Two Dominant Inhibitory Mutants of p21^ras Interfere with Insulin-Induced Gene Expression

Abstract

Insulin induces a rapid activation of p21^ras in NIH 3T3 and Chinese hamster ovary cells that overexpress the insulin receptor. Previously, we suggested that p21^ras may mediate insulin-induced gene expression. To test such a function of p21^ras more directly, we studied the effect of different dominant inhibitory mutants of p21^ras on the induction of gene expression in response to insulin. We transfected a collagenase promoter-chloramphenicol acetyltransferase (CAT) gene or a fos promoter-luciferase gene into NIH 3T3 cells that overexpressed the insulin receptor. The activities of both promoters were strongly induced after treatment with insulin. This induction could be suppressed by cotransfection of two inhibitory mutant ras genes, H-ras(Asn-17) or H-ras(Leu-61,Ser-186). In particular, insulin-induced activation of the fos promoter was inhibited completely by H-ras(Asn-17). These results show that p21^ras functions as an intermediate in the insulin signal transduction route leading to the induction of gene expression.