INDUCTION OF APOPTOSIS IN NIH3T3 CELLS AFTER SERUM DEPRIVATION BY OVEREXPRESSION OF RHO-P21, A GTPASE PROTEIN OF THE RAS SUPERFAMILY

Oncogenes appear to influence apoptosis in two ways. Some activate cel ls from a growth-arrested state to one in which both apoptosis and ent ry to S-phase become possible, the choice between them being determine d by a second signal, such as cytokine or growth factor. Cells in this state are often sensitive to apoptosis induced by a wide variety of a gents, including several drugs used in cancer chemotherapy. Other onco genes prevent activation of the apoptosis effector pathway, even in th e presence of a death stimulus, the affected cells therefore being res istant to chemotherapeutic agents. In rodent fibroblasts, c-myc or the adenovirus oncogene E1A effect the first type of change, whereas bcl- 2, v-abl, E1B or activated uas effect the second. Here we study in rod ent fibroblast the effect of expression of rho genes, members of the r as superfamily which we have previously shown to be tumorigenic when h ighly expressed in this cell type. We show that expression of wild-typ e who from Aplysia californica stimulates apoptosis in cultured cell l ines and that the apoptotic index in tumors generated by these cell li nes is similar to those induced by E1A-transformed cells. In contrast, mutated rho, activated by Val(14) substitution in the GTP binding sit e, it less potent as a stimulator of apoptosis, generating a phenotype more similar to that obtained with activated vas. Thus, rho genes may play a critical role in the regulation of apoptosis.