NTCP ubiquitination enables HBV infection

Area of Science:

• Hepatology and Virology
• Molecular Biology and Biochemistry
• Cellular Biology

Background:

• The sodium taurocholate cotransporting polypeptide (NTCP) is essential for Hepatitis B virus (HBV) and Hepatitis D virus (HDV) entry into hepatocytes.
• The precise mechanism of NTCP-mediated internalization of HBV/HDV remains incompletely understood.

Purpose of the Study:

• To investigate the role of NTCP post-translational modification, specifically ubiquitination, in transporter endocytosis and HBV infection.
• To identify specific ubiquitination sites on NTCP and their impact on HBV entry.

Main Methods:

• Immunoprecipitation was used to detect NTCP ubiquitination.
• Lysine residues in the NTCP C-terminus were mutated to arginine to identify ubiquitination sites.
• HepG2 and HepaRG cells expressing wild-type or mutant NTCP were analyzed for protein levels, bile salt uptake, endocytosis, and HBV infectivity.
• A global ubiquitination inhibitor (TAK-243) was employed to assess its effects.

Main Results:

• NTCP was found to be ubiquitinated, with Lysine 340 (K340) identified as the primary target site.
• The NTCP K340R mutant exhibited reduced ubiquitination, increased membrane abundance, enhanced bile salt uptake, impaired endocytosis, and significantly reduced HBV DNA content.
• Inhibition of ubiquitination using TAK-243 decreased NTCP endocytosis and HBV DNA levels in both HepG2 and HepaRG cells, while increasing bile salt uptake.

Conclusions:

• K340 is critical for NTCP ubiquitination, which in turn regulates NTCP endocytosis.
• Impaired NTCP endocytosis due to inhibited ubiquitination effectively reduces HBV infection.
• Targeting NTCP ubiquitination presents a potential novel therapeutic strategy for reducing HBV infection.