Hyperosmotic stress inhibits insulin receptor substrate-1 function by distinct mechanisms in 3T3-L1 adipocytes.
In 3T3-L1 adipocytes, hyperosmotic stress was found to inhibit insulin signaling, leading to an insulin-resistant state. We show here that, despite normal activation of insulin receptor, hyperosmotic stress inhibits both tyrosine phosphorylation of insulin receptor substrate-1 (IRS-1) and IRS-1-associated phosphoinositide 3 (PI 3)-kinase activity in response to physiological insulin concentrations. Insulin-induced membrane ruffling, which is dependent on PI 3-kinase activation, was also markedly reduced. These inhibitory effects were associated with an increase in IRS-1 Ser307 phosphorylation. Furthermore, the mammalian target of rapamycin (mTOR) inhibitor rapamycin prevented the osmotic shock-induced phosphorylation of IRS-1 on Ser307. The inhibition of mTOR completely reversed the inhibitory effect of hyperosmotic stress on insulin-induced IRS-1 tyrosine phosphorylation and PI 3-kinase activation. In addition, prolonged osmotic stress enhanced the degradation of IRS proteins through a rapamycin-insensitive pathway and a proteasome-independent process. These data support evidence of new mechanisms involved in osmotic stress-induced cellular insulin resistance. Short-term osmotic stress induces the phosphorylation of IRS-1 on Ser307 by an mTOR-dependent pathway. This, in turn, leads to a decrease in early proximal signaling events induced by physiological insulin concentrations. On the other hand, prolonged osmotic stress alters IRS-1 function by inducing its degradation, which could contribute to the down-regulation of insulin action.
INSERM U 568 and l'Institut Fédératif de Recherches 50, Faculté de Médecine, Avenue de Valombrose, 06107 Nice Cedex 02, France.
Philippe
P
Gual
Teresa
T
Gonzalez
Thierry
T
Grémeaux
Romain
R
Barres
Yannick
Y
Le Marchand-Brustel
Jean-François
JF
Tanti
D016475:3T3 Cells; D017667:Adipocytes / Q000187:drug effects / Q000378:metabolism*; D000818:Animals; D002462:Cell Membrane / Q000648:ultrastructure; D004789:Enzyme Activation; D007328:Insulin / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins; D007333:Insulin Resistance / Q000502:physiology*; D047908:Intracellular Signaling Peptides and Proteins; D051379:Mice; D009997:Osmotic Pressure; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010750:Phosphoproteins / Q000037:antagonists & inhibitors* / Q000737:chemistry / Q000378:metabolism*; D010766:Phosphorylation; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases / Q000378:metabolism; D011972:Receptor, Insulin / Q000378:metabolism; D012694:Serine / Q000737:chemistry; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D014443:Tyrosine / Q000737:chemistry
D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins; D047428:Protein Kinase Inhibitors; D011494:Protein Kinases; D011972:Receptor, Insulin; D012694:Serine; D020123:Sirolimus; D058570:TOR Serine-Threonine Kinases; D014443:Tyrosine; C526295:Irs1 protein, mouse; C526298:Irs2 protein, mouse; C546843:mTOR protein, mouse