Histone Variant H2A.Z Cooperates with EBNA1 to Maintain Epstein-Barr Virus Latent Epigenome
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Chromatin structure plays a central role in the regulation of Epstein-Barr Virus (EBV) latency. The histone variant H2A.Z.1 has been implicated in chromatin structures associated with initiation of transcription and DNA replication. Here, we investigate the functional role of H2AZ.1 in the regulation of EBV chromatin, gene expression and copy number during latent infection. We found that H2A.Z.1 is highly enriched with EBNA1 binding sites at oriP and Qp, and to a lesser extent with transcriptionally active CTCF binding sites on the EBV genomes in both Mutu I Burkitt lymphoma (BL) and SNU719 EBV-associated gastric carcinoma (EBVaGC) cell lines. RNA-interference depletion of H2A.Z.1 resulted in the reactivation of viral lytic genes (ZTA and EAD) and increases viral DNA copy numbers in both MutuI and SNU719 cells. H2A.Z depletion also led to a decrease in EBNA1 binding to oriP and Qp , on the viral episome as well as on oriP plasmids independently of other viral genes and genomes. H2A.Z.1 depletion also reduced peaks of H3K27ac and H4K20me3 at regulatory elements in the EBV genome. In the cellular genome, H2A.Z.1 colocalized with only a subset of EBNA1 binding sites and H2A.Z.1 depletion altered transcription of genes associated with myc targets and mTORC1 signaling . Taken together, these findings indicate that H2A.Z.1 cooperates with EBNA1 to regulate chromatin structures important for epigenetic programming of the latent episome.
Importance
Cellular factors the restrict latent viral reactivation are of fundamental importance. We have found that the cellular histone variant H2A.Z functions in cooperation with the Epstein-Barr Virus (EBV) latency maintenance protein EBNA1 to establish a stable epigenome and restrict lytic cycle reactivation during latency. We show that H2A.Z co-occupies EBNA1 binding sites on the EBV and host genome, and that depletion of H2A.Z leads to robust reactivation of EBV from latency. H2A.Z is important for the function of EBNA1 at the origin of plasmid (oriP) replication and establishing EBV epigenetic marks. H2A.Z binds with EBNA1 at cellular binding sites and controls the expression of cellular genes in the cMyc and mTORC1 pathways that are also implicated in control of EBV latency.
