title: Vav2 activates Rac1, Cdc42, and RhoA downstream from growth factor receptors but not beta1 integrins.
abstract: The Rho family of GTPases plays a major role in the organization of the actin cytoskeleton. These G proteins are activated by guanine nucleotide exchange factors that stimulate the exchange of bound GDP for GTP. In their GTP-bound state, these G proteins interact with downstream effectors. Vav2 is an exchange factor for Rho family GTPases. It is a ubiquitously expressed homologue of Vav1, and like Vav1, it has previously been shown to be activated by tyrosine phosphorylation. Because Vav1 becomes tyrosine phosphorylated and activated following integrin engagement in hematopoietic cells, we investigated the tyrosine phosphorylation of Vav2 in response to integrin-mediated adhesion in fibroblasts and epithelial cells. However, no tyrosine phosphorylation of Vav2 was detected in response to integrin engagement. In contrast, treating cells with either epidermal growth factor or platelet-derived growth factor stimulated tyrosine phosphorylation of Vav2. We have examined the effects of overexpressing either wild-type or amino-terminally truncated (constitutively active) forms of Vav2 as fusion proteins with green fluorescent protein. Overexpression of either wild-type or constitutively active Vav2 resulted in prominent membrane ruffles and enhanced stress fibers. These cells revealed elevated rates of cell migration that were inhibited by expression of dominant negative forms of Rac1 and Cdc42. Using a binding assay to measure the activity of Rac1, Cdc42, and RhoA, we found that overexpression of Vav2 resulted in increased activity of each of these G proteins. Expression of a carboxy-terminal fragment of Vav2 decreased the elevation of Rac1 activity induced by epidermal growth factor, consistent with Vav2 mediating activation of Rac1 downstream from growth factor receptors.
authors.affiliation: Department of Cell Biology and Anatomy, University of North Carolina at Chapel Hill, Chapel Hill, North Carolina 27599-7090, USA. bliu@med.unc.edu
authors.forename: B P
authors.initials: BP
authors.lastname: Liu
authors.forename: K
authors.initials: K
authors.lastname: Burridge
mesh_terms: D016475:3T3 Cells / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D008841:Actin Cytoskeleton / Q000378:metabolism / Q000648:ultrastructure; D000199:Actins / Q000378:metabolism; D019943:Amino Acid Substitution; D000818:Animals; D002462:Cell Membrane / Q000648:ultrastructure; D002478:Cells, Cultured / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D003599:Cytoskeleton / Q000502:physiology / Q000648:ultrastructure; D004815:Epidermal Growth Factor / Q000494:pharmacology; D005109:Extracellular Matrix / Q000502:physiology; D005347:Fibroblasts / Q000187:drug effects / Q000378:metabolism / Q000648:ultrastructure; D006153:Guanosine Diphosphate / Q000502:physiology; D006160:Guanosine Triphosphate / Q000502:physiology; D006801:Humans; D019012:Integrin beta1 / Q000502:physiology*; D051379:Mice; D015513:Oncogene Proteins / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D010641:Phenotype; D010766:Phosphorylation; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D011499:Protein Processing, Post-Translational; D017434:Protein Structure, Tertiary; D051567:Proto-Oncogene Proteins c-vav; D011817:Rabbits; D017978:Receptors, Growth Factor / Q000187:drug effects / Q000502:physiology*; D011993:Recombinant Fusion Proteins / Q000502:physiology; D015398:Signal Transduction / Q000187:drug effects / Q000502:physiology*; D014162:Transfection; D020764:cdc42 GTP-Binding Protein / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020830:rac1 GTP-Binding Protein / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D020742:rhoA GTP-Binding Protein / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*
chemical_list: D000199:Actins; D019012:Integrin beta1; D015513:Oncogene Proteins; D010982:Platelet-Derived Growth Factor; D051567:Proto-Oncogene Proteins c-vav; D017978:Receptors, Growth Factor; D011993:Recombinant Fusion Proteins; C093651:VAV2 protein, human; C490565:Vav2 protein, mouse; D006153:Guanosine Diphosphate; D004815:Epidermal Growth Factor; D006160:Guanosine Triphosphate; D020764:cdc42 GTP-Binding Protein; D020830:rac1 GTP-Binding Protein; D020742:rhoA GTP-Binding Protein