Proteasome inhibitors regulate tyrosine phosphorylation of IRS-1 and insulin signaling in adipocytes.
Insulin rapidly stimulates the tyrosine kinase activity of its receptor, resulting in the phosphorylation of insulin receptor substrates (IRS), which in turn associates and activates PI 3-kinase, leading to an increase in glucose uptake. Phosphorylation of IRS proteins and activation of downstream kinases by insulin are transient and the mechanisms for the subsequent downregulation of their activity are largely unknown. We report here that the insulin-induced IRS-1 tyrosine phosphorylation and PI 3-kinase association to IRS-1 were strongly sustained by the proteasome inhibitors, MG132 and lactacystin. In contrast, no effect was detected on the insulin receptor and IRS-2 tyrosine phosphorylation. Interestingly, lactacystin also preserved PKB activation and insulin-induced glucose uptake. In contrast, calpeptin, a calpain inhibitor, was ineffective. Tyrosine phosphatase assays were also performed, showing that lactacystin was not functioning directly as a tyrosine phosphatase inhibitor "in vitro." In conclusion, proteasome inhibitors can regulate the tyrosine phosphorylation of IRS-1 and the downstream insulin signaling pathway, leading to glucose transport.
Metabolic Diseases Research, Global Pharmaceutical Research and Development, Abbott Laboratories, Department 47R, Building AP10, 100 Abbott Park Road, 60064, Abbott Park, IL, USA. cristina.rondinone@abbott.com
Cristina M
CM
Rondinone
Deborah
D
Kramer
D016475:3T3 Cells; D000111:Acetylcysteine / Q000031:analogs & derivatives* / Q000494:pharmacology*; D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D001692:Biological Transport; D002460:Cell Line; D003546:Cysteine Endopeptidases; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins; D007700:Kinetics; D007976:Leupeptins / Q000494:pharmacology*; D051379:Mice; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors*; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D019000:Phosphotyrosine / Q000378:metabolism; D046988:Proteasome Endopeptidase Complex; D017346:Protein Serine-Threonine Kinases; D017027:Protein Tyrosine Phosphatases / Q000037:antagonists & inhibitors; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt; D015398:Signal Transduction / Q000187:drug effects
D000111:Acetylcysteine; D003546:Cysteine Endopeptidases; D015853:Cysteine Proteinase Inhibitors; D004791:Enzyme Inhibitors; D005947:Glucose; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D007976:Leupeptins; D009097:Multienzyme Complexes; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D019000:Phosphotyrosine; D046988:Proteasome Endopeptidase Complex; D017346:Protein Serine-Threonine Kinases; D017027:Protein Tyrosine Phosphatases; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; C526295:Irs1 protein, mouse; C067713:lactacystin; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde