Department of Veterinary Medicine, University of Cambridge, Cambridge, United Kingdom.
PLoS One. 2010 Aug 16;5(8):e12151. doi: 10.1371/journal.pone.0012151.
Chicken Mx belongs to the Mx family of interferon-induced dynamin-like GTPases, which in some species possess potent antiviral properties. Conflicting data exist for the antiviral capability of chicken Mx. Reports of anti-influenza activity of alleles encoding an Asn631 polymorphism have not been supported by subsequent studies. The normal cytoplasmic localisation of chicken Mx may influence its antiviral capacity. Here we report further studies to determine the antiviral potential of chicken Mx against Newcastle disease virus (NDV), an economically important cytoplasmic RNA virus of chickens, and Thogoto virus, an orthomyxovirus known to be exquisitely sensitive to the cytoplasmic MxA protein from humans. We also report the consequences of re-locating chicken Mx to the nucleus.
METHODOLOGY/PRINCIPAL FINDINGS: Chicken Mx was tested in virus infection assays using NDV. Neither the Asn631 nor Ser631 Mx alleles (when transfected into 293T cells) showed inhibition of virus-directed gene expression when the cells were subsequently infected with NDV. Human MxA however did show significant inhibition of NDV-directed gene expression. Chicken Mx failed to inhibit a Thogoto virus (THOV) minireplicon system in which the cytoplasmic human MxA protein showed potent and specific inhibition. Relocalisation of chicken Mx to the nucleus was achieved by inserting the Simian Virus 40 large T antigen nuclear localisation sequence (SV40 NLS) at the N-terminus of chicken Mx. Nuclear re-localised chicken Mx did not inhibit influenza (A/PR/8/34) gene expression during virus infection in cell culture or influenza polymerase activity in A/PR/8/34 or A/Turkey/50-92/91 minireplicon systems.
CONCLUSIONS/SIGNIFICANCE: The chicken Mx protein (Asn631) lacks inhibitory effects against THOV and NDV, and is unable to suppress influenza replication when artificially re-localised to the cell nucleus. Thus, the natural cytoplasmic localisation of the chicken Mx protein does not account for its lack of antiviral activity.
鸡 Mx 属于干扰素诱导的动蛋白样 GTP 酶家族，某些物种的该酶具有强大的抗病毒特性。然而，关于鸡 Mx 的抗病毒能力存在相互矛盾的数据。关于编码 Asn631 多态性的等位基因具有抗流感活性的报告并未得到后续研究的支持。鸡 Mx 的正常细胞质定位可能会影响其抗病毒能力。在这里，我们报告了进一步的研究结果，以确定鸡 Mx 对新城疫病毒（NDV）的抗病毒潜力，NDV 是一种对鸡具有重要经济意义的细胞质 RNA 病毒，以及正粘病毒属的 Thogoto 病毒，已知该病毒对人类细胞质 MxA 蛋白极为敏感。我们还报告了将鸡 Mx 重新定位到细胞核的后果。
方法/主要发现：在使用 NDV 的病毒感染实验中测试了鸡 Mx。当将 Asn631 或 Ser631 Mx 等位基因（转染到 293T 细胞中）的细胞随后感染 NDV 时，它们都没有抑制病毒指导的基因表达。然而，人 MxA 确实显著抑制了 NDV 指导的基因表达。鸡 Mx 未能抑制 Thogoto 病毒（THOV）的 minireplicon 系统，其中细胞质人 MxA 蛋白表现出强大而特异的抑制作用。通过在鸡 Mx 的 N 端插入猴病毒 40 大 T 抗原核定位序列（SV40 NLS），实现了鸡 Mx 的核重新定位。核重新定位的鸡 Mx 并未在细胞培养中抑制流感（A/PR/8/34）基因表达，也未抑制 A/PR/8/34 或 A/Turkey/50-92/91 minireplicon 系统中的流感聚合酶活性。
结论/意义：鸡 Mx 蛋白（Asn631）缺乏对 THOV 和 NDV 的抑制作用，并且当其被人为重新定位到细胞核时，无法抑制流感病毒的复制。因此，鸡 Mx 蛋白的天然细胞质定位并不能解释其缺乏抗病毒活性的原因。
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