Murine Gammaherpesvirus Research Articles

Molecular mechanism underlying selective inhibition of mRNA nuclear export by herpesvirus protein ORF10

Viruses employ multiple strategies to inhibit host mRNA nuclear export. Distinct to the generally nonselective inhibition mechanisms, ORF10 from gammaherpesviruses inhibits mRNA export in a transcript-selective manner by interacting with Rae1 (RNA export 1) and Nup98 (nucleoporin 98). We now report the structure of ORF10 from MHV-68 (murine gammaherpesvirus 68) bound to the Rae1-Nup98 heterodimer, thereby revealing detailed intermolecular interactions. Structural and functional assays highlight that two highly conserved residues of ORF10, L60 and M413, play critical roles in both complex assembly and mRNA export inhibition. Interestingly, although ORF10 occupies the RNA-binding groove of Rae1-Nup98, the ORF10-Rae1-Nup98 ternary complex still maintains a comparable RNA-binding ability due to the ORF10-RNA direct interaction. Moreover, mutations on the RNA-binding surface of ORF10 disrupt its function of mRNA export inhibition. Our work demonstrates the molecular mechanism of ORF10-mediated selective inhibition and provides insights into the functions of Rae1-Nup98 in regulating host mRNA export.

Progressive Hypoxia: A Pivotal Pathophysiologic Mechanism of COVID-19 Pneumonia

Progressive Hypoxia: A Pivotal Pathophysiologic Mechanism of COVID-19 Pneumonia

KSHV LANA acetylation-selective acidic domain reader sequence mediates virus persistence

Viruses modulate biochemical cellular pathways to permit infection. A recently described mechanism mediates selective protein interactions between acidic domain readers and unacetylated, lysine-rich regions, opposite of bromodomain function. Kaposi´s sarcoma (KS)-associated herpesvirus (KSHV) is tightly linked with KS, primary effusion lymphoma, and multicentric Castleman's disease. KSHV latently infects cells, and its genome persists as a multicopy, extrachromosomal episome. During latency, KSHV expresses a small subset of genes, including the latency-associated nuclear antigen (LANA), which mediates viral episome persistence. Here we show that LANA contains two tandem, partially overlapping, acidic domain sequences homologous to the SET oncoprotein acidic domain reader. This domain selectively interacts with unacetylated p53, as evidenced by reduced LANA interaction after overexpression of CBP, which acetylates p53, or with an acetylation mimicking carboxyl-terminal domain p53 mutant. Conversely, the interaction of LANA with an acetylation-deficient p53 mutant is enhanced. Significantly, KSHV LANA mutants lacking the acidic domain reader sequence are deficient for establishment of latency and persistent infection. This deficiency was confirmed under physiological conditions, on infection of mice with a murine gammaherpesvirus 68 chimera expressing LANA, where the virus was highly deficient in establishing latent infection in germinal center B cells. Therefore, LANA's acidic domain reader is critical for viral latency. These results implicate an acetylation-dependent mechanism mediating KSHV persistence and expand the role of acidic domain readers.

Interleukin 16 contributes to gammaherpesvirus pathogenesis by inhibiting viral reactivation.

Gammaherpesviruses have evolved various strategies to take advantage of host cellular factors or signaling pathways to establish a lifelong latent infection. Like the human gammaherpesvirus Epstein-Barr virus, murine gammaherpesvirus 68 (MHV68) establishes and maintains latency in the memory B cells during infection of laboratory mice. We have previously shown that MHV68 can immortalize fetal liver-derived B cells that induce lymphomas when injected into immunodeficient mice. Here we identify interleukin 16 (IL16) as a most abundantly expressed cytokine in MHV68-immortalized B cells and show that MHV68 infection elevates IL16 expression. IL16 is not important for MHV68 lytic infection but plays a critical role in MHV68 reactivation from latency. IL16 deficiency increases MHV68 lytic gene expression in MHV68-immortalized B cells and enhances reactivation from splenic latency. Correlatively, IL16 deficiency increases the frequency of MHV68-infected plasma cells that can be attributed to enhanced MHV68 reactivation. Furthermore, similar to TPA-mediated lytic replication of Kaposi's sarcoma-associated herpesvirus, IL16 deficiency markedly induces Tyr705 STAT3 de-phosphorylation and elevates p21 expression, which can be counteracted by the tyrosine phosphatase inhibitor orthovanadate. Importantly, orthovanadate strongly blocks MHV68 lytic gene expression mediated by IL16 deficiency. These data demonstrate that virus-induced IL16 does not directly participate in MHV68 lytic replication, but rather inhibits virus reactivation to facilitate latent infection, in part through the STAT3-p21 axis.

Dangerous Liaisons: Gammaherpesvirus Subversion of the Immunoglobulin Repertoire.

A common biologic property of the gammaherpesviruses Epstein–Barr Virus and Kaposi sarcoma herpesvirus is their use of B lymphocytes as a reservoir of latency in healthy individuals that can undergo oncogenic transformation later in life. Gammaherpesviruses (GHVs) employ an impressive arsenal of proteins and non-coding RNAs to reprogram lymphocytes for proliferative expansion. Within lymphoid tissues, the germinal center (GC) reaction is a hub of B cell proliferation and death. The goal of a GC is to generate and then select for a pool of immunoglobulin (Ig) genes that will provide a protective humoral adaptive immune response. B cells infected with GHVs are detected in GCs and bear the hallmark signatures of the mutagenic processes of somatic hypermutation and isotype class switching of the Ig genes. However, data also supports extrafollicular B cells as a reservoir engaged by GHVs. Next-generation sequencing technologies provide unprecedented detail of the Ig sequence that informs the natural history of infection at the single cell level. Here, we review recent reports from human and murine GHV systems that identify striking differences in the immunoglobulin repertoire of infected B cells compared to their uninfected counterparts. Implications for virus biology, GHV-associated cancers, and host immune dysfunction will be discussed.

Conserved Herpesvirus Kinase ORF36 Activates B2 Retrotransposons during Murine Gammaherpesvirus Infection.

Short interspersed nuclear elements (SINEs) are RNA polymerase III (RNAPIII)-transcribed, retrotransposable noncoding RNA (ncRNA) elements ubiquitously spread throughout mammalian genomes. While normally silenced in healthy somatic tissue, SINEs can be induced during infection with DNA viruses, including the model murine gammaherpesvirus 68 (MHV68). Here, we explored the mechanisms underlying MHV68 activation of SINE ncRNAs. We demonstrate that lytic MHV68 infection of B cells, macrophages, and fibroblasts leads to robust activation of the B2 family of SINEs in a cell-autonomous manner. B2 ncRNA induction requires neither host innate immune signaling factors nor involvement of the RNAPIII master regulator Maf1. However, we identified MHV68 ORF36, the conserved herpesviral kinase, as playing a key role in B2 induction during lytic infection. SINE activation is linked to ORF36 kinase activity and can also be induced by inhibition of histone deacetylases 1 and 2 (HCAC 1/2), which is one of the known ORF36 functions. Collectively, our data suggest that ORF36-mediated changes in chromatin modification contribute to B2 activation during MHV68 infection and that this activity is conserved in other herpesviral protein kinase homologs.IMPORTANCE Viral infection dramatically changes the levels of many types of RNA in a cell. In particular, certain oncogenic viruses activate expression of repetitive genes called retrotransposons, which are normally silenced due to their ability to copy and spread throughout the genome. Here, we established that infection with the gammaherpesvirus MHV68 leads to a dramatic induction of a class of noncoding retrotransposons called B2 SINEs in multiple cell types. We then explored how MHV68 activates B2 SINEs, revealing a role for the conserved herpesviral protein kinase ORF36. Both ORF36 kinase-dependent and kinase-independent functions contribute to B2 induction, perhaps through ORF36 targeting of proteins involved in controlling the accessibility of chromatin surrounding SINE loci. Understanding the features underlying induction of these elements following MHV68 infection should provide insight into core elements of SINE regulation, as well as disregulation of SINE elements associated with disease.

Protective role of overexpressed MUC5AC against fibrosis in MHV-68-induced combined pulmonary fibrosis and emphysema mouse model.

Mucins have long been regarded to play a role as a barrier to prevent mucosal infections; however, some studies report that overexpression of mucins induces obstruction and inflammation of airways. We investigated whether the secretion of overexpressed mucin, mucin5ac (MUC5AC), could improve protection against pathogens. To examine the possible roles of mucin hypersecretion in augmenting host defense against disease-promoting muco-obstructive lung disease, a mouse model that overexpressed MUC5AC was generated. We had previously proved that murine gammaherpesvirus-68 (MHV-68)infection could induce emphysema in mice, which later developed into combined pulmonary fibrosis and emphysema (CPFE). We further explored whether increased MUC5AC secretion could provide benefits against MHV-68 induced fibrosis. We initially developed a pcDNA3.1-MUC5AC mouse model. Next, the experimental mice were randomly divided into five groups: normal control, pcDNA3.1 control, pcDNA3.1-MUC5AC, CPFE, and pcDNA3.1- MUC5AC + CPFE. Morphometric analysis of each group was performed by hematoxylin and eosin staining and Masson trichrome staining. MUC5AC levels in lung tissues were analyzed by immunohistochemical staining, real-time polymerase chain reaction, and Western blot analysis. The airway inflammation was determined by differential cell counts of bronchoalveolar lavage fluid (BALF) and measurement of cytokines and chemokines in BALF by enzyme-linked immunosorbent assay. MUC5AC hypersecretion alone was not sufficient to drive goblet cell metaplasia to induce obvious mucus plugging and airway inflammation. However, MUC5AC overexpression served as a protective barrier against MHV-68 virus infection in vivo. Infectivity of MHV-68 was decreased in the pcDNA3.1-MUC5AC + CPFE group compared with that in CPFE group. Meanwhile, a reduction of MHV-68 virus attenuated the expressions of chemokine (C-C motif) ligand 2 (CCL2), chemokine (C-X-C motif) ligand 5 (CXCL5), interleukin-13 (IL-13), and transforming growth factor-β1 (TGF-β1), and weakened airway inflammation and fibrosis in the pcDNA3.1-MUC5AC + CPFE group. Overexpression of MUC5AC appears to exhibit a protective role against MHV-68 infection in mice with emphysema that subsequently developed into CPFE and to further decrease airway inflammation and fibrosis induced by MHV-68 by decreasing the expressions of CCL2, CXCL5, IL-13, and TGF-β1.

B Cell-Intrinsic Expression of Interferon Regulatory Factor 1 Supports Chronic Murine Gammaherpesvirus 68 Infection.

Gammaherpesviruses are ubiquitous pathogens that are associated with cancers, including B cell lymphomas. These viruses are unique in that they infect naive B cells and subsequently drive a robust polyclonal germinal center response in order to amplify the latent reservoir and to establish lifelong infection in memory B cells. The gammaherpesvirus-driven germinal center response in combination with robust infection of germinal center B cells is thought to precipitate lymphomagenesis. Importantly, host and viral factors that selectively affect the gammaherpesvirus-driven germinal center response remain poorly understood. Global deficiency of antiviral tumor-suppressive interferon regulatory factor 1 (IRF-1) selectively promotes the murine gammaherpesvirus 68 (MHV68)-driven germinal center response and expansion of the viral latent reservoir. To determine the extent to which antiviral effects of IRF-1 are B cell intrinsic, we generated mice with conditional IRF-1 deficiency. Surprisingly, B cell-specific IRF-1 deficiency attenuated the establishment of chronic infection and the germinal center response, indicating that MHV68 may, in a B cell-intrinsic manner, usurp IRF-1 to promote the germinal center response and expansion of the latent reservoir. Further, we found that B cell-specific IRF-1 deficiency led to reduced levels of active tyrosine phosphatase SHP1, which plays a B cell-intrinsic proviral function during MHV68 infection. Finally, results of this study indicate that the antiviral functions of IRF-1 unveiled in MHV68-infected mice with global IRF-1 deficiency are mediated via IRF-1 expression by non-B cell populations.IMPORTANCE Gammaherpesviruses establish lifelong infection in over 95% of all adults and are associated with B cell lymphomas. The virus's manipulation of the germinal center response and B cell differentiation to establish lifelong infection is thought to also precipitate malignant transformation, through a mechanism that remains poorly understood. The host transcription factor IRF-1, a well-established tumor suppressor, selectively attenuates MHV68-driven germinal center response, a phenotype that we originally hypothesized to occur in a B cell-intrinsic manner. In contrast, in testing, B cell-intrinsic IRF-1 expression promoted the MHV68-driven germinal center response and the establishment of chronic infection. Our report highlights the underappreciated multifaceted role of IRF-1 in MHV68 infection and pathogenesis.

Endogenous dendritic cell subset cDC1 mediates DC vaccine immunity against gamma herpesvirus in syngeneic BMT recipients

Abstract Dendritic cell (DC) vaccines are a promising immunotherapy for viral infections and cancers, however the mechanisms underlying their action are still not clear. The objective of this study is to understand how DC vaccines stimulate the expansion of cytotoxic T lymphocytes (CTLs) against gamma herpesvirus in bone marrow transplant (BMT) recipients. Herpesviruses commonly reactivate after transplantation of hematopoietic cells in patients and cause high mortality and morbidity. Similarly, infections with murine gamma herpesvirus 68 (MHV-68), a mouse homolog of Epstein-Barr virus, after syngeneic BMT in mice cause severe pulmonary fibrosis and pneumonitis. We prepared DC vaccines by sorting CD11c+ cells from the lungs at 3 days post infection (dpi) with MHV-68. We administered DC vaccines i.v. to BMT mice one day before infection with MHV-68. CTLs of the lung, spleen and mediastinal draining lymph nodes were analyzed by flow cytometry at 7 dpi. Lung sections were prepared at 21 dpi for histology analysis. Adoptive transfer of the DC vaccine stimulates the expansion of viral specific CD8 T cells in MHV-68 infected syn-BMT mice at 7 dpi, and protects them from pneumonitis and fibrosis at 21 dpi. Surprisingly, none of the transferred conventional DC (cDC) subsets, nor migration into draining lymph nodes, nor MHC class I or class II molecule expression are essential for the DC vaccine to activate CD8 T cells in BMT mice. Instead, DC vaccination of BMT mice lacking endogenous cDC1s resulted in reduced CD8 T cells and failed to suppress lytic viral infection. Our results suggest that endogenous cDC1s in BMT mice mediate DC vaccine immunity against gamma herpesvirus. We have thus revealed a previously unknown pathway of DC vaccination.

Activation of the hypoxia-inducible factor 1 alpha is necessary for type 1 interferon and IFN stimulatory gene expression during gammaherpesvirus infection

Abstract Oxygen availability and the hypoxia-inducible factor 1 pathway (HIF1) influence the activity of cells involved in immune responses. Initially described as a master regulator of cellular adaptation to low oxygen concentration, activation of the hypoxia-inducible factor 1 alpha (HIF1α) is now recognized as an integral part of inflammatory cytokines production, phagocytic activity and bacterial killing by myeloid-derived cells. The goal of our studies is to determine the role of HIF1α during antiviral responses. We measure type 1 interferon gene expression in mouse embryonic fibroblasts lacking HIF1α activity (HIF1α Null MEFs) during early infection against the DNA virus, murine gammaherpesvirus 68 (MHV68). We recently reported that MHV68 activates HIF1atranscription activity and this is necessary for viral replication. In this study, analysis of mRNA levels by real-time qPCR, revealed that IFNβ1 decreased by 5-fold in HIF1α Null MEFs following 8 hours post infection (hpi), relative to wild-type, whereas levels of IFNα4, IFNα6 remained unchanged. Consistently, transcript levels of the IFN-stimulated gene OAS1β were reduced 7-fold relative to HIF1α WT MEFs. However, at 24hpi absence of HIF1α diminished expression of IFNα4, IFNα6, IFNβ1, OAS1β, IFIT18 and ISG20. In conclusion, these results suggest that HIF1α activity plays an important role during antiviral responses against dsDNA viruses.

Murine gammaherpesvirus infection is skewed toward Igλ+ B cells expressing a specific heavy chain V-segment.

One of the defining characteristics of the B cell receptor (BCR) is the extensive diversity in the repertoire of immunoglobulin genes that make up the BCR, resulting in broad range of specificity. Gammaherpesviruses are B lymphotropic viruses that establish life-long infection in B cells, and although the B cell receptor plays a central role in B cell biology, very little is known about the immunoglobulin repertoire of gammaherpesvirus infected cells. To begin to characterize the Ig genes expressed by murine gammaherpesvirus 68 (MHV68) infected cells, we utilized single cell sorting to sequence and clone the Ig variable regions of infected germinal center (GC) B cells and plasma cells. We show that MHV68 infection is biased towards cells that express the Igλ light chain along with a single heavy chain variable gene, IGHV10-1*01. This population arises through clonal expansion but is not viral antigen specific. Furthermore, we show that class-switching in MHV68 infected cells differs from that of uninfected cells. Fewer infected GC B cells are class-switched compared to uninfected GC B cells, while more infected plasma cells are class-switched compared to uninfected plasma cells. Additionally, although they are germinal center derived, the majority of class switched plasma cells display no somatic hypermutation regardless of infection status. Taken together, these data indicate that selection of infected B cells with a specific BCR, as well as virus mediated manipulation of class switching and somatic hypermutation, are critical aspects in establishing life-long gammaherpesvirus infection.

Biophysical Studies of a Protein of Unknown Function from Cancer‐Associated Murine Herpesvirus‐68

Members of the Herpesvirus family cause several types of diseases to its mammalian hosts, including infectious mononucleosis, Hodgkin’s lymphoma, and primary effusion lymphomas. Herpesviruses are characterized by their ability to replicate and spread infection in the active lytic phase, but also maintain themselves within a host during the inactive latent phase. Within the gammaherpesvirus subfamily, a conserved protein of unknown function, with a highly conserved domain of unknown function, is expressed during the lytic phase. The protein was observed to be essential to viral replication during the lytic phase of infection when the gene was knocked out of the murine gammaherpesvirus‐68 (MHV68). To characterize its biophysical properties, the protein of unknown function from MHV68 was purified. Analysis of the protein through Circular Dichroism spectroscopy determined the secondary structure to be predominantly alpha‐helical. The thermal denaturation of the protein was pH dependent. Additionally, using a high throughput screen, the thermal stability of the protein was increased in the presence of small organic acids. The goal of the biophysical and structural analyses is to identify the function of the protein in the viral life cycle and to determine if the protein can be targeted to inhibit replication of gammaherpesviruses and their associated diseases.Support or Funding InformationThis work was supported by UWL College of Science and Health, UWL Undergraduate Research and Creativity, and Hardy W. Chan and Sons Chemistry Summer Undergraduate Research Fellowship.

Insights into CD8 T Cell Activation and Exhaustion from a Mouse Gammaherpesvirus Model.

(S.R.S.) I was introduced to viral immunology while working in Peter Doherty's laboratory in the early stages of my research career, inspiring a lifelong interest in this area. During those early years under Peter's mentorship, we studied a mouse gammaherpesvirus model (murine gammaherpesvirus-68 [MHV-68]) that provided a useful small animal model for investigating the immunological control of gammaherpesvirus infection. Interestingly, while CD4 T cells were not required for acute control of MHV-68 in the lung, CD8 T cell-mediated control was progressively lost in the absence of CD4 T cell help, leading to viral recrudescence. This was one of several early studies showing that CD8 T cell control of persistent viral infections was lost in the absence of CD4 T cell help, preceding the concept of CD8 T cell exhaustion. Further studies showed that MHV-68 infection of mice offered a unique model for comparing the mechanisms of acute and long-term control of a persistent viral infection and developing strategies for reversing T cell exhaustion. Here, we provide a brief review of the literature on CD8 T cell activation and exhaustion in this model, focusing on the role of CD40 and B7 family members and including some previously unpublished data.

Identification of Residues Controlling dUTPase Enzyme Activity from Epstein‐Barr Virus

Epstein Barr‐Virus (EBV) is primarily known for causing infectious mononucleosis, but also increases the incidence of lymphomas and autoimmune disorders. There is currently no vaccine or treatment once infected by EBV. The EBV genome encodes a dUTPase enzyme. This enzyme catalyzes the reaction of dUTP to dUMP which is a precursor of the thymidine nucleotide. The enzyme activity regulates the dUTP/dTTP ratio and decreases misincorporation of uracil into newly synthesized DNA. A dUTPase knockout is lethal in mice, E. coli., and S. cerevisiae. The Murine gammaherpesvirus lacking its viral dUTPase has reduced viral replication. It is hypothesized that inhibition of EBV dUTPase would result in uracil misincorporation, double stranded DNA breaks, and a reduction in replication of the viral genome. Characterization of residues required for enzyme activity in EBV dUTPase was performed using sequence alignments and structural data. Mutagenesis and comparative enzyme kinetics on these residues identified aspartate 76 as being critical for enzyme activity. Analysis of structural data identified a histidine residue hypothesized to regulate substrate specificity. A small molecule binding site was identified using computational mapping of two EBV dUTPase 3D structures. We hypothesis that this allosteric binding site contains a serine that post transcriptionally regulates dUTPase activity. This research will guide the development of inhibitors that bind to critical dUTPase residues offering a potential treatment for EBV.Support or Funding InformationThis work was supported by, UWL College of Science and Health, UWL Research and Creativity, and Toce Deans Distinguished Fellowship

Immune protection is dependent on the gut microbiome in a lethal mouse gammaherpesviral infection

Immunopathogenesis in systemic viral infections can induce a septic state with leaky capillary syndrome, disseminated coagulopathy, and high mortality with limited treatment options. Murine gammaherpesvirus-68 (MHV-68) intraperitoneal infection is a gammaherpesvirus model for producing severe vasculitis, colitis and lethal hemorrhagic pneumonia in interferon gamma receptor-deficient (IFNγR−/−) mice. In prior work, treatment with myxomavirus-derived Serp-1 or a derivative peptide S-7 (G305TTASSDTAITLIPR319) induced immune protection, reduced disease severity and improved survival after MHV-68 infection. Here, we investigate the gut bacterial microbiome in MHV-68 infection. Antibiotic suppression markedly accelerated MHV-68 pathology causing pulmonary consolidation and hemorrhage, increased mortality and specific modification of gut microbiota. Serp-1 and S-7 reduced pulmonary pathology and detectable MHV-68 with increased CD3 and CD8 cells. Treatment efficacy was lost after antibiotic treatments with associated specific changes in the gut bacterial microbiota. In summary, transkingdom host-virus-microbiome interactions in gammaherpesvirus infection influences gammaherpesviral infection severity and reduces immune modulating therapeutic efficacy.

RNA decay during gammaherpesvirus infection reduces RNA polymerase II occupancy of host promoters but spares viral promoters.

In mammalian cells, widespread acceleration of cytoplasmic mRNA degradation is linked to impaired RNA polymerase II (Pol II) transcription. This mRNA decay-induced transcriptional repression occurs during infection with gammaherpesviruses including Kaposi’s sarcoma-associated herpesvirus (KSHV) and murine gammaherpesvirus 68 (MHV68), which encode an mRNA endonuclease that initiates widespread RNA decay. Here, we show that MHV68-induced mRNA decay leads to a genome-wide reduction of Pol II occupancy at mammalian promoters. This reduced Pol II occupancy is accompanied by down-regulation of multiple Pol II subunits and TFIIB in the nucleus of infected cells, as revealed by mass spectrometry-based global measurements of protein abundance. Viral genes, despite the fact that they require Pol II for transcription, escape transcriptional repression. Protection is not governed by viral promoter sequences; instead, location on the viral genome is both necessary and sufficient to escape the transcriptional repression effects of mRNA decay. We propose a model in which the ability to escape from transcriptional repression is linked to the localization of viral DNA within replication compartments, providing a means for these viruses to counteract decay-induced transcript loss.

Murid herpesvirus 4 (MuHV-4, prototype strain MHV-68) as an important model in global research of human oncogenic gammaherpesviruses.

The aim of this work was to give an overview of murid herpesvirus 4 (MuHV-4) (synonyms: murine gammaherpesvirus 68, mouse herpesvirus strain 68), the first model for the study of human and animal oncogenic gammaherpesviruses. Based on our results confirming similarity of murine gammaherpesvirus 68 (MHV-68) to another gammaherpesvirus, human oncogenic Epstein-Barr virus (EBV), we were able to interpret some processes observed in the course of MHV-68 infection in analogy to EBV infection. In particular, that were the processes occurring during MHV-68-induced persistent infection in mice accompanied by tumor formation and leukemia following immunosuppression. Since EBV is a highly species specific virus, infecting humans only, these processes cannot be experimentally examined at the molecular, cellular, and tissue levels in natural host. However, they can be investigated in BALB/c mice infected with MHV-68, which is nowadays generally accepted model mainly thanks to experimental results achieved by our research team. The important mouse model MHV-68 is a prototype strain of MuHV-4 species and is classified as a member of the order Herpesvirales, family Herpesviridae, subfamily Gammaherpesvirinae and genus Rhadinovirus. During 40 years since its isolation from wild rodents, the virus was distributed into many virological laboratories in Europe (such as England, Slovakia, Germany, Italy, Portugal, Belgium, Denmark, Spain, Switzerland, Hungary, Russia, Sweden), USA, Canada, China, Korea, Japan and Australia. Global research of this virus, which has become an irreplaceable animal model, has expanded our understanding of the pathogenesis and immunology of human and animal gammaherpesvirus infections as well as the gammaherpesvirus-associated oncogenesis. No less important fact is that MHV-68 provides an excellent model to explore methods for controlling gammaherpesvirus infections through vaccination and chemotherapy. Keywords: MHV-68; EBV; KSHV; immunology; pathogenesis; oncogenesis; genome.

Molecular detection of murine gammaherpesvirus 68 (MHV-68) in bats from Mexico.

Molecular detection of murine gammaherpesvirus 68 (MHV-68) in bats from Mexico.

ORF6 and ORF61 Expressing MVA Vaccines Impair Early but Not Late Latency in Murine Gammaherpesvirus MHV-68 Infection.

Gammaherpesviruses (γHV) are important pathogens causing persistent infections which lead to several malignancies in immunocompromised patients. Murine γHV 68 (MHV-68), a homolog to human EBV and KSHV, has been employed as a classical pathogen to investigate the molecular pathogenicity of γHV infections. γHV express distinct antigens during lytic or latent infection and antigen-specific T cells have a significant role in controlling the acute and latent viral infection, although the quality of anti-viral T cell responses required for protective immunity is not well-understood. We have generated recombinant modified vaccinia virus Ankara (recMVA) vaccines via MVA-BAC homologous recombination technology expressing MHV-68 ORF6 and ORF61 antigens encoding both MHC class I and II-restricted epitopes. After vaccination, we examined T cell responses before and after MHV-68 infection to determine their involvement in latent virus control. We show recognition of recMVA- and MHV-68-infected APC by ORF6 and ORF61 epitope-specific T cell lines in vitro. The recMVA vaccines efficiently induced MHV-68-specific CD8+ and CD4+ T cell responses after a single immunization and more pronounced after homologous prime/boost vaccination in mice. Moreover, we exhibit protective capacity of prophylactic recMVA vaccination during early latency at day 17 after intranasal challenge with MHV-68, but failed to protect from latency at day 45. Further T cell analysis indicated that T cell exhaustion was not responsible for the lack of protection by recMVA vaccination in long-term latency at day 45. The data support further efforts aiming at improved vaccine development against γHV infections with special focus on targeting protective CD4+ T cell responses.

A role of hypoxia-inducible factor 1 alpha in Murine Gammaherpesvirus 68 (MHV68) lytic replication and reactivation from latency.

The hypoxia-inducible factor 1 alpha (HIF1α) protein and the hypoxic microenvironment are critical for infection and pathogenesis by the oncogenic gammaherpesviruses (γHV), Kaposi sarcoma herpes virus (KSHV) and Epstein-Barr virus (EBV). However, understanding the role of HIF1α during the virus life cycle and its biological relevance in the context of host has been challenging due to the lack of animal models for human γHV. To study the role of HIF1α, we employed the murine gammaherpesvirus 68 (MHV68), a rodent pathogen that readily infects laboratory mice. We show that MHV68 infection induces HIF1α protein and HIF1α-responsive gene expression in permissive cells. siRNA silencing or drug-inhibition of HIF1α reduce virus production due to a global downregulation of viral gene expression. Most notable was the marked decrease in many viral genes bearing hypoxia-responsive elements (HREs) such as the viral G-Protein Coupled Receptor (vGPCR), which is known to activate HIF1α transcriptional activity during KSHV infection. We found that the promoter of MHV68 ORF74 is responsive to HIF1α and MHV-68 RTA. Moreover, Intranasal infection of HIF1αLoxP/LoxP mice with MHV68 expressing Cre- recombinase impaired virus expansion during early acute infection and affected lytic reactivation in the splenocytes explanted from mice. Low oxygen concentrations accelerated lytic reactivation and enhanced virus production in MHV68 infected splenocytes. Thus, we conclude that HIF1α plays a critical role in promoting virus replication and reactivation from latency by impacting viral gene expression. Our results highlight the importance of the mutual interactions of the oxygen-sensing machinery and gammaherpesviruses in viral replication and pathogenesis.