Human hepatic
bile acid transporter Na+/
taurocholate cotransporting
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 downregulated 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 human embryonic kidney (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.NEW & NOTEWORTHY The hepatic
bile acid transporter NTCP is a high-affinity receptor for
hepatitis B and D viruses. This study shows that TLC rapidly accumulates in NTCP-expressing
hepatoma cells and mediates long-lasting trans-inhibition of NTCP's transporter and receptor function via an intracellularly accessible domain, without substantially affecting its membrane expression. This domain is a promising novel NTCP target site for pharmacological long-acting HBV/HDV entry inhibitors.