Differential regulation of insulin-stimulated tyrosine phosphorylation of IRS-1 and SHC by Wortmannin in intact cells

Wortmannin is an inhibitor of phosphatidylinositol (PI) 3'-kinase, a cellular kinase activated by docking to phosphotyrosyl residues of insulin receptor substrate-1 (IRS-1) that can also phosphorylate serine residues on TRS-l in vitro. After treatment of hepatoma cells with 100 nM wortmannin, the tyrosine phosphorylation of IRS-1 in response to insulin was increased by 38.3 +/- 3.3% while its phosphoserine/threonine content was reduced by 19%. Treatment with 1 mu M wortmannin further increased IRS-1 tyrosine phosphorylation to 180% of control, while under these conditions, tyrosine phosphorylation of the IR substrate p52 She was reduced to less than 50% of control. Thus, alteration of the serine phosphorylation of IR substrates by a wortmannin-sensitive kinase may regulate post-insulin receptor signaling pathways by differential modulation of their insulin-stimulated tyrosine phosphorylation. (C) 1996 Academic Press, Inc.