Herpes Simplex Virus Type 1 Blocks the Apoptotic Host Cell Defense Mechanisms That Target Bcl-2 and Manipulates Activation of p38 Mitogen-Activated Protein Kinase To Improve Viral Replication

Wild-type (wt) herpes simplex virus type 1 (HSV-1) suppresses cell death. We investigated the apoptotic pathways triggered during infection with mutant viruses tsk and 27lacZ (which lack functional ICP4 and ICP27 viral proteins, respectively) and examined the mechanisms used by wt HSV-1 to protect against programmed cell death induced by the DNA-damaging compound cisplatin. In our studies, we used BHK and HeLa cells, with similar results. We suggest that a decrease in the levels of Bcl-2 protein is a key event during apoptosis induced by the mutant viruses and that Bcl-2 levels are targeted by (i) a decrease of bcl-2 RNA, (ii) caspase-related proteolysis, and (iii) p38 mitogen-activated protein kinase (p38MAPK)-dependent destabilization of Bcl-2 protein. We show that wt HSV-1, but not the mutant viruses, maintains bcl-2 RNA and protein levels during infection and protects from the cisplatin-induced decrease in bcl-2 RNA; our data suggest that both ICP27 and ICP4 are required for this function. Additionally, wt HSV-1 evades but does not actively block activation of caspases. Although wt HSV-1 induces p38MAPK activation during infection, it prevents p38MAPK-dependent destabilization of Bcl-2 and exploits p38MAPK stimulation to enhance transcription of specific viral gene promoters to increase viral yields.

野生型（wild-type，缩写wt）1型单纯疱疹病毒（HSV-1）可抑制细胞死亡。本研究针对分别缺失功能性ICP4、ICP27病毒蛋白的突变病毒株tsk与27lacZ感染所触发的细胞凋亡通路展开探究，并分析野生型HSV-1抵御DNA损伤性化合物顺铂诱导的程序性细胞死亡的作用机制。实验中我们采用了BHK细胞与HeLa细胞，二者得到了一致的实验结果。我们提出，B细胞淋巴瘤/白血病-2蛋白（Bcl-2）水平下调是突变病毒诱导细胞凋亡过程中的关键事件，而Bcl-2的水平受到三重机制调控：（i）bcl-2 RNA水平降低，（ii）半胱天冬酶相关的蛋白水解作用，以及（iii）p38丝裂原活化蛋白激酶（p38MAPK）介导的Bcl-2蛋白不稳定化。研究结果显示，野生型HSV-1（而非上述突变病毒株）可在感染过程中维持bcl-2 RNA与蛋白的水平，并可抵御顺铂诱导的bcl-2 RNA水平下调；我们的数据表明，ICP27与ICP4均为实现该功能所必需的病毒蛋白。此外，野生型HSV-1可规避而非主动阻断半胱天冬酶的激活。尽管野生型HSV-1在感染过程中可诱导p38MAPK激活，但它可抑制p38MAPK介导的Bcl-2蛋白不稳定化，并利用p38MAPK的激活来增强特定病毒基因启动子的转录，从而提升病毒产量。