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Vascular defects in syx / mouse. A and B, CT image reconstructions of WT and syx / mouse arterial coronary vasculature (A) and kidney arterial vasculature (B). C, Lectinlabeled sections of WT and Syx knockout myocardium. Scale bar50 mm. D, Capillary density in WT and syx / myocardia. Capillaries were counted in 4 sections, six 360360 m fields per section (P10 6 ).
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Rho GTPases play an important and versatile role in several biological processes. In this study, we identified the zebrafish ortholog of the mammalian Rho A guanine exchange factor, synectin-binding guanine exchange factor (Syx), and determined its in vivo function in the zebrafish and the mouse. We found that Syx is expressed specifically in the v...
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... syx is expressed in the cardiac and vascular tissue in the mouse ( Figure 1F), and syx KD zebrafish shows defective ISVs, we imaged the coronary and kidney arterial systems by microcomputed tomography (CT) of WT and syx / mice. Both the coronary ( Figure 4A) and kidney ( Figure 4B) arterial systems of the syx / mice were sparser than those in the WT mouse. On close examination, these systems appeared to be deficient in small diameter vessels, but the major coronary and kidney arteries are present. ...
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... syx is expressed in the cardiac and vascular tissue in the mouse ( Figure 1F), and syx KD zebrafish shows defective ISVs, we imaged the coronary and kidney arterial systems by microcomputed tomography (CT) of WT and syx / mice. Both the coronary ( Figure 4A) and kidney ( Figure 4B) arterial systems of the syx / mice were sparser than those in the WT mouse. On close examination, these systems appeared to be deficient in small diameter vessels, but the major coronary and kidney arteries are present. ...
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... the CT technique cannot image capillaries be- cause of the viscosity of the contrast medium, we probed sections of WT and syx / myocardia by histochemistry. The images clearly show that the density of capillaries in the syx / was significantly lower than in the WT myocardium ( Figure 4C). Together with the CT images, these results demonstrate that the syx / mouse harbors a vascular defect affecting multiple organs. ...
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Controlled regulation of Rho GTPase activity is an essential component mediating growth factor-stimulated migration. We have previously shown that angiomotin (Amot), a membrane-associated scaffold protein, plays a critical role during vascular patterning and endothelial migration during embryogenesis. However, the signaling pathways by which Amot c...
Citations
... Amot is involved in angiogenesis and vasodilation in psoriasis (2). Loss of function studies in zebrafish and mice suggest that synectin-binding guanine exchange factor (Syx) and Amot have specific roles in angiogenesis in the vascular bed, which may be related to vascular sprouting (70). Alternatively, Amot forms a ternary complex with Patj (or its homolog MUPP1) and Syx to control directional capillary migration in the embryo (30). ...
Angiomotin (Amot) family members, including Amot, Amot-like protein 1 (Amotl1) and Amot-like protein 2 (Amotl2), have been found to interact with angiostatins. In addition, Amot family members are involved in various physiological and pathological functions such as embryonic development, angiogenesis and tumorigenesis. Some studies have also demonstrated its regulation in signaling pathways such as the Hippo signaling pathway, AMPK signaling pathway and mTOR signaling pathways. Amot family members play an important role in neural stem cell differentiation, dendritic formation and synaptic maturation. In addition, an increasing number of studies have focused on their function in promoting and/or suppressing cancer, but the underlying mechanisms remain to be elucidated. The present review integrated relevant studies on upstream regulation and downstream signals of Amot family members, as well as the latest progress in physiological and pathological functions and clinical applications, hoping to offer important ideas for further research.
... Synectin-binding RhoA exchange factor (herein referred to as Syx, human gene symbol PLEKHG5) is a RhoA GEF that regulates junction integrity, cell migration, angiogenesis, and neural differentiation (7)(8)(9)(10)(11). Syx is expressed in endothelial cells, where its localization to the apical cell-to-cell junctions is regulated by the scaffold protein Mupp1 (and its paralogue Patj), VEGF signaling, and 14-3-3 protein binding (7,12). ...
... Previously, we and others reported a crucial role of Syx in the regulation of endothelial cell junction stability, vascular permeability, and endothelial cell migration (7,9,11). To account for non-tumor-specific effects of inhibiting Syx, we assessed whether Syx silencing also induces DNA damage in primary human brain microvascular endothelial cells (HBMECs). ...
... Hippo-independent mechanisms may involve phosphorylation of YAP1-S127 and S381 by kinases other than LATS (14), a hypothesis supported by the less prominent role of Hippo signaling in cytoskeleton-mediated YAP/TAZ modulation (20,38). Finally, the ability of Syx and YAP/TAZ to associate with 14-3-3 family members and Amot (9,11,12) provides another unexplored mechanism of potential cross-regulation. ...
Glioblastomas (GBM) are aggressive tumors that lack effective treatments. Here, we show that the Rho family guanine nucleotide exchange factor Syx promotes GBM cell growth both in vitro and in orthotopic xenografts derived from patients with GBM. Growth defects upon Syx depletion are attributed to prolonged mitosis, increased DNA damage, G2/M cell cycle arrest, and cell apoptosis, mediated by altered mRNA and protein expression of various cell cycle regulators. These effects are phenocopied by depletion of the Rho downstream effector Dia1 and are due, at least in part, to increased phosphorylation, cytoplasmic retention, and reduced activity of the YAP/TAZ transcriptional coactivators. Furthermore, targeting Syx signaling cooperates with radiation treatment and temozolomide (TMZ) to decrease viability in GBM cells, irrespective of their inherent response to TMZ. The data indicate that a Syx-RhoA-Dia1-YAP/TAZ signaling axis regulates cell cycle progression, DNA damage, and therapy resistance in GBM and argue for its targeting for cancer treatment.
... These results suggest that inhibition of Syx activity may be a possible treatment modality for GBM, and therefore, Syx warrants biophysical and structural characterization to facilitate structurally guided drug design. 22,23 Several structures of Dbl homology RhoGEF DH-PH domains have been solved previously, and GEF characterization methods have been established. In contrast, Syx is in a subgroup of Dbl homology GEFs that are largely uncharacterized outside of basic proteinprotein interaction data 24 and no structural information is yet available for this protein. ...
Structural discovery of guanine nucleotide exchange factor (GEF) protein complexes is likely to become increasingly relevant with the development of new therapeutics targeting small GTPases and development of new classes of small molecules that inhibit protein‐protein interactions. Syx (also known as PLEKHG5 in humans) is a RhoA GEF implicated in the pathology of glioblastoma (GBM). Here we investigated protein expression and purification of ten different human Syx constructs and performed biophysical characterizations and computational studies that provide insights into why expression of this protein was previously intractable. We show that human Syx can be expressed and isolated and Syx is folded as observed by circular dichroism (CD) spectroscopy and actively binds to RhoA as determined by co‐elution during size exclusion chromatography (SEC). This characterization may provide critical insights into the expression and purification of other recalcitrant members of the large class of oncogenic—Diffuse B‐cell lymphoma (Dbl) homology GEF proteins. In addition, we performed detailed homology modeling and molecular dynamics simulations on the surface of a physiologically realistic membrane. These simulations reveal novel insights into GEF activity and allosteric modulation by the plekstrin homology (PH) domain. These newly revealed interactions between the GEF PH domain and the membrane embedded region of RhoA support previously unexplained experimental findings regarding the allosteric effects of the PH domain from numerous activity studies of Dbl homology GEF proteins. This work establishes new hypotheses for structural interactivity and allosteric signal modulation in Dbl homology RhoGEFs.
... Similar effects have been observed during retinal angiogenesis, showing that similar pathways are followed for vessel development in these two organs [58]. While orchestrating the patterns of vessels, RhoA GEF Syx interacts with angiomotin in the presence of VEGF-A to regulate EC migration [62,63]. A recent study showed that these two interact with a scaffold protein and form a ternary complex to promote the migration of endothelial cells [64]. ...
Members of the Ras superfamily have been found to perform several functions leading to the development of eukaryotes. These small GTPases are divided into five major subfamilies, and their regulators can “turn on” and “turn off” signals. Recent studies have shown that this superfamily of proteins has various roles in the process of vascular development, such as vasculogenesis and angiogenesis. Here, we discuss the role of these subfamilies in the development of the vascular system in zebrafish.
... Another potential player is Syx (synectin-binding guanine exchange factor), a protein belonging to the RhoGEF family. It is involved in vasculature sprouting in Zebrafish and in Mice (Garnaas et al., 2008) and was characterized as a binding partner of AMOT (but also AMOTL1 and AMOTL2) in endothelial cells (Ernkvist et al., 2009). It is involved in the migration of polarized breast tumor cells by activating Diaphanous 1 (DIA1), an enzyme involve in F-actin cables bundle polymerization, and a RhoA downstream effector (Dachsel et al., 2013). ...
During development, the behaviour of cells is tightly regulated ensuring optimal functioning of healthy epithelial tissues. Epithelial cells thus establish well organized intercellular junctions, apico/basal polarity, cytoskeletal architecture, and integrate regulatory and homeostatic inputs relayed by dedicated signalling pathways. Alterations in these processes are most often associated with cancer.My lab is interested in deciphering the mechanisms in which junctional and polarity alterations are able to induce tumorigenesis. Scaffold proteins represent important regulators of these different processes, and alterations to several key epithelial scaffolds have been linked to cancer. Recent work in the team identified Magi, a member of the MAGUK family, as a regulator of E-Caherin-based Adherens Junctions during eye development in Drosophila. The main goal of my thesis was to study the function of MAGI1, the most abundant MAGI family member in human tissues, during cancer, and more specifically its roles in luminal A Breast Cancer cells. Using mainly loss-of-function approaches, we were able to identify a tumour suppressive function of MAGI1 in luminal BCa cells both in vitro cellular assays as well as in xenografted nude mice. Moreover, this work revealed that MAGI1 inhibits an AMOTL2/P38 signalling axis that is activated upon MAGI1 loss and then responsible for the enhanced tumorigenicity phenotype obtained. Interestingly, the loss of MAGI1 induced increased myosin activity, increased compressive behaviours, and associated elevated plasma membrane tension, which we propose to be one of the activator of P38 downstream of MAGI1 loss. Strikingly, even though cells lacking MAGI1 showed increased tumorigenicity, the activity of the YAP onco-protein is lowered in MAGI1-deficient luminal breast cancer cells, suggesting that the relationship between YAP and tumorigenesis could be more complex than commonly assumed.The study of Hippo pathway regulations is indeed a major axis of the team. A secondary objective of my thesis was thus to explore the involvement of YAP/TAZ and of the Hippo pathway during Oxaliplatin exposure in colon cancer cells. As first line chemotherapy along with 5 Fluorouracil, it is important to understand the mechanism of action of Oxaliplatin beyond its major role as inducer of deleterious DNA double strand breaks. HCT116 colon cancer cells treated with relatively modest doses of Oxaliplatin (at IC50), featured a translocation of YAP/TAZ to the nucleus accompanied with increased YAP/TAZ-mediated transcription, as judged by qPCR and RNA-Seq. This effect was coupled with a re-organization of the actin cytoskeleton inside the cell upon the treatment, and many genes affected by oxaliplatin treatment were actin regulators (including several that are also potential YAP/TAZ targets). This study involves YAP/TAZ in HCT116 response to Oxaliplatin treatment, and we propose that it leads to actin re-organization.
... The PLEKHG5 (also known as TECH or Syx) gene localizes to 1p36.31, a region frequently associated with somatic tumor gene rearrangements [32]. PLEKHG5 encodes for a guanine nucleotide exchange factor that selectively couples RhoA activation at leading cell edges with Dia1 signaling and ROCK suppression. ...
Thyroid cancer, predominantly of papillary histology (PTC), is a common cancer mostly diagnosed sporadically. Hereditary PTC is encountered in ~ 5% of cases and may present at an earlier age, with greater risks of metastasis and recurrence, compared with sporadic cases. The molecular basis of hereditary PTC is unknown in most cases. In this study, the genetic basis of hereditary PTC in three Brazilian families was investigated. Whole exome sequencing (WES) was carried out for probands in each family, and validated, pathogenic/likely pathogenic sequence variants (P/LPSVs) were genotyped in additional family members to establish their putative pathogenic role. Overall, seven P/LPSVs in seven novel genes were detected: p.D283N*ANXA3, p.Y157S*NTN4, p.G172W*SERPINA1, p.G188S*FKBP10, p.R937C*PLEKHG5, p.L32Q*P2RX5, and p.Q76*SAPCD1. These results indicate that these novel genes are seemingly associated with hereditary PTC, but extension and validation in other PTC families are required.
... Although plekhg5 is not involved in neural tube closure, its expression in several other places, such as in the otic vesicle and the cells at the turning points of the protruding pharyngeal pouches, imply that it may regulate apical constriction during organogenesis. In mammalian cell culture and in zebrafish, plekhg5 homologs are also shown to regulate directional migration of cancer and endothelial cells and vasculature formation (Liu and Horowitz, 2006;Garnaas et al., 2008;Ernkvist et al., 2009;Dachsel et al., 2013). This suggests that in migrating cells, plekhg5 may interact with other partners for localized activation of Rho and actomyosin to provide a positional cue for directional movement. ...
Apical constriction regulates epithelial morphogenesis during embryonic development, but how this process is controlled is not understood completely. Here, we identify a Rho guanine nucleotide exchange factor (GEF) gene plekhg5 as an essential regulator of apical constriction of bottle cells during Xenopus gastrulation. plekhg5 is expressed in the blastopore lip and its expression is sufficient to induce ectopic bottle cells in epithelia of different germ layers in a Rho-dependent manner. This activity is not shared by arhgef3, which encodes another organizer-specific RhoGEF. Plekhg5 protein is localized in the apical cell cortex via its pleckstrin homology domain, and the GEF activity enhances its apical recruitment. Plekhg5 induces apical actomyosin accumulation and cell elongation. Knockdown of plekhg5 inhibits activin-induced bottle cell formation and endogenous blastopore lip formation in gastrulating frog embryos. Apical accumulation of actomyosin, apical constriction and bottle cell formation fail to occur in these embryos. Taken together, our data indicate that transcriptional regulation of plekhg5 expression at the blastopore lip determines bottle cell morphology via local polarized activation of Rho by Plekhg5, which stimulates apical actomyosin activity to induce apical constriction.
... Together with Patj and synectin-binding GEF (Syx), AMOT forms a ternary complex. In vivo, AMOT plays an additive role with Syx in directing endothelial sprouts [31]. AMOT-Patj/multi-PDZ-domain protein 1 (Mupp1)-Syx govern the directional migration of capillaries in the embryo signaling through controlling RhoA GTPase activity to the leading front of migrating cells [32]. ...
Members in Motin family, or Angiomotins (AMOTs), are adaptor proteins that localize in the membranous, cytoplasmic or nuclear fraction in a cell context-dependent manner. They control the bioprocesses such as migration, tight junction formation, cell polarity, and angiogenesis. Emerging evidences have demonstrated that AMOTs participate in cancer initiation and progression. Many of the previous studies have focused on the involvement of AMOTs in Hippo-YAP1 pathway. However, it has been controversial for years that AMOTs serve as either positive or negative growth regulators in different cancer types because of the various cellular origins. The molecular mechanisms of these opposite roles of AMOTs remain elusive. This review comprehensively summarized how AMOTs function physiologically and how their dysregulation promotes or inhibits tumorigenesis. Better understanding the functional roles of AMOTs in cancers may lead to an improvement of clinical interventions as well as development of novel therapeutic strategies for cancer patients.
... To elucidate the mechanistic roles of AMOTs in migrating ECs, AMOTs were applied to identify proteins that specifically interact with the PDZ-binding motif of AMOTs, because AMOTs have several requisite motifs (e.g., PPxY motifs, a WW binding motif, and a PDZ binding motif) necessary for interaction with other proteins. As AMOT-interacting proteins, the polarity-/junction-associated scaffold protein PatJ and the Rho GTPase-exchanging factor protein Syx were identified, suggesting that AMOTs control small Rho GTPase activity (26,27). Indeed, this function was verified by in vivo studies. ...
Angiogenesis is a complex, multistep process involving dynamic changes in endothelial cell (EC) shapes and behaviors, especially in specialized cell types such as tip cells (with active filopodial extensions), stalk cells (with less motility) and phalanx cells (with stable junction connections). The Hippo-Yes-associated protein (YAP)/ transcription activator with PDZ binding motif (TAZ) signaling plays a critical role in development, regeneration and organ size by regulating cell-cell contact and actin cytoskeleton dynamics. Recently, with the finding that YAP is expressed in the front edge of the developing retinal vessels, Hippo-YAP/TAZ signaling has emerged as a new pathway for blood vessel development. Intriguingly, the LATS1/2-mediated angiomotin (AMOT) family and YAP/TAZ activities contribute to EC shapes and behaviors by spatiotemporally modulating actin cytoskeleton dynamics and EC junction stability. Herein, we summarize the recent understanding of the role of Hippo-YAP/TAZ signaling in the processes of EC sprouting and junction maturation in angiogenesis.
... Translocation of MUPP1 to the cytoplasm in cells infected with tumorigenic human viruses induces disruption of tight junctions and endothelial cell polarity (49). The Rho-specific synectin-binding exchange factor (Syx) is involved in endothelial junction stabilization and endothelial barrier function during angiogenesis (50) and has been proposed to interact with MUPP1 and Crumbs polarity complexes. The MUPP1/Syx complex is recruited to endothelial cell-cell junctions to regulate cell junctions and to maintain tight junction integrity (30). ...
Durant le développement myocardique, les cardiomyocytes s'allongent et se connectent entre eux grâce à une structure spécialisée, le disque intercalaire. Cette organisation des cardiomyocytes est essentielle pour le couplage mécanique et la conduction électrique. Un des éléments responsables de l'insuffisance cardiaque est la perturbation de ces sites de contact intercellulaire. Actuellement, aucun facteur n'est connu pour coordonner l'organisation polarisée des cardiomyocytes. Ici, nous présentons une augmentation importante de Pdzrn3 dans des cardiomyopathies hypertrophiques humaines et dans des myocardes murins, corrélée à une perte de l'élongation polarisée des cardiomyocytes. De plus la délétion spécifique intramyocardique de l'expression de Pdzrn3, dans un modèle murin, protège de la survenue d'une insuffisance cardiaque secondaire à une cardiomyopathie hypertrophique. Nos résultats révèlent une nouvelle voie de signalisation qui contrôle un programme génétique essentiel pour le développement myocardique, le maintien de la géométrie et de la fonction contractile des cardiomyocytes. Cette voie de signalisation implique PDZRN3 et cette molécule constitue une cible thérapeutique potentielle pour la protection de l’insuffisance cardiaque chez l’homme.
