Truncation of PA-X Contributes to Virulence and Transmission of H3N8 and H3N2 Canine Influenza Viruses in Dogs
Truncation of PA-X Contributes to Virulence and Transmission of H3N8 and H3N2 Canine Influenza Viruses in Dogs
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PA-X 的截短有助于 H3N8 和 H3N2 犬流感病毒在狗中的毒力和传播
DOI：
10.1128/jvi.00949-20
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发表时间：
2020-08-01
影响因子：
5.4
通讯作者：
Sun, Yipeng
中科院分区：
文献类型：
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作者：
Liu, Litao;Song, Shikai;Sun, Yipeng
马源H3 N8和禽源H3 N2犬流感病毒（CIV）在狗中流行，被认为是狗与人之间亲密接触造成的公共卫生威胁。然而，我们对CIV毒力的了解仍然有限。甲型流感病毒PA-X是由片段3中的+1移码开放阅读框（X-ORF）部分编码的融合蛋白。X-ORF可以翻译成全长（61个氨基酸）或截短（41个氨基酸）形式。遗传分析表明，马H3 N8和禽H3 N2流感病毒的X-ORF编码61个氨基酸，但在引入犬后被截短。为了确定PA-X截短对CIV生物学特性的影响，我们在H3 N8和H3 N2 CIV背景下构建了四种携带截短或全长PA-X的重组病毒。我们观察到PA-X的截短增加了H3 N8和H3 N2 CIV在MDCK细胞中的生长，并抑制了MDCK细胞中共转染质粒的表达。此外，PA-X的截短增强了犬的病毒致病性，如临床症状和组织病理学变化加重、呼吸系统中病毒复制增加和病毒脱落延长所示。此外，具有截短的PA-X的CIV在狗中传播更有效。对感染犬肺组织的基因表达谱分析显示，差异表达基因主要与炎症反应有关，这可能与PA-X截短CIV的致病性有关。我们的研究结果表明，PA-X的截断可能是重要的流感病毒的适应dogs.IMPORTANCE马源H3 N8和禽源H3 N2流感病毒在犬种群的流行是成功的跨物种传播的甲型流感病毒的例子。遗传分析表明，马源H3 N8和禽源H3 N2流感病毒的PA-X基因均为全长，X-ORF编码61个氨基酸;而马源H3 N8和禽源H3 N2 CIV的PA-X基因均被截短，表明PA-X基因在传播给犬后发生了截短。在这项研究中，我们延伸了H3 N8和H3 N2 CIV的PA-X基因，并比较了携带不同长度PA-X的CIV的生物学特征。我们证明，对于H3 N8和H3 N2病毒，PA-X的截短增加了MDCK细胞中的病毒产量，并增强了病毒在犬中的复制、致病性和传播。这些结果可能反映了宿主基因表达的抑制增强和炎症反应相关基因的上调。总的来说，我们的数据部分解释了CIV中截短的PA-X的保守性。
Equine-origin H3N8 and avian-origin H3N2 canine influenza viruses (CIVs) prevalent in dogs are thought to pose a public health threat arising from intimate contact between dogs and humans. However, our understanding of CIV virulence is still limited. Influenza A virus PA-X is a fusion protein encoded in part by a +1 frameshifted open reading frame (X-ORF) in segment 3. The X-ORF can be translated in full-length (61-amino-acid) or truncated (41-amino-acid) form. Genetic analysis indicated that the X-ORFs of equine H3N8 and avian H3N2 influenza viruses encoded 61 amino acids but were truncated after introduction into dogs. To determine the effect of PA-X truncation on the biological characteristics of CIVs, we constructed four recombinant viruses on H3N8 and H3N2 CIV backgrounds bearing truncated or full-length PA-Xs. We observed that truncation of PA-X increased growth of both H3N8 and H3N2 CIVs in MDCK cells and suppressed expression from cotransfected plasmids in MDCK cells. Furthermore, truncation of PA-X enhanced viral pathogenicity in dogs, as shown by aggravated clinical symptoms and histopathological changes, increased viral replication in the respiratory system, and prolonged virus shedding. Additionally, CIVs with truncated PA-Xs were transmitted more efficiently in dogs. Global gene expression profiling of the lungs of infected dogs revealed that differentially expressed genes were mainly associated with inflammatory responses, which might contribute to the pathogenicity of PA-X-truncated CIVs. Our findings revealed that truncation of PA-X might be important for the adaptation of influenza viruses to dogs.IMPORTANCE Epidemics of equine-origin H3N8 and avian-origin H3N2 influenza viruses in canine populations are examples of successful cross-species transmission of influenza A viruses. Genetic analysis showed that the PA-X genes of equine H3N8 or avian H3N2 influenza viruses were full-length, with X-ORFs encoding 61 amino acids; however, those of equine-origin H3N8 or avian-origin H3N2 CIVs were truncated, suggesting that PA-X truncation occurred after transmission to dogs. In this study, we extended the PA-X genes of H3N8 and H3N2 CIVs and compared the biological characteristics of CIVs bearing different lengths of PA-X. We demonstrated that for both H3N8 and H3N2 viruses, truncation of PA-X increased virus yields in MDCK cells and enhanced viral replication, pathogenicity, and transmission in dogs. These results might reflect enhanced suppression of host gene expression and upregulation of genes related to inflammatory responses. Collectively, our data partially explain the conservation of truncated PA-X in CIVs.