A heat-inducible nuclear factor that binds to the heat-shock element of the human haem oxygenase gene

Haem oxygenase is a heat-shock protein in several rat tissues, as well as in certain human cells such as Hep3B hepatoma cells. In common with other heat-shock-protein genes, both the human and the rat haem oxygenase genes contain a heat-shock element (HSE) in their promoter regions. In the present study we have identified a factor in nuclear extracts of human Hep3B cells which binds specifically to the HSE of the human haem oxygenase gene. The factor in Hep3B cells was significantly induced within 1 h after heat-shock treatment, and the induction was blocked by treatment of cells with actinomycin D or cycloheximide. The factor was not detected in human HepG2 hepatoma cells, which exhibit the heat-mediated induction of heat-shock protein 70 mRNA, but not that of haem oxygenase mRNA. These findings suggest that the heat-inducible nuclear factor is increased at the level of transcription and that it may activate the human haem oxygenase gene via the HSE after heat treatment.