| Herpes simplex virus type 1 is a kind of highly infectious pathogen for human which is the only host. And at least 45 percentage of the world's population are infected with HSV-1. In its primary infection, HSV-1, which is able to induce the specific immune response of individual, can keep its long time existence in neurons of host through latent state. It will be reactivated to a lytic infection again under some certain conditions. During its replication, this viral gene expression is coordinately regulated and sequentially ordered in a cascade manner. According the sequence of gene expression, HSV-1 genes are designated asagenes,βgenes andygenes. Based on this understanding, HSV-1 is an important model for expressional regulation of eukaryotic genes.Besides core, capsid and envelope, HSV-1 has an unstructured proteinacous layer called the tegument. Although these more than 20 different kinds of tegument proteins are about 50 percentage of the viral volume and many tegument proteins have a large number of copies (1000-2500 molecules/virion), there is little systematic knowledge regarding these tegument proteins. VP22 has received notable attention for its large number of molecules in each polypeptide per virion (2400 molecules/virion). At present, VP22 is confirmed to be important for virus assembly and virus structure. Based on findings of its transcriptional regulatory functions in chloramphenicol acetyltransferase (CAT) assay, this study revealed the global transcriptional inhibitory effect of VP22 for the first time, and then analyzed the mechanisms. In addition, this study also illuminated VP22 repressing a protein ICPO transcriptional activation that attributed to the interactions of VP22, ICPO and histone acetyltransferases (HAT) PCAF. The results are shown as follow. During HSV-1 infection, overexpressed VP22 inhibited the transcriptions of HSV-1α,βand y genes during a period of time, and inhibited HSV-1 replication in Vero cells during a period of time. The CAT assay indicated that VP22 exerts a dose-dependent transcriptional inhibitory effect on HSV-1α,βand y gene promoters, and VP22 is capable of eliminating the ICPO transcriptional activation mediated by PCAF onβandγgene promoters in a dose-dependent manner. Carboxyl terminus of VP22 was absolutely required for its transcriptional inhibitory functions. And VP22 transcriptional repressive functions were not involved in recruiting histone deacetyltransferases. In analysis of interactions of VP22, ICPO, and PCAF, the results indicated that VP22 localizes in cytoplasm and nuclei, and carboxyl terminus of VP22 interacts with the RING finger domain of ICPO, but not PCAF. It was important that VP22 is able to competitively inhibit the interaction of PCAF and the ICPO RING finger domain. Chromatin Immunoprecipitation analyses revealed that VP22 do not impact the levels of acetylated histone H3K14 at virus promoters during HSV-1 infection, but VP22 can repress the enrichment of acetylated histones H3K14 at virus promoters dependent on the the ICPO RING finger domain. However, both ICPO and VP22 didn't alter global pattern of acetylated histones H3K14 in Vero cells.Based on our studies, we summarize a protein-protein interaction model of VP22, ICPO and PCAF. On one hand, enrichment of acetylated histones at virus promoters mediated by interaction of the ICPO RING finger domain and PCAF leads to transcriptional activation. On the other hand, VP22 competitively inhibits the interaction of PCAF and the ICPO RING finger domain, which contributes to VP22 represses ICPO and PCAF-mediated enrichment of acetylated histones at virus promoters. And as a result, VP22 eliminates the ICPO transcriptional activation dependent on PCAF.
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