Targeting Dynamics of CAR and PXR in the Mouse and Human Genomes

描述（由申请人提供）：摘要在哺乳动物生物体中，异生物质敏感受体CAR（组成型雄烷受体; NR 1 I3）和PXR（甾烷X受体; NR 1 I2）作为对化学品暴露的毒理学和生理学反应的介体发挥关键作用。作为核受体，CAR和PXR都作为编码功能性反应网络的大型基因网络的转录调节因子发挥作用，所述功能性反应网络包括外源性物质的代谢和转运、脂质和能量稳态的调节以及细胞增殖的调节。受体生物学的小鼠模型已被广泛部署，以表征这些功能。尽管它们很重要，但小鼠受体并不等同于人类。在其他方面中，各个受体在其配体特异性方面存在根本差异，所述配体特异性由限定其配体结合口袋的氨基酸接触残基的显著变化编码。受体在功能上也不同，例如CAR被鉴定为在小鼠中肝细胞癌的发展中在非遗传毒性受体激活剂（例如直接配体TCPOBOP）或间接激活剂（例如苯巴比妥（PB））促进后所必需的。然而，在人群中进行的广泛流行病学研究已经确定，在长期接触PB之后，没有过多的癌症风险。引人注目的是，CAR和PXR在结合DNA靶点的能力上有重叠和不同的偏好。令人惊讶的是，使用染色质免疫沉淀和生物信息学分析的结果揭示了物种之间的转录因子结合位点之间的广泛分歧。在每个受体的物种选择性剪接变异进一步定义了物种反应的固有差异。为了允许基于生物学和科学上可辩护的跨哺乳动物物种的受体功能外推，准确预测潜在的人类毒性，至关重要的是描绘这些差异反应的分子机制。该研究计划的中心假设是，小鼠和人类CAR以及PXR所贡献的独特生物学作用在其最基本的水平上通过其各自的动态和差异能力与其基因组靶标相互作用来编程。此外，我们假设在人类中，CAR的CAR 2和CAR 3剪接变体贡献了一层额外的生物多样性，部分通过与其自身独特的DNA相互作用的差异相互作用进行编程。先进的策略需要使用独特的生物模型和应用强大和公正的染色质免疫沉淀方法，再加上下一代测序和生物信息学分析。总的来说，这些研究将揭示这些受体桥接的全球相互作用组，确定受体结合的共享和不同位点，最终驱动这些关键异种受体在哺乳动物基因网络中贡献的生物学和毒理学功能。

DESCRIPTION (provided by applicant): Abstract In mammalian organisms, the xenobiotic-sensing receptors, CAR (constitutive androstane receptor; NR1I3) and PXR (pregnane X receptor; NR1I2), contribute critically as mediators of toxicological and physiological responses to chemical exposure. As nuclear receptors, both CAR and PXR function as transcriptional regulators for a large network of genes encoding a functional web of responses that include the metabolism and transport of xenobiotics, regulation of lipid and energy homeostasis, and modulation of cell proliferation. Mouse models of receptor biology have been deployed widely to characterize these features. Their importance notwithstanding, the mouse receptors are not equivalent to human. Among other aspects, the respective receptors differ fundamentally in their ligand specificity, encoded by marked variation in amino acid contact residues that define their ligand binding pockets. The receptors differ functionally as well, for example with CAR identified as necessary in the development of hepatocellular carcinoma in mice following promotion by non-genotoxic receptor activators, such as the direct ligand, TCPOBOP, or indirect activators such as phenobarbital (PB). However, extensive epidemiological studies in human populations have ascertained no excess risk of cancers following chronic PB exposures. Strikingly, CAR and PXR share overlapping as well as distinct preferences for their abilities to bind DNA targets. Surprisingly, results using chromatin immunoprecipitation and bioinformatics analyses have revealed extensive divergence among transcription factor binding sites between species. Species-selective splice variation in each receptor further defines inherent differences in species response. To allow biologically-based and scientifically defensible extrapolations of receptor function across mammalian species that accurately predict potential human toxicities, it is critical to delineate the molecular mechanisms underlying these differential responses. The central hypothesis of this research program is that unique biological roles contributed by mouse and human CAR, and PXR, are programmed at their most basic level by their respective dynamic and differential abilities to interact with their genomic targets. Further, we hypothesize that in humans, the CAR2 and CAR3 splice variants of CAR contribute an added layer of biological diversity, programmed in part through differential interaction with their own distinct DNA interactions. The strategies advanced entail the use of unique biological models and application of powerful and unbiased chromatin immunoprecipitation approaches, coupled with next-generating sequencing and bioinformatics analyses. Overall, these studies will reveal the global interactome bridged by these receptors, identifying both shared and distinct sites of receptor binding that ultimately drive the biological and toxicological functions contributed by these critical xenoreceptors across mammalian gene networks.