Pronounced enhancement of glucocorticoid-induced gene expression following severe heat shock of heat-conditioned cells hints to intricate cell survival tactics

Abstract

We have previously reported that severe heat shock of HeLa cells stably transfected with a chloramphenicol acetyltransferase (CAT) gene, transcription of which is controlled by two glucocorticoid-responsive elements and a minimal promoter, pronouncedly enhanced glucocorticoid-induced CAT expression compared to that of non-heated cells, in spite of the glucocorticoid-receptor-mediated transcription of the gene being temporarily compromised by the shock. We now report that prolonged severe heat shock of properly heat-conditioned cells resulted in far more pronounced enhancement of glucocorticoid-induced CAT mRNA and protein expressions, in spite of a similar heat-induced loss of receptor-mediated CAT gene transcription. During recovery from the shock the hormonal activation of transcription exceeded that of non-heated cells. While CAT mRNA translation was restored appreciably later than CAT gene transcription, mRNA and protein expressions were thermally enhanced to a comparable extent, consistent with the integrity of CAT mRNA being preserved during recovery. CAT mRNA turnover was fully impaired during early recovery, suggesting that stabilisation of CAT mRNA as well as stimulation of the hormonal activation of CAT gene transcription account for the thermal enhancement of glucocorticoid-induced CAT expression. This data hint to cell survival tactics designed to safeguard high expression of genes of stress-enduring function.