Epigenetic Actions of Environmental Chemicals

描述（由申请人提供）：许多工业化学品和环境污染物通过与属于核受体超家族的转录因子相互作用产生毒性，但对导致基因转录广泛（通常是长期）变化的下游表观遗传事件知之甚少。本申请的重点是肝核受体和转录因子CAR（组成型雄烷受体; NR 1 I3）的基因组和表观基因组作用，其被结构多样的环境化学物质激活，并调节重要的生理和病理生理过程，包括肝脏药物和脂质代谢，葡萄糖稳态，炎症和肿瘤促进。拟议的研究利用高通量基因组学，计算生物学和表观遗传调控机制的最新进展，在完整的动物模型中阐明CAR激活对染色质结构和表观遗传状态的影响。小鼠肝脏模型将用于解决以下基本生物学问题：原型CAR特异性激动剂配体TCPOBOP（1，4-双[2-（3，5-二氯吡啶氧基）]苯，一种非遗传毒性肝癌原）的受体活化如何改变染色质可及性并建立与肝脏基因表达的广泛且在某些情况下永久性失调相关的表观遗传环境。支持这一建议的初步研究包括：（a）绘制可接近染色质区域的全球地图（DNA酶超敏反应）和表观遗传特征（B）CAR活化在基因组中约1，000个位点诱导染色质可及性的快速变化的发现，和（c）发现了核富集的长基因间非编码（linc）RNA，其快速响应CAR，并被假设重编程CAR靶基因及其调控元件的染色质状态。这些发现提供了一个独特的机会，通过在基因组和表观遗传水平上阐明决定外来化学物质对CAR激活的复杂转录反应的基本生物学机制，推动该领域向前发展。这将通过以下发现来实现：1）肝脏染色质可接近性的CAR诱导性变化及其与CAR结合和靶基因失调的关系; 2）CAR调节的lincRNA在外源化学品暴露后染色质状态和基因转录模式的重编程中的作用;和3）CAR的新生激活在易感靶基因处建立的永久表观遗传记忆的基础机制。总之，这些研究将确定关键的机制特征，这些特征控制着CAR对控制不同代谢过程的基因的复杂的、环境化学依赖性的调节，这些代谢过程对人类健康和疾病有重大影响。所获得的结果预计将产生很大的影响，将环境化学作用的机制研究重点转移到表观基因组，并将作为以复杂方式改变基因组的其他外来化学激活受体的范例。

DESCRIPTION (provided by applicant): Many industrial chemicals and environmental pollutants exert toxicities via interactions with transcription factors belonging to the nuclear receptor superfamily but little is known about the downstream epigenetic events that lead to widespread, often long-term, changes in gene transcription. This application focuses on the genomic and epigenomic actions of the liver nuclear receptor and transcription factor CAR (constitutive androstane receptor; NR1I3), which is activated by structurally diverse environmental chemicals and regulates important physiological and pathophysiological processes, including hepatic drug and lipid metabolism, glucose homeostasis, inflammation and tumor promotion. The proposed studies capitalize on recent advances in high throughput genomics, computational biology and epigenetic regulatory mechanisms to elucidate in an intact animal model the impact of CAR activation on chromatin structure and epigenetic states. The mouse liver model will be used to address the fundamental biological question of how receptor activation by the prototypical CAR-specific agonist ligand TCPOBOP (1,4-bis[2-(3,5-dichloropyridyloxy)]benzene), a non- genotoxic hepatocarcinogen, alters chromatin accessibility and establishes an epigenetic environment associated with extensive, and in some cases permanent dysregulation of liver gene expression. Preliminary Studies supporting this proposal include (a) the development of global maps of accessible chromatin regions (DNase hypersensitivity) and epigenetic signatures (chromatin marks) that characterize targets of CAR in the basal state, (b) the finding that CAR activation induces rapid changes in chromatin accessibility at ~1,000 sites in the genome, and (c) the discovery of nuclear-enriched long intergenic non-coding (linc) RNAs that respond to CAR rapidly and are hypothesized to reprogram chromatin states of CAR target genes and their regulatory elements. These findings provide a unique opportunity to move the field forward by elucidating at the genomic and epigenetic levels the fundamental biological mechanisms that determine the complex transcriptional responses to CAR activation by foreign chemicals. This will be accomplished through the discovery of: 1) CAR- inducible changes in liver chromatin accessibility and their relationship to CAR binding and target gene dysregulation; 2) the role of CAR-regulated lincRNAs in the reprogramming of chromatin states and gene transcription patterns following foreign chemical exposure; and 3) the mechanisms that underlie the permanent epigenetic memory that neonatal activation of CAR establishes at susceptible target genes. Together, these studies will identify key mechanistic features that govern the complex, environmental chemical-dependent regulation by CAR of genes that control diverse metabolic processes with a major impact on human health and disease. The results obtained are expected to have a high impact, shifting the mechanistic focus of studies on environmental chemical action to the epigenome, and will serve as a paradigm for other foreign chemical- activated receptors that alter the genome in complex ways.