Epigenetic Actions of Environmental Chemicals

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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.