title: Interaction of FoxO1 and TSC2 induces insulin resistance through activation of the mammalian target of rapamycin/p70 S6K pathway.
abstract: Both TSC2 (tuberin) and forkhead transcription factor FoxO1 are phosphorylated and inhibited by Akt and play important roles in insulin signaling. However, little is known about the relationship between TSC2 and FoxO1. Here we identified TSC2 as a FoxO1-binding protein by using a yeast two-hybrid screening with a murine islet cDNA library. Among FoxOs, only FoxO1 can be associated with TSC2. The physical association between the C terminus of TSC2 (amino acids 1280-1499) and FoxO1 degrades the TSC1-TSC2 complex and inhibits GTPase-activating protein activity of TSC2 toward Rheb. Overexpression of wild type FoxO1 enhances p70 S6K phosphorylation, whereas overexpression of TSC2 can reverse these effects. Knockdown of endogenous FOXO1 in human vascular endothelial cells decreased phosphorylation of p70 S6K. Prolonged overexpression of wild type FoxO1 enhanced phosphorylation of serine 307 of IRS1 and decreased phosphorylation of Akt and FoxO1 itself even in the presence of serum. These data suggest a novel mechanism by which FoxO1 regulates the insulin signaling pathway through negative regulation of TSC2 function.
authors.affiliation: Department of Clinical Molecular Medicine, Division of Diabetes, Digestive and Kidney Disease, Kobe University Graduate School of Medicine, Kobe 650-0017, Japan.
authors.forename: Yongheng
authors.initials: Y
authors.lastname: Cao
authors.forename: Yuji
authors.initials: Y
authors.lastname: Kamioka
authors.forename: Norihide
authors.initials: N
authors.lastname: Yokoi
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Kobayashi
authors.forename: Okio
authors.initials: O
authors.lastname: Hino
authors.forename: Masafumi
authors.initials: M
authors.lastname: Onodera
authors.forename: Naoki
authors.initials: N
authors.lastname: Mochizuki
authors.forename: Jun
authors.initials: J
authors.lastname: Nakae
mesh_terms: D000818:Animals; D002460:Cell Line; D002461:Cell Line, Transformed; D015536:Down-Regulation / Q000502:physiology; D004730:Endothelium, Vascular / Q000166:cytology / Q000201:enzymology / Q000378:metabolism; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism* / Q000502:physiology; D006801:Humans; D007333:Insulin Resistance / Q000502:physiology*; D051379:Mice; D011494:Protein Kinases / Q000378:metabolism* / Q000502:physiology; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000037:antagonists & inhibitors / Q000378:metabolism / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D058570:TOR Serine-Threonine Kinases; D014402:Tuberous Sclerosis / Q000201:enzymology / Q000378:metabolism; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: C085126:FOXO1 protein, human; D000071161:Forkhead Box Protein O1; D051858:Forkhead Transcription Factors; C467200:Foxo1 protein, mouse; C000624653:TSC2 protein, human; C000624654:Tsc2 protein, mouse; D000077005:Tuberous Sclerosis Complex 2 Protein; D025521:Tumor Suppressor Proteins; D011494:Protein Kinases; C546842:MTOR protein, human; C546843:mTOR protein, mouse; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases