Role of p120 Ras-GAP in directed cell movement

We have used cell lines deficient in p120 Ras GTPase activating protein (Ra s-GAP) to investigate the roles of Ras-GAP and the associated p190 Rho-GAP (p190) in cell polarity and cell migration. Cell wounding assays showed tha t Ras-GAP-deficient cells were incapable of establishing complete cell pola rity and migration into the wound. Stimulation of mutant cells with growth factor rescued defects in cell spreading, Golgi apparatus fragmentation, an d polarized vesicular transport and partially rescued migration in a Ras-de pendent manner. However, for directional movement, the turnover of stress f ibers and focal adhesions to produce an elongate morphology was dependent o n the constitutive association between Ras-GAP and p190, independent of Ras regulation. Disruption of the phosphotyrosine-mediated Ras-GAP/p190 comple x by microinjecting synthetic peptides derived from p190 sequences in wild- type cells caused a suppression of actin filament reorientation and migrati on. From these observations we suggest that although Ras-GAP is not directl y required for motility per se, it is important for cell polarization by re gulating actin stress fiber and focal adhesion reorientation when complexed with 190, This observation suggests a specific function for Ras-GAP separa te from Ras regulation in cell motility.