Abstract
DGKs (diacylglycerol kinases) catalyse the conversion of diacylglycerol into PA (phosphatidic acid), a positive modulator of mTOR (mammalian target of rapamycin). We have found that chenodeoxycholic acid and the synthetic FXR (farnesoid X receptor) ligand GW4064 induce the mRNA and protein expression of DGKθ in the HepG2 cell line and in primary human hepatocytes. Reporter gene studies using 1.5 kB of the DGKθ promoter fused to the luciferase gene revealed that bile acids increase DGKθ transcriptional activity. Mutation of putative FXR-binding sites attenuated the ability of GW4046 to increase DGKθ luciferase activity. Consistent with this finding, ChIP (chromatin immunoprecipitation) assays demonstrated that bile acid signalling increased the recruitment of FXR to the DGKθ promoter. Furthermore, GW4064 evoked a time-dependent increase in the cellular concentration of PA. We also found that GW4064 and PA promote the phosphorylation of mTOR, Akt and FoxO1 (forkhead box O1), and that silencing DGKθ expression significantly abrogated the ability of GW4046 to promote the phosphorylation of these PA-regulated targets. DGKθ was also required for bile-acid-dependent decreased glucose production. Taken together, our results establish DGKθ as a key mediator of bile-acid-stimulated modulation of mTORC2 (mTOR complex 2), the Akt pathway and glucose homoeostasis.
Publication types
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Research Support, N.I.H., Extramural
MeSH terms
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Cells, Cultured
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Chenodeoxycholic Acid / metabolism*
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Diacylglycerol Kinase / antagonists & inhibitors
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Diacylglycerol Kinase / chemistry
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Diacylglycerol Kinase / genetics
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Diacylglycerol Kinase / metabolism*
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Gene Expression Regulation / drug effects
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Gene Silencing
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Genes, Reporter
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Glucose / metabolism*
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Hep G2 Cells
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Hepatocytes / cytology
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Hepatocytes / drug effects
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Hepatocytes / metabolism*
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Humans
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Isoenzymes / antagonists & inhibitors
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Isoenzymes / chemistry
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Isoenzymes / genetics
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Isoenzymes / metabolism
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Isoxazoles / pharmacology
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Mechanistic Target of Rapamycin Complex 2
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Multiprotein Complexes / metabolism
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Mutation
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Phosphatidic Acids / metabolism
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Phosphorylation / drug effects
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Promoter Regions, Genetic / drug effects
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Protein Processing, Post-Translational / drug effects
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Proto-Oncogene Proteins c-akt / metabolism*
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Receptors, Cytoplasmic and Nuclear / agonists
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Receptors, Cytoplasmic and Nuclear / genetics
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Receptors, Cytoplasmic and Nuclear / metabolism*
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Recombinant Proteins / agonists
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Recombinant Proteins / antagonists & inhibitors
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Recombinant Proteins / metabolism
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Signal Transduction* / drug effects
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TOR Serine-Threonine Kinases / metabolism
Substances
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Isoenzymes
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Isoxazoles
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Multiprotein Complexes
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Phosphatidic Acids
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Receptors, Cytoplasmic and Nuclear
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Recombinant Proteins
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farnesoid X-activated receptor
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Chenodeoxycholic Acid
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Diacylglycerol Kinase
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AKT1 protein, human
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Mechanistic Target of Rapamycin Complex 2
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Proto-Oncogene Proteins c-akt
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TOR Serine-Threonine Kinases
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Glucose
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GW 4064