Fang Jia-Long, Lazarus Philip
Department of Interdisciplinary Oncology, H. Lee Moffitt Cancer Center, University of South Florida, Tampa, Florida, USA.
Cancer Epidemiol Biomarkers Prev. 2004 Jan;13(1):102-9. doi: 10.1158/1055-9965.epi-03-0070.
Of the hepatic UDP-glucuronosyltransferases (UGTs), only UGT1A1 and UGT1A9 exhibit activity against benzo(a)pyrene-trans-7R,8R-dihydrodiol [BPD(-)], precursor to the highly mutagenic anti-(+)-benzo(a)pyrene-7R,8S-dihydrodiol-9S,10R-epoxide. The UGT1A128 allelic variant contains an additional (TA) dinucleotide repeat in the "TATAA" box [(TA)(6)>(TA)(7)] of the UGT1A1 promoter that has been linked to decreased expression of the UGT1A1 gene and decreased bilirubin conjugation, leading to the relatively nondebilitating condition known as Gilbert's syndrome. To determine whether the UGT1A1 TATAA box polymorphism may play a role in the overall glucuronidation of BPD(-) in humans, we compared UGT1A1 TATAA box genotype with BPD(-) glucuronidating activity in normal liver microsomes. Significant decreases in UGT1A1 protein (P < 0.005) and bilirubin conjugation activity (P < 0.001) were observed in liver microsomes from subjects homozygous for the UGT1A128 allelic variant compared with subjects homozygous for the wild-type UGT1A1*1 allele. Significant decreases in BPD(-) glucuronidation activity (P < 0.02) were observed in subjects with the UGT1A1(*28/*28) genotype compared with subjects having the wild-type UGT1A1(*1/*1) genotype in assays of liver microsomes that included 0.1 mM alpha-naphthylamine, a competitive inhibitor of UGT1A9 and not UGT1A1. Similar phenotype:genotype correlations were observed when we compared subjects with the UGT1A1(*28/*28) genotype with subjects having the UGT1A1(*1/*28) genotype. In assays with alpha-naphthylamine, the K(m) of liver microsomes against BPD(-) was similar to that reported for UGT1A1-overexpressing baculosomes (319 micro M versus 290 micro M; Fang et al., Cancer Res., 62: 1978-1986, 2002). These data suggest that the UGT1A1 TATAA box polymorphism plays a role in an individual's overall ability to detoxify benzo(a)pyrene and in cancer risk.
在肝脏UDP-葡糖醛酸基转移酶（UGTs）中，只有UGT1A1和UGT1A9对苯并(a)芘反式-7R,8R-二氢二醇[BPD(-)]具有活性，BPD(-)是高致突变性的反式-(+)-苯并(a)芘-7R,8S-二氢二醇-9S,10R-环氧化物的前体。UGT1A128等位基因变体在UGT1A1启动子的“TATAA”框[(TA)(6)>(TA)(7)]中含有一个额外的(TA)二核苷酸重复序列，该重复序列与UGT1A1基因表达降低和胆红素结合减少有关，导致相对不严重的吉尔伯特综合征。为了确定UGT1A1 TATAA框多态性是否可能在人类BPD(-)的整体葡糖醛酸化中起作用，我们比较了正常肝微粒体中UGT1A1 TATAA框基因型与BPD(-)葡糖醛酸化活性。与野生型UGT1A11等位基因纯合子受试者相比，UGT1A1*28等位基因变体纯合子受试者的肝微粒体中UGT1A1蛋白（P < 0.005）和胆红素结合活性（P < 0.001）显著降低。在包含0.1 mM α-萘胺（UGT1A9而非UGT1A1的竞争性抑制剂）的肝微粒体测定中，与野生型UGT1A1(*1/*1)基因型受试者相比，UGT1A1(*28/*28)基因型受试者的BPD(-)葡糖醛酸化活性显著降低（P < 0.02）。当我们将UGT1A1(*28/*28)基因型受试者与UGT1A1(*1/*28)基因型受试者进行比较时，观察到了类似的表型与基因型相关性。在α-萘胺测定中，肝微粒体对BPD(-)的K(m)与报道的过表达UGT1A1的杆状病毒体的K(m)相似（319 μM对290 μM；Fang等人，《癌症研究》，62: 1978 - 1986, 2002）。这些数据表明，UGT1A1 TATAA框多态性在个体对苯并(a)芘的整体解毒能力和癌症风险中起作用。
