Vol. 31, Issue 5, 528-532, May 2003

Functional Characterization of Wild-type and Variant (T202I and M59I) Human UDP-glucuronosyltransferase 1A10

Hideto Jinno, Mayumi Saeki, Toshiko Tanaka-Kagawa, Nobumitsu Hanioka, Yoshiro Saito, Shogo Ozawa, Masanori Ando, Kuniaki Shirao, Hironobu Minami, Atsushi Ohtsu, Teruhiko Yoshida, Nagahiro Saijo, and Jun-ichi Sawada

Project Team for Pharmacogenetics (H.J., M.S., N.H., Y.S., S.O., J.S.), Division of Environmental Chemistry (H.J., T.T.-K., N.H., M.A.), Division of Biochemistry and Immunochemistry (Y.S., J.S.), and Division of Pharmacology (S.O.), National Institute of Health Sciences, Tokyo, Japan; Gastrointestinal Oncology Division (K.S.), Medical Oncology Division (N.S.), National Cancer Center Hospital, Genetics Division (T.Y.), National Cancer Center Research Institute, Tokyo, Japan; and Division of Oncology/Hematology (H.M.), Division of Gastrointestinal Oncology/Digestive Endoscopy (A.O.), National Cancer Center Hospital East, Chiba, Japan

UDP-glucuronosyltransferase (UGT) 1A10 is an isoform of UGT1A, which is expressed in extrahepatic, biliary and aerodigestive/gastrointestinal tissues. We have previously reported two nonsynonymous single nucleotide polymorphisms in exon 1 of human UGT1A10 gene; 177G>A and 605C>T resulting in amino acid alterations, M59I and T202I, respectively. In the present study, wild-type (WT) and these variant UGT1A10 cDNAs were transiently expressed in COS-1 cells for functional characterization. Glucuronidation activities in these COS-1 membrane fractions were assayed using 7-hydroxy-4-trifluoromethylcoumarin (HTFMC) and 17-estradiol (E2) as substrates. WT and variant UGT1A10s catalyzed HTFMC glucuronidation with similar apparent K_m values of approximately 5 µM, whereas the V_max value of T202I normalized by the expressed UGT1A10 protein levels was nearly half of those of WT and M59I. High-performance liquid chromatography analysis of E2 glucuronide revealed that UGT1A10 catalyzed E2 3-O-glucuronidation but not 17-O-glucuronidation. Similarly, the three UGT1A10s catalyzed E2 3-O-glucuronidation with comparable apparent K_m values (approximately 2 µM), whereas the normalized V_max value of T202I was almost half that of WT and M59I. These results suggest that the lowered glucuronidation activity of T202I affects the gastrointestinal glucuronidation of orally administrated chemicals and the enterohepatic circulation of biliary excreted metabolites.