Transcription and post-transcriptional regulation of avian HSP70 gene expression

Transient incubation of chicken lymphoblastoid (MSB) cells at elevated temperatures induces the synthesis of three heat shock proteins of 89,000 Da (HSP89), 70,000 Da (HSP70), and 23,000 Da (HSP23). We have examined the effects of heat shock on the transcription and post-transcriptional regulation of the chicken HSP70 and beta-actin genes. The rate of HSP70 transcription is rapidly induced by heat shock, reaches maximal levels by 60 min, and thereafter decreases. The level of HSP70 mRNA increases 20-fold by 60 min and remains constant through 6 h of heat shock. Upon return of heat-shocked cells to normal growth temperatures, the level of HSP70 mRNA rapidly decreases to pre-heat shock levels. These results suggest that HSP70 mRNA is stably maintained and translated during heat shock, but rapidly degraded during recovery from heat shock. The effect of heat shock on beta-actin mRNA is opposite to the apparent stabilizing effects of elevated temperatures on HSP70 mRNA.