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Published on: July 6, 2013
The Mouse Cytomegalovirus G Protein-Coupled Receptor Homolog, M33, Coordinates Key Features of In Vivo Infection via
Jiawei Ma1, Kimberley Bruce1, Nicholas Davis-Poynter1,2
1School of Chemistry and Molecular Biosciences, The University of Queenslandgrid.1003.2, Brisbane, Australia.
Abstract:
Common to all cytomegalovirus (CMV) genomes analyzed to date is the presence of G protein-coupled receptors (GPCR). Animal models of CMV provide insights into their role in viral fitness. The mouse cytomegalovirus (MCMV) GPCR, M33, facilitates dendritic cell (DC)-dependent viremia, the extravasation of blood-borne infected DCs to the salivary gland, and the frequency of reactivation events from latently infected tissue explants. Constitutive G protein-coupled M33 signaling is required for these phenotypes, although the contribution of distinct biochemical pathways activated by M33 is unknown. M33 engages Gq/11 to constitutively activate phospholipase C β (PLCβ) and downstream cyclic AMP response-element binding protein (CREB) in vitro. Identification of a MCMV M33 mutant (M33ΔC38) for which CREB signaling was disabled but PLCβ activation was preserved provided the opportunity to investigate their relevance in vivo. Following intranasal infection with MCMV M33ΔC38, the absence of M33 CREB Gq/11-dependent signaling correlated with reduced mobilization of lytically-infected DCs to the draining lymph node high endothelial venules (HEVs) and reduced viremia compared with wild type MCMV. In contrast, M33ΔC38-infected DCs within the vascular compartment extravasated to the salivary glands via a pertussis toxin-sensitive, Gi/o-dependent, and CREB-independent mechanism. In the context of MCMV latency, spleen explants from M33ΔC38-infected mice were markedly attenuated for reactivation. Taken together, these data demonstrate that key features of the MCMV life cycle are coordinated in diverse tissues by distinct pathways of the M33 signaling repertoire. IMPORTANCE G protein-coupled receptors (GPCRs) act as cell surface molecular "switches" that regulate the cellular response to environmental stimuli. All cytomegalovirus (CMV) genomes analyzed to date possess GPCR homologs with phylogenetic evidence for independent gene capture events, signifying important in vivo roles. The mouse CMV (MCMV) GPCR homolog, designated M33, is important for cell-associated virus spread and the establishment and/or reactivation of latent MCMV infection. The signaling repertoire of M33 is distinct from cellular GPCRs and little is known of the relevance of component signaling pathways for in vivo M33 function. In this report, we showed that temporal and tissue-specific M33 signaling was required to facilitate in vivo infection. Understanding the relevance of the viral GPCR signaling profiles for in vivo function will provide opportunities for future targeted interventions.
Insights
Mouse cytomegalovirus (MCMV) G protein-coupled receptor (GPCR) M33 uses distinct signaling pathways to control viral spread and reactivation. Understanding these pathways offers opportunities for targeted interventions against MCMV infection.
Area of Science:
- Virology
- Molecular Biology
- Immunology
Background:
- Cytomegalovirus (CMV) genomes universally encode G protein-coupled receptors (GPCRs), suggesting critical in vivo roles.
- The mouse CMV (MCMV) GPCR homolog, M33, influences viral fitness, including viremia, cell-associated spread, and latent infection reactivation.
- The specific signaling pathways utilized by M33 in vivo and their contributions to distinct viral phenotypes remain largely uncharacterized.
Purpose of the Study:
- To delineate the roles of distinct M33-activated signaling pathways, specifically phospholipase C β (PLCβ) and cyclic AMP response-element binding protein (CREB), in MCMV pathogenesis.
- To investigate the in vivo relevance of M33's Gq/11-dependent CREB signaling versus its Gi/o-dependent signaling during acute infection and latency.
Main Methods:
- Utilized a mouse model of intranasal MCMV infection with wild-type and a M33 mutant (M33ΔC38) deficient in CREB signaling but retaining PLCβ activation.
- Assessed viral spread, viremia, dendritic cell (DC) mobilization and extravasation, and viral reactivation from latency.
- Employed pertussis toxin to investigate G protein-dependent mechanisms.
Main Results:
- MCMV M33ΔC38 infection showed reduced DC mobilization to lymph node high endothelial venules and decreased viremia, correlating with impaired Gq/11-dependent CREB signaling.
- DC extravasation to salivary glands was mediated by a pertussis toxin-sensitive, Gi/o-dependent, and CREB-independent pathway.
- MCMV M33ΔC38 infection significantly attenuated viral reactivation from latency in spleen explants.
Conclusions:
- Distinct signaling pathways downstream of the MCMV M33 GPCR orchestrate different aspects of the viral life cycle in a temporal and tissue-specific manner.
- M33's ability to engage both Gq/11-CREB and Gi/o-dependent pathways is crucial for efficient viral dissemination and establishment of latency.
- Elucidating the specific signaling repertoire of viral GPCRs like M33 provides a foundation for developing targeted antiviral strategies.
