UL136-33KDA and UL135 Epistasis Coordinates Reactivation of Human Cytomegalovirus

Human cytomegalovirus (HCMV) is large double stranded DNA, beta herpesvirus that persists indefinitely in the human host through a protracted, latent infection. HCMV has a global seroprevalence of 40-90% dependent on geographical region. For individuals with a competent immune system, HCMV infection is typically asymptomatic. Conversely, for those that are immuno-suppressed, HCMV infection could lead to increased morbidity and mortality. Therefore, understanding mechanisms governing latency and reactivation of HCMV is imperative for developing potential therapeutics to target the latent population of HCMV. We demonstrate here that stabilizing p33 does not compensate for the loss of UL135 or viral DNA synthesis inhibition in viral gene expression or an increase in viral yield for a replicative infection in fibroblasts. However, in a latent infection context, stabilization of p33 strikingly compensates for the loss of UL135, resulting in an inability to establish latency and enhanced virus replication and genome amplification. Importantly, this phenotype is recapitulated in humanized NOD-scid IL2Rγcnull (NSG) mice. Indeed, viruses lacking UL135 where UL136-33kDa (p33) is stabilized can synthesize genomes and replicate to levels greater than a virus where p33 is stabilized in the presence of UL135. This finding suggests that while UL135 is essential, it may have adverse effects for virus replication. Taken together, our evidence suggests an epistatic relationship between p33 and UL135 for controlling virus reactivation from latency