Role of EBV Lytic Infection in Viral Tumorigenesis

项目总结/摘要 EB病毒（Epstein-Barr virus，EBV）是世界范围内人类癌症的重要原因，包括B细胞和 上皮细胞恶性肿瘤。虽然EBV编码的潜伏蛋白在驱动这些癌症中的作用是 裂解性病毒蛋白的重要性已被广泛接受，但仍存在相对争议。尽管如此，裂解 有效的EBV诱导的淋巴瘤可能需要体内感染EBV感染细胞亚群 阵我们以前的研究表明，一个溶细胞缺陷型EBV突变体（缺失BZLF 1（Z））在EBV感染的即刻早期， (IE)基因）在人源化小鼠模型中形成淋巴瘤的能力受损， 病毒传播此外，我们和其他人已经确定了生长因子和免疫抑制因子 从溶解性感染的B细胞中释放，可能增强附近潜伏感染的细胞的生长和存活 B细胞。此外，我们最近发现BZLF 1启动子变体（称为Zp-V3）， 在某些EBV阳性恶性肿瘤（包括NPC和AIDS相关淋巴瘤）中过度表达， 由于其在非恶性组织中的频率， 将细胞NFAT转录因子转化为Zp-V3变体（但不是原型启动子Zp-P）。虽然 Zp-V3型启动子在1型EBV毒株中相对少见，它存在于所有2型毒株中 （这在非洲疟疾带很常见）。这些结果表明，增强的裂解性EBV感染 增加体内EBV诱导淋巴瘤的可能性，并且特定的癌症相关变体 在EBV感染的B细胞中，Z启动子的缺失促进裂解性感染。在本提案中，我们将使用两种不同的 人源化小鼠模型，以比较含有Zp-P形式的EBV与癌症的表型。 相关的（Zp-V3）形式的BZLF 1启动子，并探讨机制（S），通过裂解EBV感染 促进淋巴瘤发生。我们还将确定在疟疾感染者中EBV载量是否更高， 与含Zp-P的毒株相比，共感染含Zp-V3的EBV毒株的儿童。我们的具体目标是 1)使用人源化小鼠模型来检查Zp-V3相对于含Zp-P型的体内表型 1或2型EBV株; 2）比较BALF 5（病毒DNA聚合酶）缺失与 BZLF 1缺失的EBV突变体在人源化小鼠中的表达，并探索是否用BZLF 1阻断裂解性EBV DNA复制。 抗病毒药物，阿昔洛韦，抑制EBV诱导的淋巴瘤的发展;和3）确定 Zp-V3启动子变异体是否与感染疟疾的非洲人中较高的EBV血浆水平相关 孩子我们假设EBV Zp-V3变体将增强人源化细胞中EBV诱导的淋巴瘤， 小鼠通过增加裂解性EBV感染，并且该变体也与增强的裂解性EBV相关。 在疟疾感染的儿童中复制。如果是这样，这些结果将表明Zp-V3变体的存在 可能是一个有用的生物标志物，用于预测EBV诱导的人类恶性肿瘤的风险增加。

PROJECT SUMMARY / ABSTRACT Epstein-Barr virus (EBV) is an important cause of human cancers world-wide, including both B cell and epithelial cell malignancies. Although the role of EBV-encoded latency proteins in driving these cancers is well accepted, the importance of lytic viral proteins remains relatively controversial. Nevertheless, lytic infection in a subset of EBV-infected cells in vivo may be required for efficient EBV-induced lymphoma formation. We previously showed that a lytic-defective EBV mutant (missing the BZLF1 (Z) immediate-early (IE) gene) is impaired for the ability to form lymphomas in a humanized mouse model that allows horizontal virus transmission. In addition, we and others have identified growth factors and immunosuppressive factors released from lytically infected B cells that likely enhance the growth and survival of nearby latently infected B cells. Furthermore, we have recently discovered that a BZLF1 promoter variant (known as Zp-V3) that is over-represented in certain EBV-positive malignancies (including NPC and AIDS-related lymphomas) relative to its frequency in non-malignant tissues confers enhanced lytic viral reactivation in vitro due to binding of the cellular NFAT transcription factor to the Zp-V3 variant (but not the prototype promoter, Zp-P). Although the Zp-V3 form of the promoter is relatively uncommon in type 1 EBV strains, it is present in all type 2 strains (which are very common in the malaria belt of Africa). These results suggest that enhanced lytic EBV infection increases the likelihood of EBV-induced lymphomas in vivo, and that a particular cancer-associated variant of the Z promoter promotes lytic infection in EBV-infected B cells. In this proposal, we will use two different humanized mouse models to compare the phenotypes of EBV containing the Zp-P form versus the cancer- associated (Zp-V3) form of the BZLF1 promoter, and to explore mechanism(s) by which lytic EBV infection promotes lymphomagenesis. We will also determine whether EBV loads are higher in malaria-infected children co-infected with Zp-V3 containing EBV strains versus Zp-P containing strains. Our Specific Aims are 1) to use humanized mouse models to examine the in vivo phenotypes of Zp-V3 versus Zp-P containing type 1 or type 2 EBV strains; 2) to compare the phenotypes of BALF5 (the viral DNA polymerase)-deleted versus BZLF1-deleted EBV mutants in humanized mice, and explore whether blocking lytic EBV DNA replication with the antiviral drug, acyclovir, inhibits the development of EBV-induced lymphomas; and 3) to determine whether the Zp-V3 promoter variant is associated with higher plasma levels of EBV in malaria-infected African children. We hypothesize that the EBV Zp-V3 variant will enhance EBV-induced lymphomas in humanized mice by increasing lytic EBV infection, and that this variant is also associated with enhanced lytic EBV replication in malaria-infected children. If so, these results will suggest that the presence of the Zp-V3 variant may be a useful biomarker for predicting increased risk of EBV-induced malignancy in humans.