Lee Jihye, Park Ji Hoon, Min Ji-Young
Respiratory Viruses Research Laboratory, Discovery Biology Department, Institut Pasteur Korea, Gyeonggi-do, 463-400, Republic of Korea.
Arch Virol. 2017 Jan;162(1):13-21. doi: 10.1007/s00705-016-2966-9. Epub 2016 Jul 11.
The non-structural protein of influenza A virus (NS1A protein) is a multifunctional protein that antagonizes host antiviral responses and contributes to efficient viral replication during infection. However, most of its functions have been elucidated by generating recombinant viruses expressing mutated NS1 proteins that do not exist in nature. Recently, the novel H3N8 A/Equine/Kyonggi/SA1/2011 (KG11) influenza virus was isolated in Korea from horses showing respiratory disease symptoms. KG11 virus contains a naturally truncated NS gene segment with the truncation in the NS1A coding region, resulting in truncation of the effector domain of the NS1A protein. Using this KG11 virus, we investigated the role of truncated NS1A protein in the virus life cycle and its effect on host immune responses were compared to the A/Equine/Miami/1/1963 H3N8 (MA63) virus, which encodes a full-length NS1A protein. The replication of KG11 virus was attenuated by 2 logs in multiple-cycle growth, and its plaque size was significantly smaller than that of the MA63 virus. To understand the attenuation of KG11 virus, we evaluated the level of activation in Akt and interferon regulatory factor 3 (IRF-3) pathways and measured the induction of downstream genes. Our results showed that the activation of Akt was reduced, whereas phosphorylation of IRF-3 was increased in cells infected with KG11 virus when compared to MA63-virus-infected cells. We also determined that the expression of antiviral and pro-inflammatory genes was significantly increased. Taken together, these results revealed that the KG11 virus expressing the naturally truncated NS1A protein impairs the inhibition of host antiviral responses, thereby resulting in the attenuation of viral replication.
甲型流感病毒的非结构蛋白（NS1A蛋白）是一种多功能蛋白，可拮抗宿主抗病毒反应，并有助于感染期间病毒的高效复制。然而，其大部分功能是通过构建表达自然界不存在的突变NS1蛋白的重组病毒来阐明的。最近，在韩国从出现呼吸道疾病症状的马匹中分离出新型H3N8 A/Equine/Kyonggi/SA1/2011（KG11）流感病毒。KG11病毒包含一个天然截短的NS基因片段，其NS1A编码区域发生截短，导致NS1A蛋白效应结构域截短。利用这种KG11病毒，我们研究了截短的NS1A蛋白在病毒生命周期中的作用，并将其对宿主免疫反应的影响与编码全长NS1A蛋白的A/Equine/Miami/1/1963 H3N8（MA63）病毒进行了比较。KG11病毒在多轮生长中的复制减弱了2个对数级，其蚀斑大小明显小于MA63病毒。为了解KG11病毒的减毒机制，我们评估了Akt和干扰素调节因子3（IRF-3）信号通路的激活水平，并检测了下游基因的诱导情况。我们的结果表明，与感染MA63病毒的细胞相比，感染KG11病毒的细胞中Akt的激活降低，而IRF-3的磷酸化增加。我们还确定抗病毒和促炎基因的表达显著增加。综上所述，这些结果表明，表达天然截短NS1A蛋白的KG11病毒损害了对宿主抗病毒反应的抑制，从而导致病毒复制减弱。
