Hepatitis B virus genotypes B and C

描述（由申请人提供）：乙型肝炎病毒（HBV）慢性感染大大增加了发生肝细胞癌（HCC）的风险，基因型B和C占全球慢性HBV感染的大多数。尽管这两种基因型通过相同的（垂直）传播模式感染相似的人群（亚洲人），但C基因型感染与延长的活跃病毒复制、延迟的HBeAg血清转换和增加的HCC终身风险相关。基因型C也更容易发生核心启动子突变，这与HCC风险独立相关。我们的初步研究表明，当将核心启动子突变引入基因型A和C的克隆中时，核心启动子突变上调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基因型C分离株比相应的基因型B分离株产生更少的前基因组RNA，导致更低的核心蛋白表达和基因组复制。然而，它们在病毒体分泌方面更有效。考虑到核心蛋白是一种强免疫原，我们假设C基因型的低表达抑制了感染的免疫耐受期，并延迟了HBeAg血清转换，而有效的病毒体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具有增强复制能力的基因型C突变体，伴随着核心蛋白表达的增加，触发肝损伤和HCC风险。在这个R21补助金申请，我们将确定的决定因素，并阐明机制负责较低的基因组复制能力的野生型基因型C分离株，但更有效的病毒粒子分泌。我们还将测试另一种可能性，即基因型B中核心启动子突变的低发生率是由于它们不能增强该特定基因型中的基因组复制。我们的工作假设和拟议的研究将揭示C基因型核心启动子突变的更高患病率，并帮助解决长期存在的难题，即为什么C基因型在宿主中持续更长时间以诱导晚期肝病，如肝硬化和HCC。这些研究还将揭示HBV基因组复制和病毒体分泌的新控制机制。我们在表征HBV遗传变异的生物学特性方面的丰富经验和良好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.