Heat shock transcription factor, HSF, is activated by ultraviolet irradiation.

We demonstrated previously that human glioblastoma cell lines accumulated heat shock protein (hsp)72, not only after heat shock, but also after, gamma-ray or UV irradiation. In the present study, we investigated whether the binding activity of heat shock transcription factor (HSF) to the heat shock element (HSE) of the hsp72 gene promoter increased after UV irradiation of human glioblastoma A-172 cells. A gel mobility-shift assay showed that the activated HSF level increased markedly after UV irradiation. Furthermore, UV irradiation of nuclear extracts in vitro did not activate HSF, whereas in vitro heat shock treatment did. These results suggest that HSF activation can be induced by UV irradiation at normal physiological temperature and hsp72 accumulation results from an increased activated HSF level, i.e. a transcriptional up-regulation of hsp72. In addition, the mechanism responsible for UV-induced HSF activation may differ from the process that operates in heat-treated cells.