Hussain Snawar, Perlman Stanley, Gallagher Thomas M
Department of Microbiology and Immunology, Loyola University Medical Center, 2160 South First Avenue, Maywood, IL 60153, USA.
J Virol. 2008 Jul;82(14):7212-22. doi: 10.1128/JVI.02406-07. Epub 2008 Apr 30.
The severe acute respiratory syndrome coronavirus (SARS-CoV) encodes numerous accessory proteins whose importance in the natural infection process is currently unclear. One of these accessory proteins is set apart by its function in the context of a related murine hepatitis virus (MHV) infection. SARS-CoV protein 6 increases MHV neurovirulence and accelerates MHV infection kinetics in tissue culture. Protein 6 also blocks nuclear import of macromolecules from the cytoplasm, a process known to involve its C-terminal residues interacting with cellular importins. In this study, protein 6 was expressed from plasmid DNAs and accumulated in cells prior to infection by wild-type MHV. Output of MHV progeny was significantly increased by preexisting protein 6. Protein 6 with C-terminal deletion mutations no longer interfered with nuclear import processes but still retained much of the capacity to augment MHV infections. However, some virus growth-enhancing activity could be ascribed to the C-terminal end of protein 6. To determine whether this augmentation provided by the C terminus was derived from interference with nuclear import, we evaluated the virus-modulating effects of small interfering RNAs (siRNAs) directed against importin-beta mRNAs, which down-regulated classical nuclear import pathways. The siRNAs did indeed prime cells for enhanced MHV infection. Our findings indicated that protein 6-mediated nuclear import blocks augmented MHV infections but is clearly not the only way that this accessory protein operates to create a milieu conducive to robust virus growth. Thus, the SARS-CoV protein 6 accelerates MHV infections by more than one mechanism.
严重急性呼吸综合征冠状病毒（SARS-CoV）编码多种辅助蛋白，目前其在自然感染过程中的重要性尚不清楚。这些辅助蛋白之一因其在相关鼠肝炎病毒（MHV）感染中的功能而显得与众不同。SARS-CoV蛋白6可增加MHV的神经毒力，并加速其在组织培养中的感染动力学。蛋白6还会阻断大分子从细胞质的核输入，这一过程已知涉及其C末端残基与细胞输入蛋白的相互作用。在本研究中，蛋白6由质粒DNA表达，并在野生型MHV感染之前在细胞中积累。预先存在的蛋白6显著增加了MHV子代的产量。具有C末端缺失突变的蛋白6不再干扰核输入过程，但仍保留了增强MHV感染的大部分能力。然而，一些病毒生长增强活性可归因于蛋白6的C末端。为了确定C末端提供的这种增强作用是否源于对核输入的干扰，我们评估了针对输入蛋白β mRNA的小干扰RNA（siRNA）对病毒的调节作用，这些siRNA下调了经典的核输入途径。这些siRNA确实使细胞对增强的MHV感染产生了预适应。我们的研究结果表明，蛋白6介导的核输入阻断增强了MHV感染，但显然不是这种辅助蛋白促进病毒强劲生长的唯一方式。因此，SARS-CoV蛋白6通过多种机制加速MHV感染。
