Gordien E, Rosmorduc O, Peltekian C, Garreau F, Bréchot C, Kremsdorf D
INSERM U370, Institut Necker, Paris, France.
J Virol. 2001 Mar;75(6):2684-91. doi: 10.1128/JVI.75.6.2684-2691.2001.
Human MxA is an alpha/beta interferon-inducible intracytoplasmic protein that mediates antiviral activity against several RNA viruses. We had previously shown that overexpression of the hepatitis B virus (HBV) capsid led to selective downregulation of MxA gene expression, suggesting a mechanism by which the virus escapes from the host defense system (O. Rosmorduc, H. Sirma, P. Soussan, E. Gordien, P. Lebon, M. Horisberger, C. Brechot and D. Kremsdorf, J. Gen. Virol. 80:1253-1262, 1999). In the present study, we investigated the antiviral activity of MxA protein against HBV. MxA-expressing HuH7 clones were established and transiently transfected with HBV, and viral replication was then studied. Viral protein secretion was profoundly reduced in MxA-expressing clones by 80% for HBV surface antigen (HBsAg) and 70% for HBV e antigen (HBeAg). The levels of intracytoplasmic HBsAg and HBeAg were reduced by about 80 and 50% in the two MxA-positive clones tested. A nearly complete disappearance of HBV DNA replicative intermediates was observed in MxA-expressing clones. Although the expression of total viral RNAs was not modified, two- to fourfold reductions in HBV cytoplasmic RNAs were found in MxA-expressing clones. This suggests the inhibition of HBV replication at a posttranscriptional level. Indeed, using the well-characterized posttranscriptional regulation element (PRE) reporter system, we were able to demonstrate a marked reduction (three- to eightfold) in the nucleocytoplasmic export of unspliced RNA in MxA-expressing clones. In addition, MxA protein did not interact with HBV nucleocapsid or interfere with HBV nucleocapsid formation. Our results show an antiviral effect of MxA protein on a DNA virus for the first time. MxA protein acts, at least in part, by inhibiting the nucleocytoplasmic export of viral mRNA via the PRE sequence.
人MxA是一种α/β干扰素诱导的胞质内蛋白，可介导针对多种RNA病毒的抗病毒活性。我们之前已经表明，乙型肝炎病毒（HBV）衣壳的过表达导致MxA基因表达的选择性下调，这提示了病毒逃避宿主防御系统的一种机制（O. Rosmorduc、H. Sirma、P. Soussan、E. Gordien、P. Lebon、M. Horisberger、C. Brechot和D. Kremsdorf，《普通病毒学杂志》80:1253 - 1262，1999年）。在本研究中，我们研究了MxA蛋白对HBV的抗病毒活性。建立了表达MxA的HuH7克隆，并将其用HBV进行瞬时转染，然后研究病毒复制。在表达MxA的克隆中，病毒蛋白分泌显著减少，乙型肝炎表面抗原（HBsAg）减少80%，乙型肝炎e抗原（HBeAg）减少70%。在所检测的两个MxA阳性克隆中，胞质内HBsAg和HBeAg水平分别降低了约80%和50%。在表达MxA的克隆中观察到HBV DNA复制中间体几乎完全消失。尽管总病毒RNA的表达未改变，但在表达MxA的克隆中发现HBV细胞质RNA减少了2至4倍。这表明在转录后水平抑制了HBV复制。实际上，使用特征明确的转录后调控元件（PRE）报告系统，我们能够证明在表达MxA的克隆中，未剪接RNA的核质输出显著减少（3至8倍）。此外，MxA蛋白不与HBV核衣壳相互作用，也不干扰HBV核衣壳的形成。我们的结果首次显示了MxA蛋白对DNA病毒的抗病毒作用。MxA蛋白至少部分地通过PRE序列抑制病毒mRNA的核质输出发挥作用。
