Six novel UDP-glucuronosyltransferase (UGT1A3) polymorphisms with varying activity

Abstract

Human UDP-glucuronosyltransferase (UGT) is a part of a major excretion pathway for endobiotics and xenobiotics. The UGT family of genes is highly polymorphic, and our aim is to describe novel polymorphisms at the UGT1A3 locus and determine how they alter substrate metabolism and drug reactions. One hundred healthy Japanese adults volunteered for the present study. We sequenced PCR-amplified fragments of the gene directly, and calculated the frequency of the genetic variations detected. To measure variant enzyme activity, we constructed five expression models and used estrone as the substrate in the assays. We identified six novel single nucleotide polymorphisms (SNPs). Of these, four caused amino acid substitutions (17A fi G: Q6R, 31T fi C: W11R, 133C fi T: R45W, and 140T fi C: V47A) and the remaining two were silent (81G fi A: E27E and 447A fi G: A159A). We found five types of alleles having differing SNP combinations: wild type (frequency=0.61), W11R-E27E-A159A (0.10), Q6A-W11R-E27E-A159A (0.055), W11R-E27E-V47A-A159A (0.125), and R45W (0.11). Expression studies found that the variants changed the enzyme efficiencies (K m /V max ) to 121% of the wild type for W11R, 86% for Q6R-W11R, 369% for W11R-V47A, and 70% for R45W. Several UGT 1A3 polymorphisms exist in the Japanese population, having different levels of activity. These polymorphisms are capable of affecting the steady state levels of estrogens, and may increase sensitivity to adverse drug effects.

The Urinary Metabolite Profile of the Dietary Carcinogen 2-Amino-1-Methyl-6-Phenylimidazo[4,5-b]Pyridine Is Predictive of Colon DNA Adducts after a Low-Dose Exposure in Humans

“…Subjects 8 and 10 also had rapid excretion rates of N-hydroxyPhIP-N 2 -glucuronide, although these individuals were categorized as having a slow CYP1A2 phenotype. These two subjects, however, did have a UGT1A3*3 genotype, 4 which is associated with increased expression of UGT1A3 (40). The increased expression of UGT1A3 could have contributed to an increase in the formation of Nhydroxy-PhIP-N 2 -glucuronide (35).…”

Uridine diphosphoglucuronosyltransferase pharmacogenetics and cancer

“…Table 2 summarizes some functionally relevant UGT1A3 polymorphisms. The allele frequencies reported in two independent studies are similar, despite the different populations characterized in each study (Ehmer et al, 2004;Iwai et al, 2004). Iwai et al (2004) reported six single-nucleotide polymorphisms (SNPs) in exon 1 of UGT1A3.…”

“…The allele frequencies reported in two independent studies are similar, despite the different populations characterized in each study (Ehmer et al, 2004;Iwai et al, 2004). Iwai et al (2004) reported six single-nucleotide polymorphisms (SNPs) in exon 1 of UGT1A3. Several mutants were expressed in COS-7 cells, and it was determined that contrary to several UGT mutants with diminished activity, the UGT1A3 variants W11R and W11R þ V47A exhibited much greater activity toward estrone than the wild type.…”

Haplotype structures of the UGT1A gene complex in a Japanese population

“…These are similar to the previous data obtained from the Japanese. 22 Recently, linkages among the SNPs in 1A9, 1A7, 1A6, and 1A1 have been reported in Americans. 18 By our LD analysis, strong linkages were shown between the SNPs in 1A8 and 1A10, among those in 1A9, 1A7, and 1A6, and also between those in 1A3 and 1A1.…”