Marek’s disease virus U(S)3 protein kinase phosphorylates chicken HDAC 1 and 2 and regulates viral replication and pathogenesis

Marek’s disease virus (MDV) is a potent oncogenic alphaherpesvirus that elicits a rapid onset of malignant T-cell lymphomas in chickens. Three MDV types, including GaHV-2 (MDV-1), GaHV-3 (MDV-2) and MeHV-1 (HVT), have been identified and all encode a U(S)3 protein kinase. MDV-1 U(S)3 is important for efficient virus growth in vitro. To study the role of U(S)3 in MDV replication and pathogenicity, we generated an MDV-1 U(S)3-null virus and chimeric viruses by replacing MDV-1 U(S)3 with MDV-2 or HVT U(S)3. Using MD as a natural virus-host model, we showed that both MDV-2 and HVT U(S)3 partially rescued the growth deficiency of MDV-1 U(S)3-null virus. In addition, deletion of MDV-1 U(S)3 attenuated the virus resulting in higher survival rate and lower MDV specific tumor incidence, which could be partially compensated by MDV-2 and HVT U(S)3. We also identified chicken histone deacetylase 1 (chHDAC1) as a common U(S)3 substrate for all three MDV types while only U(S)3 of MDV-1 and MDV-2 phosphorylate chHDAC2. We further determined that U(S)3 of MDV-1 and HVT phosphorylate chHDAC1 at serine 406 (S406), while MDV-2 U(S)3 phosphorylates S406, S410, and S415. In addition, MDV-1 U(S)3 phosphorylates chHDAC2 at S407, while MDV-2 U(S)3 targets S407 and S411. Furthermore, biochemical studies show that MDV U(S)3 mediated phosphorylation of chHDAC1 and 2 affect their stability, transcriptional regulation activity, and interaction network. Using a class I HDAC specific inhibitor, we showed that MDV U(S)3 mediated phosphorylation of chHDAC1 and 2 is involved in regulation of virus replication. Overall, we identified novel substrates for MDV U(S)3 and characterized the role of MDV U(S)3 in MDV pathogenesis.