title: Translational activation of 5'-TOP mRNA in pressure overload myocardium.
abstract: The present study was conducted to determine the magnitude and duration of ribosomal protein translation in response to pressure overload and determine if additional, paracrine events associated with mechanical transduction, such as integrin activation using a bioactive peptide ligand, RGD or endothelin stimulation lead to ribosomal protein translation. Polysome analysis of ventricular tissue samples obtained from an in vivo model of right-ventricular pressure overload (RVPO) showed a significant shift in the proportion of a 5'-terminal oligopyrimidine (5'-TOP) mRNA, rpL32, associated with the polysomal fraction when compared with non-5'-TOP mRNAs, beta-actin and beta-myosin heavy chain (beta-MHC), in the early stages of the hypertrophic response (24-48 h). Furthermore, this increase in polysome-bound rpL32 mRNA was accompanied by the phosphorylation of mammalian target of rapamycin (mTOR), p70 S6 kinase (S6K1), and S6 ribosomal protein. In our in vitro studies, treatment of primary cultures of adult feline cardiomyocytes (cardiocytes) with 100 nM endothelin, 9 mM RGD, 100 nM insulin, or 100 nM TPA activated mTOR via distinct signaling pathways and resulted in an increased proportion of polysome-bound rpL32 mRNA. Pre-treatment of cardiocytes with the mTOR inhibitor rapamycin blocked the agonist-induced rpL32 mRNA mobilization to polysomes. These results show that mechanisms that regulate ribosomal biogenesis in the myocardium are dynamically sensitive to pressure overload. Furthermore, our in vitro studies indicate that distinct pathways are operational during the early course of hypertrophic growth and converge to activate mTOR resulting in the translational activation of 5'-TOP mRNA.
authors.affiliation: Department of Medicine and the Gazes Cardiac Research Institute, Medical University of South Carolina, Charleston, SC, USA.
authors.forename: William J
authors.initials: WJ
authors.lastname: Tuxworth
authors.forename: Hirokazu
authors.initials: H
authors.lastname: Shiraishi
authors.forename: Phillip C
authors.initials: PC
authors.lastname: Moschella
authors.forename: Kentaro
authors.initials: K
authors.lastname: Yamane
authors.forename: Paul J
authors.initials: PJ
authors.lastname: McDermott
authors.forename: Dhandapani
authors.initials: D
authors.lastname: Kuppuswamy
mesh_terms: D000199:Actins / Q000235:genetics; D000704:Analysis of Variance; D000818:Animals; D015153:Blotting, Western; D002415:Cats; D002478:Cells, Cultured; D004195:Disease Models, Animal; D016232:Endothelins / Q000494:pharmacology; D017380:Hypertrophy, Right Ventricular / Q000235:genetics / Q000378:metabolism* / Q000503:physiopathology; D007328:Insulin / Q000494:pharmacology; D032383:Myocytes, Cardiac / Q000187:drug effects / Q000378:metabolism* / Q000502:physiology; D018995:Myosin Heavy Chains / Q000235:genetics; D024501:Nonmuscle Myosin Type IIB / Q000235:genetics; D009842:Oligopeptides / Q000494:pharmacology; D010766:Phosphorylation / Q000187:drug effects; D011132:Polyribosomes / Q000378:metabolism* / Q000502:physiology; D014176:Protein Biosynthesis / Q000502:physiology*; D011494:Protein Kinases / Q000378:metabolism; D038641:RNA 5' Terminal Oligopyrimidine Sequence / Q000235:genetics / Q000502:physiology*; D012333:RNA, Messenger / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D038601:Ribosomal Protein S6 / Q000378:metabolism; D019893:Ribosomal Protein S6 Kinases / Q000378:metabolism; D015398:Signal Transduction / Q000502:physiology; D020123:Sirolimus / Q000494:pharmacology; D058570:TOR Serine-Threonine Kinases; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D000199:Actins; D016232:Endothelins; D007328:Insulin; D009842:Oligopeptides; D012333:RNA, Messenger; D038601:Ribosomal Protein S6; C047981:arginyl-glycyl-aspartic acid; D011494:Protein Kinases; C546845:mTOR protein, rat; D019893:Ribosomal Protein S6 Kinases; C526901:Rps6kb1 protein, rat; D058570:TOR Serine-Threonine Kinases; D024501:Nonmuscle Myosin Type IIB; C103815:nonmuscle myosin type IIB heavy chain; D018995:Myosin Heavy Chains; D013755:Tetradecanoylphorbol Acetate; D020123:Sirolimus