GENETIC-POLYMORPHISM IN THE HUMAN UGT1A6 (PLANAR PHENOL) UDP-GLUCURONOSYLTRANSFERASE - PHARMACOLOGICAL IMPLICATIONS

Two missense mutations were uncovered in the UGT1A6 (HLUG P1) cDNA whi ch codes for a human phenol-metabolizing UDP-glucuronosyltransferase. The mutant and a wild-type UGT1A6 cDNAs were isolated from a custom sy nthesized human liver lambda Zap cDNA library. Both an A to G transiti on 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 ge notype. Newly created BsmI and BsoFI sites at the T181 A and R184S loc ations, respectively, were confirmed by endonuclease treatment of PCR- generated DNA using the donor-liver genomic DNA as template. Screens w ith endonuclease treatment showed that 33/98 DNA samples were heterozy gous with both mutations on one allele. One other individual also carr ied the R184S mutation on the second allele. Wild-type UGT1A6 generate d a broad plateau of activity from pH 5.0 to pH 8.0 with certain exper imental phenols, while activity was 1.3-2.5-fold higher at pH 6.4 than at pH 7.2 for others. UGT1A62 (181 A+ and 184S+) metabolized 4-nitro phenol, 4-tert-butylphenol, 3-ethylphenol/4-ethylphenol, 4-hydroxycoum arin, butylated hydroxy anisole and butylated hydroxy toluene, with th e pH 6.4 preference, at only 27-75% of the rate of the wild-type isozy me whereas 1-naphthol, 3-iodophenol, 7-hydroxycoumarin, and 7-hydroxy- 4-methylcoumarin were metabolized at essentially the normal level. Fur thermore, UGT1A62 metabolized 3-O-methyl-dopa and methyl salicylate a t 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 enzym e activity is affected by different amino acids depending upon the sub strate selection.