Latency permits human cytomegalovirus (HCMV) to colonize its hosts for their lifetime by avoiding immune detection and clearance. The abilities of the virus to persist latently and reactivate productively are major factors in the serious medical issues caused by HCMV infections. HCMV is latent in undifferentiated myeloid cells and reactivates when these cells differentiate. The Immediate Early 1 (IE1) protein is a transcription factor that promotes progression through the viral lytic phase. During latency the levels of lytic (productive) phase proteins such as IE1 are kept extremely low (or completely absent) because the promoter that drives its expression, the Major Immediate Early Promoter (MIEP) is transcriptionally silenced by heterochromatin. Premature triggering of the lytic cycle in undifferentiated myeloid cells by spurious production of proteins like IE1 likely results in immune destruction of the reactivating cell before HCMV can complete a productive round of replication. Keeping full length IE1 protein levels low or absent protects latently infected cells from immune surveillance and restricts reactivation events until the cell differentiates. Our lab demonstrated the cellular protein Daxx and an associated histone deacetylase (HDAC) silences the MIEP when HCMV establishes latency. Likewise, we also published that the viral UL138 protein silences IE1 transcription during latency by inhibiting the recruitment of lysine-specific demethylases (KDMs) to the MIEP that remove repressive epigenetic histone methylations to activate transcription.
In Aim 1, we propose to define how UL138 prevents KDM recruitment to the MIEP and silences IE1 transcription during latency from its localization at the Golgi apparatus. Deletion of UL138 from the HCMV genome revealed that at least one more suppressor of IE1 transcription is encoded by clinical strains. Such functional redundancy in silencing the MIEP underscores the importance of this process for the worldwide success of HCMV. We have now identified this novel silencer of IE transcription.
In Aim 2 we propose to determine how it represses the MIEP during latency. Knowing how the MIEP is silenced during latency should reveal mechanisms through which IE1 transcription can be controlled to either inhibit or induce reactivation from latency for therapeutic effect.
Human cytomegalovirus infects almost everyone. It causes birth defects and disease in people sick with cancer, AIDS, and those undergoing organ transplants. It also seems to exacerbate cardiovascular diseases, to adversely affect the ability of the elderly to fight off other infectious diseases, and may be directly related to human glioblastoma multiforme brain tumors. HCMV can hide in the body in a latent state and reactivate at any time to cause disease and to spread from person to person. This work will study how HCMV establishes this latent state, with the hopes of identifying ways to fight the virus with antiviral drugs.
| Bristol, Jillian A; Djavadian, Reza; Albright, Emily R et al. (2018) A cancer-associated Epstein-Barr virus BZLF1 promoter variant enhances lytic infection. PLoS Pathog 14:e1007179 |
