Identification of a cellular 110 000-Da protein substrate for the insulin-receptor kinase

Abstract

Addition of insulin to wheat-germ-lectin-purified glycoproteins derived from rat hepatocytes or rabbit brown adipose tissue results in the increased phosphorylation of a MW-110,000 protein. This naturally occurring glycoprotein appears as a monomeric structure and is not part of the insulin recpetor itself, since it is not immunoprecipitated by highly specific antibodies to insulin receptor. Phosphorylation of the MW-110,000 protein and autophosphorylation of the receptor .beta.-subunit (MW 95,000) are stimulated by insulin in a remarkably similar dose-dependent fashion, with half-maximal stimulation at 1 nM-insulin. Further, kinetic studies suggest that the phosphorylation of the MW 110,000 protein occurs after autophosphorylation of the insulin-receptor kinase. The present identification of an endogenous substrate for the insulin-receptor kinase could suggest that some, if not all, effects of insulin may be mediated through activation of this kinase.