Hahn Angela M, Huye Leslie E, Ning Shunbin, Webster-Cyriaque Jennifer, Pagano Joseph S
Department of Microbiology and Immunology, University of North Carolina, Chapel Hill, 27599, USA.
J Virol. 2005 Aug;79(15):10040-52. doi: 10.1128/JVI.79.15.10040-10052.2005.
Virus infection stimulates potent antiviral responses; specifically, Epstein-Barr virus (EBV) infection induces and activates interferon regulatory factor 7 (IRF-7), which is essential for production of alpha/beta interferons (IFN-alpha/beta) and upregulates expression of Tap-2. Here we present evidence that during cytolytic viral replication the immediate-early EBV protein BZLF-1 counteracts effects of IRF-7 that are central to host antiviral responses. We initiated these studies by examining IRF-7 protein expression in vivo in lesions of hairy leukoplakia (HLP) in which there is abundant EBV replication but the expected inflammatory infiltrate is absent. This absence might predict that factors involved in the antiviral response are absent or inactive. First, we detected significant levels of IRF-7 in the nucleus, as well as in the cytoplasm, of cells in HLP lesions. IRF-7 activity in cell lines during cytolytic viral replication was examined by assay of the IRF-7-responsive promoters, IFN-alpha4, IFN-beta, and Tap-2, as well as of an IFN-stimulated response element (ISRE)-containing reporter construct. These reporter constructs showed consistent reduction of activity during lytic replication. Both endogenous and transiently expressed IRF-7 and EBV BZLF-1 proteins physically associate in cell culture, although BZLF-1 had no effect on the nuclear localization of IRF-7. However, IRF-7-dependent activity of the IFN-alpha4, IFN-beta, and Tap-2 promoters, as well as an ISRE promoter construct, was inhibited by BZLF-1. This inhibition occurred in the absence of other EBV proteins and was independent of IFN signaling. Expression of BZLF-1 also inhibited activation of IRF-7 by double-stranded RNA, as well as the activity of a constitutively active mutant form of IRF-7. Negative regulation of IRF-7 by BZLF-1 required the activation domain but not the DNA-binding domain of BZLF-1. Thus, EBV may subvert cellular antiviral responses and immune detection by blocking the activation of IFN-alpha4, IFN-beta, and Tap-2 by IRF-7 through the medium of BZLF-1 as a negative regulator.
病毒感染会激发强大的抗病毒反应；具体而言，爱泼斯坦-巴尔病毒（EBV）感染会诱导并激活干扰素调节因子7（IRF-7），而IRF-7对于α/β干扰素（IFN-α/β）的产生至关重要，并会上调Tap-2的表达。在此，我们提供证据表明，在溶细胞性病毒复制过程中，EBV的立即早期蛋白BZLF-1会抵消IRF-7对宿主抗病毒反应至关重要的作用。我们通过检测毛状白斑（HLP）病变中IRF-7蛋白的体内表达来开展这些研究，在HLP病变中有大量EBV复制，但预期的炎性浸润却不存在。这种不存在可能预示着参与抗病毒反应的因子不存在或无活性。首先，我们在HLP病变细胞的细胞核以及细胞质中检测到了显著水平的IRF-7。通过检测IRF-7反应性启动子、IFN-α4、IFN-β和Tap-2以及含干扰素刺激反应元件（ISRE）的报告构建体，研究了溶细胞性病毒复制过程中细胞系中IRF-7的活性。这些报告构建体显示在裂解复制过程中活性持续降低。内源性和瞬时表达的IRF-7与EBV BZLF-1蛋白在细胞培养中会发生物理结合，尽管BZLF-1对IRF-7的核定位没有影响。然而，IFN-α4、IFN-β和Tap-2启动子以及ISRE启动子构建体的IRF-7依赖性活性受到BZLF-1的抑制。这种抑制在没有其他EBV蛋白的情况下发生，并且独立于干扰素信号传导。BZLF-1的表达还抑制了双链RNA对IRF-7的激活以及组成型活性突变形式的IRF-7的活性。BZLF-1对IRF-7的负调控需要BZLF-1的激活结构域而非DNA结合结构域。因此，EBV可能通过作为负调控因子的BZLF-1来阻断IRF-7对IFN-α4、IFN-β和Tap-2的激活，从而颠覆细胞的抗病毒反应和免疫检测。
