title: Release of insulin receptor substrate proteins from an intracellular complex coincides with the development of insulin resistance.
abstract: Insulin receptor substrate (IRS) proteins are major substrates of the insulin receptor (IR). IRS-1 associates with an insoluble multiprotein complex, possibly the cytoskeleton, in adipocytes. This localization may facilitate interaction with the IR at the cell surface. In the present study, we examined the hypothesis that the release of IRS proteins from this location may be a mechanism for insulin desensitization. We show that a second IRS protein, IRS-2, is associated with a multiprotein complex in adipocytes with similar characteristics to the IRS-1 complex. Insulin treatment (15-60 min) caused the release of IRS-1 and IRS-2 from this complex (high speed pellet; HSP) into the cytosol, whereas the level of tyrosyl-phosphorylated IRS proteins remained constant. Chronic insulin treatment resulted in a dramatic reduction in IRS-1 and IRS-2 in the HSP, eventually (>2 h) leading to IRS protein degradation and decreased levels of tyrosyl-phosphorylated IRS proteins. Okadaic acid, which rapidly induces insulin resistance in adipocytes independently of IR function, caused an almost quantitative release of IRS-1 into the cytosol commensurate with a significant reduction in tyrosyl-phosphorylated IRS proteins. Platelet-derived growth factor, a factor known to compromise insulin signaling, caused a more moderate release of IRS proteins from the HSP. Collectively, these results suggest that the assembly of IRS-1/IRS-2 into a multiprotein complex facilitates coupling to the IR and that the regulated release from this location may represent a novel mechanism of insulin resistance.
authors.affiliation: Centre for Molecular and Cellular Biology, Department of Physiology and Pharmacology, University of Queensland, Brisbane, 4072 Australia.
authors.forename: S F
authors.initials: SF
authors.lastname: Clark
authors.forename: J C
authors.initials: JC
authors.lastname: Molero
authors.forename: D E
authors.initials: DE
authors.lastname: James
mesh_terms: D016475:3T3 Cells; D000730:Androstadienes / Q000494:pharmacology; D000818:Animals; D001483:Base Sequence; D016466:CHO Cells; D006224:Cricetinae; D005947:Glucose / Q000378:metabolism; D051275:Glucose Transporter Type 4; D007328:Insulin / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins; D007333:Insulin Resistance; D047908:Intracellular Signaling Peptides and Proteins; D046911:Macromolecular Substances; D051379:Mice; D008969:Molecular Sequence Data; D009004:Monosaccharide Transport Proteins / Q000378:metabolism; D046912:Multiprotein Complexes; D009124:Muscle Proteins; D019319:Okadaic Acid / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D010982:Platelet-Derived Growth Factor / Q000494:pharmacology; D011972:Receptor, Insulin / Q000378:metabolism*; D000077191:Wortmannin
chemical_list: D000730:Androstadienes; D051275:Glucose Transporter Type 4; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; C526295:Irs1 protein, mouse; C526298:Irs2 protein, mouse; D046911:Macromolecular Substances; D009004:Monosaccharide Transport Proteins; D046912:Multiprotein Complexes; D009124:Muscle Proteins; D010750:Phosphoproteins; D010982:Platelet-Derived Growth Factor; C495693:Slc2a4 protein, mouse; D019319:Okadaic Acid; D019869:Phosphatidylinositol 3-Kinases; D011972:Receptor, Insulin; D005947:Glucose; D000077191:Wortmannin