Abstract：
Influenza A virus (IAV) commandeers numerous host cellular factors for successful replication. However, very few host factors have been revealed to be involved in the fusion of viral envelope and late endosomal membranes. In this study, we identified cation-dependent mannose-6-phosphate receptor (M6PR) as a crucial host factor for the replication of IAV. We found that siRNA knockdown of M6PR expression significantly reduced the growth titers of different subtypes of IAV, and that the inhibitory effect of M6PR siRNA treatment on IAV growth was overcome by the complement of exogenously expressed M6PR. When A549 cells were treated with siRNA targeting M6PR, the nuclear accumulation of viral nucleoprotein (NP) was dramatically inhibited at early timepoints post-infection, indicating that M6PR engages in the early stage of the IAV replication cycle. By investigating the role of M6PR in the individual entry and post-entry steps of IAV replication, we found that the downregulation of M6PR expression had no effect on attachment, internalization, early endosome trafficking, or late endosome acidification. However, we found that M6PR expression was critical for the fusion of viral envelope and late endosomal membranes. Of note, M6PR interacted with the hemagglutinin (HA) protein of IAV, and further studies showed that the lumenal domain of M6PR and the ectodomain of HA2 mediated the interaction and directly promoted the fusion of the viral and late endosomal membranes, thereby facilitating IAV replication. Together, our findings highlight the importance of the M6PR-HA interaction in the fusion of viral and late endosomal membranes during IAV replication.
摘要：
甲型流感病毒(IAV)需要许多宿主细胞因子来成功复制。然而,很少有宿主因子参与病毒包膜和晚期内体膜的融合。在这项研究中,我们确定阳离子依赖性甘露糖-6-磷酸受体（M6PR）是IAV复制的关键宿主因子。我们发现siRNA敲低M6PR表达显著降低不同亚型IAV的生长滴度,并且通过外源表达的M6PR的补体克服了M6PRsiRNA处理对IAV生长的抑制作用。当A549细胞用靶向M6PR的siRNA处理时，病毒核蛋白（NP）的核积累在感染后的早期时间点受到显著抑制，表明M6PR参与了IAV复制周期的早期阶段。通过研究M6PR在IAV复制的个体进入和进入后步骤中的作用，我们发现M6PR表达的下调对依恋没有影响，内化，早期内体贩运，或晚期内体酸化。然而,我们发现M6PR的表达对于病毒包膜和晚期内体膜的融合至关重要.值得注意的是，M6PR与IAV血凝素（HA）蛋白相互作用，进一步的研究表明，M6PR的腔结构域和HA2的胞外域介导了相互作用，并直接促进了病毒和晚期内体膜的融合，从而促进IAV复制。一起,我们的发现强调了M6PR-HA相互作用在IAV复制过程中病毒和晚期内体膜融合中的重要性.
