QUICK SEARCH:   [advanced] Author: Keyword(s): Year:  Vol:  Page:

This Article Full Text Full Text (PDF) All Versions of this Article: mol.108.045500v1 74/3/744    most recent Submit a response Alert me when this article is cited Alert me when eLetters are posted Alert me if a correction is posted Services Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Google Scholar Articles by Court, M. H. Articles by Williams, J. A. PubMed PubMed Citation Articles by Court, M. H. Articles by Williams, J. A.

Novel Polymorphic Human UDP-glucuronosyltransferase 2A3: Cloning, Functional Characterization of Enzyme Variants, Comparative Tissue Expression, and Gene Induction

Comparative and Molecular Pharmacogenomics Laboratory, Department of Pharmacology and Experimental Therapeutics, Tufts University School of Medicine, Boston, Massachusetts (M.H.C., S.H., S.K.); Drug Discovery and Development Technology Center, Faculty of Pharmacy, University of Helsinki, Helsinki, Finland (M.F.); and Molecular Medicine, Pfizer Global Research and Development, San Diego, California (J.A.W.)

UDP-glucuronosyltransferases (UGTs) are critical to the detoxification of numerous drugs, environmental pollutants, and endogenous molecules. However, as yet not all of the human UGTs have been cloned and characterized. cDNA clones from the UGT2A3 gene (located on chromosome 4q13) were isolated using pooled human liver RNA. Approximately 10% of clones contained a c.1489A>G nucleotide substitution, yielding proteins with a residue 497 alanine (UGT2A3.2) instead of a threonine (UGT2A3.1). The allele frequency of this polymorphism (rs13128286) was 0.13 in a European-American population as determined by direct DNA sequencing. Of 81 structurally diverse glucuronidation substrates tested, UGT2A3 expressed by a baculovirus system selectively glucuronidated bile acids, particularly hyodeoxycholic acid at the 6-hydroxy position. Apparent K_m values of UGT2A3.1 and UGT2A3.2 for hyodeoxycholic acid 6-glucuronidation were 69 ± 7 and 44 ± 12 µM, respectively. Of 29 different extrahepatic tissues evaluated by real-time polymerase chain reaction, UGT2A3 mRNA was most highly expressed in small intestine (160% of liver), colon (78% of liver), and adipose tissue (91% of liver). An in silico scan of the proximal UGT2A3 promoter/5'-regulatory region identified transcription factor consensus elements consistent with tissue-selective expression in liver (HNF1) and intestine (CXD2), as well as induction by rifampicin (pregnane X receptor). In LS180 human intestinal cells, rifampicin increased UGT2A3 mRNA by more than 4.5-fold compared with vehicle, whereas levels were not significantly affected by the arylhydrocarbon receptor ligand β-naphthoflavone. This is the first report establishing UGT2A3 as a functional enzyme, and it represents significant progress toward the goal of having a complete set of recombinant human UGTs for comparative functional analyses.

Address correspondence to: Dr. Michael H. Court, Comparative and Molecular Pharmacogenomics Laboratory, Department of Pharmacology and Experimental Therapeutics, Tufts University, 136 Harrison Ave., Boston, MA 02111. E-mail: michael.court{at}tufts.edu