Regulation and function of family 1 and family 2 UDP-glucuronosyltransferase genes (UGT1A, UGT2B) in human oesophagus

Human UDP-glucuronosyltransferases (UGTs) are expressed in a tissue-specifi c fashion in hepatic and extrahepatic tissues [Strassburg, Manns and Tukey (1998) J. Biol. Chem. 273, 8719-8726]. Previous work suggests that these en zymes play a protective role in chemical carcinogenesis [Strassburg, Manns and Tukey (1997) Cancer Res. 57, 2979-2985]. In this study, UGT1 and UGT2 g ene expression was investigated in human oesophageal epithelium and squamou s-cell carcinoma in addition to the characterization of individual UGT isof orms using recombinant protein. UGT mRNA expression was characterized by du plex reverse transcriptase-PCR analysis and revealed the expression of UGT1 A7, UGT1A8, UGT1A9 and UGT1A10 mRNAs. UGT1A1, UGT1A3, UGT1A4, UGT1A5 and UG T1A6 transcripts were not detected. UGT2 expression included UGT2B7, UGT2B1 0 and UGT2B15, but UGT2B4 mRNA was absent. UGT2 mRNA was present at signifi cantly lower levels than UGT1 transcripts. This observation was in agreemen t with the analysis of catalytic activities in oesophageal microsomal prote in, which was characterized by high glucuronidation rates for phenolic xeno biotics, all of which are classical UGT1 substrates. Whereas UGT1A9 was not regulated, differential regulation of UGT1A7 and UGT1A10 mRNA was observed between normal oesophageal epithelium and squamous-cell carcinoma. Express ion and analysis in vitro of recombinant UGT1A7, UGT1A9, UGT1A10, UGT2B7 an d UGT2B15 demonstrated that UGT1A7, UGT1A9 and UGT1A10 catalysed the glucur onidation of 7-hydroxybenzo(a)pyrene, as well as other environmental carcin ogens, such as 2-hydroxyamino-1-methyl-6-phenylimidazo-(4,5-beta)-pyridine. Although UGT1A9 was not regulated in the carcinoma tissue, the five-fold r eduction in 7-hydroxybenzo(a)pyrene glucuronidation could be attributed to regulation of UGT1A7 and UGT1A10. These data elucidate an individual regula tion of human UGT1A and UGT2B genes in human oesophagus and provide evidenc e for specific catalytic activities of individual human UGT isoforms toward s environmental carcinogens that have been implicated in cellular carcinoge nesis.