Human hepatic bile acid transporter Na⁺/taurocholate co-transporting polypeptide (NTCP) represents the liver-specific entry receptor for the Hepatitis B and D Viruses (HBV/HDV). Chronic hepatitis B and D affect several million people worldwide, but treatment options are limited. Recently, HBV/HDV entry inhibitors targeting NTCP have emerged as promising novel drug candidates. Nevertheless, the exact molecular mechanism that NTCP uses to mediate virus binding and entry into hepatocytes is still not completely understood. It is already known that human NTCP mRNA expression is down-regulated under cholestasis. Furthermore, incubation of rat hepatocytes with the secondary bile acid taurolithocholic acid (TLC) triggers internalization of the rat Ntcp protein from the plasma membrane. In the present study, the long-term inhibitory effect of TLC on transport function, HBV/HDV receptor function and membrane expression of human NTCP were analyzed in HepG2 and HEK293 cells stably overexpressing NTCP. Even after short pulse preincubation, TLC had a significant long-lasting inhibitory effect on the transport function of NTCP, but the NTCP protein was still present at the plasma membrane. Furthermore, binding of the HBV/HDV myr-preS1 peptide and susceptibility for in vitro HDV infection were significantly reduced by TLC preincubation. We hypothesize that TLC rapidly accumulates in hepatocytes and mediates long-lasting trans-inhibition of the transport and receptor function of NTCP via a particular TLC binding site at an intracellularly accessible domain of NTCP. Physiologically, this trans-inhibition might protect hepatocytes from toxic overload of bile acids. Pharmacologically, it provides an interesting novel NTCP target site for potential long-acting HBV/HDV entry inhibitors.

中文翻译：

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牛磺石胆酸对乙型和丁型肝炎病毒受体NTCP的长期反式抑制

人肝胆酸转运蛋白Na ⁺/牛磺胆酸盐共转运多肽（NTCP）代表乙型和丁型肝炎病毒（HBV / HDV）的肝脏特异性进入受体。慢性乙型和丁型肝炎影响全球数百万人，但治疗选择有限。最近，靶向NTCP的HBV / HDV进入抑制剂已成为有希望的新型药物候选物。尽管如此，NTCP用于介导病毒结合和进入肝细胞的确切分子机制仍未完全了解。已知在胆汁淤积下人NTCP mRNA表达被下调。此外，将大鼠肝细胞与仲胆汁酸牛磺石胆酸（TLC）孵育会触发大鼠Ntcp蛋白从质膜内化。在本研究中，TLC对转运功能的长期抑制作用，在稳定过量表达NTCP的HepG2和HEK293细胞中分析了人类NTCP的HBV / HDV受体功能和膜表达。即使在短脉冲预温育后，TLC对NTCP的转运功能也具有明显的长期抑制作用，但NTCP蛋白仍存在于质膜上。此外，通过TLC预温育显着降低了HBV / HDV myr-preS1肽的结合和体外HDV感染的易感性。我们假设TLC在肝细胞中迅速积累，并通过NTCP的胞内可访问域中的特定TLC结合位点介导NTCP的转运和受体功能的持久反式抑制。从生理上讲，这种反式抑制作用可以保护肝细胞免受胆汁酸的毒性超载。在药理上