Regulation of p190 Rho-GAP by v-Src is linked to cytoskeletal disruption during transformation

The v-Src oncoprotein perturbs the dynamic regulation of the cellular cytos keletal and adhesion network by a mechanism that is poorly understood. Here , we have examined in detail the effects of a temperature- dependent v-Src protein on the regulation of p190 RhoGAP, a GTPase activating protein (GAP) that has been implicated in disruption of the organised actin cytoskeleton , and addressed the dependence of v-Src-induced stress fibre loss on inhibi tion of Rho activity. We found that activation of v-Src induced association of tyrosine phosphorylated p190 with p120(RasGAP) and stimulation of p120( RasGAP)-associated RhoGAP activity although p120(RasGAP) it self was not a target for phosphorylation by v-Src in chicken embryo cells. These events r equired the catalytic activity of v-Src and were linked to loss of actin st ress fibres during morphological transformation and not mitogenic signallin g. Furthermore, these effects were rapidly reversible since switching off v -Src led to dissociation of the p190/p120(RasGAP) complex, inactivation of p120(RasGAP) associated RhoGAP activity and re-induction of actin stress fi bres, In addition, transient transfection of Val(14)-RhoA, a constitutively active Rho protein that is insensitive to RhoGAPs, suppressed v-Src-induce d stress fibre loss and cell transformation, Thus, we show here for the fir st time that an activated Src kinase requires the inactivation of Rho-media ted actin stress fibre assembly to induce its effects on actin disorganisat ion, Moreover, our work supports p190 as a strong candidate effector of v-S rc-induced cytoskeletal disruption, most likely mediated by antagonism of t he cellular function of Rho.