Insulin stimulates the phosphorylation level of v-Ha-ras protein in membrane fraction

Insulin was found to stimulate the phosphorylation of the 21,000-dalton protein encoded by the ras oncogene of Harvey murine sarcoma virus in membrane fraction both in vivo and in vitro. When the human ras proteins expressed in E. coli were reconstituted with purified human insulin receptor, GTPase activity of normal or its mutated oncogenic ras protein was not stimulated by the addition of insulin. Likewise, tyrosine kinase activity or insulin binding capacity of the receptor was not influenced when assayed in the presence of the ras proteins. These results suggest that ras proteins may be coupled with the insulin receptor system through some unidentified membrane factors.