Decreased polysomal hsp70 may slow polypeptide elongation during skeletal
muscle atrophy.
Ku, Zhu, Jiwei Yang, Vandana Menon, and Donald B. Thomason.
The University of Tennessee Health Science Center, Memphis
APStracts 2:0046C, 1995.
Slowed elongation rate is the apparent cause of the rapid decrease in rat
soleus muscle protein synthesis rate during non-weightbearing. We found that
elongation factor 2 was not phosphorylated and thus could not explain the
slowed elongation rate. However, we observed a 44 +- 19 % and 28 +- 14 %
decrease in the chaperone protein HSC/HSP70 associated with the polysomes
after 12h and 18h of non-weightbearing, respectively. Size-fractionated
polysomes had less HSC/HSP70 associated with the larger polysomes in 18h non
-weightbearing soleus muscle. ATP concentration increased in the non
-weightbearing muscle so, because ATP enhances HSC/HSP70 dissociation, we
tested the potential role of ATP. Digitonin-permeabilized myoblasts treated
with increasing concentrations of ATP showed both a decreased association of
HSC/HSP70 with the polysomes and a shift toward heavier polysomes; these
responses were blocked by ATPgS. These data are consistent with the role of
HSC/HSP70 as a chaperone of nascent protein. The absence of HSC/HSP70 may
slow ribosome translocation, thus slowing elongation rate.
Received 22 July 1994; accepted in final form 8 December 1994
APS Manuscript Number C0424-4.
Article publication pending Am. J. Physiol. (Cell Physiology).
ISSN 1080-4757 Copyright 1994 The American Physiological Society.
Published in APStracts on 27 February 1995.