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Intracellular pathogenic structures or activities stimulate the formation of inflammasomes, which recruit and activate caspase-1 and trigger an inflammatory form of cell death called pyroptosis. The well-characterized mammalian inflammasome sensor proteins all detect one specific type of signal, for example double-stranded DNA or bacterial flagelli...
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... mouse genome encodes three NLRP1 paralogs, Nlrp1a, Nlrp1b, and Nlrp1c 8 , although Nlrp1c is predicted to be a pseudogene. Nlrp1a is relatively conserved 13 , but Nlrp1b is extremely polymorphic, with five alleles present in common inbred mouse strains (Nlrp1b1-5) 8 ( Table 1). Two of the NLRP1B proteins appear to be non-functional due to defective autoproteolysis (NLRP1B3) or truncation prior to the CARD (NLRP1B4) 8,11,14 . ...Context 2
... is a bipartite toxin comprised of lethal factor (LF), a zinc metalloprotease, and protective antigen (PA), a pore-forming protein that transports LF into the host cytosol. LF activates mNLRP1B alleles 1 and 5 (Table 1) and rNLRP1 alleles 1 and 2 (Table 2), but does not activate mNLRP1A, hNLRP1, or CARD8. LF directly cleaves each sensitive NLRP1 allele near its N-terminus (Fig. 1a) [17][18][19] , generating an unstable neo-N-terminus that Fig. 1 Mouse NLRP1 allele sensitivity to autoproteolysis and LT cleavage. ...Similar publications
Ulcerative colitis (UC) is a type of inflammatory bowel disease (IBD), which is a chronic, relapsing condition associated with the disorder of gut microbial communities. A previous study reported that levels of Roseburia intestinalis (R.I), a butyrate‑producing bacterium, are significantly decreased in patients with IBD and exert an anti‑inflammato...
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... It is important to mention that at the time of these clinical trials, the precise mechanism of action of VbP was unknown. Recent work has shown that VbP inhibits the serine hydrolases dipeptidyl peptidases 8 and 9 (DPP8/9), which activates the CARD8 and NLRP1 inflammasomes in humans and all functional alleles of the Nlrp1b inflammasome in mice ( Figure 1A) [38,43,58,[84][85][86][87]. Notably, CARD8 is the only canonical inflammasome that does not form an ASC-containing signaling platform, which is important for both caspase-1 and cytokine maturation ( Figure 1A) [41][42][43][44]. ...
... Notably, CARD8 is the only canonical inflammasome that does not form an ASC-containing signaling platform, which is important for both caspase-1 and cytokine maturation ( Figure 1A) [41][42][43][44]. Activation of the CARD8, NLRP1, and Nlrp1b inflammasomes leads to caspase-1 activation, which then cleaves GSDMD to induce pyroptosis [38,43,58,[84][85][86][87]. Although VbP can inhibit other serine hydrolases such as FAP and DPP4, DPP8/9 are the specific targets that induce pyroptosis as DPP8/9deficient cells are resistant to VbP-induced cell death [84,87]. ...
Cancer immunotherapy is a novel pillar of cancer treatment that harnesses the immune system to fight tumors and generally results in robust antitumor immunity. Although immunotherapy has achieved remarkable clinical success for some patients, many patients do not respond, underscoring the need to develop new strategies to promote antitumor immunity. Pyroptosis is an immunostimulatory type of regulated cell death that activates the innate immune system. A hallmark of pyroptosis is the release of intracellular contents such as cytokines, alarmins, and chemokines that can stimulate adaptive immune activation. Recent studies suggest that pyroptosis promotes antitumor immunity. Here, we review the mechanisms by which pyroptosis can be induced and highlight new strategies to induce pyroptosis in cancer cells for antitumor defense. We discuss how pyroptosis modulates the tumor microenvironment to stimulate adaptive immunity and promote antitumor immunity. We also suggest research areas to focus on for continued development of pyroptosis as an anticancer treatment. Pyroptosis-based anticancer therapies offer a promising new avenue for treating immunologically ‘cold’ tumors.
... The FIIND domain undergoes a spontaneous maturation event, i.e., an autolytic proteolysis, that appears to be necessary before NLRP1 can be responsive to stimuli [23,24]. In addition, dipeptidyl peptidases (DPP)-8 and 9 inhibit the NLRP1 inflammasome by interacting with the FIIND domain, preventing its assembly [25] while the inhibition of DPP8/9 promotes the activation of NLRP1 [26,27]. Although some studies have shown that ASC is required for the activation of the NLRP1 inflammasome [28,29], others have indicated the possibility of NLRP1 to directly recruit pro-caspase 1 [30] and caspase-5 [5], via a CARD-CARD domain interaction. ...
Neuroinflammation plays a crucial role in the onset and the progression of several neuropathologies, from neurodegenerative disorders to migraine, from Rett syndrome to post-COVID 19 neurological manifestations. Inflammasomes are cytosolic multiprotein complexes of the innate immune system that fuel inflammation. They have been under study for the last twenty years and more recently their involvement in neuro-related conditions has been of great interest as possible therapeutic target. The role of oxidative stress in inflammasome activation has been described, however the exact way of action of specific endogenous and exogenous oxidants needs to be better clarified. In this review, we provide the current knowledge on the involvement of inflammasome in the main neuropathologies, emphasizing the importance to further clarify the role of oxidative stress in its activation including the role of mitochondria in inflammasome-induced neuroinflammation.
... This longer stimulation allowed time for the TLR-mediated upregulation of IRF1 to drive NLRP12 expression. Understanding the regulation and activation mechanisms of inflammasomes has been historically difficult; for instance, even though NLRP1 and NLRP3 inflammasomes have been known for decades, and several activation mechanisms have been proposed for each, [71][72][73][74][75][76][77][78][79][80][81][82][83] no mechanism has yet been identified that encompasses all the activation processes and redundancies observed. Additionally, increasing evidence shows that inflammasomes do not need to act alone and can integrate into larger cell death complexes called PANoptosomes. ...
Cytosolic innate immune sensors are critical for host defense and form complexes, such as inflammasomes and PANoptosomes, that induce inflammatory cell death. The sensor NLRP12 is associated with infectious and inflammatory diseases, but its activating triggers and roles in cell death and inflammation remain unclear. Here, we discovered that NLRP12 drives inflammasome and PANoptosome activation, cell death, and inflammation in response to heme plus PAMPs or TNF. TLR2/4-mediated signaling through IRF1 induced Nlrp12 expression, which led to inflammasome formation to induce maturation of IL-1β and IL-18. The inflammasome also served as an integral component of a larger NLRP12-PANoptosome that drove inflammatory cell death through caspase-8/RIPK3. Deletion of Nlrp12 protected mice from acute kidney injury and lethality in a hemolytic model. Overall, we identified NLRP12 as an essential cytosolic sensor for heme plus PAMPs-mediated PANoptosis, inflammation, and pathology, suggesting that NLRP12 and molecules in this pathway are potential drug targets for hemolytic and inflammatory diseases.
... Human NLRP1 senses a wide spectrum of different activating signals, including ultraviolet B (UVB) radiation (21,22), viral 3C proteases (23)(24)(25), and long dsRNA (26). It is tonically suppressed by DPP9 (27)(28)(29)(30) and TRX1 (31,32), as well as by some viral proteins such as vaccinia virus (VACV) F1L (33). Inhibitors of DPP9 such as Val-boroPro (VbP) are potent activators of NLRP1, and the study of these molecules has provided key insights into NLRP1 activation in humans (27,28,34). ...
... It is tonically suppressed by DPP9 (27)(28)(29)(30) and TRX1 (31,32), as well as by some viral proteins such as vaccinia virus (VACV) F1L (33). Inhibitors of DPP9 such as Val-boroPro (VbP) are potent activators of NLRP1, and the study of these molecules has provided key insights into NLRP1 activation in humans (27,28,34). NLRP1 activation is characterized by functional degradation through the proteasome, which releases a biologically active UPA-CARD (conserved in UNC5, PIDD, and ankyrins)-(caspase recruitment domain) C-terminal fragment that oligomerizes with ASC (apoptosis-associated speck-like protein containing a CARD) to initiate formation of a canonical inflammasome (35)(36)(37)(38). ...
The accrual of cytosolic DNA leads to transcription of type I IFNs, proteolytic maturation of the IL-1 family of cytokines, and pyroptotic cell death. Caspase-1 cleaves pro-IL1β to generate mature bioactive cytokine and gasdermin D which facilitates IL-1 release and pyroptotic cell death. Absent in melanoma-2 ( AIM2 ) is a sensor of dsDNA leading to caspase-1 activation, although in human monocytes, cGAS-STING acting upstream of NLRP3 mediates the dsDNA-activated inflammasome response. In healthy human keratinocytes, AIM2 is not expressed yet caspase-1 is activated by the synthetic dsDNA mimetic poly(dA:dT). Here, we show that this response is not mediated by either AIM2 or the cGAS-STING-NLRP3 pathway and is instead dependent on NLRP1. Poly(dA:dT) is unique in its ability to activate NLRP1, as conventional linear dsDNAs fail to elicit NLRP1 activation. DsRNA was recently shown to activate NLRP1 and prior work has shown that poly(dA:dT) is transcribed into an RNA intermediate that stimulates the RNA sensor RIG-I. However, poly(dA:dT)-dependent RNA intermediates are insufficient to activate NLRP1. Instead, poly(dA:dT) results in oxidative nucleic acid damage and cellular stress, events which activate MAP3 kinases including ZAKα that converge on p38 to activate NLRP1. Collectively, this work defines a new activator of NLRP1, broadening our understanding of sensors that recognize poly(dA:dT) and advances the understanding of the immunostimulatory potential of this potent adjuvant.
... 3 Supporting this idea, potent DPP8/9 inhibitors, including Val-boroPro (VbP), activate all functional NLRP1 and CARD8 proteins in humans and rodents by both accelerating the rate of NT degradation and destabilizing the DPP8/9 ternary complexes ( Figure S1B). [8][9][10][11][12][19][20][21] DPP8/9 are serine proteases that cleave XP dipeptides (X is any amino acid) from the N-termini of polypeptides. [22][23][24] Intriguingly, XP peptides, which weakly bind to and inhibit DPP8/9, alone can activate the CARD8 inflammasome, suggesting they may be an endogenous danger-associated signal. ...
... However, this tripledrug cocktail was still unable to activate the mouse NLRP1B inflammasome in RAW 264.7 cells (Figure S7H), consistent with previous data that show that the mouse NLRP1 inflammasome has an especially high activation threshold. 19,41,42 Regardless, these data collectively indicate that human CARD8 and NLRP1 are activated by the same danger signals, but NLRP1 has a higher activation threshold that requires the simultaneous occurrence of several key inputs (Figures 7C and 7D). ...
The danger signals that activate the related nucleotide-binding domain leucine-rich repeat pyrin domain-containing 1 (NLRP1) and caspase activation and recruitment domain-containing 8 (CARD8) inflammasomes have not been fully established. We recently reported that the oxidized form of TRX1 binds to NLRP1 and represses inflammasome activation. These findings suggested that intracellular reductive stress, which would reduce oxidized TRX1 and thereby abrogate the NLRP1-TRX1 interaction, is an NLRP1 inflammasome-activating danger signal. However, no agents that induce reductive stress were known to test this premise. Here, we identify and characterize several radical-trapping antioxidants, including JSH-23, that induce reductive stress. We show that these compounds accelerate the proteasome-mediated degradation of the repressive N-terminal fragments of both NLRP1 and CARD8, releasing the inflammasome-forming C-terminal fragments from autoinhibition. Overall, this work validates chemical probes that induce reductive stress and establishes reductive stress as a danger signal sensed by both the NLRP1 and CARD8 inflammasomes.
... Both the human and rodent NLRP1 proteins consist of a NACHT, LRR, FIIND and CARD, but the human NLRP1 additionally contains a PYD (Finger et al., 2012;Frew et al., 2012). Cleavage and activation of NLRP1 can be induced by the lethal factor of Bacillus anthracis or inhibition of the dipeptidyl peptidases (DPP) 8 and 9 suppressing NLRP1 (Huang et al., 2021;Gai et al., 2019;Zhong et al., 2018). As the NLRP1 proteins contain a CARD they can directly recruit pro-caspase-1 without the need for the adaptor ASC. ...
Pro-inflammatory signaling mediated by immune and cytokine receptors is crucial for the induction of adequate immune responses to eliminate invading pathogens. Tight regulation of these pathways is important to prevent pathologies or the onset of autoimmune or chronic inflammatory diseases. Upon immune receptor engagement, non-degradative ubiquitylation is an essential posttranslational modification (PTM), which allows the recruitment of kinases to activate pro-survival/inflammatory NF-κB and MAPK signaling. It is mediated mainly by E3 ubiquitin ligases such as cIAP1/2 and the linear ubiquitin assembly complex (LUBAC). Deubiquitinases (DUBs) like CYLD and OTULIN play critical roles for the regulation of pro-inflammatory signaling by removing K63- and M1-linked ubiquitin chains from receptor complexes, e.g., the tumor necrosis factor (TNF) receptor I (TNFR1). The adaptor protein SPATA2, which bridges the interaction of CYLD with LUBAC, mediates recruitment of CYLD to the TNFR1 signaling complex (TNFR1-SC). Whether SPATA2 exhibits other functions independently of CYLD is not known so far. Therefore, the aim of this study was to identify if SPATA2 and CYLD can function independently of each other.
It could be shown that homozygous deletion of SPATA2 and CYLD in mice resulted in perinatal lethality of the majority of double knockout (Cyld-/-Spata2-/-) offspring. Surviving Cyld-/-Spata2-/- animals were smaller than littermates, had a kinked tail and elevated marginal zone B cell numbers, indicating unrestricted NF-κB activation in the absence of both proteins. Combined loss of SPATA2 and CYLD in murine embryonic fibroblasts (MEF) and bone marrow-derived macrophages (BMDM) induced elevated pro-inflammatory gene expression and increased NF-κB and MAPK activation. Increased TNFR1-SC ubiquitylation in Cyld-/-Spata2-/- MEF in comparison to Cyld-/- or Spata2-/- cells. TNF-induced cell death was reduced in Cyld-/-Spata2-/- MEF as compared to single knockout cells, which was reversed after reconstitution of SPATA2 or CYLD. In addition to the PUB interacting motif (PIM), the zinc finger region (ZnF) of SPATA2 was identified as novel motif required for HOIP interaction. Furthermore, it was seen that the PIM and ZnF domain of SPATA2 are necessary to attenuate pro-inflammatory signaling in the absence of CYLD. SPATA2 counteracts LUBAC activity by displacing OTULIN from HOIP, thereby promoting auto-ubiquitylation of LUBAC. In consequence, increased pro-inflammatory signaling upon combined loss of SPATA2 and CYLD depends on the presence of OTULIN. As another finding, BMDM) generated from Cyld-/-Spata2-/- animals exhibited stronger priming and induction of the NLRP1b inflammasome. Additional deletion of caspase-1 resulted in increased survival of Cyld-/-Spata2-/- mice. Furthermore, it could be seen that SPATA2 is a crucial regulator of intestinal inflammation as combined loss of SPATA2 and CYLD led to villus blunting, increased pro-inflammatory cytokine expression in intestinal epithelial cells and developmental defects of intestinal organoids. Thus, this study revealed that SPATA2 and CYLD have mutually independent functions for regulating inflammatory responses and cell death induction.
... DPP8/9 inhibitors, including Val-boroPro (VbP), both accelerate the proteasome-mediated degradation of the NT fragment through a poorly characterized pathway and destabilize the NLRP1 FL -NLRP1 CT -DPP8/9-repressive ternary complex (6,7,14,16,17). Of these three triggers, only DPP8/9 inhibitors also activate the rat and mouse NLRP1 inflammasomes (15) and the human CARD8 inflammasome (rodents do not express CARD8) (13,18). Hence, only DPP8/9 inhibitors, and not dsRNA and 3C proteases, are likely related to the primordial function of the NLRP1 inflammasome (19). ...
... VbP activates the NLRP1A and NLRP1B inflammasomes and thereby elevates the levels of many serum cytokines in C57BL/6J mice (12,15). Because TRX1 associates with mNLRP1A/B (fig. ...
The danger signals that activate the NLRP1 inflammasome have not been established. Here, we report that the oxidized, but not the reduced, form of thioredoxin-1 (TRX1) binds to NLRP1. We found that oxidized TRX1 associates with the NACHT-LRR region of NLRP1 in an ATP-dependent process, forming a stable complex that restrains inflammasome activation. Consistent with these findings, patient-derived and ATPase-inactivating mutations in the NACHT-LRR region that cause hyperactive inflammasome formation interfere with TRX1 binding. Overall, this work strongly suggests that reductive stress, the cellular perturbation that will eliminate oxidized TRX1 and abrogate the TRX1-NLRP1 interaction, is a danger signal that activates the NLRP1 inflammasome.
... Although the ligands for rodent Nlrp1 have been characterized (Boyden and Dietrich, 2006;Griswold et al., 2019;Gai et al., 2019;Sandstrom et al., 2019;Broz and Dixit, 2016;Ball et al., 2021), the natural ligands of human NLRP1 and CARD8 have remained elusive. Recently, enteroviral 3C proteases, long dsRNA, cytosolic peptide accumulation, and reductive stress were identified as the natural triggers for the human NLRP1 inflammasome Wang et al., 2022;Tsu et al., 2021;Robinson et al., 2020;Bauernfried et al., 2020). ...
... ECs undergo VbP-dependent pyroptosis We next tested whether CARD8 and/or NLRP1 are capable of inducing pyroptosis in HAECs in response to VbP (also known as Talabostat mesylate), the universal activator of NLRP1 and CARD8 (Fig. 1 B ;Okondo et al., 2018;Gai et al., 2019;Johnson et al., 2018. Using reporter HAECs expressing ASC-mCherry, we confirmed that VbP induced ASC-mCherry speck formation-a readout of NLRP1 inflammasome activation-in a dose-dependent manner (Fig. 1 C). ...
Nucleotide-binding oligomerization domain (NBD), leucine-rich repeat (LRR) containing protein family (NLRs) are intracellular pattern recognition receptors that mediate innate immunity against infections. The endothelium is the first line of defense against blood-borne pathogens, but it is unclear which NLRs control endothelial cell (EC) intrinsic immunity. Here, we demonstrate that human ECs simultaneously activate NLRP1 and CARD8 inflammasomes in response to DPP8/9 inhibitor Val-boro-Pro (VbP). Enterovirus Coxsackie virus B3 (CVB3)—the most common cause of viral myocarditis—predominantly activates CARD8 in ECs in a manner that requires viral 2A and 3C protease cleavage at CARD8 p.G38 and proteasome function. Genetic deletion of CARD8 in ECs and human embryonic stem cell–derived cardiomyocytes (HCMs) attenuates CVB3-induced pyroptosis, inflammation, and viral propagation. Furthermore, using a stratified endothelial–cardiomyocyte co-culture system, we demonstrate that deleting CARD8 in ECs reduces CVB3 infection of the underlying cardiomyocytes. Our study uncovers the unique role of CARD8 inflammasome in endothelium-intrinsic anti-viral immunity.
... Dipeptidyl peptidases (DPPs) are serine proteases that are phylogenetically related. DPP8 and DPP9 belong to the S9b subfamily of serine proteases, including DPP IV [141]. Val-boroPro, a dipeptidyl peptidase 8 and 9 (DPP8/9) inhibitor, is associated with pyroptosis. ...
Background:
Pyroptosis has been attracting much attention recently. We have briefly compared its differences and similarities with other programmed deaths and the process of its study. With further exploration of the caspase family, including caspase-1/3/4/5/8/11, new insights into the molecular pathways of action of pyroptosis have been gained. It is also closely related to the development of many cancers, which at the same time provides us with new ideas for the treatment of cancer.
Scope of review:
We describe what is known regarding the impact of pyroptosis on anticancer immunity and give insight into the potential of harnessing pyroptosis as a tool and applying it to novel or existing anticancer strategies.
Major conclusions:
Pyroptosis, a caspase-dependent cell death, causes pore formation, cell swelling, rupture of the plasma membrane, and release of all intracellular contents. The role of pyroptosis in cancer is an extremely complex issue. There is growing evidence that tumor pyroptosis has anti-tumor and pro-tumor roles. It should be discussed in different cancer periods according to the characteristics of cancer occurrence and development. In cancer treatment, pyroptosis provides us with some potential new targets. For the existing drugs, the study of pyroptosis also helps us make better use of existing drugs for anticancer treatment. Immunotherapy is a hot research direction in the field of cancer treatment.
... Moreover MG-132 treatment seemed not to affect Caspase 1 activation compared to untreated cells (Fig. 4Sb), suggesting that the selected proteasome inhibitor and the indicated experimental conditions were not able to modulate the activation of other inflammasomes. Human NLRP1 inflammasome activation has been correlated to the inhibition of DPP9, a dipeptidyl dipeptidase protein able to stabilize NLRP1 and prevent its degradation via the proteasome [34,48]. Thus, we evaluated whether DPP9 could be involved in O 3 induced NLRP1 inflammasome activation. ...
NLRP1 is one of the major inflammasomes modulating the cutaneous inflammatory responses and therefore linked to a variety of cutaneous conditions. Although NLRP1 has been the first inflammasome to be discovered, only in the past years a significant progress was achieved in understanding the molecular mechanism and the stimuli behind its activation. In the past decades a crescent number of studies have highlighted the role of air pollutants as Particulate Matter (PM), Cigarette Smoke (CS) and Ozone (O3) as trigger stimuli for inflammasomes activation, especially via Reactive Oxygen Species (ROS) mediators. However, whether NLRP1 can be modulated by air pollutants via oxidative stress and the mechanism behind its activation is still poorly understood. Here we report for the first time that O3, one of the most toxic pollutants, activates the NLRP1 inflammasome in human keratinocytes via oxidative stress mediators as hydrogen peroxide (H2O2) and 4-hydroxy-nonenal (4HNE). Our data suggest that NLRP1 represents a target protein for 4HNE adduction that possibly leads to its proteasomal degradation and activation via the possible involvement of E3 ubiquitin ligase UBR2. Of note, Catalase (Cat) treatment prevented inflammasome assemble and inflammatory cytokines release as well as NLRP1 ubiquitination in human keratinocytes upon O3 exposure.
The present work is a mechanistic study that follows our previous work where we have showed the ability of O3 to induce cutaneous inflammasome activation in humans exposed to this pollutant. In conclusion, our results suggest that O3 triggers the cutaneous NLRP1 inflammasome activation by ubiquitination and redox mechanism.
