title: Hemoprotein Bach1 regulates enhancer availability of heme oxygenase-1 gene.
abstract: Heme oxygenase-1 (HO-1) protects cells from various insults including oxidative stress. Transcriptional activators, including the Nrf2/Maf heterodimer, have been the focus of studies on the inducible expression of ho-1. Here we show that a heme-binding factor, Bach1, is a critical physiological repressor of ho-1. Bach1 bound to the multiple Maf recognition elements (MAREs) of ho-1 enhancers with MafK in vitro and repressed their activity in vivo, while heme abrogated this repressor function of Bach1 by inhibiting its binding to the ho-1 enhancers. Gene targeting experiments in mice revealed that, in the absence of Bach1, ho-1 became expressed constitutively at high levels in various tissues under normal physiological conditions. By analyzing bach1/nrf2 compound-deficient mice, we documented antagonistic activities of Bach1 and Nrf2 in several tissues. Chromatin immunoprecipitation revealed that small Maf proteins participate in both repression and activation of ho-1. Thus, regulation of ho-1 involves a direct sensing of heme levels by Bach1 (by analogy to lac repressor sensitivity to lactose), generating a simple feedback loop whereby the substrate effects repressor-activator antagonism.
mesh_terms: D016475:3T3 Cells; D000818:Animals; D001483:Base Sequence; D050976:Basic-Leucine Zipper Transcription Factors; D002460:Cell Line; D017931:DNA Primers; D015342:DNA Probes; D004742:Enhancer Elements, Genetic; D051856:Fanconi Anemia Complementation Group Proteins; D015971:Gene Expression Regulation, Enzymologic; D006419:Heme Oxygenase (Decyclizing) / Q000235:genetics*; D051547:Heme Oxygenase-1; D006801:Humans; D008565:Membrane Proteins; D051379:Mice; D018345:Mice, Knockout; D016133:Polymerase Chain Reaction; D014157:Transcription Factors / Q000172:deficiency / Q000235:genetics / Q000378:metabolism*; D014162:Transfection
chemical_list: C102108:BACH1 protein, human; C486316:Bach1 protein, mouse; D050976:Basic-Leucine Zipper Transcription Factors; D017931:DNA Primers; D015342:DNA Probes; D051856:Fanconi Anemia Complementation Group Proteins; D008565:Membrane Proteins; D014157:Transcription Factors; C496541:HMOX1 protein, human; D006419:Heme Oxygenase (Decyclizing); D051547:Heme Oxygenase-1; C496542:Hmox1 protein, mouse