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Poxviruses utilize multiple strategies to prevent activation of extrinsic and intrinsic apoptotic pathways for successful replication. Mitochondrial heat shock proteins (mtHsps), especially Hsp60 and its cofactor Hsp10, are engaged in apoptosis regulation; however, until now, the influence of poxviruses on mtHsps has never been studied. We used highly infectious Moscow strain of ectromelia virus (ECTV) to investigate the mitochondrial heat shock response and apoptotic potential in permissive L929 fibroblasts. Our results show that ECTV-infected cells exhibit mostly mitochondrial localization of Hsp60 and Hsp10, and show overexpression of both proteins during later stages of infection. ECTV infection has only moderate effect on the electron transport chain subunit expression. Moreover, increase of mtHsp amounts is accompanied by lack of apoptosis, and confirmed by reduced level of pro-apoptotic Bax protein and elevated levels of anti-apoptotic Bcl-2 and Bcl-xL proteins. Taken together, we show a positive relationship between increased levels of Hsp60 and Hsp10 and decreased apoptotic potential of L929 fibroblasts, and further hypothesize that Hsp60 and/or its cofactor play important roles in maintaining protein homeostasis in mitochondria for promotion of cell survival allowing efficient replication of ECTV.

Mitochondria are multifunctional organelles that participate in numerous processes in response to viral infection, but they are also a target for viruses. The aim of this study was to define subcellular events leading to alterations in mitochondrial morphology and function during infection with ectromelia virus (ECTV). We used two different cell lines and a combination of immunofluorescence techniques, confocal and electron microscopy, and flow cytometry to address subcellular changes following infection. Early in infection of L929 fibroblasts and RAW 264.7 macrophages, mitochondria gathered around viral factories. Later, the mitochondrial network became fragmented, forming punctate mitochondria that co-localized with the progeny virions. ECTV-co-localized mitochondria associated with the cytoskeleton components. Mitochondrial membrane potential, mitochondrial fission⁻fusion, mitochondrial mass, and generation of reactive oxygen species (ROS) were severely altered later in ECTV infection leading to damage of mitochondria. These results suggest an important role of mitochondria in supplying energy for virus replication and morphogenesis. Presumably, mitochondria participate in transport of viral particles inside and outside of the cell and/or they are a source of membranes for viral envelope formation. We speculate that the observed changes in the mitochondrial network organization and physiology in ECTV-infected cells provide suitable conditions for viral replication and morphogenesis.

Ectromelia virus (ECTV) is an orthopoxvirus responsible for mousepox, a lethal disease of certain strains of mice that is similar to smallpox in humans, caused by variola virus (VARV). ECTV, similar to VARV, exhibits a narrow host range and has co-evolved with its natural host. Consequently, ECTV employs sophisticated and host-specific strategies to control the immune cells that are important for induction of antiviral immune response. In the present study we investigated the influence of ECTV infection on immune functions of murine GM-CSF-derived bone marrow cells (GM-BM), comprised of conventional dendritic cells (cDCs) and macrophages. Our results showed for the first time that ECTV is able to replicate productively in GM-BM and severely impaired their innate and adaptive immune functions. Infected GM-BM exhibited dramatic changes in morphology and increased apoptosis during the late stages of infection. Moreover, GM-BM cells were unable to uptake and process antigen, reach full maturity and mount a proinflammatory response. Inhibition of cytokine/chemokine response may result from the alteration of nuclear translocation of NF-κB, IRF3 and IRF7 transcription factors and down-regulation of many genes involved in TLR, RLR, NLR and type I IFN signaling pathways. Consequently, GM-BM show inability to stimulate proliferation of purified allogeneic CD4+ T cells in a primary mixed leukocyte reaction (MLR). Taken together, our data clearly indicate that ECTV induces immunosuppressive mechanisms in GM-BM leading to their functional paralysis, thus compromising their ability to initiate downstream T-cell activation events.

Mitochondrial antiviral signaling protein (MAVS) transmits activation signal of type I interferon (IFN) gene transcription in the molecular intracellular pathway, which depends on the protein encoded by retinoic acid inducible gene I (RIG-I) or melanoma differentiation-associated protein-5 (MDA-5). MAVS, as a signal molecule, performs an essential function in the development of an antiviral immune response. The molecule of MAVS consists of two domains: the N-terminal domain and the C-terminal domain. The N-terminal end of MAVS contains the caspase activation and recruitment domain (CARD). CARD is responsible for MAVS interaction with RIG-I and MDA-5, which act as cytosolic sensors detecting foreign viral genetic material in the host cell. After binding to viral RNA, RIG-I or MDA-5 activates MAVS and transmits the signal of IFN type I gene expression. The C-terminal transmembrane domain (TM) of MAVS anchors the protein to the outer mitochondrial membrane. In this paper interactions between MAVS and hepatitis virus type A (HAV), type B (HBV) and type C (HCV) are presented. Mechanisms of indirect activation of MAVS by viral DNA and RNA, as well as the strategies of HAV, HBV and HCV for blocking of the intracellular signaling pathway at the level of MAVS, are described.

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., (Copyright © 2015 Elsevier Ltd. All rights reserved.)

Macrophages are antigen-presenting cells (APCs) that play a crucial role in the innate immune response and may be involved in both clearance and spread of viruses. Stimulation of macrophages via Toll-like receptors (TLRs) results in activation of nuclear factor κB (NF-κB) and synthesis of proinflammatory cytokines. In this work, we show modulation of proinflammatory NF-κB signaling by a member of the family Poxviridae, genus Orthopoxvirus--ectromelia virus (ECTV)--in RAW 264.7 murine macrophages. ECTV interfered with p65 NF-κB nuclear translocation induced by TLR ligands such as lipopolysaccharide (LPS) (TLR4), polyinosinic-polycytidylic acid (poly(I:C)) (TLR3) and diacylated lipopeptide Pam2CSK4 (TLR2/6). We observed that ECTV modulates phosphorylation of Ser32 of inhibitor of κB (IκBα) and Ser536 of p65. Interference of ECTV with TLR signaling pathways implied that proinflammatory cytokine synthesis was inhibited. Our studies provide new insights into the strategies of proinflammatory signaling modulation by orthopoxviruses during their replication cycle in immune cells. Understanding important immune interactions between viral pathogens and APCs might contribute to the identification of drug targets and the development of vaccines.

Nuclear factor kappa-light-chain enhancer of activated B-cells (NF-кB) is a pleiotropic transcription factor, which regulates processes of immune response and inflammation. NF-кB can undergo activation as a result of bacterial infections via Toll-like receptors (TLR), which recognize pathogen-associated molecular patterns (PAMP), such as lipopolysaccharides (LPS). Stimulation of the cells results in phosphorylation of inhibitor кB (IкB) and the translocation of NF-кB to the nucleus, where the transcription of genes encoding molecules, such as proinflammatory cytokines and chemokines takes place. Activation of NF-кB undergoes modulation upon heat shock, which induces the expression of heat shock proteins (HSP). NF-кB, in turn, is involved in the regulation of transcription of genes encoding HSP, while members of HSP family are modulators of NF-кB activation, which occurs as a result bacterial infections and leads to the development of inflammation. HSP90 is a major chaperone, which is associated with IкB kinase (IKK) subunits. HSP90 inhibitors enable dissociation of such complexes, thus blocking NF-кB and inflammatory process during bacterial infections. HSP72 and HSP70, in turn, modulate the expression of NF-кB controlled genes during sepsis and play a protective role, whereas exogenous HSP70 may enhance the inflammatory response. Bacterial HSP, such as HSP60 of Chlamydia pneumophila and Helicobacter pylori, or GroL of Porphyromonas gingivalis, as well as HSP65 and HSP70 of Mycobacterium tuberculosis and DnaK of Francisella tularensis activate NF-κB and inflammation. Knowledge of these interactions is extremely helpful in the development of therapeutic strategies.

Heat shock proteins (Hsps) are a class of proteins with highly conserved amino acid sequences. They are widespread in nature; they are found in archeons, true bacteria and eukaryotic organisms. Hsps from various families, commonly interact to execute essential cellular tasks, such as molecular regulation of newly synthesized protein-folding or restoration of the appropriate conformation of denatured and aggregated proteins. In this review we discuss mechanisms of spatial organization of protein structure mediated by Hsp10, Hsp40, Hsp60, Hsp70, Hsp104 (Hsp100) and Hsp110. Interactions between Hsps of different molecular weights are described.

Molluscum contagiosum virus is a human and animal dermatotropic pathogen, which causes a severe disease in immunocompromised individuals. MCV belongs to the Poxviridae family whose members exert immunomodulatory effects on the host antiviral response. Poxviruses interfere with cell signaling pathways that lead to the activation of nuclear factor кB, a pleiotropic transcription factor which is crucial for regulation of the immune response, the cell cycle and apoptosis. In resting cells, NF-κB is present in the cytoplasm, where it is associated with inhibitor κB. Upon stimulation by activators, such as proinflammatory cytokines and bacterial or viral products, the inhibitory protein undergoes phosphorylation and proteasomal degradation. NF-κB, in turn, translocates to the nucleus, where it regulates the transcription of various genes that are essential for processes mentioned above. Since poxviruses replicate exclusively in the cell cytoplasm, NF-кB became a good target for poxviral immunomodulation. MCV encodes various proteins which interfere with the signaling pathways that lead to the activation of NF-κB. Ligand inhibitor encoded by MCV, MC54, binds interleukin-18 and inhibits interferon-γ production. Other MCV proteins, MC159 and MC160, belong to intracellular inhibitors of NF-κB and are members of viral FLICE-inhibitory proteins (vFLIPs). MC159 protein encoded by MCV was shown to inhibit apoptosis of virus-infected cells. Such interactions serve immune evasion and are responsible for the persistence of MCV.

Mitochondria are extremely important organelles in the life of a cell. Recent studies indicate that mitochondria also play a fundamental role in the cellular innate immune mechanisms against viral infections. Moreover, mitochondria are able to alter their shape continuously through fusion and fission. These tightly regulated processes are activated or inhibited under physiological or pathological (e.g. viral infection) conditions to help restore homeostasis. However, many types of viruses, such as orthopoxviruses, have developed various strategies to evade the mitochondrial-mediated antiviral innate immune responses. Moreover, orthopoxviruses exploit the mitochondria for their survival. Such viral activity has been reported during vaccinia virus (VACV) infection. Our study shows that the Moscow strain of ectromelia virus (ECTV-MOS), an orthopoxvirus, alters the mitochondrial network in permissive L929 cells. Upon infection, the branching structure of the mitochondrial network collapses and becomes disorganized followed by destruction of mitochondrial tubules during the late stage of infection. Small, discrete mitochondria co-localize with progeny virions, close to the cell membrane. Furthermore, clustering of mitochondria is observed around viral factories, particularly between the nucleus and viroplasm. Our findings suggest that ECTV-MOS modulates mitochondrial cellular distribution during later stages of the replication cycle, probably enabling viral replication and/or assembly as well as transport of progeny virions inside the cell. However, this requires further investigation.

Several studies have provided evidence that complex relationships between autophagic and apoptotic cell death pathways occur in cancer and virus-infected cells. Previously, we demonstrated that infection of macrophages with Moscow strain of ectromelia virus (ECTV-MOS) induces apoptosis under in vitro and in vivo conditions. Here, we found that autophagy was induced in RAW 264.7 cells during infection with ECTV-MOS. Silencing of beclin 1, an autophagy-related gene, reduced the percentage of late apoptotic cells in virus-infected RAW 264.7 macrophages. Pharmacological modulation of autophagy by wortmannin (inhibitor) or rapamycin (inductor) did not affect or cause increased apoptosis in ECTV-MOS-infected RAW 264.7 cells, respectively. Meantime, blocking apoptosis by a pan-caspase inhibitor, Z-VAD-FMK, increased the formation of autophagosomes in infected macrophages. Taken together, three important points arise from our study. First, autophagy may co-occur with apoptosis in RAW 264.7 cells exposed to ECTV-MOS. Second, at later stages of infection, autophagy may partially participate in the execution of macrophage cell death by enhancing apoptosis. Third, when apoptosis is blocked infected macrophages undergo increased autophagy. Our results provide new information about the relationship between autophagy and apoptosis in ECTV-MOS-infected macrophages.

During mousepox in resistant (C57BL/6) or susceptible (BALB/c) strains of mice, stimulation of Th1 or Th2 cytokine immune response, respectively, is observed. Because mechanisms of different polarization of T cells remain elusive, in this study, we quantitatively assessed the phenotype of antigen-presenting cells (APCs) involved in ectromelia virus (ECTV) antigen presentation and cluster formation with effector cells in secondary lymphoid organs of BALB/c and C57BL/6 mice. We showed that both strains of mice display similar dynamics and kinetics of viral antigen presentation by CD11c(+) , CD11b(+) , and CD19(+) cells. CD11c(+) and CD11b(+) cells highly participated in viral antigen presentation during all stages of mousepox, whereas CD19(+) cells presented viral peptides later in infection. The main population of dendritic cells (DCs) engaged in ECTV antigen presentation and cell junction formation with effector cells was a population of myeloid CD11b(+) DCs (mDCs). We suggest that, on the one hand, ECTV may differentially affect the functions of APCs depending on the strain of mice. On the other hand, we suggest that some types of APCs, such as mDCs or other DCs subsets, have different abilities to direct the shape of immune response depending on the host resistance to mousepox., (© 2013 Federation of European Microbiological Societies. Published by John Wiley & Sons Ltd. All rights reserved.)

Background: The purpose of the study was to evaluate synthesis of IFN-γ, IL-2, TNF-α (Th1/Tc1) and IL-4 (Th2/Tc2) at CD4+ T and CD8+ T cell level in BALB/c and C57BL/6 mice in the course of infection with ectromelia virus Moscow strain (ECTV-MOS)., Material/methods: Synthesis of IFN-γ, IL-2, TNF-α and IL-4 in CD4+ T and CD8+ T cells in draining lymph nodes (DLNs) and spleens of BALB/c and C57BL/6 mice was detected by intracellular staining and flow cytometry analysis., Results: Our results showed an increase in percentage of IFN-γ -synthesizing CD8+ T cells only in DLNs and spleens of C57BL/6 mice at the early stages of infection. Moreover, synthesis of IL-2 by CD4+ and CD8+ T cells occurred earlier and was stronger in C57BL/6 mice compared to BALB/c mice. The increase in TNF-α synthesis by CD4+ T and CD8+ T cells was detected mainly in DLNs of infected animals. We did not observe any changes in the percentage of IL-4-synthesizing T cells (Th2 and Tc2) during ECTV-MOS infection in both strains of mice., Conclusions: Results presented in this study confirmed that during the early phase of infection, C57BL/6 mice mounted a strong Th1 and Tc1 immune response against ECTV-MOS. BALB/c mice that survived the acute stage of mousepox, were able to mount an adequate cellular response to ECTV-MOS, however successful elimination of the virus in susceptible mice may occur more slowly compared to resistant strains of mice. Intracellular detection of IL-4 by flow cytometry was not sensitive enough to distinguish the differences in IL-4-synthesizing Th2 and Tc2 cells between susceptible and resistant strains of mice during ECTV-MOS infection.

Several reports have brought to light new and interesting findings on the involvement of autophagy and apoptosis in pathogenesis of viral and bacterial diseases, as well as presentation of foreign antigens. Our model studies focused on the involvement of apoptosis during replication of highly virulent Moscow strain of ectromelia virus (ECTV-MOS). Here, we show evidence that autophagy is induced during mousepox replication in a cell line. Fluorescence microscopy revealed increase of LC3 (microtubule-associated protein 1 light chain 3) aggregation in infected as opposed to non-infected control L929 cells. Furthermore, Western blot analysis showed that replication of ECTV-MOS in L929 cells led to the increase in LC3-II (marker of autophagic activity) expression. Beclin 1 strongly colocalized with extranuclear viral replication centers in infected cells, whereas expression of Bcl-2 decreased in those centers as shown by fluorescence microscopy. Loss of Beclin 1-Bcl-2 interaction may lead to autophagy in virus-infected L929 cells. To assess if Beclin 1 has a role in regulation of apoptosis during ECTV-MOS infection, we used small interfering RNA directed against beclin 1 following infection. Early and late apoptotic cells were analyzed by flow cytometry after AnnexinV and propidium iodide staining. Silencing of beclin 1 resulted in decreased percentage of early and late apoptotic cells in the late stage of ECTV-MOS infection in L929 cells. We conclude that Beclin 1 plays an important role in regulation of both, autophagy and apoptosis, during ECTV-MOS replication in L929 permissive cells.

The mannosylated lipoarabinomanan (ManLAM) from mycobacterial species possesses strong anti-apoptotic action. Here we examined the ability of ManLAM isolated from Mycobacterium tuberculosis H37Rv to alter expression profiles of apoptosis-related genes in mouse macrophages infected with Mycobacterium bovis BCG Danish strain. ManLAM suppressed BCG-induced apoptosis and activities of caspase-1, -3, -8 and 9. Mouse Apoptosis Gene Array showed that ManLAM significantly down-regulated pro-apoptotic and proinflammatory genes: caspase-1, -3, -7, -8 and -9, TNF-alpha/TNFSF2, Fas/TNFRSF6, Bax-alpha, as well as IL-12 p35 and iNOS simultaneously up-regulating anti-apoptotic genes such as Bcl-2 and Mcl-1. The effect of ManLAM was contrary to BCG-induced up-regulation of proapoptotic and pro-inflammatory genes and consistent with the functional data.

The mannosylated lipoarabinomannan (ManLAM) from mycobacterial species possesses strong immunomodulatory effects. Here we examined the ability of Mycobacterium tuberculosis ManLAM to interfere with the apoptotic response of mouse monocyte cell line, RAW 264.7 infected with Mycobacterium bovis BCG Danish strain. Incubation of BCG-infected monocytes with ManLAM decreased production of NO and the numbers of apoptotic cells which synergized with the polarization of mitochondrial membrane. Activities of caspase-1, -3, -8 and 9 followed pattern of apoptosis suppression by ManLAM, except for caspase-1, which showed no significant change in activity. ManLAM also stabilized anti-apoptotic ratio of bcl-2/bax expression in BCG-infected cells and blocked activation of Fas/FasL-induced pathway of apoptosis. Thus, ManLAM, apart from blocking mitochondrial pathway of apoptosis, may induce several other pathways regulating apoptotic response in BCG-infected mouse monocytes.

In this study we showed that the virulent Moscow strain of Ectromelia virus (ECTV-MOS) infection leads to induction of apoptosis in the BALB/c mouse central nervous system. ECTV-MOS-infected cells and inflammation sites were found in brain parenchyma between 5 and 15 days after footpad infection with ECTV-MOS. Infected cells consisted of microglia and monocytes, astrocytes and oligodendrocytes and these type of cells underwent apoptosis within 5-15 days post infection (d.p.i.). The highest number of apoptotic cells was found at 5 and 10 d.p.i. and represented mainly microglia (61.4% and 38.6% of apoptotic cells, respectively) and astrocytes (21% and 8.9%, respectively). The number of apoptotic oligodendrocytes was 5.4% and 4.5%, respectively. Fluorometric assays demonstrated involvement of caspase-1, -3 and -8 but not caspase-9 in apoptosis in ECTV-MOS-infected mouse brains. Expression of Fas/FasL was significantly increased on ECTV-MOS-infected cells between 5 and 15 d.p.i., whereas Fas was up-regulated also on the surrounding, non-infected cells. Taking together we may conclude that ECTV-MOS infection of microglia and astrocytes leads to local inflammation resulting in Fas/FasL up-regulation and apoptosis, which limits mouse central nervous system infection with ECTV-MOS.