Department of Molecular and Cell Biology, University of California Berkeley, Berkeley, California, USA.
Department of Plant & Microbial Biology, University of California Berkeley, Berkeley, California, USA.
J Virol. 2020 Jul 1;94(14). doi: 10.1128/JVI.00262-20.
Short interspersed nuclear elements (SINEs) are RNA polymerase III (RNAPIII)-transcribed, retrotransposable noncoding RNA (ncRNA) elements ubiquitously spread throughout mammalian genomes. While normally silenced in healthy somatic tissue, SINEs can be induced during infection with DNA viruses, including the model murine gammaherpesvirus 68 (MHV68). Here, we explored the mechanisms underlying MHV68 activation of SINE ncRNAs. We demonstrate that lytic MHV68 infection of B cells, macrophages, and fibroblasts leads to robust activation of the B2 family of SINEs in a cell-autonomous manner. B2 ncRNA induction requires neither host innate immune signaling factors nor involvement of the RNAPIII master regulator Maf1. However, we identified MHV68 ORF36, the conserved herpesviral kinase, as playing a key role in B2 induction during lytic infection. SINE activation is linked to ORF36 kinase activity and can also be induced by inhibition of histone deacetylases 1 and 2 (HCAC 1/2), which is one of the known ORF36 functions. Collectively, our data suggest that ORF36-mediated changes in chromatin modification contribute to B2 activation during MHV68 infection and that this activity is conserved in other herpesviral protein kinase homologs. Viral infection dramatically changes the levels of many types of RNA in a cell. In particular, certain oncogenic viruses activate expression of repetitive genes called retrotransposons, which are normally silenced due to their ability to copy and spread throughout the genome. Here, we established that infection with the gammaherpesvirus MHV68 leads to a dramatic induction of a class of noncoding retrotransposons called B2 SINEs in multiple cell types. We then explored how MHV68 activates B2 SINEs, revealing a role for the conserved herpesviral protein kinase ORF36. Both ORF36 kinase-dependent and kinase-independent functions contribute to B2 induction, perhaps through ORF36 targeting of proteins involved in controlling the accessibility of chromatin surrounding SINE loci. Understanding the features underlying induction of these elements following MHV68 infection should provide insight into core elements of SINE regulation, as well as disregulation of SINE elements associated with disease.
短散在核元件 (SINEs) 是 RNA 聚合酶 III (RNAPIII) 转录的、反转录转座的非编码 RNA (ncRNA) 元件，广泛分布于哺乳动物基因组中。虽然在健康的体细胞组织中通常处于沉默状态，但 SINEs 可以在感染 DNA 病毒时被诱导，包括模型鼠 γ 疱疹病毒 68 (MHV68)。在这里，我们探讨了 MHV68 激活 SINE ncRNAs 的机制。我们证明，裂解性 MHV68 感染 B 细胞、巨噬细胞和成纤维细胞会以细胞自主性方式强烈激活 B2 家族的 SINE。B2 ncRNA 的诱导既不需要宿主先天免疫信号因子，也不需要参与 RNAPIII 主调控因子 Maf1。然而，我们发现 MHV68 ORF36，即保守的疱疹病毒激酶，在裂解感染期间 B2 的诱导中起着关键作用。SINE 的激活与 ORF36 激酶活性有关，也可以通过抑制组蛋白去乙酰化酶 1 和 2 (HCAC 1/2) 来诱导，这是 ORF36 的已知功能之一。总的来说，我们的数据表明，ORF36 介导的染色质修饰变化有助于 MHV68 感染期间 B2 的激活，并且这种活性在其他疱疹病毒蛋白激酶同源物中是保守的。病毒感染会导致细胞内多种类型 RNA 的水平发生剧烈变化。特别是，某些致癌病毒会激活称为反转录转座子的重复基因的表达，由于它们能够复制并在基因组中扩散，这些基因通常处于沉默状态。在这里，我们证实，感染 γ 疱疹病毒 MHV68 会导致多种细胞类型中一类称为 B2 SINE 的非编码反转录转座子的显著诱导。然后，我们探讨了 MHV68 如何激活 B2 SINE，揭示了保守的疱疹病毒蛋白激酶 ORF36 的作用。ORF36 激酶依赖性和非依赖性功能都有助于 B2 的诱导，这可能是通过 ORF36 靶向参与控制 SINE 基因座周围染色质可及性的蛋白质来实现的。了解 MHV68 感染后这些元件诱导的特征应该为 SINE 调控的核心要素以及与疾病相关的 SINE 元件的失调提供深入的了解。
