The COOH-terminal Tyrosine Phosphorylation Sites on IRS-1 Bind SHP-2 and Negatively Regulate Insulin Signaling*

Activation of tyrosine kinases by numerous growth factor and cytokine receptors leads to tyrosine phospho-rylation of the insulin receptor substrate (IRS)-proteins. Tyrosine-phosphorylated motifs on the IRS proteins bind to the SH2 domains in proteins that mediate down-stream signals, including phosphatidylinositol 3*-ki-nase, GRB-2, and SHP-2. We investigated the function of the two SHP-2 binding COOH-terminal tyrosines of IRS-1 by replacing them with phenylalanine (IRS-1FCT). IRS-1FCT failed to bind SHP-2 or mediate its tyrosine phosphorylation during insulin stimulation. Although several reports suggest a critical role for SHP-2 in insu-lin stimulated mitogen-activated protein kinase activa-tion and cell proliferation, IRS-1FCT mediated these ef-fects normally in 32D cells. Indeed, IRS-1FCT exhibite