title: c-Raf/MEK/ERK pathway controls protein kinase C-mediated p70S6K activation in adult cardiac muscle cells.
abstract: p70S6 kinase (S6K1) plays a pivotal role in hypertrophic cardiac growth via ribosomal biogenesis. In pressure-overloaded myocardium, we show S6K1 activation accompanied by activation of protein kinase C (PKC), c-Raf, and mitogen-activated protein kinases (MAPKs). To explore the importance of the c-Raf/MAPK kinase (MEK)/MAPK pathway, we stimulated adult feline cardiomyocytes with 12-O-tetradecanoylphorbol-13-acetate (TPA), insulin, or forskolin to activate PKC, phosphatidylinositol-3-OH kinase, or protein kinase A (PKA), respectively. These treatments resulted in S6K1 activation with Thr-389 phosphorylation as well as mammalian target of rapamycin (mTOR) and S6 protein phosphorylation. Thr-421/Ser-424 phosphorylation of S6K1 was observed predominantly in TPA-treated cells. Dominant negative c-Raf expression or a MEK1/2 inhibitor (U0126) treatment showed a profound blocking effect only on the TPA-stimulated phosphorylation of S6K1 and mTOR. Whereas p38 MAPK inhibitors exhibited only partial effect, MAPK-phosphatase-3 expression significantly blocked the TPA-stimulated S6K1 and mTOR phosphorylation. Inhibition of mTOR with rapamycin blocked the Thr-389 but not the Thr-421/Ser-424 phosphorylation of S6K1. Therefore, during PKC activation, the c-Raf/MEK/extracellular signal-regulated kinase-1/2 (ERK1/2) pathway mediates both the Thr-421/Ser-424 and the Thr-389 phosphorylation in an mTOR-independent and -dependent manner, respectively. Together, our in vivo and in vitro studies indicate that the PKC/c-Raf/MEK/ERK pathway plays a major role in the S6K1 activation in hypertrophic cardiac growth.
authors.affiliation: Cardiology Division of the Department of Medicine, Gazes Cardiac Research Institute, Medical University of South Carolina, Charleston, South Carolina 29425-2221, USA.
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Iijima
authors.forename: Martin
authors.initials: M
authors.lastname: Laser
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Shiraishi
authors.forename: Christopher D
authors.initials: CD
authors.lastname: Willey
authors.forename: Balasubramanian
authors.initials: B
authors.lastname: Sundaravadivel
authors.forename: Lin
authors.initials: L
authors.lastname: Xu
authors.forename: Paul J
authors.initials: PJ
authors.lastname: McDermott
authors.forename: Dhandapani
authors.initials: D
authors.lastname: Kuppuswamy
mesh_terms: D000256:Adenoviridae / Q000235:genetics; D000818:Animals; D015153:Blotting, Western; D002070:Butadienes / Q000494:pharmacology; D002415:Cats; D002478:Cells, Cultured; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D003902:Detergents / Q000494:pharmacology; D004305:Dose-Response Relationship, Drug; D054638:Dual Specificity Phosphatase 1; D004591:Electrophoresis, Polyacrylamide Gel; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005799:Genes, Dominant; D007328:Insulin / Q000378:metabolism; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; D020929:Mitogen-Activated Protein Kinase Kinases / Q000378:metabolism*; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism*; D009206:Myocardium / Q000166:cytology* / Q000378:metabolism; D009570:Nitriles / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D010766:Phosphorylation; D011485:Protein Binding; D020033:Protein Isoforms; D011493:Protein Kinase C / Q000378:metabolism*; D054645:Protein Phosphatase 1; D017346:Protein Serine-Threonine Kinases / Q000378:metabolism; D017027:Protein Tyrosine Phosphatases / Q000378:metabolism; D011505:Protein-Tyrosine Kinases / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism*; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism*; D015398:Signal Transduction; D020123:Sirolimus / Q000494:pharmacology; D013755:Tetradecanoylphorbol Acetate / Q000378:metabolism; D013912:Threonine / Q000737:chemistry; D013997:Time Factors
chemical_list: D002070:Butadienes; D017868:Cyclic AMP-Dependent Protein Kinases; D003902:Detergents; D054638:Dual Specificity Phosphatase 1; D004791:Enzyme Inhibitors; D007328:Insulin; D048369:MAP Kinase Kinase 1; D048370:MAP Kinase Kinase 2; D020929:Mitogen-Activated Protein Kinase Kinases; D020928:Mitogen-Activated Protein Kinases; D009570:Nitriles; D019869:Phosphatidylinositol 3-Kinases; D020033:Protein Isoforms; D011493:Protein Kinase C; D054645:Protein Phosphatase 1; D017346:Protein Serine-Threonine Kinases; D017027:Protein Tyrosine Phosphatases; D011505:Protein-Tyrosine Kinases; D019908:Proto-Oncogene Proteins c-raf; D019893:Ribosomal Protein S6 Kinases; D020123:Sirolimus; D013755:Tetradecanoylphorbol Acetate; D013912:Threonine; C113580:U 0126