Mechanisms of Hepadnavirus Assembly and Replication

描述（由申请人提供）：B肝炎病毒（HBV）是慢性病毒性肝炎的主要原因，可显著增加肝癌和其他终末期肝病（如肝硬化）的风险。HBV属于嗜肝DNA病毒科（Hepadnaviridae），其是具有小DNA基因组并通过独特的逆转录途径通过RNA中间体（前基因组RNA或pgRNA）复制的副逆转录病毒家族。HBV逆转录的启动是通过一种新的蛋白质引发机制完成的，其中病毒逆转录酶（RT）作为特异性蛋白质引物。在蛋白质引发后，未成熟的（含有pgRNA的）核衣壳（NC）进行逆转录，导致pgRNA转化为特征性的松弛环状（RC）DNA。含有DNA的（成熟的）NC被选择性地包膜并作为病毒体分泌到细胞外。病毒核衣壳包装宿主来源的蛋白激酶，其在病毒复制中的作用尚不清楚。使用最近建立的无细胞和细胞培养系统以及新开发的方法和模型，我们建议（1）定义HBV蛋白引发的病毒和宿主要求;（2）确定包装的宿主CDK 2在NC脱壳和感染中的作用;（3）确定HBV病毒体形态发生的调节机制。将测试关于HBV蛋白引发、NC脱壳和病毒体形成的新型和特异性模型。最近的研究表明，有效的抗病毒干预慢性病毒性肝炎可以阻断或逆转病毒引起的肝损伤及其相关的肝脏疾病。不幸的是，目前治疗HBV感染的方法非常有限。阐明了调节病毒复制和装配三个关键阶段的病毒和宿主因子，即，蛋白质引发的逆转录起始、NC脱壳和病毒体形成不仅将为嗜肝DNA病毒复制和病毒-宿主相互作用的机制提供重要的新见解，而且还促进了针对这些因子的新颖有效的抗HBV策略的开发。

DESCRIPTION (provided by applicant): Hepatitis B virus (HBV) is a major cause of chronic viral hepatitis that increases dramatically the risk of liver cancer and other end-stage liver diseases such as cirrhosis. HBV belongs to the Hepadnaviridae, a family of para-retroviruses that have a small DNA genome and replicate through an RNA intermediate (the pregenomic RNA, or pgRNA), by a unique reverse transcription pathway. The initiation of reverse transcription in HBV is accomplished via a novel protein priming mechanism whereby the viral reverse transcriptase (RT) serves as a specific protein primer. Following protein priming, the immature (containing pgRNA) nucleocapsid (NC) carries out reverse transcription, leading to the conversion of pgRNA to the characteristic, relaxed circular (RC) DNA. The DNA-containing (mature) NC is selectively enveloped and secreted extracellularly as virions. A host- derived protein kinase is packaged by the viral nucleocapsids and its role in viral replication remains unclear. Using recently established cell-free and cell culture systems and newly developed approaches and models, we propose to (1) define the viral and host requirements for HBV protein priming; (2) determine the role of the packaged host CDK2 in NC uncoating and infection; and (3) determine the mechanisms of regulation of HBV virion morphogenesis. Novel and specific models regarding HBV protein priming, NC uncoating, and virion formation will be tested. Recent studies suggest that effective antiviral interventions in chronic viral hepatitis ca block or reverse virus-induced liver damage and its associated liver diseases. Unfortunately, current therapies for HBV infections are very limited. The elucidation of the viral and host factor that modulate three critical stages of viral replication and assembly, i.e., the protein-primed initiation of reverse transcription, NC uncoating, and virion formation, will not only provide important new insights into mechanisms of hepadnavirus replication and virus-host interactions but also facilitate the development of novel and effective anti-HBV strategies targeted at these factors.