Insulin receptor substrate-1 (IRS1) and Shc compete for a limited pool of Grb2 in mediating insulin downstream signaling.
Expression of the insulin receptor substrate-1 (IRS1) or Shc cDNA resulted in both increased protein and insulin-stimulated tyrosine phosphorylation of IRS1 and Shc proteins, respectively. Although expression of Shc had no significant effect on insulin-stimulated mitogen-activated protein (MAP) kinase gel shift or c-fos transcriptional activation, expression of IRS1 inhibited these responses. The effect of IRS1 expression on the formation of multisubunit signaling complexes was determined by a series of indirect co-immunoprecipitations. Grb2 immunoprecipitation from IRS1-transfected and insulin-treated cells demonstrated an increased coimmunoprecipitation of Syp and the p85 regulatory subunit of the phosphatidylinositol 3-kinase. Similarly, cell extracts immunoprecipitated with a p85 antibody displayed an increased co-immunoprecipitation of Syp and Grb2. However, expression of IRS1 increased the extent of Grb2 associated with IRS1 with a concomitant reduction in the amount of Grb2 associated with Shc. Furthermore, increased expression of Shc reduced the amount of Grb2 bound to IRS1 with a concomitant increase in Grb2 associated with Shc. Together, these data demonstrate that IRS1 and Shc compete for a limited cellular pool of Grb2, and insulin activation of MAP kinase and c-fos transcription predominantly occur through the Shc-Grb2 signaling pathway.
Yamauchi
K
K
Department of Physiology & Biophysics, University of Iowa, Iowa City 52242.
Pessin
J E
JE
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D001667:Binding, Competitive; D016466:CHO Cells; D006224:Cricetinae; D004789:Enzyme Activation; D051380:GRB2 Adaptor Protein; D006801:Humans; D007328:Insulin / Q000378:metabolism* / Q000502:physiology; D055504:Insulin Receptor Substrate Proteins; D019950:Mitogen-Activated Protein Kinase 1; D010750:Phosphoproteins / Q000378:metabolism*; D011233:Precipitin Tests; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011506:Proteins / Q000378:metabolism*; D015398:Signal Transduction
D048868:Adaptor Proteins, Signal Transducing; D051380:GRB2 Adaptor Protein; C495948:GRB2 protein, human; C526292:IRS1 protein, human; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D010750:Phosphoproteins; D011506:Proteins; D011505:Protein-Tyrosine Kinases; D017346:Protein Serine-Threonine Kinases; D019950:Mitogen-Activated Protein Kinase 1