Nuclear factor-κB regulates the expression of multiple genes encoding liver transport proteins

In this study we identified the mechanisms underlying the inhibitory effects of NF-kappa B on the expression of genes encoding multiple liver transport proteins. Well-conserved NF-kappa B 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-kappa B p65 protein and a 32P-labeled BSEP NF-kappa B response element (NF-kappa BE). Chromatin immunoprecipitation (ChIP) analysis confirmed binding of NF-kappa B p65 to the BSEP locus but not the FXRE in vitro. NF-kappa B 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 I kappa B alpha super-repressor. NF-kappa B interacted directly with FXR on coimmunoprecipitation, suggesting another level for the inhibitory effects of NF-kappa B 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-kappa B 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-kappa B sites. We also found that NF-kappa B p65 was recruited to NF-kappa B binding sites in the promoters of organic solute transporter, OST alpha and OST beta, and unexpectedly activated rather than repressed gene expression. In mouse liver after, BDL NF-kappa B recruitment to Ost alpha and Ost beta promoters was associated with increased binding of the potent coactivator cAMP response element binding protein (CREB)-binding protein (CBP)/p300 to the NF-kappa BE and depletion of CBP/p300 at the FXR element. Overall, these studies demonstrate a novel role for NF-kappa B in adaptation to obstructive and LPS-induced cholestasis acting through recruitment to specific NF-kappa B binding sites in the promoters of FXR-target genes and possibly through direct interaction with FXR.