title: Raptor and Rheb negatively regulate skeletal myogenesis through suppression of insulin receptor substrate 1 (IRS1).
abstract: The mammalian target of rapamycin (mTOR) is essential for skeletal myogenesis through controlling distinct cellular pathways. The importance of the canonical mTOR complex 1 signaling components, including raptor, S6K1, and Rheb, had been suggested in muscle maintenance, growth, and metabolism. However, the role of those components in myogenic differentiation is not entirely clear. In this study we have investigated the functions of raptor, S6K1, and Rheb in the differentiation of C2C12 mouse myoblasts. We find that although mTOR knockdown severely impairs myogenic differentiation as expected, the knockdown of raptor, as well as Rheb, enhances differentiation. Consistent with a negative role for these proteins in myogenesis, overexpression of raptor or Rheb inhibits C2C12 differentiation. On the other hand, neither knockdown nor overexpression of S6K1 has any effect. Moreover, the enhanced differentiation elicited by raptor or Rheb knockdown is accompanied by increased Akt activation, elevated IRS1 protein levels, and decreased Ser-307 (human Ser-312) phosphorylation on IRS1. Finally, IRS1 knockdown eliminated the enhancement in differentiation elicited by raptor or Rheb knockdown, suggesting that IRS1 is a critical mediator of the myogenic functions of raptor and Rheb. In conclusion, the Rheb-mTOR/raptor pathway negatively regulates myogenic differentiation by suppressing IRS1-PI3K-Akt signaling. These findings underscore the versatility of mTOR signaling in biological regulations and implicate the existence of novel mTOR complexes and/or signaling mechanism in skeletal myogenesis.
authors.affiliation: Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801.
authors.forename: Yejing
authors.initials: Y
authors.lastname: Ge
authors.affiliation: Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801.
authors.forename: Mee-Sup
authors.initials: MS
authors.lastname: Yoon
authors.affiliation: Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801. Electronic address: jiechen@illinois.edu.
authors.forename: Jie
authors.initials: J
authors.lastname: Chen
mesh_terms: D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism*; D002454:Cell Differentiation / Q000502:physiology; D002460:Cell Line; D055785:Gene Knockdown Techniques; D006801:Humans; D055504:Insulin Receptor Substrate Proteins / Q000235:genetics / Q000378:metabolism*; D051379:Mice; D020559:Monomeric GTP-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D024510:Muscle Development / Q000502:physiology*; D018482:Muscle, Skeletal / Q000166:cytology / Q000378:metabolism*; D032448:Myoblasts, Skeletal / Q000166:cytology / Q000378:metabolism; D009479:Neuropeptides / Q000235:genetics / Q000378:metabolism*; D019869:Phosphatidylinositol 3-Kinases / Q000235:genetics / Q000378:metabolism; D010766:Phosphorylation / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt / Q000235:genetics / Q000378:metabolism; D000076205:Ras Homolog Enriched in Brain Protein; D000076223:Regulatory-Associated Protein of mTOR; D038744:Ribosomal Protein S6 Kinases, 90-kDa / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D058570:TOR Serine-Threonine Kinases / Q000235:genetics / Q000378:metabolism*
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D002352:Carrier Proteins; D055504:Insulin Receptor Substrate Proteins; D020559:Monomeric GTP-Binding Proteins; D009479:Neuropeptides; D019869:Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D000076205:Ras Homolog Enriched in Brain Protein; D000076223:Regulatory-Associated Protein of mTOR; D038744:Ribosomal Protein S6 Kinases, 90-kDa; D058570:TOR Serine-Threonine Kinases; C526295:Irs1 protein, mouse; C490213:Rheb protein, mouse; C540162:Rptor protein, mouse; C546843:mTOR protein, mouse; C512964:Rps6ka1 protein, mouse