title: Genome-wide tissue-specific farnesoid X receptor binding in mouse liver and intestine.
abstract: Farnesoid X receptor (FXR) is a bile acid-activated transcription factor belonging to the nuclear receptor superfamily. FXR is highly expressed in liver and intestine and crosstalk mediated by FXR in these two organs is critical in maintaining bile acid homeostasis. FXR deficiency has been implicated in many liver and intestine diseases. However, regulation of transcription by FXR at the genomic level is not known. This study analyzed genome-wide FXR binding in liver and intestine of mice treated with a synthetic FXR ligand (GW4064) by chromatin immunoprecipitation coupled to massively parallel sequencing (ChIP-seq). The results showed a large degree of tissue-specific FXR binding, with only 11% of total sites shared between liver and intestine. The sites were widely distributed between intergenic, upstream, intragenic, and downstream of genes, with novel sites identified within even known FXR target genes. Motif analysis revealed a half nuclear receptor binding site, normally bound by a few orphan nuclear receptors, adjacent to the FXR response elements, indicating possible involvement of some orphan nuclear receptors in modulating FXR function. Furthermore, pathway analysis indicated that FXR may be extensively involved in multiple cellular metabolic pathways.
  
  
  CONCLUSIONS
  This study reports genome-wide FXR binding in vivo and the results clearly demonstrate tissue-specific FXR/gene interaction. In addition, FXR may be involved in regulating broader biological pathways in maintaining hepatic and intestinal homeostasis.
authors.affiliation: Department of Pharmacology, Toxicology, and Therapeutics, University of Kansas Medical Center, Kansas City, KS, USA.
authors.forename: Ann M
authors.initials: AM
authors.lastname: Thomas
authors.forename: Steven N
authors.initials: SN
authors.lastname: Hart
authors.forename: Bo
authors.initials: B
authors.lastname: Kong
authors.forename: Jianwen
authors.initials: J
authors.lastname: Fang
authors.forename: Xiao-Bo
authors.initials: XB
authors.lastname: Zhong
authors.forename: Grace L
authors.initials: GL
authors.lastname: Guo
mesh_terms: D000818:Animals; D001665:Binding Sites; D047369:Chromatin Immunoprecipitation; D004247:DNA / Q000378:metabolism; D007413:Intestinal Mucosa / Q000378:metabolism*; D008099:Liver / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D009928:Organ Specificity; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism*; D015398:Signal Transduction; D000099150:Receptor, Farnesoid X-Activated
chemical_list: D004247:DNA; D018160:Receptors, Cytoplasmic and Nuclear; D000099150:Receptor, Farnesoid X-Activated