Insulin down-regulates insulin receptor substrate-2 expression through the phosphatidylinositol 3-kinase/Akt pathway.
Insulin receptor substrate (IRS)-1 and IRS-2 are the major substrates that mediate insulin action. Insulin itself regulates the expression of the IRS protein in the liver, but the underlying mechanisms of IRS-1 and IRS-2 regulation are not fully understood. Here we report that insulin suppressed the expression of both IRS-1 and IRS-2 proteins in Fao hepatoma cells. The decrease in IRS-1 protein occurred via proteasomal degradation without any change in IRS-1 mRNA, whereas the insulin-induced suppression of IRS-2 protein was associated with a parallel decrease in IRS-2 mRNA without changing IRS-2 mRNA half-life. The insulin-induced suppression of IRS-2 mRNA and protein was blocked by the phosphatidylinositol (PI) 3-kinase inhibitor, LY294002, but not by the MAP kinase-ERK kinase (MEK) inhibitor, PD098059. Inhibition of Akt by overexpression of dominant-negative Akt also caused complete attenuation of the insulin-induced decrease in IRS-2 protein and partial attenuation of its mRNA down-regulation. Some nuclear proteins bound to the insulin response element (IRE) sequence on the IRS-2 gene in an insulin-dependent manner in vitro, and the binding was also blocked by the PI 3-kinase inhibitor. Reporter gene assay showed that insulin suppressed the activity of both human and rat IRS-2 gene promoters through the IRE in a PI 3-kinase-dependent manner. Our results indicate that insulin regulates IRS-1 and IRS-2 through different mechanisms and that insulin represses IRS-2 gene expression via a PI 3-kinase/Akt pathway.
Department of Metabolic Medicine, Graduate School of Medical Sciences, Kumamoto University, 1-1-1 Honjo, Kumamoto, 860-8556, Japan.
Y
Y
Hirashima
K
K
Tsuruzoe
S
S
Kodama
M
M
Igata
T
T
Toyonaga
K
K
Ueki
C R
CR
Kahn
E
E
Araki
D000818:Animals; D006528:Carcinoma, Hepatocellular; D002460:Cell Line; D002867:Chromones / Q000494:pharmacology; D003513:Cycloheximide / Q000494:pharmacology; D003864:Depression, Chemical; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D007328:Insulin / Q000494:pharmacology*; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D008099:Liver / Q000378:metabolism*; D051379:Mice; D009025:Morpholines / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism*; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic; D017346:Protein Serine-Threonine Kinases; D011500:Protein Synthesis Inhibitors / Q000494:pharmacology; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger / Q000032:analysis; D051381:Rats; D016415:Sequence Alignment; D015398:Signal Transduction
D002867:Chromones; D003513:Cycloheximide; D004791:Enzyme Inhibitors; D005419:Flavonoids; D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D047908:Intracellular Signaling Peptides and Proteins; D009025:Morpholines; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D010750:Phosphoproteins; D017346:Protein Serine-Threonine Kinases; D011500:Protein Synthesis Inhibitors; D011518:Proto-Oncogene Proteins; D051057:Proto-Oncogene Proteins c-akt; D012333:RNA, Messenger; C526292:IRS1 protein, human; C526297:IRS2 protein, human; C526295:Irs1 protein, mouse; C526296:Irs1 protein, rat; C526298:Irs2 protein, mouse; C526299:Irs2 protein, rat; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C494918:AKT1 protein, human; C494920:Akt1 protein, rat; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one