Herpesvirus Saimiri Antagonizes Nuclear Domain 10-Instituted Intrinsic Immunity via an ORF3-Mediated Selective Degradation of Cellular Protein Sp100

Promyelocytic leukemia nuclear bodies (PML-NBs) are nuclear structures that accumulate intrinsic host factors to restrict viral infections. To ensure viral replication, these must be limited by expression of viral early regulatory proteins that functionally inhibit PML-NB-associated antiviral effects. To benefit from the activating capabilities of Sp100A and simultaneously limit repression by Sp100B, -C, and -HMG, adenoviruses (Ads) employ several features to selectively and individually target these isoforms. Ads induce relocalization of Sp100B, -C, and -HMG from PML-NBs prior to association with viral replication centers. In contrast, Sp100A is kept at the PML tracks that surround the newly formed viral replication centers as designated sites of active transcription. We concluded that the host restriction factors Sp100B, -C, and -HMG are potentially inactivated by active displacement from these sites, whereas Sp100A is retained to amplify Ad gene expression. Ad-dependent loss of Sp100 SUMOylation is another crucial part of the virus repertoire to counteract intrinsic immunity by circumventing Sp100 association with HP1, therefore limiting chromatin condensation. We provide evidence that Ad selectively counteracts antiviral responses and, at the same time, benefits from PML-NB-associated components which support viral gene expression by actively recruiting them to PML track-like structures. Our findings provide insights into novel strategies for manipulating transcriptional regulation to either inactivate or amplify viral gene expression. IMPORTANCEWe describe an adenoviral evasion strategy that involves isoform-specific and active manipulation of the PML-associated restriction factor Sp100. Recently, we reported that the adenoviral transactivator E1A targets PML-II to efficiently activate viral transcription. In contrast, the PML-associated proteins Daxx and ATRX are inhibited by early viral factors. We show that this concept is more intricate and significant than originally believed, since adenoviruses apparently take advantage of specific PML-NBassociated proteins and simultaneously inhibit antiviral measures to maintain the viral infectious program. Specifically, we observed Ad-induced relocalization of the Sp100 isoforms B, C, and HMG from PML-NBs juxtaposed with viral replication centers. In contrast, Sp100A is retained at Ad-induced PML tracks that surround the newly formed viral replication centers, acting as designated sites of active transcription. The host restriction factors Sp100B, -C, and -HMG are potentially inactivated by active displacement from these sites, whereas Sp100A is retained to amplify Ad gene expression.

Section: Discussionsupporting

confidence: 76%

Sp100 Isoform-Specific Regulation of Human Adenovirus 5 Gene Expression

Berscheminski

Wimmer

Brun

et al. 2014

“…EpsteinBarr virus (EBV) disrupts ND10 and the ATRX-hDaxx complex through the actions of BZLF1 and BNRF1, respectively (8,72), and causes a dispersal of Sp100 and hDaxx from ND10 during lytic replication (73). Along the same lines, the murine gammaherpesvirus 68 tegument protein orf75c induces degradation of PML (74), while the related protein ORF3 of herpesvirus saimiri specifically degrades Sp100 but affects neither PML nor hDaxx (75). Although via different mechanisms and mediated by viral regulatory proteins that in most cases have little or no sequence similarity, all of these viruses appear to target the same group of cellular proteins to counteract the initial repression of viral gene expression and promote virus replication.…”

Section: Discussionmentioning

confidence: 95%

Components of Promyelocytic Leukemia Nuclear Bodies (ND10) Act Cooperatively To Repress Herpesvirus Infection

Glaß

Everett

2013

102

Upon the entry of the viral genome into the nucleus, herpes simplex virus type 1 (HSV-1) gene expression is rapidly repressed by constitutively expressed cellular proteins. This intrinsic antiviral defense is normally counteracted by ICP0, which allows virus infection to proceed efficiently. Replication of ICP0-null mutant HSV-1, however, is severely repressed by mechanisms that are conferred, at least in part, by nuclear domain 10 (ND10) components, including hDaxx, the promyelocytic leukemia (PML) protein, and Sp100. To investigate if these ND10 components repress viral gene expression in a cooperative manner, we simultaneously depleted host cells for hDaxx, PML, and Sp100 by multiple short hairpin RNA (shRNA) knockdown from a single lentivirus vector. We found that replication and gene expression of ICP0-null mutant HSV-1 were cooperatively repressed by hDaxx, PML, and Sp100 immediately upon infection, and all stages of virus replication were inhibited. Plaque-forming efficiency was enhanced at least 50-fold in the triple-depleted cells, a much larger increase than achieved by depletion of any single ND10 protein. Similar effects were also observed during infection of triple-depleted cells with human cytomegalovirus (HCMV). Moreover, using a cell culture model of quiescent infection, we found that triple depletion resulted in a much larger number of viral genomes escaping repression. However, triple depletion was unable to fully overcome the ICP0-null phenotype, implying the presence of additional repressive host factors, possibly components of the SUMO modification or DNA repair pathways. We conclude that several ND10 components cooperate in an additive manner to regulate HSV-1 and HCMV infection.

“…For KSHV, it has been shown that shortly after infection, PML-NB components localize to viral genomes and prereplication compartments (147). Interestingly, PML is SUMO-2 modified by LANA2, the latency-associated nuclear antigen 2.…”

Section: Nuclear Dna Virus Replication Centersmentioning

confidence: 99%

“…Thus, members of the gammaherpesvirus family, like Kaposi's sarcoma-associated herpesvirus (KSHV) (147), herpesvirus saimiri (HVS) (148), and Epstein-Barr virus (EBV) (152), express proteins with properties similar to HSV-1 ICP0. Furthermore, viral replication compartments develop in association with PML-NB remnants (147,148,152).…”

Section: Nuclear Dna Virus Replication Centersmentioning

confidence: 99%

DNA Virus Replication Compartments

Schmid

Speiseder

Dobner

et al. 2014

150

142

bViruses employ a variety of strategies to usurp and control cellular activities through the orchestrated recruitment of macromolecules to specific cytoplasmic or nuclear compartments. Formation of such specialized virus-induced cellular microenvironments, which have been termed viroplasms, virus factories, or virus replication centers, complexes, or compartments, depends on molecular interactions between viral and cellular factors that participate in viral genome expression and replication and are in some cases associated with sites of virion assembly. These virus-induced compartments function not only to recruit and concentrate factors required for essential steps of the viral replication cycle but also to control the cellular mechanisms of antiviral defense. In this review, we summarize characteristic features of viral replication compartments from different virus families and discuss similarities in the viral and cellular activities that are associated with their assembly and the functions they facilitate for viral replication.