Histone H3K4 trimethylation by MLL3 as part of ASCOM complex is critical for NR activation of bile acid transporter genes and is downregulated in cholestasis

Am J Physiol Gastrointest Liver Physiol. 2011 May;300(5):G771-81. doi: 10.1152/ajpgi.00499.2010. Epub 2011 Feb 17.

Abstract

The nuclear receptor Farnesoid x receptor (FXR) is a critical regulator of multiple genes involved in bile acid homeostasis. The coactivators attracted to promoters of FXR target genes and epigenetic modifications that occur after ligand binding to FXR have not been completely defined, and it is unknown whether these processes are disrupted during cholestasis. Using a microarray, we identified decreased expression of mixed lineage leukemia 3 (MLL3), a histone H3 lysine 4 (H3K4) lysine methyl transferase at 1 and 3 days of post-common bile duct ligation (CBDL) in mice. Chromatin immunoprecipitation analysis (ChIP) analysis revealed that H3K4me3 of transporter promoters by MLL3 as part of activating signal cointegrator-2 -containing complex (ASCOM) is essential for activation of bile salt export pump (BSEP), multidrug resistance associated protein 2 (MRP2), and sodium taurocholate cotransporting polypeptide (NTCP) genes by FXR and glucocorticoid receptor (GR). Knockdown of nuclear receptor coactivator 6 (NCOA6) or MLL3/MLL4 mRNAs by small interfering RNA treatment led to a decrease in BSEP and NTCP mRNA levels in hepatoma cells. Human BSEP promoter transactivation by FXR/RXR was enhanced in a dose-dependent fashion by NCOA6 cDNA coexpression and decreased by AdsiNCOA6 infection in HepG2 cells. GST-pull down assays showed that domain 3 and 5 of NCOA6 (LXXLL motifs) interacted with FXR and that the interaction with domain 5 was enhanced by chenodeoxycholic acid. In vivo ChIP assays in HepG2 cells revealed ligand-dependent recruitment of ASCOM complex to FXR element in BSEP and GR element in NTCP promoters, respectively. ChIP analysis demonstrated significantly diminished recruitment of ASCOM complex components and H3K4me3 to Bsep and Mrp2 promoter FXR elements in mouse livers after CBDL. Taken together, these data show that the "H3K4me3" epigenetic mark is essential to activation of BSEP, NTCP, and MRP2 genes by nuclear receptors and is downregulated in cholestasis.

Publication types

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

MeSH terms

  • ATP Binding Cassette Transporter, Subfamily B, Member 11
  • ATP-Binding Cassette Transporters / biosynthesis
  • ATP-Binding Cassette Transporters / genetics
  • Animals
  • Bile Ducts / physiology
  • Carrier Proteins / genetics*
  • Cells, Cultured
  • Cholestasis / genetics
  • Cholestasis / metabolism*
  • Down-Regulation
  • Glutathione Transferase / metabolism
  • Histone-Lysine N-Methyltransferase / genetics
  • Histone-Lysine N-Methyltransferase / metabolism*
  • Histones / metabolism*
  • Humans
  • Immunoprecipitation
  • Ligation
  • Membrane Glycoproteins / genetics*
  • Methylation
  • Mice
  • Nuclear Receptor Coactivators / genetics
  • Nuclear Receptor Coactivators / metabolism*
  • Organic Anion Transporters, Sodium-Dependent / biosynthesis
  • Organic Anion Transporters, Sodium-Dependent / genetics
  • Plasmids / genetics
  • RNA, Small Interfering / genetics
  • Receptors, Cytoplasmic and Nuclear / genetics
  • Receptors, Cytoplasmic and Nuclear / physiology*
  • Symporters / biosynthesis
  • Symporters / genetics

Substances

  • ATP Binding Cassette Transporter, Subfamily B, Member 11
  • ATP-Binding Cassette Transporters
  • Abcb11 protein, mouse
  • Carrier Proteins
  • Histones
  • Membrane Glycoproteins
  • Ncoa6 protein, mouse
  • Nuclear Receptor Coactivators
  • Organic Anion Transporters, Sodium-Dependent
  • RNA, Small Interfering
  • Receptors, Cytoplasmic and Nuclear
  • Symporters
  • bile acid binding proteins
  • farnesoid X-activated receptor
  • sodium-bile acid cotransporter
  • Histone-Lysine N-Methyltransferase
  • MLL3 protein, mouse
  • MLL4 protein, mouse
  • Glutathione Transferase