A mutant form of the rho protein can restore stress fibers and adhesion plaques in v-src transformed fibroblasts

The organization of polymerized actin in the mammalian cell is regulated by several members of the rho family. Three rho proteins, cdc42, rac and rho act in a cascade to organize the intracellular actin cytoskeleton. Rho prot eins are involved in the formation of actin stress fibers and adhesion plaq ues in fibroblasts. During transformation of mammalian cells by oncogenes t he cytoskeleton is rearranged and stress fibers and adhesion plaques are di sintegrated. In this paper we investigate the function of the rho protein i n RR1022 rat fibroblasts transformed by the Rous sarcoma virus. Two activat ed mutants of the rho protein, rho G14V and rho Q63L, and a dominant negati ve mutant, rho N117I, were stably transfected into RR1022 cells. The result ing cell lines were analysed for the organization of polymerized actin and adhesion plaques. Cells expressing rho Q63L, but not rho wt, rho G14V or rh o N117I, showed an altered morphology. These cells displayed a flat, fibrob last like shape when compared with the RR1022 ancestor cells. Immunofluores cence analyses revealed that actin stress fibers and adhesion plaques were rearranged in these cells. We conclude from these data that an active rho p rotein can restore elements of the actin cytoskeleton in transformed cells by overriding the tyrosine kinase phosphorylation induced by the pp60(v-src ).