Abstract 4059: Molecular role of cytochrome P450 (CYP)1A2 in the regulation of hepatic and pulmonary CYP1A1 expression in mice exposed to 3-Methycholanthrene

Abstract

Abstract 3-Methylcholanthrene (MC) is one of the most potent polycyclic aromatic hydrocarbons (PAHs) carcinogens known to date. PAHs are 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. In this investigation, we tested the hypothesis that CYP1A2 plays a mechanistic role in the regulation of hepatic and pulmonary CYP1A1 by MC. Wild type (WT) (C57B6) and Cyp1a2_null mice were divided into two groups. Group I was treated with vehicle corn oil (CO) (8 ml/kg) and group II was treated with four doses of MC (100 μmol/kg), i.p. once daily for 4 days. Four animals from each group were sacrificed at 6, 12, 24, and 48 h, 8 and 15 days after MC withdrawal. The mRNA levels, protein content and enzyme activities of CYP1A1 and 1A2 were determined at different time points. In addition, the binding of MC-AHR-AHR nuclear translocator (ARNT) to the AHREs on the CYP1A1 promoter region was determined by chromatin immunoprecipitation (ChIP) assay in liver and lung tissues. In WT mice, ChIP experiments indicated that transcriptional activation of CYP1A1 was most pronounced at 6 h, followed by 12 h, but declined at later time points. In Cyp1a2_null mice, on the other hand, transcriptional activation of CYP1A1 persisted till 48 h. In lungs, AHR complex binding peak was observed at 12 h and declined later, but Cyp1a2 null mice showed more persistent binding till 48 h with a peak at 24 h. On the other hand, the expression of CYP1A1/1A2 at the mRNA, protein, and enzyme levels persisted for up to 48 h both in lung and liver tissues. These results suggest a mechanistic role for CYP1A2 in the molecular regulation of CYP1A1, and 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. These studies have important implications for carcinogenesis mediated by PAHs. Citation Format: Bhagavatula Moorthy, Paramahamsa Maturu, Lihua Wang, Weiwu Jiang. Molecular role of cytochrome P450 (CYP)1A2 in the regulation of hepatic and pulmonary CYP1A1 expression in mice exposed to 3-Methycholanthrene. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 4059.