Vanadate and rapamycin synergistically enhance insulin-stimulated glucose uptake.
Tyrosine dephosphorylation, serine phosphorylation, and proteasomal degradation of insulin receptor substrates (IRSs) are implicated in the negative regulation of insulin action. Here we show that simultaneous inhibition of IRS-1 tyrosine dephosphorylation and proteasomal degradation synergistically augments insulin-responsive glucose uptake. L6 skeletal muscle cells (L6 cells) were treated with inhibitors of protein-tyrosine phosphatases, proteasomal degradation, and mammalian target of rapamycin (mTOR), and the effects of insulin on glucose uptake, IRS-1 tyrosine phosphorylation, phosphatidylinositol (PI) 3-kinase activity, and IRS-1 mass were examined. Pretreatment of L6 cells with sodium orthovanadate (Na(3)VO(4)) plus the mTOR inhibitor rapamycin caused a 5-fold increase in insulin-responsive glucose uptake at 2 hours when compared to insulin alone. Evaluation of IRS-1 associated PI 3-kinase activity, IRS-1-associated p85 mass, and IRS-1 tyrosine phosphorylation showed that 2 hours after insulin addition they were reduced by 70% from maximal activity. Likewise, IRS-1 mass was reduced by 50%. When L6 cells were pretreated with Na(3)VO(4) plus the proteasome inhibitor MG-132 or the mTOR inhibitor rapamycin prior to insulin addition, IRS-1 mass loss as well as IRS-1/PI-3 kinase complex decay was blocked at 2 hours and PI 3-kinase activity was increased 2.5-fold and 4-fold, respectively, over insulin alone. Finally, treatment of L6 cells with subtherapeutic amounts of vanadyl sulfate and rapamycin induced a synergistic 3-fold increase in insulin-induced glucose uptake at 2 hours. These findings indicate that vanadium and rapamycin synergize to enhance glucose uptake by preventing IRS-1 mass loss and IRS-1/PI 3-kinase complex decay and may offer a new approach to enhance glucose transport in diabetes.
O'Connor
Jason C
JC
Department of Animal Sciences, University of Illinois at Urbana-Champaign, Urbana, IL 61801, USA.
Freund
Gregory G
GG
D000818:Animals; D002460:Cell Line; D003546:Cysteine Endopeptidases; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D004357:Drug Synergism; D005947:Glucose / Q000378:metabolism*; D007004:Hypoglycemic Agents / Q000494:pharmacology*; D007328:Insulin / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins; D007976:Leupeptins / Q000494:pharmacology; D009097:Multienzyme Complexes / Q000037:antagonists & inhibitors; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010750:Phosphoproteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D010766:Phosphorylation / Q000187:drug effects; D046988:Proteasome Endopeptidase Complex; D020123:Sirolimus / Q000494:pharmacology*; D014443:Tyrosine / Q000378:metabolism; D014638:Vanadates / Q000494:pharmacology*
D003546:Cysteine Endopeptidases; D015853:Cysteine Proteinase Inhibitors; D005947:Glucose; D007004:Hypoglycemic Agents; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D007976:Leupeptins; D009097:Multienzyme Complexes; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010750:Phosphoproteins; D046988:Proteasome Endopeptidase Complex; D020123:Sirolimus; D014443:Tyrosine; D014638:Vanadates; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde