Biology subjects

Brune, W.

Publications and source records attributed to Brune, W..

11 recordsLinked to original sources

bioRxiv2026

Murine cytomegalovirus m119-118 encodes a new viral Fc receptor antagonizing host Fc receptor activation

Cytomegaloviruses (CMVs) encode numerous immunomodulatory proteins to counteract innate and adaptive immunity. One class of immune evasion proteins is viral Fc receptors (vFcRs), which bind to the Fc region of IgG antibodies and interfere with antibody-mediated effector functions crucial for antiviral defense. Despite the established role of vFcRs in modulating antibody-mediated immunity, their contribution to viral pathogenesis in vivo remains incompletely understood. Although human CMV (HCMV) encodes four vFcRs, only a single vFcR, fcr-1 encoded by gene m138, has been identified in murine CMV (MCMV). By comparing and cloning the genomes of MCMV strains v70, K181+, and K181Perth, we identified a frameshift mutation affecting the spliced m119-118 transcript in K181Perth. This finding prompted us to investigate the function of the m119-118 gene. We show that it encodes a second MCMV vFcR, which we named fcr-2. It is structurally similar to its positional homolog in HCMV, UL119-118/gp68, and binds specifically to the Fc part of murine IgG. Deletion of both vFcRs genes from the MCMV genome resulted in substantially reduced Fc-binding to the surface of infected cells, indicating a complementary function of the vFcRs. Functional assays with viral deletion mutants further demonstrated that both proteins inhibit host Fc receptor activation in a cooperative fashion. Although an m119-118-deficient MCMV was only marginally attenuated in infected BALB/c mice, an m119-118 and m138 double mutant attained significantly lower organ titers than the m138-deficient mutant. These data suggest an important cooperative function of the two MCMV vFcRs for viral dissemination and pathogenesis in vivo.

microbiology↗

bioRxiv2025

Increased Infectivity of Human Cytomegalovirus Strain TB40/E Conferred by Variants of the Envelope Glycoprotein UL128 and the Regulatory Protein IE2

Human cytomegalovirus (HCMV) infects various cell types in its human host, and this broad tropism plays a vital role in viral transmission, dissemination, and pathogenesis. HCMV strains differ in their ability to infect and replicate in different cell types, but the genetic determinants of cell tropism have only begun to be understood. A widely used HCMV strain, TB40/E, contains a mixture of genetically distinct virus variants. Only a few passages in ARPE-19 epithelial cells resulted in the selective enrichment of a substrain, termed TB40/EE, which infected epithelial cells more efficiently than the parental TB40/E and induced the formation of large multinucleated syncytia. Herein, we used sequence comparison and genetic engineering of a TB40/E-derived bacterial artificial chromosome clone, TB40-BAC4, to demonstrate that the high infectivity of TB40/EE and its ability to induce syncytia in epithelial cells depends on two single-nucleotide variants (SNVs) affecting the envelope glycoprotein UL128 and the major viral transactivator protein, IE2. While the intronic SNV in UL128 increased splicing of the UL128 transcript, it surprisingly decreased viral infectivity and replication in epithelial cells. The additional introduction of the IE2 SNV reversed this phenotype, increasing infectivity and syncytium formation. This SNV resulted in a D390H substitution and increased the levels of several early and late viral proteins, suggesting that it altered the ability of IE2 to activate viral genes. The same two SNVs increased the ability to infect THP-1-derived macrophages and JEG-3 trophoblast cells. These results demonstrate that HCMV cell tropism depends on both envelope glycoproteins and regulatory proteins. ImportanceDifferent genetic versions of human cytomegalovirus (HCMV) affect its ability to infect various human cell types. Here we focused on a commonly used strain, TB40/E, which contains a mix of virus variants. After growing it in epithelial cells, a specific variant called TB40/EE became dominant. This variant infected epithelial cells more effectively and caused the formation of large, fused cells (syncytia). In this study, we discovered that two small genetic changes were responsible for this behavior. One change affected a protein on the viral envelope (UL128) by altering how its RNA was processed. Surprisingly, this change reduced the viruss ability to spread, but a second change in a regulatory protein (IE2) reversed that effect. Together, these changes enhanced the viruss ability to infect not only epithelial cells but also macrophages and placental cells. This study highlights how small genetic tweaks can influence how HCMV targets different types of human cells.

microbiology↗

bioRxiv2024

Molecular cloning and host range analysis of three cytomegaloviruses from Mastomys natalensis

Herpesvirus-based vectors are attractive for use as conventional or transmissible vaccines against emerging zoonoses in inaccessible animal populations. In both cases, cytomegaloviruses as members of the subfamily Betaherpesvirinae are particularly suitable for vaccine development as they are highly specific for their natural host species, infect a large proportion of their host population, and cause mild infections in healthy individuals. The Natal multimammate mouse (Mastomys natalensis) is the natural reservoir of Lassa virus, which causes deadly hemorrhagic fever in humans. M. natalensis was recently reported to harbor at least three different cytomegaloviruses (MnatCMV1, MnatCMV2 and MnatCMV3). Herein, we report the molecular cloning of three complete MnatCMV genomes in a yeast and bacterial artificial chromosome (YAC-BAC) hybrid vector. Purified viral genomes were cloned in yeast by single-step transformation-associated recombination (STAR cloning) and subsequently transferred to Escherichia coli for further genetic manipulation. Integrity of the complete cloned viral genomes was verified by sequencing, and replication fitness of viruses reconstituted from these clones was analyzed by replication kinetics in M. natalensis fibroblasts and kidney epithelial cells. We also found that neither parental nor cloned MnatCMVs replicated in mouse and rat fibroblasts, nor did they show sustained replication in baby hamster kidney cells, consistent with the expected narrow host range for these viruses. We further demonstrated that an exogenous sequence can be inserted by BAC-based mutagenesis between open reading frames M25 and m25.1 of MnatCMV2 without affecting replication fitness in vitro, identifying this site as potentially suitable for the insertion of vaccine target antigen genes. ImportanceCytomegaloviruses recently discovered in the Natal multimammate mouse (Mastomys natalensis) are widespread within the M. natalensis population. Since these rodents also serve as natural hosts of the human pathogen Lassa virus (LASV), we investigated the potential suitability of M. natalensis CMVs (MnatCMVs) as vaccine vectors. We describe the cloning of three different MnatCMV genomes as bacterial artificial chromosomes (BACs). Replicative capacity and species specificity of these BAC-derived MnatCMVs were analyzed in multiple cell types. We also identified a transgene insertion site within one of the MnatCMV genomes suitable for the incorporation of vaccine target antigens. Together, this study provides a foundation for the development of MnatCMVs as transmissible MnatCMV-based LASV vaccines to reduce LASV prevalence in hard-to-reach M. natalensis populations and thereby zoonotic transmission to humans.

microbiology↗

bioRxiv2024

E2F3-dependent activation of FAM111B restricts mouse cytomegalovirus replication in primate cells

Cytomegaloviruses are highly species-specific as they replicate only in cells of their own or a closely related species. For instance, human cytomegalovirus cannot replicate in rodent cells, and mouse cytomegalovirus (MCMV) cannot replicate in human and monkey cells. However, the mechanisms underlying the host species restriction remain poorly understood. We have previously shown that passaging MCMV in human retinal pigment epithelial cells allows the virus to replicate to high titers in these cells due to the accumulation of adaptive mutations, such as loss-of-function mutations in the viral M117 gene. The M117 protein interacts with E2F transcription factors and activates E2F-dependent transcription. Here we show that activation of E2F3 is primarily responsible for MCMVs inability to replicate in human cells. By transcriptome analysis, we identified two E2F3-induced serine proteases, FAM111A and FAM111B, as potential host restriction factors. By using shRNA-mediated gene knockdown and CRISPR/Cas9-mediated gene knockout, we demonstrated that FAM111B, but not its paralog FAM111A, suppresses MCMV replication in human and rhesus macaque cells. By immunofluorescence, we detected FAM111B predominantly in the nucleus of infected cells with enrichment in viral replication compartments, suggesting that it might play a role during viral replication. The fact that the FAM111B gene is conserved in primates but absent in rodents suggests that MCMV has not evolved to evade or counteract this restriction factor, which is not present in its natural host. ImportanceViruses must counteract host cell defenses to facilitate viral replication. Viruses with a narrow host range, such as the cytomegaloviruses, are unable to counteract cellular defenses in cells of a foreign species. However, little is known about the cellular host range factors restricting cytomegalovirus replication. Here we show that MCMV induces the expression of the FAM111 proteases and that FAM111B, but not FAM111A that has previously been shown to restrict the replication of polyomavirus and orthopoxvirus host range mutants, acts as a cellular factor suppressing MCMV replication in human and rhesus monkey cells. The identification of FAM111B as a host range factor should provide new insight into the physiological functions of this poorly characterized protein.

microbiology↗

bioRxiv2024

Limited protection against early-life cytomegalovirus infection results from deficiency of cytotoxic CD8T cells

Differential antiviral T cell immunity in early life impacts the clinical outcome of Cytomegalovirus (CMV) infection, but the underlying mechanisms are not well understood. Here, we found delayed enrichment of early-life murine CMV-specific CD8 T cells due to a general deficiency of {beta} T cells. Adoptive transfer of naive adult T cells into neonates did not protect due to a blockade of CD8 but not of CD4 effector T cell differentiation. Early-life deficiency of critical signal 3 cytokines during T cell priming resulted in the appearance of non-cytotoxic CD8 effector T cells whereas the effector phase of adult-primed T cells was not disrupted in neonates. Accordingly, we found an overall low number of antiviral human CD8 T cells in newborns with congenital CMV. Together, this study suggests defective CD8 T cell immunity as an important factor explaining the higher risk for CMV disease in the early-life phase.

immunology↗

bioRxiv2024

Cytomegalovirus inhibitors of programmed cell death prevent a contribution of antigen cross-presentation to the priming of antiviral CD8 T cells

CD8 T cells are the predominant effector cells of adaptive immunity in preventing cytomegalovirus (CMV) multiple-organ disease caused by cytopathogenic tissue infection. The mechanism by which CMV-specific, naive CD8 T cells become primed and clonally expand is of fundamental importance for our understanding of CMV immune control. For CD8 T-cell priming, two pathways have been identified: direct antigen presentation by infected professional antigen-presenting cells (pAPCs) and antigen cross-presentation by uninfected pAPCs that take up antigenic material derived from infected tissue cells. Studies in mouse models using murine CMV (mCMV) and precluding either pathway genetically or experimentally have shown that, in principle, both pathways can congruently generate the mouse MHC/H-2 class-I-determined epitope-specificity spectrum of the CD8 T-cell response. Own recent studies, however, have shown that direct antigen presentation is the canonical pathway when both are accessible. This raised the question of why antigen cross-presentation is ineffective even under conditions of high virus replication thought to provide high amounts of antigenic material for feeding cross-presenting pAPCs. As delivery of antigenic material for cross-presentation is associated with programmed cell death, and as CMVs encode inhibitors of different cell death pathways, we pursued the idea that these inhibitors restrict antigen delivery and thus CD8 T-cell priming by cross-presentation. To test this hypothesis, we compared the CD8 T-cell responses to recombinant mCMVs lacking expression of the apoptosis-inhibiting protein M36 or the necroptosis-inhibiting protein M45 with responses to wild-type mCMV and revertant viruses expressing the respective cell death inhibitors. The data reveal that increased programmed cell death caused by deletion of either M36 or M45 improves CD8 T-cell priming in mice capable of antigen cross-presentation but not in a mutant mouse strain unable to cross-present. These findings strongly support the conclusion that CMV cell death inhibitors restrict the priming of CD8 T cells by antigen cross-presentation. Author SummaryIn patients as well as in experimental mouse models, CD8 T cells represent the most potent antiviral effector cells in preventing CMV disease in immunocompromised recipients of hematopoietic cell transplantation. Despite the clinical relevance of mounting a protective response, the mode of CMV antigen presentation to naive CD8 T cells remained unclear. In principle, naive CD8 T cells can be sensitized through "direct antigen presentation" on the surface of infected professional antigen-presenting cells (pAPCs) or through "antigen cross-presentation" by uninfected pAPCs that take up antigenic material derived from infected cells following cell death. As CMVs are cytopathogenic, eventually killing their host cells, and as they encode immune evasion proteins interfering with the MHC/HLA class-I pathway of direct antigen presentation in infected cells, it was reasonable to propose a dominant role for antigen cross-presentation. Mouse models precluding either pathway, however, revealed that both can raise an equivalent CD8 T-cell response, and recent work has identified direct antigen presentation as the canonical pathway taken when both are accessible. Here we show that virus-encoded inhibitors of two programmed cell death modalities, apoptosis and necroptosis, prevent an antigen release sufficient for a notable cross-presentation. This answers a long-debated open question in CMV immunology.

immunology↗

bioRxiv2024

Human cytomegalovirus glycoprotein variants governing viral tropism and syncytium formation in epithelial cells and macrophages

Human cytomegalovirus (HCMV) displays a broad cell tropism, and the infection of biologically relevant cells such as epithelial, endothelial, and hematopoietic cells supports viral transmission, systemic spread, and pathogenesis in the human host. HCMV strains differ in their ability to infect and replicate in these cell types, but the genetic basis of these differences has remained incompletely understood. In this study, we investigated HCMV strain VR1814, which is highly infectious for epithelial cells and macrophages and induces cell-cell fusion in both cell types. A VR1814-derived bacterial artificial chromosome (BAC) clone, FIX-BAC, was generated many years ago but has fallen out of favor because of its modest infectivity. By sequence comparison and genetic engineering of FIX, we demonstrate that the high infectivity of VR1814 and its ability to induce syncytium formation in epithelial cells and macrophages depends on VR1814-specific variants of the envelope glycoproteins gB, UL128, and UL130. We also show that UL130-neutralizing antibodies inhibit syncytium formation, and a FIX-specific mutation in UL130 is responsible for its low infectivity by reducing the amount of the pentameric glycoprotein complex in viral particles. Moreover, we found that a VR1814-specific mutation in US28 further increases viral infectivity in macrophages, possibly by promoting lytic rather than latent infection of these cells. Our findings show that variants of gB and the pentameric complex are major determinants of infectivity and syncytium formation in epithelial cells and macrophages. Furthermore, the VR1814-adjusted FIX strains can serve as valuable tools to study HCMV infection of myeloid cells. ImportanceHCMV is a major cause of morbidity and mortality in transplant patients and the leading cause of congenital infections. HCMV infects various cell types, including epithelial cells and macrophages, and some strains induce the fusion of neighboring cells, leading to the formation of large multinucleated cells called syncytia. This process may limit the exposure of the virus to host immune factors and facilitate its spread. However, the reason why some HCMV strains exhibit a broader cell tropism and why some induce cell fusion more than others is not well understood. We compared two closely related HCMV strains and provided evidence that small differences in viral envelope glycoproteins can massively increase or decrease the virus infectivity and its ability to induce syncytium formation. The results of the study suggest that natural strain variations may influence HCMV infection and pathogenesis in humans.

microbiology↗

bioRxiv2020

Viral mediated tethering to SEL1L facilitates ER-associated degradation of IRE1

The unfolded protein response (UPR) and endoplasmic reticulum (ER)-associated degradation (ERAD) are two essential components of the quality control system for proteins in the secretory pathway. When unfolded proteins accumulate in the ER, UPR sensors such as IRE1 induce the expression of ERAD genes, thereby increasing protein export from the ER to the cytosol and subsequent degradation by the proteasome. Conversely, IRE1 itself is an ERAD substrate, indicating that the UPR and ERAD regulate each other. Viruses are intracellular parasites that exploit the host cell for their own benefit. Cytomegaloviruses selectively modulate the UPR to take advantage of beneficial and inhibit detrimental effects on viral replication. We have previously shown that murine and human cytomegaloviruses express homologous proteins (M50 and UL50, respectively) that dampen the UPR at late times post infection by inducing IRE1 degradation. However, the degradation mechanism has remained uncertain. Here we show that the cytomegalovirus M50 protein mediates IRE1 degradation by the proteasome. M50-dependent IRE1 degradation can be blocked by pharmacological inhibition of p97/VCP or by genetic ablation of SEL1L, both of which are component of the ERAD machinery. SEL1L acts as a cofactor of the E3 ubiquitin ligase HRD1, while p97/VCP is responsible for the extraction of ubiquitylated proteins from the ER to the cytosol. We further show that M50 facilitates the IRE1-SEL1L interaction by binding to both, IRE1 and SEL1L. These results indicate that the viral M50 protein dampens the UPR by tethering IRE1 to SEL1L, thereby promoting its degradation by the ERAD machinery. ImportanceViruses infect cells of their host and force them to produce virus progeny. This can impose stress on the host cell and activate counter-regulatory mechanisms. Protein overload in the endoplasmic reticulum (ER) leads to ER stress and triggers the unfolded protein response, which in turn upregulates protein folding and increases the degradation of proteins in the ER. Previous work has shown that cytomegaloviruses interfere with the unfolded protein response by degrading the sensor molecule IRE1. Herein we demonstrate how the viral M50 protein exploits the ER-associated degradation machinery to dispose of IRE1. Degradation of IRE1 curbs the unfolded protein response and helps the virus to increase the synthesis of its own proteins.

microbiology↗

bioRxiv2020

Murine cytomegaloviruses m139 targets DDX3 to curtail interferon production and promote viral replication

Cytomegaloviruses (CMV) infect many different cell types and tissues in their respective hosts. Monocytes and macrophages play an important role in CMV dissemination from the site of infection to target organs. Moreover, macrophages are specialized in pathogen sensing and respond to infection by secreting cytokines and interferons. In murine cytomegalovirus (MCMV), a model for human cytomegalovirus, several genes required for efficient replication in macrophages have been identified, but their specific functions remain poorly understood. Here we show that MCMV m139, a gene of the conserved US22 gene family, encodes a protein that interacts with the DEAD box helicase DDX3, a protein involved in pathogen sensing and interferon (IFN) induction, and the E3 ubiquitin ligase UBR5. DDX3 and UBR5 also participate in the transcription, processing, and translation of a subset of cellular mRNAs. We show that m139 inhibits DDX3-mediated IFN-{beta} induction and is necessary for efficient viral replication in bone-marrow derived macrophages. In vivo, m139 is crucial for viral dissemination to local lymph nodes and to the salivary glands. An m139-deficient MCMV also replicated to lower titers in SVEC4-10 endothelial cells. This replication defect was not accompanied by increased IFN-{beta} transcription, but was rescued by knockout of either DDX3 or UBR5. Moreover, m139 co-localized with DDX3 and UBR5 in viral replication compartments in the cell nucleus. These results suggest that m139 inhibits DDX3-mediated IFN-{beta} production in macrophages and antagonizes DDX3 and UBR5-dependent functions related to RNA metabolism in endothelial cells. Author SummaryHuman cytomegalovirus is an opportunistic pathogen that causes severe infections in immunocompromised individuals. The virus infects certain types, such as macrophages and endothelial cells, to ensure its dissemination within the body. Little is known about the viral factors that promote a productive infection of these cell types. The identification of critical viral factors and the molecular pathways they target can lead to the development of novel antiviral treatment strategies. Using the mouse cytomegalovirus as a model, we studied the viral m139 gene, which is important for virus replication in macrophages and endothelial cells and for dissemination in the mouse. This gene encodes a protein that interacts with the host proteins DDX3 and UBR5. Both proteins are involved in gene expression, and the RNA helicase DDX3 also participates in mounting an innate antiviral response. By interacting with DDX3 and UBR5, m139 ensures efficient viral replication in endothelial cells. Importantly, we identify m139 as a new viral DDX3 inhibitor, which curtails the production of interferon in macrophages.

microbiology↗

bioRxiv2019

Cross-regulation of viral kinases with cyclin A secures shutoff of host DNA synthesis

Herpesviruses encode conserved protein kinases to stimulate phosphorylation-sensitive processes during infection. How these kinases bind to cellular factors and how this impacts their regulatory functions is poorly understood. Here, we use quantitative proteomics to determine cellular interaction partners of human herpesvirus (HHV) kinases. We find that these kinases can target key regulators of transcription and replication. The interaction with Cyclin A and associated factors is identified as a specific signature of {beta}-herpesvirus kinases. Cyclin A is recruited via RXL-motifs that overlap with nuclear localization signals (NLS) and locate in the non-catalytic N-terminal regions. This architecture is conserved for viral kinases of HHV6, HHV7 and rodent CMVs. Docking to Cyclin A competes with NLS function, enabling dynamic changes in kinase localization and substrate phosphorylation. The viral kinase redirects Cyclin A to the cytosol, which is essential for the inhibition of cellular DNA replication during infection. Our data highlight a fine-tuned and physiologically important interplay between a cellular cyclin and viral kinases.

microbiology↗

bioRxiv2019

Repression of Viral Gene Expression and Replication by the Unfolded Protein Response Effector XBP1u

The unfolded protein response (UPR) is a cellular homeostatic circuit regulating protein synthesis and processing in the ER by three ER-to-nucleus signaling pathways. One pathway is triggered by the inositol-requiring enzyme 1 (IRE1), which splices the X-box binding protein 1 (XBP1) mRNA, thereby enabling expression of XBP1s. Another UPR pathway activates the activating transcription factor 6 (ATF6). Here we show that murine cytomegalovirus (MCMV), a prototypic {beta}-herpesvirus, harnesses the UPR to regulate its own life cycle. MCMV activates the IRE1-XBP1 pathway early post infection to relieve repression by XBP1u, the product of the unspliced XBP1 mRNA. XBP1u inhibits viral gene expression and replication by blocking the activation of the viral major immediate-early promoter by XBP1s and ATF6. These findings reveal a redundant function of XBP1s and ATF6 as activators of the viral life cycle, and an unexpected role of XBP1u as a potent repressor of both XBP1s and ATF6-mediated activation.

microbiology↗