title: Bach1 competes with Nrf2 leading to negative regulation of the antioxidant response element (ARE)-mediated NAD(P)H:quinone oxidoreductase 1 gene expression and induction in response to antioxidants.
abstract: The antioxidant response element (ARE) and Nrf2 are known to regulate the expression and coordinated induction of genes encoding detoxifying enzymes including NAD(P)H:quinone oxidoreductase1 (NQO1) in response to antioxidants. In this report, we demonstrate that overexpression of the transcription factor Bach1 in Hep-G2 cells negatively regulated NQO1 gene expression and induction in response to antioxidant t-BHQ. Bandshift and supershift assays revealed that Bach1 binds to the ARE as a heterodimer with small Maf proteins but not as a homodimer or heterodimer with Nrf2. The transfection and ChIP assays revealed that Bach1 and Nrf2 competed with each other to regulate ARE-mediated gene expression. Heme, a negative regulator of Bach1 relieved the Bach1 repression of NQO1 gene expression in transfected cells. The transcription of Bach1 and Nrf2 did not change in response to t-BHQ. Immunofluorescence assays and Western blot analysis revealed that both Bach1 and Nrf2 localized in the cytoplasm and nucleus of the untreated cells. The treatment of cells with t-BHQ resulted in the nuclear accumulation of both Bach1 and Nrf2. Interestingly, the t-BHQ-induced nuclear accumulation of Bach1 was significantly delayed over that of Nrf2. These results led to the conclusion that a balance of Nrf2 versus Bach1 inside the nucleus influences up- or down-regulation of ARE-mediated gene expression. The results further suggest that antioxidant-induced delayed accumulation of Bach1 contributes to the down-regulation of ARE-regulated genes, presumably to reduce the antioxidant enzymes to normal levels.
authors.affiliation: Department of Pharmacology, Baylor College of Medicine, Houston, Texas 77030, USA.
authors.forename: Saravanakumar
authors.initials: S
authors.lastname: Dhakshinamoorthy
authors.forename: Abhinav K
authors.initials: AK
authors.lastname: Jain
authors.forename: David A
authors.initials: DA
authors.lastname: Bloom
authors.forename: Anil K
authors.initials: AK
authors.lastname: Jaiswal
mesh_terms: D000975:Antioxidants / Q000378:metabolism*; D001483:Base Sequence; D050976:Basic-Leucine Zipper Transcription Factors; D001667:Binding, Competitive; D015152:Blotting, Northern; D015153:Blotting, Western; D002460:Cell Line; D045744:Cell Line, Tumor; D002467:Cell Nucleus / Q000378:metabolism; D047369:Chromatin Immunoprecipitation; D003593:Cytoplasm / Q000378:metabolism; D004268:DNA-Binding Proteins / Q000378:metabolism*; D019281:Dimerization; D015536:Down-Regulation; D051856:Fanconi Anemia Complementation Group Proteins; D005786:Gene Expression Regulation; D017930:Genes, Reporter; D006418:Heme / Q000737:chemistry; D006801:Humans; D007700:Kinetics; D008156:Luciferases / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000378:metabolism*; D051267:NF-E2-Related Factor 2; D010957:Plasmids / Q000378:metabolism; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D014176:Protein Biosynthesis; D011518:Proto-Oncogene Proteins / Q000378:metabolism; D051257:Proto-Oncogene Proteins c-maf; D012333:RNA, Messenger / Q000378:metabolism; D020218:Response Elements; D013347:Subcellular Fractions; D013997:Time Factors; D015534:Trans-Activators / Q000378:metabolism*; D014157:Transcription Factors / Q000378:metabolism*; D014158:Transcription, Genetic; D014162:Transfection; D015854:Up-Regulation
chemical_list: D000975:Antioxidants; C102108:BACH1 protein, human; D050976:Basic-Leucine Zipper Transcription Factors; D004268:DNA-Binding Proteins; D051856:Fanconi Anemia Complementation Group Proteins; C495607:MAF protein, human; D051267:NF-E2-Related Factor 2; C495635:NFE2L2 protein, human; D011518:Proto-Oncogene Proteins; D051257:Proto-Oncogene Proteins c-maf; D012333:RNA, Messenger; D015534:Trans-Activators; D014157:Transcription Factors; D006418:Heme; D008156:Luciferases; D016660:NAD(P)H Dehydrogenase (Quinone); C447479:NQO1 protein, human