Landis H, Simon-Jödicke A, Klöti A, Di Paolo C, Schnorr J J, Schneider-Schaulies S, Hefti H P, Pavlovic J
Institute of Medical Virology, University of Zürich, Switzerland.
J Virol. 1998 Feb;72(2):1516-22. doi: 10.1128/JVI.72.2.1516-1522.1998.
Mx proteins form a small family of interferon (IFN)-induced GTPases with potent antiviral activity against various negative-strand RNA viruses. To examine the antiviral spectrum of human MxA in homologous cells, we stably transfected HEp-2 cells with a plasmid directing the expression of MxA cDNA. HEp-2 cells are permissive for many viruses and are unable to express endogenous MxA in response to IFN. Experimental infection with various RNA and DNA viruses revealed that MxA-expressing HEp-2 cells were protected not only against influenza virus and vesicular stomatitis virus (VSV) but also against Semliki Forest virus (SFV), a togavirus with a single-stranded RNA genome of positive polarity. In MxA-transfected cells, viral yields were reduced up to 1,700-fold, and the degree of inhibition correlated well with the expression level of MxA. Furthermore, expression of MxA prevented the accumulation of 49S RNA and 26S RNA, indicating that SFV was inhibited early in its replication cycle. Very similar results were obtained with MxA-transfected cells of the human monocytic cell line U937. The results demonstrate that the antiviral spectrum of MxA is not restricted to negative-strand RNA viruses but also includes SFV, which contains an RNA genome of positive polarity. To test whether MxA protein exerts its inhibitory activity against SFV in the absence of viral structural proteins, we took advantage of a recombinant vector based on the SFV replicon. The vector contains only the coding sequence for the viral nonstructural proteins and the bacterial LacZ gene, which was cloned in place of the viral structural genes. Upon transfection of vector-derived recombinant RNA, expression of the beta-galactosidase reporter gene was strongly reduced in the presence of MxA. This finding indicates that viral components other than the structural proteins are the target of MxA action.
Mx蛋白构成了一个由干扰素（IFN）诱导的GTP酶组成的小家族，对多种负链RNA病毒具有强大的抗病毒活性。为了在同源细胞中检测人MxA的抗病毒谱，我们用一个指导MxA cDNA表达的质粒稳定转染了HEp-2细胞。HEp-2细胞对许多病毒敏感，并且在受到IFN刺激时无法表达内源性MxA。用各种RNA和DNA病毒进行实验性感染后发现，表达MxA的HEp-2细胞不仅对流感病毒和水疱性口炎病毒（VSV）有抵抗力，而且对塞姆利基森林病毒（SFV）也有抵抗力，SFV是一种具有正链单链RNA基因组的披膜病毒。在转染了MxA的细胞中，病毒产量降低了多达1700倍，抑制程度与MxA的表达水平密切相关。此外，MxA的表达阻止了49S RNA和26S RNA的积累，这表明SFV在其复制周期的早期就受到了抑制。在人单核细胞系U937的MxA转染细胞中也获得了非常相似的结果。这些结果表明，MxA的抗病毒谱不仅限于负链RNA病毒，还包括含有正链RNA基因组的SFV。为了测试MxA蛋白在没有病毒结构蛋白的情况下是否对SFV发挥其抑制活性，我们利用了一种基于SFV复制子的重组载体。该载体仅包含病毒非结构蛋白的编码序列和细菌LacZ基因，LacZ基因被克隆以取代病毒结构基因。转染载体衍生的重组RNA后，在存在MxA的情况下，β-半乳糖苷酶报告基因的表达被强烈降低。这一发现表明，除结构蛋白外的病毒成分是MxA作用的靶点。
