Liver-Enriched Transcription Factors

异源代谢酶负责所有临床使用的药物的代谢和失活。它们还参与毒素、诱变剂和化学致癌物的代谢活化或灭活。在人类中发现这些酶的表达水平存在显著差异，这些差异可能导致对药物和致癌物敏感性的个体间差异。不同基因表达可以解释外源性代谢酶表达水平的差异。这些酶中的大多数在肝脏中表达，并且它们的基因在不同的肝细胞富集的转录因子的控制下。几个转录因子家族优先在肝脏中表达并控制肝脏特异性基因表达。通常，体外技术，包括报告基因构建体的转染和蛋白质-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。确定肝细胞富集因子是否参与调节体内基因表达的研究可以通过使用基因敲除来破坏转录因子的表达，然后确定转录因子丢失对靶基因表达的影响来进行。为了研究肝脏富集的转录因子在控制P450基因表达和参与肝功能的其他基因表达中的作用，正在产生无效小鼠。特别是，需要条件性基因破坏，因为转录因子基因的胚胎破坏经常导致胚胎致死或早期新生儿死亡。使用Cre-loxP方法产生的条件无效小鼠针对转录因子HNF-1 α、HNF-4 α和C/EBPalpha进行开发。观察表型，并使用北方印迹和Western印迹分析确定基因表达模式。这些数据表明，缺乏这些转录因子表达的小鼠发展出严重的表型，包括糖尿病、侏儒症、高胆红素血症、高脂血症和低脂血症。最近的研究正在使用一种新的他莫昔芬激活Cre来产生时间特异性基因敲除模型，以研究肝脏基因控制的代偿机制。

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-enriched 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 protein-DNA binding assays, are used to study gene regulation. However, it is difficult to directly demonstrate that the 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 of 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. In particular, conditional gene disruption is required since embryonic disruption of transcription factor 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-4alpha and C/EBPalpha. Phenotypes are 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, hypercholestemia and hypolipidemia. Recent studies are using an novel tamoxifen-actvating Cre to generate temporal-specific gene knockout models to study compensatory mechanisms of gene control in liver.