Serine/threonine phosphorylation of insulin receptor substrate 1 modulates insulin receptor signaling.
Treatment of cells with okadaic acid, a protein phosphatase inhibitor, leads to an insulin-resistant state without modification in the tyrosine kinase activity of the receptor toward exogenous substrates. In 3T3-L1 adipocytes, okadaic acid induced a similar dose-dependent inhibition of the insulin effect on deoxyglucose uptake, phosphatidylinositol 3-kinase (PI 3-kinase) activation, and insulin receptor substrate (IRS) 1 tyrosine phosphorylation. Simultaneously, in okadaic acid-treated 3T3-L1 adipocytes, the reduced IRS 1 tyrosine phosphorylation was linked to a decrease in its electrophoretic mobility due to phosphorylation on serine/threonine residues. This phosphorylation appeared to result from the activation of cytosolic kinase(s). Furthermore, using in vitro reconstitution, we show that, compared to IRS 1 immunopurified from untreated cells, the IRS 1 obtained from okadaic acid-treated cells had a reduced capacity to be phosphorylated by insulin receptors and, concomitantly, to bind PI 3-kinase. Taken together these data suggest that serine/threonine phosphorylation of IRS 1 induced by okadaic acid reduces the ability of the insulin receptor to phosphorylate IRS 1 and to dock one of its interacting molecules, i.e. PI 3-kinase. Finally, the inhibitory effect of okadaic acid on the stimulatory action of insulin on glucose transport suggests that the serine/threonine phosphorylation of IRS 1 might represent a key regulatory mechanism of insulin action.
Tanti
J F
JF
Institut National de la Santé et de la Recherche Médicale U 145, Faculté de Médecine, Nice, France.
Grémeaux
T
T
van Obberghen
E
E
Le Marchand-Brustel
Y
Y
D016475:3T3 Cells; D017667:Adipocytes / Q000187:drug effects / Q000201:enzymology / Q000378:metabolism; D000818:Animals; D004591:Electrophoresis, Polyacrylamide Gel; D004988:Ethers, Cyclic / Q000494:pharmacology; D005947:Glucose / Q000378:metabolism; D007328:Insulin / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins; D051379:Mice; D019319:Okadaic Acid; D019869:Phosphatidylinositol 3-Kinases; D010750:Phosphoproteins / Q000378:metabolism*; D010766:Phosphorylation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D011972:Receptor, Insulin / Q000378:metabolism*; D012694:Serine / Q000378:metabolism*; D015398:Signal Transduction; D013912:Threonine / Q000378:metabolism*; D014443:Tyrosine / Q000378:metabolism
D004988:Ethers, Cyclic; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; D010750:Phosphoproteins; D019319:Okadaic Acid; D013912:Threonine; D014443:Tyrosine; D012694:Serine; D019869:Phosphatidylinositol 3-Kinases; D017853:Phosphotransferases (Alcohol Group Acceptor); D011972:Receptor, Insulin; D005947:Glucose