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Impact of CAR agonist ligand TCPOBOP on transcription factor binding in adult male mouse liver

ABSTRACT: Chromatin immunoprecipitation and sequencing for three transcription factors (RXRa, CEBPa, CEBPb) was performed on livers of male mice treated with vehicle or with TCPOBOP for either 3 h or 27 h. This dataset is part of a larger study, entitled “Widespread epigenetic changes to the enhancer landscape of mouse liver induced by a specific xenobiotic agonist ligand of the nuclear receptor CAR”, which found that active enhancer and promoter histone marks induced by TCPOBOP were enriched at opening DNase hypersensitive sites (DHS) and TCPOBOP-inducible genes. Enrichment of CAR binding and CAR motifs was seen at opening DHS and their inducible drug/lipid metabolism gene targets, and at many constitutively open DHS located nearby. TCPOBOP-responsive cell cycle and DNA replication genes co-dependent on MET/EGFR signaling for induction were also enriched for CAR binding. A subset of opening DHS and many closing DHS mapping to TCPOBOP-responsive target genes did not bind CAR, indicating an indirect mechanism for their changes in chromatin accessibility. TCPOBOP-responsive DHS were also enriched for induced binding of RXRA, CEBPA and CEBPB, and for motifs for liver-enriched factors that may contribute to liver-specific transcriptional responses to TCPOBOP exposure. These studies elucidate the enhancer landscape of TCPOBOP-exposed liver and the widespread epigenetic changes that are induced by both direct and indirect mechanisms linked to CAR activation.

ORGANISM(S): Mus musculus

PROVIDER: GSE121915 | GEO | 2019/06/17

REPOSITORIES: GEO

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Project description:TCPOBOP (1,4-Bis [2-(3,5-Dichloropyridyloxy)] benzene) is a constitutive androstane receptor (CAR) agonist that induces robust hepatocyte proliferation and hepatomegaly without any liver injury or tissue loss. TCPOBOP-induced direct hyperplasia has been considered to be CAR-dependent with no evidence of involvement of cytokines or growth factor signaling. Receptor tyrosine kinases (RTKs), MET and EGFR, are known to play a critical role in liver regeneration after partial hepatectomy, but their role in TCPOBOP-induced direct hyperplasia, not yet explored, is investigated in the current study. Disruption of the RTK-mediated signaling was achieved utilizing MET KO mice along with Canertinib treatment for EGFR inhibition. Combined elimination of MET and EGFR signaling [MET KO + EGFRi], but not individual disruption, dramatically reduced TCPOBOP-induced hepatomegaly and hepatocyte proliferation. TCPOBOP-driven CAR activation was not altered in [MET KO + EGFRi] mice, as measured by nuclear CAR translocation and analysis of typical CAR target genes. However, TCPOBOP induced cell cycle activation was impaired in [MET KO + EGFRi] mice due to defective induction of cyclins, which regulate cell cycle initiation and progression. TCPOBOP-driven induction of FOXM1, a key transcriptional regulator of cell cycle progression during TCPOBOP-mediated hepatocyte proliferation, was greatly attenuated in [MET KO + EGFRi] mice. Interestingly, TCPOBOP treatment caused transient decline in HNF4α expression concomitant to proliferative response; this was not seen in [MET KO + EGFRi] mice. Transcriptomic profiling revealed vast majority (~40%) of TCPOBOP-dependent genes mainly related to proliferative response, but not to drug metabolism, were differentially expressed in [MET KO + EGFRi] mice. Conclusion: Taken together, combined disruption of EGFR and MET signaling lead to dramatic impairment of TCPOBOP-induced proliferative response without altering CAR activation. We used microarrays to detail the global programme of gene expression in [METKO + EGFRi] mice liver following TCPOBOP treatment

Project description:Constitutive androstane receptor (CAR) agonists, such as TCPOBOP, are known to cause robust hepatocyte proliferation and hepatomegaly in mice along with induction of drug metabolism genes, without any associated liver injury. Yes-associated protein (YAP) is a key transcription regulator that tightly controls organ size including that of liver. Ours and other previous studies suggested increased nuclear localization and activation of YAP after TCPOBOP treatment in mice and potential role of YAP in CAR-driven proliferative response. Here, we investigated a direct role of YAP in CAR-driven hepatomegaly and hepatocyte proliferation using hepatocyte-specific YAP-KO mice. AAV8-TBG-CRE vector was injected to YAP-floxed mice for achieving hepatocyte-specific YAP deletion followed by TCPOBOP treatment. YAP deletion did not alter protein expression of CAR or CAR-driven induction of drug metabolism genes (including Cyp2b10, Cyp2c55 and UGT1a1). However, YAP deletion substantially reduced TCPOBOP-induced hepatocyte proliferation. TCPOBOP-driven cell cycle activation was disrupted in YAP-KO mice due to delayed (and decreased) induction of cyclin D1 and higher expression of p21, resulting in decreased phosphorylation of retinoblastoma (Rb) protein. Further, induction of other cyclins, which are sequentially involved in progression through cell cycle (including cyclin E1, A2 and B1) and important mitotic regulators (such as aurora B kinase and polo-like kinase 1) was remarkably reduced in YAP-KO mice. Microarray analysis revealed that 26% of TCPOBOP‐responsive genes mainly related to proliferation, but not to drug metabolism, were altered by YAP deletion. YAP regulated these proliferation genes via alerting expression of cMyc and FOXM1, two critical transcriptional regulators of CAR-mediated hepatocyte proliferation. Conclusion: Our study revealed an important role of YAP signaling in CAR-driven hepatocyte proliferation; however, CAR-driven induction of drug metabolism genes was independent of YAP. We used microarrays to detail the global programme of gene expression in livers of hepatocyte-specific YAP KO mice following TCPOBOP treatment

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Impact of CAR agonist ligand TCPOBOP on transcription factor binding in adult male mouse liver

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