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

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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 ΔICP0 mutant virus at low ratios of virus per cell infection, α genes are expressed but the transition to β and γ 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 (CoREST146–482) 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 ΔICP0 mutant R8501. We also replaced ICP0 with CoREST146–482 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 CoREST146–482 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.