Decrease in heart peptide initiation during head-down tilt may be modulated
by hsp70.
Menon, Vandana, Jiwei Yang, Zhu Ku, and Donald B. Thomason.
The University of Tennessee Health Science Center, Memphis, Department of
Physiology and Biophysics, 894 Union Avenue, Memphis, TN 38163 USA, current
address: Department of Cell Biology and Physiology, University of Pittsburgh
School of Medicine, Pittsburgh, PA 15261 USA
APStracts 2:0045C, 1995.
This paper examines the mechanism of the rapid decrease in cardiac muscle
protein synthesis during rodent hindlimb non-weightbearing . Polysomes
isolated from rat hearts 8 h following suspension show less RNA in the
polysome pool and a shift in polysome size toward fewer ribosomes per mRNA;
18 h following 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 h and 18 h
of suspension the cardiac polysomes show a 78% and 93% increased association
with the nascent polypeptide chaperone protein HSC/HSP70, respectively, that
persists after 7 d of non-weightbearing. Because the dissociation of
HSC/HSP70 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 where a shift of HSC/HSP70 to the
nascent polypeptide indirectly inhibits protein synthesis initiation.
Received 22 July 1994; accepted in final form 8 December 1994
APS Manuscript Number C0426-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1994 The American Physiological Society.
Published in APStracts on 27 February 1995.