HSP70 ACCUMULATION IN CHONDROCYTIC CELLS EXPOSED TO HIGH CONTINUOUS HYDROSTATIC-PRESSURE COINCIDES WITH MESSENGER-RNA STABILIZATION RATHER THAN TRANSCRIPTIONAL ACTIVATION
K. Kaarniranta et al., HSP70 ACCUMULATION IN CHONDROCYTIC CELLS EXPOSED TO HIGH CONTINUOUS HYDROSTATIC-PRESSURE COINCIDES WITH MESSENGER-RNA STABILIZATION RATHER THAN TRANSCRIPTIONAL ACTIVATION, Proceedings of the National Academy of Sciences of the United Statesof America, 95(5), 1998, pp. 2319-2324
In response to various stress stimuli, heat shock genes are induced to
express heat shock proteins (Hsps), Previous studies have revealed th
at expression of heat shock genes is regulated both at transcriptional
and posttranscriptional level, and the rapid transcriptional inductio
n of heat shock genes involves activation of the specific transcriptio
n factor, heat shock factor 1 (HSF1). Furthermore, the transcriptional
induction can vary in intensity and kinetics in a signal-and cell-typ
e-dependent manner. In this study, we demonstrate that mechanical load
ing in the form of hydrostatic pressure increases heat shock gene expr
ession in human chondrocyte-like cells. The response to continuous hig
h hydrostatic pressure was characterized by elevated mRNA and protein
levels of Hsp70, without activation of HSF1 and transcriptional induct
ion of hsp70 gene, The increased expression of Hsp70 was mediated thro
ugh stabilization of hsp70 mRNA molecules, Interestingly, in contrast
to static pressurization, cyclic hydrostatic loading did not result in
the induction of heat shock genes, Our findings show that hsp70 gene
expression is regulated posttranscriptionally without transcriptional
induction in chondrocyte-like cells upon exposure to high continuous h
ydrostatic pressure, We suggest that the posttranscriptional regulatio
n in the form of hsp70 mRNA stabilization provides an additional mode
of heat shock gene regulation that is likely to be of significant impo
rtance in certain forms of stress.