HBx Regulation on HBV Pregenome Promoter in the Episomal Form Versus the Integrated Form

Background: Hepatitis B virus (HBV) genome structure is an incomplete closed double stranded circular DNA and it uses covalently closed circular DNA (cccDNA) as template for replication. To study the antiviral effect on different HBV replication forms, a stable cell line expressing HBV using Huh7 cells with shuttle plasmid to imitate the real HBV replication form was stablished. Unlike the HepG2.2.15 cells, the replication of HBV-expressing Huh7 cells present significant decrease after 9 days of interferon-alpha (IFN-alpha) treatment. This study aimed to verify whether hepatitis B virus X (HBx) epigenetic regulation by HBV promoter is affected by the DNA form and discuss the differences between the episomal form and the integrated form. Material and Methods: Huh7 cells were used with two different plasmids containing HBV genome to imitate HBV-expressing cells with the episomal form and the integrated form. Luciferase reporting system was used to determine the activation of the promoter after treatment with IFN-alpha with different concentrations and promoter regulation factor HBx. HBx-expressing plasmid was transfected to evaluate its effect on HBV replication in the episomal form. HBV DNA and pregenomic RNA (pgRNA) in HBx knockdown cell line was determined and HBx-expressing plasmid was transfected to evaluate its effect on HBx in the episomal form.Results: The two cell lines were established successfully and used for further experiments after selection. IFN-alpha showed significant inhibition effect on HBV pregenome promoter in the episomal form DNA while was not observed in the integrated form. After HBx-expressing plasmid was transfected, HBV pregenome promoter activity was higher in the episomal form rather than the integrated form. HBx showed a concentration-dependant activation on HBV replication in the episomal form. HBx knockdown reduced HBV production and HBV concentration significantly increased after transfection by HBx-expressing plasmid. Conclusions: HBx regulation effect on HBV pregenome promoter is influenced by the HBV genome form. The epigenetic regulation effect on HBV pregenome promoter is more active in the episomal form rather than the integrated form.