Autophagy benefits the replication of Newcastle disease virus in chicken cells and tissues. J Virol. 2014;88:525-537. [PMID: 24173218 DOI: 10.1128/jvi.01849-13]

Downregulation of microRNA-30a-5p contributes to the replication of duck enteritis virus by regulating Beclin-1-mediated autophagy

BACKGROUND

MicroRNAs (miRNAs) is increasingly recognized as an important element in regulating virus-host interactions. Our previous results showed that cellular miR-30a-5p was significantly downregulated after duck enteritis virus (DEV) infection cell. However, whehter or not the miR-30a-5p is involved in DEV infection has not been known.

METHODS

Quantitative reverse-transcription PCR (qRT-PCR) was used to measure the expression levels of miRNAs(miR-30a-5p) and Beclin-1 mRNA. The miR-30a-5p - Beclin-1 target interactions were determined by Dual luciferase reporter assay (DLRA). Western blotting was utilized to analyze Beclin-1-mediated duck embryo fibroblast (DEF) cells autophagy activity. DEV titers were estimated by the median tissue culture infective dose (TCID50).

RESULTS

The miR-30a-5p was significantly downregulated and the Beclin-1 mRNA was significantly upregulated in DEV-infected DEF cells. DLRA confirmed that miR-30a-5p directly targeted the 3'- UTR of the Beclin-1 gene. Overexpression of miR-30a-5p significantly reduced the expression level of Beclin-1protein (p < 0.05), leading to the decrease of Beclin-1-mediated autophagy activity, which ultimately suppressed DEV replication (P < 0.05). Whereas transfection of miR-30a-5p inhibitor increased Beclin-1-mediated autophagy and triggered DEV replication during the whole process of DEV infection (P < 0.01).

CONCLUSIONS

This study shows that miR-30a-5p can inhibit DEV replication through reducing autophagy by targeting Beclin-1. These findings suggest a new insight into virus-host interaction during DEV infection and provide a potential new antiviral therapeutic strategy against DEV infection.

In Vitro and In Vivo Metabolomic Profiling after Infection with Virulent Newcastle Disease Virus

Newcastle disease (ND) is an acute, febrile, highly contagious disease caused by the virulent Newcastle disease virus (vNDV). The disease causes serious economic losses to the poultry industry. However, the metabolic changes caused by vNDV infection remain unclear. The objective of this study was to determine the metabolomic profiling after infection with vNDV. DF-1 cells infected with the vNDV strain Herts/33 and the lungs from Herts/33-infected specific pathogen-free (SPF) chickens were analyzed via ultra-high-performance liquid chromatography/quadrupole time-of-flight tandem mass spectrometry (UHPLC-QTOF-MS) in combination with multivariate statistical analysis. A total of 305 metabolites were found to have changed significantly after Herts/33 infection, and most of them belong to the amino acid and nucleotide metabolic pathway. It is suggested that the increased pools of amino acids and nucleotides may benefit viral protein synthesis and genome amplification to promote NDV infection. Similar results were also confirmed in vivo. Identification of these metabolites will provide information to further understand the mechanism of vNDV replication and pathogenesis.

Newcastle Disease Virus V Protein Degrades Mitochondrial Antiviral Signaling Protein To Inhibit Host Type I Interferon Production via E3 Ubiquitin Ligase RNF5

Paramyxovirus establishes an intimate and complex interaction with the host cell to counteract the antiviral responses elicited by the cell. Of the various pattern recognition receptors in the host, the cytosolic RNA helicases interact with viral RNA to activate the mitochondrial antiviral signaling protein (MAVS) and subsequent cellular interferon (IFN) response. On the other hand, viruses explore multiple strategies to resist host immunity. In this study, we found that Newcastle disease virus (NDV) infection induced MAVS degradation. Further analysis showed that NDV V protein degraded MAVS through the ubiquitin-proteasome pathway to inhibit IFN-β production. Moreover, NDV V protein led to proteasomal degradation of MAVS through Lys362 and Lys461 ubiquitin to prevent IFN production. Further studies showed that NDV V protein recruited E3 ubiquitin ligase RNF5 to polyubiquitinate and degrade MAVS. Compared with levels for wild-type NDV infection, V-deficient NDV induced attenuated MAVS degradation and enhanced IFN-β production at the late stage of infection. Several other paramyxovirus V proteins showed activities of degrading MAVS and blocking IFN production similar to those of NDV V protein. The present study revealed a novel role of NDV V protein in targeting MAVS to inhibit cellular IFN production, which reinforces the fact that the virus orchestrates the cellular antiviral response to its own benefit.IMPORTANCE Host anti-RNA virus innate immunity relies mainly on the recognition by retinoic acid-inducible gene I and melanoma differentiation-associated protein 5 and subsequently initiates downstream signaling through interaction with MAVS. On the other hand, viruses have developed various strategies to counteract MAVS-mediated signaling. The mechanism for paramyxoviruses regulating MAVS to benefit their infection remains unknown. In this article, we demonstrate that the V proteins of NDV and several other paramyxoviruses target MAVS for ubiquitin-mediated degradation through E3 ubiquitin ligase RING-finger protein 5 (RNF5). MAVS degradation leads to the inhibition of the downstream IFN-β pathway and therefore benefits virus proliferation. Our study reveals a novel mechanism of NDV evading host innate immunity and provides insight into the therapeutic strategies for the control of paramyxovirus infection.

Application of Newcastle disease virus in the treatment of colorectal cancer

Colorectal cancer (CRC) is one of the main reasons of tumor-related deaths worldwide. At present, the main treatment is surgery, but the results are unsatisfactory, and the prognosis is poor. The majority of patients die due to liver or lung metastasis or recurrence. In recent years, great progress has been made in the field of tumor gene therapy, providing a new treatment for combating CRC. As oncolytic viruses selectively replicate almost exclusively in the cytoplasm of tumor cells and do not require integration into the host genome, they are safer, more effective and more attractive as oncolytic agents. Newcastle disease virus (NDV) is a natural RNA oncolytic virus. After NDV selectively infects tumor cells, the immune response induced by NDV’s envelope protein and intracellular factors can effectively kill the tumor without affecting normal cells. Reverse genetic techniques make NDV a vector for gene therapy. Arming the virus by inserting various exogenous genes or using NDV in combination with immunotherapy can also improve the anti-CRC capacity of NDV, and good results have been achieved in animal models and clinical treatment trials. This article reviews the molecular biological characteristics and oncolytic mechanism of NDV and discusses in vitro and in vivo experiments on NDV anti-CRC capacity and clinical treatment. In conclusion, NDV is an excellent candidate for cancer treatment, but more preclinical studies and clinical trials are needed to ensure its safety and efficacy.

A Comprehensive Review of Autophagy and Its Various Roles in Infectious, Non-Infectious, and Lifestyle Diseases: Current Knowledge and Prospects for Disease Prevention, Novel Drug Design, and Therapy

Autophagy (self-eating) is a conserved cellular degradation process that plays important roles in maintaining homeostasis and preventing nutritional, metabolic, and infection-mediated stresses. Autophagy dysfunction can have various pathological consequences, including tumor progression, pathogen hyper-virulence, and neurodegeneration. This review describes the mechanisms of autophagy and its associations with other cell death mechanisms, including apoptosis, necrosis, necroptosis, and autosis. Autophagy has both positive and negative roles in infection, cancer, neural development, metabolism, cardiovascular health, immunity, and iron homeostasis. Genetic defects in autophagy can have pathological consequences, such as static childhood encephalopathy with neurodegeneration in adulthood, Crohn's disease, hereditary spastic paraparesis, Danon disease, X-linked myopathy with excessive autophagy, and sporadic inclusion body myositis. Further studies on the process of autophagy in different microbial infections could help to design and develop novel therapeutic strategies against important pathogenic microbes. This review on the progress and prospects of autophagy research describes various activators and suppressors, which could be used to design novel intervention strategies against numerous diseases and develop therapeutic drugs to protect human and animal health.

Oncolytic paramyxoviruses-induced autophagy; a prudent weapon for cancer therapy

Oncolytic virotherapy has currently emerged as a promising approach upon which scientists have been able to induce tumor-specific cell death in a broad spectrum of malignancies. Paramyxoviruses represent intrinsic oncolytic capability, which makes them excellent candidates to be widely used in oncolytic virotherapy. The mechanisms through which these viruses destroy the cancerous cells involve triggering the autophagic machinery and apoptosis in target cells. Interestingly, oncolytic paramyxoviruses have been found to induce autophagy and lead to tumor cells death rather than their survival. Indeed, the induction of autophagy has been revealed to enhance the immunogenicity of tumor cells via the release of damage-associated molecular patterns (DAMPs) and the activation of autophagy-related immunogenic cell death (ICD). Subsequent cross-presentation of tumor-associated antigens (TAA) through the MHC-I complex to CD8+ T cells results in the productive priming of the tumor-specific immune response. In this review, we first briefly discuss autophagy and explain the process of viral xenophagy. Finally, we focus on the interactions between virus and autophagy proteins, elaborating on the global preclinical studies on oncolytic paramyxoviruses.

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.

Natural Selection Footprints Among African Chicken Breeds and Village Ecotypes

Natural selection is likely a major factor in shaping genomic variation of the African indigenous rural chicken, driving the development of genetic footprints. Selection footprints are expected to be associated with adaptation to locally prevailing environmental stressors, which may include diverse factors as high altitude, disease resistance, poor nutrition, oxidative and heat stresses. To determine the existence of a selection footprint, 268 birds were randomly sampled from three indigenous ecotypes from East Africa (Rwanda and Uganda) and North Africa (Baladi), and two registered Egyptian breeds (Dandarawi and Fayoumi). Samples were genotyped using the chicken Affymetrix 600K Axiom^® Array. A total of 494,332 SNPs were utilized in the downstream analysis after implementing quality control measures. The intra-population runs of homozygosity (ROH) that occurred in >50% of individuals of an ecotype or in >75% of a breed were studied. To identify inter-population differentiation due to genetic structure, F_ST was calculated for North- vs. East-African populations and Baladi and Fayoumi vs. Dandarawi for overlapping windows (500 kb with a step-size of 250 kb). The ROH and F_ST mapping detected several selective sweeps on different autosomes. Results reflected selection footprints of the environmental stresses, breed behavior, and management. Intra-population ROH of the Egyptian chickens showed selection footprints bearing genes for adaptation to heat, solar radiation, ion transport and immunity. The high-altitude-adapted East-African populations' ROH showed a selection signature with genes for angiogenesis, oxygen-heme binding and transport. The neuroglobin gene (GO:0019825 and GO:0015671) was detected on a Chromosome 5 ROH of Rwanda-Uganda ecotypes. The sodium-dependent noradrenaline transporter, SLC6A2 on a Chromosome 11 ROH in Fayoumi breed may reflect its active behavior. Inter-population F_ST among Egyptian populations reflected genetic mechanisms for the Fayoumi resistance to Newcastle Disease Virus (NDV), while F_ST between Egyptian and Rwanda-Uganda populations indicated the Secreted frizzled related protein 2, SFRP2, (GO:0009314) on Chromosome 4, that contributes to melanogenic activity and most likely enhances the Dandarawi chicken adaptation to high-intensity of solar radiation in Southern Egypt. These results enhance our understanding of the natural selection forces role in shaping genomic structure for adaptation to the stressful African conditions.

The Ntail region of nucleocapsid protein is associated with the pathogenicity of pigeon paramyxovirus type 1 in chickens

The nucleoprotein (NP) of pigeon paramyxovirus type 1 (PPMV-1) and other paramyxoviruses plays an important role in virus proliferation. A previous study found that NP is associated with the low pathogenicity of PPMV-1 strains in chickens. Here, we investigated which domain of NP is responsible for regulating the pathogenicity of PPMV-1. We found that the Ntail sequences were more diverse for different viral genotypes compared to Ncore sequences. The chimeric rBJ-SG10Ntail strain caused more severe clinical symptoms than the parental rBJ strain, increased the viral copy number in sampled tissues and induced higher IFN-γ gene expression. This demonstrated that the Ntail sequence plays a role in regulating viral virulence. These findings increase our understanding of the Ntail of NP protein and the virulence factors associated with PPMV-1.

Goose MAVS functions in RIG-I-mediated IFN-β signaling activation

Mitochondrial antiviral-signaling protein (MAVS) is an essential adaptor protein in retinoic acid-inducible gene I (RIG-I)-mediated antiviral innate immunity in mammals. In this study, the goose MAVS gene (goMAVS) was identified. The 2019 bp-long goMAVS exhibits 96.2% amino acid similarity compared to the predicted goMAVS. Quantitative real-time polymerase chain reactions showed that goMAVS mRNA was widely expressed in different tissues. The overexpression of goMAVS in goose embryo fibroblast cells up-regulated the mRNA levels of goose interferon-stimulated genes. We concluded that MAVS mediates the activation of type I interferon (IFN) pathway in a species-specific manner. We further demonstrated that a CARD-like domain, transmembrane domain and two previously unidentified domains of goMAVS were essential for the activation of type I IFN pathway. GoMAVS inhibited Newcastle disease virus replication by activating type I IFN pathways, especially at the early stages of infection. Finally, the interaction between goMAVS and goose RIG-I was confirmed. The CARD domain of goMAVS plays a vital role in the interaction. Together, we identified goMAVS as a goRIG-I interactive protein and concluded that goMAVS is involved in the activation of type I IFN pathways in goose cells.

Influenza M2 protein regulates MAVS-mediated signaling pathway through interacting with MAVS and increasing ROS production

Influenza A virus can evade host innate immune response that is involved in several viral proteins with complicated mechanisms. To date, how influenza A M2 protein modulates the host innate immunity remains unclear. Herein, we showed that M2 protein colocalized and interacted with MAVS (mitochondrial antiviral signaling protein) on mitochondria, and positively regulated MAVS-mediated innate immunity. Further studies revealed that M2 induced reactive oxygen species (ROS) production that was required for activation of macroautophagy/autophagy and enhancement of MAVS signaling pathway. Importantly, the proton channel activity of M2 protein was demonstrated to be essential for ROS production and antagonizing the autophagy pathway to control MAVS aggregation, thereby enhancing MAVS signal activity. In conclusion, our studies provided novel insights into mechanisms of M2 protein in modulating host antiviral immunity and uncovered a new mechanism into biology and pathogenicity of influenza A virus. Abbreviations: AKT/PKB: AKT serine/threonine kinase; Apo: apocynin; ATG5: autophagy related 5; BAPTA-AM: 1,2-Bis(2-aminophenoxy) ethane-N,N,N',N'-tetraacetic acid tetrakis; BECN1: beclin 1; CARD: caspase recruitment domain; CCCP: carbonyl cyanide m-chlorophenylhydrazone; CQ: chloroquine; DCF: dichlorodihyd-rofluorescein; DPI: diphenyleneiodonium; DDX58: DExD/H-box helicase 58; eGFP: enhanced green fluorescent protein; EGTA: ethylene glycol-bis(2-aminoethylether)-N,N,N',N'-tetraacetic acid; ER: endoplasmic reticulum; hpi: hours post infection; IAV: influenza A virus; IFN: interferon; IP: immunoprecipitation; IRF3: interferon regulatory factor 3; ISRE: IFN-stimulated response elements; LIR: LC3-interacting region; MAP1LC3B/LC3B: microtubule associated protein 1 light chain 3 beta; MAVS: mitochondrial antiviral signaling protein; MMP: mitochondrial membrane potential; MOI, multiplicity of infection; mRFP: monomeric red fluorescent protein; MTOR: mechanistic target of rapamycin kinase; NC: negative control; NFKB/NF-κB: nuclear factor kappa B; PI3K: class I phosphoinositide 3-kinase; RLR: RIG-I-like-receptor; ROS: reactive oxygen species; SEV: sendai virus; TM: transmembrane; TMRM: tetramethylrhodamine methylester; VSV: vesicular stomatitis virus.

Syncytia generated by hemagglutinin-neuraminidase and fusion proteins of virulent Newcastle disease virus induce complete autophagy by activating AMPK-mTORC1-ULK1 signaling>

Autophagy triggered by glycoprotein-mediated membrane fusion has been reported for several paramyxoviruses. However, the function of HN and F glycoproteins of NDV and their role in autophagy induction have not been studied. Here, we found that co-transfection of HN and F of virulent NDV rapidly induced syncytium formation and triggered a steady state autophagy flux in adenocarcinomic human alveolar basal epithelial (A549) cells and chicken embryo fibroblast (DF-1) cells. Furthermore, we clearly identified that F and HN synergistically induced autophagosome fusion with lysosomes for subsequent degradation. The seven cleavage site mutations of F significantly decreased the autophagy induction, compared with those of wildtype virulent F. RNAi and pharmacological experiments suggested that autophagy benefitted membrane fusion and syncytium formation induced by F and HN of NDV. Activated F₁ co-operated with HN to stimulate AMPK kinase and downstream ULK1 activation to suppress mTORC1 signaling. Our data described the synergistic role of HN and F in the induction of completed autophagic flux through the activation of AMPK- mTORC1- ULK1 pathway.

Detection of viral components in exosomes derived from NDV-infected DF-1 cells and their promoting ability in virus replication

Exosomes are micro messengers encapsulating RNA, DNA, and proteins for intercellular communication associated with various physiological and pathological reactions. Several viral infection processes have been reported to pertain to exosomal pathways. However, because of the difficulty in obtaining avian-sourced exosomes, avian virus-related exosomes are scarcely investigated. In this study, we developed a protein A/G-correlated method and successfully obtained the Newcastle disease virus-related exosome (NDV Ex). These exosomes promoted NDV propagation, proven by both GW4869-mediated deprivation and exosomal supplementation. Viral structural proteins NP and F were detected in the NDV Ex and further investigation indicated that the NP protein can be transferred to DF-1 cells through exosomes. The intracellular NP protein exhibited viral replication-promoting and cytokine-suppressing abilities. Therefore, NDV infection produces exosomes, which transfer viral NP protein and promote NDV infection, emphasizing the importance of exosomes in an NDV infection.

Glutamine Deficiency Promotes PCV2 Infection through Induction of Autophagy via Activation of ROS-Mediated JAK2/STAT3 Signaling Pathway

Porcine circovirus type 2 (PCV2) is an important pathogen in swine herds. We previously reported that glutamine (Gln) deficiency promoted PCV2 infection in vitro. Here, we established a Gln deficiency model in vivo and further investigated the detailed molecular mechanisms. In vivo and in vitro, Gln deficiency promoted PCV2 infection, which was evident through increased viral yields and PCV2 Cap protein synthesis. It also induced autophagy, as demonstrated by the increases in LC3-II conversion, SQSTM1 degradation, and GFP-LC3 dot accumulation. Autophagy inhibition abolished the effects of Gln deficiency on PCV2 infection. Inhibition of ROS generation alleviated the Gln deficiency-activated JAK2/STAT3 signaling pathway, thereby inhibiting autophagy induction. In vitro, the inhibition of STAT3 by an inhibitor or RNA interference blocked autophagy, thus reversing the effects of Gln deficiency on PCV2 infection. These results indicate that Gln deficiency activates autophagy by upregulating ROS-medicated JAK2/STAT3 signaling and thereby promoting PCV2 infection.

Biochanin a Enhances the Defense Against Salmonella enterica Infection Through AMPK/ULK1/mTOR-Mediated Autophagy and Extracellular Traps and Reversing SPI-1-Dependent Macrophage (MΦ) M2 Polarization

A novel treatment regimen for bacterial infections is the pharmacological enhancement of the host's immune defenses. We demonstrated that biochanin A (BCA), an isoflavone constituent in some plants, could enhance both intra- and extracellular bactericidal activity of host cells. First, BCA could induce a complete autophagic response in nonphagocytic cells (HeLa) or macrophages (MΦ) via the AMPK/ULK1/mTOR pathway and Beclin-1-dependent manner, and BCA enhanced the killing of invading Salmonella by autophagy through reinforcing ubiquitinated adapter protein (LRSAM1, NDP52 and p62)-mediated recognition of intracellular bacteria and through the formation of autophagolysosomes. Second, we demonstrated that BCA could enhance the release of MΦ extracellular traps (METs) to remove extracellular Salmonella also via the AMPK/ULK1/mTOR pathway, not through reactive oxygen species (ROS) pathway. Furtherly, in a Salmonella-infected mouse model, BCA treatment increased intra- and extracellular bactericidal activity through the strengthening autophagy and MET production, respectively, in peritoneal MΦ, liver and spleen tissue. Additionally, our findings showed that BCA downregulated SPI-1 (Salmonella pathogenicity island 1) expression during Salmonella infection in vitro and in vivo to reverse the MΦ M2 polarization, which was different from the MΦ M1 phenotype caused by most of bacteria infection. Together, these findings suggest that BCA has an immunomodulatory effect on Salmonella-infected host cells and enhances their bactericidal activity in vitro and in vivo through autophagy, extracellular traps and regulation of MΦ polarization.

Chicken RNA-binding protein T-cell internal antigen-1 contributes to stress granule formation in chicken cells and tissues

T-cell internal antigen-1 (TIA-1) has roles in regulating alternative pre-mRNA splicing, mRNA translation, and stress granule (SG) formation in human cells. As an evolutionarily conserved response to environmental stress, SGs have been reported in various species. However, SG formation in chicken cells and the role of chicken TIA-1 (cTIA-1) in SG assembly has not been elucidated. In the present study, we cloned cTIA-1 and showed that it facilitates the assembly of canonical SGs in both human and chicken cells. Overexpression of the chicken prion-related domain (cPRD) of cTIA-1 that bore an N-terminal green fluorescent protein (GFP) tag (pntGFP-cPRD) or Flag tag (pFlag-cPRD) induced the production of typical SGs. However, C-terminal GFP-tagged cPRD induced notably large cytoplasmic granules that were devoid of endogenous G3BP1 and remained stable when exposed to cycloheximide, indicating that these were not typical SGs, and that the pntGFP tag influences cPRD localization. Finally, endogenous cTIA-1 was recruited to SGs in chicken cells and tissues under environmental stress. Taken together, our study provide evidence that cTIA-1 has a role in canonical SG formation in chicken cells and tissues. Our results also indicate that cPRD is necessary for SG aggregation.

Oncolytic Newcastle disease virus induces autophagy-dependent immunogenic cell death in lung cancer cells

In addition to direct oncolysis, oncolytic viruses trigger immunogenic cell death (ICD) and primes antitumor immunity. We have previously shown that oncolytic Newcastle disease virus (NDV), strain FMW (NDV/FMW), induces apoptosis and/or autophagy in cancer cells. In this study, we investigated whether oncolytic NDV can induce ICD in lung cancer cells and whether apoptosis or autophagy plays a role in NDV-triggered ICD. To this end, we examined cell surface expression of calreticulin (CRT) on NDV-infected lung cancer cells and measured ICD determinants, high mobility group box 1 (HMGB1), heat shock protein 70/90 (HSP70/90) and ATP in supernatants following viral infection. Flow cytometric analysis using anti-CRT antibody and PI staining of NDV-infected lung cancer cells showed an increase in the number of viable (propidium iodide-negative) cells, suggesting the induction of CRT exposure upon NDV infection. In addition, confocal and immunoblot analysis using anti-CRT antibody showed that an enhanced accumulation of CRT on the cell surface of NDV-infected cells, indicating the translocation of CRT to the cell membrane upon NDV infection. We further demonstrated that NDV infection induced the release of secreted HMGB1 and HSP70/90 by examining the concentrated supernatants of NDV-infected cells. Furthermore, pre-treatment with either the pan-caspase inhibitor z-VAD-FMK or the necrosis inhibitor Necrostain-1, had no impact on NDV-induced release of ICD determinants in lung cancer cells. Rather, depletion of autophagy-related genes in lung cancer cells significantly inhibited the induction of ICD determinants by NDV. Of translational importance, in a lung cancer xenograft model, treatment of mice with supernatants from NDV-infected cells significantly inhibited tumour growth. Together, these results indicate that oncolytic NDV is a potent ICD-inducer and that autophagy contributes to NDV-mediated induction of ICD in lung cancer cells.

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.

Resistant and susceptible chicken lines show distinctive responses to Newcastle disease virus infection in the lung transcriptome

Background

Newcastle disease virus (NDV) is a threat to poultry production worldwide. A better understanding of mechanisms of resistance and susceptibility to this virus will improve measures for NDV prevention and control. Males and females from resistant Fayoumi and susceptible Leghorn lines were either challenged with a lentogenic strain of the virus or given a mock infection at 3 weeks of age. The lung transcriptomes generated by RNA-seq were studied using contrasts across the challenged and nonchallenged birds, the two lines, and three time points post-infection, and by using Weighted Gene Co-expression Network Analysis (WGNCA).

Results

Genetic line and sex had a large impact on the lung transcriptome. When contrasting the challenged and nonchallenged birds, few differentially expressed genes (DEG) were identified within each line at 2, 6, and 10 days post infection (dpi), except for the more resistant Fayoumi line at 10 dpi, for which several pathways were activated and inhibited at this time. The interaction of challenge and line at 10 dpi significantly impacted 131 genes (False Discovery Rate (FDR) <0.05), one of which was PPIB. Many DEG were identified between the Fayoumi and Leghorns. The number of DEG between the two lines in the challenged birds decreased over time, but increased over time in the nonchallenged birds. The nonchallenged Fayoumis at 10 dpi showed enrichment of immune type cells when compared to 2 dpi, suggesting important immune related development at this age. These changes between 10 and 2 dpi were not identified in the challenged Fayoumis. The energy allocated to host defense may have interrupted normal lung development. WGCNA identified important modules and driver genes within those modules that were associated with traits of interest, several of which had no known associated function.

Conclusions

The lines’ unique response to NDV offers insights into the potential means of their resistance and susceptibility. The lung transcriptome shows a unique response to lentogenic NDV compared to a previous study on the trachea of the same birds. It is important to analyze multiple tissues in order to best understand the chicken’s overall response to NDV challenge and improve strategies to combat this devastating disease.

Electronic supplementary material

The online version of this article (10.1186/s12864-017-4380-4) contains supplementary material, which is available to authorized users.

Porcine teschovirus 2 induces an incomplete autophagic response in PK-15 cells

Autophagy is a homeostatic process that has been shown to be vital in the innate immune defense against pathogens. However, little is known about the regulatory role of autophagy in porcine teschovirus 2 (PTV-2) replication. In this study, we found that PTV-2 infection induces a strong increase in GFP-LC3 punctae and endogenous LC3 lipidation. However, PTV-2 infection did not enhance autophagic protein degradation. When cellular autophagy was pharmacologically inhibited by wortmannin or 3-methyladenine, PTV-2 replication increased. The increase in virus yield via autophagy inhibition was further confirmed by silencing atg5, which is required for autophagy. Furthermore, PTV-2 replication was suppressed when autophagy was activated by rapamycin. Together, the results suggest that PTV-2 infection activates incomplete autophagy and that autophagy then inhibits further PTV-2 replication.

Autophagy pathway induced by a plant virus facilitates viral spread and transmission by its insect vector

Many viral pathogens are persistently transmitted by insect vectors and cause agricultural or health problems. Generally, an insect vector can use autophagy as an intrinsic antiviral defense mechanism against viral infection. Whether viruses can evolve to exploit autophagy to promote their transmission by insect vectors is still unknown. Here, we show that the autophagic process is triggered by the persistent replication of a plant reovirus, rice gall dwarf virus (RGDV) in cultured leafhopper vector cells and in intact insects, as demonstrated by the appearance of obvious virus-containing double-membrane autophagosomes, conversion of ATG8-I to ATG8-II and increased level of autophagic flux. Such virus-containing autophagosomes seem able to mediate nonlytic viral release from cultured cells or facilitate viral spread in the leafhopper intestine. Applying the autophagy inhibitor 3-methyladenine or silencing the expression of Atg5 significantly decrease viral spread in vitro and in vivo, whereas applying the autophagy inducer rapamycin or silencing the expression of Torc1 facilitate such viral spread. Furthermore, we find that activation of autophagy facilitates efficient viral transmission, whereas inhibiting autophagy blocks viral transmission by its insect vector. Together, these results indicate a plant virus can induce the formation of autophagosomes for carrying virions, thus facilitating viral spread and transmission by its insect vector. We believe that such a role for virus-induced autophagy is common for vector-borne persistent viruses during their transmission by insect vectors.

Autophagy is highly targeted among host comparative proteomes during infection with different virulent RABV strains

Rabies virus (RABV) is a neurotropic virus that causes serious disease in humans and animals worldwide. It has been reported that different RABV strains can result in divergent prognoses in animal model. To identify host factors that affect different infection processes, a kinetic analysis of host proteome alterations in mouse brains infected with different virulent RABV strains was performed using isobaric tags for a relative and absolute quantification (iTRAQ)-liquid chromatography-tandem mass spectrometry (LC-MS/MS) proteomics approach, and this analysis identified 147 differentially expressed proteins (DEPs) between the pathogenic challenge virus standard (CVS)-11 strain and the attenuated SRV9 strain. Bioinformatics analyses of these DEPs revealed that autophagy and several pathways associated with autophagy, such as mammalian target of rapamycin (mTOR) signaling, p70S6K signaling, nuclear factor erythroid 2-related factor 2 (NRF2)-mediated oxidative stress and superoxide radical degradation, were dysregulated. Validation of the proteomic data showed that attenuated SRV9 induced more autophagosome accumulation than CVS-11 in an in vitro model. Our findings provide new insights into the pathogenesis of RABV and encourage further studies on this topic.

Ochratoxin A-induced autophagy in vitro and in vivo promotes porcine circovirus type 2 replication

Ochratoxin A (OTA) is a mycotoxin produced by Aspergillus and Penicillium. Porcine circovirus type 2 (PCV2) is recognized as the causative agent of porcine circovirus-associated diseases. Recently, we reported that low doses of OTA promoted PCV2 replication in vitro and in vivo, but the underlying mechanism needed further investigation. The present studies further confirmed OTA-induced PCV2 replication promotion as measured by cap protein expression, viral titer, viral DNA copies and the number of infected cells. Our studies also showed that OTA induced autophagy in PK-15 cells, as assessed by the markedly increased expression of microtubule-associated protein 1 light chain 3 (LC3)-II, autophagy-related protein 5 (ATG5), and Beclin-1 and the accumulation of green fluorescent protein (GFP)-LC3 dots. OTA induced complete autophagic flux, which was detected by monitoring p62 degradation and LC3-II turnover using immunoblotting. Inhibition of autophagy by 3-methylademine (3-MA) and chloroquine (CQ) significantly attenuated OTA-induced PCV2 replication promotion. The observed phenomenon was further confirmed by the knock-down of ATG5 or Beclin-1 by specific siRNA. Further studies showed that N-acetyl-L-cysteine (NAC), an ROS scavenger could block autophagy induced by OTA, indicating that ROS may be involved in the regulation of OTA-induced autophagy. Furthermore, we observed significant increases in OTA concentrations in lung, spleen, kidney, liver and inguinal lymph nodes (ILN) and bronchial lymph nodes (BLN) of pigs fed 75 and 150 μg/kg OTA compared with controls in vivo. Administration of 75 μg/kg OTA significantly increased PCV2 replication and autophagy in the lung, spleen, kidney and BLN of pigs. Taken together, it could be concluded that OTA-induced autophagy in vitro and in vivo promotes PCV2 replication.

Newcastle disease virus-induced autophagy mediates antiapoptotic signaling responses in vitro and in vivo

In this study, we investigated the role of autophagy and apoptosis in Newcastle disease virus (NDV)-infected chicken cells and tissues. NDV-infected and starvation-induced chick embryo fibroblasts (CEF) cells showed higher autophagosome formation than mock-infected CEF cells on transmission electron microscopy. The NDV-infected CEF cells showed enhanced conversion of microtubule-associated protein 1 light chain 3-I (LC3-I) to LC3-II and degradation of p62/SQSTM1. The diminished conversion of LC3-I to LC3-II and cleaved caspase 3 and poly (ADP-ribose) polymerase (PARP) in ultraviolet-inactivated NDV-infected cells suggested that autophagosome formation was necessary for NDV replication. Inhibition of autophagy by chloroquine (CQ) enhanced apoptosis resulting in increased cleavage of caspase 3 and PARP and AnnexinV/propidium iodide staining. Autophagy induction by rapamycin resulted in upregulation of all autophagy-related genes except Beclin 1, anti-apoptosis factors, and proinflammatory cytokines in the NDV-infected spleen and lung tissues. Subsequently, decreased apoptosis was observed in NDV-infected spleens and lungs than mock-infected organs. The pan-caspase inhibitor ZVAD-FMK promoted conversion of LC3-I to LC3-II, the degradation of p62/SQSTM1, NDV replication and cell viability by inhibiting apoptosis. Our study demonstrates that apoptosis inhibition enhances autophagy and promoted cell survival and NDV replication.

Porcine Epidemic Diarrhea Virus Induces Autophagy to Benefit Its Replication

The new porcine epidemic diarrhea (PED) has caused devastating economic losses to the swine industry worldwide. Despite extensive research on the relationship between autophagy and virus infection, the concrete role of autophagy in porcine epidemic diarrhea virus (PEDV) infection has not been reported. In this study, autophagy was demonstrated to be triggered by the effective replication of PEDV through transmission electron microscopy, confocal microscopy, and Western blot analysis. Moreover, autophagy was confirmed to benefit PEDV replication by using autophagy regulators and RNA interference. Furthermore, autophagy might be associated with the expression of inflammatory cytokines and have a positive feedback loop with the NF-κB signaling pathway during PEDV infection. This work is the first attempt to explore the complex interplay between autophagy and PEDV infection. Our findings might accelerate our understanding of the pathogenesis of PEDV infection and provide new insights into the development of effective therapeutic strategies.

Infectious Bursal Disease Virus Subverts Autophagic Vacuoles To Promote Viral Maturation and Release

Autophagy functions as an intrinsic antiviral defense. However, some viruses can subvert or even enhance host autophagic machinery to increase viral replication and pathogenesis. The role of autophagy during avibirnavirus infection, especially late stage infection, remains unclear. In this study, infectious bursal disease virus (IBDV) was used to investigate the role of autophagy in avibirnavirus replication. We demonstrated IBDV induction of autophagy as a significant increase in puncta of LC3⁺ autophagosomes, endogenous levels of LC3-II, and ultrastructural characteristics typical of autophagosomes during the late stage of infection. Induction of autophagy enhances IBDV replication, whereas inhibition of autophagy impairs viral replication. We also demonstrated that IBDV infection induced autophagosome-lysosome fusion, but without active degradation of their contents. Moreover, inhibition of fusion or of lysosomal hydrolysis activity significantly reduced viral replication, indicating that virions utilized the low-pH environment of acidic organelles to facilitate viral maturation. Using immuno-transmission electron microscopy (TEM), we observed that a large number of intact IBDV virions were arranged in a lattice surrounded by p62 proteins, some of which lay between virions. Additionally, many virions were encapsulated within the vesicular membranes, with an obvious release stage observed by TEM. The autophagic endosomal pathway facilitates low-pH-mediated maturation of viral proteins and membrane-mediated release of progeny virions.IMPORTANCE IBDV is the most extensively studied virus in terms of molecular characteristics and pathogenesis; however, mechanisms underlying the IBDV life cycle require further exploration. The present study demonstrated that autophagy enhances viral replication at the late stage of infection, and the autophagy pathway facilitates IBDV replication complex function and virus assembly, which is critical to completion of the virus life cycle. Moreover, the virus hijacks the autophagic vacuoles to mature in an acidic environment and release progeny virions in a membrane-mediated cell-to-cell manner. This autophagic endosomal pathway is proposed as a new mechanism that facilitates IBDV maturation, release, and reinternalization. This report presents a concordance in exit strategies among some RNA and DNA viruses, which exploit autophagy pathway for their release from cells.

Targeting endosomal acidification by chloroquine analogs as a promising strategy for the treatment of emerging viral diseases

Emerging viruses such as HIV, dengue, influenza A, SARS coronavirus, Ebola, and other viruses pose a significant threat to human health. Majority of these viruses are responsible for the outbreaks of pathogenic lethal infections. To date, there are no effective therapeutic strategies available for the prophylaxis and treatment of these infections. Chloroquine analogs have been used for decades as the primary and most successful drugs against malaria. Concomitant with the emergence of chloroquine‐resistant Plasmodium strains and a subsequent decrease in the use as antimalarial drugs, other applications of the analogs have been investigated. Since the analogs have interesting biochemical properties, these drugs are found to be effective against a wide variety of viral infections. As antiviral action, the analogs have been shown to inhibit acidification of endosome during the events of replication and infection. Moreover, immunomodulatory effects of analogs have been beneficial to patients with severe inflammatory complications of several viral diseases. Interestingly, one of the successful targeting strategies is the inhibition of HIV replication by the analogs in vitro which are being tested in several clinical trials. This review focuses on the potentialities of chloroquine analogs for the treatment of endosomal low pH dependent emerging viral diseases.

Newcastle disease virus induces stable formation of bona fide stress granules to facilitate viral replication through manipulating host protein translation

Mammalian cells respond to various environmental stressors to form stress granules (SGs) by arresting cytoplasmic mRNA, protein translation element, and RNA binding proteins. Virus-induced SGs function in different ways, depending on the species of virus; however, the mechanism of SG regulation of virus replication is not well understood. In this study, Newcastle disease virus (NDV) triggered stable formation of bona fide SGs on HeLa cells through activating the protein kinase R (PKR)/eIF2α pathway. NDV-induced SGs contained classic SG markers T-cell internal antigen (TIA)-1, Ras GTPase-activating protein-binding protein (G3BP)-1, eukaryotic initiation factors, and small ribosomal subunit, which could be disassembled in the presence of cycloheximide. Treatment with nocodazole, a microtubule disruption drug, led to the formation of relatively small and circular granules, indicating that NDV infection induces canonical SGs. Furthermore, the role of SGs on NDV replication was investigated by knockdown of TIA-1 and TIA-1-related (TIAR) protein, the 2 critical components involved in SG formation from the HeLa cells, followed by NDV infection. Results showed that depletion of TIA-1 or TIAR inhibited viral protein synthesis, reduced extracellular virus yields, but increased global protein translation. FISH revealed that NDV-induced SGs contained predominantly cellular mRNA rather than viral mRNA. Deletion of TIA-1 or TIAR reduced NP mRNA levels in polysomes. These results demonstrate that NDV triggers stable formation of bona fide SGs, which benefit viral protein translation and virus replication by arresting cellular mRNA.-Sun, Y., Dong, L., Yu, S., Wang, X., Zheng, H., Zhang, P., Meng, C., Zhan, Y., Tan, L., Song, C., Qiu, X., Wang, G., Liao, Y., Ding, C. Newcastle disease virus induces stable formation of bona fide stress granules to facilitate viral replication through manipulating host protein translation.

Unlocking the promise of oncolytic virotherapy in glioma: combination with chemotherapy to enhance efficacy

Malignant glioma is a relentless burden to both patients and clinicians, and calls for innovation to overcome the limitations in current management. Glioma therapy using viruses has been investigated to accentuate the nature of a virus, killing a host tumor cell during its replication. As virus mediated approaches progress with promising therapeutic advantages, combination therapy with chemotherapy and oncolytic viruses has emerged as a more synergistic and possibly efficacious therapy. Here, we will review malignant glioma as well as prior experience with oncolytic viruses, chemotherapy and combination of the two, examining how the combination can be optimized in the future.

Wild-type rabies virus induces autophagy in human and mouse neuroblastoma cell lines

Different rabies virus (RABV) strains have their own biological characteristics, but little is known about their respective impact on autophagy. Therefore, we evaluated whether attenuated RABV HEP-Flury and wild-type RABV GD-SH-01 strains triggered autophagy. We found that GD-SH-01 infection significantly increased the number of autophagy-like vesicles, the accumulation of enhanced green fluorescent protein (EGFP)-LC3 fluorescence puncta and the conversion of LC3-I to LC3-II, while HEP-Flury was not able to induce this phenomenon. When evaluating autophagic flux, we found that GD-SH-01 infection triggers a complete autophagic response in the human neuroblastoma cell line (SK), while autophagosome fusion with lysosomes was inhibited in a mouse neuroblastoma cell line (NA). In these cells, GD-SH-01 led to apoptosis and mitochondrial dysfunction while triggering autophagy, and apoptosis could be decreased by enhancing autophagy. To further identify the virus constituent causing autophagy, 5 chimeric recombinant viruses carrying single genes of HEP-Flury instead of those of GD-SH-01 were rescued. While the HEP-Flury virus carrying the wild-type matrix protein (M) gene of RABV triggered LC3-I to LC3-II conversion in SK and NA cells, replacement of genes of nucleoprotein (N), phosphoprotein (P) and glycoprotein (G) produced only minor autophagy. But no one single structural protein of GD-SH-01 induced autophagy. Moreover, the AMPK signaling pathway was activated by GD-SH-01 in SK. Therefore, our data provide strong evidence that autophagy is induced by GD-SH-01 and can decrease apoptosis in vitro. Furthermore, the M gene of GD-SH-01 may cooperatively induce autophagy.

Critical role of bacterial isochorismatase in the autophagic process induced by Acinetobacter baumannii in mammalian cells

A recent study reported that Acinetobacter baumannii could induce autophagy, but the recognition and clearance mechanism of intracytosolic A. baumannii in the autophagic process and the molecular mechanism of autophagy induced by the pathogen remains unknown. In this study, we first demonstrated that invading A. baumannii induced a complete, ubiquitin-mediated autophagic response that is dependent upon septins SEPT2 and SEPT9 in mammalian cells. We also demonstrated that autophagy induced by A. baumannii was Beclin-1 dependent via the AMPK/ERK/mammalian target of rapamycin pathway. Of interest, we found that the isochorismatase mutant strain had significantly decreased siderophore-mediated ferric iron acquisition ability and had a reduced the ability to induce autophagy. We verified that isochorismatase was required for the recognition of intracytosolic A. baumannii mediated by septin cages, ubiquitinated proteins, and ubiquitin-binding adaptor proteins p62 and NDP52 in autophagic response. We also confirmed that isochorismatase was required for the clearance of invading A. baumannii by autophagy in vitro and in the mouse model of infection. Together, these findings provide insight into the distinctive recognition and clearance of intracytosolic A. baumannii by autophagy in host cells, and that isochorismatase plays a critical role in the A. baumannii–induced autophagic process.—Wang, Y., Zhang, K., Shi, X., Wang, C., Wang, F., Fan, J., Shen, F., Xu, J., Bao, W., Liu, M., Yu, L. Critical role of bacterial isochorismatase in the autophagic process induced by Acinetobacter baumannii in mammalian cells.

Recombinant Newcastle disease virus (rL-RVG) triggers autophagy and apoptosis in gastric carcinoma cells by inducing ER stress

We have reported that the recombinant avirulent Newcastle disease virus (NDV) LaSota strain expressing the rabies virus glycoprotein (rL-RVG) could induce autophagy and apoptosis in gastric carcinoma cells. In the present study, we explored the upstream regulators, endoplasmic reticulum (ER) stress that induce autophagy and apoptosis and the relationships among them. For this purpose, SGC-7901 and HGC cells were infected with rL-RVG. NDV LaSota strain and phosphate-buffered saline (PBS) were treated as the control groups. Western blotting and immunofluorescence microscopy were used to detect the expression of the ER stress-related proteins glucose-regulated protein 78 (GRP78) and the transcription factor GADD153 (CHOP), among others. The expression of beclin-1 and the conversion of light chain (LC) 3-I were used to determine the occurrence of autophagy, and flow cytometry (FCM) and western blotting were used to examine apoptosis-related protein expression. Transmission electron microscopy was also performed to monitor the ultrastructure of the cells. Moreover, small interfering (si) RNA was used to knock down CHOP expression. rL-RVG treatment increased the expression of ER stress-related proteins, such as GRP78, CHOP, activating transcriptional factor 6 (ATF6), X-box-binding protein 1 (XBP-1), and phosphorylated eukaryotic initiation factor 2 (p-eIF2α), in a time- and concentration-dependent manner, and knockdown of CHOP reduced LC3-II conversion and beclin-1 expression. When ER stress was inhibited with 4-PBA, the expression of both autophagy-related proteins and apoptosis-related proteins markedly decreased. Interestingly, inhibition of autophagy with 3-methyladenine (3MA) decreased not only apoptosis-related protein expression but also ER stress-related protein expression. Moreover, we found that downregulation of the c-Jun N-terminal kinase (JNK) pathway by SP600125 reduced LC3-II conversion, beclin-1 expression and caspase-3 activation. Collectively, the results suggest that rL-RVG increased ER stress in three branch pathways (ATF6, inositol-requiring enzyme 1 (IRE1), and PKR-like ER protein kinase (PERK)) that are upstream regulators of autophagy and apoptosis. Moreover, the IRE1-JNK pathway played an important role in switching ER stress to autophagy. These findings will provide molecular bases for developing rL-RVG into a drug candidate for the treatment of gastric carcinoma.

Newcastle disease virus NP and P proteins induce autophagy via the endoplasmic reticulum stress-related unfolded protein response

Newcastle disease virus (NDV) can replicate and trigger autophagy in human tumor cells. Our previous study confirmed the critical role of autophagy in NDV infection. Here we studied the role of NDV structural proteins in the induction of autophagy through endoplasmic reticulum (ER) stress-related unfolded protein response (UPR) pathways. Ectopic expression of the NDV nucleocapsid protein (NP) or phosphoprotein (P) was sufficient to induce autophagy. NP or P expression also altered ER homeostasis. The PERK and ATF6 pathways, but not the XBP1 pathway, all of which are components of the UPR, were activated in both NDV-infected and NP or P-transfected cells. Knockdown of PERK or ATF6 inhibited NDV-induced autophagy and reduced the extent of NDV replication. Collectively, these data suggest not only roles for the NDV NP and P proteins in autophagy, but also offer new insights into the mechanisms of NDV-induced autophagy through activation of the ER stress-related UPR pathway.

Mitophagy promotes replication of oncolytic Newcastle disease virus by blocking intrinsic apoptosis in lung cancer cells

Apoptosis contributes to antitumor effect of Newcastle disease virus (NDV). Autophagy is a protective response under cellular stress including viral infection. How autophagy interferes with oncolysis of NDV remains unclear. In this study, we found that NDV La Sota strain induced autophagy and preserved autophagic flux in non-small cell lung cancer cells. NDV-induced autophagy promoted viral replication by blocking cancer cells from caspase-dependent apoptosis. Moreover, we found that NDV recruited SQSTM1-mediated mitophagy to control cytochrome c release, and thus blocked intrinsic pro-apoptotic signaling. Finally, we observed an enhanced oncolysis in NSCLC cells treated with NDV in the presence of an autophagy inhibitor 3-methyladenine (3-MA). Interestingly, a more profound antitumor effect could be achieved when administration of 3-MA was postponed to 24 h after NDV infection. Our findings unveil a novel way that NDV subverts mitophagy to favor its replication by blocking apoptosis, and provide rationale for systemic therapeutic cohort combining NDV with autophagy inhibitors in cancer therapy.

The therapeutic effect of death: Newcastle disease virus and its antitumor potential

Programmed cell death is essential to survival of multicellular organisms. Previously restricted to apoptosis, the concept of programmed cell death is now extended to other mechanisms, as programmed necrosis or necroptosis, autophagic cell death, pyroptosis and parthanatos, among others. Viruses have evolved to manipulate and take control over the programmed cell death response, and the infected cell attempts to neutralize viral infections displaying different stress signals and defensive pathways before taking the critical decision of self-destruction. Learning from viruses and their interplay with the host may help us to better understand the complexity of the self-defense death response that when altered might cause disorders as important as cancer. In addition, as the fields of immunotherapy and oncolytic viruses advance as promising novel cancer therapies, the programmed cell death response reemerges as a key point for the success of both therapeutic approaches. In this review we summarize the research of the multimodal cell death response induced by Newcastle disease viruses (NDV), considered nowadays a promising viral oncolytic therapeutic, and how the manipulation of the host programmed cell death response can enhance the NDV antitumor capacity.

Coxsackievirus A16 elicits incomplete autophagy involving the mTOR and ERK pathways

Autophagy is an important homeostatic process for the degradation of cytosolic proteins and organelles and has been reported to play an important role in cellular responses to pathogens and virus replication. However, the role of autophagy in Coxsackievirus A16 (CA16) infection and pathogenesis remains unknown. Here, we demonstrated that CA16 infection enhanced autophagosome formation, resulting in increased extracellular virus production. Moreover, expression of CA16 nonstructural proteins 2C and 3C was sufficient to trigger autophagosome accumulation by blocking the fusion of autophagosomes with lysosomes. Interestingly, we found that Immunity-related GTPase family M (IRGM) was crucial for the activation of CA16 infection-induced autophagy; in turn, reducing IRGM expression suppressed autophagy. Expression of viral protein 2C enhanced IRGM promoter activation, thereby increasing IRGM expression and inducing autophagy. CA16 infection inhibited Akt/mTOR signaling and activated extracellular signal-regulated kinase (ERK) signaling, both of which are necessary for autophagy induction. In summary, CA16 can use autophagy to enhance its own replication. These results raise the possibility of targeting the autophagic pathway for the treatment of hand, foot, and mouth disease (HFMD).

Therapeutic potential of oncolytic Newcastle disease virus: a critical review

Newcastle disease virus (NDV) features a natural preference for replication in many tumor cells compared with normal cells. The observed antitumor effect of NDV appears to be a result of both selective killing of tumor cells and induction of immune responses. Genetic manipulations to change viral tropism and arming the virus with genes encoding for cytokines improved the oncolytic capacity of NDV. Several intracellular proteins in tumor cells, including antiapoptotic proteins (Livin) and oncogenic proteins (H-Ras), are relevant for the oncolytic activity of NDV. Defects in the interferon system, found in some tumor cells, also contribute to the oncolytic selectivity of NDV. Notwithstanding, NDV displays effective oncolytic activity in many tumor types, despite having intact interferon signaling. Taken together, several cellular systems appear to dictate the selective oncolytic activity of NDV. Some barriers, such as neutralizing antibodies elicited during NDV treatment and the extracellular matrix in tumor tissue appear to interfere with spread of NDV and reduce oncolysis. To further understand the oncolytic activity of NDV, we compared two NDV strains, ie, an attenuated virus (NDV-HUJ) and a pathogenic virus (NDV-MTH-68/H). Significant differences in amino acid sequence were noted in several viral proteins, including the fusion precursor (F0) glycoprotein, an important determinant of replication and pathogenicity. However, no difference in the oncolytic activity of the two strains was noted using human tumor tissues maintained as organ cultures or in mouse tumor models. To optimize virotherapy in clinical trials, we describe here a unique organ culture methodology, using a biopsy taken from a patient’s tumor before treatment for ex vivo infection with NDV to determine the oncolytic potential on an individual basis. In conclusion, oncolytic NDV is an excellent candidate for cancer therapy, but more knowledge is needed to ensure success in clinical trials.

Involvement of fish signal transducer and activator of transcription 3 (STAT3) in nodavirus infection induced cell death

The Janus kinase (JAK)-signal transducer and activator of transcription (STAT) signaling pathway is an important signaling pathway activated by interferons in response to virus infection. Fish STAT3 has been demonstrated to be involved in Singapore grouper iridovirus (SGIV) infection and virus induced paraptosis, but its effects on the replication of other fish viruses still remained uncertain. Here, the roles of grouper STAT3 (Ec-STAT3) in red spotted grouper nervous necrosis virus (RGNNV) infection were investigated. The present data showed that the distribution of phosphorylated Ec-STAT3 was altered in RGNNV infected fish cells, and the promoter activity of STAT3 was significantly increased during virus infection, suggesting that STAT3 activation was involved in RGNNV infection. Using STAT3 specific inhibitor, we found that inhibition of Ec-STAT3 in vitro did not affect the transcription and protein synthesis of RGNNV coat protein (CP), however, the severity of RGNNV induced vacuolation and autophagy was significantly increased. Meanwhile, at the late stage of virus infection, RGNNV induced necrotic cell death was significantly decreased after inhibition of Ec-STAT3. Further studies indicated that Ec-STAT3 inhibition significantly increased the transcript level of autophagy related genes, including UNC-51-like kinase 2 (ULK2) and microtubule-associated protein 1 light chain 3-II (LC3-II) induced by RGNNV infection. Moreover, the expression of several pro-inflammatory factors, including TNFα, IL-1β and IL-8 were mediated by Ec-STAT3 during RGNNV infection. Together, our results not only firstly revealed that STAT3 exerted novel roles in response to fish virus infection, but also provided new insights into understanding the roles of STAT3 in different forms of programmed cell death.

Autophagic flux without a block differentiates varicella-zoster virus infection from herpes simplex virus infection

Autophagy is a process by which misfolded and damaged proteins are sequestered into autophagosomes, before degradation in and recycling from lysosomes. We have extensively studied the role of autophagy in varicella-zoster virus (VZV) infection, and have observed that vesicular cells are filled with >100 autophagosomes that are easily detectable after immunolabeling for the LC3 protein. To confirm our hypothesis that increased autophagosome formation was not secondary to a block, we examined all conditions of VZV infection as well as carrying out two assessments of autophagic flux. We first investigated autophagy in human skin xenografts in the severe combined immunodeficiency (SCID) mouse model of VZV pathogenesis, and observed that autophagosomes were abundant in infected human skin tissues. We next investigated autophagy following infection with sonically prepared cell-free virus in cultured cells. Under these conditions, autophagy was detected in a majority of infected cells, but was much less than that seen after an infected-cell inoculum. In other words, inoculation with lower-titered cell-free virus did not reflect the level of stress to the VZV-infected cell that was seen after inoculation of human skin in the SCID mouse model or monolayers with higher-titered infected cells. Finally, we investigated VZV-induced autophagic flux by two different methods (radiolabeling proteins and a dual-colored LC3 plasmid); both showed no evidence of a block in autophagy. Overall, therefore, autophagy within a VZV-infected cell was remarkably different from autophagy within an HSV-infected cell, whose genome contains two modifiers of autophagy, ICP34.5 and US11, not present in VZV.

Pharmacological modulation of autophagy enhances Newcastle disease virus-mediated oncolysis in drug-resistant lung cancer cells

Background

Oncolytic viruses represent a promising therapy against cancers with acquired drug resistance. However, low efficacy limits its clinical application. The objective of this study is to investigate whether pharmacologically modulating autophagy could enhance oncolytic Newcastle disease virus (NDV) strain NDV/FMW virotherapy of drug-resistant lung cancer cells.

Methods

The effect of NDV/FMW infection on autophagy machinery in A549 lung cancer cell lines resistant to cisplatin (A549/DDP) or paclitaxel (A549/PTX) was investigated by detection of GFP-microtubule-associated protein 1 light chain 3 (GFP-LC3) puncta, formation of double-membrane vesicles and conversion of the nonlipidated form of LC3 (LC3-I) to the phosphatidylethanolamine-conjugated form (LC3-II). The effects of autophagy inhibitor chloroquine (CQ) and autophagy inducer rapamycin on NDV/FMW-mediated antitumor activity were evaluated both in culture cells and in mice bearing drug-resistant lung cancer cells.

Results

We show that NDV/FMW triggers autophagy in A549/PTX cells via dampening the class I PI3K/Akt/mTOR/p70S6K pathway, which inhibits autophagy. On the contrary, NDV/FMW infection attenuates the autophagic process in A549/DDP cells through the activation of the negative regulatory pathway. Furthermore, combination with CQ or knockdown of ATG5 significantly enhances NDV/FMW-mediated antitumor effects on A549/DDP cells, while the oncolytic efficacy of NDV/FMW in A549/PTX cells is significantly improved by rapamycin. Interestingly, autophagy modulation does not increase virus progeny in these drug resistant cells. Importantly, CQ or rapamycin significantly potentiates NDV/FMW oncolytic activity in mice bearing A549/DDP or A549/PTX cells respectively.

Conclusions

These results demonstrate that combination treatment with autophagy modulators is an effective strategy to augment the therapeutic activity of NDV/FMW against drug-resistant lung cancers.

Oncolytic viruses as anticancer vaccines

Oncolytic virotherapy has shown impressive results in preclinical studies and first promising therapeutic outcomes in clinical trials as well. Since viruses are known for a long time as excellent vaccination agents, oncolytic viruses are now designed as novel anticancer agents combining the aspect of lysis-dependent cytoreductive activity with concomitant induction of antitumoral immune responses. Antitumoral immune activation by oncolytic virus infection of tumor tissue comprises both, immediate effects of innate immunity and also adaptive responses for long lasting antitumoral activity, which is regarded as the most prominent challenge in clinical oncology. To date, the complex effects of a viral tumor infection on the tumor microenvironment and the consequences for the tumor-infiltrating immune cell compartment are poorly understood. However, there is more and more evidence that a tumor infection by an oncolytic virus opens up a number of options for further immunomodulating interventions such as systemic chemotherapy, generic immunostimulating strategies, dendritic cell-based vaccines, and antigenic libraries to further support clinical efficacy of oncolytic virotherapy.