Hepatitis B virus genotypes B and C

描述(申请人提供)：慢性感染乙肝病毒(乙肝病毒)极大地增加了发展为肝细胞癌(肝细胞癌)的风险，B和C型占全球慢性乙肝感染的大部分。虽然这两种基因型通过相同的(垂直)传播方式感染相似的人群(亚洲人)，但感染C型病毒与延长活跃的病毒复制、延迟HBeAg血清转换以及增加患肝癌的终身风险有关。基因C也更容易发生核心启动子突变，这已经独立地与肝细胞癌风险相关。我们的初步研究表明，当将核心启动子突变引入A和C基因型的克隆时，核心启动子突变上调了基因组复制和核心蛋白表达。我们还发现，大多数具有野生型核心启动子序列的C型分离株产生的前基因组RNA比相应的B型分离株少，导致核心蛋白表达和基因组复制较低。然而，它们在分泌病毒粒子方面更有效率。考虑到核心蛋白是一种强大的免疫原，我们假设其C基因的低表达延长了感染的免疫耐受期，并延迟了HBeAg血清转换，而有效的病毒粒子分泌确保了病毒在肝脏中的快速传播，这是建立持续感染所必需的。我们还假设，免疫清除机制通过核心启动子突变选择复制能力增强的C型突变，伴随着核心蛋白表达的增加引发肝脏损伤和肝细胞癌风险。在这次R21拨款申请中，我们将确定决定因素，并阐明导致野生型C基因型分离株基因组复制能力较低但更有效地分泌病毒粒子的机制。我们还将测试另一种可能性，即B型核心启动子突变的低流行率是由于它们无法增强该特定基因型的基因组复制。我们的工作假说和拟议的研究将阐明C基因核心启动子突变的较高流行率，并有助于解决为什么C基因在宿主体内持续更长时间导致晚期肝病，如肝硬变和肝癌的长期谜题。这些研究还将揭示乙肝病毒基因组复制和病毒粒子分泌的新控制机制。我们在确定乙肝病毒基因变异的生物学特性方面的丰富经验和可靠的记录将确保成功完成拟议的研究。

DESCRIPTION (provided by applicant): Chronic infection with hepatitis B virus (HBV) greatly increases the risk to develop hepatocellular carcinoma (HCC), and genotypes B and C account for majority of chronic HBV infection worldwide. Although these two genotypes infect similar human population (Asians) via the same (vertical) mode of transmission, infection with genotype C is associated with prolonged active virus replication, delayed HBeAg seroconversion, and increased lifelong risk for HCC. Genotype C is also more prone to develop core promoter mutations, which have been independently associated with HCC risk. Our preliminary studies revealed that core promoter mutations up regulate genome replication and core protein expression when introduced into clones of genotype A and C. We also found that most genotype C isolates with wild-type core promoter sequence produce less pregenomic RNA than corresponding genotype B isolates, leading to lower core protein expression and genome replication. Nevertheless, they are more efficient at virion secretion. Considering that the core protein is a strong immunogen, we hypothesize that its low expression by genotype C prolongs the immune tolerance phase of infection and delays HBeAg seroconversion, whereas efficient virion secretion ensures rapid virus spread in the liver as required for establishment of persisten infection. We also hypothesize that immune clearance mechanisms select for genotype C mutants with augmented replication capacity through core promoter mutations, with the concomitant increase in core protein expression triggering liver damage and HCC risk. In this R21 grant application we will identify the determinants and elucidate the mechanisms responsible for lower genome replication capacity of wild-type genotype C isolates but more efficient virion secretion. We will also test the alternative possibility that the low prevalence o core promoter mutations in genotype B is due to their inability to enhance genome replication in this particular genotype. Our working hypothesis and proposed studies will shed light on the higher prevalence of core promoter mutations in genotype C, and help solve the longstanding puzzle of why genotype C persists longer in the host to induce advanced liver diseases such as cirrhosis and HCC. These studies will also reveal novel control mechanisms in HBV genome replication and virion secretion. Our rich experience and proven track record in characterizing biological properties of HBV genetic variants will ensure successful completion of the proposed study.