Abstract
BackgroundVaricella-zoster virus (VZV) is the causative agent of varicella and zoster. The immediate-early protein, IE62 is the predominant VZ virion tegument protein, transactivating the expression of all kinetic classes of VZV genes. IE62 is localized to punctae that form DNA replication compartments in the nuclei of VZV infected cells. The morphological changes and the increase in the size of replication compartments that express IE62 are correlated with production of VZ virions. Mammalian Mediator serves as a coactivator of IE62 and functions by bridging DNA-binding transcription factors¸ RNA polymerase II (RNAP II) and their target DNAs for VZV replication. While VZV is highly sensitive to type I interferons (IFNs), how IFN-α inhibits early events during VZV replication is poorly understood.ResultsIn this study, we performed in situ analysis to investigate the effects of IFN-α on the dynamic interactions of IE62 with the Mediator MED25 subunit and the RNAP II negative regulator cycle-dependent kinase 8 (CDK8) in VZV infected cells by confocal immunofluorescence. We found that in addition to dose-dependent inhibition of the yields of infectious virus by IFN treatment, IFN-α prominently impeded the development of large IE62+ nuclear compartments and significantly decreased transcription of VZV genes. Both the expression level and stable recruitment of MED25 to IE62+ replication compartments were inhibited by IFN-α. While IFN-α treatment upregulated CDK8 expression, redistribution and recruitment of CDK8 to IE62+ replication compartments in infected cells was not affected by VZV.ConclusionIFN-α exerts multiple inhibitory activities against virus infections. In this study, we provide visionary demonstration that continuous translocation of MED25 into VZV replication compartments ensures production of virions. IFN-α greatly impedes the formation of a stable complex between IE62 and the Mediator complex thereby suppresses VZV gene transcription. Our demonstration that IFN-α-induced antiviral effect against VZV infection is through inhibiting the reorganization of nuclear components uncovers a novel function of IFN-α. Targeting the interaction between IE62 and MED25 may offer a novel approach to the development of antiviral agents against VZV infection.
Highlights
Varicella-zoster virus (VZV) is the causative agent of varicella and zoster
We found that stable recruitment of Mediator 25 (MED25) to VZV replication compartments positively correlated with the progressive development of IE62-expressing large and large globular punctae in VZV-infected cells
With the advancement in digital microscopy technology, we investigated the dynamic interaction between viral transcription factor IE62 and Mediator within viral replication compartments at single cell level
Summary
Varicella-zoster virus (VZV) is the causative agent of varicella and zoster. The immediate-early protein, IE62 is the predominant VZ virion tegument protein, transactivating the expression of all kinetic classes of VZV genes. IE62 is localized to punctae that form DNA replication compartments in the nuclei of VZV infected cells. While VZV is highly sensi‐ tive to type I interferons (IFNs), how IFN-α inhibits early events during VZV replication is poorly understood. It has a double-stranded DNA genome of about 125,000 base pairs which encodes for at least 70 unique open. IFN-α treatment dose-dependently inhibits the production of VZV in human foreskin fibroblast cells. [3] and the expression of VZV immediate-early, early and late proteins are suppressed in IFN-α treated cells [4]. While IFN-induced activation of antiviral protein kinase R correlates with inhibition of VZV replication [6], how IFN-α inhibits early events of VZV replication is poorly understood
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