The mammalian target of rapamycin regulates C2C12 myogenesis via a kinase-independent mechanism.
Rapamycin inhibits differentiation of mouse C2C12 myoblasts, a tissue culture model for skeletal muscle differentiation. The mechanism by which a rapamycin-sensitive signaling pathway regulates myogenesis is largely unknown. The mammalian target of rapamycin (mTOR) is a central regulator of cell growth and proliferation, but its role in myogenesis has not been examined directly. Here we report the investigation of the function of mTOR and its downstream effectors in muscle differentiation. Rapamycin exerts an inhibitory effect on C2C12 myogenesis at different stages, implying that a rapamycin-sensitive pathway may be required for multiple processes during muscle differentiation. The mTOR protein level increases 10-fold during differentiation, via a post-transcriptional mechanism. As the first direct demonstration of the essential role of mTOR in muscle differentiation, we show that a rapamycin-resistant mTOR, but not S6 kinase 1, can rescue rapamycin-inhibited myogenesis. Remarkably, the myogenic function of mTOR does not require its kinase activity. Two downstream effectors of the rapamycin-sensitive pathway, S6 kinase 1 and eIF4E-binding protein 1, undergo differential regulation during myogenesis, but neither protein is the relevant effector for the myogenic signaling of mTOR. Taken together, our observations suggest a novel mTOR signaling mechanism essential for skeletal muscle differentiation.
Erbay
E
E
Department of Cell and Structural Biology, University of Illinois at Urbana-Champaign, Urbana, Illinois 61801, USA.
Chen
J
J
D048868:Adaptor Proteins, Signal Transducing; D000818:Animals; D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D015152:Blotting, Northern; D002352:Carrier Proteins / Q000378:metabolism; D018797:Cell Cycle Proteins; D002454:Cell Differentiation; D002460:Cell Line; D039642:Eukaryotic Initiation Factors; D051379:Mice; D008856:Microscopy, Fluorescence; D008858:Microscopy, Phase-Contrast; D018482:Muscle, Skeletal / Q000166:cytology*; D010750:Phosphoproteins; D011494:Protein Kinases / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases / Q000737:chemistry / Q000378:metabolism*; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology*; D058570:TOR Serine-Threonine Kinases; D013997:Time Factors; D014162:Transfection; D015854:Up-Regulation
D048868:Adaptor Proteins, Signal Transducing; D000903:Antibiotics, Antineoplastic; D002352:Carrier Proteins; D018797:Cell Cycle Proteins; C499527:Eif4ebp1 protein, mouse; D039642:Eukaryotic Initiation Factors; D010750:Phosphoproteins; D011494:Protein Kinases; C546843:mTOR protein, mouse; D019893:Ribosomal Protein S6 Kinases; D058570:TOR Serine-Threonine Kinases; D020123:Sirolimus