Abstract
Benzo[a]pyrene (BaP) activates the aryl hydrocarbon (AHR) and induces the expression of genes involved in xenobiotic metabolism, including CYP1A1. CYP1A1 is involved not only in BaP detoxification but also in metabolic activation, which results in DNA adduct formation. Vitamin D receptor (VDR) belongs to the NR1I subfamily of the nuclear receptor superfamily, which also regulates expression of xenobiotic metabolism genes. We investigated the cross-talk between AHR and VDR signaling pathways and found that 1α,25-dihydroxyvitamin D3 [1,25(OH)2D3], a potent physiological VDR agonist, enhanced BaP-induced transcription of CYP1A1 in human monocytic U937 cells and THP-1 cells, breast cancer cells, and kidney epithelium-derived cells. 1,25(OH)2D3 alone did not induce CYP1A1, and 1,25(OH)2D3 plus BaP did not increase CYP1A2 or CYP1B1 mRNA expression in U937 cells. The combination of 1,25(OH)2D3 and BaP increased CYP1A1 protein levels, BaP hydroxylation activity, and BaP-DNA adduct formation in U937 cells and THP-1 cells more effectively than BaP alone. The combined effect of 1,25(OH)2D3 and BaP on CYP1A1 mRNA expression in U937 cells and/or THP-1 cells was inhibited by VDR knockdown, VDR antagonists, and α-naphthoflavone, an AHR antagonist. Electrophoretic mobility shift assays and chromatin immunoprecipitation assays showed that VDR directly bound to an everted repeat (ER) 8 motif in the human CYP1A1 promoter. Thus, CYP1A1 is a novel VDR target gene involved in xenobiotic metabolism. Induction of CYP1A1 by the activation of VDR and AHR may contribute to BaP-mediated toxicity and the physiological function of this enzyme.
Footnotes
This work was supported in part by the Ministry of Education, Culture, Sports, Science, and Technology of Japan [Grant-in-Aid for Scientific Research on Priority Areas 18077005] (to M.Mak.); and Nihon University [Nihon University Multidisciplinary Research Grant for 2005 and 2006] (to M.Mak.).
Article, publication date, and citation information can be found at http://dmd.aspetjournals.org.
ABBREVIATIONS:
- BaP
- benzo[a]pyrene
- AHR
- aryl hydrocarbon receptor
- P450
- cytochrome P450
- 1,25(OH)2D3
- 1α,25-dihydroxyvitamin D3
- ER
- everted repeat
- VDR
- vitamin D receptor
- RXR
- retinoid X receptor
- LCA
- lithocholic acid
- CAR
- constitutive androstane receptor
- TCDD
- 2,3,7,8-tetrachlorodibenzo-p-dioxin
- ADTT
- (25R)-25-adamantyl-1α,25-dihydroxy-2-methylene-22,23-didehydro-19,26,27-trinor-20-epi-vitamin D3
- ADMI3
- (25S)-26-adamantyl-1α,25-dihydroxy-2-methylene-22,23-didehydro-19,27-dinor-20-epi-vitamin D3
- HEK
- human embryonic kidney
- PCR
- polymerase chain reaction
- siRNA
- small interfering RNA
- EMSA
- electrophoretic mobility shift assay
- ChIP
- chromatin immunoprecipitation
- XRE
- xenobiotic-responsive element.
- Received May 19, 2012.
- Accepted July 25, 2012.
- Copyright © 2012 by The American Society for Pharmacology and Experimental Therapeutics
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