The aberrant gene-end transcription signal of the matrix M gene of human parainfluenza virus type 3 downregulates fusion F protein expression and the F-specific antibody response in vivo.
The aberrant gene-end transcription signal of the matrix M gene of human parainfluenza virus type 3 downregulates fusion F protein expression and the F-specific antibody response in vivo.
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3型人副流感病毒基质M基因的异常基因末端转录信号下调融合F蛋白表达和体内F特异性抗体反应。
DOI：
10.1128/jvi.03148-14
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发表时间：
2015
影响因子：
5.4
通讯作者：
Munir,Shirin
中科院分区：
文献类型：
--
作者：
Lingemann,Matthias;Surman,Sonja;Amaro-Carambot,Emérito;Schaap-Nutt,Anne;Collins,PeterL;Munir,Shirin
人副流感病毒3型(HPIV3)是一种副粘病毒，是引起婴幼儿严重下呼吸道疾病的主要病毒原因。HPIV3基质(M)蛋白基因的基因末端(GE)转录信号与核蛋白和磷蛋白基因的转录信号相同，只是它含有一个明显的8核苷酸插入。这与M基因的直读转录本和下游融合(F)蛋白基因的合成增加有关。我们推测，该插入片段可能通过干扰M-F基因连接处的终止/重新启动来下调F蛋白的表达，从而以牺牲单顺反子F mRNA为代价促进M-F阅读通透mRNA的产生。为了验证这一假设，产生了两种类似的重组HPIV3病毒，其中M-GE信号中的这一插入被移除。M-Ge突变体表现出M-F通读mRNA的减少和单顺反子F mRNA的增加。这导致感染细胞中的F蛋白合成显著增加，并增强了F蛋白与病毒粒子的结合。突变病毒的复制效率与野生型(Wt)HPIV3相似。然而，与wt HPIV3相比，突变体对仓鼠的F蛋白特异性血清抗体反应增强。这项研究确定了一种以前未描述的减弱宿主获得性免疫反应的病毒机制。修复M-GE信号应该提供一种在不影响病毒复制和减毒的情况下提高对减毒活HPIV3疫苗的抗体应答的方法。以前发现HPIV3 M-GE信号包含一个明显的8核苷酸插入，这与M基因和下游F基因的通读mRNA的合成增加有关。然而，这是否对单顺反子F mRNA或F蛋白的合成、病毒复制、病毒粒子形态形成和免疫原性是否有任何显著影响尚不清楚。在这里，我们证明了这个插入片段的移除将F基因的转录从读入的M-F mRNA转移到单顺反子F mRNA。这导致在细胞中表达并包装在病毒颗粒中的F蛋白的数量大幅增加。这并没有影响病毒的复制，但增加了仓鼠的F-特异性抗体反应。因此，在野生型HPIV3中，异常的M-GE信号运行一种先前未描述的机制，减少主要中和和保护性抗原的表达，导致免疫原性降低。这对HPIV3减毒活疫苗的设计具有重要意义；具体地说，通过修复M-GE信号以获得更高水平的F抗原表达，可以提高对F的抗体反应，而对减毒没有影响。
Human parainfluenza virus type 3 (HPIV3), a paramyxovirus, is a major viral cause of severe lower respiratory tract disease in infants and children. The gene-end (GE) transcription signal of the HPIV3 matrix (M) protein gene is identical to those of the nucleoprotein and phosphoprotein genes except that it contains an apparent 8-nucleotide insert. This was associated with an increased synthesis of a readthrough transcript of the M gene and the downstream fusion (F) protein gene. We hypothesized that this insert may function to downregulate the expression of F protein by interfering with termination/reinitiation at the M-F gene junction, thus promoting the production of M-F readthrough mRNA at the expense of monocistronic F mRNA. To test this hypothesis, two similar recombinant HPIV3 viruses from which this insert in the M-GE signal was removed were generated. The M-GE mutants exhibited a reduction in M-F readthrough mRNA and an increase in monocistronic F mRNA. This resulted in a substantial increase in F protein synthesis in infected cells as well as enhanced incorporation of F protein into virions. The efficiency of mutant virus replication was similar to that of wild-type (wt) HPIV3 bothin vitroandin vivo. However, the F-protein-specific serum antibody response in hamsters was increased for the mutants compared to wt HPIV3. This study identifies a previously undescribed viral mechanism for attenuating the host adaptive immune response. Repairing the M-GE signal should provide a means to increase the antibody response to a live attenuated HPIV3 vaccine without affecting viral replication and attenuation.IMPORTANCEThe HPIV3 M-GE signal was previously shown to contain an apparent 8-nucleotide insert that was associated with increased synthesis of a readthrough mRNA of the M gene and the downstream F gene. However, whether this had any significant effect on the synthesis of monocistronic F mRNA or F protein, virus replication, virion morphogenesis, and immunogenicity was unknown. Here, we show that the removal of this insert shifts F gene transcription from readthrough M-F mRNA to monocistronic F mRNA. This resulted in a substantial increase in the amount of F protein expressed in the cell and packaged in the virus particle. This did not affect virus replication but increased the F-specific antibody response in hamsters. Thus, in wild-type HPIV3, the aberrant M-GE signal operates a previously undescribed mechanism that reduces the expression of a major neutralization and protective antigen, resulting in reduced immunogenicity. This has implications for the design of live attenuated HPIV3 vaccines; specifically, the antibody response against F can be elevated by “repairing” the M-GE signal to achieve higher-level F antigen expression, with no effect on attenuation.