title: Regulation of insulin/insulin-like growth factor-1 signaling by proteasome-mediated degradation of insulin receptor substrate-2.
abstract: Insulin and insulin-like growth factor-1 (IGF-1) regulate metabolism and body growth through homologous receptor tyrosine kinases that phosphorylate the insulin receptor substrate (IRS) proteins. IRS-2 is an important IRS protein, as it mediates peripheral insulin action and beta-cell survival. In this study, we show that insulin, IGF-1, or osmotic stress promoted ubiquitin/proteasome-mediated degradation of IRS-2 in 3T3-L1 cells, Fao hepatoma, cells and mouse embryo fibroblasts; however, insulin/IGF-1 did not promote degradation of IRS-1 in 3T3-L1 preadipocytes or mouse embryo fibroblasts. MG132 or lactacystin, specific inhibitors of 26S proteasome, blocked insulin/IGF-1-induced degradation of IRS-2 and enhanced the detection of ubiquitinated IRS-2. Insulin/IGF1-induced ubiquitination and degradation of IRS-2 was blocked by inhibitors of phosphatidylinositol 3-kinase (wortmannin or LY294002) or mTOR (rapamycin). Chronic insulin or IGF-1 treatment of IRS-1-deficient mouse embryo fibroblasts inhibited IRS-2-mediated activation of Akt and ERK1/2, which was reversed by lactacystin pretreatment. By contrast, IRS-1 activation of Akt and ERK1/2 was not inhibited by chronic insulin/IGF-1 stimulation in IRS-2-deficient mouse embryo fibroblasts. Thus, we identified a novel negative feedback mechanism by which the ubiquitin/proteasome-mediated degradation of IRS-2 limits the magnitude and duration of the response to insulin or IGF-1.
authors.affiliation: Howard Hughes Medical Institute, Joslin Diabetes Center, Harvard Medical School, One Joslin Place, Boston, MA 02215, USA.
authors.forename: L
authors.initials: L
authors.lastname: Rui
authors.forename: T L
authors.initials: TL
authors.lastname: Fisher
authors.forename: J
authors.initials: J
authors.lastname: Thomas
authors.forename: M F
authors.initials: MF
authors.lastname: White
mesh_terms: D017667:Adipocytes / Q000378:metabolism; D000818:Animals; D006528:Carcinoma, Hepatocellular / Q000378:metabolism; D003924:Diabetes Mellitus, Type 2 / Q000209:etiology; D015536:Down-Regulation; D005246:Feedback; D005347:Fibroblasts / Q000378:metabolism; D006801:Humans; D007328:Insulin / Q000378:metabolism*; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I / Q000378:metabolism*; D047908:Intracellular Signaling Peptides and Proteins; D008114:Liver Neoplasms, Experimental / Q000378:metabolism; D051379:Mice; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D009997:Osmotic Pressure; D010447:Peptide Hydrolases / Q000187:drug effects / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex; D011494:Protein Kinases / Q000378:metabolism; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D011972:Receptor, Insulin / Q000378:metabolism*; D015398:Signal Transduction; D058570:TOR Serine-Threonine Kinases; D014407:Tumor Cells, Cultured; D025801:Ubiquitin
chemical_list: D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D007334:Insulin-Like Growth Factor I; D047908:Intracellular Signaling Peptides and Proteins; D020928:Mitogen-Activated Protein Kinases; D010447:Peptide Hydrolases; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D046988:Proteasome Endopeptidase Complex; D011494:Protein Kinases; D017346:Protein Serine-Threonine Kinases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D011972:Receptor, Insulin; D058570:TOR Serine-Threonine Kinases; D025801:Ubiquitin; C526297:IRS2 protein, human; C526298:Irs2 protein, mouse; C546842:MTOR protein, human; C546843:mTOR protein, mouse; C494918:AKT1 protein, human; C061553:ATP dependent 26S protease