title: Mechanical activity in heart regulates translation of alpha-myosin heavy chain mRNA but not its localization.
abstract: Mechanical inactivity depresses protein expression in cardiac muscle tissue and results in atrophy. We explore the mechanical transduction mechanism in spontaneously beating neonatal rat cardiomyocytes expressing the alpha-myosin heavy chain (alpha-MyHC) isoform by interfering with cross-bridge function [2,3-butanedione monoxime (BDM), 7.5 mM] without affecting cell calcium. The polysome content and alpha-MyHC mRNA levels in fractions from a sucrose gradient were analyzed. BDM treatment blocked translation at initiation (162 +/- 12% in the nonpolysomal RNA fraction and 43 +/- 6% in the polysomal fraction, relative to control as 100%; P < 0.05). There was an increase in alpha-MyHC mRNA from the nonpolysomal fraction (120.5 +/- 7.7%; P < 0.05 compared with control) with no significant change in the heavy polysomes. In situ hybridization of alpha-MyHC mRNA was used to estimate message abundance as a function of the distance from the nucleus. The mRNA was dispersed through the cytoplasm in spontaneously beating cells as well as in BDM-treated cells (no significant difference). We conclude that direct inhibition of contractile machinery, but not calcium, regulates initiation of alpha-MyHC mRNA translation. However, calcium, not pure mechanical signals, appears to be important for message localization.
authors.affiliation: Department of Physiology and Biophysics, College of Medicine, University of Illinois at Chicago, Chicago, Illinois 60612, USA.
authors.forename: G
authors.initials: G
authors.lastname: Nikcevic
authors.forename: M C
authors.initials: MC
authors.lastname: Heidkamp
authors.forename: M
authors.initials: M
authors.lastname: Perhonen
authors.forename: B
authors.initials: B
authors.lastname: Russell
mesh_terms: D000818:Animals; D000831:Animals, Newborn; D002478:Cells, Cultured; D003931:Diacetyl / Q000031:analogs & derivatives / Q000494:pharmacology; D006321:Heart / Q000187:drug effects / Q000502:physiology*; D009206:Myocardium / Q000378:metabolism / Q000648:ultrastructure; D009210:Myofibrils / Q000648:ultrastructure; D018995:Myosin Heavy Chains / Q000235:genetics*; D014176:Protein Biosynthesis / Q000502:physiology*; D012313:RNA / Q000378:metabolism; D012333:RNA, Messenger / Q000187:drug effects / Q000235:genetics* / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D015398:Signal Transduction / Q000502:physiology*; D014018:Tissue Distribution / Q000502:physiology
chemical_list: D012333:RNA, Messenger; C004717:diacetylmonoxime; D012313:RNA; D018995:Myosin Heavy Chains; D003931:Diacetyl