NEDD4-binding protein 1 suppresses HBV replication by regulating HBV RNAs
Background and Aims  Chronic infection with hepatitis B virus (HBV) has been known to cause liver cirrhosis and hepatocellular carcinoma. Although nucleos(t)ide analogs are mainly used for the treatment of HBV, they require long-term administration and may lead to the emergence of drug resistance. Therefore, to identify targets for the development of novel anti-HBV therapies, we screened HBV-suppressive host factors using RNA-bnding protein (RBP) expression plasmids library.   Approach and Results  We screened the RBP library by generating overexpressing RBP cell lines and observing anti-HBV effect. As a result, we identified NEDD4-binding protein 1 (N4BP1) as a candidate showing anti-HBV effect. In hepatocellular carcinoma cell lines, overexpression of N4BP1 decreased the relaxed circular DNA (rcDNA) levels, while suppression of N4BP1 expression increased rcDNA levels. Restoring N4BP1 expression in N4BP1 knockout cells regained the anti-HBV effect of N4BP1. Next, we constructed KH-like and RNase domain-deficient mutants of N4BP1 and examined their effects on HBV replication, and found that both the KH-like and RNase domains are required for its anti-HBV effect. N4BP1 suppresses the step where pregenomic RNA (pgRNA) is synthesized in the HBV life cycle by promoting degradation of pgRNA. Transcriptome analyses of primary human hepatocytes overexpressing N4BP1 suggested that N4BP1 may have anti-HBV activity independent of other host factors.   Conclusions  In summary, N4BP1 was found to be a novel anti-HBV factor. N4BP1 inhibited HBV replication by promoting pgRNA degradation. Overall design: We performed a transcriptome analyses to determine whether other factors are involved in the anti-HBV activity of N4BP1. GFP or N4BP1 overexpressing PHHs were infected with HBV (5 Geq/cell). At 3 dpi, total RNA in PHHs was extracted using RNeasy Mini Kit following the manufacturer's protocol.