流感病毒神经氨酸酶（Neuraminidase，NA）是由流感病毒的RNA6编码的一个主要的表面抗原，属于II型膜蛋白。NA是一种糖苷外切酶，可以从α-糖苷键上除去唾液酸残基，这一功能对病毒粒子脱离宿主细胞以及防止病毒粒子聚集是非常重要的。NA在流感病毒形态发生和病毒粒子成熟过程中也发挥重要作用。此外，NA还为流感病毒感染时清理通道，在病毒接触宿主细胞中发挥作用。基于这些功能，NA与流感病毒的宿主特异性以及病毒致病力密切相关。迄今为止，NA仍然是抗流感病毒药物的最佳靶标。然而，NA在宿主细胞内转运过程和机理迄今仍不清楚，哪些宿主因子参与了NA向细胞膜转运过程仍一无所知，因此限制了针对NA唾液酸结合位点外的药物开发。
中国科学院微生物研究所陈吉龙研究员领导的病毒感染与肿瘤发生机理研究组通过microarray技术筛选到宿主因子ARHGAP21，发现在流感病毒感染A549细胞后，ARHGAP21表达水平发生了明显变化，而小G蛋白Cdc42与ARHGAP21又是紧密关联的，通过一系列的生化与分子生物学、以及细胞生物学等实验，证实了Cdc42和ARHGAP21参与了流感病毒NA蛋白向细胞膜转运的调控，从而影响了流感病毒的复制过程。
此外，陈吉龙研究组还发现了甲型流感病毒可以直接感染特异亚群的淋巴细胞，并进一步证实了宿主细胞内Itk信号通路在流感病毒感染这些细胞的过程中起重要作用。
此项研究揭示了宿主因子小G蛋白Cdc42、ARHGAP21对流感病毒NA蛋白转运调控作用，阐明了宿主细胞内Itk信号通路对流感病毒感染与复制的影响。这些结果加深了人们对流感病毒生命周期(life cycle)以及病毒致病机理的理解，为彻底阐明流感病毒感染与复制的整个调控网络提供了帮助。另外，此项研究对新型抗流感病毒药物的设计具有重要的参考意义。
相关研究论文已在线发表于国际重要学术刊物The Journal of Biological Chemistry及Journal of General Virology上。（生物谷Bioon.com）
doi:10.1074/jbc.M111.312959
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Transport of influenza A virus neuraminidase (NA) to host cell surface is regulated by ARHGAP21 and Cdc42
Song Wang1, Hua Li1, Yuhai Chen1, Haitao Wei1, George F. Gao1, Hongqiang Liu1, Shile Huang2 and Ji-Long Chen1,*
Influenza virus neuraminidase (NA) is transported to the virus assembly site at the plasma membrane and is a major viral envelope component that plays a critical role in the release of progeny virions and in determination of host range restriction. However, little is known about the host factors that are involved in regulating the intracellular and cell surface transport of NA. Here we identified the Cdc42-specific GAP, ARHGAP21 differentially expressed in host cells infected with influenza A virus using cDNA microarray analysis. Furthermore, we have investigated the involvement of Rho family GTPases in NA transport to the cell surface. We found that expression of constitutively active or inactive mutants of RhoA or Rac1 did not significantly affect the amount of NA that reached the cell surface. However, expression of constitutively active Cdc42 or depletion of ARHGAP21 promoted the transport of NA to the plasma membranes. By contrast, cells expressing shRNA targeting Cdc42 or overexpressing ARHGAP21 exhibited a significant decrease in the amount of cell surface-localized NA. Importantly, silencing Cdc42 reduced influenza A virus replication, whereas silencing ARHGAP21 increased the virus replication. Together, our results reveal that ARHGAP21 and Cdc42-based signaling regulates the NA transport and thereby impacts virus replication.
doi:10.1099/vir.0.041228-0
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Role of Itk signaling in the interaction between influenza A virus and T cells
Kewei Fan1, Yinping Jia1, Song Wang1, Hua Li1, Defeng Wu2, Guoshun Wang3 and Jilong Chen1,4
Although T cell-mediated immune response to influenza virus has been extensively studied, little information is available on direct interaction between influenza virus and T cells that pertains to severe diseases in humans and animals. To address these issues, we utilized the BALB/c mouse model combined with primary T cells infected with A/WSN/33 influenza virus to investigate whether influenza virus has an affinity for T cell in vivo. We observed that small portions of CD4+ T cells and CD8+ T cells in spleen and thymus expressed viral proteins in infected mice. A significant proportion of mouse primary T cells displayed expression of alpha-2,6 sialic acid-linked influenza virus receptor and was directly infected by influenza A virus. These experiments reveal that there exists a population of T cells that is susceptible to influenza A virus infection. Furthermore, we employed human Jurkat T cell to investigate the virus/T cell interaction with particular emphasis on understanding of whether Interleukin-2-inducible T cell kinase (Itk), a Tec family tyrosine kinase that regulates T cell activation, is involved in viral infection of T cell. Interestingly, influenza virus infection resulted in an increased expression of Itk recruited to the plasma membrane and an increased level of PLC-γ1 phosphorylation, suggesting that Itk/PLC-γ1 signaling is activated by the viral infection. We demonstrated that depletion of Itk inhibited the replication of influenza A virus, whereas overexpression of Itk increased viral replication. These results indicate that Itk is required for efficient replication of influenza virus in infected T cells.
