Distinct amino acid-sensing mTOR pathways regulate skeletal myogenesis.
Signaling through the mammalian target of rapamycin (mTOR) in response to amino acid availability controls many cellular and developmental processes. mTOR is a master regulator of myogenic differentiation, but the pathways mediating amino acid signals in this process are not known. Here we examine the Rag GTPases and the class III phosphoinositide 3-kinase (PI3K) Vps34, two mediators of amino acid signals upstream of mTOR complex 1 (mTORC1) in cell growth regulation, for their potential involvement in myogenesis. We find that, although both Rag and Vps34 mediate amino acid activation of mTORC1 in C2C12 myoblasts, they have opposing functions in myogenic differentiation. Knockdown of RagA/B enhances, whereas overexpression of active RagB/C mutants impairs, differentiation, and this inhibitory function of Rag is mediated by mTORC1 suppression of the IRS1-PI3K-Akt pathway. On the other hand, Vps34 is required for myogenic differentiation. Amino acids activate a Vps34-phospholipase D1 (PLD1) pathway that controls the production of insulin-like growth factor II, an autocrine inducer of differentiation, through the Igf2 muscle enhancer. The product of PLD, phosphatidic acid, activates the enhancer in a rapamycin-sensitive but mTOR kinase-independent manner. Our results uncover amino acid-sensing mechanisms controlling the homeostasis of myogenesis and underline the versatility and context dependence of mTOR signaling.
Department of Cell and Developmental Biology, University of Illinois at Urbana-Champaign, Urbana, IL 61801.
Mee-Sup
MS
Yoon
Jie
J
Chen
D000596:Amino Acids / Q000378:metabolism*; D000818:Animals; D002454:Cell Differentiation / Q000187:drug effects / Q000235:genetics; D058546:Class III Phosphatidylinositol 3-Kinases / Q000378:metabolism; D004742:Enhancer Elements, Genetic / Q000235:genetics; D004789:Enzyme Activation / Q000187:drug effects; D038681:Follistatin / Q000378:metabolism; D020558:GTP Phosphohydrolases / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects; D055504:Insulin Receptor Substrate Proteins / Q000378:metabolism; D007335:Insulin-Like Growth Factor II / Q000235:genetics / Q000378:metabolism; D051379:Mice; D008954:Models, Biological; D024510:Muscle Development / Q000187:drug effects / Q000235:genetics; D018482:Muscle, Skeletal / Q000187:drug effects / Q000254:growth & development* / Q000378:metabolism*; D032446:Myoblasts / Q000166:cytology / Q000201:enzymology; D009928:Organ Specificity / Q000187:drug effects; D010712:Phosphatidic Acids / Q000494:pharmacology; D010739:Phospholipase D / Q000378:metabolism; D021381:Protein Transport / Q000187:drug effects; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D013347:Subcellular Fractions / Q000187:drug effects / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases / Q000378:metabolism*
D000596:Amino Acids; D038681:Follistatin; D055504:Insulin Receptor Substrate Proteins; C526295:Irs1 protein, mouse; D010712:Phosphatidic Acids; D007335:Insulin-Like Growth Factor II; D058546:Class III Phosphatidylinositol 3-Kinases; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases; D010739:Phospholipase D; C106801:phospholipase D1; D020558:GTP Phosphohydrolases