Role of liver-enriched transcription factors and nuclear receptors in regulating the human, mouse, and rat NTCP gene.
Hepatic uptake of bile acids is mediated by the Na(+)-taurocholate cotransporting polypeptide (NTCP; SLC10A1) of the basolateral hepatocyte membrane. Several cis-acting elements in the rat Ntcp gene promoter have been characterized. However, little is known about the mechanisms that control the expression of the human or mouse NTCP/Ntcp. We, therefore, compared the transcriptional regulation of the human and mouse NTCP/Ntcp gene with that of the rat. By computer alignment, a sequence in the 5'-regulatory region that is conserved between species was identified near the transcription start site. Huh7 cells were transfected with luciferase constructs containing the conserved region from each species. The hepatocyte nuclear factors (HNF)1alpha and -4alpha and the retinoid X receptor/retinoic acid receptor dimer (RXRalpha/RARalpha) bound and transactivated the rat but not the human or mouse NTCP/Ntcp promoters. In contrast, activation by the CCAAT/enhancer binding protein-beta was specific for human and mouse NTCP/Ntcp. The only consensus motif present in all three species was HNF3beta. HNF3beta formed a specific DNA-protein complex in electrophoretic mobility shift assays and inhibited NTCP/Ntcp promoter activity in cotransfection assays. Finally, a minor repressive effect of bile acids was only found for rat Ntcp. The transcriptional repressor small heterodimer partner (SHP) did not affect NTCP/Ntcp promoter activity. We conclude that 1) the transcriptional regulation of the conserved NTCP/Ntcp 5'-regulatory region differs considerably among human, mouse, and rat; and 2) the conserved NTCP/Ntcp regulatory region is not directly regulated by SHP. Bile acids may regulate NTCP/Ntcp indirectly by modulating the capacity of nuclear factors to activate gene expression.
Jung
Diana
D
Division of Gastroenterology and Hepatology, Dept. of Internal Medicine, Univ. Hospital, CH-8091 Zurich, Switzerland.
Hagenbuch
Bruno
B
Fried
Michael
M
Meier
Peter J
PJ
Kullak-Ublick
Gerd A
GA
D000818:Animals; D001483:Base Sequence; D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D001647:Bile Acids and Salts / Q000494:pharmacology; D022782:CCAAT-Enhancer-Binding Protein-beta / Q000502:physiology; D002352:Carrier Proteins / Q000235:genetics*; D017124:Conserved Sequence; D004268:DNA-Binding Proteins; D005786:Gene Expression Regulation / Q000502:physiology*; D051537:Hepatocyte Nuclear Factor 1; D051538:Hepatocyte Nuclear Factor 1-alpha; D051539:Hepatocyte Nuclear Factor 1-beta; D051557:Hepatocyte Nuclear Factor 4; D006801:Humans; D008099:Liver / Q000378:metabolism*; D026901:Membrane Transport Proteins; D051379:Mice; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; D010750:Phosphoproteins / Q000502:physiology; D011401:Promoter Regions, Genetic / Q000502:physiology; D017434:Protein Structure, Tertiary / Q000235:genetics; D051381:Rats; D018160:Receptors, Cytoplasmic and Nuclear / Q000378:metabolism* / Q000502:physiology; D018168:Receptors, Retinoic Acid / Q000502:physiology; D000072482:Retinoic Acid Receptor alpha; D047488:Retinoid X Receptors; D027981:Symporters; D014157:Transcription Factors / Q000502:physiology*
D051778:Basic Helix-Loop-Helix Leucine Zipper Transcription Factors; D001647:Bile Acids and Salts; D022782:CCAAT-Enhancer-Binding Protein-beta; D002352:Carrier Proteins; D004268:DNA-Binding Proteins; C496487:HNF1A protein, human; C496495:HNF1B protein, human; D051538:Hepatocyte Nuclear Factor 1-alpha; D051557:Hepatocyte Nuclear Factor 4; C496488:Hnf1a protein, mouse; C496489:Hnf1a protein, rat; C496496:Hnf1b protein, mouse; C403128:MLX protein, human; D026901:Membrane Transport Proteins; D009687:Nuclear Proteins; D029363:Organic Anion Transporters, Sodium-Dependent; D010750:Phosphoproteins; C000607071:RARA protein, human; C000607072:Rara protein, mouse; C000607073:Rara protein, rat; D018160:Receptors, Cytoplasmic and Nuclear; D018168:Receptors, Retinoic Acid; D000072482:Retinoic Acid Receptor alpha; D047488:Retinoid X Receptors; D027981:Symporters; C501970:Tcfl4 protein, mouse; D014157:Transcription Factors; C099713:nuclear receptor subfamily 0, group B, member 2; D051537:Hepatocyte Nuclear Factor 1; D051539:Hepatocyte Nuclear Factor 1-beta; C071908:sodium-bile acid cotransporter