title: Ceramide inhibits insulin-stimulated Akt phosphorylation through activation of Rheb/mTORC1/S6K signaling in skeletal muscle.
abstract: Ceramide is a negative regulator of insulin activity. At the molecular level, it causes a decrease in insulin-stimulated Akt Ser473 phosphorylation in C2C12 myotubes. Interestingly, we found that the phosphorylation of S6K at Thr389 was increased under the same conditions. Utilizing both rapamycin to inhibit mTORC1 activity and shRNA to knock down Rheb, we demonstrated that the decrease in Akt Ser473 phosphorylation stimulated by insulin after C2-ceramide incubation can be prevented. The mechanism by which C2-ceramide impairs signaling would seem to involve a negative feedback of activated S6K via phosphorylation of insulin receptor substrate-1 at Ser636/639, since S6K inhibitor can block this phenomenon. Finally, rapamycin treatment was found not to affect C2-ceramide-induced PKCζ activation, suggesting that the pathway revealed in this study is parallel to the one involving PKCζ activation. We proposed a novel pathway/mechanism involving Rheb/mTORC1/S6K signaling to explain how C2-ceramide impairs insulin signaling via Akt phosphorylation. The existence of multiple pathways involved in insulin signaling impairment by C2-ceramide treatment implies that different strategies might be needed to ameliorate insulin resistance caused by C2-ceramide.
authors.affiliation: Department of Life Science, National Taiwan Normal University, Taipei 116, Taiwan.
authors.forename: Chang-Ting
authors.initials: CT
authors.lastname: Hsieh
authors.affiliation: Department of Life Science, National Taiwan Normal University, Taipei 116, Taiwan.
authors.forename: Jen-Hua
authors.initials: JH
authors.lastname: Chuang
authors.affiliation: Agricultural Biotechnology Research Center, Academia Sinica, Taipei 115, Taiwan.
authors.forename: Wen-Chin
authors.initials: WC
authors.lastname: Yang
authors.affiliation: Diabetes Unit, Medical Services, Department of Molecular Biology, Massachusetts General Hospital, Boston, MA 02114, USA.
authors.forename: Yi
authors.initials: Y
authors.lastname: Yin
authors.affiliation: Department of Life Science, National Taiwan Normal University, Taipei 116, Taiwan. Electronic address: yenshoulin@ntnu.edu.tw.
authors.forename: Yenshou
authors.initials: Y
authors.lastname: Lin
mesh_terms: D000818:Animals; D002460:Cell Line; D004789:Enzyme Activation / Q000187:drug effects; D005947:Glucose / Q000378:metabolism; D057809:HEK293 Cells; D006801:Humans; D007328:Insulin / Q000494:pharmacology; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism; D007333:Insulin Resistance; D008156:Luciferases / Q000235:genetics; D008297:Male; D000076222:Mechanistic Target of Rapamycin Complex 1; D051379:Mice; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D046912:Multiprotein Complexes / Q000037:antagonists & inhibitors / Q000378:metabolism*; D018485:Muscle Fibers, Skeletal / Q000166:cytology / Q000378:metabolism; D009479:Neuropeptides / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D051745:Protein Kinase C-delta / Q000378:metabolism; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism*; D034622:RNA Interference; D034741:RNA, Small Interfering; D000076205:Ras Homolog Enriched in Brain Protein; D051381:Rats; D017207:Rats, Sprague-Dawley; D038762:Ribosomal Protein S6 Kinases, 70-kDa / Q000378:metabolism*; D015398:Signal Transduction / Q000187:drug effects; D020123:Sirolimus / Q000494:pharmacology; D013110:Sphingosine / Q000031:analogs & derivatives* / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000378:metabolism*
chemical_list: D007328:Insulin; D055504:Insulin Receptor Substrate Proteins; D046912:Multiprotein Complexes; C064769:N-acetylsphingosine; D009479:Neuropeptides; C490211:RHEB protein, human; D034741:RNA, Small Interfering; D000076205:Ras Homolog Enriched in Brain Protein; D008156:Luciferases; D000076222:Mechanistic Target of Rapamycin Complex 1; D051057:Proto-Oncogene Proteins c-akt; D038762:Ribosomal Protein S6 Kinases, 70-kDa; D058570:TOR Serine-Threonine Kinases; C448959:ribosomal protein S6 kinase, 70kD, polypeptide 2; D051745:Protein Kinase C-delta; D020559:Monomeric GTP-Binding Proteins; D005947:Glucose; D013110:Sphingosine; D020123:Sirolimus
keywords: C2-ceramide; Insulin resistance; Myotubes; mTORC1; mTORC2