Heat shock induces the transcriptional activation of c-fos protooncogene.

Treatment of murine 3T3 fibroblasts with mild elevated temperature (43 degrees C for 45 minutes) followed by recovery at 37 degrees C induced high levels of c-fos mRNA. The maximal c-fos induction was found after recovery at 37 degrees C for 15 minutes. Sodium arsenite induced both hsp 70 and c-fos transcripts. Induction of hsp 70 and c-fos by heat shock did not require intact protein synthesis. c-fos mRNA induced by heat shock was more stable (T1/2 greater than 90 minutes) than that induced by phorbol esters (t1/2 approximately 30 minutes). Northern blot analysis in the presence of actinomycin D and nuclear run off experiments demonstrated that heat shock augmented the transcription rate of c-fos protooncogene. Human growth hormone under the control of a murine genomic c-fos fragment spanning 770 bp 5' from the start of transcription is induced in transfected cells in response to heat shock. These data indicate that heat shock induces c-fos protooncogene acting at both transcriptional and post-transcriptional (i.e. via stabilization of transcripts) levels.