The betaherpesvirus human cytomegalovirus (HCMV) is a ubiquitous pathogen that infects nearly 80% of the population by 40 years of age. Like all herpesviruses, HCMV infections are life-long, where the virus remains latent within progenitor cells of the host’s hematopoietic compartment. Healthy individuals, for the most part, remain asymptomatic. However, infection is problematic for those with weakened immune systems, where reactivation of HCMV from latency can cause severe morbidity and mortality. In addition to immunocomprimised patients, HCMV reactivation poses an additional threat to those with atherosclerosis and certain cancers (e.g., glioblastoma). In fact, viral DNA is found in the arterial walls of atherosclerosis patients and in a vast majority of glioblastoma tumors tested to-date. HCMV has the capacity to encode over 200 open reading frames (ORFs), four of which are G-protein-coupled receptor (GPCR) homologs: UL33, UL78, US27, and US28. Cellular GPCRs are signaling proteins that, when activated, can induce a variety of downstream signaling events, thereby altering the host cell environment. Although these viral GPCRs are homologous to cellular GPCRs by sequence analysis, only UL33 and US28 have known signaling properties. The four HCMV-encoded GPCRs are expressed during the lytic life cycle of the virus, yet the impact these four proteins have on this phase of the viral life cycle is incomplete. During latency, only a handful of HCMV genes are expressed, including US28. We hypothesize that US28 influences HCMV latency via specific signaling pathways during this phase of infection.
Research in the O’Connor lab aims to elucidate the functions of the HCMV-encoded GPCRs during both lytic and latent infection to better understand how these proteins influence pathogenesis and subsequent disease. The lab currently focuses on three main areas of research:
- Defining the contribution of the HCMV GPCRs to lytic replication. Previous work in Dr. O’Connor’s lab has shown that the HCMV GPCRs have a variety of functions during HCMV infection, as well as the importance of US27 in extracellular spread of the virus. In parallel, the O’Connor lab found that US27 is dispensable for viral growth in epithelial cells, where the mode of viral spread is restricted to cell-to-cell. In contrast, Dr. O’Connor has shown that UL78 is required for efficient viral infection in epithelial cells, as it functions during entry. The lab is currently investigating the additive contribution of these proteins toward promoting a successful lytic infection.
- Understanding the role of US28 during HCMV latency. US28 is expressed during both the lytic and latent cycles of HCMV infection. To elucidate its function during latent infection, Dr. O’Connor utilized a panel of mutant viruses and her novel in vitro latency model system. This work has shown that HCMV US28 is required for viral latency in hematopoietic progenitor cells, as viruses that lack the US28 ORF fail to undergo latent infection and instead favor lytic replication. Further, this research has shown that US28’s continued expression is necessary to maintain latency. Currently, Dr. O’Connor’s research aims to understand the underlying mechanisms by which US28 influences the latent state of HCMV.
- Elucidating the contribution of US28 toward the progression of atherosclerosis. Many US28-induced signaling cascades and the cellular factors that are subsequently altered are also involved arterial plaque formation during the progression to atherosclerosis, leading us to hypothesize that HCMV’s involvement in atherosclerotic progression could be due, at least in part, to US28-mediated events. Unlike cellular GPCRs, US28 signals through a variety of ligands and couples to many G-proteins. US28, like some cellular GPCRs that are dysregulated during disease, can also induce signaling events in the absence of a ligand (constitutive activation). The signaling properties of US28 vary by cell type, which may lead to an understanding of how HCMV accelerates disease states in various tissues. Lytically replicating HCMV, and more specifically US28, influences almost every stage of atherosclerosis, including the recruitment of immune cells to sites of injury at the vascular wall, aiding in the formation of plaques, and accelerating the mobilization of plaques to cause subsequent thrombosis and stroke. However, the mechanism(s) underlying HCMV’s contribution to these processes remain poorly understood. Dr. O’Connor’s goal is to define the involvement of US28 in the acceleration of atherosclerotic disease progression by defining the following:
- the host and viral factors with which US28, and the other viral GPCRs, interact to facilitate cellular processes associated with atherosclerotic progression
- the cellular signaling pathways US28 influences during plaque formation.
Taken together, research in the O’Connor lab is aimed at gaining a better understanding of how the HCMV GPCRs mediate viral infection, as well as the host cell milieu, toward accelerating disease processes. More than two-thirds of approved drugs target the GPCR family of proteins, making the HCMV GPCRs ideal therapeutic targets. Defining a role for these viral proteins in pathogenesis will provide avenues for novel therapeutics that may aid in preventing and/or slowing the progress of HCMV-associated disease.
In other words ...
Human cytomegalovirus (HCMV) is a herpesvirus that is prevalent in the population, where it remains latent, or quiet, in the host for life. However, when an individual’s immune system is weakened, the virus can wake up, or reactivate, to cause severe complications and often death. Dr. O’Connor’s research focuses on the processes that allow the virus to re-awaken after long periods of dormancy, and how this event leads to viral pathogenesis and disease progression.
Select publication (complete list of published work - http://www.ncbi.nlm.nih.gov/sites/myncbi/1J5ZF34E-255E/bibliograpahy/42502714/public/?sort=date&direction=ascending):
- Krishna BA, Humby MS, Miller WE, and O’Connor CM. (2019) The human cytomegalovirus G-protein coupled receptor US28 promotes latency by attenuating c-fos. PNAS 116(5): 1755-1764. PMCID: PMC6358704
- Nukui M, Murphy EA*, O’Connor CM*. (2018) The natural flavonoid compound deguelin inhibits HCMV lytic replication within fibroblasts.Viruses 10(11): pii: E614. PMCID: PMC6265796 (*co-corresponding authors)
- Boeck JM, Stowell GA, O’Connor CM, Spencer JV. (2018) The human cytomegalovirus US27 gene product constitutively activates ARE-mediated transcription through Gβγ, PI3K, and NRF-1. J Virol. 92(23):pii: e00644-18. PCMID: PMC6232467
- Roche KL, Nukui M, Krishna BA, O’Connor CM, Murphy EA. (2018) Selective 4-thiouracil labeling of RNA transcripts within latently infected cells after infection with human cytomegalovirus expressing functional uracil phosphoribosyltransferase. J Virol. 92(21): pii:e00880-18. PMCID: PMC6189490
- Krishna BA, Miller WE, and O’Connor CM. (2018) US28: HCMV’s Swiss Army Knife. Viruses 10(8): pii: E445. PMCID: PMC6116241 Invited Review.
- Tu CC, Arnolds KL, O’Connor CM, Spencer JV. (2018) Human cytomegalovirus UL111A and US27 gene products enhance the CXCL12/CXCR4 signaling axis via distinct mechanisms. J. Virol. 92(5):e01981-17. PMCID: PMC5809719
- O’Connor CM, Nukui M, Gurova K, Murphy EA. Inhibition of the Facilitates Chromatin Transcription (FACT) complex reduces transcription from the HCMV MIEP in models of lytic and latent replication. J Virol. 2016;90(8):4249-53.
- Humby MS and O’Connor CM. HCMV US28 is important for latent infection of hematopoietic progenitor cells. J Virol. 2015; 90(6): 2959-70.
- O'Connor CM, DiMaggio PA Jr, Shenk T, and Garcia BA. Quantitative proteomic discovery of dynamic epigenome changes that control human cytomegalovirus infection. Mol Cell Proteomics. 2014;13:2399-2410.
- O’Connor CM, Vanicek J, Murphy EA. Host miRNA regulation of human cytomegalovirus immediate early protein translation promotes viral latency. J Virol. 2014;88(10):5524-32.
- Miller WE, Zagorski WA, Brenneman JD, Avery D, Miller JLC, O’Connor CM. US28 is a ubiquitous and potent activator of phospholipase C during productive infection of clinically relevant HCMV target cells. PLoS One. 2012;7(11):e50524.
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