Hepatitis B virus e antigen expression

描述（申请人提供）：乙型肝炎病毒（HBV）感染了世界上近十分之一的人口，并导致包括癌症在内的严重肝脏疾病。抗原（HBeAg）是一种分泌性可溶性蛋白，在围产期感染期间促进免疫耐受并缓冲对HBcAg的免疫。相应的抗乙肝病毒免疫反应在清除HBV感染中起着关键作用。因此，在血清从HBeAg抗原血症转化为抗hbe后，HBeAg产生减少或不产生的HBV逃逸突变体通常取代野生型HBV基因组。核心启动子突变体在HBV基因组的1750 -1770位置周围有各种核苷酸变化，已知最常见的1762和1764突变会在转录水平上降低HBeAg的表达。前突变体在HBeAg编码序列中存在无义突变或移码突变，并在翻译水平终止HBeAg的表达。考虑到HBeAg和抗hbe在塑造HBV感染结果中的关键重要性，我们希望发现HBeAg表达的新调控机制。在这方面，围产期感染的南非患者从HBeAg血清转化为抗hbe的速度比同样感染的亚洲患者快得多。有趣的是，南非HBV变异通常在前起始密码子附近有两个或三个点突变。我们计划验证突变是否会导致泄漏扫描以减少HbeAg的翻译。其次，HBeAg的成熟需要分泌途径中的双重蛋白水解裂解事件。第一次裂解发生在内质网，去除19个残基的n端信号肽。从血清转化患者中分离的HBV基因组中经常检测到残基17处Val到Phe错义突变。由于在切割位点的-3位置有芳香残基被禁止，我们将测试该突变是否会影响HBeAg的切割和分泌。第三，我们最近发现了几种自然发生的核心启动子突变体，它们具有野生型水平的HBeAg生产。根据初步的定位实验结果，我们将确定核心启动子突变的数量和位置是否影响HBeAg的表达水平，以及HBeAg编码序列的错义突变是否也调节HBeAg的表达水平。本研究有望验证和确定调节HBeAg表达的新机制，这对HBV感染的结果有重大影响。

DESCRIPTION (provided by applicant): Hepatitis B virus (HBV) infects nearly 1/10th of the world population and causes severe liver diseases including cancer. The e antigen (HBeAg) is a secreted soluble protein that promotes immune tolerance during perinatal infection and buffers immunity against HBcAg. The corresponding anti-HBe immune response plays a critical role in the clearance of HBV infection. Therefore, following seroconversion from HBeAg antigenemia to anti-HBe, HBV escape mutants with reduced or no HBeAg production often replace wild-type HBV genomes. The core promoter mutants have various nucleotide changes around positions 1750 -1770 of the HBV genome, and the most common mutations at 1762 and 1764 are known to reduce HBeAg expression at the transcriptional level. The precore mutants have nonsense or frameshift mutations in the HBeAg coding sequence and terminate HBeAg expression at the translational level. Considering the critical importance of HBeAg and anti-HBe in shaping the outcome of HBV infection, we wish to uncover novel regulatory mechanisms for HBeAg expression. In this regard, perinatally infected South African patients seroconvert from HBeAg to anti-HBe at a much accelerated pace than similarly infected Asian patients. Interestingly, the South African HBV variants often harbor two or three point mutations near the precore initiation codon. We plan to verify whether the mutations cause leaky scanning to reduce HbeAg translation. Second, HBeAg maturation requires double proteolytic cleavage events in the secretory pathway. The first cleavage occurs in endoplasmic reticulum to remove the N-terminal signal peptide of 19 residues. A Val to Phe missense mutation at residue 17 is frequently detected in HBV genomes isolated from seroconverted patients. Since an aromatic residue at the -3 position of cleavage site is forbidden, we will test whether this mutation impairs HBeAg cleavage and secretion. Third, we recently identified several naturally occurring core promoter mutants with wild-type level of HBeAg production. Based on the results of preliminary mapping experiments, we will determine whether the number and position of core promoter mutations influence the level of HBeAg expression, and whether missense mutations in the HBeAg coding sequence also regulate HBeAg level. This study promises to verify and identify novel mechanisms regulating HBeAg expression, which has a major impact on the outcome of HBV infection.