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Objective To study the expression of VAV family (VAV1, VAV2, VAV3) in bladder [Abstract] urothelial carcinoma, and to analyze the relationship between VAV1, VAV2, VAV3 and prognosis of the patients with bladder urothelial carcinoma. Methods The data of bladder urothelial carcinoma and normal bladder urothelial tissue were downloaded by the TCGA database, which were extracted by R language for conducting the analysis. The expression situation of each gene in urinary urothelial carcinoma and normal urinary urothelial tissue of bladder was obtained. The survival curve was drawn according to the patient's outcome and the expression level in bladder urothelial carcinoma was further conducted the immunohistochemistric verification. Results The expression levels of VAVI had no significant difference between urothelial carcinoma and normal bladder urothelial tissue (P>0.05). The expression levels of VAV2 and VAV3 in the bladder urothelial carcinoma tissue were higher than that in normal bladder urothelial tissues, the difference was statistically significant (P<0.05), and had no significant correlation with the bladder differentiation degree (P>0.05). The expression levels of VAV1 and VAV2 had no significant correlation with the survival time of the patients (P>0.05). The higher the expression of VAV3, the shorter the survival time of the patients (P<0.0001). Conclusion VAV2 and VAV3 may be involved in the change progression of bladder urothelial carcinoma, and VAV3 may be related to the poor prognosis of the patients. [ABSTRACT FROM AUTHOR]

The ductus arteriosus (DA), bridging the aorta and pulmonary artery, immediately starts closing after birth. Remodeling of DA leads to anatomic obstruction to prevent repatency. Several histological changes, especially extracellular matrices (ECMs) deposition and smooth muscle cells (SMCs) migration bring to anatomic closure. The genetic etiology and mechanism of DA closure remain elusive. We have previously reported a novel copy number variant containing Vav2 in patent ductus arteriosus (PDA) patients, but its specific role in DA closure remains unknown. The present study revealed that the expression of Vav2 was reduced in human patent DA, and it was less enrichment in the adjacent aorta. Matrigel experiments demonstrated that Vav2 could promote SMC migration from PDA patient explants. Smooth muscle cells with Vav2 overexpression also presented an increased capacity in migration and downregulated contractile-related proteins. Meanwhile, SMCs with Vav2 overexpression exhibited higher expression of collagen III and lessened protein abundance of lysyl oxidase, and both changes are beneficial to DA remodeling. Overexpression of Vav2 resulted in increased activity of Rac1, Cdc42, and RhoA in SMCs. Further investigation noteworthily found that the above alterations caused by Vav2 overexpression were particularly reversed by Rac1 inhibitor. A heterozygous, rare Vav2 variant was identified in PDA patients. Compared with the wild type, this variant attenuated Vav2 protein expression and weakened the activation of downstream Rac1, further impairing its functions in SMCs. In conclusion, Vav2 functions as an activator for Rac1 in SMCs to promote SMCs migration, dedifferentiation, and ECMs production. Deleterious variant potentially induces Vav2 loss of function, further providing possible molecular mechanisms about Vav2 in PDA pathogenesis. These findings enriched the current genetic etiology of PDA, which may provide a novel target for prenatal diagnosis and treatment. Key messages: Although we have proposed the potential association between Vav2 and PDA incidence through whole exome sequencing, the molecular mechanisms underlying Vav2 in PDA have never been reported. This work, for the first time, demonstrated that Vav2 was exclusively expressed in closed DAs. Moreover, we found that Vav2 participated in the process of anatomic closure by mediating SMCs migration, dedifferentiation, and ECMs deposition through Rac1 activation. Our findings first identified a deleterious Vav2 c.701C>T variant that affected its function in SMCs by impairing Rac1 activation, which may lead to PDA defect. Vav2 may become an early diagnosis and an effective intervention target for PDA clinical therapy. [ABSTRACT FROM AUTHOR]

Background: Cadherin‐associated protein p120 catenin regulates cell adhesion and migration in cell cultures and is required for axial elongation in embryos. Its roles in adhesion and cell migration are regulated by phosphorylation. We determined the effects of phosphorylation of six serine and three threonine residues in p120 catenin during zebrafish (Danio rerio) embryogenesis. Results: We knocked down endogenous p120 catenin‐δ1 with an antisense RNA‐splice‐site morpholino (Sp‐MO) causing defects in axis elongation. These defects were rescued by co‐injections of mRNAs for wildtype mouse p120 catenin‐δ1‐3A or various mutated forms. Several mRNAs containing serine or threonine codons singly or doubly mutated to phosphomimetic glutamic acid rescued, and some nonphosphorylatable mutants did not. Conclusions: We discovered that phosphorylation of serine residue S252 or S879 is required for convergent extension of zebrafish embryos, since rescue occurred only when these residues were mutated to glutamic acid. In addition, the phosphorylation of either S268 or S269 is required, not both, consistent with the presence of only a single one of these residues in two isoforms of zebrafish and Xenopus laevis. In summary, phosphorylation of multiple serine and threonine residues of p120 catenin activates migration of presomitic mesoderm of zebrafish embryos facilitating elongation of the dorsal axis. Key Findings: Knockdown of zebrafish p120 catenin‐δ1 with a morpholino blocks migration of presomitic mesoderm and extension of the dorsal axis.We compared rescue of morphology by injecting mouse p120 catenin‐δ1‐3A (CTNND1‐3A) mRNAs mutated to phosphomimetic (E) and nonphosphorylatable (F) versions of serine and threonine residues.Convergent extension of zebrafish embryos was partially rescued by phosphorylation of T310, S905, or T916. Importantly, it required phosphorylation of serine residues S252, S879, and either of S268 or S269.We see normal morphogenesis as a dynamic interplay of motile filopodia and lamellipodia forming at the leading edge of the presomitic mesoderm cell as well as turnover of new cadherin‐mediated anchoring adherens junctions that facilitate a treadmilling action used by presomitic cells to migrate toward the dorsal aspect of the embryo. [ABSTRACT FROM AUTHOR]

Background: The cadherin‐associated protein p120 catenin regulates convergent extension through interactions with cadherin proteins, Cdc42, and Rac1, as we previously showed in zebrafish (Danio rerio). Phosphorylation of p120 catenin changes the nature of its activity in vitro but is virtually unexplored in embryos. We used our previously developed antisense RNA splice‐site morpholino targeted to endogenous p120 catenin‐δ1 to cause defects in axis elongation probing the functions of three p120 catenin tyrosine‐phosphorylation sites in gastrulating zebrafish embryos. Results: The morpholino‐induced defects were rescued by co‐injections with mouse p120 catenin‐δ1‐3A mRNAs mutated at residues Y228 and Y217 to a non‐phosphorylatable phenylalanine (F) or mutated at residue Y335 to a phosphomimetic glutamic acid (E). Co‐injection of the complementary mutations Y228E, Y217E, or Y335F mRNAs partially rescued embryos whereas dual mutation to Y228E‐Y217E blocked rescue. Immunopurification showed Y228F mutant proteins preferentially interacted with Rac1, potentially promoting cell migration. In contrast, the phosphomimetic Y228E preferentially interacted with E‐cadherin increasing adhesion. Both Y228F and Y335F strongly bind VAV2. Conclusions: p120 catenin serves dual roles during gastrulation of zebrafish. Phosphorylation and dephosphorylation of tyrosine residues Y217, Y228, and Y335 precisely balance cell adhesion and cell migration to facilitate somite compaction and axis elongation. Key Findings: Knockdown of zebrafish p120 catenin‐δ1 with a morpholino blocks migration of presomitic mesoderm and extension of the dorsal axis.We compared rescue of morphology by injecting mouse p120 catenin‐δ1‐3A (CTNND1‐3A) mRNAs mutated to phosphomimetic (E) and nonphosphorylatable (F) versions of tyrosine residues.Mutations to Y228F, Y228E, Y217F, or Y335E rescued morphology; mutation to Y217E, or Y335F mRNAs only partially rescued; and dual mutation to Y228E‐Y217E blocked rescue.Immunopurification showed Y228F mutant proteins preferentially binding to Rac1, potentially promoting cell migration, and the Y228E protein preferentially binding with E‐cadherin increasing adhesion. Both Y228F and Y335F bound strongly to VAV2.We show the importance of phosphorylation state for regulating adhesion and mesodermal cell migration in early vertebrate morphogenesis. [ABSTRACT FROM AUTHOR]

During foam cell formation and atherosclerosis development, the scavenger receptor CD36 plays critical roles in lipid uptake and triggering of atherogenicity via the activation of Vav molecules. The Vav family includes three highly conserved members known as Vav1, Vav2, and Vav3. As Vav1 and Vav3 were found to exert function in atherosclerosis development, it remains thus to decipher whether Vav2 also plays a role in the development of atherosclerosis. In this study we found that Vav2 deficiency in RAW264.7 macrophages significantly diminished oxidized LDL uptake and CD36 signaling, demonstrating that each Vav protein family member was required for foam cell formation. Genetic disruption of Vav2 in ApoE-deficient C57BL/6 mice significantly inhibited the severity of atherosclerosis. Strikingly, we further found that the genetic deletion of each member of the Vav protein family by CRISPR/Cas9 resulted in a similar alteration of transcriptomic profiles of macrophages. The three members of the Vav proteins were found to form complexes, and genetic ablation of each single Vav molecule was sufficient to prevent endocytosis of CD36. The functional interdependence of the three Vav family members in foam cell formation was due to their indispensable roles in transcriptomic programing, lipid uptake, and activation of the JNK kinase in macrophages.­

MicroRNAs have been reported to play critical roles in the regulation of non‐small‐cell cancer (NSCLC) development, but the role of microRNA (miR)‐331‐3p in NSCLC is still unclear. In this study, the expression levels of miR‐331‐3p in NSCLC tumor tissues and adjacent normal tissues were examined by quantitative RT‐PCR, and the relationship between miR‐331‐3p expression and patient clinicopathological characteristics was analyzed. The effects of miR‐331‐3p on epithelial‐mesenchymal transition (EMT), migration, and metastasis of NSCLC cells were determined in vitro and vivo. Direct functional targets of miR‐331‐3p were identified by luciferase reporter assay, western blot assay, immunohistochemical staining, and rescue assay. The downstream pathway regulated by miR‐331‐3p was identified by immunofluorescence, immunoprecipitation, and Rac1 activity examination. Our results showed that miR‐331‐3p was significantly downregulated in NSCLC tumor tissues and was correlated with clinicopathological characteristics, and miR‐331‐3p could be an independent prognostic marker for NSCLC patients. Furthermore, miR‐331‐3p significantly suppressed EMT, migration and metastasis of NSCLC cells in vitro and in vivo. Both ErbB2 and VAV2 were direct functional targets of miR‐331‐3p. The activities of Rac1, PAK1, and β‐catenin were regulated by miR‐331‐3p through ErbB2 and VAV2 targeting. These results indicated that miR‐331‐3p suppresses EMT, migratory capacity, and metastatic ability by targeting ErbB2 and VAV2 through the Rac1/PAK1/β‐catenin axis in NSCLC. [ABSTRACT FROM AUTHOR]

Ubiquitin E3 Ligase MARCH7 is involved in T cell proliferation and neuronal development. In our previous study, we demonstrated MARCH7 promoted malignant behavior of ovarian cancer via the nuclear factor (NF)-κB and Wnt/β-catenin signaling pathway. However, the expression and function of MARCH7 in cervical cancer remains unknown. The present study aimed to unravel the expression and function of MARCH7 in cervical cancer to elucidate its potential role in the diagnosis and pathogenesis of cervical cancer. Results indicated that the expression of MARCH7 was abnormally high in cervical cancer tissues than normal cervical tissues. However, silencing the expression of MARCH7 in HeLa cells resulted in decreased cell proliferation and invasion. Mechanistic investigations revealed that MARCH7 interacted with VAV2. Silencing the expression of MARCH7 in HeLa cells inhibited the VAV2-RAC1-CDC42 signaling pathway. Overall, the results of the present study identified MARCH7 as a candidate oncogene in cervical cancer, and a potential target for cervical cancer therapy. [ABSTRACT FROM AUTHOR]

Intestinal epithelial cells form a protective barrier in limiting gut luminal content potentially harmful to the host. Upon gut epithelium injury, several signals instruct epithelial cells to undergo a rapid healing process. Defects in this process induce inflammatory responses and can further evolve into chronic gut inflammatory diseases. We previously identified the transcription factor CUX1 as crucial for protecting against experimental colitis in mice. However, the precise molecular mechanisms by which CUX1 intervenes during this biological process are unknown. Our aim was to evaluate CUX1 biological and functional roles during intestinal epithelial cell wound healing. RNAi knockdown of CUX1 in intestinal epithelial cells revealed a crucial role for this regulator in migratory response following wounding assays. Gene expression profiling identified several gene transcripts modulated in absence of CUX1 during wound healing for which a significant number was associated with cell motility and cytoskeleton function. Chromatin immunoprecipitation assays identified the guanine nucleotide exchange factor Vav2 gene as a direct target for CUX1. Coincidently, reduction of VAV2 in absence of CUX1 was associated with a significant decrease of RAC1 activity in response to epithelial wounding. Our results identify a novel pathway by which CUX1 regulates normal intestinal epithelial cell restitution. [ABSTRACT FROM AUTHOR]

Metastatic prostate cancer cells display EphB receptor-mediated attraction when they contact stromal fibroblasts but EphA-driven repulsion when they contact one another. The impact of these ‘social’ interactions between cells during cancer cell invasion and the signalling mechanisms downstream of Eph receptors are unclear. Here we show that EphA receptors regulate prostate cancer cell dissemination in a 2D dispersal assay and in a 3D cancer cell spheroid assay. We show that EphA receptors signal via the exchange factor Vav2 to activate RhoA and that both Vav2 and RhoA are required for prostate cancer cell–cell repulsion. Furthermore, we find that in EphA2/EphA4, Vav2 or RhoA siRNA-treated cells, contact repulsion can be restored by partial microtubule destabilisation. We propose that EphA–Vav2–RhoA-mediated repulsion between contacting cancer cells at the tumour edge could enhance their local invasion away from the primary tumour.

Glucose-stimulated insulin secretion [GSIS] from the islet β-cell involves a well-orchestrated interplay between metabolic and cationic events. It is well established that intracellular generation of adenine and guanine nucleotide triphosphates [e.g., ATP and GTP] represents one of the requisite signaling steps in GSIS. The small molecular mass GTP-binding proteins [G-proteins; e.g., Rac1 and Cdc42] have been shown to regulate islet β-cell function including actin cytoskeletal remodeling and fusion of insulin granules with the plasma membrane for GSIS to occur. In this context, several regulatory factors for these G-proteins have been identified in the pancreatic β-cell; these include guanine nucleotide exchange factors [GEFs] and guanine nucleotide dissociation inhibitors [GDI]. Recent pharmacological and molecular biological evidence identified Tiam1 and Vav2 as GEFs for Rac1 in promoting physiological insulin secretion. Paradoxically, emerging evidence in multiple cell types, including the islet β-cell, suggests key roles for Rac1 in the onset of cellular dysfunction under conditions of metabolic stress and diabetes. Furthermore, functional inactivation of either Tiam1 or Vav2 appears to attenuate sustained activation of Rac1 and its downstream signaling events [activation of stress kinases] under conditions of metabolic stress. Together, these findings suggest both “friendly” and “non-friendly” roles for Tiam1/Vav2-Rac1 signaling axis in islet β-cell in health and diabetes. Our current understanding of the field and the knowledge gaps that exist in this area of islet biology are heighted herein. Furthermore, potential caveats in the specificity and selectivity of pharmacological inhibitors that are available currently are discussed in this Commentary . [ABSTRACT FROM AUTHOR]

Several studies have proved that Vav2 gene is associated with the carcinogenesis of some tumors, but the relationship between Vav2 gene and gastric cancer remains unclear. Purpose of this study is to detect the expression of Vav2 protein in gastric cancer tissues and to evaluate the clinical value of Vav2. Furthermore, both effect of Vav2 gene on invasion and metastasis of gastric cancer cells and its mechanism are investigated in vitro. Results showed that positive rate of Vav2 protein was significantly higher in gastric cancer tissues than in adjacent tissues and notably higher in metastatic lymph nodes than in gastric cancer tissues. Results of western blot were consistent with immunohistochemistry. Expression of Vav2 protein in gastric cancer tissues was related to degree of tumor differentiation, lymph node metastasis, and clinical stages. Inhibition of endogenous Vav2 in BGC823 cells led to significantly decreased cell activity, migration, and invasion ability in vitro, and expression of Rac1, MMP-2, and MMP-9 decreased, whereas expression of TIMP-1 increased. We concluded that Vav2 might promote invasion and metastasis of gastric cancer by regulating some invasion and metastasisrelated genes. [ABSTRACT FROM AUTHOR]

We previously demonstrated that an αvβ5 integrin/FAK- mediated pathway regulated the phagocytic properties of human trabecular meshwork (HTM) cells. Here we demonstrate that this process is mediated by Rac-1 and a previously unreported signaling pathway that utilizes the Tiam1 as well as a novel ILK/RhoG/ELMO2 signaling pathway. Phagocytosis in both a TM-1 cell line and normal HTM cells was mediated by Rac1 and could be significantly decreased by >75% using the Rac1 inhibitor EHop-016. Knockdown of Rac1 in TM-1 cells also inhibited phagocytosis by 40% whereas overexpression of a constitutively active Rac1 or stimulation with PDGF increased phagocytosis by 83% and 32% respectively. Tiam1 was involved in regulating phagocytosis. Knockdown of Tiam1 inhibited phagocytosis by 72% while overexpression of Tiam1 C1199 increased phagocytosis by 75%. Other upstream effectors of Rac1 found to be involved included ELMO2, RhoG, and ILK. Knockdowns of ELMO2, ILK, and RhoG caused a reduction in phagocytosis by 51%, 55% and 46% respectively. In contrast, knockdown of Vav2 and Dock1 or overexpression of Vav2 Y159/172F did not cause a significant change in phagocytosis. These data suggest a novel link between Tiam1 and RhoG/ILK /ELMO2 pathway as upstream effectors of the Rac1-mediated phagocytic process in TM cells. [ABSTRACT FROM AUTHOR]

Thioredoxin-interacting protein ( TXNIP) is a multifunctional protein involved in diverse cellular processes such as cell proliferation and apoptosis. TXNIP stability is controlled by the ubiquitin-proteasome pathway, and the E3 ubiquitin ligase Itch directly interacts with TXNIP via PPxY motifs of TXNIP. In a previously published study, we have shown that phosphorylation of the PPxY tyrosyl residue switches TXNIP selectivity between different binding partners. Here, we describe that tyrosine-phosphorylated PPxY motifs also bind to SH2 domains of Vav2 and Src with dissociation constants around 10 μ m and that phosphorylation is indispensable for these interactions as well. The crystal structure of the complex between a phosphorylated PPxY motif, and the SH2 domain of Vav2 reveals a conserved recognition mechanism. [ABSTRACT FROM AUTHOR]

Aims/hypothesis: Rho GTPases (Ras-related C3 botulinum toxin substrate 1 [Rac1] and cell division cycle 42 [Cdc42]) have been shown to regulate glucose-stimulated insulin secretion (GSIS) via cytoskeletal remodelling, trafficking and fusion of insulin-secretory granules with the plasma membrane. GTP loading of these G proteins, which is facilitated by GDP/GTP exchange factors, is a requisite step in the regulation of downstream effector proteins. Guanine nucleotide exchange factor VAV2 (VAV2), a member of the Dbl family of proteins, has been identified as one of the GDP/GTP exchange factors for Rac1. Despite recent evidence on the regulatory roles of VAV2 in different cell types, roles of this guanine nucleotide exchange factor in the signalling events leading to GSIS remain undefined. Using immunological, short interfering RNA (siRNA), pharmacological and microscopic approaches we investigated the role of VAV2 in GSIS from islet beta cells. Methods: Co-localisation of Rac1 and VAV2 was determined by Triton X-114 phase partition and confocal microscopy. Glucose-induced actin remodelling was quantified by live cell imaging using the LifeAct-GFP fluorescent biosensor. Rac1 activation was determined by G protein linked immunosorbent assay (G-LISA). Results: Western blotting indicated that VAV2 is expressed in INS-1 832/13 beta cells, normal rat islets and human islets. Vav2 siRNA markedly attenuated GSIS in INS-1 832/13 cells. Ehop-016, a newly discovered small molecule inhibitor of the VAV2-Rac1 interaction, or siRNA-mediated knockdown of VAV2 markedly attenuated glucose-induced Rac1 activation and GSIS in INS-1 832/13 cells. Pharmacological findings were recapitulated in primary rat islets. A high glucose concentration promoted co-localisation of Rac1 and VAV2. Real-time imaging in live cells indicated a significant inhibition of glucose-induced cortical actin remodelling by Ehop-016. Conclusions/Interpretation: Our data provide the first evidence to implicate VAV2 in glucose-induced Rac1 activation, actin remodelling and GSIS in pancreatic beta cells. [ABSTRACT FROM AUTHOR]

Abstract: Diosgenin, a naturally occurring steroidal saponin, possess tumor therapeutic potential. However, the effect of diosgenin on cancer metastasis remains poorly understood. In this study, we performed in vitro experiments to investigate the inhibitory activity of diosgenin on human breast cancer MDA-MB-231 cell migration, and reveal the possible mechanism. Diosgenin caused a marked inhibition of cell migration in MDA-MB-231 cell by transwell assay. In addition, diosgenin significantly impacted MDA-MB-231 cell migratory behavior under real-time observation. We also found diosgenin significantly inhibited actin polymerization, Vav2 phosphorylation and Cdc42 activation, which might be, at least in part, attributed to the anti-metastatic potential of diosgenin. These findings reveal a new therapeutic potential of diosgenin for human breast cancer metastasis therapy. [Copyright &y& Elsevier]

Abstract: The VAV2 and VAV3 genes have been implicated as being causative for primary open angle glaucoma (POAG) in the Japanese. We studied 168 unrelated Japanese patients with primary open-angle glaucoma (POAG), 163 unrelated Japanese patients with normal tension glaucoma (NTG), 45 unrelated Japanese patients with developmental glaucoma (DG), and 180 ethnically matched normal controls, to determine whether variants in the vav 2 guanine nucleotide exchange factor (VAV2) and vav 3 guanine nucleotide exchange factor (VAV3) genes are associated with POAG, NTG, or DG in the Japanese. Genomic DNA was extracted from peripheral blood leukocytes, and variants in the VAV2 and VAV3 genes were amplified by polymerase chain reaction (PCR) and directly sequenced. Two variants were identified: rs2156323 in VAV2 and rs2801219 in VAV3. The variants and the prevalence of POAG, NTG, and DG in unrelated Japanese patients indicated that the variants were not involved in the pathogenesis of POAG, NTG, or DG. [Copyright &y& Elsevier]

A role for Rac1 GTPase in canonical Wnt signaling has recently been demonstrated, showing that it is required for ?β-cateninatenin translocation to the nucleus. In this study, we investigated the mechanism of Rac1 stimulation by Wnt. Upregulation of Rac1 activity by Wnt3a temporally correlated with enhanced p120-catenin binding to Rac1 and Vav2. Vav2 and Rac1 association with p120-catenin was modulated by phosphorylation of this protein, which was stimulated upon serine/threonine phosphorylation by CK1 and inhibited by tyrosine phosphorylation by Src or Fyn. Acting on these two post-translational modifications, Wnt3a induced the release of p120-catenin from E-cadherin, enabled the interaction of p120-catenin with Vav2 and Rac1, and facilitated Rac1 activation by Vav2. Given that p120- catenin depletion disrupts gastrulation in Xenopus, we analyzed p120-catenin mutants for their ability to rescue this phenotype. In contrast to the wild-type protein or other controls, p120-catenin point mutants that were deficient in the release from E-cadherin or in Vav2 or Rac1 binding failed to rescue p120-catenin depletion. Collectively, these results indicate that binding of p120-catenin to Vav2 and Rac1 is required for the activation of this GTPase upon Wnt signaling. [ABSTRACT FROM AUTHOR]

Abstract: Vav2 is a ubiquitous guanine nucleotide exchange factor (GEF) for the small GTPase Rac1. It regulates processes including cell migration, neuronal development and phagocytosis through interactions with different proteins. In this study, Arap3, a dual GTPase-activating protein (GAP) for RhoA and Arf6, was first identified to be a novel interaction partner for Vav2 both in vitro and in vivo. ITC and NMR chemical shift perturbation experiments demonstrated that Vav2 SH2 domain was able to interact directly with phosphorylated Y1403 and Y1408 within the C-terminal region of Arap3 with high affinities, with the dissociation constants (Kd) of ∼0.27 and ∼1.40μM, respectively. In addition, using different phosphotyrosine peptides, the pY +3 specificity of Vav2 SH2 domain was discovered. The solution structures of Vav2 SH2 domain in free and in complex with the phosphotyrosine peptide pY1408 were therefore determined to understand the structural basis of this recognition specificity. Structural analysis revealed that the presence of a Phe residue in the BG loop (BG6) leads to the formation of a shallow hydrophobic pY +3 pocket on the surface of Vav2 SH2 domain, which determines the pY +3 specificity of Vav2 SH2 domain. [Copyright &y& Elsevier]

TGFβ has been shown to induce short- and long-term actin reorganization controlled by Rho-GTPase signaling. A number of direct Smad target genes, rapidly activated by TGFβ, have been previously reported to control the long-term Rho activation and actin reorganization. However, the molecular mechanisms that regulate the prompt stimulation of Rho GTPases by TGFβ remain unknown. In the present study we report that TGFβ rapidly stimulated RhoA and RhoB activation in JEG3 choriocarcinoma cells that lack endogenous Smad3. Inhibition of Smad2 expression via siRNA-mediated silencing or by blocking its phosphorylation using the TβRI inhibitor SB431542 did not prevent the early RhoA/B activation by TGFβ indicating that this effect is Smad2/3-independent. Pre-treatment of the cells with the general tyrosine kinase inhibitor Genistein blocked the TGFβ-induced early RhoA activation. In line with this finding, TGFβ-stimulation resulted in a quick activation of the non-receptor tyrosine kinase Src, followed by activation of the guanine nucleotide exchange factor (GEF) Vav2. Inhibition of Src kinase by the selective inhibitor of the Src family tyrosine kinases PP2 totally blocked the early TGFβ-induced RhoA activation. Similarly, Vav2 silencing via siRNA reduced the TGFβ-induced RhoA activation implying that the rapid Src/Vav2 stimulation was effective in regulating RhoA activation. Our present findings provide for the first time a clear evidence for the role of Src and Vav2-GEF in the early Smad2/3-independent Rho activation by TGFβ. Copyright © 2011 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Abstract: In a genome wide association study consisting of 592 German multiple sclerosis (MS) patients and 825 controls we were able to replicate the association of the HLA region with MS independently of previous case control studies. No SNPs outside the HLA region reached a genome wide level of significance. Nevertheless, we found suggestive evidence for an association of MS with variants in two new genes, the VAV2 gene and the gene for ZNF433. [ABSTRACT FROM AUTHOR]

Vav proteins are guanine nucleotide exchange factors for Rho GTPases that regulate cell adhesion, motility, spreading and proliferation in response to growth factor signalling. In this work, we show that Vav2 expression delayed epidermal growth factor receptor (EGFR) internalization and degradation, and enhanced EGFR, ERK and Akt phosphorylations. This effect of Vav2 on EGFR degradation is dependent on its guanine nucleotide exchange function. Knockdown of Vav2 in HeLa cells enhanced EGFR degradation and reduced cell proliferation. epidermal growth factor stimulation led to co-localization of Vav2 with EGFR and Rab5 in endosomes. We further show that the effect of Vav2 on EGFR stability is modulated by its interaction with two endosome-associated proteins and require RhoA function. Thus, in this work, we report for the first time that Vav2 can regulate growth factors receptor signalling by slowing receptor internalization and degradation through its interaction with endosome-associated proteins. [ABSTRACT FROM AUTHOR]

Abstract: Increased intraglomerular pressure is an important hemodynamic determinant of glomerulosclerosis, and can be modelled in vitro by exposing mesangial cells (MC) to cyclic mechanical stretch. We have previously shown that the GTPase RhoA mediates stretch-induced fibronectin production. Here we investigate the role of the RhoGEF Vav2 in the activation of RhoA by stretch. Primary rat MC were exposed to 1Hz cyclic stretch, previously shown to induce maximal RhoA activation at 1min. Total Vav2 tyrosine phosphorylation and specific phosphorylation on Y172, required for activation, were increased by 1min of stretch. Overexpression of dominant-negative Vav2 Y172/159F in COS-1 cells or downregulation of Vav2 by siRNA in MC prevented stretch-induced RhoA activation. Vav2 is known to be activated in response to growth factors, and we have previously shown the epidermal growth factor receptor (EGFR) to be transactivated by stretch in MC. Both Vav2 Y172 phosphorylation and RhoA activation were blocked by the EGFR inhibitor AG1478 and prevented in MC overexpressing kinase inactive EGFR. Stretch led to physical association between the EGFR and Vav2, and this was dependent on EGFR activation. EGFR Y992 phosphorylation, required for growth factor-induced Vav2 phosphorylation, was also induced by stretch. Activation of both Src and PI3K were necessary upstream mediators of stretch-induced Vav2 Y172 phosphorylation and RhoA activation. In summary, stretch-induced RhoA activation is dependent on transactivation of the EGFR and activation of the RhoGEF Vav2. Src and PI3K are both required upstream of Vav2 and RhoA activation. [Copyright &y& Elsevier]

Collagen phagocytosis is a crucial α2β1-integrin-dependent process that mediates extracellular matrix remodeling by fibroblasts. We showed previously that after initial contact with collagen, activated Rac1 accelerates collagen phagocytosis but the Rac guanine nucleotide exchange factors (GEFs) that regulate Rac are not defined. We examined here the GEFs that regulate collagen phagocytosis in mouse fibroblasts. Collagen binding enhanced Rac1 activity (5-20 min) but not Cdc42 or RhoA activity. Analysis of collagen bead-associated proteins showed enrichment with Vav2, which correlated temporally with increased Rac1 activity. Knockdown of Vav2 prevented Rac activation, recruitment of Rac1 to collagen bead binding sites, and collagen bead binding, but knockdown of Sos-1 or β-Pix had no effect on Rac activation or collagen binding. Vav2 was associated with the nucleotide-free Rac1 mutant (G15ARac1) after collagen binding. Collagen bead binding promoted phosphorylation of Vav2, which temporally correlated with Rac1 activation and which required Src kinase activity. Blockage of Src activity prevented collagen bead-induced Rac activation and collagen bead binding. Collectively these data indicate that Vav2 regulates the Rac1 activity associated with the binding step of collagen phagocytosis. [ABSTRACT FROM AUTHOR]

Summary: The Rho family of GTPases regulates cellular adhesion and motility. Guanine nucleotide exchange factors (GEFs) in turn regulate GTPases by promoting nucleotide exchange from GDP to GTP. We have determined that GTP-bound Rac1 is elevated in invasive oral squamous cell carcinoma (OSCC) cell lines. Because of the critical role of invasion in the progression and metastasis of OSCC, we investigated if the GEF Vav2 modulated Rac1 and Cdc42 activation and thus influenced OSCC invasion. Expression levels of Vav2 did not correlate with invasion but phosphorylated or activated Vav2 was associated with the more invasive cell lines. Transfection of activated Vav2 into the immortalized keratinocyte cell line HaCat and a low-level expressing Vav2 invasive OSCC cell line resulted in increased GTP-bound Rac1 and Cdc42 and increased invasion. Thus, activation of Vav2 appears to modulate cellular invasion through specific regulation of Rac1 and Cdc42 activity in OSCC. [Copyright &y& Elsevier]

Abstract: Vascular endothelial growth factor (VEGF) signaling is critical for both normal and disease-associated vascular development. Dysregulated VEGF signaling has been implicated in ischemic stroke, tumor angiogenesis, and many other vascular diseases. VEGF signals through several effectors, including the Rho family of small GTPases. As a member of this family, Rac1 promotes VEGF-induced endothelial cell migration by stimulating the formation of lamellipodia and membrane ruffles. To form these membrane protrusions, Rac1 is activated by guanine nucleotide exchange factors (GEFs) that catalyze the exchange of GDP for GTP. The goal of this study was to identify the GEF responsible for activating Rac1 in response to VEGF stimulation. We have found that VEGF stimulates biphasic activation of Rac1 and for these studies we focused on the peak of activation that occurs at 30 min. Inhibition of VEGFR-2 signaling blocks VEGF-induced Rac1 activation. Using a Rac1 nucleotide-free mutant (G15ARac1), which has a high affinity for binding activated GEFs, we show that the Rac GEF Vav2 associates with G15ARac1 after VEGF stimulation. Additionally, we show that depleting endothelial cells of endogenous Vav2 with siRNA prevents VEGF-induced Rac1 activation. Moreover, Vav2 is tyrosine phosphorylated upon VEGF treatment, which temporally correlates with Rac1 activation and requires VEGFR-2 signaling and Src kinase activity. Finally, we show that depressing Vav2 expression by siRNA impairs VEGF-induced endothelial cell migration. Taken together, our results provide evidence that Vav2 acts downstream of VEGF to activate Rac1. [Copyright &y& Elsevier]

Prolactin (PRL) stimulates the cytoskeletal re-organization and motility of breast cancer cells. During PRL receptor signaling, Vav2 becomes phosphorylated and activated, an event regulated by the serine/threonine kinase Nek3. Given the regulatory role of Vav2, the function of Nek3 in PRL-mediated motility and invasion was examined. Overexpression of Nek3 in Chinese hamster ovary transfectants potentiated cytoskeletal re-organization in response to PRL. In contrast, downregulation of Nek3 expression by small-interfering RNA (siRNA) attenuated PRL-mediated cytoskeletal reorganization, activation of GTPase Rac1, cell migration and invasion of T47D cells. In addition, PRL stimulation induced an interaction between Nek3 and paxillin and significantly increased paxillin serine phosphorylation, whereas Nek3 siRNA-transfected cells showed a marked reduction in paxillin phosphorylation. Analysis of breast tissue microarrays also demonstrated a significant up-regulation of Nek3 expression in malignant versus normal specimens. These data suggest that Nek3 contributes to PRL-mediated breast cancer motility through mechanisms involving Rac1 activation and paxillin phosphorylation.Oncogene (2007) 26, 4668–4678; doi:10.1038/sj.onc.1210264; published online 12 February 2007 [ABSTRACT FROM AUTHOR]

Abstract: Cortactin is an SH3 domain-containing protein that contributes to the formation of dynamic cortical actin-associated structures, such as lamellipodia and membrane ruffles. It was originally identified as a substrate for the protein kinase Src; however, the role of tyrosine phosphorylation in the translocation of cortactin to the cell periphery and in the subsequent actin polymerisation is still unclear. Recently, two serine/threonine kinases, Pak1 and Erk, have been implicated in the regulation of cortactin. Therefore, we systematically investigated whether phosphorylation on either tyrosine or serine/threonine residues is necessary for cortactin function. In COS7 cells over-expressing Vav2 or treated with EGF, we could not detect tyrosine phosphorylation, although cortactin was translocated to cell periphery and induced membrane ruffle formation. In addition, the selective MEK inhibitor, PD98059, did not influence in vivo the ability of cortactin to bind to and induce membrane ruffles upon Vav2 over-expression or short-term EGF treatment. Finally, using a constitutively active Pak1 mutant, Pak1 T423E, we showed that Pak1 is not capable of phosphorylating cortactin either in vitro or in COS7 cells. These results suggest that cortactin-mediated actin polymerisation at cell periphery requires only Rac activation but neither tyrosine nor serine/threonine phosphorylation. [Copyright &y& Elsevier]

Cell movement is driven by the coordinated regulation of cytoskeletal reorganization through Rho GTPases downstream of integrin and growth-factor receptor signaling. We have reported that mDia, a target protein of Rho, interacts with Src and DIP. Here we show that DIP binds to p190RhoGAP and Vav2, and that DIP is phosphorylated by Src and mediates the phosphorylation of p190RhoGAP and Vav2 upon EGF stimulation. When endogenous DIP was inhibited by expressing dominant-negative mutants of DIP or siRNA, phosphorylation of p190RhoGAP and Vav2 upon EGF stimulation was diminished, and EGF-induced actin organization, distribution of p190RhoGAP and Vav2, and cell movement were affected. Therefore, DIP seems to transfer the complex of the three proteins from cytosol to beneath the membrane, and the three proteins, in turn, can be phosphorylated by Src. DIP inactivated Rho and activated Rac following EGF stimulation in the membrane fraction. Thus, DIP acts as a regulatory molecule causing Src kinase-dependent feedback modulation of Rho GTPases downstream of Rho-mDia upon EGF stimulation, and plays an important role in cell motility. [ABSTRACT FROM AUTHOR]