Novel function of NUP153 in HNF4a transcriptional upregulation contributes to promoting HBV replication
Background & Aims: Nucleoporin 153 (NUP153) is known to facilitate the nuclear entry of the human immunodeficiency virus (HIV) nucleocapsid. Studies had also showed that immature hepatitis B virus (HBV) nucleocapsids can be arrested by NUP153, allowing them to further mature. In this study, we investigated the impact and specific mechanisms of NUP153 on HBV replication. Methods: NUP153 was knocked down using RNA interference or over-expressed through an expression plasmid in HBV cell models or in vivo in HBV-replicating mice. Luciferase reporter assays were employed to assess the activities of viral or host factor promoters. Cytoplasmic and nuclear fractionation experiments were conducted to analyze the subcellular distribution of proteins and HBV RNA. Results: In the present study, we found that HBV induced significant upregulation of NUP153 mRNA and protein in HBV cell models and HBV infected patients. Overexpression of NUP153 would markedly increase covalently closed circular DNA (cccDNA) transcription activity and progeny virus production, while downregulation of NUP153 could significantly inhibit HBV replication without affecting HBV cccDNA level directly. Similar results were observed in mice model hydrodynamically injected (HDI) with 1.2×HBV plasmid. HBV promoter assays revealed that NUP153 could promote HBV core promoter activity, likely in a hepatocyte nuclear factor 4a (HNF4a) dependent manner. Mechanistically, ERK signaling was required for NUP153-mediated promotion of HNF4a and HBV replication. Conclusions: The study here suggested that host factor NUP153 which reciprocally upregulated by the virus, is an important positive regulator of HBV replication. It also suggested that the NUP153-HBV positive feedback loop could serve as a potential therapeutic target. Overall design: To further investigate whether endogenous NUP153 exerts a functional effect on HBV transcription and replication, we downregulated NUP153 expression using siRNA targeting NUP153 (siNUP153), followed by the transfection of prcccDNA/Cre.