UGT1A10 promoter deletion/insertion polymorphisms: Characterization and effects of gene expression.

A136

The extra-hepatic uridine-5'-diphosphate-glucuronosyltransferase 1A10 (UGT1A10) is a member of the UGT1A family of genes located on 2q37 that contain common exons 2-5 with independent first exons. UGT1A10 has been previously shown to be highly active against a number of potent carcinogens including major metabolites of benzo(a)pyrene and NNK and C₁₈ steroids like ß-estradiol. Previous experiments have described important regions of regulation of some of the UGT1A genes including UGT1A10. In the present study, the promoter region of UGT1A10 was examined for polymorphic sequence alterations that may lead to altered expression of the UGT1A10 enzyme. We fully sequenced 2,000 bp upstream of the UGT1A10 translation start site in genomic DNA specimens from 42 individual Caucasian subjects. In addition to a C/G single nucleotide polymorphism (SNP) at -1271 bp and a single thymine deletion in a thymidine repeat region located at -130 to -117 relative to the UGT1A10 translation start site that were previously identified by HapMap, a novel insertion polymorphism of two thymine nucleotides was observed at position -1538 relative to the translation start site. Polymorphic prevalences were calculated for the -1271 C>G (0.17) and the TT_ins (0.07). In addition to these polymorphisms, a 1664 bp deletion located between nucleotides -191 to -1856 relative to the UGT1A10 translation start site was also identified. The presence and characterization of this deletion polymorphism was initially identified by gel electrophoresis of PCR-amplified products and characterized by direct dideoxy sequencing. This deletion had an allelic prevalence of 0.03. This deletion results in a three-fold increase in luciferase expression (p=0.01, Students t-test) as compared to the wild-type promoter in Caco-2 cells, a pattern that is consistent with previous studies demonstrating that a repressor element lies within the region spanning the newly-identified deletion. The identification of this deletion suggests that UGT1A10 may be differentially expressed between individuals and may render these subjects at altered risk for cancer. These results suggest a possible protection phenotype in individuals who contain the deletion polymorphism.