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Cloning and characterization of a simian UDP-glucuronosyltransferase enzyme UGT2B20, a novel C19 steroid-conjugating protein.

ABSTRACT: Steroid glucuronidation by UDP-glucuronosyltransferase (UGT) enzymes is a mechanism leading to catabolism and elimination of steroid hormones. To establish an animal model to investigate the conjugation of steroids by UGT enzymes, previous results revealed that simian and human are unique in having high levels of circulating androsterone glucuronide and androstane-3alpha, 17beta-diol (3d-Diol) glucuronide. A cDNA, UGT2B20, was isolated from cynomolgus monkey liver and prostate libraries. The cDNA was 2075 bp in length and contained an open reading frame of 1590 bp, encoding a protein of 530 amino acid residues. The UGT2B20 clone was transfected and stably expressed in the human embryo kidney HK293 cell line, and the transferase activity of UGT2B20 was tested with 73 compounds. This enzyme was shown to be active with androgens, such as testosterone, dihydrotestosterone (DHT) and 3alpha-Diol, and on catecholoestrogens including 1,3,5,10-oestratriene-3, 4-diol-17-one. Kinetic analysis performed with intact cells yielded apparent Km values of 1.1, 2.3 and 4.6 microM for 3alpha-Diol, DHT and testosterone respectively. Reverse transcriptase-PCR analysis demonstrated that UGT2B20 transcript is expressed in several tissues including the liver, prostate, kidney, epididymis and adrenal of the cynomolgus monkey. Amino acid sequence alignment shows that the UGT2B20 protein is 92% identical with UGT2B15. Both enzymes have similar apparent Km values for DHT and 3alpha-Diol, and demonstrate similar transcript tissue distribution. The characterization of simian UGT2B20 as a structural and functional homologue of human UGT2B15 further demonstrates the similarities of steroid glucuronidation in these two species, and indicates the relevance of using the monkey as an animal model to study and understand steroid glucuronidation in extrahepatic-steroid target tissues.

SUBMITTER: Barbier O

PROVIDER: S-EPMC1220011 | biostudies-other | 1999 Feb

REPOSITORIES: biostudies-other

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Project description:To examine UGT2A1 expression in human tissues, determine its glucuronidation activity against tobacco carcinogens, and assess the potential functional role of UGT2A1 missense single nucleotide polymorphisms on UGT2A1 enzyme activity.Reverse transcription polymerase chain reaction and real time polymerase chain reaction were used to assess UGT2A1 gene expression in various human tissues. A glucuronidation assay measured by reverse phase ultra-performance liquid chromatography was used to determine UGT2A1 activity.UGT2A1 was expressed in aerodigestive tract tissues including trachea, larynx, tonsil, lung, and colon; no expression was observed in breast, whole brain, pancreas, prostate, kidney, liver, or esophagus. UGT2A1 exhibited highest expression in the lung, followed by trachea >tonsil >larynx >colon >olfactory tissue. Cell homogenates prepared from wildtype UGT2A1(75Lys308Gly) overexpressing HEK293 cells showed significant glucuronidation activity against a variety of polycyclic aromatic hydrocarbons including, 1-hydroxy-benzo(a)pyrene, benzo(a)pyrene-7,8-diol, and 5-methylchrysene-1,2-diol. No activity was observed in UGT2A1 overexpressing cell homogenate against substrates that form N-glucuronides, such as 4-(methylnitrosamino)-1-(3-pyridyl)-1-butanol (NNAL), nicotine, or N-OH-2-amino-1-methyl-6-phenylimidazo [4,5-b] pyridine (N-OH PhIP). A significant (P<0.05) decrease (approximately 25%) in glucuronidation activity (Vmax/KM) was observed against all polycyclic aromatic hydrocarbons substrates for the UGT2A1(75Lys308Gly) variant compared with homogenates from wildtype UGT2A1(75Lys308Gly); no activity was observed for cell homogenates overexpressing the UGT2A1 variant for all substrates tested.These data suggest that UGT2A1 is an important detoxification enzyme in the metabolism of polycyclic aromatic hydrocarbons within target tissues for tobacco carcinogens and functional polymorphisms in UGT2A1 may play a role in tobacco-related cancer risk.

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Cloning and characterization of a simian UDP-glucuronosyltransferase enzyme UGT2B20, a novel C19 steroid-conjugating protein.

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