ROLE OF PHOSPHATIDYLINOSITOL-3-KINASE IN INSULIN-RECEPTOR SIGNALING -STUDIES WITH INHIBITOR, LY294002

In order to study the role of phosphatidylinositol-3-kinase (PI3K) in insulin action, we employed a specific inhibitor of PI3K, LY294002, an d measured five biological functions of insulin in mouse 3T3 fibroblas ts overexpressing human insulin receptors. LY294002 had no effect on t yrosine phosphorylation of both the insulin receptor beta-subunit and insulin receptor substrate 1 (IRS-1) and did not influence the associa tion of the p85 subunit of PI3K with IRS-1. However, LY294002 partiall y inhibited insulin stimulated glucose uptake, amino acid uptake and p rotein synthesis, while it completely inhibited insulin stimulation of DNA synthesis and p70 S6 kinase activation. These data suggest that: 1) PI3K plays a crucial role in various functions of insulin; and 2) t here exist multiple signaling pathways (both PI3K dependent and PI3K i ndependent) for the insulin receptor. (C) 1994 Academic Press,