NRF2 and HSF1 coordinately regulate heme oxygenase-1 expression

Heme oxygenase-1 (HO-1) is an inducible enzyme responding to various stresses and has cytoprotective activities. Although HO-1 has been referred to as heat shock protein (HSP) 32, the heat-mediated induction of HO-1 varies among different species and cell lines. We examined the effects of heat shock on HO-1 expression in mouse embryonic fibroblast (MEF) cells deficient in heat shock factor 1 (HSF1) or nuclear factor-erythroid-2-related factor 2 (NRF2). Heme-induced expression of HO-1 was 2-fold higher in Hsf1^−/− cells than in the wild-type cells at both mRNA and protein levels. In Nrf2^−/− cells, heme-induced expression of HO-1 was not detected. In contrast, HO-1 expression was markedly induced by heat shock at 40–42 °C in Nrf2^−/− cells while the wild-type cells were not responsive. The heat-induced expression of HO-1 in Nrf2^−/− cells were almost completely diminished by transfection of siRNA against Hsf1 gene. These results suggest that HSF1 and NRF2 suppress heme-induced and heat-induced HO-1 expression, respectively.