Effect of hyperthermia on the transcription rate of heat-shock genes in the rabbit cerebellum and retina assayed by nuclear run-ons.

The induction of heat-shock protein 70 (hsp70) mRNA in the hyperthermic rabbit brain has been examined previously by using Northern blotting and in situ hybridization procedures that measure steady-state levels of mRNA, which may be influenced by transcript stability and transcription rate. In the present investigation, the in vivo transcription rate of hsp70 has been examined by using run-on transcription assays on isolated brain nuclei. A major up-regulation in the transcription rate of hsp70 was observed between 0.75 and 1.50 hours after hyperthermia in the cerebellum and the retina. Gel-mobility shift assays revealed that the time course of conversion of heat-shock transcription factor (HSF1) to a DNA-binding form paralleled the transcriptional induction profile of hsp70. The transcription rates of several nonheat-shock genes were also studied in the hyperthermic brain, and little change was noted relative to the induction of hsp70. Thus, a physiologically relevant increase in temperature of 2.5 degrees C induces a major up-regulation in the in vivo transcription rate of hsp70 in the nervous system with little affect on the transcription rates of other genes.