INHERITED DISORDERS OF HEPATIC BILIRUBIN GLUCURONIDATION

UDP-葡萄糖醛酸基转移酶(UGT)是一类催化 内源性底物，如胆红素和激素的葡萄糖醛酸化 和外源物质，如毒素、致癌物和药物。 葡萄糖醛酸化作用是解毒和消除 胆红素；遗传性胆红素UGT活性缺陷(B-UGT) 结果导致三种程度的高胆红素血症：(I)Crigler-Najjar I型(CN-I)综合征(B-UGT活性完全缺乏， (2)Crigler-Najjar综合征，II型(CN-II) (B-UGT活性不完全缺乏，通常对 和(Iii)吉尔伯特综合征，这是一种常见的轻度疾病， B-UGT活性部分缺乏。B-UGT活性不成熟是一种 新生儿黄疸的重要原因。两种形式的B-UGT的mRNA 而对于另一种形式，其活性指向酚类底物 (P-UGT)由一系列外显子组成的一个基因座表达 编码这些UGT和四个外显子的独特的NH2末端区域 编码它们相同的COOH-末端区域。我们将确定DNA 导致CN-I的结构异常。在新生儿黄褐症和在 CN-II和Gilbert综合征，缺陷可能是在调节 UGT的表达。虽然单基因座的表达产物， B-UGT和P-UGT在发育过程中差异表达，在 不同组织和给药后的异构体特异性诱导 探员们。以确定该基因差异表达的机制 B-UGT和P-UGT，我们将识别和表征监管要素 存在于每个独特区域的上游，也可能在基因内 DNase I超敏反应和甲基化分析。装订 调控元件的位置将通过DNA酶足迹进行本地化， 甲基化干扰和迁移率改变分析。在患有 B-UGT活性部分缺乏(CN-II和Gilbert综合征) 异常可能存在于监管要素中。因此，顺序为 CN-II和吉尔伯特综合征的这些区域将被确定。功能 的调控元件将使用报告基因进行评估， 受体介导的体外转录分析和体内跟踪 靶向大鼠肝细胞。转录的可能作用 调节蛋白对细胞功能的增强或抑制作用 发育和酶诱导过程中的调节元件将是 通过体外转录分析确定。国家地理信息系统 这个独特复杂基因的多种UGT亚型的表达 应该阐明哺乳动物基因的重要和新颖的方面 表情。高胆红素血症患者及其家属的研究 成员将提供简单的非侵入性基因诊断方法， 包括产前诊断，并将澄清分子基础 遗传性胆红素葡萄糖醛酸化障碍。

UDP-glucuronosyltransferases (UGTs) are a family of enzymes that catalyze the glucuronidation of endogenous substrates, e.g. bilirubin and hormones and exogenous substances, e.g. toxins, carcinogens and drugs. Glucuronidation is critical for detoxication and elimination of bilirubin; inherited deficiencies of bilirubin-UGT (B-UGT) activity results in three grades of hyperbilirubinemia: (i) Crigler-Najjar syndrome, Type I (CN-I) (complete deficiency of B-UGT activity, potentially lethal); (ii) Crigler-Najjar syndrome, Type II (CN-II) (incomplete deficiency of B-UGT activity, usually responsive to phenobarbital) and (iii) Gilbert syndrome, a common mild disorder with partial deficiency of B-UGT activity. Immaturity of B-UGT activity is an important cause of neonatal jaundice. The mRNAs for two forms of B-UGT and that for another form with activity toward phenolic substrates (P-UGT) are expressed from one locus consisting of a series of exons encoding the unique NH2 terminal regions of these UGTs and four exons encoding their identical COOH-terminal region. We will determine the DNA structural abnormality that results in CN-I. In neonatal jaundice and in CN-II and Gilbert syndrome, the defect may be in the regulation of expression of UGTs. Although expression products of a single locus, B-UGT and P-UGT are differentially expressed during development, in various tissues and after administration of isoform-specific inducing agents. To determine the mechanism of the differential expression of the B-UGTs and P-UGT, we will identify and characterize regulatory elements present upstream of each unique region and also possibly at intragenic sites, by DNase I hypersensitivity and methylation analysis. Binding sites for regulatory elements will be localized by DNase foot-printing, methylation interference and mobility shift assays. In patients with partial deficiency of B-UGT activity (CN-II and Gilbert syndrome) the abnormality may lie in the regulatory elements. Therefore, sequence of these regions of CN-II and Gilbert syndrome will be determined. Function of the regulatory elements will be evaluated using reporter genes by in vitro transcription analysis and in vivo following receptor-mediated targeting to hepatocytes in rats. Possible role of transcription regulatory proteins on the enhancing or repressing the function of regulatory elements during development and enzyme induction will be determined by in vitro transcription analysis. Delineation of the expression of the multiple UGT isoforms from this uniquely complex gene should elucidate important and novel aspects of mammalian gene expression. Study of the hyperbilirubinemic patients and their family members will provide simple non-invasive methods for genotypic diagnosis, including prenatal diagnosis, and will clarify the molecular basis of inherited disorders of bilirubin glucuronidation.