Kim Hyoji, Choi Hoyun, Lee Suk Kyeong
Department of Medical Lifescience, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea.
Department of Medical Lifescience, College of Medicine, The Catholic University of Korea, Seoul, Republic of Korea
J Virol. 2015 Nov 18;90(3):1359-68. doi: 10.1128/JVI.02794-15. Print 2016 Feb 1.
Epstein-Barr virus (EBV) is a human gammaherpesvirus associated with a variety of tumor types. EBV can establish latency or undergo lytic replication in host cells. In general, EBV remains latent in tumors and expresses a limited repertoire of latent proteins to avoid host immune surveillance. When the lytic cycle is triggered by some as-yet-unknown form of stimulation, lytic gene expression and progeny virus production commence. Thus far, the exact mechanism of EBV latency maintenance and the in vivo triggering signal for lytic induction have yet to be elucidated. Previously, we have shown that the EBV microRNA miR-BART20-5p directly targets the immediate early genes BRLF1 and BZLF1 as well as Bcl-2-associated death promoter (BAD) in EBV-associated gastric carcinoma. In this study, we found that both mRNA and protein levels of BRLF1 and BZLF1 were suppressed in cells following BAD knockdown and increased after BAD overexpression. Progeny virus production was also downregulated by specific knockdown of BAD. Our results demonstrated that caspase-3-dependent apoptosis is a prerequisite for BAD-mediated EBV lytic cycle induction. Therefore, our data suggest that miR-BART20-5p plays an important role in latency maintenance and tumor persistence of EBV-associated gastric carcinoma by inhibiting BAD-mediated caspase-3-dependent apoptosis, which would trigger immediate early gene expression.
EBV has an ability to remain latent in host cells, including EBV-associated tumor cells hiding from immune surveillance. However, the exact molecular mechanisms of EBV latency maintenance remain poorly understood. Here, we demonstrated that miR-BART20-5p inhibited the expression of EBV immediate early genes indirectly, by suppressing BAD-induced caspase-3-dependent apoptosis, in addition to directly, as we previously reported. Our study suggests that EBV-associated tumor cells might endure apoptotic stress to some extent and remain latent with the aid of miR-BART20-5p. Blocking the expression or function of BART20-5p may expedite EBV-associated tumor cell death via immune attack and apoptosis.
爱泼斯坦-巴尔病毒（EBV）是一种与多种肿瘤类型相关的人类γ疱疹病毒。EBV可在宿主细胞中建立潜伏状态或进行裂解复制。一般来说，EBV在肿瘤中保持潜伏状态，并表达有限的潜伏蛋白库以逃避宿主免疫监视。当裂解周期由某种未知形式的刺激触发时，裂解基因表达和子代病毒产生开始。迄今为止，EBV潜伏维持的确切机制以及裂解诱导的体内触发信号尚未阐明。此前，我们已表明EBV微小RNA miR-BART20-5p在EBV相关胃癌中直接靶向立即早期基因BRLF1和BZLF1以及Bcl-2相关死亡促进因子（BAD）。在本研究中，我们发现BAD敲低后细胞中BRLF1和BZLF1的mRNA和蛋白水平均受到抑制，而BAD过表达后则升高。子代病毒产生也因BAD的特异性敲低而下调。我们的结果表明，半胱天冬酶-3依赖性凋亡是BAD介导的EBV裂解周期诱导的先决条件。因此，我们的数据表明miR-BART20-5p通过抑制BAD介导的半胱天冬酶-3依赖性凋亡在EBV相关胃癌的潜伏维持和肿瘤持续存在中起重要作用，而这种凋亡会触发立即早期基因表达。
EBV有能力在宿主细胞中保持潜伏状态，包括EBV相关肿瘤细胞逃避免疫监视。然而，EBV潜伏维持的确切分子机制仍知之甚少。在这里，我们证明miR-BART20-5p除了如我们之前报道的那样直接作用外，还通过抑制BAD诱导的半胱天冬酶-3依赖性凋亡间接抑制EBV立即早期基因的表达。我们的研究表明，EBV相关肿瘤细胞可能在一定程度上耐受凋亡应激，并借助miR-BART20-5p保持潜伏状态。阻断BART20-5p的表达或功能可能通过免疫攻击和凋亡加速EBV相关肿瘤细胞死亡。
