title: Pivotal role of mTORC2 and involvement of ribosomal protein S6 in cardioprotective signaling.
abstract: BACKGROUND
  There is tight coupling between Akt activation and suppression of cell death. Full Akt activation requires mammalian target of rapamycin complex 2 (mTORC2), but the regulation of mTORC2 is unclear.
  
  
  OBJECTIVE
  To gain new insights into mechanisms of mTORC2/Akt signaling.
  
  
  RESULTS
  The role of mTORC2 in cardioprotection was examined. In perfused mouse hearts, ischemic preconditioning increased mTORC2 activity, leading to phosphorylation of Akt on Ser473. The protective effect of ischemic preconditioning was lost by pretreatment with dual mTORC inhibitors but not with rapamycin, an mTORC1 inhibitor, which indicates the fundamental role of mTORC2 activation in cardioprotection. Next, the regulation and downstream targets of mTORC2/Akt signaling were explored. We have found that ischemic preconditioning and other Akt activators (insulin and opioids) result in phosphorylation of ribosomal protein S6 (Rps6) at Ser235/236 in mouse hearts and neonatal rat ventricular myocytes. Rps6 interacts with components of mTORC2, and siRNA-mediated knockdown of Rps6 attenuates insulin-induced mTORC2 activation and Akt-Ser473 phosphorylation. On the other hand, Rps6 overexpression enhanced Akt-Ser473 phosphorylation, indicating that Rps6 activation amplifies mTORC2/Akt signaling. Disruption of the Rps6/mTORC2 pathway by knockdown of Rps6 or rictor abrogated insulin-induced cytoprotection against oxidative stress. Although rapamycin blocks Rps6-dependent mTORC2 activation, mTORC2 is still activated by an alternative signaling pathway, demonstrating the redundancy in cardioprotective signaling.
  
  
  CONCLUSIONS
  Activation of mTORC2 plays a pivotal role in cardioprotection, and Rps6 is a convergence point of cardioprotective signaling, providing positive feedback regulation of mTORC2/Akt signaling.
authors.affiliation: From the Department of Pathology (T.Y., C.S.) and Division of Cardiology, Department of Medicine (M.F.), Johns Hopkins University, Baltimore, MD; Proteomics Core (A.A.) and Systems Biology Center (E.M.), National Heart, Lung, and Blood Institute, National Institutes of Health, Bethesda, MD; and Departments of Cardiovascular, Renal, and Metabolic Medicine (T.Y., A.K., T.M.) and Pharmacology (A.K.), Sapporo Medical University, Sapporo, Japan.
authors.forename: Toshiyuki
authors.initials: T
authors.lastname: Yano
authors.forename: Marcella
authors.initials: M
authors.lastname: Ferlito
authors.forename: Angel
authors.initials: A
authors.lastname: Aponte
authors.forename: Atsushi
authors.initials: A
authors.lastname: Kuno
authors.forename: Tetsuji
authors.initials: T
authors.lastname: Miura
authors.forename: Elizabeth
authors.initials: E
authors.lastname: Murphy
authors.forename: Charles
authors.initials: C
authors.lastname: Steenbergen
mesh_terms: D000818:Animals; D002478:Cells, Cultured; D004195:Disease Models, Animal; D025461:Feedback, Physiological / Q000502:physiology; D019157:Ischemic Preconditioning, Myocardial; D008297:Male; D000076225:Mechanistic Target of Rapamycin Complex 2; D051379:Mice; D008810:Mice, Inbred C57BL; D046912:Multiprotein Complexes / Q000502:physiology*; D017202:Myocardial Ischemia / Q000503:physiopathology / Q000517:prevention & control*; D010766:Phosphorylation / Q000502:physiology; D051057:Proto-Oncogene Proteins c-akt / Q000502:physiology*; D038601:Ribosomal Protein S6 / Q000502:physiology*; D015398:Signal Transduction / Q000502:physiology*; D058570:TOR Serine-Threonine Kinases / Q000502:physiology*
chemical_list: D046912:Multiprotein Complexes; D038601:Ribosomal Protein S6; D000076225:Mechanistic Target of Rapamycin Complex 2; D051057:Proto-Oncogene Proteins c-akt; D058570:TOR Serine-Threonine Kinases
keywords: insulin; ischemia-reperfusion injury; ischemic preconditioning; mTORC2; myocardial ischemic reperfusion injury; rapamycin; sirolimus