The cytochrome P450 (CYP) gene superfamily contains at least sixteen gene families and most likely many more. Nine of these families exist in all mammals. This laboratory has studied most extensively the CYP1 gene family. In mammals there are two tetrachlorodibenzo-p-dioxin (TCDD)- inducible genes, CYP1A1 and CYP1A2. We have examined the Cyp1a1 gene in the pSVO-cat plasmid stably transfected into mouse hepatoma Hepa-I cultures and receptor-defective and Cyp1a1 metabolism-deficient mutant cell lines. Upstream Cyp1a1 regulatory sequences include: (a) the TATA box; (b) a proximal element between -245 and -150 that is absolutely essential for constitutive and inducible gene expression; (c) a distal element, i.e. the TCDD-inducible enhancer between -1100 and -880; and (d) an additional element that participates in a negative autoregulatory loop. Both the TCDD-inducible enhancer and the negative autoregulatory loop appear to require a functional aromatic hydrocarbon (Ah) receptor. Metabolism of endogenous substrate(s) by the Cyp1a1 gene product not only appears to control its own constitutive expression but also the expression of at least five other genes encoding enzymes with coordinate metabolic functions--Cyp1a2, NAD(P)H:menadione oxidoreductase (Nmo- 1), aldehyde dehydrogenase (Aldh-l), UDP glucuronosyltransferase (Ugt-1), and glutathione transferase (Gt-l). All six of these TCDD-inducible genes have been cloned, are under control of the Ah receptor, and are defined as members of the [Ah] gene battery. The transcriptional preinitiation complex that up-regulates these genes is believed to include the Ah receptor (with foreign or endogenous ligand) and at least one other protein that confers chromatin binding capacity. Using 14CoS/14CoS radiation deletion homozygote mice, we have localized a gene (Nmo-In) on mouse chromosome 7 that encodes a negative effector of Nmo-1 (located on mouse chromosome 8). We are attempting to clone and characterize the Ah receptor gene, the Nmo-ln gene, and other genes encoding transacting 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.
