title: Role of S6K1 in regulation of SREBP1c expression in the liver.
abstract: The transcription factor sterol regulatory element-binding protein 1c (SREBP1c) plays an important role in the control of fatty acid metabolism in the liver. Evidence suggests that mammalian target of rapamycin (mTOR) complex 1 (mTORC1) contributes to the regulation of SREBP1c expression, but signaling downstream of mTORC1 remains unclear. We have now shown that medium rich in branched-chain amino acids stimulates expression of the SREBP1c gene in cultured hepatocytes in a manner sensitive both to rapamycin, a pharmacological inhibitor of mTORC1, and to a short hairpin RNA (shRNA) specific for S6 kinase 1 (S6K1), a downstream effector of mTORC1. The phosphorylation of S6K1 was increased in the liver of obese db/db mice. Furthermore, depletion of hepatic S6K1 in db/db mice with the use of an adenovirus vector encoding S6K1 shRNA resulted in down-regulation of SREBP1c gene expression in the liver as well as a reduced hepatic triglyceride content and serum triglyceride concentration. These results thus suggest that S6K1 regulates SREBP1c expression both in cultured hepatocytes and in mouse liver, and that increased hepatic activity of S6K1 contributes at least in part to the pathogenesis of obesity-induced hepatic steatosis and hypertriglyceridemia.
authors.affiliation: Department of Medicine, Division of Diabetes and Endocrinology, Kobe University Graduate School of Medicine, Kobe 650-0017, Japan.
authors.forename: Shuying
authors.initials: S
authors.lastname: Li
authors.forename: Wataru
authors.initials: W
authors.lastname: Ogawa
authors.forename: Aki
authors.initials: A
authors.lastname: Emi
authors.forename: Kumiko
authors.initials: K
authors.lastname: Hayashi
authors.forename: Yoko
authors.initials: Y
authors.lastname: Senga
authors.forename: Kazuhiro
authors.initials: K
authors.lastname: Nomura
authors.forename: Kenta
authors.initials: K
authors.lastname: Hara
authors.forename: Demin
authors.initials: D
authors.lastname: Yu
authors.forename: Masato
authors.initials: M
authors.lastname: Kasuga
mesh_terms: D000818:Animals; D002460:Cell Line; D002867:Chromones / Q000494:pharmacology; D005234:Fatty Liver / Q000235:genetics; D005786:Gene Expression Regulation; D022781:Hepatocytes / Q000187:drug effects / Q000378:metabolism; D015228:Hypertriglyceridemia / Q000235:genetics; D008099:Liver / Q000187:drug effects / Q000378:metabolism*; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D008815:Mice, Inbred Strains; D009025:Morpholines / Q000494:pharmacology; D046912:Multiprotein Complexes; D009765:Obesity / Q000235:genetics / Q000378:metabolism; D011506:Proteins / Q000037:antagonists & inhibitors / Q000378:metabolism; D034741:RNA, Small Interfering / Q000235:genetics; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000235:genetics / Q000378:metabolism*; D020123:Sirolimus / Q000494:pharmacology; D051780:Sterol Regulatory Element Binding Protein 1 / Q000235:genetics*; D058570:TOR Serine-Threonine Kinases
chemical_list: D002867:Chromones; D009025:Morpholines; D046912:Multiprotein Complexes; D011506:Proteins; D034741:RNA, Small Interfering; C497388:Srebf1 protein, mouse; D051780:Sterol Regulatory Element Binding Protein 1; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; D000076222:Mechanistic Target of Rapamycin Complex 1; D038744:Ribosomal Protein S6 Kinases, 90-kDa; C512964:Rps6ka1 protein, mouse; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus