Induction of cell-cell fusion by ectromelia virus is not inhibited by its fusion inhibitory complex

Sequence analysis of haemagglutinin gene of camelpox viruses shows deletion leading to frameshift: Circulation of diverse clusters among camelpox viruses

Orthopoxviruses (OPVs) have broad host range infecting a variety of species along with gene-specific determinants. Several genes including haemagglutinin (HA) are used for differentiation of OPVs. Among poxviruses, OPVs are sole members encoding HA protein as part of extracellular enveloped virion membrane. Camelpox virus (CMLV) causes an important contagious disease affecting mainly young camels, endemic to Indian subcontinent, Africa and the Middle East. This study describes the sequence features and phylogenetic analysis of HA gene (homologue of VACV A56R) of Indian CMLV isolates. Comparative analysis of CMLV HA gene revealed conserved nature within CMLVs but considerable variability was observed between various species of OPVs. Most Indian CMLV isolates showed 99.5%-100% and 96.3%-100% identity, at nucleotide (nt) and amino acid (aa) levels respectively, among themselves and with CMLV-M96 strain. Importantly, Indian CMLV strains along with CMLV-M96 showed deletion of seven nucleotides resulting in frameshift mutation at C-terminus of HA protein. Phylogenetic analysis displayed distinct clustering among CMLVs which might point to the circulation of diverse CMLV strains in nature. Despite different host specificity of OPVs, comparative sequence analysis of HA protein showed highly conserved N-terminal Ig V-set functional domain with tandem repeats. Understanding of molecular diversity of CMLVs and structural domains of HA protein will help in the elucidation of molecular mechanisms for immune evasion and design of novel antivirals for OPVs.

First Diagnosed Case of Camelpox Virus in Israel

An outbreak of a disease in camels with skin lesions was reported in Israel during 2016. To identify the etiological agent of this illness, we employed a multidisciplinary diagnostic approach. Transmission electron microscopy (TEM) analysis of lesion material revealed the presence of an orthopox-like virus, based on its characteristic brick shape. The virus from the skin lesions successfully infected chorioallantoic membranes and induced cytopathic effect in Vero cells, which were subsequently positively stained by an orthopox-specific antibody. The definite identification of the virus was accomplished by two independent qPCR, one of which was developed in this study, followed by sequencing of several regions of the viral genome. The qPCR and sequencing results confirmed the presence of camelpox virus (CMLV), and indicated that it is different from the previously annotated CMLV sequence available from GenBank. This is the first reported case of CMLV in Israel, and the first description of the isolated CMLV subtype.

Strategies of NF-κB signaling modulation by ectromelia virus in BALB/3T3 murine fibroblasts

Nuclear factor κB (NF-κB) is a pleiotropic transcription factor that regulates the expression of immune response genes. NF-κB signaling can be disrupted by pathogens that prevent host immune response. In this work, we examined the influence of ectromelia (mousepox) virus (ECTV) on NF-κB signaling in murine BALB/3T3 fibroblasts. Activation of NF-κB via tumor necrosis factor (TNF) receptor 1 (TNFR1) in these cells induces proinflammatory cytokine secretion. We show that ECTV does not recruit NF-κB to viral factories or induce NF-κB nuclear translocation in BALB/3T3 cells. Additionally, ECTV counteracts TNF-α-induced p65 NF-κB nuclear translocation during the course of infection. Inhibition of TNF-α-induced p65 nuclear translocation was also observed in neighboring cells that underwent fusion with ECTV-infected cells. ECTV inhibits the key step of NF-κB activation, i.e. Ser32 phosphorylation and degradation of inhibitor κBα (IκBα) induced by TNF-α. We also observed that ECTV prevents TNF-α-induced Ser536 of p65 phosphorylation in BALB/3T3 cells. Studying TNFR1 signaling provides information about regulation of inflammatory response and cell survival. Unraveling poxviral immunomodulatory strategies may be helpful in drug target identification as well as in vaccine development.

Active vaccination with vaccinia virus A33 protects mice against lethal vaccinia and ectromelia viruses but not against cowpoxvirus; elucidation of the specific adaptive immune response

Vaccinia virus protein A33 (A33^VACV) plays an important role in protection against orthopoxviruses, and hence is included in experimental multi-subunit smallpox vaccines. In this study we show that single-dose vaccination with recombinant Sindbis virus expressing A33^VACV, is sufficient to protect mice against lethal challenge with vaccinia virus WR (VACV-WR) and ectromelia virus (ECTV) but not against cowpox virus (CPXV), a closely related orthopoxvirus. Moreover, a subunit vaccine based on the cowpox virus A33 ortholog (A33^CPXV) failed to protect against cowpox and only partially protected mice against VACV-WR challenge. We mapped regions of sequence variation between A33^VACV and A33^CPXVand analyzed the role of such variations in protection. We identified a single protective region located between residues 104–120 that harbors a putative H-2Kd T cell epitope as well as a B cell epitope - a target for the neutralizing antibody MAb-1G10 that blocks spreading of extracellular virions. Both epitopes in A33^CPXV are mutated and predicted to be non-functional. Whereas vaccination with A33^VACV did not induce in-vivo CTL activity to the predicted epitope, inhibition of virus spread in-vitro, and protection from lethal VACV challenge pointed to the B cell epitope highlighting the critical role of residue L118 and of adjacent compensatory residues in protection. This epitope’s critical role in protection, as well as its modifications within the orthopoxvirus genus should be taken in context with the failure of A33 to protect against CPXV as demonstrated here. These findings should be considered when developing new subunit vaccines and monoclonal antibody based therapeutics against orthopoxviruses, especially variola virus, the etiologic agent of smallpox.

Insect cell culture: virus replication and applications in biotechnology

Insect cell lines have been initiated since the 1930s and were used to replicate insect baculoviruses as well as arboviruses. Since the latter group of viruses cause serious diseased in man and equines, efforts were expended to characterize the viruses in the new cell lines in attempts to understand the replication cycle at the cellular and molecular levels. Soon it was realized that insect baculoviruses have a potential as viable alternatives to chemicals in the control of agricultural and forest insect pests. The cell lines provided excellent tools to understand the molecular biology of baculoviruses before wide-scale use in the field. During these investigastions, it came to light that baculoviruses can be exploited as vectors for the expression of exogenous proteins and vaccines. The amenability of the virus to genetic modifications and the increasing numbers of permissive cell lines opened new avenues in protein expression. However, not all baculoviruses were able to replicate in cell lines. Indeed, there are no cell lines permissive to viruses belonging to the genera Gammabaculvirus and Deltabaculovirus. Some entomopoxviruses have been replicated in a few cell lines and this paper reports the replication of an entomopoxvirus from the spruce budworm in a homologous cell line.

Loss of cytoskeletal transport during egress critically attenuates ectromelia virus infection in vivo

Egress of wrapped virus (WV) to the cell periphery following vaccinia virus (VACV) replication is dependent on interactions with the microtubule motor complex kinesin-1 and is mediated by the viral envelope protein A36. Here we report that ectromelia virus (ECTV), a related orthopoxvirus and the causative agent of mousepox, encodes an A36 homologue (ECTV-Mos-142) that is highly conserved despite a large truncation at the C terminus. Deleting the ECTV A36R gene leads to a reduction in the number of extracellular viruses formed and to a reduced plaque size, consistent with a role in microtubule transport. We also observed a complete loss of virus-associated actin comets, another phenotype dependent on A36 expression during VACV infection. ECTV ΔA36R was severely attenuated when used to infect the normally susceptible BALB/c mouse strain. ECTV ΔA36R replication and spread from the draining lymph nodes to the liver and spleen were significantly reduced in BALB/c mice and in Rag-1-deficient mice, which lack T and B lymphocytes. The dramatic reduction in ECTV ΔA36R titers early during the course of infection was not associated with an augmented immune response. Taken together, these findings demonstrate the critical role that subcellular transport pathways play not only in orthopoxvirus infection in an in vitro context but also during orthopoxvirus pathogenesis in a natural host. Furthermore, despite the attenuation of the mutant virus, we found that infection nonetheless induced protective immunity in mice, suggesting that orthopoxvirus vectors with A36 deletions may be considered another safe vaccine alternative.

The vaccinia virus A56 protein: a multifunctional transmembrane glycoprotein that anchors two secreted viral proteins

The vaccinia virus A56 protein was one of the earliest-described poxvirus proteins with an identifiable activity. While originally characterized as a haemagglutinin protein, A56 has other functions as well. The A56 protein is capable of binding two viral proteins, a serine protease inhibitor (K2) and the vaccinia virus complement control protein (VCP), and anchoring them to the surface of infected cells. This is important; while both proteins have biologically relevant functions at the cell surface, neither one can locate there on its own. The A56-K2 complex reduces the amount of virus superinfecting an infected cell and also prevents the formation of syncytia by infected cells; the A56-VCP complex can protect infected cells from complement attack. Deletion of the A56R gene results in varying effects on vaccinia virus virulence. In addition, since the gene encoding the A56 protein is non-essential, it can be used as an insertion point for foreign genes and has been deleted in some viruses that are in clinical development as oncolytic agents.