Genetic polymorphism in the human UGT1A6 (planar phenol) UDP-glucuronosyltransferase: pharmacological implications.
Two missense mutations were uncovered in the UGT1A6 (HLUG P1) cDNA which codes for a human phenol-metabolizing UDP-glucuronosyltransferase. The mutant and a wild-type UGT1A6 cDNAs were isolated from a custom synthesized human liver lambda Zap cDNA library. Both an A to G transition at nucleotide 541 (T181 A) and an A to C transversion at nucleotide 552 (R184S) occurred in exon 1 of the UGT1A6 (UGT1F) gene at the UGT1 locus. The two mutations on a single allele created a heterozygous genotype. Newly created BsmI and BsoFI sites at the T181 A and R184S locations, respectively, were confirmed by endonuclease treatment of PCR-generated DNA using the donor-liver genomic DNA as template. Screens with endonuclease treatment showed that 33/98 DNA samples were heterozygous with both mutations on one allele. One other individual also carried the R184S mutation on the second allele. Wild-type UGT1A6 generated a broad plateau of activity from pH 5.0 to pH 8.0 with certain experimental phenols, while activity was 1.3-2.5-fold higher at pH 6.4 than at pH 7.2 for others. UGT1A6*2 (181 A+ and 184S+) metabolized 4-nitrophenol, 4-tert-butylphenol, 3-ethylphenol/4-ethylphenol, 4-hydroxycoumarin, butylated hydroxy anisole and butylated hydroxy toluene, with the pH 6.4 preference, at only 27-75% of the rate of the wild-type isozyme whereas 1-naphthol, 3-iodophenol, 7-hydroxycoumarin, and 7-hydroxy-4-methylcoumarin were metabolized at essentially the normal level. Furthermore, UGT1A6*2 metabolized 3-O-methyl-dopa and methyl salicylate at 41-74% of that of the wild-type, and a series of beta-blockers at 28-69% of the normal level. This evidence suggests that the UGT1A6 enzyme activity is affected by different amino acids depending upon the substrate selection.
Ciotti
M
M
Heritable Disorders Branch, National Institute of Child Health and Human Development, Bethesda, MD 20892-1830, USA.
Marrone
A
A
Potter
C
C
Owens
I S
IS
D000483:Alleles; D019943:Amino Acid Substitution / Q000235:genetics; D000818:Animals; D019556:COS Cells; D005787:Gene Frequency; D005820:Genetic Testing; D005965:Glucuronates / Q000378:metabolism; D014453:Glucuronosyltransferase / Q000096:biosynthesis / Q000235:genetics* / Q000378:metabolism; D006801:Humans; D007536:Isomerism; D009154:Mutation; D010636:Phenols / Q000378:metabolism; D011110:Polymorphism, Genetic
D005965:Glucuronates; D010636:Phenols; D014453:Glucuronosyltransferase