CONSTRUCTION OF AVIAN HEPADNAVIRUS VARIANTS WITH ENHANCED REPLICATIONAND CYTOPATHICITY IN PRIMARY HEPATOCYTES

Hepadnaviruses cause persistent noncytopathic infections of hepatocyte s in humans and other animals. Virus replication depends on the pool o f viral covalently closed circular DNA (cccDNA) molecules, which serve as transcriptional templates in the nuclei of infected cells. The siz e of this pool of cccDNA molecules is regulated by the ability of the large envelope protein of the virus to direct newly synthesized viral DNAs into a pathway for viral secretion and thereby inhibit their util ization for viral cccDNA synthesis. In this study, we showed that sing le amino acid changes in the large envelope protein could cause profou nd changes in cccDNA levels in transfected permissive cells or in infe cted cultured hepatocytes. While defects in cccDNA regulation were acc ompanied by a decrease of enveloped virus production in transfected ce lls, primary hepatocytes infected by such mutant viruses transiently p roduced wild-type or higher levels of enveloped virus. ?Moreover, high levels of cccDNA were always associated with cytopathic effects in th e infected hepatocytes. The results demonstrate that the large envelop e protein promotes persistent noncytopathic infection of hepatocytes b y acting as an overall repressor of virus replication.