Elimination of duck hepatitis B virus RNA-containing capsids in duck interferon-alpha-treated hepatocytes

Evidence is presented that the previously cloned type I duck interferon (Du IFN) cDNA encodes a homologue of mammalian interferon-alpha (IFN-alpha). Re combinant DuIFN-alpha was used to study the inhibition of duck hepatitis B virus (DHBV) replication in primary hepatocytes in order to determine the I FN-sensitive steps of the virus replication cycle. IFN-treated cells accumu lated two- to threefold-lower amounts of viral RNA transcripts early during infection, when IFN was added before virus, This reduction was not due to inhibition of virus entry since initial covalently closed circular DNA leve ls were not decreased in IFN-treated cells. Interestingly, the inhibitory e ffect of IFN on viral RNA levels was not observed in cells infected with a mutant DHBV that fails to synthesize core protein, suggesting that an uncha racterized core protein-mediated enhancing effect is blocked by IFN, When I FN was added at 4 days postinfection, encapsidated viral RNA pregenomes dis appeared from infected cells within 3 days. This depletion was not simply d ue to conversion of pregenomes to DNA since depletion was not blocked by ph osphonoformic acid, an inhibitor of the viral reverse transcriptase. The in tracellular concentration of intact nucleocapsids was reduced, suggesting t hat in the presence of IFN pregenome-containing capsids were selectively de pleted in hepatocytes. Thus, two steps in DHBV replication that involve the viral core protein were inhibited by DuIFN-alpha.