INTERACTION BETWEEN THE AH RECEPTOR AND PROTEINS BINDING TO THE AP-1-LIKE ELECTROPHILE RESPONSE ELEMENT (EPRE) DURING MURINE PHASE-II [AH] BATTERY GENE-EXPRESSION

We have studied three Phase II genes in the mouse dioxin-inducible [Ah ] battery: Nmol [encoding NAD(P)H:menadione oxidoreductase], Ahd4 (enc oding the cytosolic aldehyde dehydrogenase ALDH3c), and Ugt106 (a UDP glucuronosyltransferase). Oxidant-induced Nmol gene expression in the c(14CoS)/c(14CoS) mouse appears likely to be caused by homozygous los s of the fumarylacetoacetate hydrolase (Fah) gene on Chr 7 and absence of the enzyme (FAH), which leads to increased levels of endogenous ty rosine oxidative metabolites. We show here that increases in [Ah] Phas e II gene expression in the 14CoS/14CoS mouse are correlated with an A P-1-like DNA motif called the electrophile response element (EpRE), wh ich has been found in the 5' flanking regulatory regions of all murine [Ah] Phase II genes. Aromatic hydrocarbon response element (AhREs) ar e responsible for dioxin-mediated upregulation of all six [Ah] battery genes, and one or more AhREs have been found in the 5' flanking regul atory regions of all of these [Ah] genes. Gel mobility shift assays, w ith a synthetic oligonucleotide probe corresponding to the EpRE, show that EpRE-binding proteins are more than twice as abundant in 14CoS/14 CoS than in the wild-type ch/ch nuclear extracts. Competition studies of EpRE-specific binding with an excess of EpRE, mutated EpRE, AP-I, A hRE3, mutated AhRE3, and C/EBP alpha oligonucleotides suggest that sev eral common transcriptional factors bind to the EpRE and AhRE3 motifs. Two monospecific antibodies to the Ah receptor (AHR) protein block fo rmation of an EpRE-specific complex on gel mobility electrophoresis. T hese data suggest that AHR (or AHR-related protein) might be an integr al part of the EpRE-binding transcriptional complex associated with th e oxidative stress response. To our knowledge, this is among the first reports of the same transcription factor operating at two different r esponse elements upstream of a single gene.