Peste des petits ruminants virus exploits cellular autophagy machinery for replication

Insights into the different mechanisms of Autophagy and Apoptosis mediated by Morbilliviruses

Viruses are obligate intracellular parasites that have co-evolved with the host. During the course of evolution, viruses have acquired abilities to abrogate the host's immune responses by modulating the host proteins which play a pivotal role in various biological processes. One such process is the programmed cell death in virus-infected cells, which can occur via autophagy or apoptosis. Morbilliviruses are known to modulate both autophagy and apoptosis. Upon infecting a cell, the morbilliviruses can utilize autophagosomes as their nest and delay the host defense apoptotic response, and/or can promote apoptosis to escalate the virus dissemination. Moreover, there is an active interplay between these two pathways which eventually decides the fate of a virus-infected cell. Recent advances in our understanding of these processes provide a potential rationale to further explore morbilliviruses for therapeutic purposes.

Comprehensive analysis of the succinylome in Vero cells infected with peste des petits ruminants virus Nigeria 75/1 vaccine strain

BACKGROUND

Peste des petits ruminants virus (PPRV) is currently the only member of the Morbillivirus caprinae species within the genus Morbillivirus of the family Paramyoxviridae. PPRV causes a highly contagious disease in small ruminants, especially goats and sheep. Succinylation is a newly identified and conserved modification and plays an important role in host cell response to pathogen infection. However, the extent and function of succinylation in Vero cells during PPRV infection remains unknown.

RESULTS

In this study, a global profile of the succinylome in Vero cells infected with PPRV Nigeria 75/1 vaccine strain (PPRVvac) was performed by dimethylation labeling-based quantitative proteomics analysis. A total of 2633 succinylation sites derived from 823 proteins were quantified. The comparative analysis of differentially succinylated sites revealed that 228 down-regulated succinylation sites on 139 proteins and 44 up-regulated succinylation sites on 38 proteins were significantly modified in response to PPRVvac infection, seven succinylation motifs were identified. GO classification indicated that the differentially succinylated proteins (DSuPs) mainly participated in cellular respiration, biosynthetic process and transmembrane transporter activity. KEGG pathway analysis indicated that DSuPs were related to protein processing in the endoplasmic reticulum. Protein-protein interaction networks of the identified proteins provided further evidence that various ATP synthase subunits and carbon metabolism were modulated by succinylation, while the overlapped proteins between succinylation and acetylation are involved in glyoxylate and dicarboxylate metabolism.

CONCLUSIONS

The findings of the present study provide the first report of the succinylome in Vero cells infected with PPRVvac and provided a foundation for investigating the role of succinylation alone and its overlap with acetylation in response to PPRVvac.

Carboplatin restricts peste des petits ruminants virus replication by suppressing the STING-mediated autophagy

Peste des petits ruminants virus (PPRV) is a morbillivirus that causes the acute and highly pathogenic infectious disease peste des petits ruminants (PPR) in small ruminants and poses a major threat to the goat and sheep industries. Currently, there is no effective treatment for PPRV infection. Here, we propose Carboplatin, a platinum-based regimen designed to treat a range of malignancies, as a potential antiviral agent. We showed that Carboplatin exhibits significant antiviral activity against PPRV in a cell culture model. The mechanism of action of Carboplatin against PPRV is mainly attributed to its ability to block STING mediated autophagy. Together, our study supports the discovery of Carboplatin as an antiviral against PPRV and potentially other closely related viruses, sheds light on its mode of action, and establishes STING as a valid and attractive target to counteract viral infection.

Nucleocapsid Protein (N) of Peste des petits ruminants Virus (PPRV) Interacts with Cellular Phosphatidylinositol-3-Kinase (PI3K) Complex-I and Induces Autophagy

Autophagy is an essential and highly conserved catabolic process in cells, which is important in the battle against intracellular pathogens. Viruses have evolved several ways to alter the host defense mechanisms. PPRV infection is known to modulate the components of a host cell's defense system, resulting in enhanced autophagy. In this study, we demonstrate that the N protein of PPRV interacts with the core components of the class III phosphatidylinositol-3-kinase (PI3K) complex-I and results in the induction of autophagy in the host cell over, thereby expressing this viral protein. Our data shows the interaction between PPRV-N protein and different core components of the autophagy pathway, i.e., VPS34, VPS15, BECN1 and ATG14L. The PPRV-N protein can specifically interact with VPS34 of the PI3K complex-I and colocalize with the proteins of PI3K complex-I in the same sub-cellular compartment, that is, in the cytoplasm. These interactions do not affect the intracellular localization of the different host proteins. The autophagy-related genes were transcriptionally modulated in PPRV-N-expressing cells. The expression of LC3B and SQSTM1/p62 was also modulated in PPRV-N-expressing cells, indicating the induction of autophagic activity. The formation of typical autophagosomes with double membranes was visualized by transmission electron microscopy in PPRV-N-expressing cells. Taken together, our findings provide evidence for the critical role of the N protein of the PPR virus in the induction of autophagy, which is likely to be mediated by PI3K complex-I of the host.

Peste des Petits Ruminants Virus Upregulates STING to Activate ATF6-Mediated Autophagy

Peste des petits ruminants virus (PPRV) infection leads to autophagy, and the molecular mechanisms behind this phenomenon are unclear. Here, we demonstrate that PPRV infection results in morphological changes of the endoplasmic reticulum (ER) and activation of activating transcription factor 6 (ATF6) of the ER stress unfolded protein response (UPR). Knockdown of ATF6 blocked the autophagy process, suggesting ATF6 is necessary for PPRV-mediated autophagy induction. Further study showed that PPRV infection upregulates expression of the ER-anchored adaptor protein stimulator of interferon genes (STING), which is well-known for its pivotal roles in restricting DNA viruses. Knockdown of STING suppressed ATF6 activation and autophagy induction, implying that STING functions upstream of ATF6 to induce autophagy. Moreover, the STING-mediated autophagy response originated from the cellular pattern recognition receptor melanoma differentiation-associated gene 5 (MDA5). The absence of MDA5 abolished the upregulation of STING and the activation of autophagy. The deficiency of autophagy-related genes (ATG) repressed the autophagy process and PPRV replication, while it had no effect on MDA5 or STING expression. Overall, our work revealed that MDA5 works upstream of STING to activate ATF6 to induce autophagy. IMPORTANCEPPRV infection induces cellular autophagy; however, the intracellular responses and signaling mechanisms that occur upon PPRV infection are obscure, and whether innate immune responses are linked with autophagy to regulate viral replication is largely unknown. Here, we uncovered that the innate immune sensor MDA5 initiated the signaling cascade by upregulating STING, which is best known for its role in anti-DNA virus infection by inducing interferon expression. We first provide evidence that STING regulates PPRV replication by activating the ATF6 pathway of unfolded protein responses (UPRs) to induce autophagy. Our results revealed that in addition to mediating responses to foreign DNA, STING can cross talk with MDA5 to regulate the cellular stress response and autophagy induced by RNA viruses; thus, STING works as an adaptor protein for cellular stress responses and innate immune responses. Modulation of STING represents a promising approach to control both DNA and RNA viruses.

A Morbillivirus Infection Shifts DC Maturation Toward a Tolerogenic Phenotype to Suppress T Cell Activation

Viruses have evolved numerous strategies to impair immunity so that they can replicate more efficiently. Among those, the immunosuppressive effects of morbillivirus infection can be particularly problematic, as they allow secondary infections to take hold in the host, worsening disease prognosis. In the present work, we hypothesized that the highly contagious morbillivirus peste des petits ruminants virus (PPRV) could target monocytes and dendritic cells (DC) to contribute to the immunosuppressive effects produced by the infection. Monocytes isolated from healthy sheep, a natural host of the disease, were able be infected by PPRV and this impaired the differentiation and phagocytic ability of immature monocyte-derived DC (MoDC). We also assessed PPRV capacity to infect differentiated MoDC. Ovine MoDC could be productively infected by PPRV, and this drastically reduced MoDC capacity to activate allogeneic T cell responses. Transcriptomic analysis of infected MoDC indicated that several tolerogenic DC signature genes were upregulated upon PPRV infection. Furthermore, PPRV-infected MoDC could impair the proliferative response of autologous CD4⁺ and CD8⁺ T cell to the mitogen concanavalin A (ConA), which indicated that DC targeting by the virus could promote immunosuppression. These results shed new light on the mechanisms employed by morbillivirus to suppress the host immune responses. IMPORTANCE Morbilliviruses pose a threat to global health given their high infectivity. The morbillivirus peste des petits ruminants virus (PPRV) severely affects small-ruminant-productivity and leads to important economic losses in communities that rely on these animals for subsistence. PPRV produces in the infected host a period of severe immunosuppression that opportunistic pathogens exploit, which worsens the course of the infection. The mechanisms of PPRV immunosuppression are not fully understood. In the present work, we demonstrate that PPRV can infect professional antigen-presenting cells called dendritic cells (DC) and disrupt their capacity to elicit an immune response. PPRV infection promoted a DC activation profile that favored the induction of tolerance instead of the activation of an antiviral immune response. These results shed new light on the mechanisms employed by morbilliviruses to suppress the immune responses.

Extracellular vesicles derived from PPRV-infected cells enhance signaling lymphocyte activation molecular (SLAM) receptor expression and facilitate virus infection

Peste des petits ruminants virus (PPRV) is an important pathogen that seriously influences the productivity of small ruminants worldwide. PPRV is lymphotropic in nature and SLAM was identified as the primary receptor for PPRV and other Morbilliviruses. Many viruses have been demonstrated to engage extracellular vesicles (EVs) to facilitate their replication and pathogenesis. Here, we provide evidence that PPRV infection significantly induced the secretion levels of EVs from goat PBMC, and that PPRV-H protein carried in EVs can enhance SLAM receptor expression in the recipient cells via suppressing miR-218, a negative miRNA directly targeting SLAM gene. Importantly, EVs-mediated increased SLAM expression enhances PPRV infectivity as well as the expression of various cytokines related to SLAM signaling pathway in the recipient cells. Moreover, our data reveal that PPRV associate EVs rapidly entry into the recipient cells mainly through macropinocytosis pathway and cooperated with caveolin- and clathrin-mediated endocytosis. Taken together, our findings identify a new strategy by PPRV to enhance virus infection and escape innate immunity by engaging EVs pathway.

Peste des petitsruminants virus (PPRV) infection induces a transient but severe immunosuppression in the host, which threatens both small livestock and endangered susceptible wildlife populations in many countries. Despite extensive research, the mechanism underlying pathogenesis of PPRV infection remains elusive. Our data provide the first direct evidence that the EVs derived from PPRV-infected cells are involved in PPRV replication. In this study, the EVs derived from PPRV-infected goat PBMCs can enhance SLAM expression in the recipient cells, and more importantly, EVs-mediated increased SLAM expression enhances PPRV replication as well as the expression of various cytokines related to SLAM signaling pathway in the recipient cells. Taken together, our research has provided new insight into understanding the effect of EVs on PPRV replication and pathogenesis, and revealed a potential therapeutic target for antiviral intervention.

Research Progress on Emerging Viral Pathogens of Small Ruminants in China during the Last Decade

China is the country with the largest number of domestic small ruminants in the world. Recently, the intensive and large-scale sheep/goat raising industry has developed rapidly, especially in nonpastoral regions. Frequent trading, allocation, and transportation result in the introduction and prevalence of new pathogens. Several new viral pathogens (peste des petits ruminants virus, caprine parainfluenza virus type 3, border disease virus, enzootic nasal tumor virus, caprine herpesvirus 1, enterovirus) have been circulating and identified in China, which has attracted extensive attention from both farmers and researchers. During the last decade, studies examining the etiology, epidemiology, pathogenesis, diagnostic methods, and vaccines for these emerging viruses have been conducted. In this review, we focus on the latest findings and research progress related to these newly identified viral pathogens in China, discuss the current situation and problems, and propose research directions and prevention strategies for different diseases in the future. Our aim is to provide comprehensive and valuable information for the prevention and control of these emerging viruses and highlight the importance of surveillance of emerging or re-emerging viruses.

PPRV-Induced Autophagy Facilitates Infectious Virus Transmission by the Exosomal Pathway

Peste des petits ruminants virus (PPRV) is an important pathogen that seriously influences the productivity of small ruminants worldwide. We showed previously that PPRV induced sustained autophagy for their replication in host cells. Many studies have shown that exosomes released from virus-infected cells contain a variety of viral and host cellular factors that are able to modulate the recipient's cellular response and result in productive infection of the recipient host. Here, we show that PPRV infection results in packaging of the viral genomic RNA and partial viral proteins into exosomes of Vero cells and upregulates exosome secretion. We provide evidence showing that the exosomal viral cargo can be transferred to and establish productive infection in a new target cell. Importantly, our study reveals that PPRV-induced autophagy enhances exosome secretion and exosome-mediated virus transmission. Additionally, our data show that TSG101 may be involved in the sorting of the infectious PPRV RNA into exosomes to facilitate the release of PPRV through the exosomal pathway. Taken together, our results suggest a novel mechanism involving autophagy and exosome-mediated PPRV intercellular transmission. IMPORTANCE Autophagy plays an important role in PPRV pathogenesis. The role of exosomes in viral infections is beginning to be appreciated. The present study examined the role of autophagy in secretion of infectious PPRV from Vero cells. Our data provided the first direct evidence that ATG7-mediated autophagy enhances exosome secretion and exosome-mediated PPRV transmission. TSG101 may be involved in the sorting of the infectious PPRV RNA genomes into exosomes to facilitate the release of PPRV through the exosomal pathway. Inhibition of PPRV-induced autophagy or TSG101 expression could be used as a strategy to block exosome-mediated virus transmission.

Inhibition of eIF2α Phosphorylation by Peste des Petits Ruminant Virus Phosphoprotein Facilitates Viral Replication

Peste des petits ruminant virus (PPRV) causes a highly contagious disease in small ruminants. The molecular mechanism of PPRV replication and its interactions with hosts are poorly studied. In other paramyxoviruses, the viral phosphoprotein (P) has been associated with multiple functions for key biological processes such as the regulation of transcription, translation, and the control of cell cycle. Phosphorylation of the α subunit of eukaryotic initiation factor 2 (eIF2α) is an important process for gene regulation in host cells under stress, including viral infection. In the present study, molecular mechanisms associated with PPRV replication and viral interaction with host cells were investigated. We describe the ability of PPRV to dephosphorylate eIF2α and the potential of PPRV P protein to induce the host cellular growth arrest DNA damage protein (GADD34), which is known to be associated with eIF2α dephosphorylation. Furthermore, we observed that PPRV P protein alone could block PERK/eIF2α phosphorylation. We speculate that PPRV exploits eIF2α dephosphorylation to facilitate viral replication and that PPRV P protein is involved in this molecular mechanism. This work provides new insights into further understanding PPRV pathobiology and its viral/host interactions.

Antiviral responses of ATG13 to the infection of peste des petits ruminants virus through activation of interferon response

Not only are autophagy-related (ATG) proteins the essential orchestrators of the autophagy machinery, but also they regulate many other cellular pathways. Here, we demonstrated that ATG13 exerted an obviously antiviral activity against the infection of peste des petits ruminants virus (PPRV) in cell culture model. We found that PPRV infection or the treatment with interferon (IFN) against PPRV infection significantly induced ATG13 expression. Mechanistically, ATG13 stimulated interferon expression and the subsequent activation of the JAK-STAT cascade. These activations triggered the transcription of interferon-stimulated genes (ISGs) to exert antiviral activity. Conversely, the loss of ATG13 significantly attenuated the potency of RIG-IN in activating IFN responses. In summary, we have demonstrated that basal ATG13 was involved in host antiviral activities against PPRV infection and the over-expression of ATG13 activated IFN production to inhibit PPRV replication in an unconventional fashion.

Transcriptional Profiles of Murine Bone Marrow-Derived Dendritic Cells in Response to Peste des Petits Ruminants Virus

Background: Peste des petits ruminants virus (PPRV) is the causative agent of PPR, which can cause an acute, highly contagious and fatal disease of sheep and goats, resulting in significant economic losses for commercial animal husbandry due to its high mortality and morbidity. As professional antigen-presenting cells, dendritic cells (DCs) play a unique role in innate immunity. This study aimed to gain a deeper understanding of the transcriptional response of bone marrow-derived dendritic cells (BMDCs) stimulated with PPRV. Results: Transcriptional profiling was performed using RNA sequencing. Herein, we reported that compared to untreatedBMDCs, 4492 differentially expressed genes (DEGs) were identified following PPRV stimulation, out of these DEGs 2311 were upregulated and 2181 were downregulated, respectively. A total of three gene ontology (GO) term clusters of biological process, cell component and molecular function were significantly enriched in 963 GO terms in the PPRV-stimulated BMDCs. These GO clusters were related to inflammatory response, cell division and vacuole, anchoring junction, positive regulation of cellular component and nucleoside binding. Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways of DEGs were enriched in a chemokine signaling pathway, protein processing in endoplasmic reticulum, cell cycle and mTOR signaling pathway. Additionally, identified DEGs of BMDCs were further validated by qRT-PCR and the results were in accordance with the change of the genes. This study suggested the effects of PPRV stimulation on the maturation and function of BMDCs. Conclusion: We found that the dramatic BMDCs transcriptome changes triggered were predominantly related to an inflammatory response and chemokine signaling pathway.

MicroRNA-218 Regulates Signaling Lymphocyte Activation Molecular (SLAM) Mediated Peste des Petits Ruminants Virus Infectivity in Goat Peripheral Blood Mononuclear Cells

Peste des petits ruminants virus (PPRV) has emerged as a significant threat to the productivity of small ruminants worldwide. SLAM was identified as the primary receptor for PPRV and other Morbilliviruses, although the regulation of SLAM expression is not yet fully understood. In this study, we revealed a novel mechanism by which PPRV upregulates its receptor SLAM expression and thereby benefits its replication via suppressing miR-218, a novel negative miRNA directly targeting SLAM gene. We demonstrated that PPRV infection downregulates miR-218, which in turn enhances SLAM expression on the surface of goat peripheral blood mononuclear cells (PBMCs), thus promoting PPRV replication. Since SLAM signaling may modulate the immune responses induced by PPRV infection, we further examined the effect of SLAM expression on the production of various cytokines by PBMCs in the absence or presence of PPRV. We demonstrated that miR-218-mediated SLAM expression modulates the expression of IFN-γ, TNF-α, and IL-10, importantly, these modulatory effects were enhanced in the presence of PPRV infection. Furthermore, our data clearly showed that PPRV H protein is sufficient to regulate miR-218-mediated SLAM expression. Taken together, our results suggest a novel mechanism involving post-transcriptional regulation of SLAM receptor expression on goat PBMCs during PPRV infection.

Autophagy induction by the pathogen receptor NECTIN4 and sustained autophagy contribute to peste des petits ruminants virus infectivity

Macroautophagy/autophagy is an essential cellular response in the fight against intracellular pathogens. Although some viruses can escape from or utilize autophagy to ensure their own replication, the responses of autophagy pathways to viral invasion remain poorly documented. Here, we show that peste des petits ruminants virus (PPRV) infection induces successive autophagic signalling in host cells via distinct and uncoupled molecular pathways. Immediately upon invasion, PPRV induced a first transient wave of autophagy via a mechanism involving the cellular pathogen receptor NECTIN4 and an AKT-MTOR-dependent pathway. Autophagic detection showed that early PPRV infection not only increased the amounts of autophagosomes and LC3-II but also downregulated the phosphorylation of AKT-MTOR. Subsequently, we found that the binding of viral protein H to NECTIN4 ultimately induced a wave of autophagy and inactivated the AKT-MTOR pathway, which is a critical step for the control of infection. Soon after infection, new autophagic signalling was initiated that required viral replication and protein expression. Interestingly, expression of IRGM and HSPA1A was significantly upregulated following PPRV replication. Strikingly, knockdown of IRGM and HSPA1A expression using small interfering RNAs impaired the PPRV-induced second autophagic wave and viral particle production. Moreover, IRGM-interacting PPRV-C and HSPA1A-interacting PPRV-N expression was sufficient to induce autophagy through an IRGM-HSPA1A-dependent pathway. Importantly, syncytia formation could facilitate sustained autophagy and the replication of PPRV. Overall, our work reveals distinct molecular pathways underlying the induction of self-beneficial sustained autophagy by attenuated PPRV, which will contribute to improving the use of vaccines for therapy.

Abbreviations: ACTB: actin beta; ANOVA: analysis of variance; ATG: autophagy-related; BECN1: beclin 1; CDV: canine distemper virus; Co-IP: coimmunoprecipitation; FIP: fusion inhibitory peptide; GFP: green fluorescent protein; GST: glutathione S-transferase; HMOX1: heme oxygenase 1; hpi: hours post infection; HSPA1A: heat shock protein family A (Hsp70) member 1A; HSP90AA1: heat shock protein 90 kDa alpha (cytosolic), class A member 1; IFN: interferon; IgG: immunoglobulin G; INS: insulin; IRGM: immunity related GTPase M; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MeV: measles virus; MOI: multiplicity of infection; MTOR: mechanistic target of rapamycin kinase; PI3K: phosphoinositide-3 kinase; PIK3C3: phosphatidylinositol 3-kinase catalytic subunit type 3; SDS: sodium dodecyl sulfate; siRNA: small interfering RNA; SQSTM1/p62: sequestosome 1; UV: ultraviolet.

Proteomic analysis of murine bone marrow derived dendritic cells in response to peste des petits ruminants virus

Peste des petits ruminants virus (PPRV) poses a great threat to livestock husbandry, especially goat farming due to its high mortality and morbidity. Dendritic cells (DCs), as the principal stimulators of naive Th cells were widely used in antigen processing and presenting. In the previous study, we tested the effects of PPRV on murine bone marrow derived dendritic cells (BMDCs) including surface markers and cytokines. While the aim of this study is to detect the proteomic profile of BMDCs stimulated with PPRV towards key proteins involved in. Following PPRV stimulation, 110 differentially expressed proteins (DEPs) were identified through iTRAQ labelling with LC-MS/MS approach, of which 94 DEPs were up-regulated and 16 DEPs were down-regulated, respectively. Among them 15 out of 110 DGPs were related to innate immune system, three were involved in cell apoptosis, RPS15a and Smox were related to translation of viral mRNA. Additionally, western blot analysis showed identical results to iTRAQ analysis. There will be profound significance for understanding antigen-presenting of BMDCs after stimulation with PPRV.

Autophagy enhances the replication of Peste des petits ruminants virus and inhibits caspase-dependent apoptosis in vitro

Peste des petits ruminants (PPR) is an acute and highly contagious disease in small ruminants that causes significant economic losses in developing countries. An increasing number of studies have demonstrated that both autophagy and apoptosis are important cellular mechanisms for maintaining homeostasis, and they participate in the host response to pathogens. However, the crosstalk between apoptosis and autophagy in host cells during PPRV infection has not been clarified. In this study, autophagy was induced upon virus infection in caprine endometrial epithelial cells (EECs), as determined by the appearance of double- and single-membrane autophagy-like vesicles, LC3-I/LC3-II conversion, and p62 degradation. We also found that PPRV infection triggered a complete autophagic response, most likely mediated by the non-structural protein C and nucleoprotein N. Moreover, our results suggest that autophagy not only promotes the replication of PPRV in EECs but also provides a potential mechanism for inhibiting PPRV-induced apoptosis. Inhibiting autophagosome formation by wortmannin and knocking down the essential autophagic proteins Beclin-1 and ATG7 induces caspase-dependent apoptosis in EECs in PPRV infection. However, inhibiting autophagosome and lysosome fusion by NH₄Cl and chloroquine did not increase the number of apoptotic cells. Collectively, these data are the first to indicate that PPRV-induced autophagy inhibits caspase-dependent apoptosis and thus contributes to the enhancement of viral replication and maturity in host cells.

MicroRNA expression profiling of goat peripheral blood mononuclear cells in response to peste des petits ruminants virus infection

Peste des petits ruminants virus (PPRV) belongs to the genus Morbillivirus that causes an acute and highly contagious disease in goats and sheep. Virus infection can trigger the change in the cellular microRNA (miRNA) expression profile, which play important post-transcriptional regulatory roles in gene expression and can greatly influence viral replication and pathogenesis. Here, we employed deep sequencing technology to determine cellular miRNA expression profile in goat peripheral blood mononuclear cells (PBMC) infected with Nigeria 75/1 vaccine virus, a widely used vaccine strain for mass vaccination programs against Peste des petits ruminants. Expression analysis demonstrated that PPRV infection can elicit 316 significantly differentially expressed (DE) miRNA including 103 known and 213 novel miRNA candidates in infected PBMC at 24 hours post-infection (hpi) as compared with a mock control. Target prediction and functional analysis of these DEmiRNA revealed significant enrichment for several signaling pathways including TLR signaling pathways, PI3K-Akt, endocytosis, viral carcinogenesis, and JAK-STAT signaling pathways. This study provides a valuable basis for further investigation of the roles of miRNA in PPRV replication and pathogenesis.

Peste des Petits Ruminants Virus Enters Caprine Endometrial Epithelial Cells via the Caveolae-Mediated Endocytosis Pathway

Peste des petits ruminants virus (PPRV) causes an acute and highly contagious disease of sheep and goats and has spread with alarming speed around the world. The pathology of Peste des petits ruminants is linked to retrogressive changes and necrotic lesions in lymphoid tissues and epithelial cells. However, the process of PPRV entry into host epithelial cells remains largely unknown. Here, we performed a comprehensive study of the entry mechanism of PPRV into caprine endometrial epithelial cells (EECs). We clearly demonstrated that PPRV internalization was inhibited by chloroquine and ammonium chloride, which elevate the pH of various organelles. However, PPRV entry was not affected by chlorpromazine and knockdown of the clathrin heavy chain in EECs. In addition, we found that the internalization of PPRV was dependent on dynamin and membrane cholesterol and was suppressed by silencing of caveolin-1. Macropinocytosis did not play a role, but phosphatidylinositol 3-kinase (PI3K) was required for PPRV internalization. Cell type and receptor-dependent differences indicated that PPRV entry into caprine fetal fibroblast cells (FFCs) occurred via a different route. Taken together, our findings demonstrate that PPRV enters EECs through a cholesterol-dependent caveolae-mediated uptake mechanism that is pH-dependent and requires dynamin and PI3K but is independent of clathrin. This potentially provides insight into the entry mechanisms of other morbilliviruses.

Autophagy in Negative-Strand RNA Virus Infection

Autophagy is a homoeostatic process by which cytoplasmic material is targeted for degradation by the cell. Viruses have learned to manipulate the autophagic pathway to ensure their own replication and survival. Although much progress has been achieved in dissecting the interplay between viruses and cellular autophagic machinery, it is not well understood how the cellular autophagic pathway is utilized by viruses and manipulated to their own advantage. In this review, we briefly introduce autophagy, viral xenophagy and the interaction among autophagy, virus and immune response, then focus on the interplay between NS-RNA viruses and autophagy during virus infection. We have selected some exemplary NS-RNA viruses and will describe how these NS-RNA viruses regulate autophagy and the role of autophagy in NS-RNA viral replication and in immune responses to virus infection. We also review recent advances in understanding how NS-RNA viral proteins perturb autophagy and how autophagy-related proteins contribute to NS-RNA virus replication, pathogenesis and antiviral immunity.

Anti-inflammatory activity of cecropin-A2 from Musca domestica

This study aimed to investigate the anti-inflammatory activity of Musca domestica cecropin-A2 (Mdc-A2) toward Staphylococcus aureus (S. aureus) to learn more about their immunological functions. RAW264.7 cells were transfected with recombinant lentiviruses introduce pLEX-Mdc-A2into the RAW264.7 cell line (RAW-Mdc-A2). The RAW264.7 cell line with empty pLEX (RAW-pLEX) was produced in the same manner as a negative control. Real-time quantitative reverse transcription PCR (RT-PCR) was performed to analyze the mRNA expression of TNF-a, IL-1β, NFκB-1 and NFκB-2 in S. aureus-stimulated RAW-Mdc-A2 cells and RAW-pLEX cells in untreated cells and cells treated for 3 h, 6 h, 12 h and 24 h. RT-PCR was performed to analyze the mRNA expression of TNF-a, NFκB-1 and NFκB-2 stimulated by Lipoteichoic acid (LTA). Production of TNF-a was detected by enzyme-linked immunosorbent assay (ELISA). Colony counts were used to calculate the number of CFU per mL of cell culture supernatants. The results showed that compared to RAW-pLEX cells, stable transfection of Mdc-A2 in RAW264.7 cells stimulated by S. aureus significantly down-regulated the mRNA expression of TNF-a transcript variant 1 (TNF-a-tv-1) at 6 h and 12 h and the mRNA expression of TNF-a transcript variant 2 (TNF-a-tv-2) at 3 h, 6 h and 12 h. Compared to RAW-pLEX cells, stable transfection of Mdc-A2 in RAW264.7 cells stimulated by S. aureus significantly down-regulated the mRNA expression of IL-1β-T at 3 h, 6 h and 12 h as well as the mRNA expression of IL-1β at 3 h and 6 h. The expression and production of TNF-a and bacterial burden of cell culture supernatants were significantly down-regulated in RAW-Mdc-A2 cells stimulated by S. aureus, and the expression and production of TNF-a were significantly down-regulated in RAW-Mdc-A2 cells stimulated by LTA. Compared to RAW-pLEX cells, stable transfection of Mdc-A2 in RAW264.7 cells stimulated by S. aureus significantly down-regulated the mRNA expression of NFκB-1 at 3 h, 6 h and 12 h as well as the mRNA expression of NFκB-2 at 6 h. Additionally, stable transfection of Mdc-A2 in RAW264.7 cells stimulated by LTA significantly down-regulated the mRNA expression of NFκB-1. In conclusion, Mdc-A2 possesses potent anti-inflammatory activity and potent antimicrobial activity. Additionally, Mdc-A2 may interact with LTA and execute strong anti-inflammatory activity by blocking the activation of NF-κB signaling pathways.

Immunohistochemical detection of autophagy-related microtubule-associated protein 1 light chain 3 (LC3) in the cerebellums of dogs naturally infected with canine distemper virus

We investigated the expression of microtubule-associated protein 1 light chain 3 (LC3) protein in the cerebellums of dogs infected with canine distemper virus (CDV) using immunohistochemistry to detect autophagy. The cerebellums of 20 dogs infected with CDV were used. Specimens showing demyelination of white matter were considered to have an acute infection, whereas specimens showing signs of severe perivascular cuffing and demyelination of white matter were classified as having chronic CDV. Cerebellar sections were immunostained with CDV and LC3 antibodies. The cytoplasm of Purkinje cells, granular layer cells, motor neurons in large cerebellar ganglia and some neurons in white matter were positive for the LC3 antibody in both the control and CDV-infected dogs. In the infected cerebellums, however, white matter was immunostained more intensely, particularly the neurons and gemistocytic astrocytes in the demyelinated areas, compared to controls. Autophagy also was demonstrated in CDV-positive cells using double immunofluorescence staining. Our findings indicate that increased autophagy in the cerebellum of dogs naturally infected with CDV may play a role in transferring the virus from cell to cell.

Mixed infection of peste des petits ruminants virus (PPRV) and other respiratory viruses in dromedary camels in Sudan, an abattoir study

This study was intended to determine the role played by peste des petits ruminants (PPR) in causing respiratory infections in camels and its association with other respiratory viruses. A total of 474 lung specimens showing pneumonia were collected from clinically healthy camels in slaughterhouses at five different areas in Sudan. Using immunocapture ELISA (IcELISA), 214 specimens (45.1 %) were found to be positive for PPR antigen. The highest prevalence was found in central Sudan (59.9 %) then northern Sudan (56.6 %) and eastern Sudan (26.6 %). Parainfluenza virus 3 (PIV 3), respiratory syncytial virus (RSV), bovine herpes virus-1 (BHV-1), bovine viral diarrhea (BVD), and adenovirus were detected in 4.4, 2.9, 2.0, 9.0, and 1.3 % of the specimens, respectively. PPR antigen was found in about 50 % of specimens that showed positive result for other viral antigens. Twenty-five of 28 BVD, 15 of 16 PIV3, 8 of 12 RSV, 4 of 4 adenovirus, and 4 of 5 BHV-1 were found in association with other respiratory antigens. Results revealed the existence of PPRV infection in dromedary camels in Sudan and present evidence for mixed virus infection, suggesting that respiratory infections in camels might be exacerbated by PPRV.

Preparation and characterization of a stable BHK-21 cell line constitutively expressing the Schmallenberg virus nucleocapsid protein

Schmallenberg virus (SBV) is a newly emerged orthobunyavirus that predominantly infects livestock such as cattle, sheep, and goats. Its nucleocapsid (N) protein is an ideal target antigen for SBV diagnosis. In this study, a stable BHK-21 cell line, BHK-21-EGFP-SBV-N, constitutively expressing the SBV N protein was obtained using a lentivector-mediated gene transfer system combined with puromycin selection. To facilitate the purification of recombinant SBV N protein, the coding sequence for a hexa-histidine tag was introduced into the C-terminus of the SBV N gene during construction of the recombinant lentivirus vector pLV-EGFP-SBV-N. The BHK-21-EGFP-SBV-N cell line was demonstrated to spontaneously emit strong enhanced green fluorescent protein (EGFP) signals that exhibited a discrete punctate distribution throughout the cytoplasm. SBV N mRNA and protein expression in this cell line were detected by real-time RT-PCR and western blot, respectively. The expressed recombinant SBV N protein carried an N-terminal EGFP tag, and was successfully purified using Ni-NTA agarose by means of its C-terminal His tag. The purified SBV N protein could be recognized by SBV antisera and an anti-SBV monoclonal antibody (mAb) 2C8 in an indirect enzyme-linked immunosorbent assay and western blot analyses. Indirect immunofluorescence assays further demonstrated that the stable cell line reacts with SBV antisera and mAb 2C8. These results suggest that the generated cell line has the potential to be used in the serological diagnosis of SBV.

Expression and purification of the nucleocapsid protein of Schmallenberg virus, and preparation and characterization of a monoclonal antibody against this protein

Schmallenberg virus (SBV) is a novel orthobunyavirus that primarily infects ruminants such as cattle, sheep and goats. The nucleocapsid (N) protein of SBV has been shown to be an ideal target antigen for serological detection. To prepare a monoclonal antibody (mAb) against the N protein, the full-length coding sequence of the SBV N gene was cloned into pET-28a-c(+) and pMAL-c5X vectors to generate two recombinant plasmids, which were expressed in Escherichia coli BL21 as histidine (His)-tagged (His-SBV-N) and maltose-binding protein (MBP)-tagged (MBP-SBV-N) fusion proteins, respectively. After affinity purification of His-SBV-N with Ni-NTA agarose and MBP-SBV-N with amylose resin, His-SBV-N was used to immunize BALB/c mice, while MBP-SBV-N was utilized to screen for mAb-secreting hybridomas. Six hybridoma cell lines stably secreting mAbs against N were obtained. Clone 2C8 was selected for further study because of its rapid growth characteristics in vitro and good reactivity with recombinant SBV N proteins in enzyme-linked immunosorbent assays. The epitope recognized by 2C8 is located at amino acids 51-76 of the SBV N protein. Western blot analyses showed that 2C8 reacts with both recombinant SBV N proteins and SBV isolates. It is also cross-reactive with the N proteins of genetically related Shamonda, Douglas and Akabane viruses, but not with the Rift Valley fever virus N protein. The successful preparation of recombinant N proteins and mAbs provides valuable materials that can be used in the serological diagnosis of SBV.