Jung Diana, Hagenbuch Bruno, Fried Michael, Meier Peter J, Kullak-Ublick Gerd A
Division of Gastroenterology and Hepatology, Dept. of Internal Medicine, Univ. Hospital, CH-8091 Zurich, Switzerland.
Am J Physiol Gastrointest Liver Physiol. 2004 May;286(5):G752-61. doi: 10.1152/ajpgi.00456.2003. Epub 2003 Dec 30.
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.
胆汁酸的肝脏摄取由肝细胞基底外侧膜的钠-牛磺胆酸盐共转运多肽（NTCP；SLC10A1）介导。大鼠Ntcp基因启动子中的几个顺式作用元件已被鉴定。然而，关于控制人或小鼠NTCP/Ntcp表达的机制知之甚少。因此，我们比较了人、小鼠和大鼠NTCP/Ntcp基因的转录调控。通过计算机比对，在转录起始位点附近鉴定出一个在物种间保守的5'-调控区序列。用含有每个物种保守区的荧光素酶构建体转染Huh7细胞。肝细胞核因子（HNF）1α和-4α以及视黄酸X受体/视黄酸受体二聚体（RXRα/RARα）结合并激活大鼠NTCP/Ntcp启动子，但不激活人或小鼠的NTCP/Ntcp启动子。相反，CCAAT/增强子结合蛋白-β的激活对人和小鼠的NTCP/Ntcp具有特异性。所有三个物种中唯一共有的共有基序是HNF3β。在电泳迁移率变动分析中，HNF3β形成特异性的DNA-蛋白质复合物，并在共转染分析中抑制NTCP/Ntcp启动子活性。最后，仅在大鼠Ntcp中发现胆汁酸有轻微的抑制作用。转录抑制因子小异源二聚体伴侣（SHP）不影响NTCP/Ntcp启动子活性。我们得出结论：1）保守的NTCP/Ntcp 5'-调控区的转录调控在人、小鼠和大鼠之间有很大差异；2）保守的NTCP/Ntcp调控区不受SHP直接调控。胆汁酸可能通过调节核因子激活基因表达的能力间接调节NTCP/Ntcp。
