title: mTORC1 and JNK coordinate phosphorylation of the p70S6K1 autoinhibitory domain in skeletal muscle following functional overloading.
abstract: The present project was designed to investigate phosphorylation of p70S6K1 in an animal model of skeletal muscle overload. Within 24 h of male Sprague-Dawley rats undergoing unilateral tenotomy to induce functional overloading of the plantaris muscle, phosphorylation of the Thr³⁸⁹ and Thr⁴²¹/Ser⁴²⁴ sites on p70S6K1 was significantly elevated. Since the Thr⁴²¹/Ser⁴²⁴ sites are purportedly mammalian target of rapamycin complex 1 (mTORC1) independent, we sought to identify the kinase(s) responsible for their phosphorylation. Initially, we used IGF-I treatment of serum-deprived HEK-293E cells as an in vitro model system, because IGF-I promotes phosphorylation of p70S6K1 on both the Thr³⁸⁹ and Thr⁴²¹/Ser⁴²⁴ sites in skeletal muscle and in cells in culture. We found that, whereas the mTOR inhibitor TORIN2 prevented the IGF-I-induced phosphorylation of the Thr⁴²¹/Ser⁴²⁴ sites, it surprisingly enhanced phosphorylation of these sites during serum deprivation. JNK inhibition with SP600125 attenuated phosphorylation of the Thr⁴²¹/Ser⁴²⁴ sites, and in combination with TORIN2 both the effect of IGF-I and the enhanced Thr⁴²¹/Ser⁴²⁴ phosphorylation during serum deprivation were ablated. In contrast, both JNK activation with anisomycin and knockdown of the mTORC2 subunit rictor specifically stimulated phosphorylation of the Thr⁴²¹/Ser⁴²⁴ sites, suggesting that mTORC2 represses JNK-mediated phosphorylation of these sites. The role of JNK in mediating p70S6K1 phosphorylation was confirmed in the animal model noted above, where rats treated with SP600125 exhibited attenuated Thr⁴²¹/Ser⁴²⁴ phosphorylation. Overall, the results provide evidence that the mTORC1 and JNK signaling pathways coordinate the site-specific phosphorylation of p70S6K1. They also identify a novel role for mTORC1 and mTORC2 in the inhibition of JNK.
authors.affiliation: Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania.
authors.forename: Tony D
authors.initials: TD
authors.lastname: Martin
authors.affiliation: Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania.
authors.forename: Michael D
authors.initials: MD
authors.lastname: Dennis
authors.affiliation: Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania.
authors.forename: Bradley S
authors.initials: BS
authors.lastname: Gordon
authors.affiliation: Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania skimball@psu.edu.
authors.forename: Scot R
authors.initials: SR
authors.lastname: Kimball
authors.affiliation: Department of Cellular and Molecular Physiology, The Pennsylvania State University College of Medicine, Hershey, Pennsylvania.
authors.forename: Leonard S
authors.initials: LS
authors.lastname: Jefferson
mesh_terms: D000818:Animals; D002352:Carrier Proteins / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism; D012090:Cumulative Trauma Disorders / Q000378:metabolism* / Q000503:physiopathology; D004195:Disease Models, Animal; D057809:HEK293 Cells; D006801:Humans; D007334:Insulin-Like Growth Factor I / Q000378:metabolism; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008297:Male; D000076222:Mechanistic Target of Rapamycin Complex 1; D000076225:Mechanistic Target of Rapamycin Complex 2; D048055:Mitogen-Activated Protein Kinase 8 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D046912:Multiprotein Complexes / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D018482:Muscle, Skeletal / Q000187:drug effects / Q000378:metabolism* / Q000503:physiopathology; D010766:Phosphorylation / Q000187:drug effects; D054730:Protein Interaction Domains and Motifs; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D011499:Protein Processing, Post-Translational / Q000187:drug effects; D000076226:Rapamycin-Insensitive Companion of mTOR Protein; D051381:Rats; D017207:Rats, Sprague-Dawley; D019893:Ribosomal Protein S6 Kinases / Q000737:chemistry / Q000378:metabolism*; D012694:Serine / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D013912:Threonine / Q000378:metabolism
chemical_list: D002352:Carrier Proteins; D046912:Multiprotein Complexes; D047428:Protein Kinase Inhibitors; D000076226:Rapamycin-Insensitive Companion of mTOR Protein; C550254:rictor protein, rat; D013912:Threonine; D012694:Serine; D007334:Insulin-Like Growth Factor I; D000076222:Mechanistic Target of Rapamycin Complex 1; D000076225:Mechanistic Target of Rapamycin Complex 2; D019893:Ribosomal Protein S6 Kinases; C526901:Rps6kb1 protein, rat; D058570:TOR Serine-Threonine Kinases; D048055:Mitogen-Activated Protein Kinase 8
keywords: MAPK signaling; muscle hypertrophy; tenotomy