PROJECT SUMMARY/ABSTRACT – O’CONNOR, CHRISTINE M. Human cytomegalovirus (HCMV) is a wide-spread pathogen, infecting the majority of the population in the United States. This virus poses a significant threat to developing fetuses as well as to children and adults who lack a competent immune system, often causing severe disease and mortality. Once individuals acquire an HCMV infection, the virus remains with the host for life, in a latent or quiescent state in the hematopoietic compartment. During times of severe immunological stress, the virus reactivates to its active state, allowing for dissemination and subsequent disease. With the exception of the immuno-naïve and sero-negative organ transplant recipients, primary infection with HCMV rarely causes disease, but rather it is reactivation that leads to significant complications. Thus, to prevent HCMV-associated disease, we must gain a complete understanding of viral latency and reactivation. One of a handful of genes encoded during latency is one of the four viral G protein-coupled receptors (GPCRs), US28. We have shown previously that US28 is required for the establishment and maintenance latency and that US28-mediated signaling contributes to these effects. We have also found that US28 modulates the expression of specific cellular targets that regulate the Major Immediate Early Promoter (MIEP), a master regulator in the latent-to-lytic switch. Therefore, we hypothesize that US28 modulates specific host signaling pathways to regulate transcriptional silencing of the MIEP to facilitate HCMV latency. To explore this hypothesis, we will take advantage novel approaches coupled with our arsenal of US28- specific recombinants, as well as both in vitro and ex vivo latency model systems. In Aim 1, we will define mechanisms underlying US28-mediated attenuation of AP-1 transcription factor binding to the MIEP during latency by examining the upstream signaling pathways that regulate AP-1. In Aim 2, we will determine the factors that recruit YY1 to the MIEP during latency by assessing US28-regulated signaling pathways and factors that promote the binding of this repressive transcription factor. In sum, the experiments proposed herein will lead to a greater understanding of US28’s biological functions during latency and will lay the foundation for future studies to develop novel therapeutics specifically targeting the latent reservoir of HCMV infection.