Dynamic association of gammaherpesvirus DNA with core histone during de novo lytic infection of primary cells.

Association of herpesvirus DNA with histones has important implications for lytic and latent infections; thus herpesviruses arbitrate interactions with histones to productively infect host cells. While regulation of alpha and betaherpesvirus chromatin during lytic infection has been actively investigated, very little is known about interaction of gammaherpesvirus DNA with histones upon de novo lytic infection. Murine gammaherpesvirus-68 (MHV68) is a rodent pathogen that offers a tractable system to study gammaherpesvirus lytic infection in primary cells. In this study we report that MHV68 promoter and orilyt sequences underwent dynamic association with histone H3 during de novo lytic infection of primary macrophages and fibroblasts. Similar to HSV-1, the degree of MHV68 DNA association with histone H3 was dependent on the multiplicity of infection and was further regulated by viral DNA synthesis. Our work sets a precedent for future studies of gammaherpesvirus chromatin during de novo lytic infection.

Gammaherpesvirus gene expression and DNA synthesis are facilitated by viral protein kinase and histone variant H2AX.

Gammaherpesvirus protein kinases are an attractive therapeutic target as they support lytic replication and latency. Via an unknown mechanism these kinases enhance expression of select viral genes and DNA synthesis. Importantly, the kinase phenotypes have not been examined in primary cell types. Mouse gammaherpesvirus-68 (MHV68) protein kinase orf36 activates the DNA damage response (DDR) and facilitates lytic replication in primary macrophages. Significantly, H2AX, a DDR component and putative orf36 substrate, enhances MHV68 replication. Here we report that orf36 facilitated expression of RTA, an immediate early MHV68 gene, and DNA synthesis during de novo infection of primary macrophages. H2AX expression supported efficient RTA transcription and phosphorylated H2AX associated with RTA promoter. Furthermore, viral DNA synthesis was attenuated in H2AX-deficient macrophages, suggesting that the DDR system was exploited throughout the replication cycle. The interactions between a cancer-associated gammaherpesvirus and host tumor suppressor system have important implications for the pathogenesis of gammaherpesvirus infection.