Molecular Regulation of Hepatic and Pulmonary Cytochrome P4501A (CYP1A1) Enzymes by 3‐Methylcholanthrene in Mice: Role of CYP1A2

Abstract

Cytochrome P450 (CYP)1A enzymes play key roles in the activation of polycyclic aromatic hydrocarbons (PAHs) to carcinogenic metabolites. We previously showed persistent induction of CYP1A enzymes by 3-methylcholanthrene (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, and that CYP1A2 plays a significant role in this process. Thirty two C57B6 (WT) or 32 mice lacking the gene for CYP1A2 (Cyp1a2-null), 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 binding of MC-AHR-AHR nuclear translocator (ARNT) to the AHREs on the CYP1A1 promoter region were determined by chromatin immunoprecipitation (ChIP) assay at different time points. The ChIP experiments indicated that transcriptional activation of CYP1A1 promoter in WT was most pronounced at 6 h, followed by 12 h, but declined at later time points. In Cyp1a2_null mice, the CYP1A1 promoter activation was substantially higher at each time point, and persisted until 48 h. The expression of CYP1A1/1A2 at the mRNA, protein and enzyme levels persisted for up to 48 h both in lung and liver tissues in WT as well as Cyp1a2-null mice, with the later showing higher levels of expression. These results support the hypothesis that hepatic CYP1A2 plays a significant role in the regulation of CYP1A1 by PAHs, in relation to carcinogenesis.