NEDD4-binding protein 1 suppresses hepatitis B virus replication by regulating viral RNAs.

Chronic infection with hepatitis B virus (HBV) (chronic HBV infection) places patients at increased risk for liver cirrhosis and hepatocellular carcinoma. Although nucleos(t)ide analogues are mainly used for the treatment of HBV, they require long-term administration and may lead to the emergence of drug-resistant mutants. Therefore, to identify targets for the development of novel anti-HBV drugs, we screened for HBV-suppressive host factors using a plasmid expression library of RNA-binding proteins (RBPs). We tested the effect of 132 RBPs on HBV replication by ectopically expressing these proteins along with HBV in hepatocellular carcinoma and evaluated the intracellular capsid-associated HBV DNA level. Our screen identified NEDD4-binding protein 1 (N4BP1) as having an anti-HBV effect. In hepatocellular carcinoma cell lines transfected or infected with HBV, the overexpression of N4BP1 decreased core-associated HBV DNA levels, while knockdown or knockout of the gene encoding N4BP1 rescued core-associated HBV DNA levels. N4BP1 possesses the KH-like and RNase domains, and both were required for the anti-HBV effect of N4BP1. Additionally, we measured levels of HBV pregenomic RNA (pgRNA) and covalently closed circular DNA in the RBP-transfected cells and confirmed that N4BP1 binds pgRNA directly and regulates both the 3.5 and 2.4/2.1 kb HBV RNA. In summary, N4BP1 is a newly identified host factor able to counteract HBV production by regulating 3.5 and 2.1/2.4 kb HBV RNA.