Oncogene database

7409

VAV1

vav 1 guanine nucleotide exchange factor;VAV1;vav 1 guanine nucleotide exchange factor

proto-oncogene vav|vav 1 oncogene

19p13.2

protein-coding

The guanine nucleotide-exchange factor Vav is a regulator of antigen-mediated cytoskeletal reorganization required for receptor clustering, proliferation and thymic selection. Moreover, Vav has been identified as a major substrate in the CD28 signal transduction pathway and overexpression of Vav enhances TCR-mediated IL-2 secretion in T cells. Here we show that CD3- plus CD28-mediated proliferation and IL-2 production were reduced in vav gene-deficient T cells. However, Vav had no apparent role in phorbol 12-myristate 13-acetate-plus CD28-mediated proliferation and IL-2 production, suggesting that Vav acts downstream of the TCR/CD3 complex. In vivo, Vav expression was crucial to generate primary vesicular stomatitis virus (VSV)-specific cytotoxic T cell responses. In contrast, vav-/- mice exhibited a reduced but significant footpad swelling after lymphocytic choriomeningitis virus (LCMV) infections and mounted a measurable primary cytotoxic T cell response to LCMV. Upon in vitro restimulation, cytotoxic T cell responses of both VSV- and LCMV-infected mice reached near normal levels. Our data provide the first genetic evidence that Vav is an important effector molecule that relays antigen receptor signaling to IL-2 production and activation of cytotoxic T cells.

Here we identify the hematopoietic proto-oncogene Vav1 as a caspase substrate during apoptosis in lymphoid cells. Cleavage of Vav1 is prevented by the caspase inhibitors zDEVD and zVAD as well as by expression of CrmA. Vav1 is cleaved in vivo at the evolutionary conserved caspase consensus cleavage site DLYD161C, generating the carboxy-terminal cleavage product Vav1p76 of intermediate stability. In vitro caspase assays reveal cleavage of Vav1 at position 161 either by apoptotic cell lysates or by recombinant caspase-3. mutation of Asp 161 to Ala leads to the usage of the adjacent alternative cleavage sequence DQID150D. mutation of both cleavage sites at position 150 and 161 protects Vav1 from caspase-mediated proteolysis in vitro and in vivo. The cleavage product Vav1p76 is capable of activating JNK in T-cells, but fails to induce the phosphorylation of p38/HOG1. Vav1p76 displays a diminished capacity to activate the transcription factors NF-AT, AP-1 and NF-kappaB, and thus completely fails to activate IL-2 transcription. Since Vav1 is essential for IL-2 production and plays a central role for cytoskeletal reorganization, its proteolytic inactivation during apoptosis affects multiple downstream targets.

Vav and vav2 are members of the dbl family of guanine nucleotide exchange factors (GEF) for the rho/rac family of GTP binding proteins. Vav is expressed primarily in hematopoietic cells, while vav2 has a wider tissue distribution. The genomic structure of the human vav proto-oncogene was studied by identifying and sequencing ALL 27 exons of the gene from overlapping P1 and cosmid clones. The gene spans a 77-kb region on chromosome 19. In contrast, the coding region of vav2 is distributed over 30 exons spanning 227-kb. The overall organization of the exons which encode both proteins was found to be similar. In humans, alternative splicing of exons 6, 16 and 28 generated at least two distinct vav2 mRNA species. Several differences from the original vav cDNA sequence were noted. The most important difference was the identification of amino acid 718 as isoleucine, rather than threonine. This change warrants the reclassification of the vav SH2 domain as a type 3 SH2, instead of a type 2 SH2 as originally proposed by Songyang et al. (Mol. Cell. Biol. 14 (1994) 2777-2785). A series of vav promoter deletions were constructed using the enhanced green fluorescent protein (EGFP) as a reporter gene. A 23-bp segment that included a potential CBF/AML-1 binding site was found to be essential for EGFP expression in U937 cells. The same constructs were not active in HeLa cells, which do not express vav. A potential c-myb DNA binding site within the vav promoter was not required for EGFP expression.

Myelofibrosis with myeloid metaplasia (MMM) is an uncommon chronic myeloproliferative disorder characterized by clonal stem cell proliferation and reactive non-clonal proliferation of bone marrow fibroblasts with fibrosis. In the absence of curative therapy, the current management for the majority of patients is directed towards alleviation of symptoms and improvement in quality of life. A number of experimental therapies have been investigated, among which is the use of type I interferon (IFN)-alpha, whose overall results are disappointing. We recently showed that the Vav proto-oncogene product, p95Vav, which is phosphorylated under IFN-alpha treatment, associates with both chains that constitute the functional type I IFN receptor and contributes to the antiproliferative effects of IFN-alpha. The involvement of p95Vav in IFN-alpha signalling and the frequent non-responsiveness of patients to IFN-alpha led us to investigate for any functional defect(s) of Vav in response to IFN in MMM patients. Our results showed that in the majority of patients Vav is constitutively hyperphosphorylated and that IFN-alpha failed to increase substantially such a tyrosine phosphorylation of p95Vav.

Vav is a guanine nucleotide exchange factor for the Rho/Rac family predominantly expressed in hematopoietic cells and implicated in cell proliferation and cytoskeletal organization. The oncogenic tyrosine kinase Bcr-Abl has been shown to activate Rac-1, which is important for Bcr-Abl induced leukemogenesis. Previous studies by Matsuguchi et al. (Matsuguchi, T., Inhorn, R. C., Carlesso, N., Xu, G., Druker, B., and Griffin, J. D. (1995) EMBO J. 14, 257-265) describe enhanced phosphorylation of Vav in Bcr-Abl-expressing Mo7e cells yet fail to demonstrate association of the two proteins. Here, we report the identification of a direct complex between Vav and Bcr-Abl in yeast, in vitro and in vivo. Furthermore, we show tyrosine phosphorylation of Vav by Bcr-Abl. mutational analysis revealed that the SH2 domain and the C-terminal SH3 domain as well as a tetraproline motif directly adjacent to the N-terminal SH3 domain of Vav are important for establishing this phosphotyrosine dependent interaction. Activation of Rac-1 by Bcr-Abl was abrogated by co-expression of the Vav C terminus encoding the SH3-SH2-SH3 domains as a dominant negative construct. Bcr-Abl transduced primary bone marrow from Vav knock-out mice showed reduced proliferation in a culture cell transformation assay compared with wild-type bone marrow. These results suggest, that Bcr-Abl utilizes Vav as a guanine nucleotide exchange factor to activate Rac-1 in a process that involves a folding mechanism of the Vav C terminus. Given the importance of Rac-1 activation for Bcr-Abl-mediated leukemogenesis, this mechanism may be crucial for the molecular pathogenesis of chronic myeloid leukemia and of importance for other signal transduction pathways leading to the activation of Rac-1.

Vav is a guanine nucleotide exchange factor for the rho/rac GTPases that is upregulated in the embryo during the transition from primitive to definitive hematopoiesis. It is one of several genetic markers that correlates with the differentiation of the intraembryonic definitive hematopoietic stem cell. Subsequently, in the adult, vav is expressed predominantly in cells of the hematopoietic system. A heat-resistant protein complex that bound to a 23-bp segment, which is essential for vav promoter activity, was found to be present in myeloid cells but not T-cells. The complex was absent in non-hematopoietic cells which normally do not express vav. Using a saturation mutagenesis method, Mutex, a "footprint" of the protein binding site (AGAGGAAGT) was obtained that was consistent with the consensus binding site for PU.1. A specific antibody to PU.1 supershifted the complex and identified the presence of PU.1 within the complex. A GST fusion protein of the human PU.1 bound to the same consensus sequence as the heat-resistant complex from myeloid lineages. Specific mutation of the GGAA PU.1 core binding site silenced vav promoter activity and a dominant negative PU.1 inhibited the transactivation of PU.1 at the vav promoter as measured by the expression of the EGFP reporter gene. In addition, PCR analysis of immunoprecipitated chromatin using specific antibodies for PU.1 detected the co-immunoprecipitation of DNA containing the vav promoter. These results suggest that PU.1 is essential for transcriptional activity of the vav promoter in myeloid cells.

Activation of B lymphocytes by engagement of their immunoglobulin M antigen receptors results in phosphorylation of a number of proteins on tyrosine residues. One such protein is p95vav, the product of the vav proto-oncogene. Tyrosine phosphorylation of p95vav occurred within seconds of immunoglobulin M cross-linking and was independent of other events induced during stimulation of B cells, such as protein kinase C activation, guanosine triphosphate-binding protein signaling, and calcium mobilization. Moreover, engagement of antigen receptors induced the rapid (approximately 5 seconds) and transient (approximately 60 seconds) association of p95vav with a 70-kilodalton tyrosine-phosphorylated protein, Vap-1, an interaction mediated by the Src homology 2 domain of p95vav. These results suggest that the vav proto-oncogene participates in the signaling processes that mediate the antigen-induced activation of B lymphocytes.

Activation of receptor-linked and cytoplasmic protein tyrosine kinases is crucial in the control of normal and abnormal cell growth and differentiation. Some substrates of protein tyrosine kinases such as phospholipase C gamma and ras GTPase-activating protein (GAP) contain sequences homologous to the src protein domains SH2 and SH3 (refs 3-9). The proto-oncogene vav is expressed in haematopoietic cells and its product Vav contains sequence motifs commonly found in transcription factors, such as helix-loop-helix, leucine-zipper and zinc-finger motifs and nuclear localization signals, as well as a single SH2 and two SH3 domains. Here we show that stimulation of T-cell antigen receptor on normal human peripheral blood lymphocytes or on human leukaemic T cells, and the crosslinking of IgE receptors on rat basophilic leukaemia cells, both promote the phosphorylation of tyrosine residues in Vav. Moreover, activation of the receptor for epidermal growth factor leads to marked tyrosine phosphorylation of Vav in cells transiently expressing vav, and Vav associates with the receptor through its SH2 domain. We propose that vav encodes a new class of substrates whose tyrosine phosphorylation may provide a mechanism for direct signal transduction linking receptors at the cell surface to transcriptional control.

The vav proto-oncogene encodes a protein of unknown function that is rendered oncogenic by loss of a short N-terminal domain. A correction reported here to the vav sequence reveals that a central domain of some 230 amino acids is similar to the products of three genes: the human dbl oncogene, now known to encode a GDP-GTP exchange factor for the Ras-like polypeptide CDC42Hs; the CDC24 gene of Saccharomyces cerevisiae, which participates with CDC42Sc in organization of the cytoskeleton for budding; and the human bcr gene, which recombines with the abl oncogene in certain forms of leukemia. Furthermore, the N-terminal portion of Vav (and of CDC24) is similar to that of certain proteins that associate with filamentous structures. These similarities suggest that Vav, and perhaps also Bcr, may function as a GDP-GTP exchange factor for a Ras-like molecule such as CDC42Hs, and that its action may coordinate cytoplasmic architecture with the cell cycle. Reported evidence that the vav proto-oncogene is widely expressed in hematopoietic cells but not other cell types is extended here by detection of vav mRNA in 49 of 50 murine hematopoietic cell lines representing diverse hematopoietic lineages, and by in situ hybridization in embryos showing expression confined to the only hematopoietic tissue, fetal liver. Thus, like Dbl in other cell types, Vav may function throughout the hematopoietic compartment to govern a Ras-like signal transduction pathway.

Vav proteins are phosphorylation-dependent GDP/GTP exchange factors for Rho/Rac GTPases. Despite intense characterization of mammalian Vav proteins both biochemically and genetically, there is little information regarding the conservation of their biological properties in lower organisms. To approach this issue, we have performed a characterization of the regulatory, catalytic, and functional properties of the single Vav family member of Drosophila melanogaster. These analyses have shown that the intramolecular mechanisms controlling the enzyme activity of mammalian Vav proteins are already present in Drosophila, suggesting that such properties have been set up before the divergence between protostomes and deuterostomes during evolution. We also show that Drosophila and mammalian Vav proteins have similar catalytic specificities. As a consequence, Drosophila Vav can trigger oncogenic transformation, morphological change, and enhanced cell motility in mammalian cells. Gain-of-function studies using transgenic flies support the implication of this protein in cytoskeletal-dependent processes such as embryonic dorsal closure, myoblast fusion, tracheal development, and the migration/guidance of different cell types. These results highlight the important roles of Vav proteins in the signal transduction pathways regulating cytoskeletal dynamics. Moreover, they indicate that the foundations for the regulatory and enzymatic activities of this protein family have been set up very early during evolution.

Vav1 is an hematopoietic-specific Rho guanine nucleotide exchange factor coupling tyrosine kinase receptors and Rac GTPases, and has been implicated in transformation of fibroblasts and pancreas. To determine the biologic effect and oncogenic potential of Vav1 in hematopoietic lineages, we stably express oncogenic mutant of Vav1 in primary bone marrow cells using retrovirus-mediated gene transfer. Contrary to the growth stimulatory effects observed in fibroblasts, oncogenic Vav1 inhibits hematopoietic stem cell/progenitor engraftment in vivo and progenitor cell expansion in vitro via inducing apoptosis. The oncogenic Vav1-induced apoptosis is associated with reduced expression of Bcl-2 and Bcl-xL proteins and effectively suppressed by transgenic overexpression of Bcl-2, suggesting Vav1-mediated signaling via Bcl-2 in apoptosis. Also, oncogenic Vav1 stimulates sustained activation of Rac GTPases and the biologic effects of oncogenic Vav1 are Rac-dependent. Further, when expressed in the p53-deficient cells, which express elevated Bcl-2 and Bcl-xL and are resistant to the apoptosis, oncogenic Vav1 enhances both proliferation and self-renewal of hematopoietic progenitor cells. These results demonstrate clear phenotypic differences between wild-type and p53(-/-) hematopoietic cells expressing oncogenic Vav1, and suggest oncogenic potential of Vav1-mediated pathways in primary hematopoietic cell when they collaborate with additional genetic hits that affect the p53 pathway.

The expression of the VAV proto-oncogene in 57 patients with chronic myeloproliferative disease (CMD), B-cell acute lymphoblastic leukaemia (B-ALL) and B-cell non-Hodgkin Lymphoma (B-NHL), and 61 with B-cell chronic lymphocytic leukaemia (B-CLL) was analysed. VAV overexpression was observed in 19.5% of cases and 81% of VAV-positive tumours also displayed VAV phosphorylation. Overexpression was not observed in B-ALL or CMD, but 13% of B-NHL and 34.4% of B-CLL patients (P = 0.002) overexpressed VAV. The overexpression and phosphorylation of VAV was detected more frequently in 13q- chronic lymphocytic leukaemias (71.4%) versus other B-CLLs (23.4%, P = 0.001). Overexpression of VAV protein is a frequent event in patients with B-CLL displaying loss of 13q sequences.

Mammalian wild-type Vav1 (wtVav1) encodes a specific GDP/GTP nucleotide exchange factor that is exclusively expressed in the hematopoietic system. Despite numerous studies, the mechanism underlying transformation of fibroblasts by oncogenic Vav1 (oncVav1) is not well defined. We identified osteopontin, a marker for tumor aggressiveness, as an oncVav1-inducible gene. Osteopontin is highly expressed in oncVav1-transformed NIH3T3 cells (NIH/oncVav1) but is barely detected in NIH3T3 expressing wtVav1 (NIH/wtVav1) even following epidermal growth factor stimulation, which normally induces osteopontin. Depleting oncVav1 in NIH/oncVav1 using small interfering RNA led to a considerable decrease in osteopontin, whereas reducing osteopontin expression did not affect oncVav1 expression, suggesting that oncVav1 operates upstream of osteopontin. Vav1-depleted NIH/oncVav1 cells, but not osteopontin-depleted NIH/oncVav1 cells, exhibited impaired extracellular signal-regulated kinase (ERK) and c-Jun NH2-terminal kinase phosphorylation. Inhibition of ERK phosphorylation in NIH/oncVav1 cells led to a decrease in osteopontin expression, implying that the elevated osteopontin expression in these cells is dependent on ERK phosphorylation. Vav1-depleted or osteopontin-depleted NIH/oncVav1 cells lost their tumorigenic properties as judged by the soft agar and invasion assays, although loss of osteopontin expression had a less dramatic effect. Suppression of Vav1 expression in NIH/oncVav1 cells led to reversion to "normal" morphology, whereas when only osteopontin expression was diminished cells retained their transformed morphology. This work strongly supports a role for oncVav1 as a master oncogene and provides clues to the molecular mechanism underlying oncVav1 transformation.

Recent published data have shown the efficacy of gene therapy treatments of certain monogenic diseases. Risks of insertional oncogenesis, however, indicate the necessity of developing new vectors with weaker or cell-restricted promoters to minimize the trans-activation activity of integrated proviruses. We have inserted the proximal promoter of the vav proto-oncogene into self-inactivating lentiviral vectors (vav-LVs) and investigated the expression pattern and therapeutic efficacy of these vectors. Compared with other LVs frequently used in gene therapy, vav-LVs mediated a weak, though homogeneous and stable, expression in in vitro-cultured cells. Transplantation experiments using transduced mouse bone marrow and human CD34(+) cells confirmed the stable activity of the promoter in vivo. To investigate whether the weak activity of this promoter was compatible with a therapeutic effect, a LV expressing the Fanconi anemia A (FANCA) gene was constructed (vav-FANCA LV). Although this vector induced a low expression of FANCA, compared to the expression induced by a LV harboring the spleen focus-forming virus (SFFV) promoter, the two vectors corrected the phenotype of cells from a patient with FA-A with the same efficacy. We propose that self-inactivating vectors harboring weak promoters, such as the vav promoter, will improve the safety of gene therapy and will be of particular interest for the treatment of diseases where a high expression of the transgene is not required.

vav, a novel human oncogene, was originally generated in vitro by replacement of its normal 5 coding sequences with sequences from pSV2neo DNA, cotransfected as a selectable marker (S. Katzav, D. Martin-Zanca, and M. Barbacid, EMBO J. 8:2283-2290, 1989). The vav proto-oncogene is normally expressed in cells of hematopoietic origin. To determine whether the 5 rearrangement of vav or its ectopic expression in NIH 3T3 cells contributes to its transforming potential, we isolated murine and human proto-vav cDNA clones as well as human genomic clones corresponding to the 5 end of the gene. Normal proto-vav was poorly transforming in NIH 3T3 cells, whereas truncation of its 5 end greatly enhanced its transforming activity. The relative failure of full-length proto-vav cDNA clones to transform NIH 3T3 cells indicates that the transforming activity of vav is not simply due to ectopic expression. Analysis of the predicted amino terminus of the vav proto-oncogene shows that it contains a helix-loop-helix domain and a leucine zipper motif similar to that of myc family proteins, though it lacks a basic region that is usually found adjacent to helix-loop-helix domains. Loss of the helix-loop-helix domain of proto-vav, either by truncation or by rearrangement with pSV2neo sequences, activates its oncogenic potential.

Continued exposure of rats to carcinogenic doses of methapyrilene (MP) leads to elevated levels of 5-methyl-deoxycytidine (5MC) in liver DNA. Since gene expression often correlates with DNA methylation, we investigated these parameters in the MP-induced hepatocellular carcinomas of Fischer 344 rats. DNA was hypermethylated in liver tissue surrounding the tumors relative to liver tissue of untreated controls of the same age, while tumor DNA was not; DNA methylation declined to normal levels when MP treatment ceased. Gene expression analysis showed measurable levels of mRNA for c-Ki-ras, erb-B, erb-B2, hck, src, lyn, vav, trk, raf-1, l-myc, c-jun, c-yes, c-myc, c-abl, and p53. No significant differences in expression for these and other oncogenes were seen between tumors and surrounding livers, although erb-B2 and vav showed visible decreases compared with normal liver. Hypermethylation of DNA and expression of these oncogenes in MP-treated tissues were not correlated. Levels of mRNA for the same genes in MP-treated hepatocytes in culture were similar to in vivo levels; analysis of DNA synthesis levels showed that this gene expression pattern occurred in the absence of proliferation bursts or toxicity in these cells, thus suggesting that treatment in vivo may produce the same results.

A novel human oncogene, designated vav, was generated by a genetic rearrangement during gene transfer assays. The vav oncogene directs the synthesis of a 3.0 kb mRNA from which we isolated a 2.8 kb-long complementary DNA copy. Nucleotide sequence analysis of this vav oncogene cDNA clone revealed that its 5 167 bp were derived from pSV2neo DNA cotransfected as a selectable marker during gene transfer. The remaining 2597 bp were unrelated to genes included in current data banks, indicating that the vav oncogene is likely to be derived from a novel human locus. The vav oncogene cDNA clone encompasses a 2391 bp long open reading frame (ORF) capable of directing the synthesis of a 797 amino acid long polypeptide. The predicted vav oncogene protein sequence exhibits several motifs reminiscent of transcriptional factors. They include a highly acidic amino-terminal region separated from two putative nuclear localization signals by a proline-rich sequence, presumably a hinge region. In addition, we identified two zinc-finger-like domains, one of which conforms to the canonical pattern Cys-X2-Cys-X13-Cys-X2-Cys previously found to confer trans-activating activity to the adenovirus E1A protein. Transcription of its normal allele, the vav proto-oncogene, has been exclusively observed in cells of hematopoietic origin, including those of erythroid, lymphoid and myeloid lineages. These findings raise the possibility that this novel locus might play an important role in hematopoiesis.

The proto-oncogene Vav product is markedly tyrosine-phosphorylated after the recruitment of various receptors of cells of hematopoietic origin, including mature T cells. Recent studies on Vav-deficient mice have clearly implicated the product of the proto-oncogene Vav in intrathymic T cell development. Vav tyrosine phosphorylation is probably crucial to connect early tyrosine kinase(s) to downstream molecular events leading to cell division and maturation that occur in the thymus. We investigated the tyrosine phosphorylation of Vav in human thymocytes. Immunoblotting experiments demonstrate that, as in mature T cells, tyrosine phosphorylation of Vav is induced following thymocyte stimulation through the T cell receptor. The main observation, however, is that an important fraction of cellular Vav is constitutively tyrosine-phosphorylated in freshly isolated cells. This phenomenon takes place apparently both in the CD4+CD8+ and the more mature CD4+CD8- and CD4-CD8+ thymocyte cell subsets. Co-immunoprecipitation experiments showed, moreover, that a small amount of Vav is engaged in the multimolecular complex that includes elements of the T cell receptor and the T cell specific ZAP-70 tyrosine kinase. Altogether, these data suggest that a critical pathway for T cell development in the human thymus likely involves the permanent activation of Vav in vivo.

The vav proto-oncogene product (p95vav) is specifically expressed in cells of the hematopoietic system, contains one Src homology 2 and two Src homology 3 domains, and is a substrate for receptor and non-receptor tyrosine kinases. Immunoblotting experiments using an anti-phosphotyrosine monoclonal antibody showed that interferon alpha (IFN alpha) induces rapid tyrosine phosphorylation of p95vav after binding to its cell surface receptor in the U-266 human myeloma cell line. The IFN alpha-induced tyrosine phosphorylation of p95vav was time- and dose-dependent, confirming the specificity of the process. IFN alpha-dependent tyrosine phosphorylation of p95vav was also observed in other hematopoietic cell lines of B-cell origin (Daudi), T-cell origin (MOLT-4), and promyelocytic origin (HL-60). Immunoprecipitation experiments performed with 32P-labeled U-266 cells and phosphoaminoacid analysis of the bands corresponding to p95vav showed that p95vav is phosphorylated on serine residues prior to IFN alpha stimulation of the cells. After IFN alpha stimulation significant amounts of phosphorylation of p95vav on tyrosine residues were detectable. Tyrosine phosphorylation of p95vav in U-266 and HL-60 cells was also induced by two other Type I IFNs, IFN beta and IFN omega. Altogether these data suggest that the vav proto-oncogene product is a substrate for a Type I IFN-regulated tyrosine kinase(s) and may be involved in the signal transduction pathway of Type I IFNs in hematopoietic cells.

The vav proto-oncogene product (Vav) is expressed exclusively in hematopoietic cells and is reported to have guanine nucleotide exchange activity. Here we report that granulocyte-macrophage colony-stimulating factor, interleukin-3, and erythropoietin induce tyrosine phosphorylation of Vav in a human leukemia cell line UT-7. Tyrosine phosphorylation of Vav is rapid and transient; it occurs within 1 min of the stimulation and at physiological concentrations of the factors. Furthermore, we show that Vav is constitutively associated with the adapter molecule Grb2/Ash in UT-7. These data suggest that tyrosine kinases, the adapter Grb2/Ash, and the guanine nucleotide exchange factor Vav are members of a signaling pathway leading to Ras activation in hematopoietic cells.

The haematopoietic protein, p95vav, has been shown to be a tyrosine kinase substrate and to have tyrosine kinase-modulated guanine-nucleotide-releasing-factor activity. This implies a function in the control of ras or ras-like proteins. Because ras activation has been shown to be a downstream event following stimulation of the interleukin-2 (IL-2) receptor, we investigated the possibility that vav was involved in IL-2 signal transduction pathways, using human T cells as a model. We found rapid tyrosine phosphorylation of vav in response to IL-2 within 1 min, with maximum increase of phosphorylation of 5-fold occurring by 5 min after treatment in normal human T cells. IL-2 stimulation of the human T-cell line YT and a subclone of the YT cell line (YTlck-) that does not express message for the src-family kinase p56lck also results in a rapid rate of tyrosine phosphorylation of vav of more than 5-fold by 5 min. These results suggest that vav may play an important role in IL-2-stimulated signal transduction and that there is not a strict requirement for the tyrosine kinase p56lck.

The product of the vav proto-oncogene, p95vav or Vav, is tyrosine phosphorylated upon stimulation of T and B cells by antigen and other receptors, and contains motifs associated with signal transduction. To determine its role in vivo, we used vav-gene-targeted embryonic stem cells and RAG-2-/- blastocyst complementation. The vav(-/-)-RAG-2-/- chimaeras displayed thymic atrophy with reduced numbers of peripheral T cells. Whereas the total number of B cells was normal, the subset of peritoneal B-1 (CD5+) cells was missing. The vav-/- T and B cells were hyporeactive when stimulated through antigen receptors, but vav-/- T cells proliferated on exposure to phorbol ester and calcium ionophore, whereas B cells responded normally to bacterial mitogen, lipopolysaccharide or the CD40 ligand. Thus, we have established here a functional role for vav in the control of T- and B-cell development and activation.

Previous studies have suggested that the vav protooncogene plays an important role in hematopoiesis. To study this further, we have ablated the vav protooncogene by homologous recombination in embryonic stem (ES) cells. Homozygous vav (-/-) ES clones differentiate normally in culture and generate cells of erythroid, myeloid and mast cell lineages. Mice heterozygous for the targeted vav allele do not display any obvious abnormalities. However, homozygous embryos die very early during development. Crosses of vav (+/-) heterozygous mice yield apparently normal vav (-/-) E3.5 embryos but not post-implantation embryos (> or = E7.5). Furthermore, homozygous vav (-/-) blastocysts do not hatch in vitro. These results indicate that vav is essential for an early developmental step(s) that precedes the onset of hematopoiesis. Consistent with the phenotypic analysis of vav (-/-) embryos, we have identified Vav immunoreactivity in the extra-embryonic trophoblastic cell layer but not in the inner embryonic cell mass of E3.5 preimplantation embryos or in the egg cylinder of E6.5 and E7.5 post-implantation embryos. These results suggest that the vav gene is essential for normal trophoblast development and for implantation of the developing embryo.

We have used the yeast two-hybrid system to isolate proteins that interact with the carboxy-terminal SH3-SH2-SH3 region of Vav. One of the clones encoded heterogeneous nuclear ribonucleoprotein K (hnRNP K), a poly(rC)-specific RNA-binding protein. The interaction between Vav and hnRNP K involves the binding of the most carboxy-terminal SH3 domain of Vav to two proline-rich sequences present in the central region of hnRNP K. Overexpression of Vav in mouse fibroblasts leads to the formation of a stable complex with the endogenous hnRNP K and to the preferential redistribution of this protein to the cytoplasmic fraction. More importantly, Vav and hnRNP K proteins also interact in hematopoietic cells. In addition, Vav associates in vitro with a second 45-kDa poly(rC)-specific RNA-binding protein via its SH3-SH2-SH3 region. These results suggest that Vav plays a role in the regulation of the late steps of RNA biogenesis by modulating the function of poly(rC)-specific ribonucleoproteins.

Two molecules involved in signal transduction via the T cell antigen receptor, namely the protein-tyrosine kinase ZAP-70 and the proto-oncoprotein Vav, were found to be constitutively associated with tubulin in Jurkat T cells. Both were able to bind to tubulin independently of one another, as determined by transient transfection into COS-7 cells. The ZAP-70 associated with tubulin was preferentially tyrosine-phosphorylated after T cell antigen receptor stimulation of Jurkat T cells, suggesting that this interaction was functionally significant. Vav was also found to co-immunoprecipitate with ZAP-70 from cell extracts depleted of tubulin. This raised the possibility that Vav might be a substrate for ZAP-70 protein-tyrosine kinase activity. However, tyrosine phosphorylation of Vav preceded that of ZAP-70, indicating that Vav was unlikely to be a downstream target of ZAP-70. The association of ZAP-70 and Vav with tubulin implies that the microtubules may be involved in the signaling function of these two molecules, perhaps by targeting them to their appropriate intracellular location.

Vav is a signal transducing molecule containing SH2 and SH3 domains and a guanine nucleotide releasing factor-like domain. Its expression is thought to be highly specific for hematopoietic cells. Here we describe the expression of vav transcripts in human nonhematopoietic trophoblasts. By northern blotting, expression of 2.8-kb vav mRNA was detected in human decidual, placental, and chorionic villous tissues and in a choriocarcinoma cell line BeWo. By in situ hybridization, vav mRNA was found to be expressed in the cytotrophoblast shell and columns and in the extravillous trophoblasts in the maternal decidua from the first through third trimesters. Vav mRNA was also detected in villous syncytiotrophoblasts during the second and third, but not the first, trimesters. When 1 microM oligodeoxynucleotide antisense to the vav mRNA was added to the medium, growth of BeWo cells was significantly inhibited. These results suggest that vav plays an important role for successful implantation and placental development by regulating development of trophoblasts.

The vav proto-oncogene product (p95(vav)) is specifically expressed in cells of hematopoietic origin and has one src homology 2 (SH2) domain, two SH3 domains, and motifs typical of guanine exchange factors. Insulin-like growth factor-1 (IGF-1) receptors are expressed on a variety of hematopoietic cells and, upon ligand binding, mediate signals regulating hematopoietic cell proliferation. We studied the phosphorylation status of p95(var) in the U-255 human myeloma cell line, in response to IGF-1 stimulation. Immunoblotting experiments with an antiphosphotyrosine monoclonal antibody disclosed that p95(vav) is phosphorylated on tyrosine in an IGF-1-dependent manner. The tyrosine phosphorylation of 95(vav was rapid, appearing within 5 minutes of IGF-1 treatment, amd transient, diminishing by 90 minutes. Similar results were obtained when the mouse plasmacytoma J558L cell line was studied. IGF-1-dependent tyrosine phosphorylation of p95(vav) was also seen in the 32D mouse myeloid cell line that lacks expression of insulin receptor substrate (IRS) proteins, suggesting that it is not regulated by activation of the IRS-signaling system. Taken together, these data suggest that the vav proto-oncogene is a substrate for the IGF-1 receptor tyrosine++ kinase and may be involved in the signal transduction of IGF-1 in cells of hematopoietic origin.

Scr homology 3 (SH3) domain-mediated protein-protein interactions have been implicated in the localization of proteins to specific sites within the cell. We present evidence that the product of the vav proto-oncogene, p95vav, interacts specifically with the focal adhesion protein zyxin both in vitro and in yeast two hybrid system. Solution binding and two-hybrid system experiments demonstrate that association of Vav with the LIM domain protein zyxin is mediated by the C-terminal SH3 domain of the Vav and involves the proline-rich N-terminus of zyxin. The interaction appears to be selective, since no binding of the proline-rich N-terminus of zyxin with other SH3 domain-containing proteins such as GRB-2, phospholipase C gamma, GTPase-activating protein, or p85 was detected.

Syk family kinases are essential for lymphocyte development and activation. Therefore the identification of their direct effectors is of critical importance. Here, we report that Syk interacts in the yeast two-hybrid system with Vav, a proto-oncogene product exclusively expressed in hematopoietic cells. This interaction was direct, required the catalytic activity of Syk, the SH2 domain of Vav, and tyrosine residues in the linker domain of Syk. Vav also associated with Syk and Zap in antigen receptor-stimulated B or T cells, respectively. Functionally, Vav was phosphorylated by Syk family kinases both in vivo and in vitro. Furthermore, Syk and Vav cooperated to activate NF-AT synergistically. These results indicate that the interaction between Syk family kinases and Vav plays an important role in coupling immune recognition receptors to signaling pathways involved in lymphokine production.

The oncogenic protein Vav harbours a complex array of structural motifs, including leucine-rich, Dbl-homology, pleckstrin-homology, zinc-finger, SH2 and SH3 domains. Upon stimulation by antigens or mitogens, Vav becomes phosphorylated on key tyrosine residues and associates with other signalling proteins, including the mitogen receptors Zap-70 (ref. 6), Vap-1 (ref. 5) and Slp-76 (ref. 7). Disruption of the vav locus by homologous recombination causes severe defects in signalling by primary antigen receptors, leading to abnormal lymphocyte proliferation and lymphopenia. Despite the importance of Vav cell signalling, the function of this protein remains unknown. Here we show that tyrosine-phosphorylated Vav, but not the non-phosphorylated protein, catalyses GDP/GTP exchange on Rac-1, a protein implicated in cell proliferation and cytoskeletal organization, causing this GTPase to switch from its inactive to its active state. Transfection experiments also show that phosphorylation of Vav on tyrosine residues leads to nucleotide exchange on Rac-1 in vivo and stimulates c-Jun kinase, a downstream element in the signalling pathway involving this GTPase. Our results have identified a function for Vav and define a mechanism in which engaged membrane receptors activate its signalling pathway.

The vav proto-oncogene product participates in the signaling pathways activated by various cell-surface receptors, including the type I IFN receptor. During engagement of the type I IFN receptor, p95vav is phosphorylated on tyrosine residues, but the kinase regulating its phosphorylation has not been identified to date. Our studies demonstrate that p95vav forms a stable complex with the IFN-receptor-associated Tyk-2 kinase in vivo, and strongly suggest that this kinase regulates its phosphorylation on tyrosine. Thus, p95vav is engaged in IFN-signaling by a direct interaction with the functional type I IFN receptor complex to transduce downstream signals.

MRL/Mp-lpr/lpr (lpr) mice develop autoantibodies, vasculitis, and glomerulonephritis, which are similar to human systemic lupus erythematosus, and acquire a generalized, nonmalignant, lymphoproliferative disorder. CD4- CD8- CD3+ TCR alphabeta+ (double-negative, DN) T cells accumulate in spleen and lymph nodes, and become a major T cell population in vivo. These DN T cells, however, are refractory to various stimuli, including CD3, IL-2, CD28, PMA, and PHA. Recently, the lpr gene mutation has been identified as a mutant gene for Fas, resulting in expression defects of Fas Ag. It is still unclear, however, what kinds of mechanisms cause the dysfunction of lpr DN T cells. To elucidate the pathogenic mechanisms in abnormal DN T cells, biochemical analyses were conducted for the expression and tyrosine phosphorylation of the vav proto-oncogene product (Vav) in DN T cells from lpr mice. We demonstrated that Vav, a 95-kDa cytoplasmic protein, from lpr mice was constitutively tyrosine phosphorylated several times higher than in control +/+ mice, while expression of Vav protein in lpr and +/+ mice was equal. Additionally, in contrast with +/+ T cells, tyrosine phosphorylation of Vav, which normally increases within a minute of stimulation via TCR, did not increase in lpr DN T cells following PHA or Ab activation. Taken together with the suggested roles of Vav in multiple receptor-mediated signal transductions, our findings suggest that the functional abnormalities of lpr DN T cells may be related to Vav abnormal tyrosine phosphorylation, which could lead to impaired signaling between surface receptors and G proteins in this cell population.

Stimulation of high affinity IgE Fc receptors (FcepsilonRI) in basophils and mast cells activates the tyrosine kinases Lyn and Syk and causes the tyrosine phosphorylation of phospholipase C-gamma, resulting in the Ca2+- and protein kinase C-dependent secretion of inflammatory mediators. Concomitantly, FcepsilonRI stimulation initiates a number of signaling events resulting in the activation of mitogen-activated protein kinase (MAPK) and c-Jun NH2-terminal kinase (JNK), which, in turn, regulate nuclear responses, including cytokine gene expression. To dissect the signaling pathway(s) linking FcepsilonRI to MAPK and JNK, we reconstructed their respective biochemical routes by expression of a chimeric interleukin-2 receptor alpha subunit (Tac)-FcepsilonRI gamma chain (Tacgamma) in COS-7 cells. Cross-linking of Tacgamma did not affect MAPK in COS-7 cells, but when coexpressed with the tyrosine kinase Syk, Tacgamma stimulation potently induced Syk and Shc tyrosine phosphorylation and MAPK activation. In contrast, Tacgamma did not signal JNK activation, even when coexpressed with Syk. Ectopic expression of a hematopoietic-specific guanine nucleotide exchange factor (GEF), Vav, reconstituted the Tacgamma-induced, Syk- and Rac1-dependent JNK activation; and tyrosine-phosphorylation of Vav by Syk stimulated its GEF activity for Rac1. Thus, these data strongly suggest that Vav plays a critical role linking FcepsilonRI and Syk to the Rac1-JNK pathway. Furthermore, these findings define a novel signal transduction pathway involving a multimeric cell surface receptor acting on a cytosolic tyrosine kinase, which, in turn, phosphorylates a GEF, thereby regulating its activity toward a small GTP-binding protein and promoting the activation of a kinase cascade.

The vav proto-oncogene product (Vav), which is specifically expressed in hematopoietic cells, contains multiple structural motifs commonly used by intracellular signaling molecules. Although a variety of stimuli including erythropoietin (Epo) have been shown to tyrosine phosphorylate Vav, little is known about the Vav signal transduction pathway. Here, we have investigated the role of Vav in the Epo signaling pathway by characterizing its interaction with other proteins, using the human Epo-responsive cell line, F-36P. Immunoprecipitation and immunoblot analyses have demonstrated that Vav was associated with the Epo receptor (EpoR) in an Epo-independent manner and was tyrosine-phosphorylated after Epo stimulation. Furthermore, two phosphotyrosine proteins (pp70 and pp100) co-immunoprecipitated with the regulatory subunit of phosphatidylinositol 3-kinase (PI3-kinase) (p85) were identified as EpoR and Vav, respectively. The interaction between Vav and p85 was shown to be mediated through the SH2 domains of p85 by an in vitro binding assay and confirmed by the presence of in vitro PI3-kinase activity associated with Vav. Treatment of the cells with antisense-vav and -p85 abrogated Epo-induced cell proliferation and PI3-kinase activity. Finally, we found that JAK2 was associated with Vav in vivo and that Vav could be tyrosine-phosphorylated by activated JAK2 in vitro. These results suggest the possible role of JAK2 for tyrosine phosphorylation of Vav and involvement of Vav and PI3-kinase in Epo-induced proliferative signals.

The vav oncogene is expressed primarily in tissues of hematopoietic origin. While much effort has been focused on determining the role of vav in various signal transduction pathways, little is known about the mechanism by which vav is regulated in a tissue-selective manner. This issue was examined by developing somatic cell hybrids between human U937 cells, which express vav, and mouse Balb/c 3T3 cells, which do not. If vav is primarily regulated by the presence of positive acting transcription factors, then vav expression should be maintained in hybrid cells. In contrast, if the regulation of vav is primarily negative in nature, then vav expression should be extinguished in most of the somatic cell hybrids. Of the hybrid cells that were obtained, 64% were positive by reverse transcriptase-polymerase chain reaction for the expression of the vav oncogene. Differences in the pattern of restriction enzyme cleavage sites between the mouse and human PCR products were used to determine that 6 of 11 of the positive clones expressed the normally dormant mouse gene. The other positive clones were found to express the human vav gene. In ALL cases, the hybrid cells preferentially retained the chromosomes and the cellular morphological appearance of the mouse Balb/c 3T3 fusion partner, which does not express the vav oncogene. Since vav is able to be transiently expressed by hybrid cells with a predominately mouse phenotype, these results support the hypothesis that vav is regulated primarily by the presence of transactivating factors which stimulate transcription, rather than by a gene silencing mechanism.

Attachment to extracellular matrix is important in the regulation of proliferation and differentiation of hematopoietic stem and progenitor cells. Post-ligand occupancy events of integrin receptors in myeloid cells are largely unknown. We examined early signaling events after stimulation of integrin receptors (outside-in signal) using a cross-linking system in a growth factor-dependent myeloid cell line, M07e, alpha 4, alpha 5, and beta 1 integrin cross-linking induced a similar pattern of transient tyrosine phosphorylation of cellular proteins. The approximate molecular weights of these phosphoproteins were M(r) 150,000, M(r) 120,000-125,000, M(r) 95,000, M(r) 70,000, M(r) 60,000, and M(r) 40,000-50,000. Vav, Syk, and Erk2 were identified as some of the tyrosine-phosphorylated proteins, and their weights were M(r) 95,000, M(r) 70,000, and M(r) 40,000-50,000, respectively. Erk2 and Vav were also tyrosine-phosphorylated by stimulation with Steel factor (SLF) and granulocyte macrophage colony-stimulating factor, whereas tyrosine phosphorylation of Syk was not induced by stimulation with these cytokines. The degree of tyrosine phosphorylation of Vav through integrin engagement was almost equal to that by SLF stimulation, whereas that of Erk2 was much weaker than with SLF stimulation. Upon integrin engagement, antibodies raised against Syk coprecipitated several tyrosine-phosphorylated proteins. In vitro binding assays demonstrated that, among these Syk-associated proteins, pp40, which differed from Erks, Crk, and Crkl, binds Syk through SH2 domains of Syk and is a prominent tyrosine-phosphorylated protein in integrin cross-linked cells. These results suggest that tyrosine phosphorylation of Vav and Erk2 in myeloid cells might be regulated by both integrins and cytokines in the bone marrow microenvironment, whereas Syk might be involved in a distinct pathway from the shared between integrins and cytokines in myeloid cells.