Bile acid-induced negative feedback regulation of the human ileal bile acid transporter.
Ileal expression of the apical sodium-dependent bile acid transporter (ASBT) in the rat is unaffected by bile salts, yet in the mouse it is under negative-feedback regulation. The bile acid responsiveness of human ASBT is unknown. The human ASBT promoter linked to a luciferase reporter was studied in Caco-2 cells treated with chenodeoxycholic acid (CDCA) and transfected with expression plasmids for farnesoid X-receptor (FXR), short heterodimer partner (SHP), and retinoic acid receptor/retinoid X receptor (RAR/RXR). CDCA treatment of Caco-2 cells led to a 75% reduction in steady-state ASBT messenger RNA levels and a 78% reduction in human ASBT promoter activity. A dominant negative FXR abrogated the response to CDCA. Site-directed mutagenesis of an RAR/RXR cis element in the human ASBT promoter reduced its activity by 50% and eliminated the bile acid response. Retinoic acid activated the human ASBT promoter fourfold. SHP repressed the activity of the ASBT promoter and reduced activation by retinoic acid. Antisense mediated knock-down of SHP in Caco-2 cells partially offset the bile acid mediated repression of ASBT promoter activity. In conclusion, the human ASBT is positively regulated by retinoic acid. Bile acids induce a negative feedback regulation of human ASBT via an FXR-mediated, SHP-dependent effect upon RAR/RXR activation of ASBT.
Neimark
Ezequiel
E
Department of Pediatrics, Mount Sinai School of Medicine, New York, NY 10029, USA.
Chen
Frank
F
Li
Xiaoping
X
Shneider
Benjamin L
BL
D001483:Base Sequence; D001647:Bile Acids and Salts / Q000378:metabolism*; D018938:Caco-2 Cells; D002635:Chenodeoxycholic Acid / Q000494:pharmacology; D004268:DNA-Binding Proteins / Q000235:genetics; D025461:Feedback, Physiological; D005799:Genes, Dominant; D006801:Humans; D007082:Ileum / Q000378:metabolism*; D008969:Molecular Sequence Data; D016297:Mutagenesis, Site-Directed; D016376:Oligonucleotides, Antisense / Q000494:pharmacology; D029363:Organic Anion Transporters, Sodium-Dependent / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000187:drug effects / Q000235:genetics; D012333:RNA, Messenger / Q000037:antagonists & inhibitors; D018160:Receptors, Cytoplasmic and Nuclear / Q000037:antagonists & inhibitors / Q000235:genetics; D018168:Receptors, Retinoic Acid / Q000378:metabolism; D047488:Retinoid X Receptors; D027981:Symporters / Q000378:metabolism*; D014157:Transcription Factors / Q000235:genetics / Q000378:metabolism; D014212:Tretinoin / Q000494:pharmacology; D000099150:Receptor, Farnesoid X-Activated
D001647:Bile Acids and Salts; D002635:Chenodeoxycholic Acid; D004268:DNA-Binding Proteins; D016376:Oligonucleotides, Antisense; D029363:Organic Anion Transporters, Sodium-Dependent; D012333:RNA, Messenger; D018160:Receptors, Cytoplasmic and Nuclear; D018168:Receptors, Retinoic Acid; D047488:Retinoid X Receptors; D027981:Symporters; D014157:Transcription Factors; D014212:Tretinoin; D000099150:Receptor, Farnesoid X-Activated; C099713:nuclear receptor subfamily 0, group B, member 2; C071908:sodium-bile acid cotransporter