Abstract
The farnesoid X receptor (FXR, NR1H4) belongs to the nuclear receptor superfamily and is activated by bile acids such as chenodeoxycholic acid, or synthetic ligands such as GW4064. FXR is implicated in the regulation of bile acid, lipid, and carbohydrate metabolism. Posttranslational modifications regulating its activity have not been investigated yet. Here, we demonstrate that calcium-dependent protein kinase C (PKC) inhibition impairs ligand-mediated regulation of FXR target genes. Moreover, in a transactivation assay, we show that FXR transcriptional activity is modulated by PKC. Furthermore, phorbol 12-myristate 13-acetate , a PKC activator, induces the phosphorylation of endogenous FXR in HepG2 cells and PKCalpha phosphorylates in vitro FXR in its DNA-binding domain on S135 and S154. Mutation of S135 and S154 to alanine residues reduces in cell FXR phosphorylation. In contrast to wild-type FXR, mutant FXRS135AS154A displays an impaired PKCalpha-induced transactivation and a decreased ligand-dependent FXR transactivation. Finally, phosphorylation of FXR by PKC promotes the recruitment of peroxisomal proliferator-activated receptor gamma coactivator 1alpha. In conclusion, these findings show that the phosphorylation of FXR induced by PKCalpha directly modulates the ability of agonists to activate FXR.
Publication types
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Research Support, Non-U.S. Gov't
MeSH terms
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Amino Acid Sequence
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Amino Acid Substitution
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Base Sequence
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Binding Sites / genetics
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Calcium / metabolism
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Cell Line
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DNA / genetics
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DNA / metabolism
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DNA-Binding Proteins / agonists
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DNA-Binding Proteins / chemistry
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DNA-Binding Proteins / genetics
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DNA-Binding Proteins / metabolism*
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Heat-Shock Proteins / metabolism
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Humans
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Ligands
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Molecular Sequence Data
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Mutagenesis, Site-Directed
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Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha
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Phosphorylation
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Protein Kinase C-alpha / antagonists & inhibitors
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Protein Kinase C-alpha / metabolism*
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Protein Kinase Inhibitors / pharmacology
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Protein Structure, Tertiary
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Receptors, Cytoplasmic and Nuclear / agonists
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Receptors, Cytoplasmic and Nuclear / chemistry
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Receptors, Cytoplasmic and Nuclear / genetics
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Receptors, Cytoplasmic and Nuclear / metabolism*
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Recombinant Proteins / chemistry
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Recombinant Proteins / genetics
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Recombinant Proteins / metabolism
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Signal Transduction
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Tetradecanoylphorbol Acetate / pharmacology
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Transcription Factors / agonists
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Transcription Factors / chemistry
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Transcription Factors / genetics
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Transcription Factors / metabolism*
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Transcriptional Activation / drug effects
Substances
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DNA-Binding Proteins
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Heat-Shock Proteins
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Ligands
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PPARGC1A protein, human
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Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha
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Protein Kinase Inhibitors
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Receptors, Cytoplasmic and Nuclear
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Recombinant Proteins
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Transcription Factors
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farnesoid X-activated receptor
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DNA
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Protein Kinase C-alpha
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Tetradecanoylphorbol Acetate
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Calcium