Oncolytic vesicular stomatitis virus induces apoptosis via signaling through PKR, Fas, and Daxx

Oncolytic Virus Senecavirus A Inhibits Hepatocellular Carcinoma Proliferation and Growth by Inducing Cell Cycle Arrest and Apoptosis

Background and Aims

Hepatocellular carcinoma (HCC) is a highly aggressive tumor with limited treatment options and high mortality. Senecavirus A (SVA) has shown potential in selectively targeting tumors while sparing healthy tissues. This study aimed to investigate the effects of SVA on HCC cells in vitro and in vivo and to elucidate its mechanisms of action.

Methods

The cell counting kit-8 assay and colony formation assay were conducted to examine cell proliferation. Flow cytometry and nuclear staining were employed to analyze cell cycle distribution and apoptosis occurrence. A subcutaneous tumor xenograft HCC mouse model was created in vivo using HepG2 cells, and Ki67 expression in the tumor tissues was assessed. The terminal deoxynucleotidyl transferase dUTP nick end labeling assay and hematoxylin and eosin staining were employed to evaluate HCC apoptosis and the toxicity of SVA on mouse organs.

Results

In vitro, SVA effectively suppressed the growth of tumor cells by inducing apoptosis and cell cycle arrest. However, it did not have a notable effect on normal hepatocytes (MIHA cells). In an in vivo setting, SVA effectively suppressed the growth of HCC in a mouse model. SVA treatment resulted in a significant decrease in Ki67 expression and an increase in apoptosis of tumor cells. No notable histopathological alterations were observed in the organs of mice during SVA administration.

Conclusions

SVA inhibits the growth of HCC cells by inducing cell cycle arrest and apoptosis. It does not cause any noticeable toxicity to vital organs.

Enhancing Neoadjuvant Virotherapy's Effectiveness by Targeting Stroma to Improve Resectability in Pancreatic Cancer

About one-fourth of patients with pancreatic ductal adenocarcinoma (PDAC) are categorized as borderline resectable (BR) or locally advanced (LA). Chemotherapy and radiation therapy have not yielded the anticipated outcomes in curing patients with BR/LA PDAC. The surgical resection of these tumors presents challenges owing to the unpredictability of the resection margin, involvement of vasculature with the tumor, the likelihood of occult metastasis, a higher ratio of positive lymph nodes, and the relatively larger size of tumor nodules. Oncolytic virotherapy has shown promising activity in preclinical PDAC models. Unfortunately, the desmoplastic stroma within the PDAC tumor microenvironment establishes a barrier, hindering the infiltration of oncolytic viruses and various therapeutic drugs-such as antibodies, adoptive cell therapy agents, and chemotherapeutic agents-in reaching the tumor site. Recently, a growing emphasis has been placed on targeting major acellular components of tumor stroma, such as hyaluronic acid and collagen, to enhance drug penetration. Oncolytic viruses can be engineered to express proteolytic enzymes that cleave hyaluronic acid and collagen into smaller polypeptides, thereby softening the desmoplastic stroma, ultimately leading to increased viral distribution along with increased oncolysis and subsequent tumor size regression. This approach may offer new possibilities to improve the resectability of patients diagnosed with BR and LA PDAC.

Cancer immunotherapy with enveloped self-amplifying mRNA CARG-2020 that modulates IL-12, IL-17 and PD-L1 pathways to prevent tumor recurrence

Targeting multiple immune mechanisms may overcome therapy resistance and further improve cancer immunotherapy for humans. Here, we describe the application of virus-like vesicles (VLV) for delivery of three immunomodulators alone and in combination, as a promising approach for cancer immunotherapy. VLV vectors were designed to deliver single chain interleukin (IL)-12, short-hairpin RNA (shRNA) targeting programmed death ligand 1 (PD-L1), and a dominant-negative form of IL-17 receptor A (dn-IL17RA) as a single payload or as a combination payload. Intralesional delivery of the VLV vector expressing IL-12 alone, as well as the trivalent vector (designated CARG-2020) eradicated large established tumors. However, only CARG-2020 prevented tumor recurrence and provided long-term survival benefit to the tumor-bearing mice, indicating a benefit of the combined immunomodulation. The abscopal effects of CARG-2020 on the non-injected contralateral tumors, as well as protection from the tumor cell re-challenge, suggest immune-mediated mechanism of protection and establishment of immunological memory. Mechanistically, CARG-2020 potently activates Th1 immune mechanisms and inhibits expression of genes related to T cell exhaustion and cancer-promoting inflammation. The ability of CARG-2020 to prevent tumor recurrence and to provide survival benefit makes it a promising candidate for its development for human cancer immunotherapy.

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 emerging field of oncolytic virus-based cancer immunotherapy

Oncolytic viruses (OVs) provide novel and promising therapeutic options for patients with cancers resistant to traditional therapies. Natural or genetically modified OVs are multifaceted tumor killers. They directly lyse tumor cells while sparing normal cells, and indirectly potentiate antitumor immunity by releasing antigens and activating inflammatory responses in the tumor microenvironment. However, some limitations, such as limited penetration of OVs into tumors, short persistence, and the host antiviral immune response, are impeding the broad translation of oncolytic virotherapy into the clinic. If these challenges can be overcome, combination therapies, such as OVs plus immune checkpoint blockade (ICB), chimeric antigen receptor (CAR) T cells, or CAR natural killer (NK) cells, may provide powerful therapeutic platforms in the clinic.

β-Adrenergic Receptor Inhibitor and Oncolytic Herpesvirus Combination Therapy Shows Enhanced Antitumoral and Antiangiogenic Effects on Colorectal Cancer

Oncolytic viruses (OVs) are considered a promising therapeutic alternative for cancer. However, despite the development of novel OVs with improved efficacy and tumor selectivity, their limited efficacy as monotherapeutic agents remains a significant challenge. This study extended our previously observed combination effects of propranolol, a nonselective β-blocker, and the T1012G oncolytic virus into colorectal cancer models. A cell viability assay showed that cotreatment could induce synergistic killing effects on human and murine colorectal cell lines. Moreover, cotreatment caused sustained tumor regression compared with T1012G monotherapy or propranolol monotherapy in human HCT116 and murine MC38 tumor models. The propranolol activity was not via a direct effect on viral replication in vitro or in vivo. Western blotting showed that cotreatment significantly enhanced the expression of cleaved caspase-3 in HCT116 and MC38 cells compared with the propranolol or T1012G alone. In addition, propranolol or T1012G treatment induced a 35.06% ± 0.53% or 35.49% ± 2.68% reduction in VEGF secretion in HUVECs (p < 0.01/p < 0.01). Cotreatment further inhibited VEGF secretion compared with the monotherapies (compared with propranolol treatment: 75.06% ± 1.50% decrease, compared with T1012G treatment: 74.91% ± 0.68%; p＜0.001, p < 0.001). Consistent with the in vitro results, in vivo data showed that cotreatment could reduce Ki67 and enhance cleaved caspase 3 and CD31 expression in human HCT116 and murine MC38 xenografts. In summary, β-blockers could improve the therapeutic potential of OVs by enhancing oncolytic virus-mediated killing of colorectal cancer cells and colorectal tumors.

Ebola virus requires phosphatidylserine scrambling activity for efficient budding and optimal infectivity

Ebola virus (EBOV) attaches to target cells using two categories of cell surface receptors, C-type lectins and phosphatidylserine (PS) receptors. PS receptors typically bind to apoptotic cell membrane PS and orchestrate the uptake and clearance of apoptotic debris. Many enveloped viruses also contain exposed PS and can therefore exploit these receptors for cell entry. Viral infection can induce PS externalization in host cells, resulting in increased outer PS levels on budding virions. Scramblase enzymes carry out cellular PS externalization, thus, we targeted these proteins in order to manipulate viral envelope PS levels. We investigated two scramblases previously identified to be involved in EBOV PS levels, transmembrane protein 16F and Xk-related protein 8 (XKR8), as possible mediators of cellular and viral envelope surface PS levels during the replication of recombinant vesicular stomatitis virus containing its native glycoprotein (rVSV/G) or the EBOV glycoprotein (rVSV/EBOV-GP). We found that rVSV/G and rVSV/EBOV-GP virions produced in XKR8 knockout cells contain decreased levels of PS on their surfaces, and the PS-deficient rVSV/EBOV-GP virions are 70% less efficient at infecting cells through PS receptors. We also observed reduced rVSV and EBOV virus-like particle (VLP) budding in ΔXKR8 cells. Deleting XKR8 in HAP1 cells reduced rVSV/G and rVSV/EBOV-GP budding by 60% and 65% respectively, and reduced Ebola VLP budding more than 60%. We further demonstrated that caspase cleavage of XKR8 is required to promote budding. This suggests that XKR8, in addition to mediating virion PS levels, may also be critical for enveloped virus budding at the plasma membrane. Importance Within the last decade, countries in western and central Africa have experienced the most widespread and deadly Ebola outbreaks since the virus was identified in 1976. While outbreaks are primarily attributed to zoonotic transfer events, new evidence is emerging that outbreaks may be caused by a combination of spillover events and viral latency or persistence in survivors. The possibility that Ebola can remain dormant then re-emerge in survivors highlights the critical need to prevent the virus from entering and establishing infection in human cells. Thus far, host-cell scramblases TMEM16F and XKR8 have been implicated in Ebola envelope surface phosphatidylserine (PS) and cell entry using PS receptors. We assessed the contributions of these proteins using CRISPR knockout cells and two EBOV models: rVSV/EBOV-GP and EBOV VLPs. We observed that XKR8 is required for optimal EBOV envelope PS levels and infectivity, and particle budding across all viral models.

Induction of apoptosis in SSN-1cells by Snakehead Fish Vesiculovirus (SHVV) via Matrix protein dependent intrinsic pathway

An increasing important area in immunology is the process cell death mechanism, enabling the immune system triggered thru extrinsic or intrinsic signals to effectively remove unwanted or virus infected cells called apoptosis. A recently isolated infectious Snakehead fish vesiculovirus (SHVV), comprising negative strand RNA and encoded viral matrix (M) proteins, is responsible for causing cytopathic effects in infected fish cells. However, the mechanism by which viral M protein mediates apoptosis has not been elucidated. Therefore, in the present experiments, it was investigated the regulatory potential of apoptosis signals during SHVV infection. By employing the model of SHVV infection in SSN-1 cells, the accelerated apoptosis pathway involves an intrinsic pathway requiring the activation of caspase-9 but not caspase-3 or -8. In the groups of infection (SHVV) or treatment (hydrogen peroxide) were induced apoptotic morphological changes and indicated the activation of the main caspases, i.e.; executioner caspase-3, initiators caspase-8 and caspase-9 using colorimetric assays. Turning to the role of viral M protein when it was overexpressed in SSN-1 cells, it was indicated that the viral M gene alone has the ability to induce apoptosis. To elucidate the mechanism of apoptosis in SSN-1 cells, the activation inhibitors of main caspases were used showing that inhibiting of caspase-3 or caspase-8 activation did not seize induction of apoptosis in virus-infected SSN-1 cells. However, the inhibiting of caspase-9 activation reduced significantly the apoptosis initiation process and sharply the expression of viral M gene, suggesting that SHVV plays a major role in the early induction of apoptosis by caspase-9. Interestingly, there were also differences in the mitochondrial membrane potential after the apoptotic induction of caspases, which confirm that caspase-9 is primarily responsible for the cleavage of caspases during apoptosis. Taken together, these findings can therefore be assumed that viral M protein induces apoptosis via the intrinsic apoptotic pathway in SHVV infecting SSN-1 cells.

Expanding the Spectrum of Pancreatic Cancers Responsive to Vesicular Stomatitis Virus-Based Oncolytic Virotherapy: Challenges and Solutions

Pancreatic ductal adenocarcinoma (PDAC) is a devastating malignancy with poor prognosis and a dismal survival rate, expected to become the second leading cause of cancer-related deaths in the United States. Oncolytic virus (OV) is an anticancer approach that utilizes replication-competent viruses to preferentially infect and kill tumor cells. Vesicular stomatitis virus (VSV), one such OV, is already in several phase I clinical trials against different malignancies. VSV-based recombinant viruses are effective OVs against a majority of tested PDAC cell lines. However, some PDAC cell lines are resistant to VSV. Upregulated type I IFN signaling and constitutive expression of a subset of interferon-simulated genes (ISGs) play a major role in such resistance, while other mechanisms, such as inefficient viral attachment and resistance to VSV-mediated apoptosis, also play a role in some PDACs. Several alternative approaches have been shown to break the resistance of PDACs to VSV without compromising VSV oncoselectivity, including (i) combinations of VSV with JAK1/2 inhibitors (such as ruxolitinib); (ii) triple combinations of VSV with ruxolitinib and polycations improving both VSV replication and attachment; (iii) combinations of VSV with chemotherapeutic drugs (such as paclitaxel) arresting cells in the G2/M phase; (iv) arming VSV with p53 transgenes; (v) directed evolution approach producing more effective OVs. The latter study demonstrated impressive long-term genomic stability of complex VSV recombinants encoding large transgenes, supporting further clinical development of VSV as safe therapeutics for PDAC.

Effects of HPV16 E6 protein on Daxx-induced apoptosis in C33A cells

Aims

Daxx is a highly conserved nuclear protein with an important role in transcription, apoptosis and other cell processes. We investigated the role of HPV16 E6 in Daxx-induced apoptosis through their interactions in C33A cells.

Methods

The binding of HPV16 E6 and Daxx was confirmed in C33A cells using co-immunoprecipitation and indirect immunofluorescence assays. Quantitative PCR and western blotting were performed to determine the RNA and protein expressions of Daxx, respectively. Automatic cell count and MTT assays were performed to investigate the proliferation of C33A cells. The apoptosis rate of C33A cells was determined via flow cytometry using Annexin V-FITC/PI staining. The relative activity of caspase-8 was tested using ELISA.

Results

HPV16 E6 can bind with Daxx and cause its translocation in C33A cells. The transfected HPV16 E6 can cause a decrease in relative quantification for Daxx in Daxx-overexpressing cells. After Daxx transfection, cell proliferation was found to decrease sharply and cell apoptosis to increase sharply. However, when HPV16 E6 was co-transfected with Daxx, this decrease and increase both became gentle. Similarly, HPV16 E6 made the Daxx-induced increase in caspase-8 activity milder.

Conclusions

HPV16 E6 is involved in inhibiting apoptosis through deregulation of Daxx-induced caspase-8 activities.

A tool with many applications: vesicular stomatitis virus in research and medicine

INTRODUCTION

Vesicular stomatitis virus (VSV) has long been a useful research tool in virology and recently become an essential part of medicinal products. Vesiculovirus research is growing quickly following its adaptation to clinical gene and cell therapy and oncolytic virotherapy.

AREAS COVERED

This article reviews the versatility of VSV as a research tool and biological reagent, its use as a viral and vaccine vector delivering therapeutic and immunogenic transgenes and an oncolytic virus aiding cancer treatment. Challenges such as the immune response against such advanced therapeutic medicinal products and manufacturing constraints are also discussed.

EXPERT OPINION

The field of in vivo gene and cell therapy is advancing rapidly with VSV used in many ways. Comparison of VSV's use as a versatile therapeutic reagent unveils further prospects and problems for each application. Overcoming immunological challenges to aid repeated administration of viral vectors and minimizing harmful host-vector interactions remains one of the major challenges. In the future, exploitation of reverse genetic tools may assist the creation of recombinant viral variants that have improved onco-selectivity and more efficient vaccine vector activity. This will add to the preferential features of VSV as an excellent advanced therapy medicinal product (ATMP) platform.

DAXX in cancer: phenomena, processes, mechanisms and regulation

DAXX displays complex biological functions. Remarkably, DAXX overexpression is a common feature in diverse cancers, which correlates with tumorigenesis, disease progression and treatment resistance. Structurally, DAXX is modular with an N-terminal helical bundle, a docking site for many DAXX interactors (e.g. p53 and ATRX). DAXX's central region folds with the H3.3/H4 dimer, providing a H3.3-specific chaperoning function. DAXX has two functionally critical SUMO-interacting motifs. These modules are connected by disordered regions. DAXX's structural features provide a framework for deciphering how DAXX mechanistically imparts its functions and how its activity is regulated. DAXX modulates transcription through binding to transcription factors, epigenetic modifiers, and chromatin remodelers. DAXX's localization in the PML nuclear bodies also plays roles in transcriptional regulation. DAXX-regulated genes are likely important effectors of its biological functions. Deposition of H3.3 and its interactions with epigenetic modifiers are likely key events for DAXX to regulate transcription, DNA repair, and viral infection. Interactions between DAXX and its partners directly impact apoptosis and cell signaling. DAXX's activity is regulated by posttranslational modifications and ubiquitin-dependent degradation. Notably, the tumor suppressor SPOP promotes DAXX degradation in phase-separated droplets. We summarize here our current understanding of DAXX's complex functions with a focus on how it promotes oncogenesis.

M51R and Delta-M51 matrix protein of the vesicular stomatitis virus induce apoptosis in colorectal cancer cells

Colorectal cancer (CRC) is the third most common cancer in both men and women. Oncolytic viral-based therapy methods seem to be promising for CRC treatment. Vesicular stomatitis virus (VSV) is considered as a potent candidate in viral therapy for several tumors. VSV particles with mutated matrix (M) protein are capable of initiating cell death cascades while not being harmful to the immune system. In the current study, the effects of the VSV M-protein was investigated on the apoptosis of the colorectal cancer SW480 cell. Wild-type, M51R, and ΔM51 mutants VSV M-protein genes were cloned into the PCDNA3.1 vector and transfected into the SW480 cells. The results of the MTT assay, Western blotting, and Caspase 3, 8, and 9 measurement, illustrated that both wild and M51R mutant M-proteins can destroy the SW480 colorectal cancer cells. DAPI/TUNEL double-staining reconfirmed the apoptotic effects of the M-protein expression. The ΔM51 mutant M-protein is effective likewise M51R, somehow it can be considered as a safer substitution.

Targeted Nanoparticle‐Mediated Gene Therapy Mimics Oncolytic Virus for Effective Melanoma Treatment

Oncolytic virus has potential applications in cancer therapy. However, its clinical application is restricted by the virus‐associated biosafety issues. Here, inspired by the key role of vesicular stomatitis virus matrix protein (VSVMP) in the oncolytic vesicular stomatitis virus (VSV) induced apoptosis, a targeted nanoparticle‐delivered neutral VSVMP gene formulation is designed to act like the VSV for cancer therapy. This VSVMP formulation consists of a CRGDKGPDC peptide modified hybrid monomethoxy poly (ethylene glycol)‐poly(d,l‐lactide) nanoparticles complexed with VSVMP plasmid, having good blood compatibility and tumor targeting ability. The transfection efficiency is as high as that of VSV. After intravenous administration, the VSVMP formulation can efficiently target the tumor, significantly inhibit the melanoma growth and metastasis, prolong the survival time of tumor‐bearing mice, and does not cause obvious systemic toxicity. The anticancer mechanisms involve apoptosis induction, angiogenesis inhibition and some virus‐associated signal pathways activation. This work demonstrates a VSV‐inspired nonviral gene therapy that has promising clinical applications in melanoma treatment.

Oncotargeting by Vesicular Stomatitis Virus (VSV): Advances in Cancer Therapy

Modern oncotherapy approaches are based on inducing controlled apoptosis in tumor cells. Although a number of apoptosis-induction approaches are available, site-specific delivery of therapeutic agents still remain the biggest hurdle in achieving the desired cancer treatment benefit. Additionally, systemic treatment-induced toxicity remains a major limiting factor in chemotherapy. To specifically address drug-accessibility and chemotherapy side effects, oncolytic virotherapy (OV) has emerged as a novel cancer treatment alternative. In OV, recombinant viruses with higher replication capacity and stronger lytic properties are being considered for tumor cell-targeting and subsequent cell lysing. Successful application of OVs lies in achieving strict tumor-specific tropism called oncotropism, which is contingent upon the biophysical interactions of tumor cell surface receptors with viral receptors and subsequent replication of oncolytic viruses in cancer cells. In this direction, few viral vector platforms have been developed and some of these have entered pre-clinical/clinical trials. Among these, the Vesicular stomatitis virus (VSV)-based platform shows high promise, as it is not pathogenic to humans. Further, modern molecular biology techniques such as reverse genetics tools have favorably advanced this field by creating efficient recombinant VSVs for OV; some have entered into clinical trials. In this review, we discuss the current status of VSV based oncotherapy, challenges, and future perspectives regarding its therapeutic applications in the cancer treatment.

Mechanistic insights into the oncolytic activity of vesicular stomatitis virus in cancer immunotherapy

Immunotherapy and oncolytic virotherapy have both shown anticancer efficacy in the clinic as monotherapies but the greatest promise lies in therapies that combine these approaches. Vesicular stomatitis virus is a prominent oncolytic virus with several features that promise synergy between oncolytic virotherapy and immunotherapy. This review will address the cytotoxicity of vesicular stomatitis virus in transformed cells and what this means for antitumor immunity and the virus’ immunogenicity, as well as how it facilitates the breaking of tolerance within the tumor, and finally, we will outline how these features can be incorporated into the rational design of new treatment strategies in combination with immunotherapy.

Livin modulates the apoptotic effects of vesicular stomatotitis virus in lung adenocarcinoma

Vesicular stomatitis virus (VSV) has shown promise in cancer treatment. However, it achieved limited effects against lung cancer. Lung cancer has intrinsic mechanisms that render resistance to VSV. In this study, we attempted to explore the expression of the anti-apoptotic factor Livin in lung adenocarcinoma and its possible relationship to VSV vulnerability. We found VSV induced apoptosis in a time- and dose-dependent manner, with the concomitant change in the expression of Livin. We elevated the expression of Livin both transiently and stably, and the cells became insensitive to VSV treatment. We further found the BIR domain of Livin was mainly responsible for its modulation effects. This finding suggested a possible interaction with the second mitochondria-derived activator of caspase (SMAC). The knock-down of SMAC also inhibited apoptosis by VSV. The relationship was confirmed by the co-immunoprecipitation. Finally, we knocked down the endogenous Livin, and the knock-down sensitized cells to VSV treatment. Our results suggested the important role of Livin and its partner molecule in the process of VSV treatment.

Induction of apoptosis in pancreatic cancer cells by vesicular stomatitis virus

Effective oncolytic virus (OV) therapy is dependent on the ability of replication-competent viruses to kill infected cancer cells. We previously showed that human pancreatic ductal adenocarcinoma (PDAC) cell lines are highly heterogeneous in their permissiveness to vesicular stomatitis virus (VSV), in part due to differences in type I interferon (IFN) signaling. Here, using 10 human PDAC cell lines and three different VSV recombinants (expressing ΔM51 or wild type matrix protein), we examined cellular and viral factors affecting VSV-mediated apoptosis activation in PDACs. In most cell lines, VSVs activated both extrinsic and intrinsic apoptosis pathways, and VSV-ΔM51 primarily activated the type II extrinsic pathway. In cells with defective IFN signaling, all VSV recombinants induced robust apoptosis, whereas VSV-ΔM51 was a more effective apoptosis activator in PDACs with virus-inducible IFN signaling. Three cell lines constitutively expressing high levels of IFN-stimulated genes (ISGs) were resistant to apoptosis under most experimental conditions, even when VSV replication levels were dramatically increased by Jak inhibitor I treatment. Two of these cell lines also poorly activated apoptosis when treated with Fas activating antibody, suggesting a general defect in apoptosis.

Signaling pathways in murine dendritic cells that regulate the response to vesicular stomatitis virus vectors that express flagellin

Vesicular stomatitis virus (VSV) vectors that express heterologous antigens have shown promise as vaccines in preclinical studies. The efficacy of VSV-based vaccines can be improved by engineering vectors that enhance innate immune responses. We previously generated a VSV vaccine vector that incorporates two enhancing strategies: an M protein mutation (M51R) that prevents the virus from suppressing host antiviral responses and a gene encoding bacterial flagellin (M51R-F vector). The rationale was that intracellular expression of flagellin would activate innate immune pathways in addition to those activated by virus alone. This was tested with dendritic cells (DCs) from mice containing deletions in key signaling molecules. Infection of DC with either M51R or M51R-F vector induced the production of interleukin-12 (IL-12) and IL-6 and increased surface expression of T cell costimulatory molecules. These responses were dramatically reduced in DCs from IPS-1(-/-) mice. Infection with M51R-F vector also induced the production of IL-1β. In addition, in approximately half of the DCs, M51R-F vector induced pyroptosis, a proinflammatory-type of cell death. These responses to flagellin were ablated in DCs from NLRC4(-/-) mice but not Toll-like receptor 5-deficient (TLR5(-/-)) mice, indicating that they resulted from inflammasome activation. These results demonstrate that flagellin induces additional innate immune mechanisms over those induced by VSV alone.

Chandipura virus induces neuronal death through Fas-mediated extrinsic apoptotic pathway

Chandipura virus (CHPV; genus Vesiculovirus, family Rhabdoviridae) is an emerging tropical pathogen with a case fatality rate of 55 to 75% that predominantly affects children in the age group of 2 to 16 years. Although it has been established as a neurotropic virus causing encephalitis, the molecular pathology leading to neuronal death is unknown. The present study elucidates for the first time the mechanism of cell death in neurons after CHPV infection that answers the basic cause of CHPV-mediated neurodegeneration. Through various cell death assays in vitro and in vivo, a relationship between viral replication within neuron and neuronal apoptosis has been established. We report that expression of CHPV phosphoprotein increases up to 6 h postinfection and diminishes thereafter in neuronal cell lines, signifying the replicative phase of CHPV. Various analyses conducted during the investigation established that CHPV-infected neurons are undergoing apoptosis through an extrinsic pathway mediated through the Fas-associated death domain (FADD) following activation of caspase-8 and -3 and prominent cleavage of poly(ADP-ribose) polymerase (PARP). Knocking down the expression of caspase-3, the final executioner of apoptosis, in a neuronal cell line by endoribonuclease-prepared small interfering RNA (siRNA) validated its pivotal role in CHPV-mediated neurodegeneration by showing reduction in apoptosis after CHPV infection.

Oncolytic myxoma virus: the path to clinic

Many common neoplasms are still noncurative with current standards of cancer therapy. More therapeutic modalities need to be developed to significantly prolong the lives of patients and eventually cure a wider spectrum of cancers. Oncolytic virotherapy is one of the promising new additions to clinical cancer therapeutics. Successful oncolytic virotherapy in the clinic will be those strategies that best combine tumor cell oncolysis with enhanced immune responses against tumor antigens. The current candidate oncolytic viruses all share the common property that they are relatively nonpathogenic to humans, yet they have the ability to replicate selectively in human cancer cells and induce cancer regression by direct oncolysis and/or induction of improved anti-tumor immune responses. Many candidate oncolytic viruses are in various stages of clinical and preclinical development. One such preclinical candidate is myxoma virus (MYXV), a member of the Poxviridae family that, in its natural setting, exhibits a very restricted host range and is only pathogenic to European rabbits. Despite its narrow host range in nature, MYXV has been shown to productively infect various classes of human cancer cells. Several preclinical in vivo modeling studies have demonstrated that MYXV is an attractive and safe candidate oncolytic virus, and hence, MYXV is currently being developed as a potential therapeutic for several cancers, such as pancreatic cancer, glioblastoma, ovarian cancer, melanoma, and hematologic malignancies. This review highlights the preclinical cancer models that have shown the most promise for translation of MYXV into human clinical trials.

Understanding and altering cell tropism of vesicular stomatitis virus

Vesicular stomatitis virus (VSV) is a prototypic nonsegmented negative-strand RNA virus. VSV's broad cell tropism makes it a popular model virus for many basic research applications. In addition, a lack of preexisting human immunity against VSV, inherent oncotropism and other features make VSV a widely used platform for vaccine and oncolytic vectors. However, VSV's neurotropism that can result in viral encephalitis in experimental animals needs to be addressed for the use of the virus as a safe vector. Therefore, it is very important to understand the determinants of VSV tropism and develop strategies to alter it. VSV glycoprotein (G) and matrix (M) protein play major roles in its cell tropism. VSV G protein is responsible for VSV broad cell tropism and is often used for pseudotyping other viruses. VSV M affects cell tropism via evasion of antiviral responses, and M mutants can be used to limit cell tropism to cell types defective in interferon signaling. In addition, other VSV proteins and host proteins may function as determinants of VSV cell tropism. Various approaches have been successfully used to alter VSV tropism to benefit basic research and clinically relevant applications.

BCL-2 inhibitors sensitize therapy-resistant chronic lymphocytic leukemia cells to VSV oncolysis

Many primary cancers including chronic lymphocytic leukemia (CLL) are resistant to vesicular stomatitis virus (VSV)-induced oncolysis due to overexpression of the antiapoptotic and antiautophagic members of the B-cell lymphoma-2 (BCL-2) family. In the present study, we investigated the mechanisms of CLL cell death induced as a consequence of VSV infection in the presence of BCL-2 inhibitors, obatoclax, and ABT-737 in primary ex vivo CLL patient samples. Microarray analysis of primary CD19⁺ CD5⁺ CLL cells treated with obatoclax and VSV revealed changes in expression of genes regulating apoptosis, the mechanistic target of rapamycin (mTOR) pathway, and cellular metabolism. A combined therapeutic effect was observed for VSV and BCL-2 inhibitors in cells from untreated patients and from patients unresponsive to standard of care therapy. In addition, combination treatment induced several markers of autophagy--LC3-II accumulation, p62 degradation, and staining of autophagic vacuoles. Inhibition of early stage autophagy using 3-methyladenine (3-MA) led to increased apoptosis in CLL samples. Mechanistically, a combination of BCL-2 inhibitors and VSV disrupted inhibitory interactions of Beclin-1 with BCL-2 and myeloid cell leukemia-1 (MCL-1), thus biasing cells toward autophagy. We propose a mechanism in which changes in cellular metabolism, coupled with pharmacologic disruption of the BCL-2-Beclin-1 interactions, facilitate induction of apoptosis and autophagy to mediate the cytolytic effect of VSV.

Daxx upregulation within the cytoplasm of reovirus-infected cells is mediated by interferon and contributes to apoptosis

Reovirus infection is a well-characterized experimental system for the study of viral pathogenesis and antiviral immunity within the central nervous system (CNS). We have previously shown that c-Jun N-terminal kinase (JNK) and the Fas death receptor each play a role in neuronal apoptosis occurring in reovirus-infected brains. Death-associated protein 6 (Daxx) is a cellular protein that mechanistically links Fas signaling to JNK signaling in several models of apoptosis. In the present study, we demonstrate that Daxx is upregulated in reovirus-infected brain tissue through a type I interferon-mediated mechanism. Daxx upregulation is limited to brain regions that undergo reovirus-induced apoptosis and occurs in the cytoplasm and nucleus of neurons. Cytoplasmic Daxx is present in Fas-expressing cells during reovirus encephalitis, suggesting a role for Daxx in Fas-mediated apoptosis following reovirus infection. Further, in vitro expression of a dominant negative form of Daxx (DN-Daxx), which binds to Fas but which does not transmit downstream signaling, inhibits apoptosis of reovirus-infected cells. In contrast, in vitro depletion of Daxx results in increased expression of caspase 3 and apoptosis, suggesting that Daxx plays an antiapoptotic role in the nucleus. Overall, these data imply a regulatory role for Daxx in reovirus-induced apoptosis, depending on its location in the nucleus or cytoplasm.

Resistance of pancreatic cancer cells to oncolytic vesicular stomatitis virus: role of type I interferon signaling

Oncolytic virus (OV) therapy takes advantage of common cancer characteristics, such as defective type I interferon (IFN) signaling, to preferentially infect and kill cancer cells with viruses. Our recent study (Murphy et al., 2012. J. Virol. 86, 3073-87) found human pancreatic ductal adenocarcinoma (PDA) cells were highly heterogeneous in their permissiveness to vesicular stomatitis virus (VSV) and suggested at least some resistant cell lines retained functional type I IFN responses. Here we examine cellular responses to infection by the oncolytic VSV recombinant VSV-ΔM51-GFP by analyzing a panel of 11 human PDA cell lines for expression of 33 genes associated with type I IFN pathways. Although all cell lines sensed infection by VSV-ΔM51-GFP and most activated IFN-α and β expression, only resistant cell lines displayed constitutive high-level expression of the IFN-stimulated antiviral genes MxA and OAS. Inhibition of JAK/STAT signaling decreased levels of MxA and OAS and increased VSV infection, replication and oncolysis, further implicating IFN responses in resistance. Unlike VSV, vaccinia and herpes simplex virus infectivity and killing of PDA cells was independent of the type I IFN signaling profile, possibly because these two viruses are better equipped to evade type I IFN responses. Our study demonstrates heterogeneity in the type I IFN signaling status of PDA cells and suggests MxA and OAS as potential biomarkers for PDA resistance to VSV and other OVs sensitive to type I IFN responses.

Vesicular stomatitis virus as a flexible platform for oncolytic virotherapy against cancer

Oncolytic virus (OV) therapy is an emerging anti-cancer approach that utilizes viruses to preferentially infect and kill cancer cells, while not harming healthy cells. Vesicular stomatitis virus (VSV) is a prototypic non-segmented, negative-strand RNA virus with inherent OV qualities. Antiviral responses induced by type I interferon pathways are believed to be impaired in most cancer cells, making them more susceptible to VSV than normal cells. Several other factors make VSV a promising OV candidate for clinical use, including its well-studied biology, a small, easily manipulated genome, relative independence of a receptor or cell cycle, cytoplasmic replication without risk of host-cell transformation, and lack of pre-existing immunity in humans. Moreover, various VSV-based recombinant viruses have been engineered via reverse genetics to improve oncoselectivity, safety, oncotoxicity and stimulation of tumour-specific immunity. Alternative delivery methods are also being studied to minimize premature immune clearance of VSV. OV treatment as a monotherapy is being explored, although many studies have employed VSV in combination with radiotherapy, chemotherapy or other OVs. Preclinical studies with various cancers have demonstrated that VSV is a promising OV; as a result, a human clinical trial using VSV is currently in progress.

Gene therapy using the human telomerase catalytic subunit gene promoter enables targeting of the therapeutic effects of vesicular stomatitis virus matrix protein against human lung adenocarcinoma

The catalytic subunit of telomerase, human telomerase reverse transcriptase (hTERT), is highly active in immortalized cells and more than 90% of human cancer cells, but is quiescent in the majority of normal somatic cells. Thus, the hTERT promoter has been extensively used in targeted cancer gene therapy. Vesicular stomatitis virus (VSV) matrix protein (MP) induces the apoptosis of tumor cells in the absence of other viral components. In our previous studies, we successfully constructed the pVAX-M plasmid from the pVAX plasmid, which expressed wild-type VSV MP (VSV MP is under the control of the CMV promoter) and demonstrated that pVAX-M efficiently suppresses the growth of malignant tumors via the induction of apoptosis in vitro and in vivo. The present study was designed to construct the plasmid phTERTM (VSV MP is under the control of the hTERT promoter) and investigate whether it had a targeted antitumor effect in nude mice bearing human lung adenocarcinoma. In vitro, A549 human lung adenocarcinoma cells were treated with NS, Lip-null, etoposide, Lip-pVAX-M or Lip-phTERT-M, and examined for cell viability through MTT assays or for apoptosis by flow cytometry and TUNEL assays. In vivo, A549 human lung carcinoma models in nude mice were established. Mice were treated with 10 4-weekly intravenous administrations of NS, Lip-null, etoposide (2 mg/kg), Lip-pVAX-M or Lip-phTERT-M. Subsequently, Lip-phTERT-M was found to be the most efficient inhibitor of tumor growth and inducer of tumor cell apoptosis when compared with the other groups in vivo and in vitro (P<0.05). Notably, immunohistochemical staining showed that Lip-phTERT-M significantly limited the overexpression of VSV MP to the tumor tissues and reduced VSV MP expression in other organs in comparison with Lip-pVAX-M (P<0.05). Therefore, it can be concluded that phTERT-M demonstrates a targeted antitumor effect on A549 human lung adenocarcinoma cells. These observations suggest that phTERT-M gene therapy may be a novel and potent strategy for targeting human lung adenocarcinoma.

Enhanced vesicular stomatitis virus (VSVΔ51) targeting of head and neck cancer in combination with radiation therapy or ZD6126 vascular disrupting agent

BACKGROUND

Head and neck squamous cell carcinoma (HNSCC) is the 5th most common cancer worldwide. Locally advanced HNSCC are treated with either radiation or chemo-radiotherapy, but still associated with high mortality rate, underscoring the need to develop novel therapies. Oncolytic viruses have been garnering increasing interest as anti-cancer agents due to their preferential killing of transformed cells. In this study, we evaluated the therapeutic potential of mutant vesicular stomatitis virus (VSVΔ51) against the human hypopharyngeal FaDu tumour model in vitro and in vivo.

RESULTS

Our data demonstrated high toxicity of the virus against FaDu cells in vitro, which was associated with induction of apoptosis. In vivo, systemic injection of 1 × 109 pfu had minimal effect on tumour growth; however, when combined with two doses of ionizing radiation (IR; 5 Gy each) or a single injection of the vascular disrupting agent (ZD6126), the virus exhibited profound suppression of tumour growth, which translated to a prolonged survival in the treated mice. Concordantly, VSVΔ51 combined with ZD6126 led to a significant increase in viral replication in these tumours.

CONCLUSIONS

Our data suggest that the combinations of VSVΔ51 with either IR or ZD6126 are potentially novel therapeutic opportunities for HNSCC.

Vesicular stomatitis virus as an oncolytic agent against pancreatic ductal adenocarcinoma

Vesicular stomatitis virus (VSV) is a promising oncolytic agent against a variety of cancers. However, it has never been tested in any pancreatic cancer model. Pancreatic ductal adenocarcinoma (PDA) is the most common and aggressive form of pancreatic cancer. In this study, the oncolytic potentials of several VSV variants were analyzed in a panel of 13 clinically relevant human PDA cell lines and compared to conditionally replicative adenoviruses (CRAds), Sendai virus and respiratory syncytial virus. VSV variants showed oncolytic abilities superior to those of other viruses, and some cell lines that exhibited resistance to other viruses were successfully killed by VSV. However, PDA cells were highly heterogeneous in their susceptibility to virus-induced oncolysis, and several cell lines were resistant to all tested viruses. Resistant cells showed low levels of very early VSV RNA synthesis, indicating possible defects at initial stages of infection. In addition, unlike permissive PDA cell lines, most of the resistant cell lines were able to both produce and respond to interferon, suggesting that intact type I interferon responses contributed to their resistance phenotype. Four cell lines that varied in their permissiveness to VSV-ΔM51 and CRAd dl1520 were tested in mice, and the in vivo results closely mimicked those in vitro. While our results demonstrate that VSV is a promising oncolytic agent against PDA, further studies are needed to better understand the molecular mechanisms of resistance of some PDAs to oncolytic virotherapy.

Oncolytic poxvirus armed with Fas ligand leads to induction of cellular Fas receptor and selective viral replication in FasR-negative cancer

The TNF superfamily members including Fas ligand and TRAIL have been studied extensively for cancer therapy, including as components of gene therapy. We examined the use of FasL expression to achieve tumor selective replication of an oncolytic poxvirus (vFasL) and explored its biology and therapeutic efficacy for FasR− and FasR+ cancers. Infection of FasR+ normal and MC38 cancer cells by vFasL led to abortive viral replication due to acute apoptosis and subsequently displayed both reduced pathogenicity in non-tumor bearing mice and reduced efficacy in FasR+ tumor-bearing mice. Infection of FasR− B16 cancer cells by vFasL led to efficient viral replication, followed by late induction of FasR and subsequent apoptosis. Treatment with vFasL compared to its parental virus (vJS6) led to increased tumor regression and prolonged survival of mice with FasR− cancer (B16), but not with FasR+ cancer (MC38). The delayed induction of FasR by viral infection in FasR− cells provides for potential increased efficacy beyond the limit of the direct oncolytic effect. FasR induction provides one mechanism for tumor selective replication of oncolytic poxviruses in FasR− cancers with enhanced safety. The overall result is both a safer and more effective oncolytic virus for FasR− cancer.

Equine torovirus (BEV) induces caspase-mediated apoptosis in infected cells

Toroviruses are gastroenteritis causing agents that infect different animal species and humans. To date, very little is known about how toroviruses cause disease. Here, we describe for the first time that the prototype member of this genus, the equine torovirus Berne virus (BEV), induces apoptosis in infected cells at late times postinfection. Observation of BEV infected cells by electron microscopy revealed that by 24 hours postinfection some cells exhibited morphological characteristics of apoptotic cells. Based on this finding, we analyzed several apoptotic markers, and observed protein synthesis inhibition, rRNA and DNA degradation, nuclear fragmentation, caspase-mediated cleavage of PARP and eIF4GI, and PKR and eIF2α phosphorylation, all these processes taking place after peak virus production. We also determined that both cell death receptor and mitochondrial pathways are involved in the apoptosis process induced by BEV. BEV-induced apoptosis at late times postinfection, once viral progeny are produced, could facilitate viral dissemination in vivo and contribute to viral pathogenesis.

Oncolytic vesicular stomatitis virus induces apoptosis in U87 glioblastoma cells by a type II death receptor mechanism and induces cell death and tumor clearance in vivo

Vesicular stomatitis virus (VSV) is a potential oncolytic virus for treating glioblastoma multiforme (GBM), an aggressive brain tumor. Matrix (M) protein mutants of VSV have shown greater selectivity for killing GBM cells versus normal brain cells than VSV with wild-type M protein. The goal of this research was to determine the contribution of death receptor and mitochondrial pathways to apoptosis induced by an M protein mutant (M51R) VSV in U87 human GBM tumor cells. Compared to controls, U87 cells expressing a dominant negative form of Fas (dnFas) or overexpressing Bcl-X(L) had reduced caspase-3 activation following infection with M51R VSV, indicating that both the death receptor pathway and mitochondrial pathways are important for M51R VSV-induced apoptosis. Death receptor signaling has been classified as type I or type II, depending on whether signaling is independent (type I) or dependent on the mitochondrial pathway (type II). Bcl-X(L) overexpression inhibited caspase activation in response to a Fas-inducing antibody, similar to the inhibition in response to M51R VSV infection, indicating that U87 cells behave as type II cells. Inhibition of apoptosis in vitro delayed, but did not prevent, virus-induced cell death. Murine xenografts of U87 cells that overexpress Bcl-X(L) regressed with a time course similar to that of control cells following treatment with M51R VSV, and tumors were not detectable at 21 days postinoculation. Immunohistochemical analysis demonstrated similar levels of viral antigen expression but reduced activation of caspase-3 following virus treatment of Bcl-X(L)-overexpressing tumors compared to controls. Further, the pathological changes in tumors following treatment with virus were quite different in the presence versus the absence of Bcl-X(L) overexpression. These results demonstrate that M51R VSV efficiently induces oncolysis in GBM tumor cells despite deregulation of apoptotic pathways, underscoring its potential use as a treatment for GBM.

Mechanisms underlying vesicular stomatitis virus-induced apoptosis of HepG2 cells in vitro

AIM: To investigate the apoptosis-inducing effect of a laboratory-attenuated vesicular stomatitis virus (VSV) strain on HepG2 cells and to explore the underlying mechanisms.

METHODS: After HepG2 cells were infected with VSV at a multiplicity of infection (MOI) of 1.0, cell viability was determined by MTT assay; morphological assessment of apoptosis was performed by acridine orange (AO)/ethidium bromide (EB) and Hoechst/PI staining; apoptotic cells were quantified by annexin V/PI double-staining and cell cycle analysis; mitochondrial membrane potential (ΔΨm) was measured by JC-1 staining; and activation of caspase proteolytic cascade was measured with caspase-9, caspase-8 and -3 colorimetric assay kits.

RESULTS: The attenuated VSV strain could markedly inhibit HepG2 cell proliferation in a time-dependent manner. After HepG2 cells were exposed to VSV at an MOI of 1.0 for 24 h, the percentages of early apoptotic cells (26.46% ± 6.01% vs 4.86% ± 2. 28%, t = -5.817, P < 0.01) and cells in sub-G1 phase (14.07% ± 3.83% vs 3.99% ± 1.36%, t = -4.293, P < 0.05) were increased compared with mock-infected cells. VSV infection significantly decreased mitochondria membrane potential (ΔΨm) (t = -4.586, P < 0.05) and increased the activity of caspase-9 and caspase-3 (both P < 0.05).

CONCLUSION: Human hepatoma cell line HepG2 is highly susceptible to infection with oncolytic VSV. VSV can inhibit the proliferation of HepG2 cell and promote apoptosis through the intrinsic mitochondria pathway. VSV-induced collapse of the mitochondrial trans-membrane potential could exert a feedback effect to elicit caspase-9, and then lead to the activation of the key downstream factor caspase-3.

Dominant inhibition of Akt/protein kinase B signaling by the matrix protein of a negative-strand RNA virus

Vesicular stomatitis virus (VSV) is a rhabdovirus that alters host nuclear and cytoplasmic function upon infection. We have investigated the effect of VSV infection on cellular signaling through the phosphatidylinositol-3 kinase (PI3k)/Akt signaling pathway. Akt phosphorylation at both threonine 308 (Thr308) and serine 473 (Ser473) was inhibited in cells infected with VSV. This inhibition was rapid (beginning within the first 2 to 3 h postinfection) and correlated with the dephosphorylation of downstream effectors of Akt, such as glycogen synthase kinase 3β (GSK3β) and mammalian target of rapamycin (mTOR). The dephosphorylation of Akt occurred in the presence of growth factor stimulation and was not overcome through constitutive membrane targeting of Akt or high levels of phosphatidylinositol-3,4,5-triphosphate (PIP3) accumulation in the membrane. Akt dephosphorylation was not a result of alterations in PDK1 phosphorylation or activity, changes in phosphatase and tensin homologue deleted on chromosome 10 (PTEN) levels, or the downregulation of PI3k signaling. Inactivation of Akt was caused by the expression of the viral M protein in the absence of other viral components, and an M protein mutant that does not inhibit RNA polymerase II (Pol II) transcription and nuclear/cytoplasmic transport was also defective in inhibiting Akt phosphorylation. These data illustrate that VSV utilizes a novel mechanism to alter this central player in cell signaling and oncogenesis. It also suggests an inside-out model of signal transduction where VSV interruption of nuclear events has a rapid and significant effect on membrane signaling events.

VSV oncolysis in combination with the BCL-2 inhibitor obatoclax overcomes apoptosis resistance in chronic lymphocytic leukemia

In chronic lymphocytic leukemia (CLL), overexpression of antiapoptotic B-cell leukemia/lymphoma 2 (BCL-2) family members contributes to leukemogenesis by interfering with apoptosis; BCL-2 expression also impairs vesicular stomatitis virus (VSV)-mediated oncolysis of primary CLL cells. In the effort to reverse resistance to VSV-mediated oncolysis, we combined VSV with obatoclax (GX15-070)-a small-molecule BCL-2 inhibitor currently in phase 2 clinical trials-and examined the molecular mechanisms governing the in vitro and in vivo antitumor efficiency of combining the two agents. In combination with VSV, obatoclax synergistically induced cell death in primary CLL samples and reduced tumor growth in severe combined immunodeficient (SCID) mice-bearing A20 lymphoma tumors. Mechanistically, the combination stimulated the mitochondrial apoptotic pathway, as reflected by caspase-3 and -9 cleavage, cytochrome c release and BAX translocation. Combination treatment triggered the release of BAX from BCL-2 and myeloid cell leukemia-1 (MCL-1) from BAK, whereas VSV infection induced NOXA expression and increased the formation of a novel BAX-NOXA heterodimer. Finally, NOXA was identified as an important inducer of VSV-obatoclax driven apoptosis via knockdown and overexpression of NOXA. These studies offer insight into the synergy between small-molecule BCL-2 inhibitors such as obatoclax and VSV as a combination strategy to overcome apoptosis resistance in CLL.

Fusion-active glycoprotein G mediates the cytotoxicity of vesicular stomatitis virus M mutants lacking host shut-off activity

The cytopathogenicity of vesicular stomatitis virus (VSV) has been attributed mainly to the host shut-off activity of the viral matrix (M) protein, which inhibits both nuclear transcription and nucleocytoplasmic RNA transport, thereby effectively suppressing the synthesis of type I interferon (IFN). The M protein from persistently VSV-infected cells was shown to harbour characteristic amino acid substitutions (M51R, V221F and S226R) implicated in IFN induction. This study demonstrates that infection of human fibroblasts with recombinant VSV containing the M51R substitution resulted in IFN induction, whereas neither the V221F nor the S226R substitution effected an IFN-inducing phenotype. Only when V221F was combined with S226R were the host shut-off activity of the M protein abolished and IFN induced, independently of M51R. The M33A substitution, previously implicated in VSV cytotoxicity, did not affect host shut-off activity. M-mutant VSV containing all four amino acid substitutions retained cytotoxic properties in both Vero cells and IFN-competent primary fibroblasts. Infected-cell death was associated with the formation of giant polynucleated cells, suggesting that the fusion activity of the VSV G protein was involved. Accordingly, M-mutant VSV expressing a fusion-defective G protein or with a deletion of the G gene showed significantly reduced cytotoxic properties and caused long-lasting infections in Vero cells and mouse hippocampal slice cultures. In contrast, a G-deleted VSV expressing wild-type M protein remained cytotoxic. These findings indicate that the host shut-off activity of the M protein dominates VSV cytotoxicty, whilst the fusion-active G protein is mainly responsible for the cytotoxicity remaining with M-mutant VSV.

A laboratory-attenuated vesicular stomatitis virus induces apoptosis and alters the cellular microRNA expression profile in BHK cells

In the present study, we characterized the pathways by which a laboratory-attenuated vesicular stomatitis virus (La-VSV) induces apoptosis in BHK cells. It was found that La-VSV induced a loss of mitochondrial membrane potential (ΔΨm) and activated caspase-9 and -3, but not caspase-8, indicating that the induction of apoptosis by La-VSV may involve an intrinsic apoptotic pathway. Although aberrant expression of microRNAs (miRNAs) has been linked to viral infection, little is known about changes in the cellular miRNA expression profile following VSV infection. Here, we attempted to identify miRNA expression profiles in VSV-infected BHK cells using miRNA microarray. Data analysis revealed that 28 miRNAs consistently responded to VSV-infection, 12 of which were down-regulated and 16 of which were up-regulated. miR-146a of these miRNAs has been found to be up-regulated in LPS-stimulated monocytes and VSV-infected macrophages, suggesting that VSV-induced miR-146a expression occurs not only in immune cells but also in other host cells. We further found that miR-706 inhibited VSV-induced apoptosis by decreasing caspase-3 and -9 activation, suggesting that induction of miR-706 expression may be a novel strategy for survival of VSV, allowing it to escape the apoptosis response of the host. In summary, our results indicate that miRNAs might play important roles in VSV infection and that their aberrant expression could be involved in VSV pathogenesis.

Modulation of apoptosis and immune signaling pathways by the Hantaan virus nucleocapsid protein

Herein, we show a direct relationship between the Hantaan virus (HTNV) nucleocapsid (N) protein and the modulation of apoptosis. We observed an increase in caspase-7 and -8, but not -9 in cells expressing HTNV N protein mutants lacking amino acids 270-330. Similar results were observed for the New World hantavirus, Andes virus. Nuclear factor kappa B (NF-kappaB) was sequestered in the cytoplasm after tumor necrosis factor receptor (TNFR) stimulation in cells expressing HTNV N protein. Further, TNFR stimulated cells expressing HTNV N protein inhibited caspase activation. In contrast, cells expressing N protein truncations lacking the region from amino acids 270-330 were unable to inhibit nuclear import of NF-kappaB and the mutants also triggered caspase activity. These results suggest that the HTNV circumvents host antiviral signaling and apoptotic response mediated by the TNFR pathway through host interactions with the N protein.

To kill or be killed: how viruses interact with the cell death machinery

A virus (from the Latin virus meaning toxin or poison) is a small infectious agent that can only replicate inside the cells of another organism. Viruses are found wherever there is life and have probably existed since living cells first evolved. Viruses do not have their own metabolism and require a host cell to make new products. The range of structural and biochemical (i.e., cytopathic) effects that viruses have on the host cell is extensive. Most viral infections eventually result in the death of the host cell. The causes of death include cell lysis, alterations to the cell's surface membrane and various modes of programmed cell death. Some viruses cause no apparent changes to the infected cell. Cells in which the virus is latent and inactive show few signs of infection and often function normally. This causes persistent infection and the virus is often dormant for many months or years. Some viruses can cause cells to proliferate without causing malignancy, whereas others are established causes of cancer. Human organisms use a genetically controlled cell death programme that prevents the spreading of viral infection and kills the virus. Between 19 and 21 November 2009, with sponsorship from the Journal of Internal Medicine, the Swedish Research Foundation and the Swedish Cancer Society hosted a conference in Stockholm entitled: 'To kill or to be killed. Viral evasion strategies and interference with cell death machinery'. Four comprehensive reviews from this conference are presented in this issue of the Journal of Internal Medicine. These reviews include descriptions of: the modulation of host innate and adaptive immune defenses by cytomegalovirus; the impact of gamma-chain family cytokines on T cell homoeostasis in HIV-1 infection and the therapeutic implications; approaches to killing tumours by depriving them of the mechanisms for detoxification; and viral strategies for the evasion of immunogenic cell death.

Combination of vesicular stomatitis virus matrix protein gene therapy with low-dose cisplatin improves therapeutic efficacy against murine melonoma

Vesicular stomatitis virus (VSV) matrix protein (MP) can directly induce apoptosis via the mitochondrial pathway due to the inhibition of host gene expression. Our previous studies have demonstrated that MP gene therapy efficiently suppressed the growth of malignant tumor in vitro and in vivo. The present study was designed to determine the possibility that the combination of MP gene therapy with low-dose cisplatin would improve therapeutic efficacy against murine melanoma. Immunocompetent C57BL/6 mice bearing B16-F10 melanoma were established. Mice were treated once every 5 days with i.v. administration of 10 microg pVAX-MP/30 microg liposome complex per mouse for 16 days and i.p. delivery of cisplatin at 4 mg/kg/mouse on days 6 and 12 after the initiation of MP treatment. We found that MP + cisplatin treatment resulted in significant inhibition of tumor growth and improved the survival time of melanoma-bearing mice. MP successfully inhibited angiogenesis as assessed by CD31. Histological examination revealed that the combination therapy led to significant increased induction of apoptosis, tumor necrosis, and elevated CD8(+) lymphocyte infiltration. Furthermore, the induction efficacy of the CTL response was dramatically enhanced by the combination therapy. Our findings may prove useful in further explorations of the application of these combinational approaches to the treatment of malignant melanoma.

Protection against lethal vaccinia virus challenge by using an attenuated matrix protein mutant vesicular stomatitis virus vaccine vector expressing poxvirus antigens

Recombinant vesicular stomatitis viruses (VSV) are excellent candidate vectors for vaccination against human diseases. The neurovirulence of VSV in animal models requires the attenuation of the virus for use in humans. Previous efforts have focused on attenuating virus replication. Studies presented here test an alternative approach for attenuation that uses a matrix (M) protein mutant (rM51R) VSV as a vaccine vector against respiratory infection. This mutant is attenuated for viral virulence by its inability to suppress the innate immune response. The ability of rM51R VSV vectors to protect against lethal respiratory challenge was tested using a vaccinia virus intranasal challenge model. Mice immunized intranasally with rM51R vectors expressing vaccinia virus antigens B5R and L1R were protected against lethal vaccinia virus challenge. A single immunization with the vectors provided protection against vaccinia virus-induced mortality; however, a prime-boost strategy reduced the severity of the vaccinia virus-induced disease progression. Antibody titers measured after the prime and boost were low despite complete protection against lethal challenge. However, immunized animals had higher antibody titers during the challenge, suggesting that memory B-cell responses may be important for the protection. Depletion experiments demonstrated that B cells but not CD8 T cells were involved in the protection mediated by rM51R vaccine vectors that express B5R and L1R. These results demonstrate the potential of M protein mutant VSVs as candidate vaccine vectors against human diseases.

Apoptosis induction in BEFV-infected Vero and MDBK cells through Src-dependent JNK activation regulates caspase-3 and mitochondria pathways

Our previous report demonstrated that bovine ephemeral fever virus (BEFV)-infected cultured cells could induce caspase-dependent apoptosis. This study aims to further elucidate how BEFV activates the caspase cascade in bovine cells. BEFV replicated and induced apoptosis in Vero and Madin-Darby bovine kidney (MDBK) cells, and a kinetic study showed a higher efficiency of replication and a greater apoptosis induction ability of BEFV in Vero cells. Src and c-Jun N-terminal kinase (JNK) inhibitor, but not extracellular signal-regulated kinase (ERK) or p38 inhibitor, alleviated BEFV-mediated cytopathic effect and apoptosis. In BEFV-infected Vero and MDBK cells, BEFV directly induced Src tyrosine-418 phosphorylation and JNK phosphorylation and kinase activity, which was inhibited specifically by SU6656 and SP600125, respectively. The caspase cascade and its downstream effectors, Poly (ADP-ribose) polymerase (PARP) and DFF45, were also activated simultaneously upon BEFV infection. In addition, cytochrome c, but not Smac/DIABLO, was released gradually from mitochondria after BEFV infection. SU6656 suppressed Src, JNK, and caspase-3 and -9 activation, as well as PARP and DFF45 cleavage; SP600125 reduced JNK and caspase-3 and -9 activation, as well as PARP and DFF45 cleavage. Taken together, these results strongly support the hypothesis that a Src-dependent JNK signaling pathway plays a key role in BEFV-induced apoptosis. The molecular mechanism identified in our study may provide useful information for the treatment of BEFV.

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

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

Vesicular stomatitis virus as a novel cancer vaccine vector to prime antitumor immunity amenable to rapid boosting with adenovirus

Vesicular stomatitis virus (VSV) has proven to be an effective vaccine vector for immunization against viral infection, but its potential to induce an immune response to a self-tumor antigen has not been investigated. We constructed a recombinant VSV expressing human dopachrome tautomerase (hDCT) and evaluated its immunogenicity in a murine melanoma model. Intranasal delivery of VSV-hDCT activated both CD4(+) and CD8(+) DCT-specific T-cell responses. The magnitude of these responses could be significantly increased by booster immunization with recombinant adenovirus (Ad)-hDCT, which led to enhanced efficacy against B16-F10 melanoma in both prophylactic and therapeutic settings. Notably, the interval of VSV/Ad heterologous vaccination could be shortened to as few as 4 days, making it a potential regimen to rapidly expand antigen-specific effector cells. Furthermore, VSV-hDCT could increase DCT-specific T-cell responses primed by Ad-hDCT, suggesting VSV is efficient for both priming and boosting of the immune response against a self-tumor antigen.

Vesicular stomatitis virus induces apoptosis primarily through Bak rather than Bax by inactivating Mcl-1 and Bcl-XL

Vesicular stomatitis virus (VSV) induces apoptosis via the mitochondrial pathway. The mitochondrial pathway is regulated by the Bcl-2 family of proteins, which consists of both pro- and antiapoptotic members. To determine the relative importance of the multidomain proapoptotic Bcl-2 family members Bak and Bax, HeLa cells were transfected with Bak and/or Bax small interfering RNA (siRNA) and subsequently infected with recombinant wild-type VSV. Our results showed that Bak is more important than Bax for the induction of apoptosis in this system. Bak is regulated by two antiapoptotic Bcl-2 proteins, Mcl-1, which is rapidly turned over, and Bcl-X(L), which is relatively stable. Inhibition of host gene expression by the VSV M protein resulted in the degradation of Mcl-1 but not Bcl-X(L). However, inactivation of both Mcl-1 and Bcl-X(L) was required for cells to undergo apoptosis. While inactivation of Mcl-1 was due to inhibition of its expression, inactivation of Bcl-X(L) indicates a role for one or more BH3-only Bcl-2 family members. VSV-induced apoptosis was inhibited by transfection with siRNA against Bid, a BH3-only protein that is normally activated by the cleavage of caspase-8, the initiator caspase associated with the death receptor pathway. Similarly, treatment with an inhibitor of caspase-8 inhibited VSV-induced apoptosis. These results indicate a role for cross talk from the death receptor pathway in the activation of the mitochondrial pathway by VSV.

VSV virotherapy improves chemotherapy by triggering apoptosis due to proteasomal degradation of Mcl-1

Overexpression of myeloid cell leukemia 1 protein (Mcl-1), an anti-apoptotic B-cell lymphoma 2 (Bcl-2) family member, contributes to chemotherapy resistance of tumors. The short half-life of Mcl-1 makes it an interesting target for therapeutic agents that negatively interfere with cellular protein biosynthesis, such as oncolytic viruses. Vesicular Stomatitis Virus (VSV) has been established as the oncolytic virus that efficiently disrupts de novo protein biosynthesis of infected cells. Here, we show that after VSV infection, Mcl-1 protein levels rapidly declined, whereas the expression of other members of the Bcl-2 family remained unchanged. Mcl-1 elimination was a consequence of proteasomal degradation, as overexpression of a degradation-resistant Mcl-1 mutant restored Mcl-1 levels. Mcl-1 rescue inhibited apoptosis and thereby confirmed that Mcl-1 downregulation contributes to VSV-induced apoptosis. In vitro, VSV virotherapy in combination with chemotherapy revealed an enhanced therapeutic effect compared with the single treatments, which could be reverted by Mcl-1 rescue or RNA interference (RNAi)-mediated knockdown of pro-apoptotic Bax and Bak proteins. Finally, in a tumor mouse model, combinations of doxorubicin and VSV showed a superior therapeutic efficacy compared with VSV or doxorubicin alone. In summary, our data indicate that VSV virotherapy is an attractive strategy to overcome tumor resistance against conventional chemotherapy by elimination of Mcl-1.