Pharmacogenetics Of Microsomal Steroid Hydroxylases

工作概述：细胞色素P450和特定转移酶的代谢是抵御环境毒物和致癌物的一种防御系统。P450和转移酶基因在遇到结构不同的外来化学物质时，能够被诱导以响应化学物质的暴露，并提高它们的代谢能力。找到诱导机制对于我们预测人类对辐射的易感性至关重要。苯巴比妥(PB)是诱导P450和转移酶基因集的大量化学物质的原型。我们现在已经将在这些基因(在小鼠、大鼠和人类中)中发现的保守的51个碱基对的DNA定义为PB反应增强模块或PBREM。我们还鉴定了核孤儿受体CAR，它能在PB诱导下激活PBREM。在CAR功能受损的大鼠中，包括基因工程CAR缺失的小鼠，发现PB诱导存在缺陷。除了众多的PB型诱导剂外，内源性类固醇激素还调节受体CAR；雌激素是激活剂，而雄激素和孕激素是阻滞剂。CAR是一种非诱导性肝细胞胞浆受体，在PB处理后移位到细胞核。胞浆CAR复合体招募蛋白质磷相2A进行核转位。建立了内源性CAR在肝细胞中表达的系统，我们发现C端的LXXLXXL序列调控着PB诱导的CAR的核转位。

Summary of Work: Metabolism by cytochromes P450 and specific transferases is a defense system against environmental toxicants and carcinogens. To encounter virtually unlimited numbers of structurally diverse xenochemicals, P450 and transferase genes are capable of being induced in response to chemical exposures and increase their metabolic capability. Finding the induction mechanism is critical for our ability to predict human susceptability to the exposures. Phenobarbital (PB) is the prototype of a large number of chemicals that induce the sets of P450 and transferase genes. We have now defined the conserved 51-bp DNA found in these genes (in mouse, rat, and human) as the PB-responsive enhancer module or PBREM. We have also identified the nuclear orphan receptor CAR that activates PBREM in response to PB induction. PB induction was found to be defected in rats in which CAR function is impaired, which include genetically engineered CAR-null mice. In addition to numerous PB-type inducers, endgenous steroid hormones regulate the receptor CAR; estrogens are activators while androgens and progesterone are repressors. CAR is a cytosolic receptor in non-induced livers and translocates to nucleus following PB treatment. Cytosolic CAR complex recruites protein phosphase 2A for the nuclear translocation. Establishing a system in which endodogenous CAR can be expressed in liver cells, we found that the C-terminal LXXLXXL sequence regulates the PB-inducible nuclear translocation of CAR.