Heat shock‐induced heme oxygenase‐1 expression in a mouse hepatoma cell line is dependent on HSF1 and modified by NRF2 and BACH1

The induction mechanism of heme oxygenase‐1 (HO‐1) by heat shock (HS) is still unknown. Here, we discovered that HS activates the HO‐1 expression in a mouse hepatoma cell line (Hepa 1–6). Knockdown experiments showed that the HS‐induced HO‐1 expression was dependent on HS factor 1 (HSF1). A chromatin immunoprecipitation (ChIP) assay demonstrated that the HS‐activated HSF1 bound to the HS elements (HSEs) in the upstream enhancer 1 region (E1). Unexpectedly, HS also facilitates the BTB and CNC homology 1 (BACH1) binding to the Maf recognition elements (MAREs) in E1. We examined the effects of a catalytically inactive CRISPR‐associated 9 nucleases (dCas9) with short guide RNAs (sgRNAs), and demonstrated that the HSF1 binding to HSEs in E1 was indispensable for the HS‐induced HO‐1 expression. Heme treatment (HA) dissociates BACH1 from MAREs and facilitated the binding of nuclear factor‐erythroid‐2‐related factor 2 (NRF2) to MAREs. Following treatment with both HS and HA, the HO‐1 induction and the HSF1 binding to HSEs in E1 were most notably observed. These results indicate that the HS‐induced HO‐1 expression is dependent on the HSF1 binding to HSEs in E1, although modulated by the BACH1 and NRF2 binding to MAREs within the same E1.