Wang Yongqiang, Duan Yulu, Han Chunyan, Yao Shuai, Qi Xiaole, Gao Yulong, Maier Helena J, Britton Paul, Chen Lei, Zhang Lizhou, Gao Li, Gao Honglei, Shen Nan, Wang Jingfei, Wang Xiaomei
Division of Avian Infectious Diseases, State Key Laboratory of Veterinary Biotechnology, Harbin Veterinary Research Institute, Chinese Academy of Agricultural Sciences, Harbin, China.
The Pirbright Institute, Pirbright, Guildford, Surrey, United Kingdom.
J Virol. 2017 Feb 14;91(5). doi: 10.1128/JVI.01883-16. Print 2017 Mar 1.
Autophagy functions as an intrinsic antiviral defense. However, some viruses can subvert or even enhance host autophagic machinery to increase viral replication and pathogenesis. The role of autophagy during avibirnavirus infection, especially late stage infection, remains unclear. In this study, infectious bursal disease virus (IBDV) was used to investigate the role of autophagy in avibirnavirus replication. We demonstrated IBDV induction of autophagy as a significant increase in puncta of LC3 autophagosomes, endogenous levels of LC3-II, and ultrastructural characteristics typical of autophagosomes during the late stage of infection. Induction of autophagy enhances IBDV replication, whereas inhibition of autophagy impairs viral replication. We also demonstrated that IBDV infection induced autophagosome-lysosome fusion, but without active degradation of their contents. Moreover, inhibition of fusion or of lysosomal hydrolysis activity significantly reduced viral replication, indicating that virions utilized the low-pH environment of acidic organelles to facilitate viral maturation. Using immuno-transmission electron microscopy (TEM), we observed that a large number of intact IBDV virions were arranged in a lattice surrounded by p62 proteins, some of which lay between virions. Additionally, many virions were encapsulated within the vesicular membranes, with an obvious release stage observed by TEM. The autophagic endosomal pathway facilitates low-pH-mediated maturation of viral proteins and membrane-mediated release of progeny virions. IBDV is the most extensively studied virus in terms of molecular characteristics and pathogenesis; however, mechanisms underlying the IBDV life cycle require further exploration. The present study demonstrated that autophagy enhances viral replication at the late stage of infection, and the autophagy pathway facilitates IBDV replication complex function and virus assembly, which is critical to completion of the virus life cycle. Moreover, the virus hijacks the autophagic vacuoles to mature in an acidic environment and release progeny virions in a membrane-mediated cell-to-cell manner. This autophagic endosomal pathway is proposed as a new mechanism that facilitates IBDV maturation, release, and reinternalization. This report presents a concordance in exit strategies among some RNA and DNA viruses, which exploit autophagy pathway for their release from cells.
自噬作为一种内在的抗病毒防御机制发挥作用。然而，一些病毒可以破坏甚至增强宿主自噬机制，以增加病毒复制和发病机制。自噬在禽双RNA病毒感染期间，尤其是晚期感染中的作用仍不清楚。在本研究中，传染性法氏囊病病毒（IBDV）被用于研究自噬在禽双RNA病毒复制中的作用。我们证明IBDV诱导自噬表现为感染后期LC3自噬体斑点、内源性LC3-II水平显著增加以及自噬体典型的超微结构特征。自噬的诱导增强了IBDV复制，而自噬的抑制则损害病毒复制。我们还证明IBDV感染诱导了自噬体-溶酶体融合，但没有其内容物的主动降解。此外，融合或溶酶体水解活性的抑制显著降低了病毒复制，表明病毒粒子利用酸性细胞器的低pH环境促进病毒成熟。使用免疫透射电子显微镜（TEM），我们观察到大量完整的IBDV病毒粒子排列在由p62蛋白包围的晶格中，其中一些位于病毒粒子之间。此外，许多病毒粒子被包裹在囊泡膜内，TEM观察到明显的释放阶段。自噬内体途径促进了低pH介导的病毒蛋白成熟和膜介导的子代病毒粒子释放。就分子特征和发病机制而言，IBDV是研究最广泛的病毒；然而，IBDV生命周期的潜在机制需要进一步探索。本研究表明，自噬在感染后期增强病毒复制，自噬途径促进IBDV复制复合体功能和病毒组装，这对病毒生命周期的完成至关重要。此外，病毒劫持自噬泡在酸性环境中成熟，并以膜介导的细胞间方式释放子代病毒粒子。这种自噬内体途径被认为是促进IBDV成熟、释放和再内化的新机制。本报告展示了一些RNA和DNA病毒在释放策略上的一致性，它们利用自噬途径从细胞中释放。
