de Brogniez Alix, Bouzar Amel Baya, Jacques Jean-Rock, Cosse Jean-Philippe, Gillet Nicolas, Callebaut Isabelle, Reichert Michal, Willems Luc
Molecular Biology (GxABT) and Molecular and Cellular Epigenetics (GIGA), University of Liege, Gembloux and Liege, Belgium
Molecular Biology (GxABT) and Molecular and Cellular Epigenetics (GIGA), University of Liege, Gembloux and Liege, Belgium.
J Virol. 2015 Sep;89(17):8945-56. doi: 10.1128/JVI.00261-15. Epub 2015 Jun 17.
Viruses have coevolved with their host to ensure efficient replication and transmission without inducing excessive pathogenicity that would indirectly impair their persistence. This is exemplified by the bovine leukemia virus (BLV) system in which lymphoproliferative disorders develop in ruminants after latency periods of several years. In principle, the equilibrium reached between the virus and its host could be disrupted by emergence of more pathogenic strains. Intriguingly but fortunately, such a hyperpathogenic BLV strain was never observed in the field or designed in vitro. In this study, we sought to understand the role of envelope N-linked glycosylation with the hypothesis that this posttranslational modification could either favor BLV infection by allowing viral entry or allow immune escape by using glycans as a shield. Using reverse genetics of an infectious molecular provirus, we identified a N-linked envelope glycosylation site (N230) that limits viral replication and pathogenicity. Indeed, mutation N230E unexpectedly leads to enhanced fusogenicity and protein stability.
Infection by retroviruses requires the interaction of the viral envelope protein (SU) with a membrane-associated receptor allowing fusion and release of the viral genomic RNA into the cell. We show that N-linked glycosylation of the bovine leukemia virus (BLV) SU protein is, as expected, essential for cell infection in vitro. Consistently, mutation of all glycosylation sites of a BLV provirus destroys infectivity in vivo. However, single mutations do not significantly modify replication in vivo. Instead, a particular mutation at SU codon 230 increases replication and accelerates pathogenesis. This unexpected observation has important consequences in terms of disease control and managing.
病毒与宿主共同进化，以确保高效复制和传播，同时不会引发过度致病性，否则会间接损害其持久性。牛白血病病毒（BLV）系统就是一个例证，反刍动物在数年潜伏期后会发生淋巴增生性疾病。原则上，病毒与其宿主之间达成的平衡可能会因更具致病性的毒株出现而被打破。有趣的是但幸运的是，在野外从未观察到这种高致病性的BLV毒株，也未在体外设计出这样的毒株。在本研究中，我们试图了解包膜N-连接糖基化的作用，提出的假设是这种翻译后修饰可能通过促进病毒进入而有利于BLV感染，或者通过利用聚糖作为屏障实现免疫逃逸。利用感染性分子原病毒的反向遗传学，我们鉴定出一个限制病毒复制和致病性的N-连接包膜糖基化位点（N230）。事实上，N230E突变意外地导致融合活性增强和蛋白质稳定性提高。
逆转录病毒感染需要病毒包膜蛋白（SU）与膜相关受体相互作用，从而使病毒基因组RNA融合并释放到细胞中。我们发现，正如预期的那样，牛白血病病毒（BLV）SU蛋白的N-连接糖基化对于体外细胞感染至关重要。一致的是，BLV原病毒所有糖基化位点的突变都会破坏体内感染性。然而，单个突变并不会显著改变体内复制。相反，SU密码子230处的特定突变会增加复制并加速发病机制。这一意外发现对疾病控制和管理具有重要意义。
