Chromatin profiling of Epstein-Barr virus latency control region.

Epstein-Barr virus (EBV) escapes host immunity by the reversible and epigenetic silencing of immunogenic viral genes. We previously presented evidence that a dynamic chromatin domain, which we have referred to as the latency control region (LCR), contributes to the reversible repression of EBNA2 and LMP1 gene transcription. We now explore the protein-DNA interaction profiles for a few known regulatory factors and histone modifications that regulate LCR structure and activity. A chromatin immunoprecipitation assay combined with real-time PCR analysis was used to analyze protein-DNA interactions at approximately 500-bp intervals across the first 60,000 bp of the EBV genome. We compared the binding patterns of EBNA1 with those of the origin recognition complex protein ORC2, the chromatin boundary factor CTCF, the linker histone H1, and several histone modifications. We analyzed three EBV-positive cell lines (MutuI, Raji, and LCL3459) with distinct transcription patterns reflecting different latency types. Our findings suggest that histone modification patterns within the LCR are complex but reflect differences in each latency type. The most striking finding was the identification of CTCF sites immediately upstream of the Qp, Cp, and EBER transcription initiation regions in all three cell types. In transient assays, CTCF facilitated EBNA1-dependent transcription activation of Cp, suggesting that CTCF coordinates interactions between different chromatin domains. We also found that histone H3 methyl K4 clustered with CTCF and EBNA1 at sites of active transcription or DNA replication initiation. Our findings support a model where CTCF delineates multiple domains within the LCR and regulates interactions between these domains that correlate with changes in gene expression.