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1.  Identification of Common Mechanisms by Which Human and Mouse Cytomegalovirus Seven-Transmembrane Receptor Homologues Contribute to In Vivo Phenotypes in a Mouse Model 
Journal of Virology  2013;87(7):4112-4117.
The mouse cytomegalovirus chemokine receptor homologue (CKR) M33 is required for salivary gland tropism and efficient reactivation from latency, phenotypes partially rescued by the human cytomegalovirus CKR US28. Herein, we demonstrate that complementation of salivary gland tropism is mediated predominantly by G protein-dependent signaling conserved with that of M33; in contrast, both G protein-dependent and -independent pathways contribute to the latency phenotypes. A novel M33-dependent replication phenotype in cultured bone marrow macrophages is also described.
PMCID: PMC3624218  PMID: 23345521
2.  Structural Diversity in Conserved Regions Like the DRY-Motif among Viral 7TM Receptors—A Consequence of Evolutionary Pressure? 
Advances in Virology  2012;2012:231813.
Several herpes- and poxviruses have captured chemokine receptors from their hosts and modified these to their own benefit. The human and viral chemokine receptors belong to class A 7 transmembrane (TM) receptors which are characterized by several structural motifs like the DRY-motif in TM3 and the C-terminal tail. In the DRY-motif, the arginine residue serves important purposes by being directly involved in G protein coupling. Interestingly, among the viral receptors there is a greater diversity in the DRY-motif compared to their endogenous receptor homologous. The C-terminal receptor tail constitutes another regulatory region that through a number of phosphorylation sites is involved in signaling, desensitization, and internalization. Also this region is more variable among virus-encoded 7TM receptors compared to human class A receptors. In this review we will focus on these two structural motifs and discuss their role in viral 7TM receptor signaling compared to their endogenous counterparts.
PMCID: PMC3414077  PMID: 22899926
3.  Partial Functional Complementation between Human and Mouse Cytomegalovirus Chemokine Receptor Homologues▿ 
Journal of Virology  2011;85(12):6091-6095.
The human cytomegalovirus (CMV) proteins US28 and UL33 are homologous to chemokine receptors (CKRs). Knockout of the mouse CMV M33 protein (UL33 homologue) results in substantial attenuation of salivary gland infection/replication and reduced efficiency of reactivation from tissue explants. M33-mediated G protein-coupled signaling is critical for the salivary gland phenotype. In this report, we demonstrate that US28 and (to a lesser degree) UL33 restore reactivation from tissue explants and partially restore replication in salivary glands (compared to a signaling-deficient M33 mutant). These studies provide a novel small animal model for evaluation of therapies targeting the human CMV CKRs.
PMCID: PMC3126309  PMID: 21490099
4.  The M33 Chemokine Receptor Homolog of Murine Cytomegalovirus Exhibits a Differential Tissue-Specific Role during In Vivo Replication and Latency▿  
Journal of Virology  2009;83(15):7590-7601.
M33, encoded by murine cytomegalovirus (MCMV), is a member of the UL33 homolog G-protein-coupled receptor (GPCR) family and is conserved across all the betaherpesviruses. Infection of mice with recombinant viruses lacking M33 or containing specific signaling domain mutations in M33 results in significantly diminished MCMV infection of the salivary glands. To determine the role of M33 in viral dissemination and/or infection in other tissues, viral infection with wild-type K181 virus and an M33 mutant virus, ΔM33BT2, was characterized using two different routes of inoculation. Following both intraperitoneal (i.p.) and intranasal (i.n.) inoculation, M33 was attenuated for infection of the spleen and pancreas as early as 7 days after infection. Following i.p. inoculation, ΔM33BT2 exhibited a severe defect in latency as measured by a diminished capacity to reactivate from spleens and lungs in reactivation assays (P < 0.001). Subsequent PCR analysis revealed markedly reduced ΔM33BT2 viral DNA levels in the latently infected spleens, lungs, and bone marrow. Following i.n. inoculation, latent ΔM33BT2 viral DNA was significantly reduced in the spleen and, in agreement with results from i.p. inoculation, did not reactivate from the spleen (P < 0.001). Furthermore, in vivo complementation of ΔM33BT2 virus replication and/or dissemination to the salivary glands and pancreas was achieved by coinfection with wild-type virus. Overall, our data suggest a critical tissue-specific role for M33 during infection in the salivary glands, spleen, and pancreas but not the lungs. Our data suggest that M33 contributes to the efficient establishment or maintenance of long-term latent MCMV infection.
PMCID: PMC2708650  PMID: 19439478
5.  Functional Analysis of the Murine Cytomegalovirus Chemokine Receptor Homologue M33: Ablation of Constitutive Signaling Is Associated with an Attenuated Phenotype In Vivo▿  
Journal of Virology  2007;82(4):1884-1898.
The murine cytomegalovirus (MCMV) M33 gene is conserved among all betaherpesviruses and encodes a homologue of seven-transmembrane receptors (7TMR) with the capacity for constitutive signaling. Previous studies have demonstrated that M33 is important for MCMV dissemination to or replication within the salivary glands. In this study, we probed N- and C-terminal regions of M33 as well as known 7TMR signature motifs in transmembrane (TM) II and TM III to determine the impact on cell surface expression, constitutive signaling, and in vivo phenotype. The region between amino acids R340 and A353 of the C terminus was found to be important for CREB- and NFAT-mediated signaling, although not essential for phosphatidylinositol turnover. Tagging or truncation of the N terminus of M33 resulted in loss of cell surface expression. Within TM II, an F79D mutation abolished constitutive signaling, demonstrating a role, as in other cellular and viral 7TMR, of TM II in receptor activation. In TM III, the arginine (but not the asparagine) residue of the NRY motif (the counterpart of the common DRY motif in cellular 7TMR) was found to be essential for constitutive signaling. Selected mutations incorporated into recombinant MCMV showed that disruption of constitutive signaling for a viral 7TMR homologue resulted in a reduced capacity to disseminate to or replicate in the salivary glands. In addition, HCMV UL33 was found to partially compensate for the lack of M33 in vivo, suggesting conserved biological roles of the UL33 gene family.
PMCID: PMC2258698  PMID: 18057236
6.  A Point Mutation in a Herpesvirus Polymerase Determines Neuropathogenicity 
PLoS Pathogens  2007;3(11):e160.
Infection with equid herpesvirus type 1 (EHV-1) leads to respiratory disease, abortion, and neurologic disorders in horses. Molecular epidemiology studies have demonstrated that a single nucleotide polymorphism resulting in an amino acid variation of the EHV-1 DNA polymerase (N752/D752) is significantly associated with the neuropathogenic potential of naturally occurring strains. To test the hypothesis that this single amino acid exchange by itself influences neuropathogenicity, we generated recombinant viruses with differing polymerase sequences. Here we show that the N752 mutant virus caused no neurologic signs in the natural host, while the D752 virus was able to cause inflammation of the central nervous system and ataxia. Neurologic disease induced by the D752 virus was concomitant with significantly increased levels of viremia (p = 0.01), but the magnitude of virus shedding from the nasal mucosa was similar between the N752 and D752 viruses. Both viruses replicated with similar kinetics in fibroblasts and epithelial cells, but exhibited differences in leukocyte tropism. Last, we observed a significant increase (p < 0.001) in sensitivity of the N752 mutant to aphidicolin, a drug targeting the viral polymerase. Our results demonstrate that a single amino acid variation in a herpesvirus enzyme can influence neuropathogenic potential without having a major effect on virus shedding from infected animals, which is important for horizontal spread in a population. This observation is very interesting from an evolutionary standpoint and is consistent with data indicating that the N752 DNA pol genotype is predominant in the EHV-1 population, suggesting that decreased viral pathogenicity in the natural host might not be at the expense of less efficient inter-individual transmission.
Author Summary
Equid herpesvirus type 1 (EHV-1), a close relative of varicella-zoster virus and herpes simplex virus of humans, is spread by aerosol and is the causative agent of the most common neurologic disease of horses. Outbreaks of the neurologic form of EHV-1 can be devastating to individual animals and entire herds, and approximately one-third of the affected horses generally are at risk of death or suffer so extensively that euthanasia becomes necessary. Our report provides evidence for a direct causal link between the genotype of EHV-1 strains and their neurovirulence, and thereby gives a long-awaited explanation for the conundrum of the different clinical outcomes following EHV-1 infection. We proved that alteration of one amino acid in the key viral enzyme, DNA polymerase, which is conserved in all herpesviruses, renders the virus unable to cause neurologic disease. The improved clinical outcome is likely due to the reduction in virus levels in the bloodstream, ultimately resulting in less virus reaching the central nervous system. In summary, our study shows that herpesvirus virulence and tissue tropism in the natural host are linked with the function of a key virus-encoded enzyme involved in DNA replication.
PMCID: PMC2065875  PMID: 17997600
7.  The Murine Cytomegalovirus Chemokine Homolog, m131/129, Is a Determinant of Viral Pathogenicity 
Journal of Virology  1999;73(8):6800-6809.
Chemokines are important mediators of the early inflammatory response to infection and modify a wide range of host immune responses. Functional homologs of cellular chemokines have been identified in a number of herpesviruses, suggesting that the subversion of the host chemokine response contributes to the pathogenesis of these viruses. Transcriptional and reverse transcription-PCR analyses demonstrated that the murine cytomegalovirus (MCMV) chemokine homolog, m131, was spliced at the 3′ end to the adjacent downstream open reading frame, m129, resulting in a predicted product of 31 kDa, which is significantly larger than most known chemokines. The in vivo impact of m131/129 was investigated by comparing the replication of MCMV mutants having m131/129 deleted (Δm131/129) with that of wild-type (wt) MCMV. Our studies demonstrate that both wt and Δm131/129 viruses replicated to equivalent levels during the first 2 to 3 days following in vivo infection. However, histological studies demonstrated that the early inflammatory response elicited by Δm131/129 was reduced compared with that of wt MCMV. Furthermore, the Δm131/129 mutants failed to establish a high-titer infection in the salivary glands. These results suggest that m131/129 possesses proinflammatory properties in vivo and is important for the dissemination of MCMV to or infection of the salivary gland. Notably, the Δm131/129 mutants were cleared more rapidly from the spleen and liver during acute infection compared with wt MCMV. The accelerated clearance of the mutants was dependent on NK cells and cells of the CD4+ CD8+ phenotype. These data suggest that m131/129 may also contribute to virus mechanisms of immune system evasion during early infection, possibly through the interference of NK cells and T cells.
PMCID: PMC112765  PMID: 10400778
8.  A novel streptococcal integrative conjugative element involved in iron acquisition 
Molecular Microbiology  2008;70(5):1274-1292.
In this study, we determined the function of a novel non-ribosomal peptide synthetase (NRPS) system carried by a streptococcal integrative conjugative element (ICE), ICESe2. The NRPS shares similarity with the yersiniabactin system found in the high-pathogenicity island of Yersinia sp. and is the first of its kind to be identified in streptococci. We named the NRPS product ‘equibactin’ and genes of this locus eqbA–N. ICESe2, although absolutely conserved in Streptococcus equi, the causative agent of equine strangles, was absent from all strains of the closely related opportunistic pathogen Streptococcus zooepidemicus. Binding of EqbA, a DtxR-like regulator, to the eqbB promoter was increased in the presence of cations. Deletion of eqbA resulted in a small-colony phenotype. Further deletion of the irp2 homologue eqbE, or the genes eqbH, eqbI and eqbJ encoding a putative ABC transporter, or addition of the iron chelator nitrilotriacetate, reversed this phenotype, implicating iron toxicity. Quantification of 55Fe accumulation and sensitivity to streptonigrin suggested that equibactin is secreted by S. equi and that the eqbH, eqbI and eqbJ genes are required for its associated iron import. In agreement with a structure-based model of equibactin synthesis, supplementation of chemically defined media with salicylate was required for equibactin production.
PMCID: PMC3672683  PMID: 18990191

Results 1-8 (8)