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

Abstract

Human UDP-glucuronosyltransferases (UGTs) are expressed in a tissue-specific fashion in hepatic and extrahepatic tissues [Strassburg, Manns and Tukey (1998) J. Biol. Chem. 273, 8719–8726]. Previous work suggests that these enzymes play a protective role in chemical carcinogenesis [Strassburg, Manns and Tukey (1997) Cancer Res. 57, 2979–2985]. In this study, UGT1 and UGT2 gene expression was investigated in human oesophageal epithelium and squamous-cell carcinoma in addition to the characterization of individual UGT isoforms using recombinant protein. UGT mRNA expression was characterized by duplex reverse transcriptase-PCR analysis and revealed the expression of UGT1A7, UGT1A8, UGT1A9 and UGT1A10 mRNAs. UGT1A1, UGT1A3, UGT1A4, UGT1A5 and UGT1A6 transcripts were not detected. UGT2 expression included UGT2B7, UGT2B10 and UGT2B15, but UGT2B4 mRNA was absent. UGT2 mRNA was present at significantly lower levels than UGT1 transcripts. This observation was in agreement with the analysis of catalytic activities in oesophageal microsomal protein, which was characterized by high glucuronidation rates for phenolic xenobiotics, 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. Expression and analysis in vitro of recombinant UGT1A7, UGT1A9, UGT1A10, UGT2B7 and UGT2B15 demonstrated that UGT1A7, UGT1A9 and UGT1A10 catalysed the glucuronidation of 7-hydroxybenzo(α)pyrene, as well as other environmental carcinogens, such as 2-hydroxyamino-1-methyl-6-phenylimidazo-(4,5-β)-pyridine. Although UGT1A9 was not regulated in the carcinoma tissue, the five-fold reduction in 7-hydroxybenzo(α)pyrene glucuronidation could be attributed to regulation of UGT1A7 and UGT1A10. These data elucidate an individual regulation of human UGT1A and UGT2B genes in human oesophagus and provide evidence for specific catalytic activities of individual human UGT isoforms towards environmental carcinogens that have been implicated in cellular carcinogenesis.

Characterization of UGTs Active against SAHA and Association between SAHA Glucuronidation Activity Phenotype with UGT Genotype

“…This effect could potentially be most important in terms of target tissues where these enzymes are expressed and for which SAHA is being used as a chemotherapeutic target including lung, breast, colon, small intestine, and tissues of the aerodigestive tract (17, 29, 41, 42). As colon is a high expresser of extrahepatic UGTs (41, 43), the significant levels of glucuronidation activity against SAHA exhibited by colon homogenate in this study is consistent with a potential role for UGTs 1A8 and/or 1A10 in SAHA glucuronidation in extrahepatic tissues.…”

Developmental aspects of human hepatic drug glucuronidation in young children and adults

“…9 Cross reactivity was excluded using sequence alignments and PCGene (Oxford Molecular, Campbell, California, USA) software, as well as a computerised databank search using the Blastn software (GenBank). UGT2B cDNA was coamplified with β-actin cDNA in a starting volume of 92 µl containing 10 mM KCl, 20 mM Tris-HCl (pH 8.8), 10 mM ammonium sulphate, 2 mM magnesium sulphate, 1% Triton X-100, 0.2 mM each dNTP, and 2 µM of UGT2B primers and VENT (exo-) DNA polymerase (NEB, Beverly, Massachusetts, USA).…”

Polymorphisms of the human UDP-glucuronosyltransferase (UGT) 1A7 gene in colorectal cancer

“…3 5 UGT1A7, UGT1A8, and UGT1A10 are not expressed in hepatic tissues and have been shown to be differentially regulated in gastrointestinal organs such as the oesophagus, 6 stomach, 3 small intestine, 2 and colon. 7 In addition, regulation and function of the UGT1A genes has been linked to gastrointestinal carcinogenesis.…”

“…2 8 In gastric mucosa, UGT1A regulation leading to interindividual variations in UGT activity has been implicated as a cancer risk factor 2 while in oesophageal cancer, downregulation of UGT1A7 transcripts is correlated with a decrease in overall oesophageal benzo(α)pyrene metabolite glucuronidation. 6 This is significant as the cloning and characterisation of UGT1A7 has demonstrated its capacity to glucuronidate polycyclic aromatic hydrocarbons as well as dietary derived heterocyclic amines, 3 6 both of which are known carcinogens. These findings prompted us to predict that alterations in UGT1A7 gene expression or in the functional properties of UGT1A7 may be an indicator of potential cancer risk.…”