Molecular Virology Laboratory, VA-MD Regional College of Veterinary Medicine and Maryland Pathogen Research Institute, University of Maryland, College Park, Maryland, United States of America.
PLoS One. 2012;7(6):e39438. doi: 10.1371/journal.pone.0039438. Epub 2012 Jun 20.
Rhesus monkey rhadinovirus (RRV) is a gamma-2 herpesvirus closely related to human herpesvirus 8 (HHV8). RRV encodes viral FLICE inhibitory protein (vFLIP), which has death effector domains. Little is known about RRV vFLIP. This study intended to examine its function in apoptosis. Here we found that RRV vFLIP inhibits apoptosis induced by tumor necrosis factor-α (TNF-α) and cycloheximide. In HeLa cells with vFLIP expression, the cleavage of poly [ADP-ribose] polymerase 1 (PARP-1) and activities of caspase 3, 7, and 9 were much lower than those in controls. Cell viability of HeLa cells with vFLIP expression was significantly higher than control cells after apoptosis induction. However, RRV vFLIP appears unable to induce NF-κB signaling when tested in NF-κB reporter assay. RRV vFLIP was able to enhance cell survival under starved conditions or apoptosis induction. At early time points after apoptosis induction, autophagosome formation was enhanced and LC3-II level was elevated in cells with vFLIP and, when autophagy was blocked with chemical inhibitors, these cells underwent apoptosis. Moreover, RRV latent infection of BJAB B-lymphoblastoid cells protects the cells against apoptosis by enhancing autophagy to maintain cell survival. Knockdown of vFLIP expression in the RRV-infected BJAB cells with siRNA abolished the protection against apoptosis. These results indicate that vFLIP protects cells against apoptosis by enhancing autophagosome formation to extend cell survival. The finding of vFLIP's inhibition of apoptosis via the autophagy pathway provides insights of vFLIP in RRV pathogenesis.
恒河猴疱疹病毒（RRV）是一种与人类疱疹病毒 8（HHV8）密切相关的γ-2 疱疹病毒。RRV 编码病毒 FLICE 抑制蛋白（vFLIP），它具有死亡效应结构域。目前对 RRV vFLIP 的了解甚少。本研究旨在研究其在细胞凋亡中的功能。研究发现，RRV vFLIP 抑制肿瘤坏死因子-α（TNF-α）和环已亚胺诱导的细胞凋亡。在表达 vFLIP 的 HeLa 细胞中，多聚[ADP-核糖]聚合酶 1（PARP-1）的切割和 caspase 3、7、9 的活性明显低于对照组。在诱导细胞凋亡后，表达 vFLIP 的 HeLa 细胞的细胞活力明显高于对照组细胞。然而，在 NF-κB 报告基因检测中，RRV vFLIP 似乎不能诱导 NF-κB 信号。RRV vFLIP 能够在饥饿条件下或诱导细胞凋亡时增强细胞存活。在细胞凋亡诱导后的早期时间点，自噬体的形成增强，LC3-II 水平升高，在表达 vFLIP 的细胞中，当用化学抑制剂阻断自噬时，这些细胞发生凋亡。此外，RRV 对 BJAB B 淋巴细胞样细胞的潜伏感染通过增强自噬来维持细胞存活，从而保护细胞免受凋亡。用 siRNA 敲低感染 RRV 的 BJAB 细胞中的 vFLIP 表达，会消除对细胞凋亡的保护作用。这些结果表明，vFLIP 通过增强自噬体的形成来保护细胞免受凋亡，从而延长细胞的存活时间。vFLIP 通过自噬途径抑制细胞凋亡的发现为 vFLIP 在 RRV 发病机制中的作用提供了新的认识。
