Apoptosis induction by avian reovirus through p53 and mitochondria-mediated pathway

Oncolytic avian reovirus-sensitized tumor infiltrating CD8+ T cells triggering immunogenic apoptosis in gastric cancer

BACKGROUND

Gastric cancer (GC) is a leading malignant disease in numerous countries, including Taiwan with limited therapeutic options. Animal viruses including oncolytic avian reovirus (ARV) have the possibility to avoid pre-existing immunity in humans, while being safe and immunostimulatory. Here, we provide a novel insight into oncolytic ARV and UV-ARV-sensitized patient's peripheral blood mononuclear cells (P-PBMCs) and tumor infiltrating lymphocytes (TILs) killing primary GC (PGC) cells through the surface TLR3 and TRAIL/DR4/DR5 immunogenic apoptosis pathway.

METHODS

We conducted a comprehensive study to reveal whether ARV- or UV-inactivated ARV (UV-ARV)-modulated P-PBMCs or TILs killing ARV- and UV-ARV-sensitized AGS cells and PGC cells derived from clinical patients and to investigate the regulation of surface TLR3 receptor and upstream signaling pathways. Apoptosis analysis by flow cytometry and Western blot, suppression of signal pathway by specific inhibitors, in situ proximity ligation assay (PLA), time-resolved flurometry and lactate dehydrogenase (LDH) cytotoxicity assays, and an in vitro co-culture model were established to study the interplay between ARV- and UV-ARV-sensitized P-PBMCs and TILs to kill PGC cells and their upstream pathways.

RESULTS

Our results reveal that increased levels of DR4 and DR5 were observed in ARV and UV-ARV sensitized PGC cells through the TLR3/p38/p53 signaling pathway. Importantly, we found that the σC protein of ARV or UV-ARV interacted with surface TLR3 of CD8+ TILs, thereby triggering the TLR3/NF-κB/IFN-γ/TRAIL signaling pathway which induces immunogenic apoptosis of PGC cells. This study sheds further light on the molecular basis behind ARV oncolysis and facilitates the ARV or UV-ARV as a cancer therapeutic.

CONCLUSIONS

The study provides novel insights into ARV- or UV-ARV-sensitized P-PBMCs and CD8+ TILs to kill PGC cells through the immunogenic apoptosis pathway. We conclude that P-PBMCs can easily be obtained from GC patients and provide a rich source as TILs to kill PGC cells.

Gga-miR-200a-3p suppresses avian reovirus-induced apoptosis and viral replication via targeting GRB2

Avian reovirus (ARV) is a significant pathogen that causes various clinical diseases in chickens, including viral arthritis, chronic respiratory diseases, retarded growth, and malabsorption syndrome. These conditions result in substantial economic losses for the global poultry industry. MicroRNAs (miRNAs), a type of small noncoding RNAs that regulate gene expression post transcriptionally by silencing or degrading their RNA targets, play crucial roles in response to pathogenic infections. In this study, transfection of DF-1 cells with gga-miR-200a-3p, an upregulated miRNA observed in ARV-infected cells, significantly suppressed ARV-induced apoptosis by directly targeting GRB2 and impeded ARV replication. Conversely, knockdown of endogenous gga-miR-200a-3p in DF-1 cells using a specific miRNA inhibitor enhanced ARV-induced apoptosis and promoted GRB2 expression, thereby facilitating viral growth within cells. Consistently, inhibition of GRB2 activity through siRNA-mediated knockdown reduced viral titers. Therefore, gga-miR-200a-3p plays a vital antiviral role in the host response to ARV infection by suppressing apoptosis via direct targeting of GRB2 protein. This information enhances our understanding of the mechanisms by which host cells combat against ARV infection through self-encoded small RNA molecules and expands our knowledge regarding the involvement of microRNAs in the host response to pathogenic infections.

VP5 protein of oncolytic herpes simplex virus type 2 induces apoptosis in A549 cells through TP53I3 protein

Oncolytic virotherapy stands out as a burgeoning and promising therapeutic paradigm, harnessing the intrinsic cytotoxicity of oncolytic viruses for selective replication and dissemination within tumors. The primary mode of action revolves around the direct eradication of tumor cells. In our previous investigations, we formulated an oncolytic herpes simplex virus type 2 (OH2) and substantiated its anti-tumor efficacy both in vivo and in vitro. Subsequently, we embarked on a phase I/II clinical trial in China (NMPA, 2018L02743) and the USA (FDA, IND 27137) to assess OH2's safety, biodistribution, and anti-tumor activity as a standalone agent in patients with advanced solid tumors. In this investigation, our primary focus was to comprehend the influence of the major capsid protein VP5 of OH2 on its efficacy as an antitumor agent. Our findings underscore that the VP5 protein significantly amplifies OH2's oncolytic impact on A549 cells. Additionally, we observed that VP5 actively promotes the induction of apoptosis in A549 cells, both in vivo and in vitro. Through comprehensive transcriptional sequencing, we further authenticated that the VP5 protein triggers apoptosis-related signaling pathways and Gene Ontology (GO) terms in A549 cells. Moreover, we scrutinized differentially expressed genes in the p53-dependent apoptosis pathway and conducted meticulous in vitro validation of these genes. Subsequently, we delved deeper into unraveling the functional significance of the TP53I3 gene and conclusively affirmed that the VP5 protein induces apoptosis in A549 cells through the TP53I3 gene. These revelations illuminate the underlying mechanisms of OH2's antitumor activity and underscore the pivotal role played by the VP5 protein. The outcomes of our study harbor promising implications for the formulation of effective oncolytic virotherapy strategies in cancer treatment.

Cell Entry of Avian Reovirus Modulated by Cell-Surface Annexin A2 and Adhesion G Protein-Coupled Receptor Latrophilin-2 Triggers Src and p38 MAPK Signaling Enhancing Caveolin-1- and Dynamin 2-Dependent Endocytosis

The specifics of cell receptor-modulated avian reovirus (ARV) entry remain unknown. By using a viral overlay protein-binding assay (VOPBA) and an in-gel digestion coupled with liquid chromatography-tandem mass spectrometry (LC-MS/MS), we determined that cell-surface annexin A2 (AnxA2) and adhesion G protein-coupled receptor Latrophilin-2 (ADGRL2) modulate ARV entry. Direct interaction between the ARV σC protein and AnxA2 and ADGRL2 in Vero and DF-1 cells was demonstrated in situ by proximity ligation assays. By using short hairpin RNAs (shRNAs) to silence the endogenous AnxA2 and ADGRL2 genes, ARV entry could be efficiently blocked. A significant decrease in virus yields and the intracellular specific signal for σC protein was observed in Vero cells preincubated with the specific AnxA2 and ADGRL2 monoclonal antibodies, indicating that AnxA2 and ADGRL2 are involved in modulating ARV entry. Furthermore, we found that cells pretreated with the AnxA2/S100A10 heterotetramer (A2t) inhibitor A2ti-1 suppressed ARV-mediated activation of Src and p38 mitogen-activated protein kinase (MAPK), demonstrating that Src and p38 MAPK serve as downstream molecules of cell-surface AnxA2 signaling. Our results reveal that suppression of cell-surface AnxA2 with the A2ti-1 inhibitor increased Csk-Cbp interaction, suggesting that ARV entry suppresses Cbp-mediated relocation of Csk to the membrane, thereby activating Src. Furthermore, reciprocal coimmunoprecipitation assays revealed that σC can interact with signaling molecules, lipid raft, and vimentin. The current study provides novel insights into cell-surface AnxA2- and ADGRL2-modulated cell entry of ARV which triggers Src and p38 MAPK signaling to enhance caveolin-1-, dynamin 2-, and lipid raft-dependent endocytosis. IMPORTANCE By analyzing results from VOPBA and LC-MS/MS, we have determined that cell-surface AnxA2 and ADGRL2 modulate ARV entry. After ARV binding to receptors, Src and p38 MAPK signaling were triggered and, in turn, increased the phosphorylation of caveolin-1 (Tyr14) and upregulated dynamin 2 expression to facilitate caveolin-1-mediated and dynamin 2-dependent endocytosis. In this work, we demonstrated that ARV triggers Src activation by impeding Cbp-mediated relocation of Csk to the membrane in the early stages of the life cycle. This work provides better insight into cell-surface AnxA2 and ADGRL2, which upregulate Src and p38MAPK signaling pathways to enhance ARV entry and productive infection.

Oncolytic viruses-modulated immunogenic cell death, apoptosis and autophagy linking to virotherapy and cancer immune response

Recent reports have revealed that oncolytic viruses (OVs) play a significant role in cancer therapy. The infection of OVs such as oncolytic vaccinia virus (OVV), vesicular stomatitis virus (VSV), parvovirus, mammalian reovirus (MRV), human adenovirus, Newcastle disease virus (NDV), herpes simplex virus (HSV), avian reovirus (ARV), Orf virus (ORFV), inactivated Sendai virus (ISV), enterovirus, and coxsackievirus offer unique opportunities in immunotherapy through diverse and dynamic pathways. This mini-review focuses on the mechanisms of OVs-mediated virotherapy and their effects on immunogenic cell death (ICD), apoptosis, autophagy and regulation of the immune system.

Non-pathogenic grass carp reovirus infection leads to both apoptosis and autophagy in a grass carp cell line

A novel GCRV strain isolated from healthy grass carp was named as grass carp reovirus - HH196 (GCRV-HH196), and its infection mechanism remains unclear. In this study, the grass carp ovary cell line (GCO cells) was used to investigate the cell death involved in GCRV-HH196 infection. The results showed that DNA damage, cells volume reduction and cytoplasm shrinkage happened during GCRV-HH196 infection. The mRNA expression levels of pro-apoptotic genes were up-regulated during infection. Two initiators of apoptosis, caspase 8 and caspase 9, and the executioner of apoptosis, caspase 3, were all significantly activated in GCRV-HH196-infected cells. Flow cytometry analysis showed that the number of apoptotic cells in infected cells was significantly higher than that in control cells as the infection progress. Meanwhile, autophagy was also involved in the regulation of GCRV - HH196 infection. We observed that LC3 puncta existed in cytoplasm in GCRV-HH196-infected cells. Furthermore, the protein level of LC3-Ⅱ and Beclin-1 increased, while that of p-Akt decreased in GCRV-HH196-infected cells. These results demonstrated that GCRV-HH196 may regulate apoptosis and autophagy for the virus proliferation and spread, which set a foundation for further research on the interaction between GCRV-HH196 and host.

Virulence of Emerging Arthrotropic Avian Reoviruses Correlates With Their Ability to Activate and Traffic Interferon-γ Producing Cytotoxic CD8+ T Cells Into Gastrocnemius Tendon

Newly emerging arthrotropic avian reoviruses (ARVs) are genetically divergent, antigenically heterogeneous, and economically costly. Nevertheless, the mechanism of emerging ARV-induced disease pathogenesis and potential differences in virulence between virus genotypes have not been adequately addressed. In this study, the life cycle of ARV, including the formation of cytoplasmic ARV neo-organelles, paracrystalline structures, and virus release mechanisms, were characterized in the infected host cell by transmission electron microscopy (TEM). In addition, progressive changes in the structure of infected cells were investigated by time-lapse and field emission scanning electron (FE-SE) microscopy. ARVs from the four genotypic cluster groups included in the study caused gross and microscopic lesions in the infected birds. Marked infiltration of γδT cells, CD4⁺ and CD8⁺ T lymphocytes were observed in ARV infected tendon tissues starting day 3 post-infection. The ARV variant from genotype cluster-2 triggered significantly high trafficking of IFN-γ producing CD8⁺ T lymphocytes in tendon tissues and concomitantly showed high morbidity and severe disease manifestations. In contrast, the ARV variant from genotype cluster-4 was less virulent, caused milder disease, and accompanied less infiltration of IFN-γ producing CD8⁺ T cells. Interestingly, when we blunted antiviral immune responses using clodronate liposomes (which depletes antigen-presenting cells) or cyclosporin (which inhibits cytokine production that regulates T-cell proliferation), significantly lower IFN-γ producing CD8⁺ T cells infiltrated into tendon tissues, resulting in reduced tendon tissues apoptosis and milder disease manifestations. In summary, these data suggest that the degree of ARV virulence and tenosynovitis/arthritis are potentially directly associated with the ability of the virus to traffic massive infiltration of cytotoxic CD8⁺ T cells into the infected tissues. Moreover, the ability to traffic cytotoxic CD8⁺ T cells into infected tendon tissues and the severity of tenosynovitis differ between variants from different ARV genotype cluster groups. However, more than one virus isolate per genotype group needs to be tested to further confirm the association of pathogenicity with genotype. These findings can be used to further examine the interaction of viral and cellular pathways which are essential for the pathogenesis of the disease at the molecular level and to develop effective disease control strategies.

Adaptive homeostasis and the p53 isoform network

All living organisms have developed processes to sense and address environmental changes to maintain a stable internal state (homeostasis). When activated, the p53 tumour suppressor maintains cell and organ integrity and functions in response to homeostasis disruptors (stresses) such as infection, metabolic alterations and cellular damage. Thus, p53 plays a fundamental physiological role in maintaining organismal homeostasis. The TP53 gene encodes a network of proteins (p53 isoforms) with similar and distinct biochemical functions. The p53 network carries out multiple biological activities enabling cooperation between individual cells required for long‐term survival of multicellular organisms (animals) in response to an ever‐changing environment caused by mutation, infection, metabolic alteration or damage. In this review, we suggest that the p53 network has evolved as an adaptive response to pathogen infections and other environmental selection pressures.

Development and evaluation of an indirect ELISA based on recombinant structural protein σC to detect antibodies against avian orthoreovirus

The avian orthoreovirus (ARV) causes large economic losses to poultry industry around the whole world. ARV viral proteins can be classified into three sizes: λ (large), μ (medium) and σ (small). σC, one of the capsid protein of ARV, contains various specific neutralizing epitopes and can induce robust immune responses in infected chickens. An indirect enzyme-linked immunosorbent assay (I-ELISA) was established using the recombinant σC protein. The optimal dilutions of antigen, serum and conjugate goat anti-chicken IgY conjugate were 2.5 μg/ml, 1:80 and 1:4000, respectively. The optimal antigen coating condition was 4℃ for overnight. Hyperimmune serum of high-yielding hens of different age produced stronger reaction against σC. Chicken serum samples were randomly collected and total coincidence rate between commercial kit and σC-ARV-ELISA kit was 97.8%. Importantly, those discrepant serums were further verified using Western blot assay and three of them were determined to be positive. Thus, the method based on σC protein has higher sensitivity compared with the commercial kit and provide a rapid and simple method for serodiagnosis of ARV, contributing to convenient epidemiological monitoring of ARV.

Gga-miR-29a-3p suppresses avian reovirus-induced apoptosis and viral replication via targeting Caspase-3

Avian reovirus (ARV) is an important pathogen causing multiple types of clinical diseases in chickens, including viral arthritis, chronic respiratory diseases, retarded growth, and malabsorption syndrome, leading to considerable economic losses to the poultry industry across the globe. MicroRNAs (miRNAs) are small noncoding RNAs that regulate gene expression post transcriptionally by silencing or degrading their targets, thus playing important roles in the host response to pathogenic infection. However, the role of miRNAs in host response to ARV infection is still not clear. Here, we show that infection of DF-1 cells (a chicken fibroblast cell line) with ARV markedly altered the expressions of 583 chicken miRNAs(gga-miR), and that transfection of DF-1 cells with gga-miR-29a-3p, an upregulated miRNA in ARV-infected cells, significantly suppressed ARV-induced apoptosis via directly targeting Caspase-3, retarding ARV growth in cells. In contrast, knockdown of endogenous gga-miR-29a-3p in DF-1 cells by specific miRNA inhibitor enhanced ARV-induced apoptosis and increased the content and activity of caspase-3, facilitating viral growth in cells. Consistently, inhibition of Caspase-3 activity by inhibitors decreased viral titers in cell cultures. Thus, gga-miR-29a-3p plays an important antiviral role in host response to ARV infection by suppression of apoptosis via targeting Caspase-3. This information will further our understandings of how host cells combat against ARV infection by self-encoded small RNA and increase our knowledge of the role of microRNAs in host response to pathogenic infection.

Viral Proteins as Emerging Cancer Therapeutics

Simple Summary

This review is focused on enlisting viral proteins from different host sources, irrespective of their origin, that may act as future cancer curatives. Unlike the viral proteins that are responsible for tumor progression, these newly emerged viral proteins function as tumor suppressors. Their ability to regulate various cell signaling mechanisms specifically in cancer cells makes them interesting candidates to explore their use in cancer therapy. The discussion about such viral components may provide new insights into cancer treatment in the absence of any adverse effects to normal cells. The study also highlights avian viral proteins as a substitute to human oncolytic viruses for their ability to evade pre-existing immunity.

Abstract

Viruses are obligatory intracellular parasites that originated millions of years ago. Viral elements cover almost half of the human genome sequence and have evolved as genetic blueprints in humans. They have existed as endosymbionts as they are largely dependent on host cell metabolism. Viral proteins are known to regulate different mechanisms in the host cells by hijacking cellular metabolism to benefit viral replication. Amicable viral proteins, on the other hand, from several viruses can participate in mediating growth retardation of cancer cells based on genetic abnormalities while sparing normal cells. These proteins exert discreet yet converging pathways to regulate events like cell cycle and apoptosis in human cancer cells. This property of viral proteins could be harnessed for their use in cancer therapy. In this review, we discuss viral proteins from different sources as potential anticancer therapeutics.

Avian reovirus infection activate the cellular unfold protein response and induced apoptosis via ATF6-dependent mechanism

Avian reovirus (ARV) infection induced apoptosis in vitro and vivo; nevertheless, the intracellular molecular mechanisms have not been sufficiently revealed. In the previous studies, there have been shown that cellular apoptosis caused by ARV were related with GRP78/IRE1/XBP1 pathway. Protein kinase RNA-like endoplasmic reticulum kinase (PERK), inositol-requiring enzyme 1 (IRE1) and activating transcription factor 6 (ATF6) are core molecules in unfold protein response (UPR) and play critical role in ER stress related apoptosis, as well as downstream regulation factors, as Caspase-12 and C/EBP homologous protein (CHOP). In this study, we investigated with a focus on the contribution of UPR related signal pathways in the mechanism of ARV mediated apoptosis. Our results showed that the key molecules of UPR pathways proteins, ATF6, PERK and IRE1 as well as Caspase-12 and cleaved-Caspase-3 expression significant increased both in transcript and protein level in ARV infected cultured Vero cells. In the same time, the ARV induces apoptosis was observed by flow cytometric analysis. Further study revealed that when inhibit the UPR effect by 4PBA pretreated or knockdown of ATF6 by lentivirus mediated shRNA abolished the activation effect of UPR, Caspase-12, cleaved-Caspase-3 activation, as well as the apoptosis induction by ARV infection. The present study provides mechanistic insights into that UPR particular ATF6 played critical roles and works upstream of caspase in the process of cellular apoptosis induced by ARV infection.

Bovine ephemeral fever virus triggers autophagy enhancing virus replication via upregulation of the Src/JNK/AP1 and PI3K/Akt/NF-κB pathways and suppression of the PI3K/Akt/mTOR pathway

Autophagy plays an important role in cellular response to pathogens. However, the impact of the autophagy machinery on bovine ephemeral fever virus (BEFV) infection is not yet determined. A recent study in our laboratory demonstrated that BEFV triggers simultaneously the PI3K/Akt/NF-κB and Src/JNK-AP1 pathways in the stage of virus binding to enhance virus entry. In this work, we report that BEFV induces autophagy via upregulation of the PI3K/Akt/NF-κB and Src/JNK/AP1 pathways in the early to middle stages of infection and suppresses the PI3K/Akt/mTOR pathway at the late stage of infection. To activate NF-κB, BEFV promotes degradation of IκBα and activates Akt to stimulate NF-κB translocation into the nucleus. Immunoprecipitation assays revealed that BEFV disrupts Beclin 1 and Bcl-2 interaction by JNK-mediated Bcl-2 phosphorylation, thereby activating autophagy. Overexpression of Bcl-2 reversed the BEFV-induced increase in the LC3 II levels. Suppression of autophagy either by knockdown of autophagy-related genes with shRNAs or treatment with a pharmacological inhibitor 3-MA reduced BEFV replication, suggesting that BEFV-induced autophagy benefits virus replication. Our results revealed that the BEFV M protein is one of the viral proteins involved in inducing autophagy via suppression of the PI3K/Akt/mTORC1 pathway. Furthermore, degradation of p62 was observed by immunoblotting, suggesting that BEFV infection triggers a complete autophagic response. Disruption of autophagosome-lysosome fusion by depleting LAMP2 resulted in reduction of virus yield, suggesting that formation of autolysosome benefits virus production.

Cdc20 and molecular chaperone CCT2 and CCT5 are required for the Muscovy duck reovirus p10.8-induced cell cycle arrest and apoptosis

This study demonstrates that the Muscovy duck reovirus (MDRV) p10.8 protein is one of many viral non-structural proteins that induces both cell cycle arrest and apoptosis. The p10.8 but not σC is a nuclear targeting protein that shuttles between the nucleus and the cytoplasm. Our results reveal that p10.8-induced apoptosis in cultured cells occurs by the nucleoporin Tpr/p53-dependent and Fas/caspase 8-mediated pathways. Furthermore, a compelling finding from this study is that the p10.8 and σC proteins of MDRV facilitate CDK2 and CDK4 degradation via the ubiquitin-proteasome pathway. We found that depletion of Cdc20 reversed the p10.8- and σC- mediated CDK4 degradation and p10.8-induced apoptosis, suggesting that Cdc20 plays a critical role in modulating p10.8-mediated cell cycle and apoptosis. Furthermore, we found that depletion of chaperonin-containing tailless complex polypeptide 1 (CCT) 2 and CCT5 reduced the level of Cdc20 and reversed the p10.8- and σC-mediated CDK4 degradation and p10.8-induced apoptosis, indicating that molecular chaperone CCT2 and CCT5 are required for stabilization of Ccd20 for mediating both cell cycle arrest and apoptosis. This study provides mechanistic insights into how p10.8 induces both cell cycle arrest and apoptosis.

Autophagy induced by avian reovirus enhances viral replication in chickens at the early stage of infection

BACKGROUND

Avian reovirus (ARV) is an important pathogen that can cause serious disease in poultry. Though several in vitro studies revealed some molecular mechanisms that are responsible for ARV-induced autophagy, it is still largely unknown how ARV manipulates autophagy to promote its own propagation.

RESULTS

In this study, we demonstrated that ARV infection triggered autophagy in chicken tissues, evident from the enhancement of LC3-I/-II conversion and the appearance of abundant autophagosomes. Moreover, viral replication and the expression of IL-1β were coupled with the process of ARV-induced autophagy in the early stage of infection. Furthermore, regulation of autophagy affected the accumulation of LC3-II, the production of ARV and the expression of IL-1β.

CONCLUSIONS

Altogether, our data suggest that ARV induces autophagy, which benefits its replication and dissemination in chicken tissues at the early infection stage.

Muscovy duck reovirus p10.8 protein induces ER stress and apoptosis through the Bip/IRE1/XBP1 pathway

In the present study, the mechanisms underlying Muscovy duck reovirus (MDRV) p10.8 protein-induced ER stress and apoptosis in DF-1 cells and Muscovy duckling hepatic tissues were explored. On the fifth day post-infection, an increase in the mRNA levels of binding immunoglobulin protein (Bip) and X-box binding protein (XBP1), activation of XBP1/s, and an increase in percentage of apoptotic cells were observed in Muscovy duckling livers. The use of ER stress inducer Tunicamycin and ER stress inhibitor Tauroursodeoxycholic acid demonstrated that MDRV induces apoptosis via ER stress, leading to apoptosis. The use of Tunicamycin increased viral protein synthesis while Tauroursodeoxycholic acid reduced viral protein synthesis, suggesting that MDRV induces ER stress benefiting virus replication. The MDRV p10.8 is the major protein to induce ER stress and apoptosis. We found that p10.8 promotes the conversion of XBP1/u to XBP1/s and expands ER diameter, and increases the percentages of apoptotic cells in DF-1 and duckling liver tissues. To investigate the mechanism underlying the MDRV p10.8-induced ER stress and apoptosis, Western blot, siRNA, and co-immunoprecipitation (Co-IP) assays were performed. We found that the MDRV p10.8 protein up-regulates Bip, p-IRE1, XBP1s, and cleaved-caspase 3. Co-IP results reveal that the MDRV p10.8 protein disassociates the Bip/IRE1 complex. Inhibition of IRE1 by 4-methyl umbelliferone 8-carbaldehyde (4u8c) dramatically reversed the MDRV p10.8-modulated increase in levels of XBP1s and cleaved-caspase 3. Knockdown of XBP1 by siRNA reversed the increased level of p10.8-modulated cleaved-caspase 3. The present study provides mechanistic insights into the MDRV p10.8 protein induces ER stress, resulting in apoptosis via the Bip/IRE1/XBP1 pathway in DF-1 cells and duckling livers.

The E3 Ubiquitin Ligase Siah-1 Suppresses Avian Reovirus Infection by Targeting p10 for Degradation

Avian reovirus (ARV) causes viral arthritis, chronic respiratory diseases, retarded growth, and malabsorption syndrome. The ARV p10 protein, a viroporin responsible for the induction of cell syncytium formation and apoptosis, is rapidly degraded in host cells. Our previous report demonstrated that cellular lysosome-associated membrane protein 1 (LAMP-1) interacted with p10 and was involved in its degradation. However, the molecular mechanism underlying LAMP-1-mediated p10 degradation remains elusive. We report here that the E3 ubiquitin ligase seven in absentia homolog 1 (Siah-1) is critical for p10 ubiquitylation. Our data show that Siah-1 ubiquitylated p10 and targeted it for proteasome degradation. Furthermore, the ubiquitylation of p10 by Siah-1 required the participation of LAMP-1 by forming a multicomponent complex. Thus, LAMP-1 promotes the proteasomal degradation of p10 via interacting with both p10 and the E3 ligase Siah-1. These data establish a novel host defense mechanism where LAMP-1 serves as a scaffold for both Siah-1 and p10 that allows the E3 ligase targeting p10 for ubiquitylation and degradation to suppress ARV infection.IMPORTANCE Avian reovirus (ARV) is an important poultry pathogen causing viral arthritis, chronic respiratory diseases, retarded growth, and malabsorption syndrome, leading to considerable economic losses to the poultry industry across the globe. The ARV p10 protein is a virulence factor responsible for the induction of cell syncytium formation and apoptosis and is rapidly degraded in host cells. We previously found that cellular lysosome-associated membrane protein 1 (LAMP-1) interacts with p10 and is involved in its degradation. Here we report that the E3 ubiquitin ligase seven in absentia homolog 1 (Siah-1) ubiquitylated p10 and targeted it for proteasomal degradation. Furthermore, the ubiquitylation of p10 by Siah-1 required the participation of LAMP-1 by forming a multicomponent complex. Thus, LAMP-1 serves as an adaptor to allow Siah-1 to target p10 for degradation, thereby suppressing ARV growth in host cells.

Mitochondrial p53 Contributes to Reovirus-Induced Neuronal Apoptosis and Central Nervous System Injury in a Mouse Model of Viral Encephalitis

The tumor suppressor p53 plays a critical part in determining cell fate both as a regulator of the transcription of several proapoptotic genes and through its binding interactions with Bcl-2 family proteins at mitochondria. We now demonstrate that p53 protein levels are increased in infected brains during reovirus encephalitis. This increase occurs in the cytoplasm of reovirus-infected neurons and is associated with the activation of caspase 3. Increased levels of p53 in reovirus-infected brains are not associated with increased expression levels of p53 mRNA, suggesting that p53 regulation occurs at the protein level. Increased levels of p53 are also not associated with the increased expression levels of p53-regulated, proapoptotic genes. In contrast, upregulated p53 accumulates in mitochondria. Previous reports demonstrated that the binding of p53 to Bak at mitochondria causes Bak activation and results in apoptosis. We now show that Bak is activated and that activated Bak is bound to p53 during reovirus encephalitis. In addition, survival is enhanced in reovirus-infected Bak(-/-) mice compared to controls, demonstrating a role for Bak in reovirus pathogenesis. Inhibition of the mitochondrial translocation of p53 with pifithrin μ prevents the formation of p53/Bak complexes following reovirus infection of ex vivo brain slice cultures and results in decreased apoptosis and tissue injury. These results suggest that the mitochondrial localization of p53 regulates reovirus-induced pathogenesis in the central nervous system (CNS) through its interactions with Bak.

IMPORTANCE

There are virtually no specific treatments of proven efficacy for virus-induced neuroinvasive diseases. A better understanding of the pathogenesis of virus-induced CNS injury is crucial for the rational development of novel therapies. Our studies demonstrate that p53 is activated in the brain following reovirus infection and may provide a therapeutic target for virus-induced CNS disease.

A critical role of LAMP-1 in avian reovirus P10 degradation associated with inhibition of apoptosis and virus release

Avian reovirus (ARV) causes viral arthritis, chronic respiratory diseases, retarded growth and malabsorption syndrome. The ARV p10 protein, a viroporin responsible for the induction of cell syncytium formation and apoptosis, is rapidly degraded in host cells. However, the mechanism of p10 degradation and its relevance are still unclear. We report here the identification of cellular lysosome-associated membrane protein 1 (LAMP-1) as an interaction partner of p10 by yeast two-hybrid screening, immunoprecipitation and confocal microscopy assays. We found that rapid degradation of p10 was associated with ubiquitination. Importantly, ARV p10 degradation in host cells could be completely abolished by knockdown of LAMP-1 by siRNA, indicating that LAMP-1 is required for ARV p10 degradation in host cells. In contrast, overexpression of LAMP-1 facilitated p10 degradation. Furthermore, knockdown of LAMP-1 allowed p10 accumulation, enhancing p10-induced apoptosis and viral release. Thus, LAMP-1 plays a critical role in ARV p10 degradation associated with inhibition of apoptosis and viral release.

Avian reovirus S1133-induced apoptosis is associated with Bip/GRP79-mediated Bim translocation to the endoplasmic reticulum

In this study the mechanism of avian reovirus (ARV) S1133-induced pathogenesis was investigated, with a focus on the contribution of ER stress to apoptosis. Our results showed that upregulation of the ER stress response protein, as well as caspase-3 activation, occurred in ARV S1133-infected cultured cells and in SPF White Leghorn chicks organs. Upon infection, Bim was translocated specifically to the ER, but not mitochondria, in the middle to late infectious stages. In addition, ARV S1133 induced JNK phosphorylation and promoted JNK-Bim complex formation, which correlated with the Bim translocation and apoptosis induction that was observed at the same time point. Knockdown of BiP/GRP78 by siRNA and inhibition of BiP/GRP78 using EGCG both abolished the formation of the JNK-Bim complex, caspase-3 activation, and subsequent apoptosis induction by ARV S1133 efficiently. These results suggest that BiP/GRP78 played critical roles and works upstream of JNK-Bim in response to the ARV S1133-mediated apoptosis process.

RhoA/ROCK1 regulates Avian Reovirus S1133-induced switch from autophagy to apoptosis

BACKGROUND

Autophagy is an essential process in the control of cellular homeostasis. It enables cells under certain stress conditions to survive by removing toxic cellular components, and may protect cells from apoptosis. In the present study, the signaling pathways involved in ARV S1133 regulated switch from autophagy to apoptosis were investigated.

RESULTS

ARV S1133 infection caused autophagy in the early to middle infectious stages in Vero and DF1 cells, and apoptosis in the middle to late stages. Conversion of the autophagy marker LC3-I to LC3-II occurred earlier than cleavage of the apoptotic marker caspase-3. ARV S1133 also activated the Beclin-1 promoter in the early to middle stages of infection. Levels of RhoA-GTP and ROCK1 activity were elevated upon ARV S1133 infection, while inhibition of RhoA and ROCK1 reduced autophagy and subsequent apoptosis. Conversely, inhibition of caspase-3 did not affect the level of autophagy. Beclin-1 knockdown and treatment with autophagy inhibitors, 3-MA and Bafilomycin A1, suppressed ARV S1133-induced autophagy and apoptosis simultaneously, suggesting the shift from autophagy to apoptosis. A co-immunoprecipitation assay demonstrated that the formation of a RhoA, ROCK1 and Beclin-1 complex coincided with the induction of autophagy.

CONCLUSION

Our results demonstrate that RhoA/ROCK1 signaling play critical roles in the transition of cell activity from autophagy to apoptosis in ARV S1133-infected cells.

Autophagy inhibitors reduce avian-reovirus-mediated apoptosis in cultured cells and in chicken embryos

Avian reovirus (ARV)-induced apoptosis contributes to the pathogenesis of reovirus in infected chickens. However, methods for effectively reducing ARV-triggered apoptosis remain to be explored. Here, we show that pretreatment with chloroquine (CQ) or E64d plus pepstatin A decreases ARV-mediated apoptosis in chicken DF-1 cells. By acting as autophagy inhibitors, CQ and E64d plus pepstatin A increase microtubule-associated protein 1 light chain 3-II (LC3II) accumulation in ARV-infected cells, which results in decreased ARV protein synthesis and virus yield and thereby contributes to the reduction of apoptosis. Furthermore, ARV-mediated apoptosis in the bursa, heart and intestines of chicken embryos is attenuated by CQ and E64d plus pepstatin A treatment. Importantly, treatment with these autophagy inhibitors increases the survival of infected chicken embryos. Together, our data suggest that pharmacological inhibition of autophagy might represent a novel strategy for reducing ARV-mediated apoptosis.

Critical role of eukaryotic elongation factor 1 alpha 1 (EEF1A1) in avian reovirus sigma-C-induced apoptosis and inhibition of viral growth

Avian reovirus (ARV) causes viral arthritis, chronic respiratory diseases, retarded growth and malabsorption syndrome. It is well established that the ARV sigma-C protein induces apoptosis in host cells. However, the underlying molecular mechanism of this induction is still unclear. We report here the identification of eukaryotic elongation factor 1 alpha 1 (EEF1A1) as the interacting partner of σC. We found that σC-induced apoptosis in DF-1 cells could be completely abolished by knockdown of EEF1A1 by siRNA. Furthermore, knockdown of EEF1A1 markedly reduced ARV-induced apoptosis associated with decreased caspase-9 and -3 activation and cytochrome C release, leading to increased ARV growth in host cells. Thus, EEF1A1 plays a critical role in σC-induced apoptosis and inhibition of viral growth.

Proteomics analysis of the DF-1 chicken fibroblasts infected with avian reovirus strain S1133

BACKGROUND

Avian reovirus (ARV) is a member of the Orthoreovirus genus in the Reoviridae family. It is the etiological agent of several diseases, among which viral arthritis and malabsorption syndrome are the most commercially important, causing considerable economic losses in the poultry industry. Although a small but increasing number of reports have characterized some aspects of ARV infection, global changes in protein expression in ARV-infected host cells have not been examined. The current study used a proteomics approach to obtain a comprehensive view of changes in protein levels in host cells upon infection by ARV.

METHODOLOGY AND PRINCIPAL FINDINGS

The proteomics profiles of DF-1 chicken fibroblast cells infected with ARV strain S1133 were analyzed by two-dimensional differential-image gel electrophoresis. The majority of protein expression changes (≥ 1.5 fold, p<0.05) occurred at 72 h post-infection. Matrix-assisted laser desorption ionization time-of-flight mass spectrometry identified 51 proteins with differential expression levels, including 25 that were upregulated during ARV infection and 26 that were downregulated. These proteins were divided into eight groups according to biological function: signal transduction, stress response, RNA processing, the ubiquitin-proteasome pathway, lipid metabolism, carbohydrate metabolism, energy metabolism, and cytoskeleton organization. They were further examined by immunoblotting to validate the observed alterations in protein expression.

CONCLUSION/SIGNIFICANCE

This is the first report of a time-course proteomic analysis of ARV-infected host cells. Notably, all identified proteins involved in signal transduction, RNA processing, and the ubiquitin-proteasome pathway were downregulated in infected cells, whereas proteins involved in DNA synthesis, apoptosis, and energy production pathways were upregulated. In addition, other differentially expressed proteins were linked with the cytoskeleton, metabolism, redox regulation, and stress response. These proteomics data provide valuable information about host cell responses to ARV infection and will facilitate further studies of the molecular mechanisms underlying ARV pathogenesis.

The interplay of reovirus with autophagy

Autophagy participates in multiple fundamental physiological processes, including survival, differentiation, development, and cellular homeostasis. It eliminates cytoplasmic protein aggregates and damaged organelles by triggering a series of events: sequestering the protein substrates into double-membrane vesicles, fusing the vesicles with lysosomes, and then degrading the autophagic contents. This degradation pathway is also involved in various disorders, for instance, cancers and infectious diseases. This paper provides an overview of modulation of autophagy in the course of reovirus infection and also the interplay of autophagy and reovirus.

Identification of a linear B-Cell epitope on avian reovirus protein sigmaC

SigmaC (σC) protein, which mediates virus attachment to target cells, is the most variable proteins of avian reovirus (ARV). It is responsible for inducing protective antibody immune responses in animals. To understand the antigenic determinants of σC protein, a set of partially overlapping and consecutive peptides spanning σC were expressed and then screened with the monoclonal antibody (mAb) 2B5 directed against σC. The mAb 2B5 recognized peptides with the σC motif (45)ELLHRSISDISTTV(58). Further identification of the displayed B-cell epitope was conducted with a set of truncated peptides expressed as GST fusion proteins. The Western blot and ELISA results indicated that (45)ELLHRSISDI(54) was the minimal determinant of the linear B-cell epitope. Using sequences analysis, we found that this epitope was not a common motif shared among the other members of the ARV and DRV groups. Furthermore, cross reactivity analysis showed that the associated coding motif of other ARV and DRV groups was not recognized by 2B5. These data suggested that (45)ELLHRSISDI(54) was a type-specific linear B-cell epitope of avian reovirus. The results in this study may have potential applications in the development of diagnostic techniques and epitope-based marker vaccines against ARV, which is prevalent in China.

The p17 nonstructural protein of avian reovirus triggers autophagy enhancing virus replication via activation of phosphatase and tensin deleted on chromosome 10 (PTEN) and AMP-activated protein kinase (AMPK), as well as dsRNA-dependent protein kinase (PKR)/eIF2α signaling pathways

Autophagy has been shown to facilitate replication or production of avian reovirus (ARV); nevertheless, how ARV induces autophagy remains largely unknown. Here, we demonstrate that the nonstructural protein p17 of ARV functions as an activator of autophagy. ARV-infected or p17-transfected cells present a fast and strong induction of autophagy, resulting in an increased level of autophagic proteins Beclin 1 and LC3-II. Although autophagy was suppressed by 3-methyladenine or shRNAs targeting autophagic proteins (Beclin 1, ATG7, and LC3) as well as by overexpression of Bcl-2, viral transcription, σC protein synthesis, and virus yield were all significantly reduced, suggesting a key role of autophagosomes in supporting ARV replication. Furthermore, we revealed for the first time that p17 positively regulates phosphatase and tensin deleted on chromosome 10 (PTEN), AMP-activated protein kinase (AMPK), and dsRNA dependent protein kinase RNA (PKR)/eIF2α signaling pathways, accompanied by down-regulation of Akt and mammalian target of rapamycin complex 1, thereby triggering autophagy. By using p53, PTEN, PKR, AMPK, and p17 short hairpin RNA (shRNA), activation of signaling pathways and LC3-II levels was significantly suppressed, suggesting that p17 triggers autophagy through activation of p53/PTEN, AMPK, and PKR signaling pathways. Furthermore, colocalization of LC3 with viral proteins (p17 and σC), p62 with LAMP2 and LC3 with Rab7 was observed under a fluorescence microscope. The expression level of p62 was increased at 18 h postinfection and then slightly decreased 24 h postinfection compared with mock infection and thapsigargin treatment. Furthermore, disruption of autophagosome-lysosome fusion by shRNAs targeting LAMP2 or Rab7a resulted in inhibition of viral protein synthesis and virus yield, suggesting that formation of autolysosome benefits virus replication. Taken together, our results suggest that ARV induces formation of autolysosome but does not induce complete autophagic flux.

Avian reovirus S1133-induced DNA damage signaling and subsequent apoptosis in cultured cells and in chickens

In this study, intracellular signaling in ARV S1133-mediated apoptosis was investigated. A microarray was used to examine the gene expression profiles of cells upon ARV S1133 infection and ARV-encoded pro-apoptotic protein σC overexpression. The analysis indicated that in the set of DNA-damage-responsive genes, DDIT-3 and GADD45α were both upregulated by viral infection and σC overexpression. Further investigation demonstrated that both treatments caused DNA breaks, which increased the expression and/or phosphorylation of DNA damage response proteins. ROS and lipid peroxidation levels were increased, and ARV S1133 and σC caused apoptosis mediated by DNA damage signaling. ROS scavenger NAC, caffeine and an ATM-specific inhibitor significantly reduced ARV S1133- and σC-induced DNA breaks, DDIT-3 and GADD45α expression, H2AX phosphorylation, and apoptosis. Overexpression of DDIT-3 and GADD45α enhanced the oxidative stress and apoptosis induced by ARV S1133 and σC. In conclusion, our results demonstrate the involvement of the DNA-damage-signaling pathway in ARV S1133- and σC-induced apoptosis.

Cell entry of avian reovirus follows a caveolin-1-mediated and dynamin-2-dependent endocytic pathway that requires activation of p38 mitogen-activated protein kinase (MAPK) and Src signaling pathways as well as microtubules and small GTPase Rab5 protein

Very little is known about the mechanism of cell entry of avian reovirus (ARV). The aim of this study was to explore the mechanism of ARV entry and subsequent infection. Cholesterol mainly affected the early steps of the ARV life cycle, because the presence of cholesterol before and during viral adsorption greatly blocked ARV infectivity. Although we have demonstrated that ARV facilitating p38 MAPK is beneficial for virus replication, its mechanism remains unknown. Here, we show that ARV-induced phosphorylation of caveolin-1 (Tyr(14)), dynamin-2 expression, and Rac1 activation through activation of p38 MAPK and Src in the early stage of the virus life cycle is beneficial for virus entry and productive infection. The strong inhibition by dynasore, a specific inhibitor of dynamin-2, and depletion of endogenous caveolin-1 or dynamin-2 by siRNAs as well as the caveolin-1 colocalization study implicate caveolin-1-mediated and dynamin-2-dependent endocytosis as a significant avenue of ARV entry. By means of pharmacological inhibitors, dominant negative mutants, and siRNA of various cellular proteins and signaling molecules, phosphorylation of caveolin-1, dynamin-2 expression, and Rac1 activation were suppressed, suggesting that by orchestrating p38 MAPK, Src, and Rac1 signaling cascade in the target cells, ARV creates an appropriate intracellular environment facilitating virus entry and productive infection. Furthermore, disruption of microtubules, Rab5, or endosome acidification all inhibited ARV infection, suggesting that microtubules and small GTPase Rab5, which regulate transport to early endosome, are crucial for survival of ARV and that exposure of the virus to acidic pH is required for productive infection.

Expression of avian reovirus minor capsid protein in plants

The minor coat protein of the avian reovirus (ARV), σC, encoded by the S1 genome segment, is one of the major candidates for the development of a subunit vaccine against ARV infection. To develop a plant-based vaccine to immunize poultry against ARV infection, we constructed 4 plant nuclear expression vectors with or without codon modification of the S1 gene, and their expression was driven by a CaMV 35S promoter or rice actin1 promoter. In addition, the expressed σC proteins were targeted subcellularly to cytosol or chloroplasts, respectively. Agrobacterium containing the S1 expression constructs was used to transform tobacco leaf disks, and transformants were selected with kanamycin (100 μg/ml). The integration of the S1 transgene into the tobacco chromosome was confirmed by PCR and Southern blot analysis. Western blot analysis with antiserum against σC was performed to determine the expression of σC protein in transgenic tobacco plants. The highest expression levels of σC protein in the cellular extracts of selected p35S1, pActS1 and p35UmS1 transgenic lines were 0.013%, 0.021% and 0.0013% of the total soluble protein, respectively, but the protein was barely detectable in p35TmS1 transgenic lines. However, the level of σC protein expression was not associated with the level of corresponding RNA transcripts in selected transgenic lines. Taken together, the results suggest that the major limiting factor for the expression of σC protein in plants might be at the post-transcriptional level.

Virus susceptibility of Chinese hamster ovary (CHO) cells and detection of viral contaminations by adventitious agent testing

Biopharmaceuticals are of increasing importance in the treatment of a variety of diseases. A remaining concern associated with their production is the potential introduction of adventitious agents into their manufacturing process, which may compromise the pathogen safety of a product and potentially cause stock-out situations for important medical supplies. To ensure the safety of biological therapeutics, regulatory guidance requires adventitious agent testing (AAT) of the bulk harvest. AAT is a deliberately promiscuous assay procedure which has been developed to indicate, ideally, the presence of any viral contaminant. One of the most important cell lines used in the production of biopharmaceuticals is Chinese hamster ovary (CHO) cells and while viral infections of CHO cells have occurred, a systematic screen of their virus susceptibility has never been published. We investigated the susceptibility of CHO cells to infection by 14 different viruses, including members of 12 families and representatives or the very species that were implicated in previously reported production cell infections. Based on our results, four different infection outcomes were distinguished, based on the possible combinations of the two factors (i) the induction, or not, of a cytopathic effect and (ii) the ability, or not, to replicate in CHO cells. Our results demonstrate that the current AAT is effective for the detection of viruses which are able to replicate in CHO cells. Due to the restricted virus susceptibility of CHO cells and the routine AAT of bulk harvests, our results provide re-assurance for the very high safety margins of CHO cell-derived biopharmaceuticals.

Avian reovirus nonstructural protein p17-induced G(2)/M cell cycle arrest and host cellular protein translation shutoff involve activation of p53-dependent pathways

The effects of avian reovirus (ARV) p17 protein on cell cycle progression and host cellular protein translation were studied. ARV infection and ARV p17 transfection resulted in the accumulation of infected and/or transfected cells in the G(2)/M phase of the cell cycle. The accumulation of cells in the G(2)/M phase was accompanied by upregulation and phosphorylation of the G(2)/M-phase proteins ATM, p53, p21(cip1/waf1), Cdc2, cyclin B1, Chk1, Chk2, and Cdc25C, suggesting that p17 induces a G(2)/M cell cycle arrest through activation of the ATM/p53/p21(cip1/waf1)/Cdc2/cyclin B1 and ATM/Chk1/Chk2/Cdc25C pathways. The G(2)/M cell cycle arrest resulted in increased virus replication. In the present study, we also provide evidence demonstrating that p17 protein is responsible for ARV-induced host cellular protein translation shutoff. Increased phosphorylation levels of the eukaryotic translation elongation factor 2 (eEF2) and initiation factor eIF2alpha and reduced phosphorylation levels of the eukaryotic translation initiation factors eIF4E, eIF4B, and eIF4G, as well as 4E-BP1 and Mnk-1 in p17-transfected cells, demonstrated that ARV p17 suppresses translation initiation factors and translation elongation factors to induce host cellular protein translation shutoff. Inhibition of mTOR by rapamycin resulted in a decrease in the levels of phosphorylated 4E-BP1, eIF4B, and eIF4G and an increase in the levels eEF2 but did not affect ARV replication, suggesting that ARV replication was not hindered by inhibition of cap-dependent translation. Taken together, our data indicate that ARV p17-induced G(2)/M arrest and host cellular translation shutoff resulted in increased ARV replication.

Intracellular cleavage of sigmaA protein of avian reovirus

By Western blot analyzes of expression of avian reovirus proteins, one unknown fragment was detected by an anti-sigmaA monoclonal antibody in virus-infected cells lysate. It was interesting to note that RNA interference against sigmaA resulted in the suppression of the unknown fragment. Using various lengths of sigmaA constructs conjugated with different tags, we present evidences to demonstrate that the fragment comes from the cleavage of sigmaA and is the larger carboxyl-terminus, termed sigmaAC. Cleavage of sigmaA simultaneously produces a smaller amino-terminus, named sigmaAN. sigmaAC could be seen early in viral infection and accumulated with time and dose of infection, indicating that the derived products are not just transient intermediates of protein degradation. The same type of cleaved products were also observed in different genotypes and serotypes of ARV as well as in different cell lines, suggesting that this intracellular modification of sigmaA is common to all ARVs. Similar localization of sigmaAC in both cytosol and nucleus with sigmaA suggested that further modification of sigmaA may be important for its function. Our evidences suggest that besides the outer capsid protein muB, sigmaA may also have post-translational cleavage which has never been reported before even in related mammalian reovirus.

Bovine ephemeral fever virus-induced apoptosis requires virus gene expression and activation of Fas and mitochondrial signaling pathway

Although induction of apoptosis by bovine ephemeral fever virus (BEFV) in several cell lines has been previously demonstrated by our laboratory, less information is available on the process of BEFV-induced apoptosis in terms of cellular pathways and specific proteins involved. In order to determine the step in viral life cycle at which apoptosis of infected cells is triggered, chemical and physical agents were used to block viral infection. Treatment of BHK-21 infected cells with ammonium chloride (NH4Cl) or cells infected with UV-inactivated BEFV was seen to abrogate virus apoptosis induction, suggesting that virus uncoating and gene expression are required for the induction of apoptosis. Using soluble death receptors Fc:Fas chimera to block Fas signaling, BEFV-induced apoptosis was inhibited in cells. BEFV infection of BHK-21 cells results in the Fas-dependent activation of caspase 8 and cleavage of Bid. This initiated the dissipation of the membrane potential and the release of cytochrome c but not AIF or Smac/DIABLO from mitochondrial into cytoplasm leading to activation of caspase 9. Combined activation of the death receptor and mitochondrial pathways results in activation of the downstream effecter caspase 3 leading to cleavage of PARP. Fas-mediated BEFV-induced apoptosis could be suppressed by the overexpression of Bcl-2 or by treatment with caspase inhibitors and soluble death receptors Fc:Fas chimera. Taken together, this study provided first evidence demonstrating that BEFV-induced apoptosis requires viral gene expression and occurs through the activation of Fas and mitochondrion-mediated caspase-dependent pathways.

Seroprevalence of avian reovirus in egg-laying chicken flocks in China

In the present study, the epidemiologic status of avian reovirus (ARV) infections was investigated from egg-laying chicken flocks in China with an enzyme-linked immunosorbent assay (ELISA) kit. Because the chickens were not vaccinated against ARV, antibodies were attributed to the infection. Antibodies specific to ARV were found in more than 92% (542/587) of the average positivity and ranged from 30% to 100% in different chicken population. A virus, designated HB06, was isolated from flocks with suspicious ARV infections. Sequence analysis of the S1 gene revealed that strain HB06 was closely related with the most ARVs with less than 2% nucleotide divergence, and the homology was highest with the vaccine strain S1133, with a 98.97% nucleotide identity. The potential significance of vaccination against ARV in egg-laying chicken flocks in China is also discussed.

Baculovirus surface display of sigmaC and sigmaB proteins of avian reovirus and immunogenicity of the displayed proteins in a mouse model

Avian reovirus (ARV), an important pathogen in poultry, causes arthritis, chronic respiratory disease, and malabsorption syndrome that cause considerable economic losses to the poultry industry. In present study, we have succeeded in construction of a universal baculovirus surface display system (UBSDS) that can display different foreign proteins on the envelope of baculovirus. Sequences encoding the signal peptide (SS), transmembrane domain (TM), and cytoplasmic domain (CTD) derived from the gp64 protein of baculovirus and histidine tag, respectively were inserted into the pBacCE vector. Four restriction enzyme sites between the histidine tag and gp64 transmembrane domain were established for expression of different foreign proteins. The transmembrane domain and CTD of gp64 in the platform were designed in order to improve stability and quantity of foreign proteins on the envelope of baculovirus. The sigmaC and sigmaB proteins of ARV are known to elicit neutralizing antibodies against ARV. The UBSDS was therefore used to express sigmaC and sigmaB proteins on the envelope of baculovirus. Two recombinant baculoviruses BacSC-sigmaC and BacSC-sigmaB have been successfully constructed. After infection, both His6-tagged recombinant sigmaC (rsigmaC) and sigmaB (rsigmaB) proteins were displayed on the envelope of recombinant baculoviruses and the recombinant viral proteins were anchored on the plasma membrane of Sf-9 cells, as revealed by immunofluorescence staining (IFS) and confocal microscopy. The antigenicity of rsigmaC and rsigmaB proteins was demonstrated by Western blotting assay. Immunogold electron microscopy demonstrated that both recombinant viruses displayed rsigmaC and rsigmaB proteins on the viral surface. Immunization of BALB/c mice with recombinant viruses, demonstrated that serum from the BacSC-sigmaC and BacSC-sigmaB treated models had significant higher levels of virus neutralization activities than the control groups. This demonstrates that the recombinant baculoviruses BacSC-sigmaC and BacSC-sigmaB can be a potential vaccine against ARV infections.

Proteasome inhibition reduces avian reovirus replication and apoptosis induction in cultured cells

The interplay between avian reovirus (ARV) replication and apoptosis and proteasome pathway was studied in cultured cells. It is shown that inhibition of the proteasome did not affect viral entry and host cell translation but had influence on ARV replication and ARV-induced apoptosis. Evidence is provided to demonstrate that ubiquitin-proteasome blocked ARV replication at an early step in viral life cycle. However, viral transcription and protein translation were also reduced markedly after addition of proteasome inhibitor MG132. Treatment of BHK-21 cells with the MG132 markedly decreased virus titer as well as prevented virus-induced apoptosis. The expression of ARV proteins sigmaC, sigmaA, and sigmaNS was also reduced markedly, suggesting that suppression of virus replication is due to down-regulation of these ARV proteins by ubiquitin-proteasome system. MG132 was also shown to suppress ARV sigmaC-induced phosphrylation of p53 on serine 46, caspase 3 activities, and DNA fragmentation leading to complete inhibition of ARV-induced apoptosis.

Development of a reliable assay protocol for identification of diseases (RAPID)-bioactive amplification with probing for detection of avian reovirus

Avian reovirus (ARV) causes several disease syndromes in poultry including arthritis, malabsorption syndrome and chronic respiratory disease that result in major economic losses. Early detection is very important for the control of the ARV-induced infections. This study was therefore aimed at developing a reliable assay protocol for identification of diseases (RAPID)-bioactive amplification with probing (BAP) assay for detection of ARV. This assay combines nested polymerase chain reaction (PCR) and magnetic bead-based DNA probing systems greatly increasing its sensitivity and specificity. Alignment of ARV S2 gene from different ARV genotypes and serotypes was done to find the highly conserved regions for primer and probe design. Two reverse transcription (RT)-PCR primer pairs, six nested PCR primer pairs, and one magnetic probe were tested to find the most specific ones for ARV detection. The optimal conditions for RT-PCR, nested PCR, and hybridization of magnetic probe were established. The optimal annealing temperatures for RT-PCR and nested PCR were 62.1 and 54.8 degrees C, respectively. The optimal hybridization temperature was 51.2 degrees C using hybridization buffer (5x SSC and 0.5% SDS). The sensitivity of the kit was 5 copies/microl of ARV genomic RNA. The kit was very specific as all negative controls failed to show any positive reactions. The kit shows good reproducibility with intra- and inter-assay coefficient of variation (CV) of 1.3 and 1.7%, respectively. In addition, different serotypes and genotypes of ARV were tested by RAPID-BAP assay to estimate the practicability of the kit in clinical samples. All of ARV serotypes and genotypes tested could be detected by this kit proving that the kit is suitable for clinical application.