Insulin receptor substrate 1 rescues insulin action in CHO cells expressing mutant insulin receptors that lack a juxtamembrane NPXY motif.
Insulin signals are mediated through tyrosine phosphorylation of specific proteins such as insulin receptor substrate 1 (IRS-1) and Shc by the activated insulin receptor (IR). Phosphorylation of both proteins is nearly abolished by an alanine substitution at Tyr-960 (A960) in the beta-subunit of the receptor. However, overexpression of IRS-1 in CHO cells expressing the mutant receptor (A960 cells) restored sufficient tyrosine phosphorylation of IRS-1 to rescue IRS-1/Grb-2 binding and phosphatidylinositol 3' kinase activation during insulin stimulation. Shc tyrosine phosphorylation and its binding to Grb-2 were impaired in the A960 cells and were unaffected by overexpression of IRS-1. Although overexpression of IRS-1 increased IRS-1 binding to Grb-2, ERK-1/ERK-2 activation was not rescued. These data suggest that signaling molecules other than IRS-1, perhaps including Shc, are critical for insulin stimulation of p21ras. Interestingly, overexpression of IRS-1 in the A960 cells restored insulin-stimulated mitogenesis and partially restored insulin stimulation of glycogen synthesis. Thus, IRS-1 tyrosine phosphorylation is sufficient to increase the mitogenic response to insulin, whereas insulin stimulation of glycogen synthesis appears to involve other factors. Moreover, IRS-1 phosphorylation is either not sufficient or not involved in insulin stimulation of ERK.
Chen
D
D
Department of Molecular Pharmacology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
Van Horn
D J
DJ
White
M F
MF
Backer
J M
JM
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D016466:CHO Cells; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism; D006224:Cricetinae; D004247:DNA / Q000096:biosynthesis; D004305:Dose-Response Relationship, Drug; D051380:GRB2 Adaptor Protein; D006003:Glycogen / Q000096:biosynthesis; D007328:Insulin / Q000378:metabolism*; D055504:Insulin Receptor Substrate Proteins; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases; D009154:Mutation; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D011506:Proteins / Q000378:metabolism; D011972:Receptor, Insulin / Q000235:genetics / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D015398:Signal Transduction; D013329:Structure-Activity Relationship
D048868:Adaptor Proteins, Signal Transducing; D051380:GRB2 Adaptor Protein; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D010750:Phosphoproteins; D011506:Proteins; D011994:Recombinant Proteins; D006003:Glycogen; D004247:DNA; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D011505:Protein-Tyrosine Kinases; D011972:Receptor, Insulin; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases