Insulin-like growth factor-I (IGF-I) stimulates tyrosine kinase activity in purified receptors from a rat liver cell line.

Solubilized, lectin-purified receptor preparations from BRL 3A2 rat liver cells are rich in Type I and Type II IGF receptors, but possess few insulin receptors. High concentrations of IGF-I or insulin stimulate phosphorylation of a Mr congruent to 98K membrane protein in these preparations. Phosphorylation of a synthetic polymer of tyrosine and glutamic acid was stimulated by IGF-I greater than IGF-II congruent to insulin. These relative potencies, together with the results of immunodepletion experiments using an autoantibody to the insulin receptor, suggest that the effects of each of these hormones is mediated by the Type I IGF receptor. Our results are consistent with the Type I IGF receptor having intrinsic tyrosine kinase activity capable of phosphorylating the receptor itself and other substrates.