E3泛素连接酶MARCH1和MARCH8抑制冠状病毒进入机制的研究

冠状病毒是一类引起人类呼吸道感染的重要病原体，其中的SARS和MERS病毒的感染能导致严重肺炎，危及生命。在真核细胞中，蛋白质的泛素化修饰广泛存在，参与调节多种生理功能，包括抗病毒感染。最近在HIV中的研究发现，宿主E3泛素连接酶MARCH8通过抑制包膜蛋白掺入病毒颗粒中，从而降低HIV感染。MARCH1与MARCH8具有较高的同源性。目前它们在冠状病毒感染中的作用仍然是个空白。在前期研究中，我们发现过表达MARCH1和8蛋白能够有效地抑制SARS和MERS病毒S蛋白在细胞中的表达，降低S蛋白包装入慢病毒颗粒，进而抑制S蛋白介导的慢病毒转导。这提示我们MARCH1和8可能是冠状病毒的宿主限制因子。本项目将在此基础上，深入研究它们在SARS和MERS病毒感染中的作用机制，以及冠状病毒编码的非结构蛋白nsp3的去泛素化酶活性是否能拮抗MARCH1和8，为冠状病毒的治疗提供新的潜在靶点和思路。

Human coronaviruses (CoVs) are important respiratory pathogens of which Severe Acute Respiratory Syndrome Coronavirus (SARS-CoV) and Middle East Respiratory Syndrome Coronavirus (MERS-CoV) can cause severe pneumonia leading to death. Currently no approved drug treatment is available. Ubiquitination is one of the most common protein modifications in eukaryotic cells and regulates many essential cellular processes. Recent studies in HIV reveal that ubiquitination of viral envelope glycoprotein (Env) by a cellular E3 ubiquitin ligase, MARCH8, prevents Env from efficient incorporation into virus particles, resulting in lower virus infectivity. MARCH1 and MARCH8 belongs to the same family of E3 ubiquitin ligases and share high sequence homology. Their roles in CoV’s infection has not been determined. We recently found that over-expression of MARCH1 and MARCH8 significantly reduced the expression of MERS-CoV and SARS-CoV spike (S) proteins in the cell, decreased the level of S protein incorporation into virus particles, and led to significant reduction in viral entry, indicating that MARCH1 and MARCH8 may play important roles in coronavirus infection. In this study, we propose to determine the underlying mechanisms of how MARCH1 and MARCH8 influence the expression of SARS and MERS S proteins and cause reduction in S protein mediated virus entry. In addition, we will further investigate whether viral non-structural protein 3 (nsp3) with deubiquitination activity can counter the action of MARCH1 and MARCH8. Our results will provide new potential targets and ideas for the treatment of coronaviruses.