title: Decrease in heart peptide initiation during head-down tilt may be modulated by HSP-70.
abstract: This study examines the mechanism of the rapid decrease in cardiac muscle protein synthesis during rodent hindlimb non-weight bearing. Polysomes isolated from rat hearts 8 h after suspension show less RNA in the polysome pool and a shift in polysome size toward fewer ribosomes per mRNA; 18 h after suspension, the size shift persists, but the amount of RNA in the polysome pool returns to control values. These data are consistent with a decrease in the rate of initiation of protein synthesis. At both 8 and 12 h of suspension, the cardiac polysomes show a 78 and 93% increase association with the nascent polypeptide chaperone protein 70-kDa heat-shock cognate/heat-shock protein (HSC/HSP-70), respectively, that persists after 7 days of non-weight bearing. Because the dissociation of HSC/HSP-70 from unfolded protein can be modulated by ATP, we measured the adenosine nucleotide pools and found a 53% decrease in ATP levels after 18 h of suspension. We propose a mechanism in which a shift of HSC/HSP-70 to the nascent polypeptide indirectly inhibits protein synthesis initiation.
authors.affiliation: Department of Physiology and Biophysics, University of Tennessee Health Science Center, Memphis 38163, USA.
authors.forename: V
authors.initials: V
authors.lastname: Menon
authors.forename: J
authors.initials: J
authors.lastname: Yang
authors.forename: Z
authors.initials: Z
authors.lastname: Ku
authors.forename: D B
authors.initials: DB
authors.lastname: Thomason
mesh_terms: D000255:Adenosine Triphosphate / Q000378:metabolism; D000818:Animals; D015153:Blotting, Western; D005260:Female; D018840:HSP70 Heat-Shock Proteins / Q000302:isolation & purification / Q000378:metabolism*; D006257:Head; D018475:Head-Down Tilt / Q000502:physiology*; D008954:Models, Biological; D009206:Myocardium / Q000378:metabolism*; D010452:Peptide Biosynthesis; D010442:Peptide Chain Initiation, Translational; D011132:Polyribosomes / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D013997:Time Factors
chemical_list: D018840:HSP70 Heat-Shock Proteins; D000255:Adenosine Triphosphate