Duguay Brett A, Saffran Holly A, Ponomarev Alina, Duley Shayla A, Eaton Heather E, Smiley James R
Li Ka Shing Institute of Virology, Department of Medical Microbiology and Immunology, University of Alberta, Edmonton, Alberta, Canada.
J Virol. 2014 Mar;88(5):2967-76. doi: 10.1128/JVI.03129-13. Epub 2013 Dec 26.
Infection with herpes simplex virus type 1 (HSV-1) results in the rapid elimination of mitochondrial DNA (mtDNA) from host cells. It is known that a mitochondrial isoform of the viral alkaline nuclease (UL12) called UL12.5 triggers this process. However, very little is known about the impact of mtDNA depletion on viral replication or the biology of HSV-1 infections. These questions have been difficult to address because UL12.5 and UL12 are encoded by overlapping transcripts that share the same open reading frame. As a result, mutations that alter UL12.5 also affect UL12, and UL12 null mutations severely impair viral growth by interfering with the intranuclear processing of progeny viral genomes. Therefore, to specifically assess the impact of mtDNA depletion on viral replication, it is necessary to eliminate the activity of UL12.5 while preserving the nuclear functions of UL12. Previous work has shown that the human cytomegalovirus alkaline nuclease UL98 can functionally substitute for UL12 during HSV-1 replication. We found that UL98 is unable to deplete mtDNA in transfected cells and therefore generated an HSV-1 variant in which UL98 coding sequences replace the UL12/UL12.5 open reading frame. The resulting virus was severely impaired in its ability to trigger mtDNA loss but reached titers comparable to those of wild-type HSV-1 in one-step and multistep growth experiments. Together, these observations demonstrate that the elimination of mtDNA is not required for HSV-1 replication in cell culture.
Herpes simplex virus types 1 and 2 destroy the DNA of host cell mitochondria, the powerhouses of cells. Epstein-Barr virus, a distantly related herpesvirus, has a similar effect, indicating that mitochondrial DNA destruction is under positive selection and thus confers a benefit to the virus. The present work shows that mitochondrial DNA destruction is not required for efficient replication of herpes simplex virus type 1 in cultured Vero kidney epithelial cells, suggesting that this activity likely benefits the virus in other cell types or in the intact human host.
单纯疱疹病毒1型（HSV-1）感染会导致宿主细胞中的线粒体DNA（mtDNA）迅速清除。已知病毒碱性核酸酶（UL12）的一种线粒体异构体UL12.5会触发这一过程。然而，关于mtDNA消耗对病毒复制或HSV-1感染生物学的影响，人们了解甚少。由于UL12.5和UL12由共享相同开放阅读框的重叠转录本编码，这些问题一直难以解决。因此，改变UL12.5的突变也会影响UL12，而UL12无效突变会通过干扰子代病毒基因组的核内加工严重损害病毒生长。因此，为了具体评估mtDNA消耗对病毒复制的影响，有必要在保留UL12核功能的同时消除UL12.5的活性。先前的研究表明，人巨细胞病毒碱性核酸酶UL98在HSV-1复制过程中可以在功能上替代UL12。我们发现UL98无法在转染细胞中消耗mtDNA，因此产生了一种HSV-1变体，其中UL98编码序列取代了UL12/UL12.5开放阅读框。在一步和多步生长实验中，产生的病毒触发mtDNA丢失的能力严重受损，但达到了与野生型HSV-1相当的滴度。这些观察结果共同表明，在细胞培养中HSV-1复制不需要消除mtDNA。
单纯疱疹病毒1型和2型会破坏宿主细胞线粒体（细胞的动力源）的DNA。爱泼斯坦-巴尔病毒是一种亲缘关系较远的疱疹病毒，也有类似的作用，这表明线粒体DNA破坏处于正选择之下，因此对病毒有益。目前的研究表明，在培养的非洲绿猴肾上皮细胞中，单纯疱疹病毒1型的有效复制不需要线粒体DNA破坏，这表明这种活性可能在其他细胞类型或完整的人类宿主中对病毒有益。
