A rapamycin-sensitive pathway down-regulates insulin signaling via phosphorylation and proteasomal degradation of insulin receptor substrate-1

Mol Endocrinol. 2000 Jun;14(6):783-94. doi: 10.1210/mend.14.6.0446.


Insulin receptor substrate-1 (IRS-1) is a major substrate of the insulin receptor and acts as a docking protein for Src homology 2 domain containing signaling molecules that mediate many of the pleiotropic actions of insulin. Insulin stimulation elicits serine/threonine phosphorylation of IRS-1, which produces a mobility shift on SDS-PAGE, followed by degradation of IRS-1 after prolonged stimulation. We investigated the molecular mechanisms and the functional consequences of these phenomena in 3T3-L1 adipocytes. PI 3-kinase inhibitors or rapamycin, but not the MEK inhibitor, blocked both the insulin-induced electrophoretic mobility shift and degradation of IRS-1. Adenovirus-mediated expression of a membrane-targeted form of the p110 subunit of phosphatidylinositol (PI) 3-kinase (p110CAAX) induced a mobility shift and degradation of IRS-1, both of which were inhibited by rapamycin. Lactacystin, a specific proteasome inhibitor, inhibited insulin-induced degradation of IRS-1 without any effect on its electrophoretic mobility. Inhibition of the mobility shift did not significantly affect tyrosine phosphorylation of IRS-1 or downstream insulin signaling. In contrast, blockade of IRS-1 degradation resulted in sustained activation of Akt, p70 S6 kinase, and mitogen-activated protein (MAP) kinase during prolonged insulin treatment. These results indicate that insulin-induced serine/threonine phosphorylation and degradation of IRS-1 are mediated by a rapamycin-sensitive pathway, which is downstream of PI 3-kinase and independent of ras/MAP kinase. The pathway leads to degradation of IRS-1 by the proteasome, which plays a major role in down-regulation of certain insulin actions during prolonged stimulation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 3T3 Cells
  • Acetylcysteine / analogs & derivatives*
  • Acetylcysteine / pharmacology
  • Adenoviridae / genetics
  • Adipocytes / metabolism
  • Animals
  • Cell Line
  • Cysteine Endopeptidases / metabolism*
  • Deoxyglucose / metabolism
  • Embryo, Mammalian
  • Enzyme Inhibitors / pharmacology
  • Gene Expression
  • Humans
  • Insulin / pharmacology*
  • Insulin Receptor Substrate Proteins
  • Kidney
  • Mice
  • Multienzyme Complexes / antagonists & inhibitors
  • Multienzyme Complexes / metabolism*
  • Phosphatidylinositol 3-Kinases / genetics
  • Phosphatidylinositol 3-Kinases / metabolism
  • Phosphoinositide-3 Kinase Inhibitors
  • Phosphoproteins / metabolism*
  • Phosphorylation
  • Proteasome Endopeptidase Complex
  • Signal Transduction / drug effects*
  • Sirolimus / pharmacology*
  • Transfection


  • Enzyme Inhibitors
  • IRS1 protein, human
  • Insulin
  • Insulin Receptor Substrate Proteins
  • Irs1 protein, mouse
  • Multienzyme Complexes
  • Phosphoinositide-3 Kinase Inhibitors
  • Phosphoproteins
  • lactacystin
  • Deoxyglucose
  • Cysteine Endopeptidases
  • Proteasome Endopeptidase Complex
  • Sirolimus
  • Acetylcysteine