Department of Biotechnology, College of Life Science and Technology, Jinan University, Guangzhou, Guangdong, China.
School of Public Health, University of California, Berkeley, Berkeley, California, United States of America.
PLoS Pathog. 2018 Jan 29;14(1):e1006867. doi: 10.1371/journal.ppat.1006867. eCollection 2018 Jan.
Interferon-γ (IFN-γ) represents one of the most important innate immunity responses in a host to combat infections of many human viruses including human herpesviruses. Human N-myc interactor (Nmi) protein, which has been shown to interact with signal transducer and activator of transcription (STAT) proteins including STAT1, is important for the activation of IFN-γ induced STAT1-dependent transcription of many genes responsible for IFN-γ immune responses. However, no proteins encoded by herpesviruses have been reported to interact with Nmi and inhibit Nmi-mediated activation of IFN-γ immune responses to achieve immune evasion from IFN-γ responses. In this study, we show strong evidence that the UL23 protein of human cytomegalovirus (HCMV), a human herpesvirus, specifically interacts with Nmi. This interaction was identified through a yeast two-hybrid screen and co-immunoprecipitation in human cells. We observed that Nmi, when bound to UL23, was not associated with STAT1, suggesting that UL23 binding of Nmi disrupts the interaction of Nmi with STAT1. In cells overexpressing UL23, we observed (a) significantly reduced levels of Nmi and STAT1 in the nuclei, the sites where these proteins act to induce transcription of IFN-γ stimulated genes, and (b) decreased levels of the induction of the transcription of IFN-γ stimulated genes. UL23-deficient HCMV mutants induced higher transcription of IFN-γ stimulated genes and exhibited lower titers than parental and control revertant viruses expressing functional UL23 in IFN-γ treated cells. Thus, UL23 appears to interact directly with Nmi and inhibit nuclear translocation of Nmi and its associated protein STAT1, leading to a decrease of IFN-γ induced responses and an increase of viral resistance to IFN-γ. Our results further highlight the roles of UL23-Nmi interactions in facilitating viral immune escape from IFN-γ responses and enhancing viral resistance to IFN antiviral effects.
干扰素-γ (IFN-γ) 是宿主对抗多种人类病毒感染的最重要的固有免疫反应之一，包括人类疱疹病毒。人类 N- myc 相互作用蛋白 (Nmi) 已被证明与信号转导和转录激活剂 (STAT) 蛋白相互作用，包括 STAT1，对于激活 IFN-γ 诱导的许多与 IFN-γ 免疫反应相关的 STAT1 依赖性转录至关重要。然而，尚未报道疱疹病毒编码的任何蛋白与 Nmi 相互作用并抑制 Nmi 介导的 IFN-γ 免疫反应的激活，以逃避 IFN-γ 反应。在这项研究中，我们提供了强有力的证据表明人类巨细胞病毒 (HCMV) 的 UL23 蛋白，一种人类疱疹病毒，与 Nmi 特异性相互作用。这种相互作用是通过酵母双杂交筛选和人细胞中的共免疫沉淀鉴定的。我们观察到，当 Nmi 与 UL23 结合时，它不与 STAT1 相关，这表明 UL23 结合 Nmi 破坏了 Nmi 与 STAT1 的相互作用。在过量表达 UL23 的细胞中，我们观察到 (a) 细胞核中 Nmi 和 STAT1 的水平显著降低，这些蛋白质在这些部位作用以诱导 IFN-γ 刺激基因的转录，以及 (b) IFN-γ 刺激基因转录的诱导水平降低。UL23 缺失的 HCMV 突变体在 IFN-γ 处理的细胞中诱导更高水平的 IFN-γ 刺激基因转录，并且比表达功能性 UL23 的亲本和对照回复病毒的滴度更低。因此，UL23 似乎直接与 Nmi 相互作用并抑制 Nmi 和其相关蛋白 STAT1 的核易位，导致 IFN-γ 诱导的反应减少和病毒对 IFN-γ 的抗病毒作用的抗性增加。我们的结果进一步强调了 UL23-Nmi 相互作用在促进病毒从 IFN-γ 反应中免疫逃逸和增强病毒对 IFN 抗病毒作用的抗性中的作用。
