INHERITED DISORDER OF HEPATIC BILIRUBIN GLUCURONIDATION

UDP-葡萄糖醛酸基转移酶（UGT）是催化葡萄糖醛酸转移的酶家族。 内源性底物（如胆红素和激素）的葡萄糖醛酸化 和外源性物质，例如毒素、致癌物质和药物。 葡萄糖醛酸化对于解毒和消除 胆红素;遗传性胆红素-UGT活性缺乏 导致三个等级的高胆红素血症：（i）Crigler-Najjar 综合征，I型（CN-I）（B-UGT活性完全缺乏， 潜在致死）;（ii）Crigler-Najjar综合征，II型（CN-II） （B-UGT活性不完全缺乏，通常对以下反应有反应： 苯巴比妥）和（iii）吉尔伯特综合征，一种常见的轻度疾病， B-UGT活性部分缺乏。 B-UGT活性的不成熟是一种 新生儿黄疸的重要原因。 两种形式的B-UGT的mRNA 而另一种对酚类底物具有活性的形式 （P-UGT）从由一系列外显子组成的一个基因座表达 编码这些UGT的独特NH 2末端区域和四个外显子 编码相同的COOH末端区域。 我们会确定DNA 导致CN-1的结构异常。 在新生儿黄疸和 CN-Ⅱ和吉尔伯特综合征，缺陷可能是在调节 UGT的表达。 尽管表达产物是单个基因座的， B-UGT和P-UGT在发育过程中差异表达， 各种组织和给予同种型特异性诱导后 剂. 为了确定差异表达的机制， B-UGT和P-UGT，我们将识别和表征调控元件 存在于每个独特区域的上游，也可能存在于基因内 位点，通过DNase I超敏反应和甲基化分析。 结合 调节元件的位点将通过DNA酶足迹法定位， 甲基化干扰和迁移率改变分析。 患者 B-UGT活性部分缺乏（CN-II和吉尔伯特综合征）， 异常可能在于调节元件。 因此， 将确定CN-II和吉尔伯特综合征的这些区域。 功能 的调控元件将使用报告基因进行评估， 体外转录分析和体内受体介导的 靶向大鼠肝细胞。 转录的可能作用 调节蛋白对增强或抑制 在发育和酶诱导过程中的调节元件将被 通过体外转录分析确定。 划定 从这个独特的复杂基因表达多种UGT同工型 应该阐明哺乳动物基因重要和新的方面， 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型诊断方法， 包括产前诊断，并将澄清的分子基础， 胆红素葡萄糖醛酸化的遗传性疾病。

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.