TRANSCRIPTIONAL REGULATION OF GENES ENCODING XENOBIOTIC METABOLIZING ENZYMES

异源生物代谢酶负责代谢和 停用所有临床使用的药物。他们还参与了 毒素、诱变剂和化学物质的代谢激活或失活 致癌物质。这些酶的表达水平有显著差异 已经在人类身上发现，这些差异可能有助于 药物和致癌物敏感性的个体间差异。 可变的基因表达可以解释水平的一些差异 外源代谢酶的表达。大多数这些酶 在肝脏中表达，它们的基因受到 不同的肝细胞转录因子。几个家族 转录因子优先在肝脏和 控制肝脏特异性基因的表达。通常，在体外技术中， 包括报告基因构建体的转染和DNA结合 检测，是用来研究基因调控的。然而，很难做到 直接证明了使用体外研究获得的结果 实际上反映了完好无损的动物的基因表达。研究到 确定富含肝细胞的因子是否参与调节 体内的基因表达可以通过使用基因敲除来干扰 转录因子的表达，然后确定其影响 转录因子缺失对靶基因表达的影响。然而，标准 转录因子的基因敲除通常会导致 胚胎前或胚胎后的致命性。为了绕过这个问题，老鼠 缺乏转录因子的表达是使用 Cre/loxP条件基因敲除系统。含有重组基因的小鼠 C/EBPalpha基因两侧的信号loxP已经产生并展示 正常表型表明loxP位点不干扰 基因表达。将Cre重组酶引入成年小鼠体内 包含loxP修饰的C/EBPalpha等位基因的重组 产生90%重组和缺失C/EBPalpha的腺病毒 肝脏中的基因。这导致了几个靶标的表达缺失 包括UDP-葡萄糖醛酸基转移酶UGT1在内的基因负责 胆红素结合物。编码外源基因的其他基因的表达- 正在分析代谢酶。

Xenobiotic-metabolizing enzymes are responsible for metabolism and inactivation of all clinically used drugs. They are also involved in the metabolic activation or inactivation of toxins, mutagens and chemical carcinogens. Marked differences in levels of expression of these enzymes have been found in humans and these differences could contribute to interindividual differences in sensitivities to drugs and carcinogens. Variable gene expression could account for some differences in levels of expression of xenobiotic-metabolizing enzymes. Most of these enzymes are expressed in the liver and their genes are under control of different hepatocyte transcription factors. Several families of transcription factors are preferentially expressed in the liver and control liver-specific gene expression. Typically, in vitro techniques, including transfections of reporter gene constructs and DNA binding assays, are used to study gene regulation. However, it is difficult to directly demonstrate that results obtained using in vitro studies actually reflect gene expression in the intact animal. Studies to determine whether hepatocyte-enriched factors are involved in regulating gene expression in vivo can be done by using gene knockouts to disrupt expression of transcription factors and then determine the effects transcription factor loss on target gene expression. However, standard gene knockouts of transcription factors frequently results in either pre- or post-embryonic lethality. To circumvent this problem, mice lacking transcription factor expression are being produced using the Cre/LoxP conditional knockout system. Mice containing the recombination signal LoxP flanking the C/EBPalpha gene have been produced and exhibit normal phenotypes indicating that the LoxP sites do not interfere with gene expression. The Cre recombinase was introduced to adult mice containing the LoxP-modified C/EBPalpha allele using a recombinant adenovirus yielding 90% recombination and deletion of the C/EBPalpha gene in liver. This resulted in loss of expression of several target genes including the UDP-glucuronosyltransferase, UGT1, responsible for conjugation of bilirubin. Expression of other genes encoding xenobiotic- metabolizing enzymes are being analyzed.