Ah receptor interacts with Nrf2 to mediate the induction of NQO1 by 2,3,7,8-tetrachlorodibenzo-p-dioxin and benzo[a]pyrene.
The aryl hydrocarbon receptor (AhR) mediates the induction of a set of drug metabolizing enzymes including NQO1, GSTs, and UGTs by halogenated aromatic hydrocarbons and polycyclic aromatic hydrocarbons, such as 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) and benzo[a]pyrene (B[a]P); whereas, the nuclear factor erythroid 2-related factor 2 (Nrf2) is critical for the induction of the genes by antioxidants and electrophilic inducers, such as tertbutylhydroquinone (tBHQ). Induction of the genes by AhR agonists or antioxidants requires consensus DNA sequence known as "dioxin response element" (DRE) or "antioxidant response element" (ARE) located in the enhancers of the genes, respectively. We have used induction of NQO1 as a prototype to elucidate the molecular steps governing the induction of the genes. We previously reported a novel role of Nrf2 in regulating the induction of NQO1 by AhR agonists, which implicates a cross-interaction between AhR and Nrf2 signal transduction for gene induction (Ma et al, Biochem J 377, 205-213, 2004). In this study, we analyzed the interaction between AhR and Nrf2 at the promoter of NQO1. Chromatin immunoprecipitation (ChIP) analyses revealed that treatment with TCDD recruits both AhR and Nrf2 to the promoter region where a DRE and an ARE locate; the finding is in agreement with the result from genetic studies in which induction by TCDD or B[a]P was shown to require both AhR and Nrf2. TCDD-induced binding of Nrf2 and AhR to DNA is time-dependent. Consistent with the activation of Nrf2, TCDD treatment was found to inhibit Keap1-dependent ubiquitination and proteasomal degradation of Nrf2 resulting in the stabilization and nuclear accumulation of Nrf2. Finally, coimmunoprecipitation experiments revealed that AhR directly interacts with Nrf2 in the presence of TCDD. Our findings demonstrate that AhR interacts with Nrf2 to induce NQO1 and provide a molecular model for studying the induction of NQO1, GSTs, and UGTs by AhR agonists.
Molecular-biology; Chemical-analysis; Chemical-synthesis; Pharmacodynamics; Pharmacology; Aryls; Hydrocarbons; Drug-interaction; Drugs; Enzyme-activity; Enzymes; Dioxins; Benzopyrenes; Polycyclic-aromatic-hydrocarbons; Halogenated-hydrocarbons; Aromatic-hydrocarbons; Antioxidants; Genes; Metabolic-activation; Metabolism