oxygen and loss of glucose, which can both activate a cascade of events leading to neuronal death. In addition, the toxic overactivation of neuronal excitatory receptors, leading to Ca2+ overload, may contribute to ischemic neuronal injury. Brain ischemia can be simulated in vitro by oxygen/glucose deprivation, which can be reversible by the re-establishment of physiological conditions. Accordingly, we examined the effects of glucose deprivation on the PI3K/Akt survival signaling pathway and its crosstalk with HIF-1α and Ca2+ homeostasis in SH-SY5Y human neuroblastoma cells. It was found that glucose withdrawal decreased HIF-1α protein levels even in the presence of the ischemia-mimicking CoCl2. On the contrary, and despite neuronal death, we identified a strong activation of the master pro-survival kinase Akt, a finding that was also confirmed by the increased phosphorylation of GSK3, a direct target of p-Akt. Remarkably, the elevated Ca2+ influx recorded was found to promptly trigger the activation of Akt, while a re-addition of glucose resulted in rapid restoration of both Ca2+ entry and p-Akt levels, highlighting the plasticity of neurons to respond to ischemic challenges and the important role of glucose homeostasis for multiple neurological disorders.
... The details of structural insights, molecular characterization, physiological functions, pathological defects of STIM and Orai proteins, as well as their dynamic protein-protein interactions that mediated the mediate the activation of SOCE, have been extensively investigated and comprehensively reviewed [166][167][168][169][170][171][172][173][174][175][176]. Increasing evidence demonstrating the essential roles of STIM and Orai proteins have made them potential prognostic biomarkers or antitumor therapeutic targets [177][178][179][180][181][182][183]. ...
Cervical cancer is a significant gynecological cancer and causes cancer-related deaths worldwide. Human papillomavirus (HPV) is implicated in the etiology of cervical malignancy. However, much evidence indicates that HPV infection is a necessary but not sufficient cause in cervical carcinogenesis. Therefore, the cellular pathophysiology of cervical cancer is worthy of study. This review summarizes the recent findings concerning the ion transport processes involved in cell volume regulation and intracellular Ca2+ homeostasis of epithelial cells and how these transport systems are themselves regulated by the tumor microenvironment. For cell volume regulation, we focused on the volume-sensitive Cl− channels and K+-Cl− cotransporter (KCC) family, important regulators for ionic and osmotic homeostasis of epithelial cells. Regarding intracellular Ca2+ homeostasis, the Ca2+ store sensor STIM molecules and plasma membrane Ca2+ channel Orai proteins, the predominant Ca2+ entry mechanism in epithelial cells, are discussed. Furthermore, we evaluate the potential of these membrane ion transport systems as diagnostic biomarkers and pharmacological interventions and highlight the challenges.
... In ischemic brain injury, reduced expression of STIM1 and Orai1 has been suggested to underlie hypoxic/ischemic neuronal death in rats undergone focal ischemia and in primary cortical neurons exposed to oxygen and glucose deprivation (OGD) followed by reoxygenation [114]. In fact, under ischemic conditions, massive ER Ca 2+ depletion may trigger neuronal death through ER stress, while Ca 2+ refilling through SOCE underlies neuronal protection [115][116][117]. Accordingly, ischemic tolerance induced by ischemic preconditioning (IPC) has been reported to occur via the attenuation of ER stress response in ischemic neurons, while STIM1/Orai1-dependent Ca 2+ refilling is considered a crucial mechanism involved in IPC-induced neuroprotection in rats [114,118]. ...
Located at the level of the endoplasmic reticulum (ER) membrane, stromal interacting molecule 1 (STIM1) undergoes a complex conformational rearrangement after depletion of ER luminal Ca2+. Then, STIM1 translocates into discrete ER-plasma membrane (PM) junctions where it directly interacts with and activates plasma membrane Orai1 channels to refill ER with Ca2+. Furthermore, Ca2+ entry due to Orai1/STIM1 interaction may induce canonical transient receptor potential channel 1 (TRPC1) translocation to the plasma membrane, where it is activated by STIM1. All these events give rise to store-operated calcium entry (SOCE). Besides the main pathway underlying SOCE, which mainly involves Orai1 and TRPC1 activation, STIM1 modulates many other plasma membrane proteins in order to potentiate the influxof Ca2+. Furthermore, it is now clear that STIM1 may inhibit Ca2+ currents mediated by L-type Ca2+ channels. Interestingly, STIM1 also interacts with some intracellular channels and transporters, including nuclear and lysosomal ionic proteins, thus orchestrating organellar Ca2+ homeostasis. STIM1 and its partners/effectors are significantly modulated in diverse acute and chronic neurodegenerative conditions. This highlights the importance of further disclosing their cellular functions as they might represent promising molecular targets for neuroprotection.
... STIM1 protein functions as an ER Ca 2+ sensor, which clusters proximally to plasma membranes to activate Orai1 during ER Ca 2+ depletion. 23,24 Accumulating evidence shows that altered SOCE is associated with diabetes complications. 25,26 Impaired SOCE and STIM1 loss cause decreased insulin secretion and increased ER stress in the diabetic pancreatic β cells. ...
Recent studies emphasize the importance of 5‐HT2C receptor (5‐HT2CR) signaling in the regulation of energy homeostasis. The 5‐HT2CR is the only G‐protein‐coupled receptor known to undergo post‐transcriptional adenosine to inosine (A‐to‐I) editing by adenosine deaminase acting on RNA (ADAR). 5‐HT2CR has emerged as an important role in the modulation of pancreatic β cell functions. This study investigated mechanisms behind the effects of palmitic acid (PA) on insulin secretion in different overexpressed 5‐HT2CR edited isoforms in pancreatic MIN6 β cells. Results showed that the expressions of 5HT2CR and ADAR2 were upregulated in the pancreatic islets of mice fed with high‐fat diet (HFD) compared to control mice. PA treatment significantly induced the expressions of 5‐HT2CR and ADAR2 in pancreatic MIN6 β cells. PA treatment significantly induced the editing of 5‐HT2CR in pancreatic MIN6 β cells. There was no significant difference in cell viability between naïve cells and three overexpressed 5‐HT2CR edited isoforms in pancreatic MIN6 β cells. Overexpressed 5‐HT2CR edited isoforms showed reduced glucose‐stimulated insulin secretion (GSIS) compared with green fluorescent protein (GFP) expressed cells. Moreover, 5‐HT2CR edited isoforms displayed reduced endoplasmic reticulum (ER) calcium release and store‐operated calcium entry (SOCE) activation, probably through inhibition of stromal interaction molecule 1 trafficking under PA treatment. Altogether, our results show that PA‐mediated editing of 5‐HT2CR modulates GSIS through alteration of ER calcium release and SOCE activation in pancreatic MIN6 β cells.
... Tumour cells exhibit distinct and acquired traits that are relevant to or influenced by changes in Ca 2+ handling (Monteith et al., 2007;Parekh, 2010;Roderick and Cook, 2008). MS4A12 was first reported to show increased expression in patients with colon cancer (Koslowski et al., 2008). ...
Uniquely expressed in the colon, MS4A12 exhibits store-operated Ca2+ entry (SOCE) activity. However, compared to MS4A1 (CD20), a Ca2+ channel and ideal target for successful leukaemia immunotherapy, MS4A12 has rarely been studied. In this study, we investigated the involvement of MS4A12 in Ca2+ influx and expression changes in MS4A12 in human colonic malignancy. Fluorescence of GCaMP-fused MS4A12 (GCaMP-M12) was evaluated to analyse MS4A12 activity in Ca2+ influx. Plasma membrane expression of GCaMP-M12 was achieved by homo- or hetero-complex formation with no-tagged MS4A12 (nt-M12) or Orai1, respectively. GCaMP-M12 fluorescence in plasma membrane increased only after thapsigargin-induced depletion of endoplasmic reticulum Ca2+ stores, and this fluorescence was inhibited by typical SOCE inhibitors and siRNA for Orai1. Furthermore, GCaMP-MS4A12 and Orai1 co-transfection elicited greater plasma membrane fluorescence than GCaMP-M12 co-transfected with nt-M12. Interestingly, the fluorescence of GCaMP-M12 was decreased by STIM1 over-expression, while increased by siRNA for STIM1 in the presence of thapsigargin and extracellular Ca2+. Moreover, immunoprecipitation assay revealed that Orai1 co-expression decreased protein interactions between MS4A12 and STIM1. In human colon tissue, MS4A12 was expressed in the apical region of the colonic epithelium, although its expression was dramatically decreased in colon cancer tissues. In conclusion, we propose that MS4A12 contributes to SOCE through complex formation with Orai1, but does not cooperate with STIM1. Additionally, we discovered that MS4A12 is expressed in the apical membrane of the colonic epithelium and that its expression is decreased with cancer progression.
... Calcium ion and Ca2+-dependent channels are now considered key regulators of tumor progression, calcium ion Ca2+, one of the most versatile and universal signaling molecules, is known to regulate numerous cellular activities, ranging from short-term responses such as contraction and secretion to long-term control of transcription, cell division and cell death [7]. Ca2+ homeostasis in mammalian cells is maintained through the coordinated actions of a repertoire of Ca2+ signaling components, including Ca2+ channels, pumps and exchangers, that are situated in the plasma membrane (PM) or in intracellular organelles such as the endoplasmic reticulum (ER) and mitochondria [8] Interruptions in Ca2+ homeostasis may result in human diseases such as cancer [9]. Calcium may decrease the risk of developing colorectal cancer [10]. ...
Colorectal cancer (CRC) is one of the most common malignancies of the digestive system worldwide with the incidence has being increased significantly over the past three decades. CRC could present as sporadic (70%), more than half (55%) of all CRCs are attributable to lifestyle factors, including an unhealthy diet. Some studies refer higher circulating vitamin D (25(OH)D)was related to a statistically significant, substantially lower colorectal cancer risk , and other studies proposed the total calcium intake was inversely associated with the risk of developing colorectal cancer and other studies showed high total oxidant status (TOS) are involved in the occurrence and development of malignant tumors. This study aims to investigate the change in the levels of calcium, vitamin D and total oxidant status levels in colorectal Patients. The results showed significance increased in total oxidant status in colorectal cancer patients but not for benign tumor and healthy peoples. Calcium levels were within the ideal limits for all groups and had not relationship with colorectal cancer. While vitamin D levels were below the normal level for all groups and Vitamin D levels was lower in the colorectal cancer group. Found inverse relationship between vitamin D levels and total oxidant status.
... [3][4][5] They also play an important role in the control of gene expression, secretion, and immune response. [6][7][8] The last two decades have seen an extensive study of the molecular mechanism of Ca 2+ influx through SOCs, leading to a number of findings about the structure and function of SOCs. 5,7,[9][10][11] According to a widely accepted theory, SOCs are plasma membrane ion channels mainly composed of the pore-forming subunit calcium release-activated calcium channel protein 1 (Orai1) and are activated to open in response to the depletion of Ca 2+ in the lumen of the endoplasmic reticulum (ER) sensed by the ER-localized protein stromal interaction molecule 1 (STIM1), which polymerizes and relocates near the plasma membrane, where it covalently binds Orai1 and triggers its formation to be hexamers for the formation of SOCs. ...
Ca ²⁺ channels are essential to cell birth, life, and death. They can be externally activated by optogenetic tools, but this requires robust introduction of exogenous optogenetic genes for expression of photosensitive proteins in biological systems. Here we present femtoSOC, a method for direct control of Ca ²⁺ channels solely by ultrafast laser without the need for optogenetic tools or any other exogenous reagents. Specifically, by focusing and scanning wavelength-tuned low-power femtosecond laser pulses on the plasma membrane for multiphoton excitation, we directly induced Ca ²⁺ influx in cultured cells. Mechanistic study reveals that photoexcited flavins covalently bind cysteine residues in Orai1 via thioether bonds, which facilitates Orai1 polymerization to form store-operated calcium channels (SOCs) independently of STIM1, a protein generally participating in SOC formation, enabling all-optical activation of Ca ²⁺ influx and downstream signaling pathways. Moreover, we used femtoSOC to demonstrate direct neural activation both in brain slices in vitro and in intact brains of living mice in vivo in a spatiotemporal-specific manner, indicating potential utility of femtoSOC.
... Among the currently available CRAC channel drugs, only a few possess higher, but not full, selectivity for Orai channels. Moreover, their sites of action are widely unknown [115,132,133]. Presently, available and ongoing characterizations of the structure-function relationship of CRAC channel components pave the way for the development of novel, selective drugs to treat, for instance, allergic disorders and autoimmune diseases. ...
Cell survival and normal cell function require a highly coordinated and precise regulation of basal cytosolic Ca2+ concentrations. The primary source of Ca2+ entry into the cell is mediated by the Ca2+ release-activated Ca2+ (CRAC) channel. Its action is stimulated in response to internal Ca2+ store depletion. The fundamental constituents of CRAC channels are the Ca2+ sensor, stromal interaction molecule 1 (STIM1) anchored in the endoplasmic reticulum, and a highly Ca2+-selective pore-forming subunit Orai1 in the plasma membrane. The precise nature of the Orai1 pore opening is currently a topic of intensive research. This review describes how Orai1 gating checkpoints in the middle and cytosolic extended transmembrane regions act together in a concerted manner to ensure an opening-permissive Orai1 channel conformation. In this context, we highlight the effects of the currently known multitude of Orai1 mutations, which led to the identification of a series of gating checkpoints and the determination of their role in diverse steps of the Orai1 activation cascade. The synergistic action of these gating checkpoints maintains an intact pore geometry, settles STIM1 coupling, and governs pore opening. We describe the current knowledge on Orai1 channel gating mechanisms and summarize still open questions of the STIM1–Orai1 machinery.
... This seems to be sensed by stromal interaction molecule 1 (STIM1) located within the ER through interaction with plasma proteins, namely Orai1 protein. In turn, this results in sustained activation of calcium release-activated channels (CRACs) resulting in calcium influx, a process known as store-operated calcium entry (SOCE) (reviewed in [13]). Such sustained calcium influx across the cell membrane is important for lymphocyte activation and the initiation of both innate and adaptive immune response [11,14,15]. ...
Calcium is the most abundant mineral in the human body and is central to many physiological processes, including immune system activation and maintenance. Studies continue to reveal the intricacies of calcium signalling within the immune system. Perhaps the most well-understood mechanism of calcium influx into cells is store-operated calcium entry (SOCE), which occurs via calcium release-activated channels (CRACs). SOCE is central to the activation of immune system cells; however, more recent studies have demonstrated the crucial role of other calcium channels, including transient receptor potential (TRP) channels. In this review, we describe the expression and function of TRP channels within the immune system and outline associations with murine models of disease and human conditions. Therefore, highlighting the importance of TRP channels in disease and reviewing potential. The TRP channel family is significant, and its members have a continually growing number of cellular processes. Within the immune system, TRP channels are involved in a diverse range of functions including T and B cell receptor signalling and activation, antigen presentation by dendritic cells, neutrophil and macrophage bactericidal activity, and mast cell degranulation. Not surprisingly, these channels have been linked to many pathological conditions such as inflammatory bowel disease, chronic fatigue syndrome and myalgic encephalomyelitis, atherosclerosis, hypertension and atopy.
... The SERCA inhibition prevents Ca 2+ refilling of the ER, producing a net passive leak from the ER store that results in ER emptying and increased [Ca 2+ ] c (Thastrup et al., 1990). Besides the Ca 2+ depletion in the ER, the SERCA arrest may also induce a subsequent Ca 2+ influx from the extracellular medium via store-operated channel entry (SOCE), since microglia express Ca 2+ release-activated Ca 2+ channels, similar to other immune cells (Parekh, 2010). In fact, SOCE has been reported for BV2 cells and primary microglia (Bagur & Hajnoczky, 2017;Heo, Lim, Nam, Lee, & Kim, 2015;Michaelis, Nieswandt, Stegner, Eilers, & Kraft, 2015), and the activation of this capacitive Ca 2+ pathway can sustain long-lasting signals (Toescu et al., 1998). ...
Activation of microglia is an early immune response to damage in the brain. Although a key role for Ca2+ as trigger of microglial activation has been considered, little is known about the molecular scenario for regulating Ca2+ homeostasis in these cells. Taking into account the importance of the endoplasmic reticulum as a cellular Ca2+ store, the sarco(endo)plasmic reticulum Ca2+‐ATPase (SERCA2b) is an interesting target to modulate intracellular Ca2+ dynamics. We found upregulation of SERCA2b in activated microglia of human brain with Alzheimer's disease and we further studied the participation of SERCA2b in microglial functions by using the BV2 murine microglial cell line and primary microglia isolated from mouse brain. To trigger microglia activation, we used the bacterial lipopolysaccharide (LPS), which is known to induce an increase of cytosolic Ca2+. Our results showed an upregulated expression of SERCA2b in LPS‐induced activated microglia likely associated to an attempt to restore the increased cytosolic Ca2+ concentration. We analyzed SERCA2b contribution in microglial migration by using the specific SERCA inhibitor thapsigargin in scratch assays. Microglial migration was strongly stimulated with thapsigargin, even more than with LPS‐induction, but delayed in time. However, phagocytic capacity of microglia was blocked in the presence of the SERCA inhibitor, indicating the importance of a tight control of cytosolic Ca2+ in these processes. All together, these results provide for the first time compelling evidence for SERCA2b as a major player regulating microglial functions, affecting migration and phagocytosis in an opposite manner. Main points SERCA2b is upregulated in activated microglia in vitro and in Alzheimer's disease‐affected brains. SERCA2b inhibition stimulates migration but prevents phagocytosis in microglia.
... 27 However, if this is also the case for prostate cancer needs further investigation, including a detailed analysis of SOCE, that is impaired upon downregulation of TRPM4 and plays a pivotal role in cancer cell progression. 37,38 A previous study showed a 50% increased Ca 2+ entry rate and 20% higher Ca 2+ plateau in DU145 TRPM4 knockdown cells with only 40% transfection efficiency, indicating that reduced TRPM4 currents may still affect calcium signaling. 9 Following this study it would be interesting to analyze the differences in effect of blockers in long term vs short term treatments. ...
Transient receptor potential melastatin 4 (TRPM4) is a broadly expressed Ca²⁺ activated monovalent cation channel that contributes to the pathophysiology of several diseases.
For this study, we generated stable CRISPR/Cas9 TRPM4 knockout (K.O.) cells from the human prostate cancer cell line DU145 and analyzed the cells for changes in cancer hallmark functions. Both TRPM4-K.O. clones demonstrated lower proliferation and viability compared to the parental cells. Migration was also impaired in the TRPM4-K.O. cells. Additionally, analysis of 210 prostate cancer patient tissues demonstrates a positive association between TRPM4 protein expression and local/metastatic progression. Moreover, a decreased adhesion rate was detected in the two K.O. clones compared to DU145 cells.
Next, we tested three novel TRPM4 inhibitors with whole-cell patch clamp technique for their potential to block TRPM4 currents. CBA, NBA and LBA partially inhibited TRPM4 currents in DU145 cells. However, none of these inhibitors demonstrated any TRPM4-specific effect in the cellular assays.
To evaluate if the observed effect of TRPM4 K.O. on migration, viability, and cell cycle is linked to TRPM4 ion conductivity, we transfected TRPM4-K.O. cells with either TRPM4 wild-type or a dominant-negative mutant, non-permeable to Na⁺. Our data showed a partial rescue of the viability of cells expressing functional TRPM4, while the pore mutant was not able to rescue this phenotype. For cell cycle distribution, TRPM4 ion conductivity was not essential since TRPM4 wild-type and the pore mutant rescued the phenotype.
In conclusion, TRPM4 contributes to viability, migration, cell cycle shift, and adhesion; however, blocking TRPM4 ion conductivity is insufficient to prevent its role in cancer hallmark functions in prostate cancer cells.
... The STIM and ORAI isoforms are important regulators in both normal and tumor tissue (106,107). While there are multiple isoforms of both, namely STIM1, STIM2, ORAI1, ORAI2 and ORAI3, the expression of the isoforms determines the SOCE response in different cells (108), and the amplitude of SOCE is determined by the relative expression of STIM and ORAI in such contexts (109). ...
... As one of the most multifaceted, ubiquitous and dynamic intracellular secondary messengers, calcium (Ca 2+ ) is known to be involved in regulating multiple cellular processes, including cell proliferation, differentiation, apoptosis, migration, as well as cell contraction and secretion [1,2]. It is believed that dysregulation of Ca 2+ cellular homeostasis could result in several pathological conditions such as cardiovascular diseases, neurodegenerative ailments, developmental abnormalities, diabetes, immunodeficiency disorders and cancer [3,4]. Maintaining the cellular homeostasis of Ca 2+ depends on the synchronized functioning of various calcium channels, exchangers and pumps, which are located either on the plasma membrane of the cell or the membranes of endoplasmic reticulum and mitochondria [5,6]. ...
Introduction
The Ca2+ release-activated Ca2+ (CRAC) channel, composed of Orai and STIM proteins, represents one of the main routes of Ca²⁺ entry in most nonexcitable cells. There is accumulating evidence to suggest that CRAC channel can influence various processes associated with tumorigenesis. Overexpression of CRAC channel proteins has been observed in several types of cancer tissues and cells, indicating that blocking CRAC channel activated Ca²⁺ influx can have therapeutic benefits.
Areas covered
In this review, we have focused on the molecular composition and activation mechanism of CRAC channel as well as the myriad roles this Ca²⁺ channel play in various cancers. We further describe relevant information about several efforts aimed at developing CRAC channel blockers and their likely implications for cancer therapy. We have extensively utilized the available literature on PubMed to this end.
Expert opinion
The possibility of targeting CRAC channel mediated Ca²⁺ entry in cancer cells has generated considerable interest in recent years. Use of CRAC channel blockers in cancer preclinical studies and clinical trials has been relatively limited as compared to other diseases. The future lies in developing and testing more potent and selective drugs that target cancer cell specific CRAC channel proteins, hence opening better avenues for cancer therapeutic development.
... In this research, we have proposed that, bi-component staphylococcal leukotoxins after their specific binding to their membrane receptors, might enhance the opening of at least, three different types of Ca 2+ channels: i) store-operated Ca 2+ influx termed Ca 2+ -release activated Ca 2+ (CRAC) channels [88] involving trimeric G-proteins, in the presence of extracellular Ca 2+ ; ii) non-store operated Ca 2+ channels protein kinase C-dependent, which exhibit a very low permeability to Mn 2+ in the presence of extracellular Ca 2+ ; and iii) non-store-operated Ca 2+ channels mediated independently to PKC-and pertussis toxin sensitive-G proteins effect, as clearly evidenced in the absence of extracellular Ca 2+ . ...
... Ca 2+ entry via store-operated Ca 2+ channels (SOCs) provides an essential signaling mechanism for cellular immune responses and is required to control the filling state of the endoplasmic reticulum (ER) in virtually every cell type [1][2][3][4]. Activation of this sustained SOC entry (SOCE) is provided on a molecular basis by the ER Ca 2+ -sensing proteins stromal interaction molecule 1 (STIM1) and STIM2 and the plasma membrane (PM) Ca 2+ channels Orai1, 2, and 3 [5][6][7][8][9]. STIM1 senses luminal Ca 2+ with a canonical EF-hand and responds to a reduced Ca 2+ concentration within the ER [10,11]. ...
Stromal interaction molecule 1 (STIM1) is a ubiquitously expressed Ca2+ sensor protein that induces permeation of Orai Ca2+ channels upon endoplasmic reticulum Ca2+-store depletion. A drop in luminal Ca2+ causes partial unfolding of the N-terminal STIM1 domains and thus initial STIM1 activation. We compared the STIM1 structure upon Ca2+ depletion from our molecular dynamics (MD) simulations with a recent 2D NMR structure. Simulation- and structure-based results showed unfolding of two α-helices in the canonical and in the non-canonical EF-hand. Further, we structurally and functionally evaluated mutations in the non-canonical EF-hand that have been shown to cause tubular aggregate myopathy. We found these mutations to cause full constitutive activation of Ca2+-release-activated Ca2+ currents (ICRAC) and to promote autophagic processes. Specifically, heterologously expressed STIM1 mutations in the non-canonical EF-hand promoted translocation of the autophagy transcription factors microphthalmia-associated transcription factor (MITF) and transcription factor EB (TFEB) into the nucleus. These STIM1 mutations additionally stimulated an enhanced production of autophagosomes. In summary, mutations in STIM1 that cause structural unfolding promoted Ca2+ down-stream activation of autophagic processes.
... SOCE is negatively regulated by SOCE-associated regulatory factor (SARAF), an ER membrane protein that associates with STIM1 to facilitate a slow form of Ca 2+ -dependent inactivation of SOCE, thus preventing excess Ca 2+ refilling and maintain proper intracellular Ca 2+ levels (Palty et al., 2012). Following an ischemic insult, extensive depletion of Ca 2+ from ER prompts neuronal demise trough ER stress; whereby, Ca 2+ refilling via SOCE may represent a precious mechanism of neuronal protection (Sirabella et al., 2009;Parekh, 2010;Lang et al., 2018). Accordingly, reduced expression of STIM1 and Orai1 has been suggested to underlie hypoxic/ischemic neuronal death in rats subjected to focal ischemia and in primary cortical neurons (Secondo et al., 2019). ...
Store-operated Ca²⁺entry (SOCE) contributes to Ca²⁺ refilling of endoplasmic reticulum (ER), but also provides Ca²⁺ influx involved in physiological and pathological signalling functions. Upon depletion of Ca²⁺ store, the sensor protein stromal interaction molecule (STIM) activates Orai1, forming an ion-conducting pore highly selective for Ca²⁺. SOCE-associated regulatory factor (SARAF) associates with STIM1 to facilitate a slow form of Ca²⁺-dependent inactivation of SOCE or interacts with Orai1 to stimulate SOCE in STIM1-independent manner. We have investigated whether cerebral ischemic damage and neuroprotection conferred by ischemic preconditioning (PC) in mouse are associated with changes in the expression of the molecular components of SOCE.
Ischemic PC induced by 15-min occlusion of the middle cerebral artery (MCAo) resulted in significant amelioration of histological and functional outcomes produced, 72h later, by a more severe ischemia (1h MCAo). Neither ischemia, nor PC affected the expression of Orai1 in the frontoparietal cortex. However, the number of Orai1-immunopositive cells, mostly corresponding to Ly-6G+ neutrophils, was significantly elevated in the blood after the ischemic insult, regardless of previous PC. The expression of Stim1 and SARAF, mainly localized in NeuN-immunopositive neurons, was reduced in the ischemic cortex. Interestingly, neuroprotection by ischemic PC prevented the reduction of SARAF expression in the lesioned cortex and this could be interpreted as a compensatory mechanism to restore ER Ca²⁺ refilling in neurons in the absence of STIM1. Thus, preventing SARAF downregulation may represent a pivotal mechanism implicated in neuroprotection provided by ischemic PC and should be exploited as an original target for novel stroke therapies.
... Through its effector proteins such as Alix and ALG-2, calcium ion itself also regulates the ESCRT complexes involved in the biogenesis of mutivesicular body ESCRT (Mattei et al., 2006;Zhou et al., 2009). More importantly, aberrant calcium homeostasis has been associated with cancers, immunodeficiency and autoimmunity disorders, allergy and inflammatory bowel diseases, cardiovascular diseases as well as neurodegenerative diseases such as Alzheimer (Monteith et al., 2007;Parekh, 2010;Cali et al., 2012;Kho et al., 2012). Although loss of one copy of the human ATP2C1 gene, the orthologous gene of yeast PMR1, causes HHD, adult ATP2C1(+/2) heterozygous mice exhibit no evidence of HHD but an increased incidence of squamous cell tumors of keratinized epithelial cells of the skin and esophagus (Okunade et al., 2007). ...
The endosomal sorting complex required for transport (ESCRT) complexes function to form multivesicular bodies for sorting of proteins destined for the yeast vacuole or the mammalian lysosome. ESCRT components are well conserved in eukaryotes, and their mutations cause neurodegenerative diseases and other cellular pathologies in humans. PMR1 is the orthologous gene of two human genes for calcium pumps secretory pathway Ca 21-ATPase (SPCA1, ATP2C1) and sarco/endoplasmic reticulum Ca 21-ATPase (SERCA, ATP2A2), which are mutated in Hailey-Hailey and Darier genetic diseases, respectively. Here we show that deletion mutation of ESCRT components Snf7, Snf8, Stp22, Vps20, Vps25, Vps28, or Vps36 activates the calcium/calcineurin signaling in yeast cells, but surprisingly leads to a nearly 50% reduction in expression of the ER/Golgi calcium pump gene PMR1 independent of calcium stress. These ESCRT mutants are known to have a defect in Rim101 activation. Ectopic expression of a constitutively active form of Rim101 or further deletion of NRG1 in these mutants partially suppresses their calcium hypersensitivity. Deletion of NRG1 also completely rescues the expression of PMR1 in these mutants to the level of the wild type. Promoter mutagenesis, gel electrophoretic mobility shift assay, and chromatin immunoprecipitation analysis demonstrate that Nrg1 binds to two motifs in the PMR1 promoter. In addition, expression of PMR1 under the control of its promoters with mutated Nrg1-binding motifs suppresses the calcium hypersensitivity of these ESCRT mutants. Collectively, these data have uncovered a function of ESCRT components in regulating PMR1 expression through the Nrg1/Rim101 pathway. Our findings provide important clues for understanding human diseases related to calcium homeostasis.
Immune‐mediated inflammatory diseases (IMIDs) impose an immeasurable burden on individuals and society. While the conventional use of immunosuppressants and disease‐modifying drugs has provided partial relief and control, their inevitable side effects and limited efficacy cast a shadow over finding a cure. Promising nucleic acid drugs have shown the potential to exert precise effects at the molecular level, with different classes of nucleic acids having regulatory functions through varying mechanisms. For the better delivery of nucleic acids, safe and effective viral vectors and non‐viral delivery systems (including liposomes, polymers, etc.) have been intensively explored. Herein, after describing a range of nucleic acid categories and vectors, we focus on the application of therapeutic nucleic acid delivery in various IMIDs, including rheumatoid arthritis, inflammatory bowel disease, psoriasis, multiple sclerosis, asthma, ankylosing spondylitis, systemic lupus erythematosus, and uveitis. Molecules implicated in inflammation and immune dysregulation are abnormally expressed in a series of IMIDs, and their meticulous modulation through nucleic acid therapy results in varying degrees of remission and improvement of these diseases. By synthesizing findings centered on specific molecular targets, this review delivers a systematic elucidation and perspective towards advancing and utilization of nucleic acid therapeutics for managing IMIDs.
Acute pancreatitis (AP) is a life-threatening inflammatory disease with no specific therapy. Excessive cytoplasmic Ca 2+ elevation and intracellular ATP depletion are responsible for the initiation of AP. Inhibition of CRAC channels has been proposed as a potential treatment and currently, a novel selective CRAC channel inhibitor CM4620 (Auxora TM , CalciMedica), is in Phase 2b human trials. While CM4620 is on track to become the first effective treatment for AP, it does not produce complete protection in animal models. Recently, an alternative approach has suggested reducing ATP depletion with a natural carbohydrate galactose. Here we have investigated the possibility of using the smallest effective concentration of CM4620 in combination with galactose. Protective effects of CM4620, in the range of 1-100 nM, have been studied against necrosis induced by either bile acids, palmitoleic acid or L-asparaginase. CM4620 markedly protected against necrosis induced by bile acids or asparaginase starting from 50 nM, and palmitoleic acid starting from 1 nM. Combining CM4620 and galactose (1 mM) significantly reduced the extent of necrosis to near-control levels. In the palmitoleic acids-alcohol-induced experimental mouse model of AP, CM4620 at a concentration of 0.1 mg/kg alone significantly reduced oedema, necrosis, inflammation, and the total histopathological score. A combination of 0.1 mg/kg CM4620 with galactose (100 mM) significantly reduced further necrosis, inflammation, and histopathological score. Our data show that CM4620 can be used at much lower concentrations than reported previously, reducing potential side effects. The novel combination of CM4620 with galactose synergistically targets complementary pathological mechanisms of AP. Graphical Abstract Downloaded from https:
Many essential biological processes are triggered by the proximity of molecules. Meanwhile, diverse approaches in synthetic biology, such as new biological parts or engineered cells, have opened up avenues to precisely control the proximity of molecules and eventually downstream signaling processes. This also applies to a main Ca2+ entry pathway into the cell, the so-called Ca2+ release-activated Ca2+ (CRAC) channel. CRAC channels are among other channels are essential in the immune response and are activated by receptor–ligand binding at the cell membrane. The latter initiates a signaling cascade within the cell, which finally triggers the coupling of the two key molecular components of the CRAC channel, namely the stromal interaction molecule, STIM, in the ER membrane and the plasma membrane Ca2+ ion channel, Orai. Ca2+ entry, established via STIM/Orai coupling, is essential for various immune cell functions, including cytokine release, proliferation, and cytotoxicity. In this review, we summarize the tools of synthetic biology that have been used so far to achieve precise control over the CRAC channel pathway and thus over downstream signaling events related to the immune response.
Sir Michael Berridge was a giant in the fields of physiology and biochemistry who, by his discovery in 1983 of inositol 1,4,5-trisphosphate (IP 3 ) as the ubiquitous intracellular messenger releasing Ca ²⁺ from intracellular stores, revolutionized our concepts of signal transduction mechanisms. Mike, as he was universally known, discovered one of the most important regulatory mechanisms in animal cells, involved in the control of virtually all bodily functions, including secretion, contraction and memory. Mike, working at the Department of Zoology at the University of Cambridge, personally identified IP 3 as one of the two initial products of hormone- or neurotransmitter-elicited inositol phospholipid breakdown and then, in collaboration with the research group led by Irene Schulz at the Max Planck Institute for Biophysics in Frankfurt, demonstrated directly the Ca ²⁺ -releasing effect of IP 3 in pancreatic acinar cells. Subsequently, in collaborations with research groups in Switzerland and the USA, Mike confirmed the Ca 2 + -releasing action of IP 3 in insulin-secreting cells, hepatocytes and photoreceptors. The IP 3 –Ca 2 + -releasing pathway became accepted amazingly quickly as one of the key elements of cellular signal transduction mechanisms and is now featured in virtually all textbooks of physiology and biochemistry. Mike was also a great synthesizer, who created an entirely new field, namely calcium signalling. Through his numerous, highly cited review articles, and his insightful keynote lectures at the most important biomedical congresses, he dominated this large and increasingly important research field for more than 30 years following his momentous 1983 discovery.
The family of stromal interaction molecules (STIM) includes two widely expressed single‐pass endoplasmic reticulum (ER) transmembrane proteins and additional splice variants that act as precise ER‐luminal Ca²⁺ sensors. STIM proteins mainly function as one of the two essential components of the so‐called Ca²⁺ release‐activated Ca²⁺ (CRAC) channel. The second CRAC channel component is constituted by pore‐forming Orai proteins in the plasma membrane. STIM and Orai physically interact with each other to enable CRAC channel opening, which is a critical prerequisite for various downstream signalling pathways such as gene transcription or proliferation. Their activation commonly requires the emptying of the intracellular ER Ca²⁺ store. Using their Ca²⁺ sensing capabilities, STIM proteins confer this Ca²⁺ content‐dependent signal to Orai, thereby linking Ca²⁺ store depletion to CRAC channel opening. Here we review the conformational dynamics occurring along the entire STIM protein upon store depletion, involving the transition from the quiescent, compactly folded structure into an active, extended state, modulation by a variety of accessory components in the cell as well as the impairment of individual steps of the STIM activation cascade associated with disease. image
Biological activities require a delicate balance between excitatory and inhibitory signals in the brain. Disruption of this balance could lead to neurological disorders, such as epilepsydue to a relative enhancement of excitatory signals. In general, cytosolic calcium plays a key role in the transmission of excitatory signals mainly by promoting the release of synaptic vesicles containing neurotransmitters. A series of molecular components responsible for maintaining intracellular calcium homeostasis, including voltage-gated calcium (CaV) channels, the endoplasmic reticulum (ER) calcium sensor stromal interaction molecule (STIM), the PM calcium channel Orai, ER-resident inositol trisphosphate receptors (IP3Rs) and ryanodine receptors (RyRs), sarco-endoplasmic reticulum calcium ATPase (SERCA), and transmembrane and coiled-coil domains 1 (TMCO1), have been demonstrated to be involved in calcium dysregulation that underlies epileptic seizures. More importantly, epileptic phenotypes were confirmed in several molecular components by transgenic animal models, including CACNA1A, CACNA1E, CACNA1G, CACNA2D1, ORAI1 and IP3R1. Calcium-binding proteins (CaBPs), such as calmodulin, parvalbumin, calretinin, and calbindin, provide an additional layer of defense by acting as calcium reservoirs to buffer rapid increases in cytosolic calcium concentrations and participate in cellular functions by regulating the activities of ion channels or acting as calcium-modulated sensors, and a series of lines of evidence support their implication with epileptic activities. Overall, stroke represents the most common environmental cause of acquired epilepsy in older adults, and preventing calcium disruption due to reperfusion injury might be an effective way to treat acute symptomatic seizures and decrease the risk for acquired poststroke epilepsy.
The Ca²⁺ entry from store-operated Ca²⁺ channel (SOC) is involved in regulating colorectal cancer progression, such as cell migration. SOC activation is due to STIM1 translocation and interaction with Orai1 upon Ca²⁺ depletion in the ER. Numerous SOC inhibitors, like 2-APB, have been developed and demonstrated their inhibition effects in the preclinical stage. However, most currently used SOC inhibitors have higher cytotoxicity or opposite effects at different doses, and the drugs to target SOC in the clinic are lacking. In this study, a total of 13 difluorobenzamide compounds had been synthesized and examined the inhibitory effects on SOC with Ca²⁺ imaging and wound-healing migration assay. Among them, 2,6-Difluoro-N-(5-(4-fluorophenyl)pyridine-2-yl)benzamide (MPT0M004, 8a) demonstrated a prominent inhibitory ability on SOC. Furthermore, the cell proliferation assay results showed that MPT0M004 (8a) had lower cytotoxicity than 2-APB, the reference compound. In the pharmacokinetic study, MPT0M004 (8a) has a long half-life (T1/2 = 24 h) and lower daily dose administered intravenously with an oral bioavailability (F = 34%). Therefore, MPT0M004 (8a) has the potential to be a lead compound as a SOC inhibitor and further develop into a potential drug to treat colorectal cancer.
Deregulated store-operated calcium entry (SOCE) mediated by aberrant STIM1-ORAI1 signaling is closely implicated in cancer initiation and progression. Here the authors report the identification of an alternatively spliced variant of STIM1, designated STIM1 , that harbors an extra exon to encode 31 additional amino acids in the cytoplasmic domain. STIM1 , highly conserved in mammals, is aberrantly upregulated in glioma tissues to perturb Ca 2+ signaling. At the molecular level, the 31-residue insertion destabilizes STIM1 by perturbing its cytosolic inhibitory domain and accelerating its activation kinetics to efficiently engage and gate ORAI calcium channels. Functionally, STIM1 depletion affects SOCE in glioblastoma cells, suppresses tumor cell proliferation and growth both in vitro and in vivo. Collectively, their study establishes a splicing variant-specific tumor-promoting role of STIM1 that can be potentially targeted for glioblastoma intervention.
Tumor metastasis is the primary cause of treatment failure and cancer-related deaths. Store-operated Ca²⁺ entry (SOCE), which is mediated by stromal interaction molecules (STIM) and ORAI proteins, has been implicated in the tumor invasion-metastasis cascade. Epithelial-mesenchymal transition (EMT) is a cellular program that enables tumor cells to acquire the capacities needed for migration and invasion and the formation of distal metastases. Tumor-associated angiogenesis contributes to metastasis because aberrantly developed vessels offer a path for tumor cell dissemination as well as supply sufficient nutrients for the metastatic colony to develop into metastasis. Recently, increasing evidence has indicated that SOCE alterations actively participate in the multi-step process of tumor metastasis. In addition, the dysregulated expression of STIM/ORAI has been reported to be a predictor of poor prognosis. Herein, we review the latest advances about the critical role of SOCE in the tumor metastasis cascade and the underlying regulatory mechanisms. We emphasize the contributions of SOCE to the EMT program, tumor cell migration and invasion, and angiogenesis. We further discuss the possibility of modulating SOCE or intervening in the downstream signaling pathways as a feasible targeting therapy for cancer treatment.
Targeted therapy for acute pancreatitis (AP) remains absent from the essential management toolkit, despite an increasing worldwide disease burden, an extensive range of preclinical research, and numerous clinical trials. A critical mass of international researchers has now gathered with the common goal of successfully establishing pharmacological treatment for AP, providing essential light at the end of a long tunnel. This chapter discusses the front‐running candidate drugs and their associated disease mechanisms, followed by suggested improvements to trial design and funding to pave the way for future successful drug treatment. New molecular entities that inhibit calcium toxicity and repositioned drugs that block inflammatory pathways have progressed into clinical trials, the results of which are eagerly awaited. Mitochondrial dysfunction as a result of intracellular calcium overload induced by toxins that include bile acids and ethanol metabolites has become established as a key pathogenic mechanism in acute pancreatitis.
What is known and objective
RP3128, a novel, orally available modulator of calcium released activated calcium (CRAC) channel, is being developed for the potential treatment of autoimmune and inflammatory diseases. RP3128 showed nano‐molar potency and activity in a range of in vitro and in vivo models of inflammation. We report a first‐in‐human study investigating the safety, tolerability, pharmacokinetics (PK) and pharmacodynamics (PD) of RP3128 in healthy subjects.
Methods
A randomized, double‐blind, placebo‐controlled trial of single (25, 50, 100, 200 and 400 mg) and multiple (7 days: 25, 100 and 400 mg once daily) doses of RP3128 were performed. Thirty‐two and 24 subjects were randomized in the single ascending dose (SAD) and multiple ascending dose (MAD) parts, respectively.
Results and discussion
RP3128 was well tolerated, with no dose‐limiting toxicity at single and multiple doses. Incidence of treatment emergent adverse events (TEAEs) did not increase with ascending RP3128 doses. No changes were seen in cognitive function and ECG parameters. RP3128 was rapidly absorbed. Elimination was slow with a half‐life of more than 80 h. Exposures increased with increasing doses. Accumulation was seen on repeated dosing. PD response, as evidenced by lower plasma levels of tumour necrosis factor‐alfa (TNFα) and interleukin‐4 (IL‐4), was seen when compared to pre‐dose values or placebo.
What is new and conclusion
The safety, tolerability and PK/PD profile of RP3128 demonstrates its potential to be developed in inflammatory disorders and support further clinical development (ClinicalTrials.gov number: NCT02958982).
Over the last two decades, the understanding of how dysregulated ion channels and transporters are involved in carcinogenesis and tumor growth and progression, including invasiveness and metastasis, has been increasing exponentially. The present review specifies virtually all ion channels and transporters whose faulty expression or regulation contributes to esophageal, hepatocellular, and colorectal cancer. The variety reaches from Ca²⁺, K⁺, Na⁺, and Cl⁻ channels over divalent metal transporters, Na⁺ or Cl⁻ coupled Ca²⁺, HCO3⁻ and H⁺ exchangers to monocarboxylate carriers and organic anion and cation transporters. In several cases, the underlying mechanisms by which these ion channels/transporters are interwoven with malignancies have been fully or at least partially unveiled. Ca²⁺, Akt/NF-κB, and Ca²⁺- or pH-dependent Wnt/β-catenin signaling emerge as cross points through which ion channels/transporters interfere with gene expression, modulate cell proliferation, trigger epithelial-to-mesenchymal transition, and promote cell motility and metastasis. Also miRs, lncRNAs, and DNA methylation represent potential links between the misexpression of genes encoding for ion channels/transporters, their malfunctioning, and cancer. The knowledge of all these molecular interactions has provided the basis for therapeutic strategies and approaches, some of which will be broached in this review.
Objective:
To determine the effect of Wenyang Huazhuo Fang (WHF), a Traditional Chinese Medicine decoction, on renal function in a rat model of doxorubicin-induced nephropathy, and to elucidate the underlying mechanism.
Methods:
Sprague-Dawley rats were randomly divided into six groups: control, doxorubicin-nephropathy, and prednisone-treated (6.45 mg·kg-1·d－1) doxorubicin nephropathy groups, as well as high- (7.26 g·kg-1·d－1, medium- (2.42 g·kg-1·d－1, and low-dose (0.81 g·kg-1·d－1 WHF-treated doxorubicin-nephropathy groups. The nephropathy rat model was established by two tail vein injections of doxorubicin, followed by prednisone or WHF treatment for 8 weeks. Body weights were monitored and urinary protein was measured every 2 weeks. After the end of the treatment period, the rats were euthanized. Serum biochemical indicators were determined and renal morphological alterations were assessed using histological staining. The expression of transient receptor potential cation channel subfamily C member 6 (TRPC6), stromal interaction molecule 1 (STIM1), and calcium release-activated calcium channel protein 1 (Orai1) was detected using western blotting, and their mRNA levels were examined using quantitative real-time reverse transcription-polymerase chain reaction.
Results:
WHF treatment was found to significantly ameliorate weight loss, proteinuria, hypoalbuminemia, and dyslipidemia in doxorubicin-nephropathy rats. The protein and mRNA levels of TRPC6, STIM1, and Orai1 were partially, but significantly suppressed by prednisone or WHF treatment.
Conclusion:
Treatment with WHF significantly ameliorates renal injury in a rat model of doxorubicin-induced nephropathy, which could be at least partially related to repression of the TRPC6 pathway.
Baicalin, a component of traditional Chinese medicine, is one of the main compounds present in Scutellaria baicalensis Georgi. Pseudo-allergy induced by the injection of these medicines is a frequent adverse drug reaction. Therefore, elucidation of the anaphylactoid reaction of baicalin and its underlying mechanisms are important. Mast cells are primary effectors of allergic reactions, including pseudo-allergy. Studies have shown that Mrgprx2 in human mast cells is a specific receptor that is crucial for pseudo-allergic drug reactions, Mrgprb3 is the rat ortholog of human Mrgprx2, which in mice is designated as Mrgprb2. Here, we aimed to investigate baicalin-induced pseudo-allergy and the association of Mrgprb3 and Mrgprb2 with this effect. We examined the allergenic effect of baicalin on RBL-2H3 cells and Mrgprb3-knockdown RBL-2H3 cells. Mrgprb2-expressing HEK293 cells and Mrgprb2-knockout mice were used to evaluate the role of Mrgprb2 in baicalin-induced allergy. Baicalin was found to dose-dependently induce pseudo-allergy both in vitro and in vivo. RBL-2H3 cells were activated by baicalin, whereas in Mrgprb3-knockout RBL-2H3 cells, baicalin showed a negligible effect on cell activation. Furthermore, baicalin activated the Mrgprb2-expressing HEK293 cells. Our data showed that baicalin did not induce allergy in Mpgprb2-knockout mice. We conclude that baicalin induces pseudo-allergy via Mrgprb2 in mice.
Agents such as thapsigargin and endothelin elevate intracellular calcium levels by a combination of calcium release from intracellular stores and calcium influx across the plasma membrane; however, the relative contribution of influx vs. release in modulating calcium-dependent gene expression is not as well understood in nonexcitable cells as in excitable cells. In this report we have been able to separate thapsigargin-induced elevation of intracellular calcium into release and influx components, using carboxyamido-triazole (CAI), a known inhibitor of calcium influx with antiproliferative activity against a number of human carcinomas, to selectively inhibit influx without affecting release. The results of these experiments indicate that the ability of thapsigargin to induce calcium-dependent gene expression in nonexcitable cells is dependent on the induction of calcium influx, presumably through store-operated calcium channels. CAI treatment specifically inhibited thapsigargin- or endothelin-stimulated expression from the c-fos promoter in Rat-1 cells and in epithelial cell lines derived from ovary and breast. Use of the VL30 model system confirmed the ability of CAI to inhibit calcium-dependent gene expression and further demonstrated that the ability of elevated calcium to synergize with other signaling pathways required close temporal coupling. In addition to inhibiting endothelin-induced calcium influx, CAI treatment also resulted in a partial inhibition of IP3 production and calcium release. CAI treatment also blocked the increase in ERK1 kinase activity observed in response to either endothelin or thapsigargin, suggesting a role for calcium influx in the activation of mitogen-activated protein kinase pathways.
CRAC channels generate Ca(2+) signals critical for the activation of immune cells and exhibit an intriguing pore profile distinguished by extremely high Ca(2+) selectivity, low Cs(+) permeability, and small unitary conductance. To identify the ion conduction pathway and gain insight into the structural bases of these permeation characteristics, we introduced cysteine residues in the CRAC channel pore subunit, Orai1, and probed their accessibility to various thiol-reactive reagents. Our results indicate that the architecture of the ion conduction pathway is characterized by a flexible outer vestibule formed by the TM1-TM2 loop, which leads to a narrow pore flanked by residues of a helical TM1 segment. Residues in TM3, and specifically, E190, a residue considered important for ion selectivity, are not close to the pore. Moreover, the outer vestibule does not significantly contribute to ion selectivity, implying that Ca(2+) selectivity is conferred mainly by E106. The ion conduction pathway is sufficiently narrow along much of its length to permit stable coordination of Cd(2+) by several TM1 residues, which likely explains the slow flux of ions within the restrained geometry of the pore. These results provide a structural framework to understand the unique permeation properties of CRAC channels.
Prolonged Ca(2+) entry through Ca(2+) release-activated Ca(2+) (CRAC) channels is crucial in activating the Ca(2+)-sensitive transcription factor NFAT, which is responsible for directing T cell proliferation and cytokine gene expression. To establish whether targeting CRAC might counteract intestinal inflammation, we evaluated the in vitro effect of a selective CRAC inhibitor on T cell cytokine production and T-bet expression by lamina propria mononuclear cells (LPMC) and biopsy specimens from inflammatory bowel disease (IBD) patients. The inhibitory activity of the CRAC blocker was investigated through patch-clamp experiments on rat basophilic leukemia cells and fluorometric imaging plate reader intracellular Ca(2+) assays using thapsigargin-stimulated Jurkat T cells and its detailed selectivity profile defined using a range of in vitro radioligand binding and functional assays. Anti-CD3/CD28-stimulated LPMC and biopsy specimens from 51 patients with IBD were cultured with a range of CRAC inhibitor concentrations (0.01-10 microM). IFN-gamma, IL-2, IL-8, and IL-17 were analyzed by ELISA. T-bet was determined by immunoblotting. We found that the CRAC blocker concentration-dependently inhibited CRAC current in rat basophilic leukemia cells and thapsigargin-induced Ca(2+) influx in Jurkat T cells. A concentration-dependent reduction in T-bet expression and production of IFN-gamma, IL-2, IL-17, but not IL-8, was observed in IBD LPMC and biopsy specimens treated with the CRAC inhibitor. In conclusion, we provide evidence that the suppression of CRAC channel function may dampen the increased T cell response in the inflamed gut, thus suggesting a promising role for CRAC inhibitor drugs in the therapeutic management of patients with IBD.
Communication between the cell surface and the nucleus is essential for regulated gene expression. In neurons, Ca2+-dependent gene transcription is sensitive to local Ca2+ entry. In immune cells, excitation-transcription coupling is thought to involve global Ca2+ signals. Here, we show that in mast cells, Ca2+ microdomains from store-operated Ca2+ release-activated Ca2+ channels activate expression of the transcription factor c-fos. Local Ca2+ entry is sensed by the tyrosine kinase Syk, which signals to the nucleus through the transcription factor STAT5. Ca2+ microdomains also promote secretion of proinflammatory messengers, which, like gene expression, requires Syk. Syk therefore
couples Ca2+ microdomains to the activation of two spatially and temporally distinct cellular responses, revealing the versatility of
local Ca2+ signals in driving cell activation.
Store-operated Ca(2+) entry (SOCE) is a universal mechanism to increase intracellular Ca(2+) concentrations in non-excitable cells. It is initiated by the depletion of ER Ca(2+) stores, activation of stromal interaction molecule (STIM) 1 and gating of the Ca(2+) release activated Ca(2+) (CRAC) channel ORAI1 in the plasma membrane. We identified a minimal activation domain in the cytoplasmic region of STIM1 (CCb9) which activated Ca(2+) influx and CRAC currents (I(CRAC)) in the absence of store depletion similar to but more potently than the entire C terminus of STIM1. A STIM1 fragment (CCb7) that is longer by 39 [corrected] amino acids than CCb9 at its C terminal end showed reduced ability to constitutively activate I(CRAC) consistent with our observation that CCb9 but not CCb7 efficiently colocalized with and bound to ORAI1. Intracellular application of a 31 amino acid peptide contained in CCb7 but not CCb9 inhibited constitutive and store-dependent CRAC channel activation. In summary, these findings suggest that CCb9 represents a minimal ORAI1 activation domain within STIM1 that is masked by an adjacent 31 amino acid peptide preventing efficient CRAC channel activation in cells with replete Ca(2+) stores.
A mutation in ORAI1, the gene encoding the pore-forming subunit of the Ca(2+)-release-activated Ca(2+) (CRAC) channel, abrogates the store-operated entry of Ca(2+) into cells and impairs lymphocyte activation. Stromal interaction molecule 1 (STIM1) in the endoplasmic reticulum activates ORAI1-CRAC channels. We report on three siblings from one kindred with a clinical syndrome of immunodeficiency, hepatosplenomegaly, autoimmune hemolytic anemia, thrombocytopenia, muscular hypotonia, and defective enamel dentition. Two of these patients have a homozygous nonsense mutation in STIM1 that abrogates expression of STIM1 and Ca(2+) influx.
Ca2+ signaling plays a central role in microglial activation, and several studies have demonstrated a store-operated Ca2+ entry (SOCE) pathway to supply this ion. Due to the rapid pace of discovery of novel Ca2+ permeable channels, and limited electrophysiological analyses of Ca2+ currents in microglia, characterization of the SOCE channels remains incomplete. At present, the prime candidates are 'transient receptor potential' (TRP) channels and the recently cloned Orai1, which produces a Ca2+-release-activated Ca2+ (CRAC) current. We used cultured rat microglia and real-time RT-PCR to compare expression levels of Orai1, Orai2, Orai3, TRPM2, TRPM7, TRPC1, TRPC2, TRPC3, TRPC4, TRPC5, TRPC6 and TRPC7 channel genes. Next, we used Fura-2 imaging to identify a store-operated Ca2+ entry pathway that was reduced by depolarization and blocked by Gd3+, SKF-96365, diethylstilbestrol (DES), and a high concentration of 2-aminoethoxydiphenyl borate (50 microM 2-APB). The Fura-2 signal was increased by hyperpolarization, and by a low concentration of 2-APB (5 microM), and exhibited Ca(2+)-dependent potentiation. These properties are entirely consistent with Orai1/CRAC, rather than any known TRP channel and this conclusion was supported by patch-clamp electrophysiological analysis. We identified a store-operated Ca2+ current with the same properties, including high selectivity for Ca2+ over monovalent cations, pronounced inward rectification and a very positive reversal potential, Ca(2+)-dependent current potentiation, and block by SKF-96365, DES and 50 microM 2-APB. Determining the contribution of Orai1/CRAC in different cell types is crucial to future mechanistic and therapeutic studies; this comprehensive multi-strategy analysis demonstrates that Orai1/CRAC channels are responsible for SOCE in primary microglia.
Depletion of Ca(2+) from the endoplasmic reticulum (ER) results in activation of plasma membrane Ca(2+) entry channels. This 'store-operated' process requires translocation of a transmembrane ER Ca(2+) sensor protein, stromal interaction molecule 1 (STIM1), to sites closely apposed to Ca(2+) channels at the cell surface. However, it is not known whether a reduction in Ca(2+) stores is coupled to other signalling pathways by this mechanism. We found that lowering the concentration of free Ca(2+) in the ER, independently of the cytosolic Ca(2+) concentration, also led to recruitment of adenylyl cyclases. This resulted in enhanced cAMP accumulation and PKA activation, measured using FRET-based cAMP indicators. Translocation of STIM1 was required for efficient coupling of ER Ca(2+) depletion to adenylyl cyclase activity. We propose the existence of a pathway (store-operated cAMP signalling or SOcAMPS) in which the content of internal Ca(2+) stores is directly connected to cAMP signalling through a process that involves STIM1.
In immune cells, generation of sustained Ca(2+) levels is mediated by the Ca(2+) release-activated Ca(2+) (CRAC) current. Molecular key players in this process comprise the stromal interaction molecule 1 (STIM1) that functions as a Ca(2+) sensor in the endoplasmic reticulum and ORAI1 located in the plasma membrane. Depletion of endoplasmic reticulum Ca(2+) stores leads to STIM1 multimerization into discrete puncta, which co-cluster with ORAI1 to couple to and activate ORAI1 channels. The cytosolic C terminus of STIM1 is sufficient to activate ORAI1 currents independent of store depletion. Here we identified an ORAI1-activating small fragment (OASF, amino acids 233-450/474) within STIM1 C terminus comprising the two coiled-coil domains and additional 50-74 amino acids that exhibited enhanced interaction with ORAI1, resulting in 3-fold increased Ca(2+) currents. This OASF, similar to the complete STIM1 C terminus, displayed the ability to homomerize by a novel assembly domain that occurred subsequent to the coiled-coil domains. A smaller fragment (amino acids 233-420) generated by a further deletion of 30 amino acids substantially reduced the ability to homomerize concomitant to a loss of coupling to as well as activation of ORAI1. Extending OASF by 35 amino acids (233-485) did not alter homomerization but substantially decreased efficiency in coupling to and activation of ORAI1. Expressing OASF in rat basophilic leukemia (RBL) mast cells demonstrated its enhanced plasma membrane targeting associated with 2.5-fold larger CRAC currents in comparison with the complete STIM1 C terminus. In aggregate, we have identified two cytosolic key regions within STIM1 C terminus that control ORAI1/CRAC activation: a homomerization domain indispensable for coupling to ORAI1 and a modulatory domain that controls the extent of coupling to ORAI1.
Ca(2+)-release-activated Ca(2+) (CRAC) channels underlie sustained Ca(2+) signalling in lymphocytes and numerous other cells after Ca(2+) liberation from the endoplasmic reticulum (ER). RNA interference screening approaches identified two proteins, Stim and Orai, that together form the molecular basis for CRAC channel activity. Stim senses depletion of the ER Ca(2+) store and physically relays this information by translocating from the ER to junctions adjacent to the plasma membrane, and Orai embodies the pore of the plasma membrane calcium channel. A close interaction between Stim and Orai, identified by co-immunoprecipitation and by Förster resonance energy transfer, is involved in the opening of the Ca(2+) channel formed by Orai subunits. Most ion channels are multimers of pore-forming subunits surrounding a central channel, which are preassembled in the ER and transported in their final stoichiometry to the plasma membrane. Here we show, by biochemical analysis after cross-linking in cell lysates and intact cells and by using non-denaturing gel electrophoresis without cross-linking, that Orai is predominantly a dimer in the plasma membrane under resting conditions. Moreover, single-molecule imaging of green fluorescent protein (GFP)-tagged Orai expressed in Xenopus oocytes showed predominantly two-step photobleaching, again consistent with a dimeric basal state. In contrast, co-expression of GFP-tagged Orai with the carboxy terminus of Stim as a cytosolic protein to activate the Orai channel without inducing Ca(2+) store depletion or clustering of Orai into punctae yielded mostly four-step photobleaching, consistent with a tetrameric stoichiometry of the active Orai channel. Interaction with the C terminus of Stim thus induces Orai dimers to dimerize, forming tetramers that constitute the Ca(2+)-selective pore. This represents a new mechanism in which assembly and activation of the functional ion channel are mediated by the same triggering molecule.
Mast cell activation involves cross-linking of IgE receptors followed by phosphorylation of the non-receptor tyrosine kinase Syk. This results in activation of the plasma membrane-bound enzyme phospholipase Cgamma1, which hydrolyzes the minor membrane phospholipid phosphatidylinositol 4,5-bisphosphate to generate diacylglycerol and inositol trisphosphate. Inositol trisphosphate raises cytoplasmic Ca2+ concentration by releasing Ca2+ from intracellular stores. This Ca2+ release phase is accompanied by sustained Ca2+ influx through store-operated Ca2+ release-activated Ca2+ (CRAC) channels. Here, we find that engagement of IgE receptors activates Syk, and this leads to Ca2+ release from stores followed by Ca2+ influx. The Ca2+ influx phase then sustains Syk activity. The Ca2+ influx pathway activated by these receptors was identified as the CRAC channel, because pharmacological block of the channels with either a low concentration of Gd3+ or exposure to the novel CRAC channel blocker 3-fluoropyridine-4-carboxylic acid (2',5'-dimethoxybiphenyl-4-yl)amide or RNA interference knockdown of Orai1, which encodes the CRAC channel pore, all prevented the increase in Syk activity triggered by Ca2+ entry. CRAC channels and Syk are spatially close together, because increasing cytoplasmic Ca2+ buffering with the fast Ca2+ chelator 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid tetrakis failed to prevent activation of Syk by Ca2+ entry. Our results reveal a positive feedback step in mast cell activation where receptor-triggered Syk activation and subsequent Ca2+ release opens CRAC channels, and the ensuing local Ca2+ entry then maintains Syk activity. Ca2+ entry through CRAC channels therefore provides a means whereby the Ca2+ and tyrosine kinase signaling pathways can interact with one another.
Two proteins, STIM1 in the endoplasmic reticulum and Orai1 in the plasma membrane, are required for the activation of Ca²⁺ release-activated Ca²⁺ (CRAC) channels at the cell surface. How these proteins interact to assemble functional CRAC channels has remained uncertain. Here, we determine how many Orai1 and STIM1 molecules are required to form a functional CRAC channel. We engineered several genetically expressed fluorescent Orai1 tandem multimers and a fluorescent, constitutively active STIM1 mutant. The tandem multimers assembled into CRAC channels, as seen by rectifying inward currents and by cytoplasmic calcium elevations. CRAC channels were visualized as fluorescent puncta in total internal reflection microscopy. With single-molecule imaging techniques, it was possible to observe photo-bleaching of individual fluorophores and to count the steps of bleaching as a measure of the stoichiometry of each CRAC channel complex. We conclude that the subunit stoichiometry in an active CRAC channel is four Orai1 molecules and two STIM1 molecules. Fluorescence resonance energy transfer experiments also showed that four Orai1 subunits form the assembled channel. From the fluorescence intensity of single fluorophores, we could estimate that our transfected HEK293 cells had almost 400,000 CRAC channels and that, when intracellular Ca²⁺ stores were depleted, the channels clustered in aggregates containing ≈1,300 channels, amplifying the local Ca²⁺ entry.
• endoplasmic reticulum
• fluorescence resonance energy transfer
In many cell types, receptor-mediated Ca2+ release from internal stores is followed by Ca2+ influx across the plasma membrane. The sustained entry of Ca2+ is thought to result partly from the depletion of intracellular Ca2+ pools. Most investigations have characterized Ca2+ influx indirectly by measuring Ca(2+)-activated currents or using Fura-2 quenching by Mn2+, which in some cells enters the cells by the same influx pathway. But only a few studies have investigated this Ca2+ entry pathway more directly. We have combined patch-clamp and Fura-2 measurements to monitor membrane currents in mast cells under conditions where intracellular Ca2+ stores were emptied by either inositol 1,4,5-trisphosphate, ionomycin, or excess of the Ca2+ chelator EGTA. The depletion of Ca2+ pools by these independent mechanisms commonly induced activation of a sustained calcium inward current that was highly selective for Ca2+ ions over Ba2+, Sr2+ and Mn2+. This Ca2+ current, which we term ICRAC (calcium release-activated calcium), is not voltage-activated and shows a characteristic inward rectification. It may be the mechanism by which electrically nonexcitable cells maintain raised intracellular Ca2+ concentrations and replenish their empty Ca2+ stores after receptor stimulation.
In order to understand the structural bases of ion conduction, ion selectivity, and gating in the nicotinic acetylcholine
receptor, mutagenesis and covalent modification were combined to identify the amino acid residues that line the channel. The
side chains of alternate residues--Ser248, Leu250, Ser252, and Thr254--in M2, a membrane-spanning segment of the alpha subunit,
are exposed in the closed channel. Thus alpha 248-254 probably forms a beta strand, and the gate is closer to the cytoplasmic
end of the channel than any of these residues. On channel opening, Leu251 is also exposed. These results lead to a revised
view of the closed and open channel structures.
A Ca2+ current activated by store depletion has been described recently in several cell types and has been termed I
CRAC (for Ca2+ release-activated Ca2+ current). In this paper, the Ca2+ and Ba2+ permeability of CRAC channels is investigated in mast cells, rat basophilic leukaemia cells (RBL) and human T-lymphocytes (Jurkat). The selectivity of CRAC channels for Ca2+ over monovalent cations is identical in all three cell types and is at least as high as that of voltage-operated Ca2+ (VOC) channels in the various tissues tested. The amplitude of Ba2+ currents relative to Ca2+ currents (I
Ba/I
Ca) through CRAC channels was found to be strongly dependent on the membrane potential and was much smaller in Jurkat cells compared to mast and RBL cells. An anomalous mole-fraction behavior was observed at very negative membrane potentials in all three cell types when using different mixtures of external Ca2+ and Ba2+. In contrast to VOC channels, the anomalous mole-fraction effect was not observed at potentials positive to−20 mV.
We investigated a T-cell activation deficiency in a 3-month-old boy with protracted diarrhea, serious cytomegalovirus pneumonia, and a family history (in a brother) of cytomegalovirus infection and toxoplasmosis. In spite of detection of normal number of peripheral lymphocytes, T cells did not proliferate after activation by anti-CD3 and anti-CD2 antibodies, although proliferation induced by antigens was detectable. We sought to determine the origin of this defect as it potentially represented a valuable tool to analyze T-cell physiology. T-cell activation by anti-CD3 antibody or phytohemagglutinin (PHA) led to reduced interleukin-2 (IL-2) production and abnormal nuclear factor-activated T cell (NF-AT; a complex regulating the IL-2 gene transcription) binding activity to a specific oligonucleotide. T-cell proliferation was restored by IL-2. Early events of T-cell activation, such as anti-CD3 antibody-induced cellular protein tyrosine phosphorylation, p59fyn and p56lck kinase activities, and phosphoinositide turnover, were found to be normal. In contrast, anti-CD3 antibody-induced Ca2+ flux was grossly abnormal. Release from endoplasmic reticulum stores was detectable as tested in the presence of anti-CD3 antibody or thapsigargin after cell membrane depolarization in a K+ rich medium, whereas extracellular entry of Ca2+ was defective. The latter abnormality was not secondary to defective K+ channel function, which was found to be normal. A similar defect was found in other hematopoietic cell lineages and in fibroblasts as evaluated by both cytometry and digital video imaging experiments at a single-cell level. This primary T-cell immunodeficiency appears, thus, to be due to defective Ca2+ entry through the plasma membrane. The same abnormality did not alter B-cell proliferation, platelet function, and polymorphonuclear neutrophil (PMN) function. Elucidation of the mechanism underlying this defect would help to understand the physiology of Ca2+ mobilization in T cells.
Stimulation of antigen receptors of lymphocytes triggers a transitory release of Ca2+ from internal stores and the opening of a transmembrane Ca2+ conductive pathway. The latter underlies the sustained increase of intracellular free calcium concentration, and it seems to be a key event in the Ca(2+)-dependent biochemical cascade leading to T cell proliferation. Alternatively, pharmacological depletion of internal stores by itself activates Ca2+ influx. This has led to the hypothesis that antigen-triggered Ca2+ influx is secondary to Ca2+ release from internal stores. However, the precise relationship between antigen and Ca2+ release-activated Ca2+ currents remains unclear, particularly since neither of them has been electrophysiologically recorded in normal lymphocytes. Using the whole-cell and the perforated configurations of the patch clamp technique on peripheral blood lymphocytes, we found that a low amplitude Ca(2+)-selective current was triggered when intracellular stores were depleted by stimuli such as the intracellular perfusion of inositol triphosphate or thapsigargin and the extracellular perfusion of ionomycin. A similar current was elicited by the cross-linking of the T cell receptor-CD3 complex. This current displayed an inward rectification below 0 mV and was completely blocked by the divalent cation Cd2+. It was very selective for Ca2+ over Na+ and insensitive to changes in chloride concentration. The physiological relevance of this conductance was investigated with the analysis of abnormal Ca2+ signaling in lymphocytes from a patient suffering from a primary immunodeficiency associated with a defective T cell proliferation. Using fura-2 video imaging, an absence of Ca2+ influx was established in the patient's lymphocytes, whereas the Ca2+ release from internal stores was normal. This was the case whether cells were stimulated physiologically through their antigen receptors or with store depleting pharmacological agents. Most importantly, no Ca(2+)-selective current was elicited in these cells. Our data strongly suggest that the Ca2+ release-activated current underlies the sustained Ca2+ influx during antigenic stimulation and that it plays a key role in the immune function.
Calcium entry in non-excitable cells occurs through calcium-selective currents activated secondarily to store depletion and/or through non-selective cation channels (e.g., receptor- or second-messenger-activated channels). The driving force for calcium influx can be modified by chloride or potassium channels, which set the membrane potential of cells. Together, these conductances determine the extent of calcium entry. Mast cells are an excellent model system for studying calcium influx, because calcium-release-activated calcium currents (ICRAC), second-messenger-activated non-selective currents and chloride currents are present in these cells. Whole-cell patch-clamp recordings were used to test the effects of the commonly used calcium entry blockers econazole and SK&F 96365, as well as the antiallergic and anti-inflammatory drugs tenidap, ketotifen and cromolyn on these channels. All tested drugs blocked the three different channel types with a similar order of magnitude (IC50 values ranging from micromolar to millimolar). Hence, these drugs cannot be used to discriminate between different calcium entry mechanisms.
Inositol trisphosphate is a second messenger that controls many cellular processes by generating internal calcium signals. It operates through receptors whose molecular and physiological properties closely resemble the calcium-mobilizing ryanodine receptors of muscle. This family of intracellular calcium channels displays the regenerative process of calcium-induced calcium release responsible for the complex spatiotemporal patterns of calcium waves and oscillations. Such a dynamic signalling pathway controls many cellular processes, including fertilization, cell growth, transformation, secretion, smooth muscle contraction, sensory perception and neuronal signalling.
The depletion of intracellular Ca2+ stores triggers the opening of Ca2+ release-activated Ca2+ (CRAC) channels in the plasma membrane of T lymphocytes. We have investigated the additional role of extracellular Ca2+ (Ca02+) in promoting CRAC channel activation in Jurkat leukemic T cells. Ca2+ stores were depleted with 1 microM thapsigargin in the nominal absence of Ca02+ with 12 mM EGTA or BAPTA in the recording pipette. Subsequent application of Ca02+ caused ICRAC to appear in two phases. The initial phase was complete within 1 s and reflects channels that were open in the absence of Ca02+. The second phase consisted of a severalfold exponential increase in current amplitude with a time constant of 5-10 s; we call this increase Ca(2+)-dependent potentiation, or CDP. The shape of the current-voltage relation and the inferred single-channel current amplitude are unchanged during CDP, indicating that CDP reflects an alteration in channel gating rather than permeation. The extent of CDP is modulated by voltage, increasing from approximately 50% at +50 mV to approximately 350% at -75 mV in the presence of 2 mM Ca02+. The voltage dependence of CDP also causes ICRAC to increase slowly during prolonged hyperpolarizations in the constant presence of Ca02+. CDP is not affected by exogenous intracellular Ca2+ buffers, and Ni2+, a CRAC channel blocker, can cause potentiation. Thus, the underlying Ca2+ binding site is not intracellular. Ba2+ has little or no ability to potentiate CRAC channels. These results demonstrate that the store-depletion signal by itself triggers only a small fraction of capacitative Ca2+ entry and establish Ca2+ as a potent cofactor in this process. CDP confers a previously unrecognized voltage dependence and slow time dependence on CRAC channel activation that may contribute to the dynamic behavior of ICRAC.
Purpose of review: Nasal polyposis is a chronic inflammatory disease of the upper airway characterized histologically by the infiltration of inflammatory cells like eosinophils or neutrophils. Several hypotheses have been put forward regarding the underlying mechanisms including chronic infection, aspirin intolerance, alteration in aerodynamics with trapping of pollutants, epithelial disruptions, epithelial cell defects/gene deletions (CFTR gene), inhalant or food allergies. The present review is an update on the pathomechanisms of nasal polyposis. Recent findings: In the majority of nasal polyps, eosinophils comprise more than 60% of the cell population. Besides eosinophils, mast cells and activated T cells are also increased. An increased production of cytokines/chemokines like granulocyte/macrophage colony-stimulating factor, IL-5, RANTES and eotaxin contribute to eosinophil migration and survival. Increased levels of IL-8 can induce neutrophil infiltration. Increased expression of vascular endothelial growth factor and its upregulation by transforming growth factor-β can contribute to the edema and increased angiogenesis in nasal polyps. Again, transforming growth factor-β can modulate fibroblast function and thus contribute to eosinophil infiltration and stromal fibrosis. Other mediators like albumin, histamine and immunoglobulins IgE and IgG are also increased in nasal polyps. In addition, the local production of IgE in nasal polyps can contribute to the increased recurrence of nasal polyps via the IgE-mast cell-FcεRI cascade. Finally, mast cell/T cell-epithelial cell/fibroblast interactions can contribute to the persistent eosinophilic inflammation seen in polyps. Summary: Thus although nasal polyposis is a multifactorial disease with several different etiological factors, chronic persistent inflammation is undoubtedly a major factor irrespective of the etiology.
Calcium influx through plasma membrane store-operated Ca2+ (SOC) channels is triggered when the endoplasmic reticulum (ER) Ca2+ store is depleted — a homeostatic Ca2+ signalling mechanism that remained enigmatic for more than two decades. RNA-interference (RNAi) screening and molecular and cellular physiological analysis recently identified STIM1 as the mechanistic 'missing link' between the ER and the plasma membrane. STIM proteins sense the depletion of Ca2+ from the ER, oligomerize, translocate to junctions adjacent to the plasma membrane, organize Orai or TRPC (transient receptor potential cation) channels into clusters and open these channels to bring about SOC entry.
Work in my laboratory related to the subject of this review is supported by the Behrens-Weise-Stiftung and by the Deutsche Forschungsgemeinschaft (SFB 406 and SFB 523), by a grant from the European Community (No. CHRX-CT94–0500), and by the Human Science Frontier Program (RG-4/95B). I would like to thank my colleagues Eric Kandel, Tom Jessell, Bert Sakmann, Alain Marty, Tobias Moser, and Christian Rosenmund for helpful suggestions on the manuscript.
Defects in the development or activation of T cells result in immunodeficiency associated with severe infections early in life. T-cell activation requires Ca2+ influx through Ca2+-release activated Ca2+ (CRAC) channels encoded by the gene ORAI1.
Investigation of the genetic causes and the clinical phenotype of immunodeficiency in patients with impaired Ca2+ influx and CRAC channel function.
DNA sequence analysis for mutations in the genes ORAI1, ORAI2, ORAI3, and stromal interaction molecule (STIM) 1 and 2, as well as mRNA and protein expression analysis of ORAI1 in immunodeficient patients. Immunohistochemical analysis of ORAI1 tissue distribution in healthy human donors.
We identified mutations in ORAI1 in patients from 2 unrelated families. One patient is homozygous for a frameshift nonsense mutation in ORAI1 (ORAI1-A88SfsX25), and a second patient is compound heterozygous for 2 missense mutations in ORAI1 (ORAI1-A103E/L194P). All 3 mutations abolish ORAI1 expression and impair Ca2+ influx and CRAC channel function. The clinical syndrome associated with ORAI1 deficiency is characterized by immunodeficiency with a defect in the function but not in the development of lymphocytes, congenital myopathy, and anhydrotic ectodermal dysplasia with a defect in dental enamel calcification. In contrast with the limited clinical phenotype, we found ORAI1 protein expression in a wide variety of cell types and organs.
Ca2+ influx through ORAI1 is crucial for lymphocyte function in vivo. Despite almost ubiquitous ORAI1 expression, the channel has a nonredundant role in only a few cell types judging from the limited clinical phenotype in ORAI1-deficient patients.
Nasal polyposis is a chronic inflammatory disease of the upper respiratory tract that affects around 2% of the population and almost 67% of patients with aspirin-intolerant asthma. Polyps are rich in mast cells and eosinophils, resulting in high levels of the proinflammatory cysteinyl leukotrienes.
To better understand the role of the proinflammatory leukotrienes in nasal polyposis, we asked the following questions: (1) How do nasal polyps produce leukotriene C(4) (LTC(4))? (2) Can LTC(4) feed back in a paracrine way to maintain mast cell activation? (3) Could a combination therapy targeting the elements of this feed-forward loop provide a novel therapy for allergic disease?
We have used immunohistochemistry, enzyme immunoassay, and cytoplasmic calcium ion (Ca(2+)) imaging to address these questions on cultured and acutely isolated human mast cells from patients with polyposis.
Ca(2+) entry through store-operated Ca(2+) release-activated Ca(2+) (CRAC) channels in polyps produced LTC(4) in a manner dependent on protein kinase C. LTC(4) thus generated activated mast cells through cysteinyl leukotriene type I receptors. Hence Ca(2+) influx into mast cells stimulates LTC(4) production, which then acts as a paracrine signal to activate further Ca(2+) influx. A combination of a low concentration of both a CRAC channel blocker and a leukotriene receptor antagonist was as effective at suppressing mast cell activation as a high concentration of either antagonist alone.
A drug combination directed against CRAC channels and leukotriene receptor antagonist suppresses the feed-forward loop that leads to aberrant mast cell activation. Hence our results identify a new potential strategy for combating polyposis and mast cell-dependent allergies.
When cells are activated by calcium-mobilizing agonists at low, physiological concentrations, the resulting calcium signals generally take the form of repetitive regenerative discharges of stored calcium, termed calcium oscillations [1]. These intracellular calcium oscillations have long fascinated biologists as a mode of digitized intracellular signaling. Recent work has highlighted the role of calcium influx as an essential component of calcium oscillations [2]. This influx occurs through a process known as store-operated calcium entry, which is initiated by calcium sensor proteins, STIM1 and STIM2, in the endoplasmic reticulum [3]. STIM2 is activated by changes in endoplasmic reticulum calcium near the resting level, whereas a threshold of calcium depletion is required for STIM1 activation [4]. Here we show that, surprisingly, it is STIM1 and not STIM2 that is exclusively involved in calcium entry during calcium oscillations. The implication is that each oscillation produces a transient drop in endoplasmic reticulum calcium and that this drop is sufficient to transiently activate STIM1. This transient activation of STIM1 can be observed in some cells by total internal reflection fluorescence microscopy. This arrangement nicely provides a clearly defined and unambiguous signaling system, translating a digital calcium release signal into calcium influx that can signal to downstream effectors.
Store-operated Ca2+ entry (SOCE) is a mechanism used by many cells types including lymphocytes and other immune cells to increase intracellular Ca2+ concentrations to initiate signal transduction. Activation of immunoreceptors such as the T-cell receptor, B-cell receptor, or Fc receptors results in the release of Ca2+ ions from endoplasmic reticulum (ER) Ca2+ stores and subsequent activation of plasma membrane Ca2+ channels such as the well-characterized Ca2+ release-activated Ca2+ (CRAC) channel. Two genes have been identified that are essential for SOCE: ORAI1 as the pore-forming subunit of the CRAC channel in the plasma membrane and stromal interaction molecule-1 (STIM1) sensing the ER Ca2+ concentration and activating ORAI1-CRAC channels. Intense efforts in the past several years have focused on understanding the molecular mechanism of SOCE and the role it plays for cell functions in vitro and in vivo. A number of transgenic mouse models have been generated to investigate the role of ORAI1 and STIM1 in immunity. In addition, mutations in ORAI1 and STIM1 identified in immunodeficient patients provide valuable insight into the role of both genes and SOCE. This review focuses on the role of ORAI1 and STIM1 in vivo, discussing the phenotypes of ORAI1- and STIM1-deficient human patients and mice.
Cytoplasmic Ca(2+) oscillations are a universal signaling mode that activates numerous cellular responses [1, 2]. Oscillations are considered the physiological mechanism of Ca(2+) signaling because they occur at low levels of stimulus intensity [3]. Ca(2+) oscillations are proposed to convey information in their amplitude and frequency, leading to activation of specific downstream targets [4-6]. Here, we report that the spatial Ca(2+) gradient within the oscillation is key. Ca(2+) oscillations in mast cells evoked over a range of agonist concentrations in the presence of external Ca(2+) were indistinguishable from those in the absence of Ca(2+) when plasmalemmal Ca(2+) extrusion was suppressed. Nevertheless, only oscillations with accompanying Ca(2+) entry through store-operated CRAC channels triggered gene expression. Increased cytoplasmic Ca(2+) buffering prevented oscillations but not gene activation. Local Ca(2+) influx and not global Ca(2+) oscillations therefore drives gene expression at physiological levels of stimulation. Rather than serving to maintain Ca(2+) oscillations by replenishing stores, we suggest that the role of oscillations might be to activate CRAC channels, thereby ensuring the generation of spatially restricted physiological Ca(2+) signals driving gene activation. Furthermore, we show that the spatial profile of a Ca(2+) oscillation provides a novel mechanism whereby a pleiotropic messenger specifically activates gene expression.
Store-operated Ca(2+) channels activated by the depletion of Ca(2+) from the endoplasmic reticulum (ER) are a major Ca(2+) entry pathway in nonexcitable cells and are essential for T cell activation and adaptive immunity. After store depletion, the ER Ca(2+) sensor STIM1 and the CRAC channel protein Orai1 redistribute to ER-plasma membrane (PM) junctions, but the fundamental issue of how STIM1 activates the CRAC channel at these sites is unresolved. Here, we identify a minimal, highly conserved 107-aa CRAC activation domain (CAD) of STIM1 that binds directly to the N and C termini of Orai1 to open the CRAC channel. Purified CAD forms a tetramer that clusters CRAC channels, but analysis of STIM1 mutants reveals that channel clustering is not sufficient for channel activation. These studies establish a molecular mechanism for store-operated Ca(2+) entry in which the direct binding of STIM1 to Orai1 drives the accumulation and the activation of CRAC channels at ER-PM junctions.
Tumor metastasis is the primary cause of death of cancer patients. Understanding the molecular mechanisms underlying tumor metastasis will provide potential drug targets. We report here that Orai1 and STIM1, both of which are involved in store-operated calcium entry, are essential for breast tumor cell migration in vitro and tumor metastasis in mice. Reduction of Orai1 or STIM1 by RNA interference in highly metastatic human breast cancer cells or treatment with a pharmacological inhibitor of store-operated calcium channels decreased tumor metastasis in animal models. Our data demonstrate a role for Orai1 and STIM1 in tumor metastasis and suggest store-operated calcium entry channels as potential cancer therapeutic targets.
Influx of Ca(2+) through store-operated Ca(2+) channels (SOCs) is a central component of receptor-evoked Ca(2+) signals. Orai channels are SOCs that are gated by STIM1, a Ca(2+) sensor located in the ER but how it gates and regulates the Orai channels is unknown. Here, we report the molecular basis for gating of Orais by STIM1. All Orai channels are fully activated by the conserved STIM1 amino acid fragment 344-442, which we termed SOAR (the STIM1 Orai activating region). SOAR acts in combination with STIM1 (450-485) to regulate the strength of interaction with Orai1. Activation of Orai1 by SOAR recapitulates all the kinetic properties of Orai1 activation by STIM1. However, mutations of STIM1 within SOAR prevent activation of Orai1 but not co-clustering of STIM1 and Orai1 in response to Ca(2+) store depletion, indicating that STIM1-Orai1 co-clustering is not sufficient for Orai1 activation. An intact carboxy terminus alpha-helicial region of Orai is required for activation by SOAR. Deleting most of the Orai1 amino terminus impaired Orai1 activation by STIM1, but Orai1(Delta1-73) interacted with and was fully activated by SOAR. Accordingly, the characteristic inward rectification of Orai is mediated by an interaction between the polybasic STIM1 (672-685) and a Pro-rich region in the N terminus of Orai1. Hence, the essential properties of Orai1 function can be rationalized by interactions with discrete regions of STIM1.
Mast cells are key components of the immune system, where they help orchestrate the inflammatory response. Aberrant mast cell activation is linked to a variety of allergic diseases, including asthma, eczema, rhinitis, and nasal polyposis, which in combination affect up to 20% of the population in industrialized countries. On activation, mast cells release a variety of signals that target the bronchi and vasculature and recruit other immune cells to the inflammatory site. Prominent among such signals are the cysteinyl leukotrienes, a family of potent proinflammatory lipid mediators comprising leukotriene C(4) (LTC(4)), LTD(4), and LTE(4). LTC(4), the parent compound, is secreted from mast cells following Ca(2+) influx through store-operated calcium release-activated calcium (CRAC) channels. Here, we show that activated mast cells release a paracrine signal that evokes Ca(2+) signals in spatially separate resting mast cells. The paracrine signal was identified as a cysteinyl leukotriene because 1) RNAi knockdown or pharmacological block of the 5-lipoxygenase enzyme prevented activated mast cells from stimulating resting cells. 2) Block of cysteinyl leukotriene type I receptors on resting mast cells with the clinically prescribed receptor antagonist montelukast prevented their activation by active mast cells. 3) RNAi knockdown of cysteinyl leukotriene type I receptors on resting cells prevented them from responding to the paracrine signal derived from activated mast cells. 4) Purified LTC(4) evoked Ca(2+) signals in mast cells that were identical to those triggered by the paracrine signal. Low levels of stimulus intensity released sufficient levels of leukotriene to activate resting cells. Leukotriene secretion still occurred tens of minutes after stimulation, suggesting a role as a long-lasting trigger in mast cell activation. Stimulation of the cysteinyl leukotriene receptor activated CRAC channels and evoked prominent store-operated Ca(2+) entry. This resulted in further cysteinyl leukotriene production, triggering a positive feedback cascade. Acutely isolated mast cells from patients with allergic rhinitis exhibited store-operated Ca(2+) influx through CRAC channels and responded to cysteinyl leukotrienes. Histological analysis of samples taken from patients revealed clustering of mast cells, often located within 20 microm of each other, a distance sufficient for paracrine signaling by leukotrienes to operate effectively. We conclude that a positive-feedback cascade involving CRAC channels and cysteinyl leukotrienes constitute a novel mechanism for sustaining mast cell activation.
Stromal interaction molecule-1 (STIM1) activates store-operated Ca2+ entry (SOCE) in response to diminished luminal Ca2+ levels. Here, we present the atomic structure of the Ca2+-sensing region of STIM1 consisting of the EF-hand and sterile alpha motif (SAM) domains (EF-SAM). The canonical EF-hand is paired with a previously unidentified EF-hand. Together, the EF-hand pair mediates mutually indispensable hydrophobic interactions between the EF-hand and SAM domains. Structurally critical mutations in the canonical EF-hand, "hidden" EF-hand, or SAM domain disrupt Ca2+ sensitivity in oligomerization via destabilization of the entire EF-SAM entity. In mammalian cells, EF-SAM destabilization mutations within full-length STIM1 induce punctae formation and activate SOCE independent of luminal Ca2+. We provide atomic resolution insight into the molecular basis for STIM1-mediated SOCE initiation and show that the folded/unfolded state of the Ca2+-sensing region of STIM is crucial to SOCE regulation.
Ca(2+) entry through store-operated Ca(2+) release-activated Ca(2+) (CRAC) channels initiates key functions such as gene expression and exocytosis of inflammatory mediators. Activation of CRAC channels by store depletion involves the redistribution of the ER Ca(2+) sensor, stromal interaction molecule 1 (STIM1), to peripheral sites where it co-clusters with the CRAC channel subunit, Orai1. However, how STIM1 communicates with the CRAC channel and initiates the subsequent events culminating in channel opening is unclear. Here, we show that redistribution of STIM1 and Orai1 occurs in parallel with a pronounced increase in fluorescence resonance energy transfer (FRET) between STIM1 and Orai1, supporting the idea that activation of CRAC channels occurs through physical interactions with STIM1. Co-expression of Orai1-CFP and Orai1-YFP results in a high degree of FRET in resting cells, indicating that Orai1 exists as a multimer. However, store depletion triggers molecular rearrangements in Orai1 resulting in a decline in Orai1-Orai1 FRET. The decline in Orai1-Orai1 FRET is not seen in the absence of STIM1 co-expression and is abolished in Orai1 mutants with impaired STIM1 interaction. Both the STIM1-Orai1 interaction as well as the molecular rearrangements in Orai1 are altered by two powerful modulators of CRAC channel activity: extracellular Ca(2+) and 2-APB. These studies identify a STIM1-dependent conformational change in Orai1 during the activation of CRAC channels and reveal that STIM1-Orai1 interaction and the downstream Orai1 conformational change can be independently modulated to fine-tune CRAC channel activity.
Intestinal T lymphocytes are normally unresponsive to microbial and recall antigens in vitro, whereas the same antigens induce strong immune responses in peripheral-blood-derived T cells. We obtained T lymphocytes from peripheral blood and from the non-inflamed and inflamed intestinal mucosa of 6 patients (3 male, 3 female; mean age 33 years) with Crohn's disease. The T cells were stimulated in vitro with a range of microbial antigens. Whereas T cells from normal mucosa were unresponsive, those from inflamed mucosa had a proliferative response comparable to that of the peripheral-blood-derived T cells. These findings suggest that physiologic unresponsiveness to luminal antigens is abrogated in the inflammatory lesions of Crohn's disease patients. Infiltrating T lymphocytes may therefore mediate chronic inflammation on encountering the many antigens present in the intestine.
A model is proposed for the mechanism by which activation of surface membrane receptors causes sustained Ca2+ entry into cells from the extracellular space. Reassessment of previously published findings on the behavior of receptor-regulated intracellular Ca2+ pools leads to the conclusion that when such pools are empty, a pathway from the extracellular space to the pool is opened; conversely when the pool is filled, the pathway is closed and it becomes relatively stable to depletion by low Ca2+ media or chelating agents. The biphasic nature of agonist-activated Ca2+-mobilization is thus seen as an initial emptying of the intracellular Ca2+ pool by inositol (1,4,5) trisphosphate, followed by rapid entry of Ca2+ into the pool and, in the continued presence of inositol (1,4,5) trisphosphate, into the cytosol. On withdrawal of agonist, inositol (1,4,5) trisphosphate is then rapidly degraded, the pathway from the pool to the cytosol is closed, and rapid entry from the outside continues until the Ca2+ content of the pool reaches a level that inactivates Ca2+ entry. This capacitative model allows for Ca2+ release and Ca2+ entry to be controlled by a single messenger, inositol (1,4,5) trisphosphate.
1. Whole-cell patch clamp recordings of membrane currents and fura-2 measurements of free intracellular calcium concentration ([Ca2+]i) were used to study the biophysical properties of a calcium current activated by depletion of intracellular calcium stores in rat peritoneal mast cells. 2. Calcium influx through an inward calcium release-activated calcium current (ICRAC) was induced by three independent mechanisms that result in store depletion: intracellular infusion of inositol 1,4,5-trisphosphate (InsP3) or extracellular application of ionomycin (active depletion), and intracellular infusion of calcium chelators (ethylene glycol bis-N,N,N',N'-tetraacetic acid (EGTA) or 1,2-bis(2-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid (BAPTA)) to prevent reuptake of leaked-out calcium into the stores (passive depletion). 3. The activation of ICRAC induced by active store depletion has a short delay (4-14 s) following intracellular infusion of InsP3 or extracellular application of ionomycin. It has a monoexponential time course with a time constant of 20-30 s and, depending on the complementary Ca2+ buffer, a mean normalized amplitude (at 0 mV) of 0.6 pA pF-1 (with EGTA) and 1.1 pA pF-1 (with BAPTA). 4. After full activation of ICRAC by InsP3 in the presence of EGTA (10 mM), hyperpolarizing pulses to -100 mV induced an instantaneous inward current that decayed by 64% within 50 ms. This inactivation is probably mediated by [Ca2+]i, since the decrease of inward current in the presence of the fast Ca2+ buffer BAPTA (10 mM) was only 30%. 5. The amplitude of ICRAC was dependent on the extracellular Ca2+ concentration with an apparent dissociation constant (KD) of 3.3 mM. Inward currents were nonsaturating up to -200 mV. 6. The selectivity of ICRAC for Ca2+ was assessed by using fura-2 as the dominant intracellular buffer (at a concentration of 2 mM) and relating the absolute changes in the calcium-sensitive fluorescence (390 nm excitation) with the calcium current integral. This relationship was almost identical to the one determined for Ca2+ influx through voltage-activated calcium currents in chromaffin cells, suggesting a similar selectivity. Replacing Na+ and K+ by N-methyl-D-glucamine (with Ca2+ ions as exclusive charge carriers) reduced the amplitude of ICRAC by only 9% further suggesting a high specificity for Ca2+ ions. 7. The current amplitude was not greatly affected by variations of external Mg2+ in the range of 0-12 mM. Even at 12 mM Mg2+ the current amplitude was reduced by only 23%. 8. ICRAC was dose-dependently inhibited by Cd2+.(ABSTRACT TRUNCATED AT 250 WORDS)
Voltage-gated Ca2+ channels link changes in membrane potential to the delivery of Ca2+, a key second messenger for many cellular responses. Ca2+ channels show selectivity for Ca2+ over more plentiful ions such as Na+ or K+ by virtue of their high-affinity binding of Ca2+ within the pore. It has been suggested that this binding involves four conserved glutamate residues in equivalent positions in the putative pore-lining regions of repeats I-IV in the Ca2+ channel a1 subunit. We have carried out a systematic series of single amino-acid substitutions in each of these positions and find that all four glutamates participate in high-affinity binding of Ca2+ or Cd2+. Each glutamate carboxylate makes a distinct contribution to ion binding, with the carboxylate in repeat III having the strongest effect. Some single glutamate-to-lysine mutations completely abolish micromolar Ca2+ block, indicating that the pore does not possess any high-affinity binding site that acts independently of the four glutamate residues. The prevailing model of Ca2+ permeation must thus be modified to allow binding of two Ca2+ ions in close proximity, within the sphere of influence of the four glutamates. The functional inequality of the glutamates may be advantageous in allowing simultaneous interactions with multiple Ca2+ ions moving single-file within the pore. Competition among Ca2+ ions for individual glutamates, together with repulsive ion-ion electrostatic interaction, may help achieve rapid flux rates through the channel.
Stimulated influx of Ca2+ across the plasma membrane of T lymphocytes is an essential triggering signal for T-cell activation by antigen. Regulation of the T-cell Ca2+ conductance is not understood; conflicting evidence supports direct activation by inositol 1,4,5-trisphosphate (IP3) or by a signal generated by the depletion of intracellular Ca2+ stores. We have used the perforated-patch recording technique to compare the biophysical properties of Ca2+ currents activated by T-cell receptor stimulation and by thapsigargin, a Ca(2+)-ATPase inhibitor that depletes intracellular stores without generating IP3. Both currents are blocked by Ni2+, are inwardly rectifying, are highly Ca(2+)-selective, and exhibit voltage-independent gating with a unitary chord conductance of approximately 24 fS in isotonic Ca2+. Fluctuation analysis suggests that the underlying Ca2+ transporter is a channel rather than an iron carrier. Thus, in terms of ion permeation, gating, and unitary conductance, the Ca2+ current activated by thapsigargin is indistinguishable from the elicited by crosslinking of T-cell receptors. Moreover, the unitary Ca2+ conductance is > 100-fold smaller than that of previously described IP3-gated, Ca(2+)-permeable channels in T cells [Kuno, M. & Gardner, P. (1987) Nature (London) 326, 301-304]. These results demonstrate that mitogen-activated Ca2+ influx is controlled by the state of intracellular Ca2+ stores rather than by the direct action of IP3 on Ca2+ channels in the plasma membrane.
Peripheral blood lymphocytes (PBL) and alloreactive T cell lines of two male infants born to consanguinous parents and presenting with severe combined immunodeficiency (SCID) showed a pronounced deficiency in T cell activation. Although phenotypically normal, the proliferative response of the childrens' T cells was strongly reduced but could be improved by the addition of interleukin-2 (IL-2). Furthermore both childrens' T cells were unable to produce the cytokines IL-2, interferon-gamma (IFN-gamma), IL-4 and tumor necrosis factor-alpha (TNF-alpha). This multiple cytokine production deficiency could not be restored by IL-2 or co-stimulatory signals provided by antigen-presenting cells (APC). Moreover, mRNA for IL-2 and IFN-gamma could not be detected. In contrast, expression of the activation-dependent cell surface markers CD25 and CD69 was within normal limits. To determine whether the functional defect of the patients' T cells was due to the absence or abnormal binding of transcription factors involved in cytokine gene expression, electrophoretic mobility shift assays were used to examine the DNA binding of AP-1, Oct, CREB, SP1, NF-kappa B and the nuclear factor of activated T cells (NF-AT) to their respective response elements in the promoter of the IL-2 gene. Whereas AP-1, NF-kappa B, Oct, CREB and SP1 displayed normal binding activities in nuclear extracts, the binding of NF-AT to its IL-2 promoter response element was barely detectable both before and after T cell stimulation. Our results strongly suggest that this NF-AT/DNA binding defect is responsible for the multiple cytokine deficiency and the SCID phenotype observed in the two infant brothers.
Intracellular Ca2+ store depletion induces Ca2+ entry across the plasma membrane, allowing the store to recharge. In our experiments, Ca2+ stores in pancreatic acinar cells were depleted by acetylcholine (ACh) stimulation in Ca2+-free solution. Thereafter, Ca2+ entry was only allowed through a CaCl2-containing pipette attached to the basal membrane. Recharging intracellular Ca2+ stores via a patch pipette occurred without a rise in the cytosolic Ca2+ concentration and depended on the operation of a thapsigargin-sensitive Ca2+ pump. After a period of focal Ca2+ entry, ACh could again evoke a rise in the cytosolic Ca2+ concentration, and this rise always started in the apical secretory pole. Recharging the apical Ca2+ store therefore depends on Ca2+ flow through a tunnel from the basal to the secretory pole, and the endoplasmic reticulum Ca2+ pump is essential for this process.
Cytosolic calcium ([Ca2+]i) oscillations are a nearly universal mode of signalling in excitable and non-excitable cells. Although Ca2+ is known to mediate a diverse array of cell functions, it is not known whether oscillations contribute to the efficiency or specificity of signalling or are merely an inevitable consequence of the feedback control of [Ca2+]i. We have developed a Ca2+ clamp technique to investigate the roles of oscillation amplitude and frequency in regulating gene expression driven by the proinflammatory transcription factors NF-AT, Oct/OAP and NF-kappaB. Here we report that oscillations reduce the effective Ca2+ threshold for activating transcription factors, thereby increasing signal detection at low levels of stimulation. In addition, specificity is encoded by the oscillation frequency: rapid oscillations stimulate all three transcription factors, whereas infrequent oscillations activate only NF-kappaB. The genes encoding the cytokines interleukin (IL)-2 and IL-8 are also frequency-sensitive in a way that reflects their degree of dependence on NF-AT versus NF-kappaB. Our results provide direct evidence that [Ca2+]i oscillations increase both the efficacy and the information content of Ca2+ signals that lead to gene expression and cell differentiation.
Nasal polyposis (NP) is a frequent inflammatory chronic disease of the upper respiratory tract, which may impair quality of life (QOL). The NP impact, which is frequently associated with lower respiratory disorders, has never before been studied.
We initiated this prospective study to establish internal validity and reliability of the generic SF-36 questionnaire in NP and to determine to what level daily functioning becomes impaired as a result of NP.
Forty-nine consecutive patients with NP were included. They were assessed for the severity of nasal symptoms and underwent pulmonary function tests. The QOL profiles in patients with NP were compared with those of patients with perennial rhinitis (n = 111) and healthy subjects (n = 116).
Cronbach's coefficient alpha demonstrated the high reliability and validity of the SF-36 questionnaire for patients with NP (alpha =.89). NP impaired QOL more than perennial allergic rhinitis (P <.05). The impairment of QOL was greater when NP was associated with asthma (P <.05). SF-36 scores appeared highly correlated to pulmonary function (FEV1, maximal midexpiratory flow, forced vital capacity), suggesting relationships between QOL in NP and associated bronchial obstruction. Severity of nasal symptoms were not related to QOL scales. In addition, sequential evaluations of QOL, nasal symptoms, and pulmonary function were performed 10 months after the first evaluation in 28 patients with NP. These evaluations demonstrated that NP treatment either with nasal steroids or endonasal ethmoidectomy significantly improved both nasal symptoms and QOL without significant change of pulmonary function.
Our study clearly demonstrated that the SF-36 questionnaire presented a high internal validity and reliability in patients with NP. NP impaired QOL to a greater degree than perennial allergic rhinitis. QOL improvement after NP treatment is related to nasal symptoms improvement.
1. Tight-seal whole-cell patch clamp experiments were performed to examine the ability of different intracellular Ca2+ mobilising agents to activate the Ca2+ release-activated Ca2+ current (ICRAC) in rat basophilic leukaemia (RBL-1) cells under conditions of weak cytoplasmic Ca2+ buffering. 2. Dialysis with a maximal concentration of inositol 1,4,5-trisphosphate (IP3) routinely failed to activate macroscopic ICRAC in low buffer (0.mM EGTA, BAPTA or dimethyl BAPTA), whereas it activated the current to its maximal extent in high buffer (10 mM EGTA). Dialysis with a poorly metabolisable analogue of IP3, with ionomycin, or with IP3 and ionomycin all failed to generate macroscopic ICRAC in low Ca2+ buffering conditions. 3. Dialysis with the sarco/endoplasmic reticulum Ca2+-ATPase (SERCA) pump blocker thapsigargin was able to activate ICRAC even in the presence of low cytoplasmic Ca2+ buffering, albeit at a slow rate. Exposure to IP3 together with the SERCA blockers thapsigargin, thapsigargicin or cyclopiazonic acid rapidly activated ICRAC in low buffer. 4. Following activation of ICRAC by intracellular dialysis with IP3 and thapsigargin in low buffer, the current was very selective for Ca2+ (apparent KD of 1 mM) Sr2+ and Ba2+ were less effective charge carriers and Na+ was not conducted to any appreciable extent. The ionic selectivity of ICRAC was very similar in low or high intracellular Ca2+ buffer. 5. Fast Ca2+-dependent inactivation of ICRAC occurred at a similar rate and to a similar extent in low or high Ca2+ buffer. Ca2+-dependent inactivation is not the reason why macroscopic ICRAC cannot be seen under conditions of low cytoplasmic Ca2+ buffering. 6. ICRAC could be activated by combining IP3 with thapsigargin, even in the presence of 100 microM Ca2+ and the absence of any exogenous Ca2+ chelator, where ATP and glutamate represented the only Ca2+ buffers in the pipette solution. 7. Our results suggest that a threshold exists within the IP3-sensitive Ca2+ store, below which intraluminal Ca2+ needs to fall before ICRAC activates. Possible models to explain the results are discussed.
A series of bis(trifluoromethyl)pyrazoles (BTPs) has been found to be a novel inhibitor of cytokine production. Identified initially as inhibitors of IL-2 synthesis, the BTPs have been optimized in this regard and even inhibit IL-2 production with a 10-fold enhancement over cyclosporine in an ex vivo assay. Additionally, the BTPs show inhibition of IL-4, IL-5, IL-8, and eotaxin production. Unlike the IL-2 inhibitors, cyclosporine and FK506, the BTPs do not directly inhibit the dephosphorylation of NFAT by calcineurin.