HSP70 ACCUMULATION IN CHONDROCYTIC CELLS EXPOSED TO HIGH CONTINUOUS HYDROSTATIC-PRESSURE COINCIDES WITH MESSENGER-RNA STABILIZATION RATHER THAN TRANSCRIPTIONAL ACTIVATION

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.