Lenhoff R J, Summers J
Department of Cell Biology, University of New Mexico School of Medicine, Albuquerque 87131.
J Virol. 1994 Sep;68(9):5706-13. doi: 10.1128/JVI.68.9.5706-5713.1994.
Hepadnaviruses cause persistent noncytopathic infections of hepatocytes in humans and other animals. Virus replication depends on the pool of viral covalently closed circular DNA (cccDNA) molecules, which serve as transcriptional templates in the nuclei of infected cells. The size 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 utilization for viral cccDNA synthesis. In this study, we showed that single amino acid changes in the large envelope protein could cause profound changes in cccDNA levels in transfected permissive cells or in infected cultured hepatocytes. While defects in cccDNA regulation were accompanied by a decrease of enveloped virus production in transfected cells, primary hepatocytes infected by such mutant viruses transiently produced wild-type or higher levels of enveloped virus. Moreover, high levels of cccDNA were always associated with cytopathic effects in the infected hepatocytes. The results demonstrate that the large envelope protein promotes persistent noncytopathic infection of hepatocytes by acting as an overall repressor of virus replication.
嗜肝DNA病毒可在人类和其他动物的肝细胞中引起持续性非细胞病变感染。病毒复制依赖于病毒共价闭合环状DNA（cccDNA）分子池，这些分子在受感染细胞的细胞核中作为转录模板。该cccDNA分子池的大小受病毒大包膜蛋白将新合成的病毒DNA引导至病毒分泌途径的能力调控，从而抑制其用于病毒cccDNA合成。在本研究中，我们发现大包膜蛋白中的单个氨基酸变化可导致转染的允许细胞或受感染的培养肝细胞中cccDNA水平发生深刻变化。虽然cccDNA调节缺陷伴随着转染细胞中包膜病毒产生的减少，但受此类突变病毒感染的原代肝细胞会短暂产生野生型或更高水平的包膜病毒。此外，高水平的cccDNA总是与受感染肝细胞中的细胞病变效应相关。结果表明，大包膜蛋白通过作为病毒复制的整体抑制因子来促进肝细胞的持续性非细胞病变感染。
