CHARACTERIZATION OF TRANSCRIPTIONAL REGULATION OF GAMMA-GLUTAMYL-TRANSPEPTIDASE IN RAT-LIVER INVOLVING BOTH POSITIVE AND NEGATIVE REGULATORY ELEMENTS

gamma-Glutamyl transpeptidase is normally not present in adult rat hep atocytes, but its expression is induced by a range of xenobiotics, inc luding carcinogens and chemopreventive agents. Synthesis of the enzyme is mediated by at least six mRNAs transcribed from tandemly arranged promoters on a single gene. We previously identified and partially cha racterized promoter III as being responsible for upregulation of gamma -glutamyl transpeptidase in rat liver in response to inducing agents. In this study, we examined response elements involved in the regulatio n of this promoter by using reporter gene assays and in vitro DNase I footprinting and electrophoretic mobility shift assays. Among the resp onse elements was a region with negative regulatory activity upstream of a 240-bp basal regulatory region covering the transcriptional start site. This negative regulatory region, lying between nt -465 and -185 , contained sequences with considerable homology to silencer elements in the glutathione 5-transferase P gene. The region of basal regulatio n (nt -185 to +55) contained a CCAAT box, a TFIID binding site, and a GAGA box. A hepatocyte nuclear factor S-like sequence was identified a t nt -234 to -254 and had a DNase I hypersensitive site characteristic of binding of members of the hepatocyte nuclear factor 3/fork head fa mily of proteins and may be involved in the regulation of this promote r. (C) 1997 Wiley-Liss, Inc.