Interaction between the Ah receptor and proteins binding to the AP-1-like electrophile response element (EpRE) during...

We have studied three Phase II genes in the mouse dioxin-inducible [Ah] battery: Nmo1 [encoding NAD(P)H:menadione oxidoreductase], Ahd4 (encoding the cytosolic aldehyde dehydrogenase ALDH3c), and Ugt1*06 (a UDP glucuronosyltransferase). Oxidant-induced Nmo1 gene expression in the c14CoS/c14CoS mouse appears likely to be caused by homozygous loss of the fumarylacetoacetate hydrolase (Fah) gene on Chr 7 and absence of the enzyme (FAH), which leads to increased levels of endogenous tyrosine oxidative metabolites. We show here that increases in [Ah] Phase II gene expression in the 14CoS/14CoS mouse are correlated with an AP-1-like DNA motif called the electrophile response element (EpRE), which has been found in the 5' flanking regulatory regions of all murine (Ah) Phase II genes. Aromatic hydrocarbon response element (AhREs) are responsible for dioxin-mediated upregulation of all six [Ah] battery genes, and one or more AhREs have been found in the 5' flanking regulatory regions of all of these [Ah] genes. Gel mobility shift assays, with a synthetic oligonucleotide probe corresponding to the EpRE, show that EpRE-binding proteins are more than twice as abundant in 14CoS/14CoS than in the wild-type ch/ch nuclear extracts. Competition studies of EpRE-specific binding with an excess of EpRE, mutated EpRE, AP-1, AhRE3, mutated AhRE3, and C/EBP alpha oligonucleotides suggest that several common transcriptional factors bind to the EpRE and AhRE3 motifs. Two monospecific antibodies to the Ah receptor (AHR) protein block formation of an EpRE-specific complex on gel mobility electrophoresis. These data suggest that AHR (or AHR-related protein) might be an integral part of the EpRE-binding transcriptional complex associated with the oxidative stress response. To our knowledge, this is among the first reports of the same transcription factor operating at two different response elements upstream of a single gene.