Herpes simplex virus-infected cell protein 0 blocks the silencing of viral DNA by dissociating histone deacetylases from the CoREST–REST complex

Abstract

A preeminent phenotype of the infected cell protein 0 (ICP0) of herpes simplex virus 1 (HSV-1) is that it acts as a promiscuous transactivator. In most cell lines exposed to ⌬ICP0 mutant virus at low ratios of virus per cell infection, ␣ genes are expressed but the transition to ␤ and ␥ gene expression does not ensue, but can be enhanced by inhibitors of histone deacetylases (HDACs). Earlier studies have shown that ICP0 interacts with CoREST and displaces HDAC1 from the CoREST-REST-HDAC1/2 complex. HDAC1 and CoREST are then independently translocated to the cytoplasm. Here, we test the hypothesis that ICP0 blocks the silencing of HSV DNA by displacing HDAC1 from the CoREST-REST complex. Specifically, first, mapping studies led us to construct a truncated CoREST (CoREST 146 -482) that in transfected cells displaced HDAC1 from the CoREST-REST complex. Second, we constructed two viruses. In BACs encoding the entire HSV-1, we replaced the gene encoding ICP0 with AmpR to yield a ⌬ICP0 mutant R8501. We also replaced ICP0 with CoREST 146 -482 to yield recombinant R8502. The yield of R8502 mutant virus in Vero, HEp-2, and human embryonic lung cells exposed to 0.1 pfu of virus per cell was 100-, 10-, and 10-fold higher, respectively, than those of R8501 mutant virus. In Vero cells, the yield of R8502 was identical with that of wild-type virus. We conclude that CoREST 146 -482 functionally replaced ICP0 and that, by extension, ICP0 acts to block the silencing of viral DNA by displacing HDAC1/2 from the CoREST-REST complex.interactive domains ͉ IFN signaling ͉ protein kinases I n humans and in experimental animal systems, herpes simplex viruses 1 or 2 (HSV-1 or HSV-2) replicate at the portal of entry into the body, infect nerve endings of sensory or dorsal root ganglia, and ascend to the nucleus where, in some neurons, they establish latent infections. In the latently infected cells, all viral genes except that encoding the latency-associated RNA (LAT) are turned off (reviewed in ref. 1). These observations suggested that HSV DNA possess the properties of being activated or silenced by viral and or host factors. Indeed, a viral protein carried by the infecting virion designated ␣-transinducing factor or viral protein 16 (VP16) has been shown to interact with host transcriptional factors to enhance the expression of ␣ or immediate-early genes (reviewed in ref. 2). Studies published recently have linked LAT to the maintenance of viral DNA in neuronal nuclei in a silenced form (3).The studies described in this article center on the role of the infected cell protein 0 (ICP0). This protein, the product of the ␣0 gene, is made immediately after infection. It is dispensable in cells infected at a high multiplicity. With few exceptions (e.g., U2OS cell; ref. 4), in cell lines infected at low multiplicity with ⌬ICP0 mutants, ␣ genes are expressed but the transition from ␣ to ␤ or ␥ genes does not ensue, and, as illustrated schematically in Fig. 1A, the virus fails to replicate (5). Related to this phenotype of ICP0 mutants is the o...

Nuclear retention of ICP0 in cells exposed to HDAC inhibitor or transfected with DNA before infection with herpes simplex virus 1

“…4. whereas in others ICP0 filled the nucleus but was nevertheless not exported to the cytoplasm. This result is identical with that observed in cells infected with a HSV-1 mutant in which the silencing function mapping close to the carboxyl terminus of ICP0 was impaired whereas the PML degradation function mapping more than 500 codons upstream was unaffected (5). The hypothesis we propose is that in the performance of its task to block silencing of DNA, ICP0 does not differentiate between the cellular and viral DNA accumulating at the ND10 bodies.…”

“…In cells infected with a mutant virus in which ICP0 was replaced with a dominant negative CoREST, the silencing is blocked even though PML is not degraded and the ND10 structures remain intact. Hence the two functions are independent of each other although evidence supports the conclusion that they are executed in tandem (5).…”

“…ICP0 interacts with many diverse cellular and viral proteins and acts as a promiscuous transactivator of genes introduced into cells by transfection or infection (1)(2)(3). Its two most prominent functions are to render the infected cells resistant to antiviral activity of interferons and to block the silencing of viral DNA (4)(5)(6)(7). At the molecular level, it acts as an E3 ubiquitin ligase to degrade PML and SP100.…”

“…In addition ICP0 blocks the silencing of viral DNA through dissociation of the HDAC1 or 2 from the CoREST/REST/LSD1 complex. The components of the complex are then translocated to the cytoplasm (5).…”

Disruption of HDAC/CoREST/REST repressor by dnREST reduces genome silencing and increases virulence of herpes simplex virus

“…ICP0 interacts with CoREST (7). In infected cells in the presence of ICP0, HDAC1 is displaced from the CoREST/REST/LSD1 complex (7,8). Subsequently, HDAC1, CoREST/REST, and LSD1 are at least in part translocated from the nucleus to the cytoplasm (7).…”