Signaling of the Pregnane X Receptor

描述(申请人提供)：孕烷X受体(PXR)被认为是化学消除基因表达的主要调节者，如细胞色素P450 3A4(CYP3A4)，最丰富的CYP酶，负责超过50%的治疗药物的新陈代谢。对PXR信号调节因子的研究已将DEC转录因子与细胞因子抑制的PXR和CyP3A的表达联系起来。促炎细胞因子(如IL-6)显著增加DEC1和DEC2的水平，同时抑制PXR和CyP3A的表达。DECS共转染可有效抑制PXR和CYP3A启动子。对CYP3A4转录的基因组基础的研究已经证实，PXR通过两个区域反式激活CYP3A4启动子：近端和远端区域。PXR通过PXR元件在两个区域中物理存在，然而，远端区域的删除不再响应PXR。这些研究旨在验证这样的假设，即远端和近端区域协同支持PXR导向的辅阻遏子和辅激活子的置换/募集，并且PXR和CYP3A基因是DEC转录因子的序列特异性靶标。这些研究的具体目的是：(1)明确远端和近端区域在PXR引导的转录中的不同作用；(2)阐明PXR和CYP3A下调表达的机制。为了确定共调控因子的区域特异性招募，将对PXR、辅助抑制因子SMRT和辅助激活因子SRC-1(被发现调节PXR导向的转录)进行芯片分析。将确定PXR中调节相互作用的重要残基。为了阐明.DECs抑制PXR和CyP3A表达的分子基础，将通过慢病毒转导上调或下调DECs，并确定其对PXR和CyP3A表达的影响。将进行一系列实验，以定位PXR和CYP3A启动子中支持去抑制的DMA序列。PXR介导的诱导和细胞因子介导的抑制药物代谢酶是消除化学物质的两个主要决定因素。因此，这些研究将有助于我们对PXR、CYP3A和DECS作为一组结构不同但功能相关的蛋白质如何参与药理测定和异物解毒/生物激活的基本理解。行业相关性：两种或两种以上同时使用的药物可能会相互干扰。细菌/病毒感染降低了药物清除能力。拟议研究的结果将为如何防止药物不相容和在感染期间调整剂量提供重要信息。

DESCRIPTION (provided by applicant): The pregnane X receptor (PXR) is recognized as a master regulator on the expression of chemical elimination genes such as cytochrome P450 3A4 (CYP3A4), the most abundant CYP enzyme that is responsible for the metabolism of more than 50% of therapeutic agents. Studies on the modulators for PXR signaling have linked DEC transcription factors to cytokine-suppressed expression of PXR and CYP3A. Pro-inflammatory cytokines (e.g., IL-6) markedly increase the levels of DEC1 and DEC2, and simultaneously suppress the expression of PXR and CYP3A. Co-transfection of DECs effectively represses PXR and CYP3A promoters. Studies on the genomic basis for CYP3A4 transcription have established that PXR transactivates the CYP3A4 promoter through two regions: the proximal and distal regions. PXR is physically present in both regions through a PXR element, however, deletion of the distal region no longer responds to PXR. The proposed studies are designed to test the hypotheses that the distal and proximal regions coordinately support PXR-directed displacement/recruitment of corepressor and coactivator, and that PXR and CYP3A genes are sequence-specific targets of DEC transcription factors. The specific aims of the proposed studies are: (1) to define the differential roles of the distal and proximal regions in PXR-directed transcription, and (2) to elucidate the mechanisms on DECs-repressed expression of PXR and CYP3A. To determine the region- specific recruitment of co-regulators, ChIP will be performed for PXR, corepressor SMRT and coactivator SRC-1 (found to regulate PXR-directed transcription). The important residues in PXR to mediate the interactions will be established. To elucidate the molecular basis for .DECs-repressed expression of PXR and CYP3A, lentiviral transduction will be performed to up-regulate or knockdown DECs and the effect on PXR and CYP3A expression will be determined. A set of experiments will be conducted to locate in the PXR and CYP3A promoters DMA sequences that support DECs-repression. PXR-directed induction and cytokines- mediated suppression of drug-metabolizing enzymes are two major determinants on the elimination of chemicals. Therefore, these studies will contribute significantly to our basic understanding of how PXR, CYP3A and DECs, as a group of structurally distinct but functionally related proteins, are involved in pharmacologic determination and xenobiotic detoxication/bioactivation. Lay Relevance: Two or more drugs concurrently administered may interfere with each other. Bacterial/viral infection lowers the capacity of drug-elimination. Results from the proposed studies will provide important information on how to prevent drug incompatibility and adjust dosage during infection.