A pharmacogenomics study of the human estrogen glucuronosyltransferase UGT1A3.
UGT1A3 is one of the most efficient at conjugating estrone, a precursor for biosynthesis of estradiol in peripheral tissues. We established the genetic mechanisms that might contribute to individual variation in UGT1A3 expression and activity. UGT1A3 first exon and 5'-flanking regions were sequenced in 249 Caucasians. We identified 17 polymorphisms, among them seven regulatory and 10 exonic polymorphisms with six leading to amino-acid changes. Luciferase reporter assays, site-directed mutagenesis and electrophoretic mobility shift assays using hepatoma HepG2 cells were carried out to show functionality of variant promoters. Reduced transcriptional activity was associated with all six variant promoters (two-fold; P<0.001). One of the potential mechanisms would involve the -148 T>C and -581 C>T variations that modulate gene function by affecting hepatocyte nuclear factor-1alpha and hepatocyte nuclear factor-4alpha binding, respectively. Then, estrone-conjugating activity was assessed with 11 heterologously expressed allozymes. Three phenotypes were observed; UGT1A3*1, *2 (WR, VA) and *3 (WR) with high intrinsic clearance values; UGT1A3*5 (QR, WR), *7 (FI), *9 (WR, ML), *10 (VA) and *11 (WR, VA and MI) had intermediate CLint (2X-10X lower vs. *1), whereas UGT1A3*4 (RW), *6 (WR, VA, MV) and *8 (AV) had low CLint (>10X lower vs. *1). Diplotype analyses indicate that 20.1% of individuals carry two alleles affecting UGT1A3 expression and/or activity. This study did not investigate genotype-phenotype association, but raise the possibility that genetically determined variation might contribute to variability in the inactivation of estrone by UGT1A3 and subsequent changes in lifetime exposure to estrogens potentially modifying risk of cancer.
Caillier
Bertrand
B
Laboratory of Pharmacogenomics, Oncology and Molecular Endocrinology Research Center, CHUQ Research Center and Faculty of Pharmacy, Laval University, Québec, Canada.
Lépine
Johanie
J
Tojcic
Jelena
J
Ménard
Vincent
V
Perusse
Louis
L
Bélanger
Alain
A
Barbier
Olivier
O
Guillemette
Chantal
C
D024506:5' Flanking Region; D001483:Base Sequence; D002460:Cell Line; D004247:DNA / Q000235:genetics / Q000378:metabolism; D004970:Estrone / Q000378:metabolism; D005091:Exons; D005260:Female; D014644:Genetic Variation; D014453:Glucuronosyltransferase / Q000235:genetics* / Q000378:metabolism*; D006239:Haplotypes; D006801:Humans; D007700:Kinetics; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D010597:Pharmacogenetics; D010641:Phenotype; D011110:Polymorphism, Genetic; D011401:Promoter Regions, Genetic; D011485:Protein Binding; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D044465:White People / Q000235:genetics
D011994:Recombinant Proteins; D004970:Estrone; D004247:DNA; C122075:UDP-glucuronosyltransferase, UGT1A3; D014453:Glucuronosyltransferase