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 β-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. 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 β-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. insulin-like growth factor 1 insulin receptor substrate phosphatidylinositol mouse embryo fibroblast mitogen-activated protein Dulbecco's modified Eagle's medium ubiquitin-activating enzyme ubiquitin carrier protein ubiquitin-protein isopeptide ligase fetal bovine serum phosphate-buffered saline mitogen-activated protein kinase/extracellular signal-regulated kinase kinase polyacrylamide gel electrophoresis epidermal growth factor platelet-derived growth factor extracellular signal-regulated kinase Insulin and insulin-like growth factor 1 (IGF-1)1 regulate a variety of biological functions through homologous tyrosine kinases that phosphorylate the insulin receptor substrate (IRS) proteins. IRS proteins mediate signal specificity and diversity in various cellular backgrounds (1Yenush L. White M.F. BioEssays. 1997; 19: 491-500Crossref PubMed Scopus (257) Google Scholar). Upon ligand binding, the activated insulin/IGF-1 receptors engage IRS proteins and promote the phosphorylation of multiple tyrosine residues, which activate various downstream signaling pathways, including the phosphatidylinositol (PI) 3-kinase and MAP kinase cascades (1Yenush L. White M.F. BioEssays. 1997; 19: 491-500Crossref PubMed Scopus (257) Google Scholar, 2Myers Jr., M.G. White M.F. Annu. Rev. Pharmacol. Toxicol. 1996; 36: 615-658Crossref PubMed Scopus (298) Google Scholar). These signaling pathways coordinate a network of protein kinases that regulate the activity of cytoplasmic enzymes and nuclear transcription factors (1Yenush L. White M.F. BioEssays. 1997; 19: 491-500Crossref PubMed Scopus (257) Google Scholar, 2Myers Jr., M.G. White M.F. Annu. Rev. Pharmacol. Toxicol. 1996; 36: 615-658Crossref PubMed Scopus (298) Google Scholar, 3Pessin J.E. Saltiel A.R. J. Clin. Invest. 2000; 106: 165-169Crossref PubMed Scopus (685) Google Scholar, 4Shulman G.I. J. Clin. Invest. 2000; 106: 171-176Crossref PubMed Scopus (2201) Google Scholar). Four IRS proteins are known, including IRS-1 and IRS-2, which play a central role in many tissue and organ systems. Deletion of IRS-1 in mice impairs somatic growth and causes peripheral insulin resistance, but diabetes rarely develops owing to lifelong compensatory hyperinsulinemia (5Tamemoto H. Kadowaki T. Tobe K. Yagi T. Sakura H. Hayakawa T. Terauchi Y. Ueki K. Kaburagi Y. Satoh S. Sekihara H. Yoshioka S. Horikoshi H. Furuta Y. Ikawa Y. Kasuga M. Yazaki Y. Aizawa S. Nature. 1994; 372: 182-186Crossref PubMed Scopus (906) Google Scholar, 6Araki E. Lipes M.A. Patti M.E. Bruning J.C. Haag III, B. Johnson R.S. Kahn C.R. Nature. 1994; 372: 186-190Crossref PubMed Scopus (1099) Google Scholar). By contrast, IRS-2 is essential for normal nutrient homeostasis because it mediates both peripheral insulin action and the effect of IGF-1 on β-cell growth; mice lacking IRS-2 fail to maintain sufficient compensatory insulin secretion and develop diabetes as young adults (7Withers D.J. Gutierrez J.S. Towery H. Burks D.J. Ren J.M. Previs S. Zhang Y. Bernal D. Pons S. Shulman G.I. Bonner-Weir S. White M.F. Nature. 1998; 391: 900-904Crossref PubMed Scopus (1347) Google Scholar). Moreover, female mice lacking IRS-2 are hyperplasic and infertile, owing to a failure of the hypothalamic-pituitary-ovarian axis (8Burks D.J. de Mora J.F. Schubert M. Withers D.J. Myers M.G. Towery H.H. Altamuro S.L. Flint C.L. White M.F. Nature. 2000; 407: 377-382Crossref PubMed Scopus (400) Google Scholar). Many mechanisms are proposed to explain the inhibition of IRS protein signaling, including phosphotyrosine dephosphorylation, serine/threonine phosphorylation, and degradation (9Elchebly M. Payette P. 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Recent studies suggest that proteasome-mediated degradation of IRS-1 might be involved in the down-regulation of signaling by insulin and IGF-1 and contribute to insulin resistance (12Stephens J.M. Lee J. Pilch P.F. J. Biol. Chem. 1997; 272: 971-976Abstract Full Text Full Text PDF PubMed Scopus (471) Google Scholar, 13Egawa K. Nakashima N. Sharma P.M. Maegawa H. Nagai Y. Kashiwagi A. Kikkawa R. Olefsky J.M. Endocrinology. 2000; 141: 1930-1935Crossref PubMed Scopus (57) Google Scholar, 15Sun X.J. Goldberg J.L. Qiao L.Y. Mitchell J.J. Diabetes. 1999; 48: 1359-1364Crossref PubMed Scopus (197) Google Scholar, 16Haruta T. Tatsuhito U. Kawahara J. Takano A. Egawa K. Sharma P.M. Olefsky J.M. Kobayashi M. Mol. Endocrinol. 2000; 14: 783-794Crossref PubMed Scopus (322) Google Scholar, 17Lee A.V. Gooch J.L. Oesterreich S. Guler R.L. Yee D. Mol. Cell. Biol. 2000; 20: 1489-1496Crossref PubMed Scopus (111) Google Scholar). However, there is no convincing evidence showing that the decrease of endogenous IRS-1 via the ubiquitin/proteasome system contributes to an inhibition of insulin signaling. Proteasome-mediated degradation regulates many biological processes including gene transcription and cell cycle progression (18Tyers M. Willems A.R. Science. 1999; 284: 601-603Crossref PubMed Scopus (142) Google Scholar, 19Palombella V.J. Rando O.J. Goldberg A.L. Maniatis T. Cell. 1994; 78: 773-785Abstract Full Text PDF PubMed Scopus (1922) Google Scholar, 20Kirschner M. Trends Cell Biol. 1999; 9: M42-M45Abstract Full Text Full Text PDF PubMed Scopus (40) Google Scholar). Proteins targeted for destruction by 26 S proteasome are usually ubiquitinated by a complex containing an ubiquitin-activating enzyme (E1), ubiquitin-conjugating enzyme (E2), and ubiquitin-protein ligase (E3) (20Kirschner M. Trends Cell Biol. 1999; 9: M42-M45Abstract Full Text Full Text PDF PubMed Scopus (40) Google Scholar, 21Ciechanover A. Schwartz A.L. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: 2727-2730Crossref PubMed Scopus (348) Google Scholar, 22Wojcik C. Drug Discov. Today. 1999; 4: 188-189Crossref PubMed Google Scholar). In certain cases, phosphorylation promotes ubiquitination and degradation of signaling proteins, including IκBα and β-catenin (18Tyers M. Willems A.R. Science. 1999; 284: 601-603Crossref PubMed Scopus (142) Google Scholar, 23Winston J.T. Strack P. Beer-Romero P. Chu C.Y. Elledge S.J. Harper J.W. Genes Dev. 1999; 13: 270-283Crossref PubMed Scopus (817) Google Scholar, 24Spencer E. Jiang J. Chen Z.J. Genes Dev. 1999; 13: 284-294Crossref PubMed Scopus (377) Google Scholar, 25Laney J.D. Hochstrasser M. Cell. 1999; 97: 427-430Abstract Full Text Full Text PDF PubMed Scopus (392) Google Scholar). Overexpressed recombinant IRS-1 is ubiquitinated in response to IGF-1, and PI 3-kinase inhibitors block IRS-1 degradation (12Stephens J.M. Lee J. Pilch P.F. J. Biol. Chem. 1997; 272: 971-976Abstract Full Text Full Text PDF PubMed Scopus (471) Google Scholar, 13Egawa K. Nakashima N. Sharma P.M. Maegawa H. Nagai Y. Kashiwagi A. Kikkawa R. Olefsky J.M. Endocrinology. 2000; 141: 1930-1935Crossref PubMed Scopus (57) Google Scholar, 15Sun X.J. Goldberg J.L. Qiao L.Y. Mitchell J.J. Diabetes. 1999; 48: 1359-1364Crossref PubMed Scopus (197) Google Scholar, 16Haruta T. Tatsuhito U. Kawahara J. Takano A. Egawa K. Sharma P.M. Olefsky J.M. Kobayashi M. Mol. Endocrinol. 2000; 14: 783-794Crossref PubMed Scopus (322) Google Scholar, 17Lee A.V. Gooch J.L. Oesterreich S. Guler R.L. Yee D. Mol. Cell. Biol. 2000; 20: 1489-1496Crossref PubMed Scopus (111) Google Scholar). However, it is unclear whether insulin promotes ubiquitination of endogenous IRS proteins or whether the ubiquitin/proteasome system inhibits IRS protein signaling. In this work, we show that insulin and IGF-1 stimulate ubiquitination and degradation of IRS-2 in multiple cell types via a PI 3-kinase/Akt/mTOR-dependent pathway, which correlates closely with the inhibition of insulin signaling. This negative feedback mechanism might limit the magnitude and duration of IRS-2-mediated signals, and contribute to insulin resistance associated with hyperglycemia and hyperinsulinemia. Human insulin and IGF-1 were a gift from Eli Li. Protein A-agarose was purchased from Repligen; 3-isobutylmethylxanthine, dexamethasone, aprotinin, and leupeptin were purchased from Sigma. Enhanced chemiluminescence (ECL) detection system was purchased from Amersham Pharmacia Biotech. Lactacystin, MG132, rapamycin, PD98059, LY294002, wortmannin, and Nonidet P-40 were purchased from Calbiochem. Polyclonal anti-active ERK1/2 (αpERK) was purchased from Promega. Polyclonal anti-phospho-Akt (on Ser-473) (αpAkt) was purchased from New England Biolabs Inc. (Beverly, MA); monoclonal anti-ubiquitin was purchased from Santa Cruz Inc; polyclonal anti-IRS-1 antibodies were raised against the full-length rat IRS-1 (JD#159, used at a dilution of 1:15,000 for immunoblotting). Polyclonal anti-IRS-2 antibodies were raised in the laboratory against amino acids 976–1094 (JD#110) or 618–747 (JD#101) of rat IRS-2. Polyclonal anti-p85 antibodies were raised against the N-terminal SH2 domain of p85 regulatory subunit of PI 3-kinase. Fao cells were grown at 37 °C in 5% CO2 in RPMI 1640 supplemented with 100 units/ml penicillin, 100 µg/ml streptomycin, and 10% fetal bovine serum (FBS). 3T3-L1 preadipocytes were grown at 37 °C in 10% CO2 in Dulbecco's modified Eagle's medium (DMEM) containing 25 mm glucose, 100 units/ml penicillin, 100 µg/ml streptomycin, and 10% calf serum (HyClone Laboratories, Inc). For adipocyte differentiation, confluent preadipocytes were cultured for 3 days in differentiation medium supplemented with 25 mm glucose, 1 insulin, 1 dexamethasone, and 10% and 3 days in supplemented with 1 insulin and 10% cells were grown for an days in containing 25 mm and 10% cells are of IRS-1 and IRS-2 mice (5Tamemoto H. Kadowaki T. Tobe K. Yagi T. Sakura H. Hayakawa T. Terauchi Y. Ueki K. Kaburagi Y. Satoh S. Sekihara H. Yoshioka S. Horikoshi H. Furuta Y. Ikawa Y. Kasuga M. Yazaki Y. Aizawa S. Nature. 1994; 372: 182-186Crossref PubMed Scopus (906) Google Scholar, 6Araki E. Lipes M.A. Patti M.E. Bruning J.C. Haag III, B. Johnson R.S. Kahn C.R. Nature. 1994; 372: 186-190Crossref PubMed Scopus (1099) Google Scholar, D.J. Gutierrez J.S. Towery H. Burks D.J. Ren J.M. Previs S. Zhang Y. Bernal D. Pons S. Shulman G.I. Bonner-Weir S. White M.F. Nature. 1998; 391: 900-904Crossref PubMed Scopus (1347) Google Scholar). or were on of of the and embryo were with with and with on were for an at 37 °C to activate medium supplemented with 25 mm glucose, 10% 100 units/ml penicillin, and 100 µg/ml was to and the were by cell was for at cell was in growth medium and cultured at 37 °C in 5% cells in days and were at a of the of cell cells were of serum in 3T3-L1 and or RPMI 1640 Fao containing bovine serum and with at 37 cells were with mm mm 1 mm in mm Nonidet mm mm 1 mm 100 mm mm 1 mm µg/ml aprotinin, µg/ml and at for at was for in mm 10% and and by In the was with the on for were on protein A-agarose a at were with mm Nonidet mm mm and for in proteins were by Proteins on the gel were to Pharmacia and by with the were at °C for in mm mm to for a of cell cells were in at for 1 at and for in whether insulin and IGF-1 decrease IRS-2 protein 3T3-L1 preadipocytes were for with insulin or IGF-1 Cell in Nonidet P-40 were by and by with polyclonal antibodies against IRS-2 IRS-2 was in cell but not in or cells that this protein was IRS-2, 3T3-L1 preadipocytes were or with insulin, and proteins in the cell were and with Insulin the of IRS-2 By contrast, insulin and IGF-1 the of and did not the of the p85 regulatory subunit of PI 3-kinase 1 the that IRS-2 was an cells were in containing and were by and with with the insulin the of IRS-2 but not p85 1 were with polyclonal antibodies raised against of IRS-2, the that phosphorylation of IRS-2 inhibited by degradation of IRS-2 was by growth factors and in various cell 3T3-L1 preadipocytes were with epidermal growth factor platelet-derived growth or insulin of IRS-2, but the of the of p85 was not in response to insulin, or 1 insulin and phosphorylation and activation of Akt to a 1 degradation of IRS-1 or IRS-2 was in cell including 3T3-L1 Fao cells, or cells from or cells were with insulin for and proteins in cell were with or IRS-2 in of the cell IRS-1 was not in and p85 did not stress by hyperglycemia might peripheral insulin resistance and β-cell by insulin/IGF-1 signaling Rev. 1997; Scholar). whether osmotic stress of IRS-2, Fao cells were for with various of stress the of IRS-2 but not p85 in a IRS-1 protein but to a suggest that hyperinsulinemia hyperglycemia might promote degradation of IRS-2 that insulin/IGF-1 IRS-2 protein 1 of insulin treatment and the 3 not This of IRS-2 was by degradation by inhibition of transcription that protein degradation was 3T3-L1 preadipocytes were or with lactacystin or MG132, specific inhibitors of 26S proteasome C. Drug Discov. Today. 1999; 4: 188-189Crossref PubMed Google Scholar). insulin the of IRS-2, as However, both lactacystin and MG132 inhibited of IRS-2 protein lactacystin and MG132 inhibited of IRS-2 not of IRS-2 was inhibited by lactacystin in Fao cells and not and MG132 did not the of p85 Insulin a in of IRS-2, owing to phosphorylation and MG132 did not the of IRS-2, that inhibitors did not phosphorylation of IRS-2 and with this lactacystin and MG132 did not phosphorylation of IRS-1 and IRS-2 of insulin stimulation not the suggest that 26 S proteasome mediates the degradation of IRS-2 insulin/IGF-1 proteins for degradation by 26 S proteasome A.L. Elledge S.J. Harper J.W. Sci. 2001; 284: PubMed Scopus Google Scholar). whether insulin promoted the ubiquitination of IRS-2, Fao cells were for 1 with 100 IRS-2 was by and by with anti-ubiquitin however, ubiquitination of IRS-2 was not by this However, cells were with lactacystin or MG132, ubiquitination of IRS-2 was by with and the of ubiquitinated IRS-2 was Thus, ubiquitinated IRS-2 might not to sufficient to be by owing to proteasome-mediated IRS proteins mediate the activation of the PI 3-kinase and the MAP kinase cascades insulin/IGF-1 stimulation (1Yenush L. White M.F. BioEssays. 1997; 19: 491-500Crossref PubMed Scopus (257) Google Scholar, 2Myers Jr., M.G. White M.F. Annu. Rev. Pharmacol. Toxicol. 1996; 36: 615-658Crossref PubMed Scopus (298) Google Scholar). whether signaling pathways mediate degradation of IRS-2, 3T3-L1 preadipocytes or cells were with or of PI or of both and blocked activation of the PI pathways the activation of the kinase inhibited activation of ERK1/2 effect on the PI pathways not Moreover, and LY294002, but not PD98059, inhibited degradation of IRS-2 and and but not inhibited degradation of IRS-2 in 3T3-L1 preadipocytes not These did not the of p85 with inhibited ubiquitination of IRS-2 in the of lactacystin mTOR is a serine/threonine kinase downstream of the PI that contributes to the activation of kinase S. Dev. 1999; 9: PubMed Scopus Google Scholar, Jr., J.C. Proc. Natl. Acad. Sci. U. S. A. 1998; 95: PubMed Scopus Google Scholar, S. K. C. H. J. K. J. Biol. Chem. 1999; Full Text Full Text PDF PubMed Scopus Google Scholar, M. Withers D.J. Biochem. J. 1999; PubMed Scopus Google Scholar, A. C.C. J.L. P. 2000; Google Scholar). whether mTOR mediates the degradation of IRS-2, Fao cells were to insulin stimulation with rapamycin, an of inhibited degradation of IRS-2, as by cell with blocked degradation of IRS-2 in 3T3-L1 preadipocytes not inhibited the activation of as by the inhibition of in of kinase that phosphorylation and activation of kinase and insulin did not the of kinase IRS-1 and IRS-2 mediate and insulin/IGF-1 degradation of IRS proteins important on However, this is to in cell backgrounds that both IRS-1 and IRS-2. cells from IRS-1 and IRS-2 mice were of IRS-1 or IRS-2 was in and cells, not Deletion of IRS-1 or IRS-2 did not the of insulin/IGF-1 receptors not insulin and IGF-1 promoted activation of Akt as as ERK1/2 in or as by cell with antibodies against or These suggest that IRS-1 and IRS-2 are in activation of the PI and the pathways in this cell However, insulin degradation of IRS-2 in but insulin did not promote IRS-1 degradation in cells whether degradation of IRS-2 inhibits signaling by insulin and IGF-1, cells were for with 100 insulin or 100 IGF-1. were in medium for and for with 100 insulin or 100 IGF-1. of the PI 3-kinase Akt and the ERK1/2 pathways was by cell with antibodies against or Insulin or IGF-1 did not the of Akt or ERK1/2 in cells and However, insulin the activation of both Akt and ERK1/2 in response to a insulin or IGF-1 stimulation IGF-1 inhibited the activation of Akt and ERK1/2 by a insulin/IGF-1 stimulation to a and IGF-1 inhibited activation of Akt by insulin stimulation in the magnitude of inhibition insulin and IGF-1 might a of IGF-1 receptors in cells not In the with cells, insulin IGF-1 inhibited the activation of Akt and ERK1/2 by a stimulation with insulin or IGF-1 and This resistance to the inhibition by insulin/IGF-1 is with the resistance of IRS-1 to degradation in Moreover, that insulin or IGF-1 did not activation of the receptors for insulin or IGF-1, did it the PI and the inhibition of Akt and ERK1/2 by insulin or IGF-1 in cells is by degradation of IRS-2. the that proteasome-mediated degradation of IRS-2 contributes to down-regulation of signaling by insulin and IGF-1, cells were for with or the proteasome lactacystin to IGF-1 pretreatment. IGF-1 inhibited activation of Akt and ERK1/2 in response to a IGF-1 stimulation as However, lactacystin reversed the inhibition of Akt and ERK1/2 by IGF-1 causes of of diabetes are develop insulin resistance and to compensatory insulin to insulin resistance, in hyperinsulinemia. hyperinsulinemia might be in the chronic hyperglycemia and hyperinsulinemia insulin this fail to in diabetes J.E. Saltiel A.R. J. Clin. Invest. 2000; 106: 165-169Crossref PubMed Scopus (685) Google Scholar, 4Shulman G.I. J. Clin. Invest. 2000; 106: 171-176Crossref PubMed Scopus (2201) Google Scholar, Rev. 1997; Scholar). IRS-2 is in both insulin action and β-cell as by the that of IRS-2 in mice causes insulin resistance and β-cell failure (7Withers D.J. Gutierrez J.S. Towery H. Burks D.J. Ren J.M. Previs S. Zhang Y. Bernal D. Pons S. Shulman G.I. Bonner-Weir S. White M.F. Nature. 1998; 391: 900-904Crossref PubMed Scopus (1347) Google Scholar). In IRS-2 protein is in which correlates with hyperglycemia and of insulin resistance D. Pons S. Kahn C.R. J. Clin. Invest. 1997; PubMed Scopus Google Scholar, M. Y. J.L. Mol. Cell. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). treatment not insulin resistance, but IRS-2 protein to a normal M. Y. J.L. Mol. Cell. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). Thus, the decrease of IRS-2 might be a for insulin resistance C. Previs Shulman G.I. M.A. Kahn C.R. Mol. Cell. 2000; Full Text Full Text PDF PubMed Scopus Google Scholar). In this study, we that insulin IRS-2 protein in multiple cell which is blocked by specific inhibitors of the 26 S These suggest that proteasome-mediated degradation of IRS-2, inhibition of transcription of IRS-2, IRS-2 protein and activation of IRS-2-mediated signaling with this insulin ubiquitination of IRS-2. the ubiquitinated IRS-2 is in the of proteasome that ubiquitinated IRS-2 is by the 26 S with of insulin receptor in IRS-2 by C. Previs Shulman G.I. M.A. Kahn C.R. Mol. Cell. 2000; Full Text Full Text PDF PubMed Scopus Google that the of the insulin might block IRS-2 degradation in a of IRS-2 by ubiquitin/proteasome-mediated in mouse embryo fibroblasts lacking IRS-1 inhibits the activation of Akt and ERK1/2 in response to proteasome inhibitors this inhibition of the PI 3-kinase Akt mTOR pathway, but not the ERK1/2 pathway, degradation of IRS-2. These suggest that the activation of the PI 3-kinase Akt mTOR by insulin ubiquitination and degradation of IRS-2 by 26 S proteasome, in inhibition of signaling pathways downstream of IRS-2 insulin This negative feedback mechanism is to insulin action in the body by the magnitude and duration of insulin insulin and osmotic stress stimulate proteasome-mediated degradation of IRS-2, and insulin and osmotic stress effect on destruction of IRS-2 not the activity of the ubiquitin/proteasome system is in that IRS-2 degradation might be S. A. B. Mol. Biol. 1999; PubMed Google Scholar, C. D. J. 1999; PubMed Google Scholar). Thus, proteasome-mediated degradation of IRS-2 might be involved in the of insulin resistance and phosphorylation an important role in ubiquitin/proteasome-mediated destruction of signaling proteins. For factor phosphorylation of IκBα at and by which a subunit of the to and to IκBα with in the ubiquitination of ubiquitinated IκBα is by the 26 S proteasome V.J. Rando O.J. 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Science. 1996; PubMed Scopus Google Scholar, Diabetes. 2001; PubMed Scopus Google Scholar). phosphorylation of IRS-1 was to promote degradation in cell types Diabetes. 2001; PubMed Scopus Google and we degradation of IRS-1 in 3T3-L1 and Fao However, insulin degradation of IRS-2 in 3T3-L1 preadipocytes and but to promote IRS-1 Thus, degradation of IRS-1 and be by In an in certain insulin/IGF-1 cells, degradation of IRS-2 might signaling by the by IRS-2 of signaling including receptors for insulin/IGF-1 and downstream proteasome-mediated degradation of IRS-2 might insulin/IGF-1 in In insulin and IGF-1 stimulate degradation of IRS-2 by the ubiquitin/proteasome system in multiple cell to an inhibition of insulin/IGF-1 signaling. PI 3-kinase Akt mTOR is for insulin/IGF-1-induced degradation of IRS-2. that the ubiquitin/proteasome-mediated degradation of IRS-2 is a of negative feedback inhibition the action of insulin and IGF-1. of 26 S proteasome insulin that types of might in the treatment of with for and and for in