Inhibition of the SETD8 H4K20-mono-methyltransferase Limits the Global Accessibility of the Infecting Herpes Simplex Virus Genome [ATAC-seq]

Epigenetic modulation of herpes simplex virus (HSV) immediate early (IE) genes is a critical regulatory parameter governing lytic infection, latency, and viral reactivation. Multiple factors, including epigenetic complexes associated with the cellular transcriptional coactivator HCF-1, modulate the state of HSV-1 chromatin. As an approach to identify novel epigenetic factors that regulate the initial stage of HSV-1 infection, an epigenetic chemical probe library was screened for their impact on viral IE gene expression. This screen identified several epigenetic inhibitors that modulated IE expression. Notably, UNC0379, an inhibitor of the histone H4K20 mono-methyltransferase SETD8, potently repressed HSV-1 infection in vitro and in vivo. Furthermore, SETD8 inhibition suppressed HSV-1 reactivation in a mouse ganglia explant model. Importantly, these results correlated with enhanced heterochromatin suppression and decreased accessibility of HSV-1 chromatin. Reduced IE transcription was concomitant with disruption in recruitment of HCF-1 and RNA polymerase II (RNAPII). These results are consistent with the established roles of SETD8 in promoting chromatin accessibility through H4K20me1 deposition and regulating transcriptional elongation, suggesting that SETD8 may facilitate multiple steps in regulation of HSV-1 IE gene expression.