The human Na+-taurocholate cotransporting polypeptide gene is activated by glucocorticoid receptor and peroxisome proliferator-activated receptor-gamma coactivator-1alpha, and suppressed by bile acids via a small heterodimer partner-dependent mechanism.
Na+-taurocholate cotransporting polypeptide (NTCP) is the major bile acid uptake system in human hepatocytes. NTCP and the ileal transporter ASBT (apical sodium-dependent bile acid transporter) are two sodium-dependent transporters critical for the enterohepatic circulation of bile acids. The hASBT gene is known to be activated by the glucocorticoid receptor (GR). Here we show that GR also induces the endogenous hNTCP gene and transactivates the reporter-linked hNTCP promoter, in the presence of its ligand dexamethasone. Mutational analysis of the hNTCP promoter identified a functional GR response element, with which GR directly interacts within living cells. The GR/dexamethasone activation of endogenous hNTCP expression was suppressed by bile acids, in a manner dependent on the bile acid receptor farnesoid X receptor. Overexpression of the farnesoid X receptor-inducible transcriptional repressor small heterodimer partner also suppressed the GR/dexamethasone-activation of the hNTCP promoter. The peroxisome proliferator-activated receptor-gamma coactivator-1alpha enhanced the GR/dexamethasone activation of the hNTCP promoter. In conclusion, the hNTCP promoter is activated by GR in a ligand-dependent manner, similarly to the hASBT promoter. Thus, glucocorticoids may coordinately regulate the major bile acid uptake systems in human liver and intestine. The GR/dexamethasone activation of the hNTCP promoter is counteracted by bile acids and small heterodimer partner, providing a negative feedback mechanism for bile acid uptake in human hepatocytes.
Eloranta
Jyrki J
JJ
Laboratory of Molecular Gastroenterology and Hepatology, Department of Internal Medicine, University of Hospital Zurich, Zurich, Switzerland.
Jung
Diana
D
Kullak-Ublick
Gerd A
GA
D001647:Bile Acids and Salts / Q000502:physiology*; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000378:metabolism; D003907:Dexamethasone / Q000494:pharmacology; D025461:Feedback, Physiological; D006360:Heat-Shock Proteins / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D009154:Mutation; D029363:Organic Anion Transporters, Sodium-Dependent / Q000235:genetics / Q000378:metabolism*; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D011401:Promoter Regions, Genetic; D018160:Receptors, Cytoplasmic and Nuclear / Q000235:genetics / Q000502:physiology*; D011965:Receptors, Glucocorticoid / Q000819:agonists / Q000235:genetics / Q000378:metabolism*; D027981:Symporters / Q000235:genetics / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism*; D015533:Transcriptional Activation; D000099150:Receptor, Farnesoid X-Activated
D001647:Bile Acids and Salts; D004268:DNA-Binding Proteins; D003907:Dexamethasone; D006360:Heat-Shock Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; D000071248:Peroxisome Proliferator-Activated Receptor Gamma Coactivator 1-alpha; D018160:Receptors, Cytoplasmic and Nuclear; D011965:Receptors, Glucocorticoid; D027981:Symporters; D014157:Transcription Factors; D000099150:Receptor, Farnesoid X-Activated; C486497:PPARGC1A protein, human; C099713:nuclear receptor subfamily 0, group B, member 2; C071908:sodium-bile acid cotransporter