Project description:Open reading frame 11 (ORF11) is a conserved gammaherpesvirus gene that remains undefined. We identified the product of murine gammaherpesvirus 68 (MHV-68) ORF11, p43, as a virion component with a predominantly perinuclear distribution in infected cells. MHV-68 lacking p43 grew normally in vitro but showed reduced lytic replication in vivo and a delay in seeding to the spleen. Subsequent latency amplification was normal. Thus, MHV-68 ORF11 encoded a virion component that was important for in vivo lytic replication but dispensable for the establishment of latency.
Project description:Persistent viruses disseminate from immune hosts. They must therefore resist neutralization by antibody. Murine gammaherpesvirus-68 (MHV-68) represents an accessible model with which to address how resistance to neutralization is achieved and how overcoming it might improve infection control. The MHV-68 glycoprotein B (gB), like that of other herpesviruses, is a virion protein that is essential for infectivity. As such, it presents a potential neutralization target. In order to test whether virus-induced antibodies reduce virion infectivity by binding to gB, monoclonal antibodies (mAbs) were derived from MHV-68-infected mice. gB-specific mAbs were common, but only an IgM specific for the gB N terminus reduced virion infectivity significantly. It inhibited MHV-68 entry into BHK-21 cells at a post-binding step that was linked closely to membrane fusion. Reducing the mAb to IgM monomers compromised neutralization severely, suggesting that a pentameric structure was crucial to its function. Antibody treatment never blocked BHK-21 cell infection completely and blocked the infection of NMuMG epithelial cells hardly at all. Virions saturated with antibody also remained infectious to mice. Thus, the MHV-68 gB presents at best a very difficult target for antibody-mediated neutralization.
Project description:Murine gammaherpesvirus 68 (MHV-68) glycoprotein B (gB) was identified in purified virions by immunoblotting, immunoprecipitation, and immunoelectron microscopy. It was synthesized as a 120-kDa precursor in infected cells and cleaved into 65-kDa and 55-kDa disulfide-linked subunits close to the time of virion release. The N-linked glycans on the cleaved, virion gB remained partially endoglycosidase H sensitive. The processing of MHV-68 gB therefore appears similar to that of Kaposi's sarcoma-associated herpesvirus gB and human cytomegalovirus gB.
Project description:Gammaherpesviruses, including the human pathogens Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus, are causative agents of lymphomas and other malignancies. The structural characterization of these viruses has been limited due to difficulties in obtaining adequate amount of virion particles. Here we report the first three-dimensional structural characterization of a whole gammaherpesvirus virion by an emerging integrated approach of cryo-electron tomography combined with single-particle cryo-electron microscopy, using murine gammaherpesvirus-68 (MHV-68) as a model system. We found that the MHV-68 virion consists of distinctive envelope and tegument compartments, and a highly conserved nucleocapsid. Two layers of tegument are identified: an inner tegument layer tethered to the underlying capsid and an outer, flexible tegument layer conforming to the overlying, pleomorphic envelope, consistent with the sequential viral tegumentation process inside host cells. Surprisingly, comparison of the MHV-68 virion and capsid reconstructions shows that the interactions between the capsid and inner tegument proteins are completely different from those observed in alpha and betaherpesviruses. These observations support the notion that the inner layer tegument across different subfamilies of herpesviruses has evolved significantly to confer specific characteristics related to viral-host interactions, in contrast to a highly conserved capsid for genome encapsidation and protection.
Project description:Viral replication in the liver is generally detected by cellular endosomal Toll-like receptors (TLRs) and cytosolic helicase sensors that trigger antiviral inflammatory responses. Recent evidence suggests that surface TLR2 may also contribute to viral detection through recognition of viral coat proteins but its role in the outcome of acute viral infection remains elusive. In this study, we examined in vivo the role of TLR2 in acute infections induced by the highly hepatotrophic mouse hepatitis virus (MHV) type 3 and weakly hepatotrophic MHV-A59 serotype. To address this, C57BL/6 (wild-type; WT) and TLR2 knockout (KO) groups of mice were intraperitoneally infected with MHV3 or MHV-A59. MHV3 infection provoked a fulminant hepatitis in WT mice, characterized by early mortality and high alanine and aspartate transaminase levels, histopathological lesions and viral replication whereas infection of TLR2 KO mice was markedly less severe. MHV-A59 provoked a comparable mild and subclinical hepatitis in WT and TLR2 KO mice. MHV3-induced fulminant hepatitis in WT mice correlated with higher hepatic expression of interferon-?, interleukin-6, tumour necrosis factor-?, CXCL1, CCL2, CXCL10 and alarmin (interleukin-33) than in MHV-A59-infected WT mice and in MHV3-infected TLR2 KO mice. Intrahepatic recruited neutrophils, natural killer cells, natural killer T cells or macrophages rapidly decreased in MHV3-infected WT mice whereas they were sustained in MHV-A59-infected WT mice and MHV3-infected TLR2 KO. MHV3 in vitro infection of macrophagic cells induced rapid and higher viral replication and/or interleukin-6 induction in comparison to MHV-A59, and depended on viral activation of TLR2 and p38 mitogen-activated protein kinase. Taken together, these results support a new aggravating inflammatory role for TLR2 in MHV3-induced acute fulminant hepatitis.
Project description:The outbreak of severe acute respiratory syndrome (SARS) in 2003 reinforces the potential of lethal pandemics of respiratory viral infections. The underlying mechanisms of SARS are still largely undefined. Long pentraxin PTX3, a humoral mediator of innate immunity, has been reported to have anti-viral effects. We examined the role of PTX3 in coronavirus murine hepatitis virus strain 1 (MHV-1)-induced acute lung injury, a previously reported animal model for SARS. PTX3-deficient mice (129/SvEv/C57BL6/J) and their wild-type (WT) littermates were intranasally infected MHV-1. These mice were also treated with recombinant PTX3. Effects of PTX3 on viral binding and infectivity were determined in vitro. Cytokine expression, severity of lung injury, leukocyte infiltration and inflammatory responses were examined in vivo. In PTX3 WT mice, MHV-1 induced PTX3 expression in the lung and serum in a time-dependent manner. MHV-1 infection led to acute lung injury with greater severity in PTX3-deficient mice than that in WT mice. PTX3 deficiency enhanced early infiltration of neutrophils and macrophages in the lung. PTX3 bound to MHV-1 and MHV-3 and reduced MHV-1 infectivity in vitro. Administration of recombinant PTX3 significantly accelerated viral clearance in the lung, attenuated MHV-1-induced lung injury, and reduced early neutrophil influx and elevation of inflammatory mediators in the lung. Results from this study indicate a protective role of PTX3 in coronaviral infection-induced acute lung injury.
Project description:Ribosome profiling (RiboSeq) (maps positions of translating ribosomes on the transcriptome) and RNASeq (quantifies the transcriptome) analysis of murine 17 clone 1 (17Cl-1) cells infected with Murine coronavirus strain A59 (MHV-A59). Samples comprise 1 and 8 h mocks, 1, 2.5, 5 and 8 h post infection timecourse, for each of RiboSeq with cycloheximide (CHX), RiboSeq with harringtonine (HAR), and RNASeq, performed in duplicate (6 x 3 x 2 libraries); RiboSeq CHX, RiboSeq HAR and RNASeq at 1 h post infection for high multiplicity of infection (3 libraries); and 1 \long-read\ library for 5 h post infection RiboSeq CHX to test for larger-than-normal ribosome footprints.
Project description:Tegument is a unique structure of herpesvirus, which surrounds the capsid and interacts with the envelope. Morphogenesis of gammaherpesvirus is poorly understood due to lack of efficient lytic replication for Epstein-Barr virus and Kaposi's sarcoma-associated herpesvirus/human herpesvirus 8, which are etiologically associated with several types of human malignancies. Murine gammaherpesvirus 68 (MHV-68) is genetically related to the human gammaherpesviruses and presents an excellent model for studying de novo lytic replication of gammaherpesviruses. MHV-68 open reading frame 33 (ORF33) is conserved among Alpha-, Beta-, and Gammaherpesvirinae subfamilies. However, the specific role of ORF33 in gammaherpesvirus replication has not yet been characterized. We describe here that ORF33 is a true late gene and encodes a tegument protein. By constructing an ORF33-null MHV-68 mutant, we demonstrated that ORF33 is not required for viral DNA replication, early and late gene expression, viral DNA packaging or capsid assembly but is required for virion morphogenesis and egress. Although the ORF33-null virus was deficient in release of infectious virions, partially tegumented capsids produced by the ORF33-null mutant accumulated in the cytoplasm, containing conserved capsid proteins, ORF52 tegument protein, but virtually no ORF45 tegument protein and the 65-kDa glycoprotein B. Finally, we found that the defect of ORF33-null MHV-68 could be rescued by providing ORF33 in trans or in an ORF33-null revertant virus. Taken together, our results indicate that ORF33 is a tegument protein required for viral lytic replication and functions in virion morphogenesis and egress.