Muscovy duck reovirus σNS protein triggers autophagy enhancing virus replication

Infection with novel duck reovirus induces stress granule and methylation-mediated host translational shutoff in Muscovy ducklings

The recently identified novel duck reovirus (NDRV) is a waterfowl reovirus that can seriously harm or kill various waterfowl species. However, how NDRV interacts with host cells in Muscovy ducklings beyond the typical pathogenesis resulting from a viral infection is unknown. The current study examined the global translation efficiency of the Fabricius bursa of Muscovy ducklings infected with NDRV HN10 using mass spectrometry and ribosome footprint sequencing. Protein-protein interactions were investigated using immunogold labeling, transmission electron microscopy, and immunocytochemistry. An analysis of the relationship between m6A and translation was performed using RNA immunoprecipitation and m6A methylation immunoprecipitation. We found that both in vivo and in vitro, the translation efficiency of RNA modified with m6A could be significantly reduced by σB, a structural protein component of NDRV HN10. Furthermore, σB might simultaneously interact with the stress granule complex CAPRIN1 and G3BP1 and the m6A reader protein YTHDF1/3. Significant overlap was observed between m6A-modified and G3BP1-enriched RNA, indicating that granule stress could capture m6A-methylated RNA. We discovered a new function for NDRV HN10 in translational shutoff by recruiting m6A-modified RNA into stress granules located in the Fabricius bursa of Muscovy ducklings.

Simultaneous detection and differentiation of classical Muscovy duck reovirus and goose-origin Muscovy duck reovirus by RT-qPCR assay with high-resolution melting analysis

Introduction

Classical Muscovy duck reovirus (C-MDRV) and goose-origin Muscovy duck reovirus (Go-MDRV) infections cause "Liver white-spots disease" in Muscovy duckling and gosling. It is difficult to differentiate the infections caused by C-MDRV and Go-MDRV using conventional serological methods.

Methods

Specific primers were designed and synthesized according to σNS and λA nucleotide sequences of C-MDRV and Go-MDRV, respectively. The PCR amplified products were cloned into the pMD-18-T vector. The recombinant plasmid DNA was used to establish an SYBR Green І based duplex real-time PCR assay for the simultaneous detection and differentiation of C-MDRV and Go-MDRV using high-resolution melting (HRM) analysis. The specificity, sensitivity, and repeatability of the methodology were examined based on the optimization of the reaction system and amplification conditions.

Results

C-MDRV and Go-MDRV were identified by their distinctive melting temperatures with 84.50 ± 0.25°C for C-MDRV and 87.50 ± 0.20°C for Go-MDRV, respectively. The amplifications were specific, and other non-targeted waterfowl viruses employed in this study did not show normalized melting peaks. The intra- and inter-assay coefficients of variations were between 0.05 and 1.83%, demonstrating good repeatability. The detection limits of this assay were 51.4 copies·μl-1 for C-MDRV and 61.8 copies·μl-1 for Go-MDRV, respectively. A total of 45 clinical samples were tested by RT-qPCR, with positive rates of 15.56% for C-MDRV and 22.22% for Go-MDRV, without co-infections.

Discussion

These results suggest that this duplex RT-qPCR method is highly sensitive, specific, and reproducible. The HRM assay established in this study provides a powerful tool for the differential detection and epidemiological investigation of C-MDRV and Go-MDRV.

A small protein encoded by PCBP1-AS1 is identified as a key regulator of influenza virus replication via enhancing autophagy

Many annotated long noncoding RNAs (lncRNAs) contain small open reading frames (sORFs), some of which have been demonstrated to encode small proteins or micropeptides with fundamental biological importance. However, functions of lncRNAs-encoded small proteins or micropeptides in viral pathogenesis remain largely unexplored. Here, we identified a 110-amino acid small protein as a key regulator of influenza A virus (IAV) replication. This small protein that we call PESP was encoded by the putative lncRNA PCBP1-AS1. It was observed that both PCBP1-AS1 and PESP were significantly upregulated by IAV infection. Furthermore, they were markedly induced by treatment with either type I or type III interferon. Overexpression of either PCBP1-AS1 or PESP alone significantly enhanced IAV replication. In contrast, shRNA-mediated knockdown of PCBP1-AS1 or CRISPR/Cas9-mediated knockout of PESP markedly inhibited the viral production. Moreover, the targeted deletion or mutation of the sORF within the PCBP1-AS1 transcript, which resulted in the disruption of PESP expression, significantly diminished the capacity of PCBP1-AS1 to enhance IAV replication, underscoring the indispensable role of PESP in the facilitation of IAV replication by PCBP1-AS1. Interestingly, overexpression of PESP enhanced the IAV-induced autophagy by increasing the expression of ATG7, an essential autophagy effector enzyme. We also found that the 7-22 amino acids at the N-terminus of PESP were crucial for its functionality in modulating ATG7 expression and action as an enhancer of IAV replication. Additionally, HSP90AA1, a protein identified previously as a facilitator of autophagy, was found to interact with PESP, resulting in the stabilization of PESP and consequently an increase in the production of IAV. These data reveal a critical lncRNA-encoded small protein that is induced and exploited by IAV during its infection, and provide a significant insight into IAV-host interaction network.

Molecular characterization, complete genome sequencing, and pathogenicity of Novel Duck Reovirus from South Coastal Area in China

Novel Duck Reovirus (NDRV) that has been found throughout the world in waterfowl, and it has been extensively described. Here, we report the complete genome sequence of a NDRV strain isolated in China called NDRV YF10. This strain was collected from 87 samples with infected ducks in South Coastal Area. The NDRV genome consists of 23,419 bp. With the assistance of computer analysis, the promoter and terminator of each gene segment and 10 viral genes segments were identified, which encode polypeptides ranging from 98 to 1,294 amino acids. All gene fragments of this virus strain were determined and compared to previously reported strains, revealing genetic variation with similarity rates ranging from 96 to 99% for each gene segment. Each gene segment formed 2 host-associated groups, the waterfowl-derived reovirus and the avian-derived reovirus, except for the S1 gene segment, which was closely related to ARV evolution and formed a host-independent subcluster. This difference may be due to Avian Reovirus (ARV) evolving in a host-dependent manner. In order to evaluate the pathogenicity of YF10, a novel isolated strain of NDRV was tested in 2 types of ducks. It was observed that the YF10 isolated strain exhibits varying degrees of virulence, highlighting the potential risk posed to different types of ducks. In conclusion, our findings emphasize the importance of epidemiology studies, molecular characterization, and prevention of NDRV in waterfowl.

Orf virus induces complete autophagy to promote viral replication via inhibition of AKT/mTOR and activation of the ERK1/2/mTOR signalling pathway in OFTu cells

Orf virus (ORFV) is the causative agent of contagious ecthyma, which is an important zoonotic pathogen with a widespread distribution affecting sheep, goats and humans. Our previous research showed that autophagy can be induced in host cells by ORFV infection. However, the exact mechanism of ORFV-induced autophagy remains unknown. In this study, we investigated the underlying mechanisms of autophagy induced by ORFV in OFTu cells and the impact of autophagy on ORFV replication. By using specific autophagy inhibitors and activators, Western blotting, immunofluorescence and transmission electron microscopy imaging, we confirmed that ORFV infection triggered intracellular autophagosome accumulation and the activation of autophagic flux. Moreover, ORFV-induced autophagic activity was found to rely on an increase in the phosphorylation of tuberous sclerosis complex 2 (TSC2) and a decrease in the phosphorylation of mammalian target of rapamycin (mTOR), which is mediated by the suppression of the PI3K/AKT/mTOR signalling pathway and activation of the ERK1/2/mTOR signalling pathway. Furthermore, we investigated the role of mTOR-mediated autophagy during ORFV replication using pharmacological agents and demonstrated that ORFV-induced autophagy correlated positively with viral replication. Taken together, our data reveal the pathways of ORFV-induced autophagy and the impact of autophagy on ORFV replication, providing new insights into ORFV pathogenesis.

Grass Carp Reovirus triggers autophagy enhancing virus replication via the Akt/mTOR pathway

Autophagy impacts the replication cycle of many viruses. Grass Carp Reovirus (GCRV) is an agent that seriously affects the development of the grass carp aquaculture industry. The role of autophagy in GCRV infection is not clearly understood. In this study, we identified that GCRV infection triggered autophagy in CIK cells, which was demonstrated by transmission electron microscopy, the conversion of LC3B I to LC3B II and the level of autophagy substrate p62. Furthermore, we found that GCRV infection activated Akt-mTOR signaling pathway, and the conversion of LC3B I to LC3B II was increased by inhibiting mTOR with rapamycin (Rap) but decreased by activating Akt with insulin. We then assessed the effects of autophagy on GCRV replication. We found that inducing autophagy with Rap promoted GCRV proliferation but inhibiting autophagy with 3 MA or CQ inhibited GCRV replication in CIK cells. Moreover, it was found that enhancing Akt-mTOR activity by insulin, GCRV VP7 protein and viral titers of GCRV were decreased. Collectively, these results indicated that GCRV infection induced autophagy involved in GCRV replication via the Akt-mTOR signal pathway. Thus, new insights into GCRV pathogenesis and antiviral treatment strategies are provided.

African Swine Fever Virus: A Review

African swine fever (ASF) is a viral disease with a high fatality rate in both domestic pigs and wild boars. ASF has greatly challenged pig-raising countries and also negatively impacted regional and national trade of pork products. To date, ASF has spread throughout Africa, Europe, and Asia. The development of safe and effective ASF vaccines is urgently required for the control of ASF outbreaks. The ASF virus (ASFV), the causative agent of ASF, has a large genome and a complex structure. The functions of nearly half of its viral genes still remain to be explored. Knowledge on the structure and function of ASFV proteins, the mechanism underlying ASFV infection and immunity, and the identification of major immunogenicity genes will contribute to the development of an ASF vaccine. In this context, this paper reviews the available knowledge on the structure, replication, protein function, virulence genes, immune evasion, inactivation, vaccines, control, and diagnosis of ASFV.

Radix Actinidia chinensis Suppresses Renal Cell Carcinoma Progression: Network Pharmacology Prediction and In Vivo Experimental Validation

Background

Renal cell carcinoma (RCC) is a frequent disease with limited curative methods. This study is aimed at investigating the role and mechanism of Radix Actinidia chinensis (RAC) on RCC.

Methods

The ingredients, target, and crucial pathways of RAC in RCC therapy were analyzed by network pharmacology. Then, an RCC animal model was established by subcutaneously injecting A498 cell suspension to BALB/c nude mice. After 1 week, the mice in the RAC-L/M/H groups were administered with RAC at 5, 10, and 20 mg/kg/d, respectively. The histopathology of the tumor was evaluated. The contents of tumor inflammatory cytokines and serum oxidative stress factors were detected by ELISA. The apoptosis of tumor tissues was assessed by TUNEL staining. The expressions of apoptosis-, proliferate-, autophagy-, and MAPK-related proteins were measured.

Results

There were 13 active ingredients, and 20 RCC-relevant targets were selected from RAC; KEGG pathway indicated that these targets were enriched in the PI3K/AKT/mTOR and MAPK pathway. In in vivo experiments, RAC not only obviously damaged tumor cells and decreased the release of inflammatory cytokines and oxidative stress factors but also enhanced the apoptosis of the tumor cell in RCC mice. Besides, the expressions of apoptosis-, proliferate-, autophagy-, PI3K/AKT/mTOR path-, and MAPK path-related proteins were all affected by RAC.

Conclusion

RAC attenuated RCC by regulating inflammation response, oxidative stress, apoptosis, proliferation, and autophagy, and its effects were partly linked to the PI3K/AKT/mTOR and MAPK pathway, which indicated that RAC may be a candidate drug for RCC.

The Multi-Faceted Role of Autophagy During Animal Virus Infection

Autophagy is a process of degradation to maintain cellular homeostatic by lysosomes, which ensures cellular survival under various stress conditions, including nutrient deficiency, hypoxia, high temperature, and pathogenic infection. Xenophagy, a form of selective autophagy, serves as a defense mechanism against multiple intracellular pathogen types, such as viruses, bacteria, and parasites. Recent years have seen a growing list of animal viruses with autophagy machinery. Although the relationship between autophagy and human viruses has been widely summarized, little attention has been paid to the role of this cellular function in the veterinary field, especially today, with the growth of serious zoonotic diseases. The mechanisms of the same virus inducing autophagy in different species, or different viruses inducing autophagy in the same species have not been clarified. In this review, we examine the role of autophagy in important animal viral infectious diseases and discuss the regulation mechanisms of different animal viruses to provide a potential theoretical basis for therapeutic strategies, such as targets of new vaccine development or drugs, to improve industrial production in farming.

Autophagy in farm animals: current knowledge and future challenges

Autophagy (a process of cellular self-eating) is a conserved cellular degradative process that plays important roles in maintaining homeostasis and preventing nutritional, metabolic, and infection-mediated stresses. Surprisingly, little attention has been paid to the role of this cellular function in species of agronomical interest, and the details of how autophagy functions in the development of phenotypes of agricultural interest remain largely unexplored. Here, we first provide a brief description of the main mechanisms involved in autophagy, then review our current knowledge regarding autophagy in species of agronomical interest, with particular attention to physiological functions supporting livestock animal production, and finally assess the potential of translating the acquired knowledge to improve animal development, growth and health in the context of growing social, economic and environmental challenges for agriculture.Abbreviations: AKT: AKT serine/threonine kinase; AMPK: AMP-activated protein kinase; ASC: adipose-derived stem cells; ATG: autophagy-related; BECN1: beclin 1; BNIP3: BCL2 interacting protein 3; BVDV: bovine viral diarrhea virus; CALCOCO2/NDP52: calcium binding and coiled-coil domain 2; CMA: chaperone-mediated autophagy; CTSB: cathepsin B; CTSD: cathepsin D; DAP: Death-Associated Protein; ER: endoplasmic reticulum; GFP: green fluorescent protein; Gln: Glutamine; HSPA8/HSC70: heat shock protein family A (Hsp70) member 8; IF: immunofluorescence; IVP: in vitro produced; LAMP2A: lysosomal associated membrane protein 2A; LMS: lysosomal membrane stability; MAP1LC3/LC3: microtubule associated protein 1 light chain 3; MDBK: Madin-Darby bovine kidney; MSC: mesenchymal stem cells; MTOR: mechanistic target of rapamycin kinase; MTORC1: MTOR complex 1; NBR1: NBR1 autophagy cargo receptor; NDV: Newcastle disease virus; NECTIN4: nectin cell adhesion molecule 4; NOD1: nucleotide-binding oligomerization domain 1; OCD: osteochondritis dissecans; OEC: oviduct epithelial cells; OPTN: optineurin; PI3K: phosphoinositide-3-kinase; PPRV: peste des petits ruminants virus; RHDV: rabbit hemorrhagic disease virus; SQSTM1/p62: sequestosome 1; TEM: transmission electron microscopy.

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.

Muscovy duck reovirus promotes virus replication by inhibiting autophagy-lysosomal degradation pathway

Autophagy plays a momentous role in cellular responses against pathogens. However, the influence of the autophagy machinery on Muscovy duck reovirus (MDRV) infection is not yet confirmed. In this study, it was shown that MDRV infection significantly increased the number of autophagy-like vesicles in DF-1 cells under electron microscope and the LC3-I/LC3-II conversion, which was considered important indicators of autophagy. It was worth noting that the level of autophagy was positively correlated with MDRV replication. Further test results showed that MDRV-induced autophagy can promote virus replication in DF-1 cells, and both the envelope protein sigma A and non-structural protein sigma NS that play an important role in virus replication process can colocalize with the autophagosome marker molecule LC3-II by confocal immunofluorescence analysis. These results indicated that MDRV utilized the autophagosomes for replication. Through transfection of the dual fluorescent plasmid mcherry-EGFP-LC3 and fluorescence microscope observation, it was found that autophagosomes were more likely to fuse with lysosomes in MDRV-infected cells compared with the blank group. The phenomenon of pEGFP-LC3B fluorescent spot and LAMP1 co-localization appeared in MDRV infected cells, indicating that MDRV infection would promote the fusion of autophagosomes and the lysosomes. Conversely, accumulation of p62 was observed by immunoblotting, suggesting that autolysosomes does not exert effective degradation. MDRV infection triggered a incomplete autophagic response. Further studies found that the expression of LAMP1, a marker protein of late endosome/early lysosome, increased significantly in MDRV-infected cells, suggesting an increase in the number of immature lysosomes. In addition, the experiment detected the maturation of the lysosomal acid hydrolase Cathepsin D in the cells, and found that the expression of the 33 kDa mature form of Cathepsin D was significantly reduced after MDRV infection, indicating that MDRV inhibits the maturation of lysosomes. In general, MDRV infection induces autophagy of DF-1 cells, promotes the fusion of autophagosomes and lysosomes, inhibits autophagolysosome degradation, and promotes virus replication.

Aspirin and 5-Aminoimidazole-4-carboxamide Riboside Attenuate Bovine Ephemeral Fever Virus Replication by Inhibiting BEFV-Induced Autophagy

Recent study in our laboratory has demonstrated that BEFV-induced autophagy via activation of the PI3K/Akt/NF-κB and Src/JNK pathways and suppression of the PI3K-AKt-mTORC1 pathway is beneficial for virus replication. In the current study, we found that both aspirin and 5-aminoimidazole-4-carboxamide-1-β-riboside (AICAR) siginificantly attenuated virus replication by inhibiting BEFV-induced autophagy via suppressing the BEFV-activated PI3K/Akt/NF-κB and Src/JNK pathways as well as inducing reversion of the BEFV-suppressed PI3K-Akt-mTORC1 pathway. AICAR reversed the BEFV-activated PI3K/Akt/NF-κB and Src/JNK pathways at the early to late stages of infection and induced reversion of the BEFV-suppressed PI3K-AKt-mTORC1 pathway at the late stage of infection. Our findings reveal that inhibition of BEFV-induced autophagy by AICAR is independent of AMPK. Furthermore, we found that AICAR transcriptionally downregulates the ATG related genes ULK1, Beclin 1, and LC3 and enhances Atg7 degradation by the proteasome pathway. Aspirin suppresses virus replication by inhibiting BEFV-induced autophagy. It directly suppressed the NF-κB pathway and reversed the BEFV-activated Src/JNK pathway at the early stage of infection and reversed the BEFV-suppressed PI3K/Akt/mTOR pathway at the late stage of infection. The current study provides mechanistic insights into the effects of aspirin and AICAR on BEFV replication through suppression of BEFV-induced autophagy.

The genomic constellation of a novel duck reovirus strain associated with hemorrhagic necrotizing hepatitis and splenitis in Muscovy ducklings in Fujian, China

The complete sequence of a reovirus, strain NP03 associated with necrotic focus formation in the liver and spleen of Muscovy ducklings in Fujian Province, China in 2009, was determined and compared with sequences of other waterfowl and chicken-origin avian reoviruses (ARVs). Sequencing of the complete genomes of strain NP03 showed that they consisted of 23,418 bp and were divided into 10 segments, ranging from 1191 bp (S4) to 3959 bp (L1) in length, and all segments contained conserved sequences in the 5' non-coding region (GCUUUU) and 3' non-coding region (UCAUC). Pairwise sequence comparisons demonstrated that NP03 strain showed the highest similarity with novel waterfowl origin reoviruses (WRVs). The genome analysis revealed that the S1 segment of novel WRV is a tricistronic gene, encoding the overlapping open reading frames (ORFs) for p10, p18, and σC, similar to the ARV S1 gene, but distinct from classical WRV S4 genome segment, which contained two overlapping ORFs encoding p10 and σC. Phylogenetic analyses of the nucleotide sequences of all 10 segments revealed that NP03 strain was clustered together with other novel WRVs and were distinct from classical WRVs and chicken-origin ARVs. The analyses also showed possible intra-segmental reassortment events in the segments encoding λA, λB, μB, μNS, σA, and σNS between novel and classical WRVs. Potential recombination events detection in segment L1 suggests that NP03 strain may be recombinants of novel WRVs. Based on our genetic analyses, multiple reassortment events, intra-segmental recombination, and accumulation of point mutations have possibly contributed to the emergence of this novel genotype of WRV, identified in China.

A TaqMan-MGB real-time RT-PCR assay with an internal amplification control for rapid detection of Muscovy duck reovirus

A real-time reverse transcriptase-polymerase chain reaction (RT-PCR) for the detection of Muscovy duck reovirus (MDRV) RNA in clinical samples is described. The assay is based on TaqMan-MGB technology, consisting of two primers and one probe labeled with the reporter dye 6-carboxyfluorescein that binds selectively to the sigma B-protein gene of MDRV. This technique also includes an Internal Positive Control (IPC). The real-time RT-PCR assay was able to detect MDRVs, whereas other common waterfowl-origin viral pathogens were not recognised by the established oligonucleotide set, thus showing that the test was specific for MDRV. The sensitivity of the assay was 2.83 × 10¹ copies/μL and was 100 times higher than that of the conventional RT-PCR. The variation coefficients of intra-assay and inter-assay were less than 1.5% which verified sufficient repeatability of this assay. The use of β-actin mRNA as an IPC in order not to reduce the efficiency of the assay was adopted. The detection for 100 clinical samples showed that the positive rate of the established TaqMan-MGB real-time RT-PCR method was 87% (87/100), while the positive rate of the conventional RT-PCR was 83% (83/100), with the coincidence rate was 97.14%. Sensitivity and positive rate for clinical samples of TaqMan fluorescent quantitative RT-PCR were higher than conventional RT-PCR. The high specificity, sensitivity, and rapidity TaqMan-MGB real-time RT-PCR assay with the use of IPC to monitor for false negative results can make this method suitable for the pathogenic surveillance and epidemiological investigation of MDRV infection.

Genetic and pathogenic characteristics of newly emerging avian reovirus from infected chickens with clinical arthritis in China

In recent years, emerging avian reovirus (ARV) strains causing viral arthritis have become a challenge to the worldwide chicken industry, and were responsible for significant economic losses. In this study, we characterized emerging variant ARV strains and examined their genetic relationship and pathogenicity variation with reference strains. A total of 18 emerging variant ARV strains were isolated from tendon and capsular synovial fluid of broiler chickens with clinical cases of arthritis/tenosynovitis at commercial farms in China. Comparative analysis based on σC sequence showed that 4/18 isolates were in the same cluster (Cluster 1) as vaccine strains (S1133), whereas 14 of 18 isolates were in Clusters 2, 3, and 6. The field isolates shared a rather low identity (38.1 to 81.9%) with S1133 in Cluster 1, especially for those from Cluster 6 (38.1 to 67.2%). A higher ARV isolation rate was observed in chicken embryos (47/61) compared to cell culture (37/61) through PCR with a detection primer. A total of 3 isolates were selected to infect specific-pathogen-free (SPF) chickens, showing that the tested isolates, especially that from Cluster 6, displayed greater pathogenicity than S1133 strain, characterized by higher incidence. These findings suggest that the virulence of Chinese ARVs has been increasing rapidly in recent years, and the vaccine need to be updated correspondingly.

Classical Swine Fever Virus Infection Induces Endoplasmic Reticulum Stress-Mediated Autophagy to Sustain Viral Replication in vivo and in vitro

Endoplasmic reticulum (ER) stress-mediated autophagy plays significant roles in replication and pathogenesis of many animal viruses. However, the relationship between ER stress, autophagy, and viral replication during in vivo and in vitro infection of classical swine fever virus (CSFV) remains unclear. In this study, we established a pig model for CSFV infection and found that viral loads of CSFV differed in 10 kinds of infected organs, and that the degree of tissue lesions was to some extent positively correlated with CSFV replication in vivo. Next, we found that CSFV infection not only induced ER stress and subsequently activated three unfolded protein responses (UPR) pathways including protein kinase R-like ER kinase (PERK), inositol requiring enzyme 1 (IRE1), and activating transcription factor-6 (ATF-6) pathways, but also triggered complete autophagy in main immune organs and partial nonimmune organs exhibiting severer pathological injuries and higher viral loads. However, only the IRE1 pathway and no autophagy were activated in some other nonimmune organs with slighter pathologies and lower viral loads. These results indicate a potential link between CSFV-induced ER stress and autophagy, both of which are associated with the CSFV replication in vivo. We further performed in vitro experiments and found that CSFV infection activates the PERK and IRE1 pathways and autophagy in cultured porcine kidney cell lines (PK-15) and macrophage cell lines (3D4/2), and pharmacological regulation of ER stress remarkably changed autophagic activities induced by CSFV, suggesting that CSFV-induced autophagy can be mediated by ER stress possibly via the PERK and IRE1 pathway. Furthermore, treatment with ER stress regulators significantly altered copy numbers of NS5B genes, expression of Npro proteins, and viral titers in CSFV-infected cells or in cells treated with autophagy regulators prior to CSFV infection, suggesting the requirement of ER stress-mediated autophagy for CSFV replication in vitro. Collectively, our data demonstrate that CSFV induces ER stress-mediated autophagy to sustain its replication in vivo and in vitro, which may be one of the potential strategies exploited by CSFV for immune evasion. This finding will provide new insights into mechanisms of replication and pathogenesis of CSFV, and development of new strategies for controlling CSF.

Muscovy duck reovirus enters susceptible cells via a caveolae-mediated endocytosis-like pathway

Muscovy duck reovirus (MDRV) causes immunosuppression and results in high mortality among Muscovy ducklings. Cell entry is the first step of virus infection and represents a potential therapeutic target. However, very little is known about the mechanism by which MDRV penetrates the cells. The aim of this study was to explore the mechanism of MDRV cell entry and subsequent infection. DF-1 and Vero cells were pretreated with the inhibitors chlorpromazine (CPZ), cytochalasin D, methyl-beta-cyclodextrin (M-β-CD), genistein, dynasore, nocodazole, or NH₄Cl, and then infected with MDRV. The copy number of the MDRV p10.8 gene and the expression of viral sigma A protein were determined by RT-PCR and western blot, respectively. Both sigma A expression and p10.8 gene copy number were decreased by treatment with M-β-CD, genistein, dynasore, nocodazole, and NH₄Cl. In contrast, no effects on virus infection were detected when inhibitors of clathrin-mediated endocytosis or macropinocytosis were used. In addition, the colocalization between MDRV sigma A protein and caveolin-1 was evaluated by double-label immunofluorescence. Collectively, our data revealed that MDRV can enter susceptible cells through caveolin-dependent endocytosis involving dynamin and microtubules. Moreover, the acidic environment of the endosomes was found to be critical for efficient infection. Our findings provide new insights into the infection process of MDRV.

The effects of autophagy on the replication of Nelson Bay orthoreovirus

BACKGROUND

Nelson Bay orthoreovirus (NBV) was first isolated over 40 years ago from a fruit bat in Australia. Normally, NBV does not cause human diseases, but recently several NBV strains have been associated with human respiratory tract infections, thus attracting clinical attention. Autophagy, an evolutionarily conserved process in eukaryotic cells, degrades intracellular substrates, participates in multiple physiological processes, and maintains cellular homeostasis. In addition, autophagy is intimately involved in viral infection.

METHODS

A new strain of NBV, isolated from a patient with a respiratory tract infection who returned to Japan from Bali, Indonesia, in 2007, was used in this study. NBV was rescued using a reverse genetics system involving cotransfection of BHK cells with 11 plasmids (pT7-L1 MB, pT7-L2 MB, pT7-L3 MB, pT7-M1 MB, pT7-M2 MB, pT7-M3 MB, pT7-S1 MB, pT7-S2 MB, pT7-S3 MB, pT7-S4 MB, and pcDNA3.1-T7), yielding NBV-MB. Recovered viruses were confirmed by immunofluorescence. The effect of NBV-MB on autophagy was evaluated by measuring the LC3-I/II proteins by immunoblot analysis after infection of BHK cells. Furthermore, after treatment with rapamycin (RAPA), 3-methyladenine (3-MA), chloroquine (CQ), or plasmid (GFP-LC3) transfection, the changes in expression of the LC3 gene and the amount of LC3-I/II protein were examined. In addition, variations in viral titer were assayed after treatment of BHK cells with drugs or after transfection with plasmids pCAGM3 and pCAGS3, which encode virus nonstructural proteins μNS and σNS, respectively.

RESULTS

NBV-MB infection induced autophagy in host cells; however, the level of induction was dependent on viral replication. Induction of autophagy increased viral replication. By contrast, inhibiting autophagy suppressed NBV replication, albeit not significantly. The NBV-MB nonstructural protein μNS was involved in the induction of autophagy with viral infection.

CONCLUSIONS

NBV-MB infection triggered autophagy. Also, the NBV nonstructural protein μNS may contribute to augmentation of autophagy upon viral infection.

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.

BmAtg13 promotes the replication and proliferation of Bombyx mori nucleopolyhedrovirus

Autophagy is a cell adaptive response that involves the process of microbial infections. Our previous study has indicated that Bombyx mori nucleopolyhedrovirus (BmNPV) infection triggers the complete autophagic process in BmN-SWU1 cells, which is beneficial to the viral infection. Autophagy-related (ATG) protein ATG13, as part of the ULK complex (a serine-threonine kinase complex composed of ULK1, ULK2, ATG13, ATG101, and FIP200), is the most upstream component of the autophagy pathway, and how it affects virus infections will improve our understanding of the interaction between the virus and the host. This study has determined that the overexpression of the BmAtg13 gene promotes the expression of viral genes and increases viral production in BmN-SWU1 cells, whereas knocking down the BmAtg13 gene suppresses BmNPV replication. Moreover, the BmAtg13 overexpression transgenic line contributed to viral replication and increased mortality rate of BmNPV infection. In contrast, the BmAtg13 knockout transgenic line reduced viral replication 96 h post-infection. Furthermore, BmATG13 directly interacted with viral protein BRO-B, forming a protein complex. Taken together, the findings of this study suggest that BmATG13 may be utilized by the BRO-B protein to promote BmNPV replication and proliferation, which, in turn, provides important insights into the mechanism that autophagy influences viral infection.

Endoplasmic Reticulum Stress Mediated MDRV p10.8 Protein-Induced Cell Cycle Arrest and Apoptosis Through the PERK/eIF2α Pathway

In this study, the mechanism of Muscovy duck reovirus (MDRV) p10.8 protein-induced pathogenesis was investigated, with a focus on endoplasmic reticulum (ER) stress. In chicken embryo fibroblasts cell lines (DF1), pCI-neo-flg-p10.8 protein transfection increased the phosphorylation (p-) levels of PERK and eIF2α as shown by Western blotting analysis and led to the dissociation of BiP from PERK as shown by co-immunoprecipitation (Co-IP) analysis. Results of treatment with both ER stress activator and inhibitor further confirmed that p10.8 protein induced ER stress. Subsequently, using flow cytometry analysis, it was also found that p10.8 protein induced cell cycle arrest during the G0/G1 phase. Furthermore, p10.8 transfection increased the phosphorylation levels of PERK and eIF2α, and reduced the expression levels of CDK2, CDK4, and Cyclin E according to Western blotting analysis. Treatment with ER stress activator and ER stress inhibitor after p10.8 protein transfection in DF1 cells further indicated that p10.8 protein induced ER stress, which resulted in cell cycle arrest. The results of knockdown of either PERK or eIF2α genes further confirmed that p10.8 protein-induced ER stress led to cell cycle arrest through the PERK/eIF2α pathway. Further results showed that p10.8 protein induced ER stress and apoptosis in DF1 cells. The expression levels of p-PERK, p-eIF2α, CHOP, cleaved-Caspase12, and cleaved-Caspase3 were increased by p10.8 protein. Test results of treatment with each of Tunicamycin, TUDCA and knockdown of PERK, and eIF2α, confirmed that p10.8 protein induced ER stress involving apoptosis via the PERK/eIF2α pathway. In conclusion, MDRV p10.8 protein induced ER stress that caused cell cycle arrest and apoptosis through the PERK/eIF2α pathway.

Bombyx mori Nuclear Polyhedrosis Virus (BmNPV) Induces Host Cell Autophagy to Benefit Infection

Bombyx mori nuclear polyhedrosis virus (BmNPV) is an important pathogen of silkworms. Despite extensive studies in recent decades, the interaction between BmNPV and host cells is still not clearly understood. Autophagy is an intrinsic innate immune mechanism and it controls infection autonomously in virus-infected cells. In this study, we found that BmNPV infection could trigger autophagy, as demonstrated by the formation of autophagosomes, fluorescent Autophagy-related gene 8-Green Fluorescent Protein (ATG8-GFP) punctate, and lipidated ATG8. Meanwhile, autophagic flux increased significantly when monitored by the ATG8-GFP-Red Fluorescent Protein (RFP) autophagy tandem sensor and protein degradation of p62. In addition, almost all of the identified autophagy-related genes (Atgs) had been up-regulated post infection in mRNA levels. Then, we screened Atgs with the greatest fold-change during virus infection. Interestingly, all of the screened Atgs positively regulated the expression of virus genes. Further studies showed that Atg7 and Atg9 could contribute to the level of autophagy caused by viral infection. Our results demonstrated that BmNPV induced host cell autophagy to benefit its infection. These results offer insight into the complex interactions between virus and host cell, and viral pathogenesis.