Center for Retrovirus Research, Department of Veterinary Biosciences, The Ohio State University, Columbus, Ohio, United States of America.
Department of Microbiology and Immunology, Carver College of Medicine, University of Iowa, Iowa City, Iowa, United States of America.
PLoS Pathog. 2021 Mar 10;17(3):e1009421. doi: 10.1371/journal.ppat.1009421. eCollection 2021 Mar.
N6-methyladenosine (m6A) is a prevalent RNA modification that plays a key role in regulating eukaryotic cellular mRNA functions. RNA m6A modification is regulated by two groups of cellular proteins, writers and erasers that add or remove m6A, respectively. HIV-1 RNA contains m6A modifications that modulate viral infection and gene expression in CD4+ T cells. However, it remains unclear whether m6A modifications of HIV-1 RNA modulate innate immune responses in myeloid cells that are important for antiviral immunity. Here we show that m6A modification of HIV-1 RNA suppresses the expression of antiviral cytokine type-I interferon (IFN-I) in differentiated human monocytic cells and primary monocyte-derived macrophages. Transfection of differentiated monocytic U937 cells with HIV-1 RNA fragments containing a single m6A-modification significantly reduced IFN-I mRNA expression relative to their unmodified RNA counterparts. We generated HIV-1 with altered m6A levels of RNA by manipulating the expression of the m6A erasers (FTO and ALKBH5) or pharmacological inhibition of m6A addition in virus-producing cells, or by treating HIV-1 RNA with recombinant FTO in vitro. HIV-1 RNA transfection or viral infection of differentiated U937 cells and primary macrophages demonstrated that HIV-1 RNA with decreased m6A levels enhanced IFN-I expression, whereas HIV-1 RNA with increased m6A modifications had opposite effects. Our mechanistic studies indicated that m6A of HIV-1 RNA escaped retinoic acid-induced gene I (RIG-I)-mediated RNA sensing and activation of the transcription factors IRF3 and IRF7 that drive IFN-I gene expression. Together, these findings suggest that m6A modifications of HIV-1 RNA evade innate immune sensing in myeloid cells.
N6-甲基腺苷(m6A)是一种普遍存在的 RNA 修饰,在调节真核细胞 mRNA 功能方面发挥着关键作用。RNA m6A 修饰受两组细胞蛋白调节,分别为加合物和去修饰物,它们分别添加或去除 m6A。HIV-1 RNA 含有 m6A 修饰,可调节 CD4+T 细胞中的病毒感染和基因表达。然而,目前尚不清楚 HIV-1 RNA 的 m6A 修饰是否调节髓样细胞中的固有免疫反应,而髓样细胞对抗病毒免疫至关重要。在这里,我们表明 HIV-1 RNA 的 m6A 修饰可抑制分化的人单核细胞和原代单核细胞衍生的巨噬细胞中抗病毒细胞因子 I 型干扰素(IFN-I)的表达。与未修饰的 RNA 相比,用含有单个 m6A 修饰的 HIV-1 RNA 片段转染分化的单核细胞 U937 细胞,显著降低了 IFN-I mRNA 的表达。我们通过操纵 m6A 去修饰酶(FTO 和 ALKBH5)的表达或在产生病毒的细胞中抑制 m6A 加合物来改变 HIV-1 RNA 的 m6A 水平,或者通过体外用重组 FTO 处理 HIV-1 RNA,生成具有改变的 m6A 水平的 HIV-1 RNA。HIV-1 RNA 转染或分化的 U937 细胞和原代巨噬细胞的病毒感染表明,m6A 水平降低的 HIV-1 RNA 增强了 IFN-I 的表达,而 m6A 修饰增加的 HIV-1 RNA 则具有相反的作用。我们的机制研究表明,HIV-1 RNA 的 m6A 逃避了维甲酸诱导基因 I(RIG-I)介导的 RNA 感应以及转录因子 IRF3 和 IRF7 的激活,这些转录因子驱动 IFN-I 基因的表达。总之,这些发现表明 HIV-1 RNA 的 m6A 修饰逃避了髓样细胞中的固有免疫感应。