Signaling of the Pregnane X Receptor

描述（由申请人提供）：已确认胆甾烷X受体（PXR）是化学消除基因（如细胞色素P450 3A 4（CYP 3A 4））表达的主要调节剂，细胞色素P450 3A 4是最丰富的辅酶，负责超过50%治疗药物的代谢。对PXR信号传导调节剂的研究已将DEC转录因子与奎宁抑制的PXR和CYP 3A表达联系起来。促炎细胞因子（例如，IL-6可显著增加DEC 1和DEC 2的表达，同时抑制PXR和CYP 3A的表达。德克斯的共转染有效地抑制PXR和CYP 3A启动子。对CYP 3A 4转录的基因组基础的研究已经确定，PXR通过两个区域反式激活CYP 3A 4启动子：近端和远端区域。PXR通过PXR元件物理地存在于两个区域中，然而，远端区域的缺失不再响应PXR。拟议的研究旨在测试的假设，即远端和近端区域协调支持PXR定向置换/招募辅阻遏物和辅激活物，PXR和CYP 3A基因是DEC转录因子的序列特异性靶点。这些研究的具体目的是：（1）确定远端和近端区域在PXR指导的转录中的不同作用，（2）阐明DEC抑制PXR和CYP 3A表达的机制。为了确定共调节子的区域特异性募集，将对PXR、共阻遏子SMRT和共激活子SRC-1（发现调节PXR指导的转录）进行ChIP。将确定PXR中介导相互作用的重要残基。为了阐明DEC抑制PXR和CYP 3A表达的分子基础，将进行慢病毒转导以上调或敲低德克斯，并确定对PXR和CYP 3A表达的影响。将进行一组实验，以在PXR和CYP 3A启动子中定位支持DEC抑制的DMA序列。PXR介导的诱导和细胞因子介导的药物代谢酶抑制是消除化学物质的两个主要决定因素。因此，这些研究将大大有助于我们的基本了解如何PXR，CYP 3A和德克斯，作为一组结构不同，但功能相关的蛋白质，参与药理学测定和异生物质解毒/生物活化。非专业相关性：两种或多种药物同时给药可能会相互干扰。细菌/病毒感染降低药物消除能力。拟议研究的结果将为如何预防药物不相容性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.