Limited disassembly of cytoplasmic hepatitis B virus nucleocapsids restricts viral infection in murine hepatic cells

Murine hepatic cells cannot support hepatitis B virus (HBV) infection even with supplemental expression of viral receptor, human sodium taurocholate cotransporting polypeptide (hNTCP). However, the specific restricted step remains elusive. In this study, we aimed to dissect HBV infection process in murine hepatic cells.Cells expressing hNTCP were inoculated with HBV or hepatitis delta virus (HDV). HBV pregenomic RNA (pgRNA), covalently closed circular DNA (cccDNA), and different relaxed circular DNA (rcDNA) intermediates were produced in vitro . The repair process from rcDNA to cccDNA was assayed by in vitro repair experiments and in mouse with hydrodynamic injection. Southern blotting and in situ hybridization were used to detect HBV DNA. HBV, but not its satellite virus HDV, was restricted from productive infection in murine hepatic cells expressing hNTCP. Transfection of HBV pgRNA could establish HBV replication in human, but not in murine, hepatic cells. HBV replication-competent plasmid, cccDNA, and recombinant cccDNA could support HBV transcription in murine hepatic cells. Different rcDNA intermediates could be repaired to form cccDNA both in vitro and in vivo . In addition, rcDNA could be detected in the nucleus of murine hepatic cells, but cccDNA could not be formed. Interestingly, nuclease sensitivity assay showed that the protein-linked rcDNA isolated from cytoplasm was completely nuclease resistant in murine, but not in human, hepatic cells.Our results imply that the disassembly of cytoplasmic HBV nucleocapsids is restricted in murine hepatic cells. Overcoming this limitation may help to establish an HBV infection mouse model.