Xenobiotic responsive element-mediated transcriptional activation in the UDP-glucuronosyltransferase family 1 gene complex.

We have isolated genomic DNA clones containing rat UDP-glucuronosyltransferase family 1 (UGT1) sequences and have shown drug-responsive and tissue-specific alternative expression of multiple first exons (Emi, Y., Ikushiro, S., and Iyanagi, T. (1995) J. Biochem. (Tokyo) 117, 392-399). The UGT1 locus encodes at least nine UGT1 isoforms. UGT1A1 is a major 3-methylcholanthrene (MC)-inducible form in rat liver. In this report, we have identified a cis-acting element necessary for transcriptional activation of UGT1A1 in hepatocytes. A promoter region was fused to a chloramphenicol acetyltransferase gene, and the resultant construct was transiently transfected into hepatocytes. A DNA fragment carrying 1,100 nucleotides derived from the 5'-flanking region of the UGT1A1 gene was enough for MC induction. Unidirectional deletion of this region revealed that there existed one xenobiotic responsive element (XRE), TGCGTG, between -134 and -129. When a single base substitution was introduced into the XRE, MC-induced expression of the UGT1A1 gene was completely abolished. In addition, an XRE-deleted construct failed to respond to MC. Gel mobility shift assays showed MC-inducible binding of the nuclear aromatic hydrocarbon receptor-ligand complex to this motif. Gel shift-coupled DNase I protection analyses revealed that the GCGTG-core sequence was a target site of the liganded aromatic hydrocarbon receptor. These results suggest that the XRE participates in induction of the rat UGT1A1 gene by MC.