Function of Hepatocyte-enriched Transcription Factors

外源代谢酶负责所有临床使用药物的代谢和失活。它们还参与毒素、诱变剂和化学致癌物的代谢激活或失活。这些酶的表达水平在人类中存在显著差异，这些差异可能导致对药物和致癌物敏感性的个体差异。基因表达的变化可以解释异种代谢酶表达水平的一些差异。这些酶大多在肝脏中表达，它们的基因受不同肝细胞转录因子的控制。几个转录因子家族在肝脏中优先表达，并控制肝脏特异性基因的表达。通常，体外技术，包括报告基因构建的转染和DNA结合测定，用于研究基因调控。然而，很难直接证明使用体外研究获得的结果实际上反映了完整动物中的基因表达。研究肝细胞富集因子是否参与体内基因表达调控，可以通过基因敲除破坏转录因子的表达，进而确定转录因子缺失对靶基因表达的影响。为了研究富肝转录因子在控制P450基因表达和其他与肝功能有关的基因表达中的作用，我们正在制造空小鼠。有条件的基因破坏是必需的，因为转录事实基因的狭窄胚胎破坏经常导致胚胎致死或早期新生儿死亡。使用Cre-LoxP方法制备条件无效小鼠，用于转录因子HNF-1alpha， HNF-4和C/EBPalpha。使用Northern blot和Western blot分析观察表型和基因表达模式。这些数据表明，缺乏这些转录因子表达的小鼠会出现严重的表型，包括糖尿病、侏儒症、高胆红素血症和低血脂。

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. To investigate the role of liver-enriched transcription factors in control of P450 gene expression and expression of other genes involved in liver function, null mice are being produced. Conditional gene disruption is required since strait embryonic disruption of transcription facto genes frequently results in embryonic lethality or early neonatal death. Conditional-null mice produced using the Cre-LoxP method were developed for the transcription factors HNF-1alpha, HNF-4 and C/EBPalpha. Phenotypes were observed and gene expression patterns determined using Northern blot and Western blot analyses. The data indicate that mice lacking expression of these transcription factors develop severe phenotypes including diabetes, dwarfism, hyperbilirubinemia, hypolipidemia.