INHIBITION OF SERUM-STIMULATED AND RAS-STIMULATED DNA-SYNTHESIS BY ANTIBODIES TO PHOSPHOLIPASE-C

Several immunologically distinct isozymes of inositol phospholipid-specific phospholipase C (PLC) have been purified from bovine brain. Murine NIH 3T3 fibroblasts were found to express PLC-γ, but the expression of PLC-β was barely detectable by radioimmunoassay or protein immunoblot. A mixture of monoclonal antibodies was identified that neutralizes the biological activity of both endogenous and injected purified PLC-γ. When co-injected with oncogenic Ras protein or PLC-γ, this mixture of antibodies inhibited the induction of DNA synthesis that characteristically results from the injection of these proteins into quiescent 3T3 cells. However, when oncogenic Ras protein or PLC-γ was co-injected with a neutralizing monoclonal antibody to Ras, only the DNA synthesis induced by the Ras protein was inhibited - that induced by PLC was unaffected. These results suggest that the Ras protein is an upstream effector of PLC activity in phosphoinositide-specific signal transduction and that PLC-γ activity is necessary for Ras-mediated induction of DNA synthesis.