title: Molecular mechanism of insulin-induced degradation of insulin receptor substrate 1.
abstract: Insulin receptor substrate 1 (IRS-1) plays an important role in the insulin signaling cascade. In vitro and in vivo studies from many investigators have suggested that lowering of IRS-1 cellular levels may be a mechanism of disordered insulin action (so-called insulin resistance). We previously reported that the protein levels of IRS-1 were selectively regulated by a proteasome degradation pathway in CHO/IR/IRS-1 cells and 3T3-L1 adipocytes during prolonged insulin exposure, whereas IRS-2 was unaffected. We have now studied the signaling events that are involved in activation of the IRS-1 proteasome degradation pathway. Additionally, we have addressed structural elements in IRS-1 versus IRS-2 that are required for its specific proteasome degradation. Using ts20 cells, which express a temperature-sensitive mutant of ubiquitin-activating enzyme E1, ubiquitination of IRS-1 was shown to be a prerequisite for insulin-induced IRS-1 proteasome degradation. Using IRS-1/IRS-2 chimeric proteins, the N-terminal region of IRS-1 including the PH and PTB domains was identified as essential for targeting IRS-1 to the ubiquitin-proteasome degradation pathway. Activation of phosphatidylinositol 3-kinase is necessary but not sufficient for activating and sustaining the IRS-1 ubiquitin-proteasome degradation pathway. In contrast, activation of mTOR is not required for IRS-1 degradation in CHO/IR cells. Thus, our data provide insight into the molecular mechanism of insulin-induced activation of the IRS-1 ubiquitin-proteasome degradation pathway.
authors.affiliation: Endocrinology Division, University of Vermont College of Medicine, Burlington, Vermont 05405, USA.
authors.forename: Rachel
authors.initials: R
authors.lastname: Zhande
authors.forename: John J
authors.initials: JJ
authors.lastname: Mitchell
authors.forename: Jiong
authors.initials: J
authors.lastname: Wu
authors.forename: Xiao Jian
authors.initials: XJ
authors.lastname: Sun
mesh_terms: D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D016466:CHO Cells; D002867:Chromones / Q000494:pharmacology; D006224:Cricetinae; D003546:Cysteine Endopeptidases / Q000378:metabolism*; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D006801:Humans; D015151:Immunoblotting; D007328:Insulin / Q000378:metabolism* / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins; D009025:Morpholines / Q000494:pharmacology; D009097:Multienzyme Complexes / Q000378:metabolism*; D009842:Oligopeptides / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex; D017346:Protein Serine-Threonine Kinases; D017434:Protein Structure, Tertiary; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D011972:Receptor, Insulin / Q000235:genetics / Q000378:metabolism; D011993:Recombinant Fusion Proteins / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000494:pharmacology; D025801:Ubiquitin / Q000378:metabolism
chemical_list: D000903:Antibiotics, Antineoplastic; D002867:Chromones; D003546:Cysteine Endopeptidases; D004791:Enzyme Inhibitors; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D009025:Morpholines; D009097:Multienzyme Complexes; D009842:Oligopeptides; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D046988:Proteasome Endopeptidase Complex; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011972:Receptor, Insulin; D011993:Recombinant Fusion Proteins; D020123:Sirolimus; D025801:Ubiquitin; C526292:IRS1 protein, human; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C078846:epoxomicin