STIMULATION OF MEMBRANE RUFFLING AND MAP KINASE ACTIVATION BY DISTINCT EFFECTORS OF RAS

The RAS guanine nucleotide binding proteins activate multiple signalin g events that regulate cell growth and differentiation. In quiescent f ibroblasts, ectopic expression of activated H-RAS (H-RAS(V12), where V 12 indicates valine-12) induces membrane ruffling, mitogen-activated p rotein (MAP) kinase activation, and stimulation of DNA synthesis. A mu tant of activated H-RAS, H-RAS(V12C40) (where C40 indicates cysteine-4 0), was identified that was defective for MAP kinase activation and st imulation of DNA synthesis, but retained the ability to induce membran e ruffling. Another mutant of activated H-RAS, H-RAS(V12S35) (where S3 5 indicates serine-35), which activates MAP kinase, was defective for stimulation of membrane ruffling and induction of DNA synthesis. Expre ssion of both mutants resulted in a stimulation of DNA synthesis that was comparable to that induced by H-RAS(V12). These results indicate t hat membrane ruffling and activation of MAP kinase represent distinct RAS effector pathways and that input from both pathways is required fo r the mitogenic activity of RAS.