Impact of CAR Agonist Ligand TCPOBOP on Mouse Liver Chromatin Accessibility

Toxicol Sci. 2018 Jul 1;164(1):115-128. doi: 10.1093/toxsci/kfy070.

Abstract

Activation of the nuclear receptor and transcription factor CAR (Nr1i3) by its specific agonist ligand TCPOBOP (1, 4-bis[2-(3, 5-dichloropyridyloxy)]benzene) dysregulates hundreds of genes in mouse liver and is linked to male-biased hepatocarcinogenesis. To elucidate the genomic organization of CAR-induced gene responses, we investigated the distribution of TCPOBOP-responsive RefSeq coding and long noncoding RNA (lncRNA) genes across the megabase-scale topologically associating domains (TADs) that segment the genome, and which provide a structural framework that functionally constrains enhancer-promoter interactions. We show that a subset of TCPOBOP-responsive genes cluster within TADs, and that TCPOBOP-induced genes and TCPOBOP-repressed genes are often found in different TADs. Further, using DNase-seq and DNase hypersensitivity site (DHS) analysis, we identified several thousand genomic regions (ΔDHS) where short-term exposure to TCPOBOP induces localized changes (increases or decreases) in mouse liver chromatin accessibility, many of which cluster in TADs together with TCPOBOP-responsive genes. Sites of chromatin opening were highly enriched nearby genes induced by TCPOBOP and chromatin closing was highly enriched nearby genes repressed by TCPOBOP, consistent with TCPOBOP-responsive ΔDHS serving as enhancers and promoters that positively regulate CAR-responsive genes. Gene expression changes lagged behind chromatin opening or closing for a subset of TCPOBOP-responsive ΔDHS. ΔDHS that were specifically responsive to TCPOBOP in male liver were significantly enriched for genomic regions with a basal male bias in chromatin accessibility; however, the male-biased response of hepatocellular carcinoma-related genes to TCPOBOP was not associated with a correspondingly male-biased ΔDHS response. These studies elucidate the genome-wide organization of CAR-responsive genes and of the thousands of associated genomic sites where TCPOBOP exposure induces both rapid and persistent changes in chromatin accessibility.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Chromatin Assembly and Disassembly / drug effects*
  • Chromatin Assembly and Disassembly / genetics
  • Constitutive Androstane Receptor
  • Female
  • Gene Expression Regulation / drug effects
  • Ligands
  • Liver / drug effects*
  • Liver / metabolism
  • Male
  • Mice, Inbred Strains
  • Promoter Regions, Genetic
  • Pyridines / toxicity*
  • RNA, Long Noncoding / genetics
  • Receptors, Cytoplasmic and Nuclear / agonists*
  • Receptors, Cytoplasmic and Nuclear / genetics
  • Sex Factors

Substances

  • Constitutive Androstane Receptor
  • Ligands
  • Nr1i3 protein, mouse
  • Pyridines
  • RNA, Long Noncoding
  • Receptors, Cytoplasmic and Nuclear
  • 1,4-bis(2-(3,5-dichloropyridyloxy))benzene