title: Phosphorylation of insulin receptor substrate 1 by glycogen synthase kinase 3 impairs insulin action.
abstract: The phosphorylation of insulin receptor substrate 1 (IRS-1) on tyrosine residues by the insulin receptor (IR) tyrosine kinase is involved in most of the biological responses of insulin. IRS-1 mediates insulin signaling by recruiting SH2 proteins through its multiple tyrosine phosphorylation sites. The phosphorylation of IRS-1 on serine/threonine residues also occurs in cells; however, the particular protein kinase(s) promoting this type of phosphorylation are unknown. Here we report that glycogen synthase kinase 3 (GSK-3) is capable of phosphorylating IRS-1 and that this modification converts IRS-1 into an inhibitor of IR tyrosine kinase activity in vitro. Expression of wild-type GSK-3 or an "unregulated" mutant of the kinase (S9A) in CHO cells overexpressing IRS-1 and IR, resulted in increased serine phosphorylation levels of IRS-1, suggesting that IRS-1 is a cellular target of GSK-3. Furthermore, insulin-induced tyrosine phosphorylation of IRS-1 and IR was markedly suppressed in cells expressing wild-type or the S9A mutant, indicating that expression of GSK-3 impairs IR tyrosine kinase activity. Taken together, our studies suggest a new role for GSK-3 in attenuating insulin signaling via its phosphorylation of IRS-1 and may provide new insight into mechanisms important in insulin resistance.
authors.affiliation: Department of Pharmacology, University of Washington, Seattle, WA 98195, USA.
authors.forename: H
authors.initials: H
authors.lastname: Eldar-Finkelman
authors.forename: E G
authors.initials: EG
authors.lastname: Krebs
mesh_terms: D000818:Animals; D016466:CHO Cells; D017871:Calcium-Calmodulin-Dependent Protein Kinases / Q000378:metabolism*; D006224:Cricetinae; D038362:Glycogen Synthase Kinase 3; D038341:Glycogen Synthase Kinases; D007328:Insulin / Q000378:metabolism*; D055504:Insulin Receptor Substrate Proteins; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D011994:Recombinant Proteins / Q000378:metabolism; D013379:Substrate Specificity
chemical_list: D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D010750:Phosphoproteins; D011994:Recombinant Proteins; D038341:Glycogen Synthase Kinases; D017871:Calcium-Calmodulin-Dependent Protein Kinases; D038362:Glycogen Synthase Kinase 3