title: Increased protein stability as a mechanism that enhances Nrf2-mediated transcriptional activation of the antioxidant response element. Degradation of Nrf2 by the 26 S proteasome.
abstract: Nrf2 (NF-E2-related factor 2) is a central transcription factor involved in the transcriptional activation of many genes encoding phase II drug-metabolizing enzymes via the antioxidant response element. Nrf2 has previously been found to undergo nuclear translocation by a phosphorylation-dependent mechanism mediated by protein kinase C in HepG2 cells treated with tert-butylhydroquinone, beta-naphthoflavone, or 12-O-tetradecanoylphorbol-13-acetate. In the present report, we have found that the levels of Nrf2 were increased in cells treated with tert-butylhydroquinone or beta-naphthoflavone by a post-transcriptional mechanism. Treatment of HepG2 cells with cycloheximide resulted in the loss of Nrf2 within 30 min. By contrast, treatment with the proteasome inhibitors (lactacystin or MG-132) caused an accumulation of Nrf2 as well as an induction of reporter gene activity in cells transfected with the GSTA2 antioxidant response element-chloramphenicol acetyl transferase construct. Similarly, the protein phosphatase inhibitor okadaic acid also caused an accumulation of Nrf2, whereas the reverse effects were observed with PD 98059 and U 0126, two compounds that block the activation of the MAPK/ERK signaling cascade. These data suggest that Nrf2 is degraded by the ubiquitin-dependent pathway and that phosphorylation of Nrf2 leads to an increase in its stability and subsequent transactivation activity.
authors.affiliation: Schering-Plough Research Institute, Kenilworth, New Jersey 07033, USA.
authors.forename: Truyen
authors.initials: T
authors.lastname: Nguyen
authors.forename: Philip J
authors.initials: PJ
authors.lastname: Sherratt
authors.forename: H-C
authors.initials: HC
authors.lastname: Huang
authors.forename: Chung S
authors.initials: CS
authors.lastname: Yang
authors.forename: Cecil B
authors.initials: CB
authors.lastname: Pickett
mesh_terms: D000975:Antioxidants / Q000494:pharmacology; D002070:Butadienes / Q000494:pharmacology; D002460:Cell Line; D004268:DNA-Binding Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005419:Flavonoids / Q000494:pharmacology; D006801:Humans; D006873:Hydroquinones / Q000494:pharmacology; D016350:Leucine Zippers; D051267:NF-E2-Related Factor 2; D009570:Nitriles / Q000494:pharmacology; D018384:Oxidative Stress / Q000235:genetics; D010447:Peptide Hydrolases / Q000378:metabolism*; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex; D021122:Protein Subunits / Q000235:genetics / Q000378:metabolism; D012323:RNA Processing, Post-Transcriptional / Q000187:drug effects; D015534:Trans-Activators / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism*; D015533:Transcriptional Activation / Q000187:drug effects; D019324:beta-Naphthoflavone / Q000494:pharmacology
chemical_list: D000975:Antioxidants; D002070:Butadienes; D004268:DNA-Binding Proteins; D004791:Enzyme Inhibitors; D005419:Flavonoids; D006873:Hydroquinones; D051267:NF-E2-Related Factor 2; C495635:NFE2L2 protein, human; D009570:Nitriles; D021122:Protein Subunits; D015534:Trans-Activators; C113580:U 0126; D019324:beta-Naphthoflavone; C018855:2-tert-butylhydroquinone; D010447:Peptide Hydrolases; D046988:Proteasome Endopeptidase Complex; C061553:ATP dependent 26S protease; C093973:2-(2-amino-3-methoxyphenyl)-4H-1-benzopyran-4-one