Developmental Pharmacogenetics Of Microsomal Steroid Hyd

工作概述：细胞色素P450和特异性转移酶的代谢是抵御环境毒物和致癌物质的防御系统。为了应对几乎无限数量的结构多样的异种化学物质，P450和转移酶基因能够被诱导以响应化学物质暴露并增加其代谢能力。找到诱导机制对于我们预测人类对暴露的易感性至关重要。苯巴比妥（PB）是大量诱导P450和转移酶基因的化学物质的原型。我们现在已经将这些基因（小鼠、大鼠和人类）中发现的保守的51-bp DNA定义为pb响应增强子模块或PBREM。我们还发现了核孤儿受体CAR，它在PB诱导下激活PBREM。在CAR功能受损的大鼠（包括基因工程的CAR缺失小鼠）中发现PB诱导存在缺陷。除了许多pb型诱导剂外，内源性类固醇激素调节受体CAR；雌激素是激活剂，而雄激素和黄体酮是抑制剂。CAR是非诱导肝脏中的细胞质受体，在PB治疗后易位到细胞核。胞质CAR复合体招募蛋白磷酸酶2A进行核易位。我们建立了内源性CAR在肝细胞中表达的系统，发现c端LXXLXXL序列调控了pb诱导的CAR核易位。

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.