Antioxidant-induced phosphorylation of tyrosine 486 leads to rapid nuclear export of Bach1 that allows Nrf2 to bind to the antioxidant response element and activate defensive gene expression.
Antioxidants cause stabilization and nuclear translocation of NF-E2-related factor 2 (Nrf2), where it binds to the antioxidant response element (ARE) and induces up-regulation of defensive genes that protect cells against oxidative and electrophilic stress. Bach1, the negative regulator of Nrf2, competes with Nrf2 for binding to the ARE in the human NQO1 promoter. In this study, we demonstrate that Bach1 exits the nucleus within 1-2 h upon antioxidant treatment. Genistein, an inhibitor of tyrosine kinases, blocked nuclear export of Bach1. Site-directed mutagenesis and immunoprecipitation assays identified tyrosine 486 that was phosphorylated in response to the antioxidant and was essential for nuclear export of Bach1. Chromatin immunoprecipitation assays revealed a competitive interplay between Bach1 and Nrf2 at 1-2 and 4 h for binding to the human NQO1 ARE. Luciferase and real time PCR assays showed a significant decrease in antioxidant induction of reporter activity and mRNA levels in cells transfected with mutant Bach1 compared with wild type. This decrease was due to the absence of nuclear export of the mutant protein. Bach1 levels inside the nucleus returned to normal at 4 h after antioxidant treatment in the absence but not in the presence of protein synthesis inhibitor cycloheximide. In addition, antioxidant treatment increased the transcription of Bach1 as shown by pulse chase and real time PCR experiments. Taken together, these results indicate that increased synthesis of Bach1 restored its nuclear levels to normal at 4 h. In conclusion, antioxidant-induced tyrosine 486 phosphorylation leads to nuclear exit of Bach1, thus allowing Nrf2 access to the ARE.
Kaspar
James W
JW
Department of Pharmacology and Experimental Therapeutics, University of Maryland School of Medicine, Baltimore, Maryland 21201, USA.
Jaiswal
Anil K
AK
D021581:Active Transport, Cell Nucleus / Q000187:drug effects; D000818:Animals; D000975:Antioxidants / Q000494:pharmacology*; D050976:Basic-Leucine Zipper Transcription Factors / Q000737:chemistry / Q000235:genetics / Q000378:metabolism*; D002104:Cadmium / Q000494:pharmacology; D002467:Cell Nucleus / Q000187:drug effects / Q000378:metabolism*; D003513:Cycloheximide / Q000494:pharmacology; D051856:Fanconi Anemia Complementation Group Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D005786:Gene Expression Regulation / Q000187:drug effects*; D056945:Hep G2 Cells; D006801:Humans; D006873:Hydroquinones / Q000494:pharmacology; D028884:Karyopherins / Q000378:metabolism; D051379:Mice; D050505:Mutant Proteins; D009154:Mutation / Q000235:genetics; D016660:NAD(P)H Dehydrogenase (Quinone) / Q000378:metabolism; D051267:NF-E2-Related Factor 2 / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D019000:Phosphotyrosine / Q000378:metabolism*; D011485:Protein Binding / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism; D020218:Response Elements / Q000235:genetics*; D000097606:Exportin 1 Protein
D000975:Antioxidants; D050976:Basic-Leucine Zipper Transcription Factors; D002104:Cadmium; D003513:Cycloheximide; D051856:Fanconi Anemia Complementation Group Proteins; D006873:Hydroquinones; D028884:Karyopherins; D050505:Mutant Proteins; D016660:NAD(P)H Dehydrogenase (Quinone); D051267:NF-E2-Related Factor 2; D019000:Phosphotyrosine; D047428:Protein Kinase Inhibitors; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D000097606:Exportin 1 Protein; C102108:BACH1 protein, human; C486316:Bach1 protein, mouse; C018855:2-tert-butylhydroquinone; C447479:NQO1 protein, human