Regulation of the rat cytochrome P450IA1 gene by polycyclic hydrocarbons and a dioxin congener.

摘要

Cytochrome P450IA1 is associated with metabolic detoxification of many drugs and chemicals and is also responsible for the activation of procarcinogenic forms of the polycyclic aromatic hydrocarbons (PAHs), e.g., benzo(a)pyrene (BP), to proximal carcinogenic species. This study examined the mechanisms of induction of the rat cytochrome P450IA1 gene by PAHs and a dioxin congener, 2,3,7,8-tetrachlorodibenzo-p-furan (TCDBF), in order to provide an understanding of the regulation of the gene expression.;The H4IIE rat hepatoma cell line was chosen for the study of regulation of the rat cytochrome P450IA1 gene expression. Some of the details of the induction of the endogenous P450IA1 gene and its recombinant construct, containing the cytochrome P450IA1 promoter linked to the chloramphenicol acetyl transferase (CAT) gene, by BP, 3-methycholanthrene (3MC) or TCDBF have been characterized at both the mRNA and the protein levels. The results demonstrate that in the H4IIE cells, the P450IA1 gene is highly inducible and responds to these inducing agents with different kinetics dependent upon the inducer. Nuclear run-off experiments show that induction of P450IA1 is regulated at the transcriptional level. Taken together, these studies indicate that the H4IIE cell line is a valid model for studying the regulation of the rat P450IA1 gene expression.;Another important goal of this study was to define the regulatory elements responsible for rat P450IA1 gene expression. A series of mutants with deletions involving various downstream or upstream regions of the gene have been constructed. These experiments indicate that there might be several important regulatory elements in the 5