The human cytomegalovirus G-protein coupled receptor US28 promotes latency by attenuating c-fos

Abstract

Human cytomegalovirus (HCMV) is a ubiquitous pathogen that undergoes latency in cells of the hematopoietic compartment, though the mechanisms underlying establishment and maintenance of latency remain elusive. We previously reported that the HCMV-encoded G-protein coupled receptor (GPCR) homolog, US28 is required for successful latent infection. We now show that US28 protein (pUS28) provided in trans complements the US28{Delta} lytic phenotype in myeloid cells, suggesting that sustained US28 expression is necessary for long-term latency. Furthermore, expression of pUS28 at the time of infection represses transcription from the major immediate early promoter (MIEP) within 24 hours. However, this repression is only maintained in the presence of continual pUS28 expression provided in trans. Our data also reveal that pUS28-mediated signaling attenuates both expression and phosphorylation of cellular fos (c-fos), an AP-1 transcription factor subunit, to repress MIEP-driven transcription. AP-1 binds to the MIEP and promotes lytic replication, and in line with this, we find that US28{Delta} infection results in an increase in AP-1 binding to the MIEP, compared to wild type latent infection. Pharmacological inhibition of c-fos represses the MIEP during US28{Delta} infection to similar levels we observe during wild type latent infection. Together, our data reveal that US28 is required for both establishment and long-term maintenance of HCMV latency, which is modulated, at least in part, by repressing functional AP-1 binding to the MIEP.\n\nSignificance StatementHuman cytomegalovirus (HCMV) is a wise-spread pathogen that remains with an individual for life in a quiescent/latent state, posing little threat to an otherwise healthy person. However, when an individuals immune system is severely compromised, HCMV can reactivate to its active/lytic state, resulting in viral spread and disease that is often fatal. The biological mechanisms underlying HCMV latency and reactivation remain poorly understood. Herein we show that the viral-encoded G-protein coupled receptor (GPCR) US28 aids in the establishment and the maintenance of viral latency. Furthermore, we find that US28 modulates host cell proteins to suppress viral processes associated with active/lytic replication, thereby promoting latent infection. This work provides mechanism by which HCMV modulates the host cell environment to its advantage.