Abstract 825: Molecular mechanisms of regulation of cytochrome P4501A enzymes by 3-methylcholanthrene (MC) in mice in vivo

Abstract

Abstract 3-Methylcholanthrene (MC) is one of the most potent polycyclic aromatic hydrocarbons (PAHs) present in cigarette smoke, diesel exhausts, and charcoal broiled meats, etc. Cytochrome P450 (CYP)1A enzymes play key roles in the activation of PAHs to carcinogenic metabolites. We previously showed persistent induction of CYP1A enzymes by MC in vivo. In this study, we tested the hypothesis that MC elicits persistent induction of CYP1A1 in vivo by sustained transcriptional activation of the CYP1A1 promoter. Thirty two C57B6 (WT) mice were divided into two groups. Group I was treated with vehicle corn oil (CO) (8ml/kg) and group II was treated with a single dose of MC (100 μmol/kg), i.p. Four animals from each group were sacrificed at 6, 12, 24, and 48 h after MC withdrawal. The mRNA levels, protein content and enzyme activities of CYP1A1 were determined by real-time PCR, Western blotting, and fluorimetry, respectively at different time points. In addition, the binding of MC-AHR-AHR nuclear translocator (ARNT) to the AHREs on the CYP1A1 promoter region were determined by chromatin immunoprecipitation (ChIP) assay. The translocation of AHR was also analyzed by immunofluorescence. The ChIP experiments indicated that transcriptional activation of CYP1A1 was most pronounced at 6 h, followed by 12 h, but declined at later time points. On the other hand, the expression of CYP1A1 at the mRNA, protein and enzyme levels persisted for up to 48 h both in lung and liver tissues. These results suggest that transcriptional activation of CYP1A1 at 6-12 h is sufficient to result in sustained induction of CYP1A mRNA and protein expression for up to 48 h. Isolation of the immunoprecipitated promoter fragment (containing the xenobiotic response elements), which binds to the MC-AHR complex, followed by 32P-postlabeling revealed the formation of MC-DNA adducts, suggesting that DNA adducts are sequence-specific and target the CYP1A1 promoter. Our results suggest that DNA adducts might play a role in regulation of CYP1A1 by MC, a phenomenon that may be of relevance to PAH-mediated carcinogenesis. Citation Format: Bhagavatula Moorthy, Jiang Weiwu, Lihua Wang, Chun Chu, Sudha R. Kondraganti, Paramahamsa Maturu. Molecular mechanisms of regulation of cytochrome P4501A enzymes by 3-methylcholanthrene (MC) in mice in vivo. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 825. doi:10.1158/1538-7445.AM2015-825