The cytochrome P450 gene superfamily is known to contain at least eleven 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, P450IA1 and P450IA2, trivial names P1450 and P3450, respectively. We have examined the P1 gene (P4590IA1) in mouse hepatoma Hepa-1 cultures and receptor-defective and P1 metabolism-deficient mutant cell lines. Upstream P1 regulatory sequences include: (a) the TATA box; (b) a TCDD-inducible enhancer, which includes (c) an element that augments constitutive gene expression; and (d) a separate control element involved in a negative autoregulatory loop. The negative regulatory element involved in derepression of constitutive transcription, as well as the TCDD-inducible enhancer, appear to require a functional aromatic hydrocarbon (Ah) receptor. Metabolism of substrate(s) by the product of the P1 gene not only controls its own constitutive expression but also regulates the activities of at least two other enzymes having coordinate metabolic functions--UDP glucuronosyltransferase (UDPGT1) and NAD(P)H:menadione oxidoreductase (NMOR1). The P1, P3, UDPGT, and NMOR1 genes (which we have cloned) are all under control of the Ah receptor and are defined as members of the (Ah) gene battery. The Ah receptor is postulated to comprise a TCDD- binding subunit encoded by Gene B and a chromatinbinding subunit encoded by Gene C. THe negative control element interacts with a P1 metabolism--dependent repressor encoded by Gene N. We intend to clone and characterize all three of these 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.
