title: Nuclear factor-κB regulates the expression of multiple genes encoding liver transport proteins.
abstract: In this study we identified the mechanisms underlying the inhibitory effects of NF-κB on the expression of genes encoding multiple liver transport proteins. Well-conserved NF-κB binding sites were found in the promoters of farnesoid X receptor (FXR)-target genes. An electromobility shift assay (EMSA) demonstrated the specific interaction between the NF-κB p65 protein and a (32)P-labeled BSEP NF-κB response element (NF-κBE). Chromatin immunoprecipitation (ChIP) analysis confirmed binding of NF-κB p65 to the BSEP locus but not the FXRE in vitro. NF-κB p65 overexpression in Huh-7 cells markedly repressed FXR/RXR transactivation of the BSEP, ABCG5/G8, MRP2, and FXR promoters, which was totally reversed by expression of the IκBα super-repressor. NF-κB interacted directly with FXR on coimmunoprecipitation, suggesting another level for the inhibitory effects of NF-κB on FXR-target genes. In vivo ChIP analysis with liver nuclei obtained from mice after 3 days of common bile duct ligation (BDL) or 6 h post-lipopolysaccharide (LPS) injection showed a markedly increased recruitment of NF-κB p65 to the Bsep promoter compared with controls. There was also increased recruitment of the corepressor silencing mediator of retinoic acid and thyroid hormone receptor (SMRT) and histone deacetylase (HDAC)3 and HDAC2 to the NF-κB sites. We also found that NF-κB p65 was recruited to NF-κB binding sites in the promoters of organic solute transporter, OSTα and OSTβ, and unexpectedly activated rather than repressed gene expression. In mouse liver after BDL NF-κB recruitment to Ostα and Ostβ promoters was associated with increased binding of the potent coactivator cAMP response element binding protein (CREB)-binding protein (CBP)/p300 to the NF-κBE and depletion of CBP/p300 at the FXR element. Overall, these studies demonstrate a novel role for NF-κB in adaptation to obstructive and LPS-induced cholestasis acting through recruitment to specific NF-κB binding sites in the promoters of FXR-target genes and possibly through direct interaction with FXR.
authors: Department of Pediatrics, Children's Hospital Colorado Research Institute, University of Colorado School of Medicine, Aurora, Colorado; and.
authors: Natarajan
authors: N
authors: Balasubramaniyan
authors: Department of Internal Medicine, Yale University School of Medicine, New Haven, Connecticut.
authors: Meenakshisundaram
authors: M
authors: Ananthanarayanan
authors: Department of Pediatrics, Children's Hospital Colorado Research Institute, University of Colorado School of Medicine, Aurora, Colorado; and frederick.suchy@childrenscolorado.org.
authors: Frederick J
authors: FJ
authors: Suchy
mesh_terms: D018528:ATP-Binding Cassette Transporters / Q000235:genetics* / Q000378:metabolism; D000818:Animals; D045744:Cell Line, Tumor; D017362:Cyclic AMP Response Element-Binding Protein / Q000235:genetics / Q000378:metabolism; D006655:Histone Deacetylases / Q000235:genetics / Q000378:metabolism; D006801:Humans; D008099:Liver / Q000378:metabolism*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D056985:Nuclear Receptor Co-Repressor 2 / Q000235:genetics / Q000378:metabolism; D011485:Protein Binding; D020218:Response Elements; D051996:Transcription Factor RelA / Q000378:metabolism*; D015533:Transcriptional Activation
chemical_list: D018528:ATP-Binding Cassette Transporters; D017362:Cyclic AMP Response Element-Binding Protein; D056985:Nuclear Receptor Co-Repressor 2; D051996:Transcription Factor RelA; D006655:Histone Deacetylases
keywords: FXR; NF-κB; bile acid transporters; cholestasis; gene regulation