CHROMOSOMAL LOCALIZATION, STRUCTURE, AND REGULATION OF THE UGT2B17 GENE, ENCODING A C19 STEROID METABOLIZING ENZYME

UGT2B17 is a UDP-glucuronosyltransferase enzyme expressed in several e xtrahepatic steroid target tissues, including the human prostate, wher e it glucuronidates C19 steroids such as dihydrotestosterone (DHT), an drosterone (ADT), and androstane-3 alpha, 17 beta-diol (3 alpha-diol). To determine if UGT2B17 is regulated by physiological effecters of th e human prostate, DHT and epidermal growth factor (EGF) were demonstra ted to specifically down-regulate the steady-state levels of UGT2B17 t ranscript and protein in LNCaP cells (Guillemette et al., 1997). These results implicate regulation of UGT2B17 at the level of gene transcri ption, therefore, a P-1-derived artificial chromosome (PAC) clone of 1 20 kb containing the entire UGT2B17 gene was isolated. The gene is com prised of six exons spanning approximately 30 kb, and fluorescence in situ hybridization of the UGT2B17 PAC clone to normal human lymphocyte chromosomes, mapped the gene to chromosome 4q13. To determine if the 5'-flanking DNA of the UGT2B17 gene is sufficient to confer gene expre ssion, a 2,942-bp fragment was subcloned into a luciferase reporter pl asmid and yielded an activity of 25-fold over background when transfec ted in LNCaP cells. However, transfection of the construct into HK-293 , MCF-7, JEG-3, and HepG2 cells yielded only a moderate activity of tw o-to five-fold over background. Treatment of transfected LNCaP cells w ith 10 nM R1881, a nonmetabolizable analog of DHT, and 10 ng/ml EGF de creased the luciferase activity by 60%. This suggests that at least pa rt, if not all, of the inhibitory effect of EGF and DHT on UGT2B17 is at the level of transcription. Progressive 5' deletions of the UGT2B17 5'-f1anking region in the luciferase constructs alleviated the inhibi tion by R1881 and EGF, and revealed several potential responsive eleme nts that may confer the observed regulation of the UGT2B17 gene. This study demonstrates regulation of the UGT2B17 gene by physiological eff ecters of the human prostate and supports the hypothesis that UGT enzy mes are involved in steroid metabolism in extrahepatic tissues.