Yueh Mei-Fei, Huang Yue-Hua, Hiller Anita, Chen Shujuan, Nguyen Nghia, Tukey Robert H
Departments of Pharmacology, Chemistry & Biochemistry, Laboratory of Environmental Toxicology, University of California San Diego, La Jolla, California 92093-0636, USA.
J Biol Chem. 2003 Apr 25;278(17):15001-6. doi: 10.1074/jbc.M300645200. Epub 2003 Feb 3.
UDP-glucuronosyltransferase 1A1 (UGT1A1) plays an important physiological role by contributing to the metabolism of endogenous substances such as bilirubin in addition to xenobiotics and drugs. The UGT1A1 gene has been shown to be inducible by nuclear receptors steroid xenobiotic receptor (SXR) and the constitutive active receptor, CAR. In this report, we show that in human hepatoma HepG2 cells the UGT1A1 gene is also inducible with aryl hydrocarbon receptor (Ah receptor) ligands such as 2,3,7,8-tetrachlodibenzo-p-dioxin (TCDD), beta-naphthoflavone, and benzo[a]pyrene metabolites. Induction was monitored by increases in protein and catalytic activity as well as UGT1A1 mRNA. To examine the molecular interactions that control UGT1A1 expression, the gene was characterized and induction by Ah receptor ligands was regionalized to bases -3338 to -3287. Nucleotide sequence analysis of this UGT1A1 enhancer region revealed a xenobiotic response element (XRE) at -3381/-3299. The dependence of the XRE on UGT1A1-luciferase activity was demonstrated by a loss of Ah receptor ligand inducibility when the XRE core region (CACGCA) was deleted or mutated. Gel mobility shift analysis confirmed that TCDD induction of nuclear proteins specifically bound to the UGT1A1-XRE, and competition experiments with Ah receptor and Arnt antibodies demonstrated that the nuclear protein was the Ah receptor. These observations reveal that the Ah receptor is involved in human UGT1A1 induction.
尿苷二磷酸葡萄糖醛酸基转移酶1A1（UGT1A1）除了参与外源性物质和药物的代谢外，还通过促进内源性物质如胆红素的代谢发挥重要的生理作用。UGT1A1基因已被证明可被核受体类固醇异生素受体（SXR）和组成型活性受体CAR诱导。在本报告中，我们表明在人肝癌HepG2细胞中，UGT1A1基因也可被芳烃受体（Ah受体）配体如2,3,7,8 - 四氯二苯并 - p - 二恶英（TCDD）、β - 萘黄酮和苯并[a]芘代谢物诱导。通过蛋白质和催化活性以及UGT1A1 mRNA的增加来监测诱导情况。为了研究控制UGT1A1表达的分子相互作用，对该基因进行了表征，并将Ah受体配体的诱导定位到 - 3338至 - 3287碱基区域。对该UGT1A1增强子区域的核苷酸序列分析揭示了位于 - 3381 / - 3299处的一个异生素反应元件（XRE）。当XRE核心区域（CACGCA）被缺失或突变时，Ah受体配体诱导性丧失，这证明了XRE对UGT1A1 - 荧光素酶活性的依赖性。凝胶迁移率变动分析证实TCDD诱导的核蛋白特异性结合到UGT1A1 - XRE，并且用Ah受体和Arnt抗体进行的竞争实验表明该核蛋白是Ah受体。这些观察结果揭示Ah受体参与了人UGT1A1的诱导。
