Insulin-stimulated GLUT4 Translocation is Relevant to the Phosphorylation of IRS-1 and the Activity of PI3-kinase

We examined the role of 185-kDa insulin receptor substrate-1 (IRS-1) and phosphatidylinositol 3-kinase (PI3-kinase) in the signaling pathway of insulin-stimulated GLUT4 translocation. We had already developed a novel cell line to detect GLUT4 on the cell surface, directly and sensitively (Kanai, F., Nishioka, Y., Hayashi, H., Kamohara, S., Todaka, M., and Ebina, Y. (1993) J. Biol. Chem. 268, 14523-14526). We stably expressed a mutant insulin receptor in which Tyr972 was replaced with phenylalanine. Insulin-stimulated tyrosyl phosphorylation of IRS-1 and GLUT4 translocation were decreased in cells expressing the mutant receptor, as compared to findings in cells expressing the normal receptor. Wortmannin, an inhibitor of PI3-kinase, inhibits the insulin-stimulated PI3-kinase activity and GLUT4 translocation at 50 nM, but not the NaF-stimulated GLUT4 translocation. These results suggest that the tyrosine phosphorylation of IRS-1 and activation of PI3-kinase may be involved in the signaling pathway of the insulin-stimulated GLUT4 translocation.