Induction of murine NAD(P)H:quinone oxidoreductase by 2,3,7,8-tetrachlorodibenzo-p-dioxin requires the CNC (cap n collar) basic leucine zipper transcription factor Nrf2 (nuclear factor erythroid 2-related factor 2): cross-interaction between AhR (aryl hydrocarbon receptor) and Nrf2 signal transduction

Abstract

TCDD (2,3,7,8-tetrachlorodibenzo- p -dixoin) induces phase II drug-metabolizing enzyme NQO1 [NAD(P)H:quinone oxidoreductase; EC 1.6.99.2; DT-diaphorase] in a wide range of mammalian tissues and cells. Here, we analysed the molecular pathway mediating NQO1 induction by TCDD in mouse hepatoma cells. Inhibition of protein synthesis with CHX (cycloheximide) completely blocks induction of NQO1 by TCDD as well as the basal expression and induction by phenolic antioxidant tBHQ (2-t-butylbenzene-1,4-diol), implicating a labile factor in NQO1 mRNA expression. The inhibition is both time- and concentration-dependent, requires inhibition of protein synthesis, and occurs at a transcriptional level. Inhibition of NQO1 transcription by CHX correlates with a rapid reduction of the CNC bZip (cap 'n' collar basic leucine zipper) transcription factor Nrf2 (nuclear factor erythroid 2-related factor 2) through the 26 S proteasome pathway. Moreover, blocking Nrf2 degradation with proteasome inhibitor MG132 increases the amount of Nrf2 and superinduces NQO1 in the presence of TCDD or tBHQ. Finally, genetic experiments using AhR (aryl hydrocarbon receptor)-, Arnt (aryl hydrocarbon receptor nuclear translocator)- or Nrf2-deficient cells reveal that, while induction of NQO1 by TCDD depends on the presence of AhR and Arnt, the basal and inducible expression of NQO1 by either TCDD or tBHQ requires functional Nrf2. The findings demonstrate a novel role of Nrf2 in the induction of NQO1 by TCDD and provide new insights into the mechanism by which Nrf2 regulates the induction of phase II enzymes by both phenolic antioxidants and AhR ligands.

From differential induction of UDP-glucuronosyltransferases in rat liver to characterization of responsible ligand-activated transcription factors, and their multilevel crosstalk in humans

“…However, coordinate induction of UGTs by AhR and Nrf2 may also be possible by direct or indirect (via coregulators) interaction between the two transcription factors, as discussed for the control of NQO1 [92]. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 12 liver: rifampicin induces CYP1A1 and 1A2 via AhR in human primary hepatocyte cultures [94], although this finding remains complex and controversial [22].…”

Arsenic Induces NAD(P)H-quinone Oxidoreductase I by Disrupting the Nrf2·Keap1·Cul3 Complex and Recruiting Nrf2·Maf to the Antioxidant Response Element Enhancer

“…The cells were grown in ␣-minimal essential medium with 10% fetal bovine serum and 5% CO 2 . Mouse Nrf2 ϩ/ϩ and Nrf2 Ϫ/Ϫ embryonic fibroblast cells were derived from wild type and Nrf2 null mice as described previously (19). The cells were cultured in Dulbecco's modified Eagle's medium with 10% fetal bovine serum and 5% CO 2 .…”

“…Many of the genes, exemplified by Nqo1, are induced by a wide range of oxidative and electrophilic chemicals through the antioxidant response element (ARE) located in the enhancers of the genes (19,20). This ARE paradigm of gene regulation is shared by a second set of enzymes/ proteins, including heme oxygenase 1, glutathione synthetase, and ␥-glutamylcysteine synthetase that combat against reactive oxygen species and other stress signals (21).…”

“…The cap 'n' collar basic leucine zipper protein Nrf2 (nuclear factor erythroid 2-related factor 2) is a member of the leucine zipper family of transcription factors. Genetic and biochemical studies have uncovered an essential function of Nrf2 in the regulation of ARE-controlled gene transcription (19,22,23). Nrf2 is required for both the basal and inducible expression of a number of ARE-controlled genes.…”

Phosphorylation of Nrf2 in the transcription activation domain by casein kinase 2 (CK2) is critical for the nuclear translocation and transcription activation function of Nrf2 in IMR‐32 neuroblastoma cells

“…Nrf2 controls the basal expression and induction of several xenobiotic-metabolizing enzymes such as the NAD(P)H:quinont oxidoreductase (Nqo1) and detoxification enzymes/proteins such as heme oxygenase 1 (Ho-1) through the antioxidant response element (ARE) dependent transcription [2,10,13,14]. Nrf2 localizes in the cytoplasm in the absence of an activator, though a small fraction of Nrf2 mediates constitutive transcription of a number of target genes in the nucleus in uninduced cells.…”