Original ArticlesIdentification and functional characterization of UDP-glucuronosyltransferases UGT1A8*1, UGT1A8*2 and UGT1A8*3Huang, Yue-Huaa; Galijatovic, Alemaa; Nguyen, Nghiaa; Geske, Donalda; Beaton, Deirdrea; Green, Juditha; Green, Marka; Peters, Wilbert H.b; Tukey, Robert H.aAuthor Information aLaboratory of Environmental Toxicology, Department of Chemistry and Biochemistry and Pharmacology, Cancer Center, University of California, San Diego, La Jolla, California, USA and bDepartment of Gastroenterology, St Radbound University Hospital, Nijmegen, The Netherlands Correspondence to Robert H. Tukey, PhD, Department of Chemistry and Biochemistry and Pharmacology, UCSD, La Jolla, CA 92093-0636, USA Tel: +1 858 8220288; fax: +1 858 8220363; e-mail: [email protected] Received 27 December 2001 Accepted 13 February 2002 Pharmacogenetics: June 2002 - Volume 12 - Issue 4 - p 287-297 Buy Abstract UDP-glucuronosyltransferase (UGT) 1A8 is part of the UGT1 locus and is expressed exclusively in extrahepatic tissues. Analysis of UGT1A8 exon 1 sequence has identified four genotypes from a population of 69 individuals. While there are four alleles, one of the single base pair changes leads to a silent mutation at T255, while the other mutations lead to amino acid substitutions at positions 173 and 277, creating three allelic variants. UGT1A8*1 (A173C277), UGT1A8*1a (T255A > G), UGT1A8*2 (G173C277) and UGT1A8*3 (A173Y277). The allelic frequencies of UGT1A8*1, UGT1A8*1a, UGT1A8*2 and UGT1A8*3 are 0.551, 0.282, 0.145 and 0.022, respectively. To examine the properties of the UGT1A8 proteins, UGT1A8*1 and UGT1A8*2 were cloned from a human colon cDNA library and UGT1A8*3 generated by mutagenesis using UGT1A8*1 as template. The cDNAs were expressed in HK293 cells to examine catalytic function as well as abundance as observed by analysis of UGT1A8-GFP (green fluorescent protein) expression. The single amino acid change that identifies UGT1A8*1 (A173) and UGT1A8*2 (G173) has little impact on function, while the UGT1A8*3 (Y277) is a conserved amino acid alteration represented by a dramatic reduction in catalytic activity. Protein abundance, as determined by Western blot analysis following transient transfection, is not altered. In addition, functional UGT1A8-GFP variants displayed staining in the cytoplasmic region, indicating that each protein is expressed in similar cellular compartments. Together, these data suggest that the null UGT1A8*3 results from structural changes and not a lack of protein expression. Allelic variation leading to singular codon changes could potentially alter drug metabolism in extrahepatic tissues. © 2002 Lippincott Williams & Wilkins, Inc.