Morphogenesis of hepatitis B and hepatitis D virus particles: Strategies, mechanisms and host factors

人类乙肝病毒是一种包膜副病毒，可引起急性和慢性肝脏炎症。持续的乙肝病毒感染通常会导致致命的肝功能衰竭，在全球范围内位居最常见的传染病之列。伴随着乙肝病毒卫星的丁型肝炎病毒(HDV)的感染，通常会增强肝脏的致病作用。目前已批准的治疗方法是有限的，在大多数情况下是非治愈的。由于它们的编码能力有限，这两种病毒都严重依赖宿主细胞，并开发了不同的策略来利用细胞功能。我们对乙肝病毒颗粒的形态发生及其与宿主因素的协调的研究表明，病毒颗粒(VP)通过利用细胞自噬复合体、Rab GTP酶、泛素适配器、泛素连接酶和多囊内体网络的特定蛋白(ESCRT)在细胞膜上发芽。除VP外，受感染的肝细胞还分泌大量非传染性的亚病毒包膜颗粒(SVP)，也称为乙肝表面抗原。SVP被认为耗尽了免疫反应，从而促进了病毒的持续和致病。在这个更新方案中，我们将把我们的研究扩展到HDV，并将重点放在两种病原体共享的构成SVP支架的HBV膜上。作为一个完整的目标，我们将探索SVP/病毒包膜生物发生的机制和宿主因素。特别是，在我们的准备工作的基础上，我们将破译细胞外壳蛋白复合体II(COPII)囊泡萌发机制在乙型肝炎病毒和丁型肝炎病毒生物学中的作用。COPII复合体与Rab1 GTPase和TANGO1家族蛋白一起，在指导分泌系统内的货物运输方面发挥着重要作用。基于蛋白质组学的研究揭示了HBV膜和COPII的一个货物适配子亚基之间的相互作用。通过使用细胞培养系统结合细胞生物学方法，我们将调查乙肝病毒和丁型肝炎病毒是否以及如何利用COPII萌芽和运输机制来获益。通过对病毒包膜-COPII相互作用的分子洞察，我们期待着有助于设计针对病毒-宿主串扰的治疗方法的证据。穿透细胞的干扰肽将被开发和批准，因为它们具有抑制病毒颗粒释放的潜力，理想地影响乙肝病毒和丁型肝炎病毒的SVP和VP出口。此外，我们实验室新建立的HDV复制系统使我们能够研究这种特征不佳的病原体的辅助宿主因子要求。

The human hepatitis B virus (HBV) is an enveloped pararetrovirus that causes acute and chronic liver inflammation. Persistent HBV infections often result in fatal liver failure and globally rank among the most common infectious diseases. Concomitant infections with the hepatitis D virus (HDV), a satellite of HBV, usually enhance liver pathogenesis. Currently approved therapies are limited and in most cases non-curative. Due to their limited coding capacities, both viruses are heavily dependent on the host cell and have developed diverse strategies to exploit cellular functions. Our investigations on HBV particle morphogenesis and its coordination by host factors reveal that viral particles (VPs) bud at intracellular membranes by the exploitation of cellular autophagy complexes, Rab GTPases, ubiquitin adaptors, ubiquitin ligases and specific proteins of the multivesicular endosome network (ESCRT). Besides VPs, infected hepatocytes also secrete in huge amounts non-infectious, subviral envelope particles (SVPs), also known as HBsAg. SVPs are thought to exhaust immune responses thereby contributing to viral persistence and pathogenesis. In this renewal proposal, we will extend our research to HDV and focus on the HBV envelope that is shared by both pathogens and forms the scaffold of SVPs. As an integral aim, we will explore mechanisms and host factors guiding SVP/viral envelope biogenesis. In particular, based on our preparatory works, we will decipher the role of the cellular coat protein complex II (COPII) vesicle budding machinery in HBV and HDV biology. The COPII complex, in conjunction with the Rab1 GTPase and TANGO1 family proteins, is instrumental in guiding cargo trafficking within the secretory system. Proteomics-based studies revealed an interplay between the HBV envelope and a cargo adaptor subunit of COPII. By using cell culture systems combined with cell biological methods, we will investigate if and how HBV and HDV may engage the COPII budding and trafficking machinery for benefit. By probing molecular insights into the virus envelope-COPII interaction, we are expecting evidence which will help to design therapeutic approaches targeting the virus-host crosstalk. Cell penetrating interfering peptides will be developed and approved for their potential to inhibit virus particle release, ideally affecting SVP and VP egress of both, HBV and HDV. Moreover, the newly setup of an HDV replication system in our lab enables to study auxiliary host factor requirements of this poorly characterized pathogen.