The cytochrome P450 gene superfamily is known to contain at least thirteen gene families and most likely many more. Eight of these families exist in all mammals. This laboratory has studied most extensively the tetrachlorodibenzo-p-dioxin (TCDD; in the lay press called """"""""dioxin"""""""")-inducible P450I gene family, which has two members, CYP1A1 and CYP1A2, trivial names P1 and P3, respectively. We have examined the P1 gene (CYP1A1) in the pSV0-cat plasmid stably transfected into mouse hepatoma Hepa-1 cultures and receptor-defective an P1 metabolism-deficient mutant cell lines. Upstream P1 regulatory sequences include: (a) the TATA box; (b) a TCDD-inducible enhancer which includes an element that augments constitutive gene expression and (c) a separate control element that involves endogenous signals rather that foreign chemical inducers. This latter element may participate in a negative autoregulatory loop. Both the TCDD-inducible enhancer and the endogenous regulatory element appear to require a functional aromatic hydrocarbon (Ah) receptor. Metabolism of substrate(s) by the product of the P1 gene not only appears to control its own constitutive expression but may also regulate the activities of at least five other enzymes having coordinate metabolic functions-- P3450 (CYP1A2), NAD(P)H:menadione oxidoreductase (NM01), glutathione transferase (GT1), aldehyde dehydrogenase (A1DH1) and UDP glucuronosyltransferase (UGT1). All six of these genes have been cloned, are under control of the Ah receptor, and are defined as members of the (Ah) gene battery. The transcriptional activation unit that up-regulates these genes is believed to include the Ah receptor (with foreign or endogenous ligand) and another protein that confers chromatin binding capacity. The endogenous control element interacts with a P1 metabolism-dependent repressor encoded by the AHN gene. We intend to clone and characterize the Ah receptor gene, the AHN gene, and other genes encoding trans-acting factors. One long-range goal of this laboratory is to develop assays, based on recombinant DNA technology, to assess the human Ah phenotype and other pharmacogenetic disorders. Such assays may predict who is at increased risk for certain types of environmentally-caused birth defects, cancers, and toxicity.
