Critical role of the pleckstrin homology and cysteine-rich domains in Vav signaling and transforming activity.
Vav family proteins are members of the Dbl family of guanine nucleotide exchange factors and activators of Rho family small GTPases. In addition to the Dbl homology (DH) domain important for guanine nucleotide exchange factor catalytic function, all Dbl family proteins contain an adjacent pleckstrin homology (PH) domain that serves to regulate DH domain activity. Although the role of the PH domain in Vav function has been evaluated extensively, its precise role and whether it serves a distinct role in different Vav proteins remain unresolved. Additionally, the precise role of an adjacent cysteine-rich domain (CRD) in regulating DH domain function is also unclear. In this study, we evaluated the contribution of these putative protein-protein or protein-lipid interaction domains to Vav signaling and transforming activity. In contrast to previous observations, we found that the PH domain is critical for Vav transforming activity. Similarly, the CRD was also essential and served a function distinct from that of the PH domain. Although mutation of either domain reduced Vav membrane association, addition of plasma membrane targeting sequences to either the CRD or PH domain mutant proteins did not restore Vav transforming activity. This result contrasts with other Dbl family proteins, where a membrane targeting sequence alone was sufficient to restore the loss of function caused by mutation of the PH domain. Furthermore, green fluorescent protein fusion proteins containing the PH domain or CRD, or both, failed to target to the plasma membrane, suggesting that these two domains also serve regulatory functions independent of promoting membrane localization. Finally, we found that phosphatidylinositol 3-kinase activation may promote Vav membrane association via phosphatidylinositol 3,4,5-triphosphate binding to the PH domain.
Palmby
Todd R
TR
Department of Pharmacology, University of North Carolina at Chapel Hill School of Medicine, Lineberger Comprehensive Cancer Center, Chapel Hill, North Carolina 27599-7295, USA.
Abe
Karon
K
Der
Channing J
CJ
D016475:3T3 Cells; D000818:Animals; D001798:Blood Proteins / Q000737:chemistry*; D002384:Catalysis; D018797:Cell Cycle Proteins; D002460:Cell Line; D002462:Cell Membrane / Q000378:metabolism; D003545:Cysteine / Q000737:chemistry*; D018076:DNA, Complementary / Q000378:metabolism; D017353:Gene Deletion; D017930:Genes, Reporter; D006801:Humans; D051379:Mice; D018613:Microscopy, Confocal; D009154:Mutation; D018129:Phosphatidylinositol Phosphates / Q000378:metabolism; D010750:Phosphoproteins / Q000737:chemistry*; D017354:Point Mutation; D011485:Protein Binding; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000737:chemistry* / Q000378:metabolism*; D051567:Proto-Oncogene Proteins c-vav; D015398:Signal Transduction; D013347:Subcellular Fractions / Q000378:metabolism; D014162:Transfection; D018909:src Homology Domains
D001798:Blood Proteins; D018797:Cell Cycle Proteins; D018076:DNA, Complementary; D018129:Phosphatidylinositol Phosphates; D010750:Phosphoproteins; D011518:Proto-Oncogene Proteins; D051567:Proto-Oncogene Proteins c-vav; C496618:VAV1 protein, human; C496619:Vav1 protein, mouse; C060974:phosphatidylinositol 3,4,5-triphosphate; C039077:platelet protein P47; D003545:Cysteine