Newcastle disease virus triggers autophagy in U251 glioma cells to enhance virus replication

The heterogeneous sensitivity of pediatric brain tumors to different oncolytic viruses is predicted by unique gene expression profiles

Despite decades of research, the prognosis of high-grade pediatric brain tumors (PBTs) remains dismal; however, recent cases of favorable clinical responses were documented in clinical trials using oncolytic viruses (OVs). In the current study, we employed four different species of OVs: adenovirus Delta24-RGD, herpes simplex virus rQNestin34.5v1, reovirus R124, and the non-virulent Newcastle disease virus rNDV-F0-GFP against three entities of PBTs (high-grade gliomas, atypical teratoid/rhabdoid tumors, and ependymomas) to determine their in vitro efficacy. These four OVs were screened on 14 patient-derived PBT cell cultures and the degree of oncolysis was assessed using an ATP-based assay. Subsequently, the observed viral efficacies were correlated to whole transcriptome data and Gene Ontology analysis was performed. Although no significant tumor type-specific OV efficacy was observed, the analysis revealed the intrinsic biological processes that associated with OV efficacy. The predictive power of the identified expression profiles was further validated in vitro by screening additional PBTs. In summary, our results demonstrate OV susceptibility of multiple patient-derived PBT entities and the ability to predict in vitro responses to OVs using unique expression profiles. Such profiles may hold promise for future OV preselection with effective oncolytic potency in a specific tumor, therewith potentially improving OV responses.

The Application of Newcastle Disease Virus (NDV): Vaccine Vectors and Tumor Therapy

Newcastle disease virus (NDV) is an avian pathogen with an unsegmented negative-strand RNA genome that belongs to the Paramyxoviridae family. While primarily pathogenic in birds, NDV presents no threat to human health, rendering it a safe candidate for various biomedical applications. Extensive research has highlighted the potential of NDV as a vector for vaccine development and gene therapy, owing to its transcriptional modularity, low recombination rate, and lack of a DNA phase during replication. Furthermore, NDV exhibits oncolytic capabilities, efficiently eliciting antitumor immune responses, thereby positioning it as a promising therapeutic agent for cancer treatment. This article comprehensively reviews the biological characteristics of NDV, elucidates the molecular mechanisms underlying its oncolytic properties, and discusses its applications in the fields of vaccine vector development and tumor therapy.

Viruses and autophagy: bend, but don't break

Autophagy is a constitutive cellular process of degradation required to maintain homeostasis and turn over spent organelles and aggregated proteins. For some viruses, the process can be antiviral, degrading viral proteins or virions themselves. For many other viruses, the induction of the autophagic process provides a benefit and promotes viral replication. In this Review, we survey the roles that the autophagic pathway plays in the replication of viruses. Most viruses that benefit from autophagic induction block autophagic degradation, which is a 'bend, but don't break' strategy initiating but limiting a potentially antiviral response. In almost all cases, it is other effects of the redirected autophagic machinery that benefit these viruses. This rapid mechanism to generate small double-membraned vesicles can be usurped to shape membranes for viral genome replication and virion maturation. However, data suggest that autophagic maintenance of cellular homeostasis is crucial for the initiation of infection, as viruses have evolved to replicate in normal, healthy cells. Inhibition of autophagic degradation is important once infection has initiated. Although true degradative autophagy is probably a negative for most viruses, initiating nondegradative autophagic membranes benefits a wide variety of viruses.

Autophagy inhibition suppresses Newcastle disease virus-induced cell death by inhibiting viral replication in human breast cancer cells

Newcastle disease virus (NDV) is an oncolytic virus which selectively replicates in cancer cells without harming normal cells. Autophagy is a cellular mechanism that breaks down unused cytoplasmic constituents into nutrients. In previous studies, autophagy enhanced NDV-induced oncolysis in lung cancer and glioma cells. However, the effect of autophagy inhibition on NDV-induced oncolysis in breast cancer cells remains unknown. This study aimed to examine the effect of autophagy inhibition on NDV-induced oncolysis in human breast cancer cells, MCF7. To inhibit autophagy, we knocked down the expression of the autophagy protein beclin-1 (BECN1) by short interfering RNA (siRNA). The cells were infected with the recombinant NDV strain AF2240 expressing green fluorescent protein. We found that NDV induced autophagy and knockdown of BECN1 significantly reduced the NDV-induced autophagy in MCF7 cells. Importantly, BECN1 knockdown significantly suppressed cell death by inhibiting viral replication, as observed at 24 h post infection. Overall, our data suggest that autophagy inhibition may not be a suitable strategy to enhance NDV oncolytic efficacy against breast cancer.

The Viral Knock: Ameliorating Cancer Treatment with Oncolytic Newcastle Disease Virus

The prospect of cancer treatment has drastically transformed over the last four decades. The side effects caused by the traditional methods of cancer treatment like surgery, chemotherapy, and radiotherapy through the years highlight the prospect for a novel, complementary, and alternative cancer therapy. Oncolytic virotherapy is an evolving treatment modality that utilizes oncolytic viruses (OVs) to selectively attack cancer cells by direct lysis and can also elicit a strong anti-cancer immune response. Newcastle disease virus (NDV) provides a very high safety profile compared to other oncolytic viruses. Extensive research worldwide concentrates on experimenting with and better understanding the underlying mechanisms by which oncolytic NDV can be effectively applied to intercept cancer. This review encapsulates the potential of NDV to be explored as an oncolytic agent and discusses current preclinical and clinical research scenarios involving various NDV strains.

NDV-induced autophagy enhances inflammation through NLRP3/Caspase-1 inflammasomes and the p38/MAPK pathway

Newcastle disease (ND), caused by the Newcastle disease virus (NDV), is a highly virulent infectious disease of poultry. Virulent NDV can cause severe autophagy and inflammation in host cells. While studies have shown a mutual regulatory relationship between autophagy and inflammation, this relationship in NDV infection remains unclear. This study confirmed that NDV infection could trigger autophagy in DF-1 cells to promote cytopathic and viral replication. NDV-induced autophagy was positively correlated with the mRNA levels of inflammatory cytokines such as IL-1β, IL-8, IL-18, CCL-5, and TNF-α, suggesting that NDV-induced autophagy promotes the expression of inflammatory cytokines. Further investigation demonstrated that NLRP3 protein expression, Caspase-1 activity, and p38 phosphorylation level positively correlated with autophagy, suggesting that NDV-induced autophagy could promote the expression of inflammatory cytokines through NLRP3/Caspase-1 inflammasomes and p38/MAPK pathway. In addition, NDV infection also triggered mitochondrial damage and mitophagy in DF-1 cells, but did not result in a large leakage of reactive oxygen species (ROS) and mitochondrial DNA (mtDNA), indicating that mitochondrial damage and mitophagy do not contribute to the inflammation response during NDV infection.

Pathologic Mechanisms of the Newcastle Disease Virus

Newcastle disease (ND) has been a consistent risk factor to the poultry industry worldwide. Its pathogen, Newcastle disease virus (NDV), is also a promising antitumor treatment candidate. The pathogenic mechanism has intrigued the great curiosity of researchers, and advances in the last two decades have been summarized in this paper. The NDV’s pathogenic ability is highly related to the basic protein structure of the virus, which is described in the Introduction of this review. The overall clinical signs and recent findings pertaining to NDV-related lymph tissue damage are then described. Given the involvement of cytokines in the overall virulence of NDV, cytokines, particularly IL6 and IFN expressed during infection, are reviewed. On the other hand, the host also has its way of antagonizing the virus, which starts with the detection of the pathogen. Thus, advances in NDV’s physiological cell mechanism and the subsequent IFN response, autophagy, and apoptosis are summarized to provide a whole picture of the NDV infection process.

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

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

The game between host antiviral innate immunity and immune evasion strategies of senecavirus A - A cell biological perspective

Innate immunity is the first line of the cellular host to defend against viral infection. Upon infection, viruses can be sensed by the cellular host's pattern recognition receptors (PRRs), leading to the activation of the signaling cascade and the robust production of interferons (IFNs) to restrict the infection and replication of the viruses. However, numerous cunning viruses have evolved strategies to evade host innate immunity. The senecavirus A (SVA) is a newly identified member of the Picornaviridae family, causing severe vesicular or ulcerative lesions on the oral mucosa, snout, coronary bands, and hooves of pigs of different ages. During SVA infection, the cellular host will launch the innate immune response and various physiological processes to restrict SVA. In contrast, SVA has evolved several strategies to evade the porcine innate immune responses. This review focus on the underlying mechanisms employed by SVA to evade pattern recognition receptor signaling pathways, type I interferon (IFN-α/β) receptor (IFNAR) signaling pathway, interferon-stimulated genes (ISGs) and autophagy, and stress granules. Deciphering the antiviral immune evasion mechanisms by SVA will enhance our understanding of SVA's pathogenesis and provide insights into developing antiviral strategies and improving vaccines.

When ferroptosis meets pathogenic infections

Apoptosis, necrosis, or autophagy are diverse types of regulated cell death (RCD), recognized as the strategies that host cells use to defend against pathogens such as viruses, bacteria, or fungi. Pathogens can induce or block different types of host cell RCD, promoting propagation or evading host immune surveillance. Ferroptosis is a newly identified RCD. Evidence has demonstrated how pathogens regulate ferroptosis to promote their replication, dissemination, and pathogenesis. However, the interaction between ferroptosis and pathogenic infections still needs to be completely elucidated. This review summarizes the advances in the interaction between pathogenic infections and host ferroptotic processes, focusing on the underlying mechanisms of how pathogens exploit ferroptosis, and discussing possible therapeutic measures against pathogen-associated diseases in a ferroptosis-dependent manner.

SLC1A3 facilitates Newcastle disease virus replication by regulating glutamine catabolism

As obligate intracellular parasites, viruses rely completely on host metabolic machinery and hijack host nutrients for viral replication. Newcastle disease virus (NDV) causes acute, highly contagious avian disease and functions as an oncolytic agent. NDV efficiently replicates in both chicken and tumour cells. However, how NDV reprograms host cellular metabolism for its efficient replication is still ill-defined. We previously identified a significantly upregulated glutamate transporter gene, solute carrier family 1 member 3 (SLC1A3), during NDV infection via transcriptome analysis. To investigate the potential role of SLC1A3 during NDV infection, we first confirmed the marked upregulation of SLC1A3 in NDV-infected DF-1 or A549 cells through p53 and NF-κB pathways. Knockdown of SLC1A3 inhibited NDV infection. Western blot analysis further confirmed that glutamine, but not glutamate, asparagine, or aspartate, was required for NDV replication. Metabolic flux data showed that NDV promotes the decomposition of glutamine into the tricarboxylic acid cycle. Importantly, the level of glutamate and glutaminolysis were reduced by SLC1A3 knockdown, indicating that SLC1A3 propelled glutaminolysis for glutamate utilization and NDV replication in host cells. Taken together, our data identify that SLC1A3 serves as an important regulator for glutamine metabolism and is hijacked by NDV for its efficient replication during NDV infection. These results improve our understanding of the interaction between NDV and host cellular metabolism and lay the foundation for further investigation of efficient vaccines.

Gospel of malignant Glioma: Oncolytic virus therapy

Glioma accounts for nearly 80% of all intracranial malignant tumors. It is a major challenge to society as it is causes to impaired brain function in many patients. Currently, gliomas are mainly treated with surgery, postoperative radiotherapy, and chemotherapy. However, the curative effects of these treatments are not satisfactory. Oncolytic virus (OV) is a novel treatment which works by activating the immune functions and inducing apoptosis of tumor cells. The OV propagates indefinitely in the host cell, eventually leading to the death of host cell. Subsequently, a large number of antigens and signal molecules are released which exert antitumor immunity. Several preclinical and clinical studies have shown that G207, DNX2401, Zika and other viruses have important roles in malignant tumors. For example, these viruses can reduce the growth of tumor cells without causing severe complications. However, the known OVs have not been clearly classified. Herein, we divided OVs into neurotropic and non-neurophilic OVs based on whether the OVs are naturally neurotropic or not. The therapeutic effects of each group were compared. Finally, challenges encountered in the clinical application of OVs in the treatment of malignant gliomas were summarized.

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.

SARS-CoV-2 spike promotes inflammation and apoptosis through autophagy by ROS-suppressed PI3K/AKT/mTOR signaling

Background

Severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2) infection-induced inflammatory responses are largely responsible for the death of novel coronavirus disease 2019 (COVID-19) patients. However, the mechanism by which SARS-CoV-2 triggers inflammatory responses remains unclear. Here, we aimed to explore the regulatory role of SARS-CoV-2 spike protein in infected cells and attempted to elucidate the molecular mechanism of SARS-CoV-2-induced inflammation.

Methods

SARS-CoV-2 spike pseudovirions (SCV-2-S) were generated using the spike-expressing virus packaging system. Western blot, mCherry-GFP-LC3 labeling, immunofluorescence, and RNA-seq were performed to examine the regulatory mechanism of SCV-2-S in autophagic response. The effects of SCV-2-S on apoptosis were evaluated by terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL), Western blot, and flow cytometry analysis. Enzyme-linked immunosorbent assay (ELISA) was carried out to examine the mechanism of SCV-2-S in inflammatory responses.

Results

Angiotensin-converting enzyme 2 (ACE2)-mediated SCV-2-S infection induced autophagy and apoptosis in human bronchial epithelial and microvascular endothelial cells. Mechanistically, SCV-2-S inhibited the PI3K/AKT/mTOR pathway by upregulating intracellular reactive oxygen species (ROS) levels, thus promoting the autophagic response. Ultimately, SCV-2-S-induced autophagy triggered inflammatory responses and apoptosis in infected cells. These findings not only improve our understanding of the mechanism underlying SARS-CoV-2 infection-induced pathogenic inflammation but also have important implications for developing anti-inflammatory therapies, such as ROS and autophagy inhibitors, for COVID-19 patients.

Autophagy Modulation by Viral Infections Influences Tumor Development

Autophagy is a self-degradative process important for balancing cellular homeostasis at critical times in development and/or in response to nutrient stress. This is particularly relevant in tumor model in which autophagy has been demonstrated to have an important impact on tumor behavior. In one hand, autophagy limits tumor transformation of precancerous cells in early stage, and in the other hand, it favors the survival, proliferation, metastasis, and resistance to antitumor therapies in more advanced tumors. This catabolic machinery can be induced by an important variety of extra- and intracellular stimuli. For instance, viral infection has often been associated to autophagic modulation, and the role of autophagy in virus replication differs according to the virus studied. In the context of tumor development, virus-modulated autophagy can have an important impact on tumor cells' fate. Extensive analyses have shed light on the molecular and/or functional complex mechanisms by which virus-modulated autophagy influences precancerous or tumor cell development. This review includes an overview of discoveries describing the repercussions of an autophagy perturbation during viral infections on tumor behavior.

Newcastle disease virus degrades SIRT3 via PINK1-PRKN-dependent mitophagy to reprogram energy metabolism in infected cells

Lacking a self-contained metabolism network, viruses have evolved multiple mechanisms for rewiring the metabolic system of their host to hijack the host's metabolic resources for replication. Newcastle disease virus (NDV) is a paramyxovirus, as an oncolytic virus currently being developed for cancer treatment. However, how NDV alters cellular metabolism is still far from fully understood. In this study, we show that NDV infection reprograms cell metabolism by increasing glucose utilization in the glycolytic pathway. Mechanistically, NDV induces mitochondrial damage, elevated mitochondrial reactive oxygen species (mROS) and ETC dysfunction. Infection of cells depletes nucleotide triphosphate levels, resulting in elevated AMP:ATP ratios, AMP-activated protein kinase (AMPK) phosphorylation, and MTOR crosstalk mediated autophagy. In a time-dependent manner, NDV shifts the balance of mitochondrial dynamics from fusion to fission. Subsequently, PINK1-PRKN-dependent mitophagy was activated, forming a ubiquitin chain with MFN2 (mitofusin 2), and molecular receptor SQSTM1/p62 recognized damaged mitochondria. We also found that NDV infection induces NAD⁺-dependent deacetylase SIRT3 loss via mitophagy to engender HIF1A stabilization, leading to the switch from oxidative phosphorylation (OXPHOS) to aerobic glycolysis. Overall, these studies support a model that NDV modulates host cell metabolism through PINK1-PRKN-dependent mitophagy for degrading SIRT3.Abbreviations: AMPK: AMP-activated protein kinase; CCCP: carbonyl cyanide 3-chlorophenylhydrazone; ECAR: extracellular acidification rate; hpi: hours post infection LC-MS: liquid chromatography-mass spectrometry; mito-QC: mCherry-GFP-FIS1[mt101-152]; MFN2: mitofusin 2; MMP: mitochondrial membrane potential; mROS: mitochondrial reactive oxygen species; MOI: multiplicity of infection; 2-NBDG: 2-(N-(7-nitrobenz-2-oxa-1, 3-diazol-4-yl) amino)-2-deoxyglucose; NDV: newcastle disease virus; OCR: oxygen consumption rate; siRNA: small interfering RNA; SIRT3: sirtuin 3; TCA: tricarboxylic acid; TCID₅₀: tissue culture infective doses.

Oncolytic Viruses: Newest Frontier for Cancer Immunotherapy

Cancer remains a leading cause of death worldwide. Despite many signs of progress, currently available cancer treatments often do not provide desired outcomes for too many cancers. Therefore, newer and more effective therapeutic approaches are needed. Oncolytic viruses (OVs) have emerged as a novel cancer treatment modality, which selectively targets and kills cancer cells while sparing normal ones. In the past several decades, many different OV candidates have been developed and tested in both laboratory settings as well as in cancer patient clinical trials. Many approaches have been taken to overcome the limitations of OVs, including engineering OVs to selectively activate anti-tumor immune responses. However, newer approaches like the combination of OVs with current immunotherapies to convert "immune-cold" tumors to "immune-hot" will almost certainly improve the potency of OVs. Here, we discuss strategies that are explored to further improve oncolytic virotherapy.

Autophagy in Tumor Immunity and Viral-Based Immunotherapeutic Approaches in Cancer

Autophagy is a fundamental catabolic process essential for the maintenance of cellular and tissue homeostasis, as well as directly contributing to the control of invading pathogens. Unsurprisingly, this process becomes critical in supporting cellular dysregulation that occurs in cancer, particularly the tumor microenvironments and their immune cell infiltration, ultimately playing a role in responses to cancer therapies. Therefore, understanding "cancer autophagy" could help turn this cellular waste-management service into a powerful ally for specific therapeutics. For instance, numerous regulatory mechanisms of the autophagic machinery can contribute to the anti-tumor properties of oncolytic viruses (OVs), which comprise a diverse class of replication-competent viruses with potential as cancer immunotherapeutics. In that context, autophagy can either: promote OV anti-tumor effects by enhancing infectivity and replication, mediating oncolysis, and inducing autophagic and immunogenic cell death; or reduce OV cytotoxicity by providing survival cues to tumor cells. These properties make the catabolic process of autophagy an attractive target for therapeutic combinations looking to enhance the efficacy of OVs. In this article, we review the complicated role of autophagy in cancer initiation and development, its effect on modulating OVs and immunity, and we discuss recent progress and opportunities/challenges in targeting autophagy to enhance oncolytic viral immunotherapy.

Oncolytic Virus-Induced Autophagy in Glioblastoma

Simple Summary

Glioblastoma (GBM) is the most common and aggressive brain tumor with an incidence rate of nearly 3.19/100,000. Current therapeutic options fall short in improving the survival of patients with GBM. Various genetic and microenvironmental factors contribute to GBM progression and resistance to therapy. The development of gene therapies using self-replicating oncolytic viruses can advance GBM treatment. Due to GBM heterogeneity, oncolytic viruses have been genetically modified to improve the antiglioma effect in vitro and in vivo. Oncolytic viruses can activate autophagy signaling in GBM upon tumoral infection. Autophagy can be cytoprotective, whereby the GBM cells catabolize damaged organelles to accommodate to virus-induced stress, or cytotoxic, whereby it leads to the destruction of GBM cells. Understanding the molecular mechanisms that control oncolytic virus-induced autophagic signaling in GBM can fuel further development of novel and more effective genetic vectors.

Abstract

Autophagy is a catabolic process that allows cells to scavenge damaged organelles and produces energy to maintain cellular homeostasis. It is also an effective defense method for cells, which allows them to identify an internalized pathogen and destroy it through the fusion of the autophagosome and lysosomes. Recent reports have demonstrated that various chemotherapeutic agents and viral gene therapeutic vehicles provide therapeutic advantages for patients with glioblastoma as monotherapy or in combination with standards of care. Despite nonstop efforts to develop effective antiglioma therapeutics, tumor-induced autophagy in some studies manifests tumor resistance and glioma progression. Here, we explore the functional link between autophagy regulation mediated by oncolytic viruses and discuss how intracellular interactions control autophagic signaling in glioblastoma. Autophagy induced by oncolytic viruses plays a dual role in cell death and survival. On the one hand, autophagy stimulation has mostly led to an increase in cytotoxicity mediated by the oncolytic virus, but, on the other hand, autophagy is also activated as a cell defense mechanism against intracellular pathogens and modulates antiviral activity through the induction of ER stress and unfolded protein response (UPR) signaling. Despite the fact that the moment of switch between autophagic prosurvival and prodeath modes remains to be known, in the context of oncolytic virotherapy, cytotoxic autophagy is a crucial mechanism of cancer cell death.

Newcastle-disease-virus-induced ferroptosis through nutrient deprivation and ferritinophagy in tumor cells

A number of new cell death processes have been discovered in recent years, including ferroptosis, which is characterized by the accumulation of lipid peroxidation products derived from iron metabolism. The evidence suggests that ferroptosis has a tumor-suppressor function. However, the mechanism by which ferroptosis mediates the response of tumor cells to oncolytic viruses remains poorly understood. The Newcastle disease virus (NDV) can selectively replicate in tumor cells. We show that NDV-induced ferroptosis acts through p53-SLC7A11-GPX4 pathway. Meanwhile, the levels of intracellular reactive oxygen species and lipid peroxides increased in tumor cells. Ferritinophagy was induced by NDV promotion of ferroptosis through the release of ferrous iron and an enhanced Fenton reaction. Collectively, these observations demonstrated that the NDV can kill tumor cells through ferroptosis. Our study provides novel insights into the mechanisms of NDV-induced ferroptosis and highlights the critical role of viruses in treating therapy-resistant cancers.

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Oncolytic viruses NDV caused tumor cells death through ferroptosis

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NDV-induced ferroptosis acts through nutrient deprivation by suppression of System Xc⁻

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P53 activation is required for NDV-induced ferroptosis initiation

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Ferritinophagy induced by NDV promotes ferroptosis through release of ferrous iron

Intratumoral Virotherapy with Wild-Type Newcastle Disease Virus in Carcinoma Krebs-2 Cancer Model

The results of experimental and clinical trials of the agents based on oncolytic Newcastle disease virus (NDV) strains provided hope for the development of virotherapy as a promising method for treating human tumors. However, the mechanism of the antitumor effect of NDV and realization of its cytotoxic potential in a cancer cell remains to be elucidated. In the current work, we have studied the antitumor effect of NDV in a syngeneic model of mouse Krebs-2 carcinoma treated with intratumoral injections of a wild-type strain NDV/Altai/pigeon/770/2011. Virological methods were used for preparation of a virus-containing sample. Colorimetric MTS assay was used to assess the viability of Krebs-2 tumor cells infected with a viral strain in vitro. In vivo virotherapy was performed in eight-week-old male BALB/c mice treated with serial intratumoral injections of NDV in an experimental model of Krebs-2 solid carcinoma. Changes in the tumor nodes of Krebs-2 carcinoma after virotherapy were visualized by MRI and immunohistological staining. Light microscopy examination, immunohistochemical and morphometric analyses have shown that intratumoral viral injections contribute to the inhibition of tumor growth, appearance of necrosis-like changes in the tumor tissue and the antiangiogenic effect of the virus. It has been established that a course of intratumoral virotherapy with NDV/Altai/pigeon/770/2011 strain in a mouse Krebs-2 carcinoma resulted in increased destructive changes in the tumor tissue, in the volume density of necrotic foci and numerical density of endothelial cells expressing CD34 and VEGFR. These results indicate that intratumoral NDV injection reduces tumor progression of an aggressive tumor.

Personalizing Oncolytic Virotherapy for Glioblastoma: In Search of Biomarkers for Response

Simple Summary

Glioblastoma (GBM) is the most frequent and aggressive primary brain tumor. Despite multimodal treatment, the prognosis of GBM patients remains very poor. Oncolytic virotherapy is being evaluated as novel treatment for this patient group and clinical trials testing oncolytic viruses have shown impressive responses, albeit in a small subset of GBM patients. Obtaining insight into specific tumor- or patient-related characteristics of the responding patients, may in the future improve response rates. In this review we discuss factors related to oncolytic activity of the most widely applied oncolytic virus strains as well as potential biomarkers and future assays that may allow us to predict response to these agents. Such biomarkers and tools may in the future enable personalizing oncolytic virotherapy for GBM patients.

Abstract

Oncolytic virus (OV) treatment may offer a new treatment option for the aggressive brain tumor glioblastoma. Clinical trials testing oncolytic viruses in this patient group have shown promising results, with patients achieving impressive long-term clinical responses. However, the number of responders to each OV remains low. This is thought to arise from the large heterogeneity of these tumors, both in terms of molecular make-up and their immune-suppressive microenvironment, leading to variability in responses. An approach that may improve response rates is the personalized utilization of oncolytic viruses against Glioblastoma (GBM), based on specific tumor- or patient-related characteristics. In this review, we discuss potential biomarkers for response to different OVs as well as emerging ex vivo assays that in the future may enable selection of optimal OV for a specific patient and design of stratified clinical OV trials for GBM.

Crosstalk between oncolytic viruses and autophagy in cancer therapy

Oncolytic viruses have attracted attention as a promising strategy in cancer therapy owing to their ability to selectively infect and kill tumor cells, without affecting healthy cells. They also exert their anti-tumor effects by releasing immunostimulatory molecules from dying cancer cells. Several regulatory mechanisms, such as autophagy, contribute to the anti-tumor properties of oncolytic viruses. Autophagy is a conserved catabolic process in responses to various stresses, such as nutrient deprivation, hypoxia, and infection that produces energy by lysosomal degradation of intracellular contents. Autophagy can support infectivity and replication of the oncolytic virus and enhance their anti-tumor effects via mediating oncolysis, autophagic cell death, and immunogenic cell death. On the other hand, autophagy can reduce the cytotoxicity of oncolytic viruses by providing survival nutrients for tumor cells. In his review, we summarize various types of oncolytic viruses in clinical trials, their mechanism of action, and autophagy machinery. Furthermore, we precisely discuss the interaction between oncolytic viruses and autophagy in cancer therapy and their combinational effects on tumor cells.

Eating the unknown: Xenophagy and ER-phagy are cytoprotective defenses against pathogens

Autophagy is an evolutionary conserved catabolic process devoted to the removal of unnecessary and harmful cellular components. In its general form, autophagy governs cellular lifecycle through the formation of double membrane vesicles, termed autophagosomes, that enwrap and deliver unwanted intracellular components to lysosomes. In addition to this omniscient role, forms of selective autophagy, relying on specialized receptors for cargo recognition, exert fine-tuned control over cellular homeostasis. In this regard, xenophagy plays a pivotal role in restricting the replication of intracellular pathogens, thus acting as an ancient innate defense system against infections. Recently, selective autophagy of the endoplasmic reticulum (ER), more simply ER-phagy, has been uncovered as a critical mechanism governing ER network shape and function. Six ER-resident proteins have been characterized as ER-phagy receptors and their orchestrated function enables ER homeostasis and turnover overtime. Unfortunately, ER is also the preferred site for viral replication and several viruses hijack ER machinery for their needs. Thus, it is not surprising that some ER-phagy receptors can act to counteract viral replication and minimize the spread of infection throughout the organism. On the other hand, evolutionary pressure has armed pathogens with strategies to evade and subvert xenophagy and ER-phagy. Although ER-phagy biology is still in its infancy, the present review aims to summarize recent ER-phagy literature, with a special focus on its role in counteracting viral infections. Moreover, we aim to offer some hints for future targeted approaches to counteract host-pathogen interactions by modulating xenophagy and ER-phagy pathways.

Kinase inhibitors with viral oncolysis: Unmasking pharmacoviral approaches for cancer therapy

There are more than 500 kinases in the human genome, many of which are oncogenic once constitutively activated. Fortunately, numerous hyperactive kinases are druggable, and several targeted small molecule kinase inhibitors have demonstrated impressive clinical benefits in cancer treatment. However, their often cytostatic rather than cytotoxic effect on cancer cells, and the development of resistance mechanisms, remain significant limitations to these targeted therapies. Oncolytic viruses are an emerging class of immunotherapeutic agents with a specific oncotropic nature and excellent safety profile, highlighting them as a promising alternative to conventional therapeutic modalities. Nonetheless, the clinical efficacy of oncolytic virotherapy is challenged by immunological and physical barriers that limit viral delivery, replication, and spread within tumours. Several of these barriers are often associated with oncogenic kinase activity and, in some cases, worsened by the action of oncolytic viruses on kinase signaling during infection. What if inhibiting these kinases could potentiate the cancer-lytic and anti-tumour immune stimulating properties of oncolytic virotherapies? This could represent a paradigm shift in the use of specific kinase inhibitors in the clinic and provide a novel therapeutic approach to the treatment of cancers. A phase III clinical trial combining the oncolytic Vaccinia virus Pexa-Vec with the kinase inhibitor Sorafenib was initiated. While this trial failed to show any benefits over Sorafenib monotherapy in patients with advanced liver cancer, several pre-clinical studies demonstrate that targeting kinases combined with oncolytic viruses have synergistic effects highlighting this strategy as a unique avenue to cancer therapy. Herein, we review the combinations of oncolytic viruses with kinase inhibitors reported in the literature and discuss the clinical opportunities that represent these pharmacoviral approaches.

Siniperca chuatsi rhabdovirus (SCRV) induces autophagy via PI3K/Akt-mTOR pathway in CPB cells

Autophagy is an important mechanism for organisms to eliminate viruses and other intracellular pathogens. Siniperca chuatsi rhabdovirus (SCRV) is an agent that has caused devastating losses in Chinese perch (Siniperca chuatsi) industry. But the role of autophagy in Siniperca chuatsi rhabdovirus (SCRV) infection is not clearly understood. In this study, we identified that SCRV infection triggered autophagy in CPB cells, which was demonstrated by the appearance of the membrane vesicles, GFP-LC3 punctuate pattern, conversion of LC3-I to LC3-II, and the co-localization of autophagosomes and lysosomes. The changes of autophagy flux in SCRV infection indicated that autophagy was inhibited at the early stage of SCRV infection, but was promoted at the late stage. UV-inactivated SCRV can induce autophagy, suggesting that SCRV replication is not essential for the induction of autophagy. Furthermore, we found inducing autophagy with Rapa inhibited SCRV proliferation, but inhibiting autophagy with 3-MA or CQ increased SCRV production in CPB cells. Then we assessed the effects of PI3K/Akt-mTOR signaling pathway on SCRV induced autophagy. We found that SCRV infection activated PI3K/AKT signaling pathway at 4 hpi, but inhibited it at 8 hpi. SCRV-N mRNA and protein level were decreased by inhibiting PI3K with LY294002, but increased by activating PI3K with 740Y-P. Those results indicated that SCRV infection induced autophagy via the PI3K/Akt-mTOR signal pathway, which will provide new insights into SCRV pathogenesis and antiviral treatment strategies.

Newcastle Disease virus infection activates PI3K/Akt/mTOR and p38 MAPK/Mnk1 pathways to benefit viral mRNA translation via interaction of the viral NP protein and host eIF4E

Newcastle disease virus (NDV), a member of the Paramyxoviridae family, can activate PKR/eIF2α signaling cascade to shutoff host and facilitate viral mRNA translation during infection, however, the mechanism remains unclear. In this study, we revealed that NDV infection up-regulated host cap-dependent translation machinery by activating PI3K/Akt/mTOR and p38 MAPK/Mnk1 pathways. In addition, NDV infection induced p38 MAPK/Mnk1 signaling participated 4E-BP1 hyperphosphorylation for efficient viral protein synthesis when mTOR signaling is inhibited. Furthermore, NDV NP protein was found to be important for selective cap-dependent translation of viral mRNAs through binding to eIF4E during NDV infection. Taken together, NDV infection activated multiple signaling pathways for selective viral protein synthesis in infected cells, via interaction between viral NP protein and host translation machinery. Our results may help to design novel targets for therapeutic intervention against NDV infection and to understand the NDV anti-oncolytic mechanism.

Viruses are obligate intracellular parasites and have no protein translation machinry of their own. Therefore, viruses remain exclusively dependent on host translation machinery to ensure viral protein synthesis and progeny virion production during infection. We previous reported that Newcastle disease virus (NDV) shutoff host and facilitate viral mRNA translation by activating PKR/eIF2α signaling cascade. Here, we demonstrated that NDV infection up-regulated host cap-dependent translation machinery by activating PI3K/Akt/mTOR and p38 MAPK/Mnk1 pathways. Furthermore, NDV NP protein was found to be important for selective cap-dependent translation of viral mRNAs. Our findings highlight a new strategy how virus used host translation machinery for selective viral protein synthesis.

Targeting STAT3 enhances NDV-induced immunogenic cell death in prostate cancer cells

Oncolytic Newcastle disease virus (NDV) induces immunogenic cell death (ICD), liberating danger-associated molecular patterns (DAMPs) that provokes defiance in neoplastic malignancy. The present study aims to investigate whether and how oncolytic NDV triggers ICD in prostate cancer cells. We show that NDV/FMW, an oncolytic NDV strain FMW, elicited the expression and release of several ICD markers, that is calreticulin (CRT), heat shock proteins (HSP70/90) and high-mobility group box 1 (HMGB1), in prostate cancer cells. Furthermore, pharmacological repression of apoptosis, necroptosis, autophagy or endoplasmic reticulum (ER) stress exerted diverse effects on the HMGB1 and HSP70/90 evacuation in NDV/FMW-infected prostate cancer cells. Moreover, ICD markers induced in prostate cancer cells upon NDV/FMW infection, were enhanced by either treatment with a STAT3 (signal transducer and activator of transcription 3) inhibitor or shRNA-mediated knockdown of STAT3. In nude mice bearing prostate cancer cell-derived tumours, the tumours injected with the supernatants of NDV/FMW-infected cells grew smaller than mock-treated tumours. These results indicate that oncolytic NDV provokes the expression of ICD makers in prostate cancer cells. Our data also suggest that a combination of inhibition of STAT3 with oncolytic NDV could boost NDV-based anti-tumour effects against prostate cancer.

Seneca valley virus activates autophagy through the PERK and ATF6 UPR pathways

Diverse effects on autophagy, a cell degradation pathway, have been associated with the infectious mechanisms of different pathogens. Here, we demonstrated that Seneca valley virus (SVV), an important emerging porcine virus characterized by vesicular lesions and neonatal mortality, can induce autophagy in cultured PK-15 and BHK-21 cells by detecting autophagosome formation, GFP-LC3 puncta and accumulation of LC3-II proteins. Treatment with pharmacological inducers/inhibitors and small interfering RNA sequences targeting genes critical for autophagosome formation affected autophagy induction and viral yields. SVV induced a complete autophagic process to enhance its replication. The PERK and ATF6 pathways, two components of the endoplasmic reticulum (ER)-related unfolded protein response (UPR), were also activated in SVV-infected cells and downregulation of their expression suppressed SVV-induced autophagy and viral yields. Overall, these results reveal that SVV induces autophagy in cultured cells through the PERK and ATF6 pathways, thereby contributing to understanding of the molecular mechanisms underlying SVV pathogenesis.

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.

Glutamine starvation inhibits snakehead vesiculovirus replication via inducing autophagy associated with the disturbance of endogenous glutathione pool

Autophagy is a degradation cellular process which also plays an important role in virus infection. Glutamine is an essential substrate for the synthesis of glutathione which is the most abundant thiol-containing compound within the cells and plays a key role in the antioxidant defense and intracellular signaling. There is an endogenous cellular glutathione pool which consists of two forms of glutathione, i.e. the reduced form (GSH) and the oxidized form (GSSG). GSH serves as an intracellular antioxidant to maintain cellular redox homeostasis by scavenging free radicals and other reactive oxygen species (ROS) which can lead to autophagy. Under physiological conditions, the concentration of GSSG is only about 1% of total glutathione, while stress condition can result in a transient increase of GSSG. In our previous report, we showed that the replication of snakehead fish vesiculovirus (SHVV) was significant inhibited in SSN-1 cells cultured in the glutamine-starvation medium, however the underlying mechanism remains enigmatic. Here, we revealed that the addition of L-Buthionine-sulfoximine (BSO), a specific inhibitor of the GSH synthesis, could decrease the γ-glutamate-cysteine ligase (GCL) activity and GSH levels, resulting in autophagy and significantly inhibition of the replication of SHVV in SSN-1 cells cultured in the complete medium. On the other hand, the replication of SHVV was rescued and the autophagy was inhibited in the SSN-1 cells cultured in the glutamine-starvation medium supplemented with additional GSH. Furthermore, the inhibition of the synthesis of GSH had not significantly affected the generation of reactive oxygen species (ROS). However, it significantly decreased level of GSH and enhanced the level of GSSG, resulting in the decrease of the value of GSH/GSSG, indicating that it promoted the cellular oxidative stress. Overall, the present study demonstrated that glutamine starvation impaired the replication of SHVV in SSN-1 cells via inducing autophagy associated with the disturbance of the endogenous glutathione pool.

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.

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.

Zika Virus Induces Autophagy in Human Umbilical Vein Endothelial Cells

Autophagy is a common strategy for cell protection; however, some viruses can in turn adopt cellular autophagy to promote viral replication. Zika virus (ZIKV) is the pathogen that causes Zika viral disease, and it is a mosquito-borne virus. However, its pathogenesis, especially the interaction between ZIKV and target cells during the early stages of infection, is still unclear. In this study, we demonstrate that infecting human umbilical vein endothelial cells (HUVEC) with ZIKV triggers cellular autophagy. We observed both an increase in the conversion of LC3-I to LC3-II and increased accumulation of fluorescent cells with LC3 dots, which are considered to be the two key indicators of autophagy. The ratio of LC3-II/GAPDH in each group was significantly increased at different times after ZIKV infection at different MOIs, indicating that the production of lipidated LC3-II increased. Moreover, both the ratio of LC3-II/GAPDH and the expression of viral NS3 protein increased with increasing time of viral infection. The expression level of p62 decreased gradually from 12 h post-infection. Expression profile of double fluorescent protein labelling LC3 indicated that the autophagy induced by ZIKV infection was a complete process. We further investigated the role of autophagy in ZIKV replication. We demonstrated that either the treatment with inhibitors of autophagosomes formation or short hairpin RNA targeting the Beclin-1 gene, which is critical for the formation of autophagosomes, significantly reduced viral production. Taken together, our results indicate that ZIKV infection induces autophagy of HUVEC, and inhibition of ZIKV-induced autophagy restrains viral replication.

Oncolytic effect of wild-type Newcastle disease virus isolates in cancer cell lines in vitro and in vivo on xenograft model

Oncolyic virotherapy is one of the modern experimental techniques to treat human cancers. Here we studied the antitumor activity of wild-type Newcastle disease virus (NDV) isolates from Russian migratory birds. We showed that NDV could selectively kill malignant cells without affecting healthy cells. We evaluated the oncolytic effect of 44 NDV isolates in 4 histogenetically different human cell lines (HCT116, HeLa, A549, MCF7). The safety of the isolates was also tested in normal peripheral blood mononuclear (PBMC) cells. The viability of tumor cell lines after incubation with NDV isolates was evaluated by MTT. All cell lines, except for normal PBMC primary cells, had different degrees of susceptibility to NDV infection. Seven NDV strains had the highest oncolytic activity, and some NDV strains demonstrated oncolytic selectivity for different cell lines. In vivo, we described the intratumoral activity of NDV/Altai/pigeon/770/2011 against subcutaneous non-small cell lung carcinoma using xenograft SCID mice model. All animals were responsive to therapy. Histology confirmed therapy-induced destructive changes and growing necrotic bulk density in tumor tissue. Our findings indicate that wild-type NDV strains selectively kill tumor cells with no effect on healthy PBMC cells, and intratumoral virotherapy with NDV suppresses the subcutaneous tumor growth in SCID mice.

Overexpression of p53 delivered using recombinant NDV induces apoptosis in glioma cells by regulating the apoptotic signaling pathway

Malignant glioma is the most common primary brain carcinoma in the world and has a poor survival rate. Previous studies have demonstrated that p53 dysfunction contributes to the development and severity of malignant glioma. It has also been demonstrated that Newcastle disease virus (NDV) may be a viable candidate for the treatment of various types of cancer. In the present study, a p53 oncolytic agent delivered using recombinant NDV (rNDV-p53) was constructed and its anti-tumor effects in vitro and in vivo were assessed. Glioma cell lines and a xenograft mouse model were utilized to assess the ability of p53 and rNDV to promote apoptosis and induce immunotherapy, respectively. The mechanism of rNDV-p53 in glioma therapy was investigated using quantitative polymerase chain reaction and immunohistochemistry. Tumor-specific cytotoxic T-lymphocyte (CTL) responses and lymphocyte infiltration were also analyzed in glioma-bearing models. The results of the present study demonstrate that rNDV-p53 may be a potential therapeutic agent that improves the prognosis of mice with glioma. It was revealed that rNDV-p53 inhibits glioma cell growth and aggressiveness in vitro and in vivo compared with rNDV and p53 alone. The results also demonstrated that rNDV-p53 induced glioma cell apoptosis by upregulating apoptosis-related genes. In addition, the present study demonstrated that rNDV-p53 significantly stimulated CTL responses and lymphocyte infiltration whilst increasing the number of apoptotic bodies in vivo. Furthermore, rNDV-p53 therapy inhibited tumor regression and prolonged the survival of glioma-bearing mice. In conclusion, rNDV-p53 invoked an immune response against glioma cells, which may serve as a comprehensive immunotherapeutic schedule for glioma.

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.

Tumor suppressor Spred2 interaction with LC3 promotes autophagosome maturation and induces autophagy-dependent cell death

The tumor suppressor Spred2 (Sprouty-related EVH1 domain-2) induces cell death in a variety of cancers. However, the underlying mechanism remains to be elucidated. Here we show that Spred2 induces caspase-independent but autophagy-dependent cell death in human cervical carcinoma HeLa and lung cancer A549 cells. We demonstrate that ectopic Spred2 increased both the conversion of microtubule-associated protein 1 light chain 3 (LC3), GFP-LC3 puncta formation and p62/SQSTM1 degradation in A549 and HeLa cells. Conversely, knockdown of Spred2 in tumor cells inhibited upregulation of autophagosome maturation induced by the autophagy inducer Rapamycin, which could be reversed by the rescue Spred2. These data suggest that Spred2 promotes autophagy in tumor cells. Mechanistically, Spred2 co-localized and interacted with LC3 via the LC3-interacting region (LIR) motifs in its SPR domain. Mutations in the LIR motifs or deletion of the SPR domain impaired Spred2-mediated autophagosome maturation and tumor cell death, indicating that functional LIR is required for Spred2 to trigger tumor cell death. Additionally, Spred2 interacted and co-localized with p62/SQSTM1 through its SPR domain. Furthermore, the co-localization of Spred2, p62 and LAMP2 in HeLa cells indicates that p62 may be involved in Spred2-mediated autophagosome maturation. Inhibition of autophagy using the lysosomal inhibitor chloroquine, reduced Spred2-mediated HeLa cell death. Silencing the expression of autophagy-related genes ATG5, LC3 or p62 in HeLa and A549 cells gave similar results, suggesting that autophagy is required for Spred2-induced tumor cell death. Collectively, these data indicate that Spred2 induces tumor cell death in an autophagy-dependent manner.

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.

Avian metapneumovirus subgroup C induces autophagy through the ATF6 UPR pathway

An increasing number of studies have demonstrated that macroautophagy/autophagy plays an important role in the infectious processes of diverse pathogens. However, it remains unknown whether autophagy is induced in avian metapneumovirus (aMPV)-infected host cells, and, if so, how this occurs. Here, we report that aMPV subgroup C (aMPV/C) induces autophagy in cultured cells. We demonstrated this relationship by detecting classical autophagic features, including the formation of autophagsomes, the presence of GFP-LC3 puncta and the conversation of LC3-I into LC3-II. Also, we used pharmacological regulators and siRNAs targeting ATG7 or LC3 to examine the role of autophagy in aMPV/C replication. The results showed that autophagy is required for efficient replication of aMPV/C. Moreover, infection with aMPV/C promotes autophagosome maturation and induces a complete autophagic process. Finally, the ATF6 pathway, of which one component is the unfolded protein response (UPR), becomes activated in aMPV/C-infected cells. Knockdown of ATF6 inhibited aMPV/C-induced autophagy and viral replication. Collectively, these results not only show that autophagy promotes aMPV/C replication in the cultured cells, but also reveal that the molecular mechanisms underlying aMPV/C-induced autophagy depends on regulation of the ER stress-related UPR pathway.

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.

MicroRNA-30a-5p promotes replication of porcine circovirus type 2 through enhancing autophagy by targeting 14-3-3

Accumulating evidence demonstrates that autophagy and microRNAs (miRNAs) play key roles in regulating virus-host interactions and can restrict or facilitate viral replication. In the present study we examined whether a functional relationship exists between autophagy, miRNA and porcine circovirus type 2 (PCV2) infection, using several approaches. We demonstrated that there was a positive correlation between PCV2 infection and autophagy in 3D4/21 cells and autophagy induced by PCV2 infection triggered PCV2 replication. Four miRNA were selected by real-time PCR and further studied, but only miR-30a-5p mimic had a significant effect on PCV2 replication. Overexpression of miR-30a-5p significantly enhanced PCV2 infection and autophagy in a dose-dependent manner. Blockage of miR-30a-5p significantly decreased PCV2 replication. We provided further evidence that miR-30a-5p regulate the link between PCV2 infection and host immune system. Furthermore, miR-30a-5p targeted and regulated 14-3-3 gene, which is a regulator of autophagy. Flow cytometry data demonstrated that miR-30a-5p promotes cell cycle arrest at the G2 phase to regulate PCV2 replication and autophagy by interacting directly with 14-3-3, but not with the PCV2 genome. These data not only provide new insights into virus-host interactions during PCV2 infection but also suggest a potential new antiviral therapeutic strategy against PCV2 infection.

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.

Oncolytic Virotherapy and the Tumor Microenvironment

Oncolytic viral therapy is a promising approach to treat many malignancies, including breast, colorectal, hepatocellular, and melanoma. The best results are seen when using "targeted and armed" viruses. These are viruses that have been genetically modified to selectively replicate within cancer cells and express specific transgenes that alter the tumor microenvironment to inhibit tumor progression. The products of these transgenes induce cell death, make the virus less virulent, compromise tumor vascularity, and are capable of modulating or enhancing the immune system-such as cytokines and chemokines. In addition, oncolytic viruses can induce anti-vascular effects and disrupt the extracellular matrix to improve viral spread within the tumor. Oncolytic viruses also improve crosstalk between fibroblasts, cytokine-induced killer cells, and cancer cells within the microenvironment, leading to enhanced tumor cell death.

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.

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.