Personne : Guillemette, Chantal
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Guillemette
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Chantal
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Université Laval. Faculté de pharmacie
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ncf13674031
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Publication Accès libre UGT genomic diversity : beyond gene duplication(Informa Healthcare, 2009-10-26) Lévesque, Éric; Bellemare, Judith.; Harvey, Mario.; Ménard, Vincent; Guillemette, ChantalThe human uridine diphospho (UDP)-glucuronosyltransferase (UGT) superfamily comprises enzymes responsible for a major biotransformation phase II pathway: the glucuronidation process. The UGT enzymes are located in the endoplasmic reticulum of almost all tissues, where they catalyze the inactivation of several endogenous and exogenous molecules, including bilirubin, sex steroids, numerous prescribed drugs, and environmental toxins. This metabolic pathway is particularly variable. The influence of inheritable polymorphisms in human UGT-encoding genes has been extensively documented and was shown to be responsible for a fraction of the observed phenotypic variability. Other key genomic processes are likely underlying this diversity; these include copy-number variations, epigenetic factors, and newly discovered splicing mechanisms. This review will discuss novel molecular aspects that may be determinant to UGT phenotypes.Publication Accès libre A pharmacogenetics study of the human glucuronosyltransferase UGT1A4(Lippincott Williams & Wilkins, 2009-12-01) Benoît-Biancamano, Marie-Odile; Leblanc, Marie-Hélène; Bernard, Olivier; Court, Michael H.; Guillemette, Chantal; Caron, Patrick; Adam, Jean-PhilippeUGT1A4 is primarily expressed in the liver and exhibits catalytic activities for various drugs. Amongst the few UGT1A4 polymorphisms evaluated, studies support the alteration of UGT1A4-mediated glucuronidation by a few variations including the Pro24Thr and Leu48Val variants (referred to as UGT1A4*2 and *3). We therefore investigated genetic mechanisms that might contribute to interindividual variation in UGT1A4 expression and activity. The UGT1A4 gene was sequenced from -4963 bp relative to the ATG to 2000 bp after the first exon in 184 unrelated Caucasians and African-Americans. We identified a large number of genetic variations, including 13 intronic, 39 promoter, as well as 14 exonic polymorphisms, with 10 that lead to aminoacid changes. Of the nucleotide variations found in the -5kb promoter region, 5 are located in the proximal region (first 500 bp), and positioned in putative HNF-1 and OCT-1 binding sites. Four of these variants, placed at -163, -219, -419 and -463, are in complete linkage disequilibrium with the Leu48Val coding region variant and with several variants in the upstream region of the promoter. Transient transfections of reference and variant promoter constructs (from position -500 to +1) in different cell lines with or without co-expression of HNF-1 and/or OCT-1, demonstrated limited effect of these variations. However, several coding variants significantly modified the enzyme kinetics for tamoxifen and Z-4-hydroxytamoxifen (Val48, Asp50, Gln56, Phe176, Asn250, Leu276). Our results reveal that, despite a large number of polymorphisms located in the promoter region, the exonic variants are those expected to have a potential in vivo effect.