Reovirus-induced apoptosis is mediated by TRAIL

Cell Killing by Reovirus: Mechanisms and Consequences

Infection of host cells by mammalian reovirus in culture or in tissues of infected animals results in cell death. Cell death of infected neurons and myocytes contributes to the pathogenesis of reovirus-induced encephalitis and myocarditis in a newborn mouse model. Thus, reovirus-induced cell death has been used to investigate the basis of viral disease. Depending on the cell type, infection of host cells by reovirus results in one of two forms of cell death-apoptosis and necroptosis. In addition to the obvious differences in how these two forms of cell death are executed, the mechanisms by which reovirus infection initiates and transduces signals that lead to each of these types of cell death are distinct. In this review, we discuss how apoptosis and necroptosis are triggered by events at different stages of infection. We also describe how innate immune recognition of reovirus genomic material and type I interferon signaling pathways connect with the core components of the apoptosis and necroptosis machinery. The impact of different cell death mediators on viral pathogenesis and the potential of reovirus as an oncolytic vector are also outlined.

Apoptosis and Phagocytosis as Antiviral Mechanisms

Viruses are infectious entities that make use of the replication machinery of their hosts to produce more progenies, causing disease and sometimes death. To counter viral infection, metazoan hosts are equipped with various defense mechanisms, from the rapid-evoking innate immune responses to the most advanced adaptive immune responses. Previous research demonstrated that cells in fruit flies and mice infected with Drosophila C virus and influenza, respectively, undergo apoptosis, which triggers the engulfment of apoptotic virus-infected cells by phagocytes. This process involves the recognition of eat-me signals on the surface of virus-infected cells by receptors of specialized phagocytes, such as macrophages and neutrophils in mice and hemocytes in fruit flies, to facilitate the phagocytic elimination of virus-infected cells. Inhibition of phagocytosis led to severe pathologies and death in both species, indicating that apoptosis-dependent phagocytosis of virus-infected cells is a conserved antiviral mechanism in multicellular organisms. Indeed, our understanding of the mechanisms underlying apoptosis-dependent phagocytosis of virus-infected cells has shed a new perspective on how hosts defend themselves against viral infection. This chapter explores the mechanisms of this process and its potential for developing new treatments for viral diseases.

Non-pathogenic grass carp reovirus infection leads to both apoptosis and autophagy in a grass carp cell line

A novel GCRV strain isolated from healthy grass carp was named as grass carp reovirus - HH196 (GCRV-HH196), and its infection mechanism remains unclear. In this study, the grass carp ovary cell line (GCO cells) was used to investigate the cell death involved in GCRV-HH196 infection. The results showed that DNA damage, cells volume reduction and cytoplasm shrinkage happened during GCRV-HH196 infection. The mRNA expression levels of pro-apoptotic genes were up-regulated during infection. Two initiators of apoptosis, caspase 8 and caspase 9, and the executioner of apoptosis, caspase 3, were all significantly activated in GCRV-HH196-infected cells. Flow cytometry analysis showed that the number of apoptotic cells in infected cells was significantly higher than that in control cells as the infection progress. Meanwhile, autophagy was also involved in the regulation of GCRV - HH196 infection. We observed that LC3 puncta existed in cytoplasm in GCRV-HH196-infected cells. Furthermore, the protein level of LC3-Ⅱ and Beclin-1 increased, while that of p-Akt decreased in GCRV-HH196-infected cells. These results demonstrated that GCRV-HH196 may regulate apoptosis and autophagy for the virus proliferation and spread, which set a foundation for further research on the interaction between GCRV-HH196 and host.

Comparison of the Effect of Adipose Mesenchymal Stem Cells-Derived Secretome with and without Reovirus in CT26 Cells

Colorectal cancer is the fourth leading cause of cancer-related deaths that has significantly increased over the past three decades. New therapeutic approaches, such as oncolytic viruses, have become very imperative recently to destroy cancer cells. The use of mesenchymal stem cells (MSCs) secretome that is produced in response to variant conditions involves different paracrine molecules secretion that has therapeutic potential in several chronic diseases. Mesenchymal stem cells and their derivatives are employed as regenerative medicine; nevertheless, there is ambiguity in the function of these cells in the control of malignancy. This study aimed to examine the apoptotic effect of secretomes derived from MSCs affected by encompassing oncolytic reoviruses. Mesenchymal stem cells were cultured after separation from abdominal adipose tissue of BALB/c mice. After three passages, the cells were infected by reovirus at the multiplicity of infection of 1 plaque-forming unit per cell. Uninfected and infected secretomes with reovirus were collected separately. The colorectal cancer CT26 cells were confronted with uninfected secretome, infected secretions, reovirus as a positive control, and Dulbecco's Modified Eagle Medium/High Glucose as negative control separately. Finally, apoptosis and necrosis were evaluated by flow cytometry. The infected secretome with reovirus was capable to induce apoptosis more than the uninfected secretome in CT26. However, the supernatant of reovirus infected cells was more capable to induce cell death, in comparison to the infected secretome. Infected MSCs with oncolytic reovirus produced a type of condition media that enhanced apoptosis induction and could have a therapeutic effect on cancer cells. Nonetheless, tumoral cells confronted with the oncolytic reovirus showed more capability in inducing apoptosis in CT26 cells. As a result, the use of oncolytic virus and infected secretome are more effective than uninfected secretome in inducing apoptosis.

Comprehensive review on signaling pathways of dietary saponins in cancer cells suppression

Nutrigenomics utilizes high-throughput genomic technologies to reveal changes in gene and protein levels. Excitingly, ever-growing body of scientific findings has provided sufficient evidence about the interplay between diet and genes. Cutting-edge research and advancements in genomics, epigenetics and metabolomics have deepened our understanding on the role of dietary factors in the inhibition of carcinogenesis and metastasis. Dietary saponins, a type of triterpene glycosides, are generally found in Platycodon grandifloras, Dioscorea oppositifolia, asparagus, legumes, and sea cucumber. Wealth of information has started to shed light on pleiotropic mechanistic roles of dietary saponins in cancer prevention and inhibition. In this review, we have attempted to summarize the in vitro research of dietary saponins in the last two decades by searching common databases such as Google Scholar, PubMed, Scopus, and Web of Science. The results showed that dietary saponins exerted anti-cancer activities via regulation of apoptosis, autophagy, arrest cell cycle, anti-proliferation, anti-metastasis, and anti-angiogenesis, by regulation of several critical signaling pathways, including MAPK, PI3K/Akt/mTOR, NF-κB, and VEGF/VEGFR. However, there is no data about the dosage of dietary saponins for practical anti-cancer effects in human bodies. Extensive clinical studies are needed to confirm the effectiveness of dietary saponins for further commercial and medical applications.

The multifaceted role of TRAIL signaling in cancer and immunity

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily that can lead to the induction of apoptosis in tumor or infected cells. However, activation of TRAIL signaling may also trigger nonapoptotic pathways in cancer and in nontransformed cells, that is, immune cells. Here, we review the current knowledge on noncanonical TRAIL signaling. The biological outcomes of TRAIL signaling in immune and malignant cells are presented and explained, with a focus on the role of TRAIL for natural killer (NK) cell function. Furthermore, we highlight the technical difficulties in dissecting the precise molecular mechanisms involved in the switch between apoptotic and nonapoptotic TRAIL signaling. Finally, we discuss the consequences thereof for a therapeutic manipulation of TRAIL in cancer and possible approaches to bypass these difficulties.

Past, Present and Future of Oncolytic Reovirus

Oncolytic virotherapy (OVT) has received significant attention in recent years, especially since the approval of talimogene Laherparepvec (T-VEC) in 2015 by the Food and Drug administration (FDA). Mechanistic studies of oncolytic viruses (OVs) have revealed that most, if not all, OVs induce direct oncolysis and stimulate innate and adaptive anti-tumour immunity. With the advancement of tumour modelling, allowing characterisation of the effects of tumour microenvironment (TME) components and identification of the cellular mechanisms required for cell death (both direct oncolysis and anti-tumour immune responses), it is clear that a "one size fits all" approach is not applicable to all OVs, or indeed the same OV across different tumour types and disease locations. This article will provide an unbiased review of oncolytic reovirus (clinically formulated as pelareorep), including the molecular and cellular requirements for reovirus oncolysis and anti-tumour immunity, reports of pre-clinical efficacy and its overall clinical trajectory. Moreover, as it is now abundantly clear that the true potential of all OVs, including reovirus, will only be reached upon the development of synergistic combination strategies, reovirus combination therapeutics will be discussed, including the limitations and challenges that remain to harness the full potential of this promising therapeutic agent.

Noncanonical Cell Death Induction by Reassortant Reovirus

Triple-negative breast cancer (TNBC) constitutes 10 to 15% of all breast cancer and is associated with worse prognosis than other subtypes of breast cancer. Current therapies are limited to cytotoxic chemotherapy, radiation, and surgery, leaving a need for targeted therapeutics to improve outcomes for TNBC patients. Mammalian orthoreovirus (reovirus) is a nonenveloped, segmented, double-stranded RNA virus in the Reoviridae family. Reovirus preferentially kills transformed cells and is in clinical trials to assess its efficacy against several types of cancer. We previously engineered a reassortant reovirus, r2Reovirus, that infects TNBC cells more efficiently and induces cell death with faster kinetics than parental reoviruses. In this study, we sought to understand the mechanisms by which r2Reovirus induces cell death in TNBC cells. We show that r2Reovirus infection of TNBC cells of a mesenchymal stem-like (MSL) lineage downregulates the mitogen-activated protein kinase/extracellular signal-related kinase pathway and induces nonconventional cell death that is caspase-dependent but caspase 3-independent. Infection of different MSL lineage TNBC cells with r2Reovirus results in caspase 3-dependent cell death. We map the enhanced oncolytic properties of r2Reovirus in TNBC to epistatic interactions between the type 3 Dearing M2 gene segment and type 1 Lang genes. These findings suggest that the genetic composition of the host cell impacts the mechanism of reovirus-induced cell death in TNBC. Together, our data show that understanding host and virus determinants of cell death can identify novel properties and interactions between host and viral gene products that can be exploited for the development of improved viral oncolytics.IMPORTANCE TNBC is unresponsive to hormone therapies, leaving patients afflicted with this disease with limited treatment options. We previously engineered an oncolytic reovirus (r2Reovirus) with enhanced infective and cytotoxic properties in TNBC cells. However, how r2Reovirus promotes TNBC cell death is not known. In this study, we show that reassortant r2Reovirus can promote nonconventional caspase-dependent but caspase 3-independent cell death and that the mechanism of cell death depends on the genetic composition of the host cell. We also map the enhanced oncolytic properties of r2Reovirus in TNBC to interactions between a type 3 M2 gene segment and type 1 genes. Our data show that understanding the interplay between the host cell environment and the genetic composition of oncolytic viruses is crucial for the development of efficacious viral oncolytics.

The immune system on the TRAIL of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia, characterized by progressive degeneration and loss of neurons in specific regions of the central nervous system. Chronic activation of the immune cells resident in the brain, peripheral immune cell trafficking across the blood-brain barrier, and release of inflammatory and neurotoxic factors, appear critical contributors of the neuroinflammatory response that drives the progression of neurodegenerative processes in AD. As the neuro-immune network is impaired in course of AD, this review is aimed to point out the essential supportive role of innate and adaptive immune response either in normal brain as well as in brain recovery from injury. Since a fine-tuning of the immune response appears crucial to ensure proper nervous system functioning, we focused on the role of the TNF superfamily member, TNF-related apoptosis-inducing ligand (TRAIL), which modulates both the innate and adaptive immune response in the pathogenesis of several immunological disorders and, in particular, in AD-related neuroinflammation. We here summarized mounting evidence of potential involvement of TRAIL signaling in AD pathogenesis, with the aim to provide clearer insights about potential novel therapeutic approaches in AD.

Multiple Routes of Bluetongue Virus Egress

Bluetongue virus (BTV) is an arthropod-borne virus infecting livestock. Its frequent emergence in Europe and North America had caused significant agricultural and economic loss. BTV is also of scientific interest as a model to understand the mechanisms underlying non-enveloped virus release from mammalian and insect cells. The BTV particle, which is formed of a complex double-layered capsid, was first considered as a lytic virus that needs to lyse the infected cells for cell to cell transmission. In the last decade, however, a more in-depth focus on the role of the non-structural proteins has led to several examples where BTV particles are also released through different budding mechanisms at the plasma membrane. It is now clear that the non-structural protein NS3 is the main driver of BTV release, via different interactions with both viral and cellular proteins of the cell sorting and exocytosis pathway. In this review, we discuss the most recent advances in the molecular biology of BTV egress and compare the mechanisms that lead to lytic or non-lytic BTV release.

HTNV Sensitizes Host Toward TRAIL-Mediated Apoptosis-A Pivotal Anti-hantaviral Role of TRAIL

Hantaviruses can cause hemorrhagic fever with renal syndrome (HFRS) in Eurasia and have led to public health threat in China. The pathogenesis of HFRS is complex and involves capillary leakage due to the infection of vascular endothelial cells. Accumulating evidence has demonstrated that hantavirus can induce apoptosis in many cells, but the mechanism remains unclear. Our studies showed that Hantaan virus (HTNV) infection could induce TNF-related apoptosis-inducing ligand (TRAIL) expression in primary human umbilical vein endothelial cells (HUVECs) and sensitize host cells toward TRAIL-mediated apoptosis. Furthermore, TRAIL interference could inhibit apoptosis and enhance the production of HTNV as well as reduce IFN-β production, while exogenous TRAIL treatment showed reverse outcome: enhanced apoptosis and IFN-β production as well as a lower level of viral replication. We also observed that nucleocapsid protein (NP) and glycoprotein (GP) of HTNV could promote the transcriptions of TRAIL and its receptors. Thus, TRAIL was upregulated by HTNV infection and then exhibited significant antiviral activities in vitro, and it was further confirmed in the HTNV-infected suckling mice model that TRAIL treatment significantly reduced viral load, alleviated virus-induced tissue lesions, increased apoptotic cells, and decreased the mortality. In conclusion, these results demonstrate that TRAIL-dependent apoptosis and IFN-β production could suppress HTNV replication and TRAIL treatment might be a novel therapeutic target for HTNV infection.

ITGB1b-Deficient Rare Minnows Delay Grass Carp Reovirus (GCRV) Entry and Attenuate GCRV-Triggered Apoptosis

Integrin β-1 (ITGB1) is a transmembrane protein belonging to the integrin family and it plays an important role in viral entry. In this study, the itgb1b gene of the rare minnow, Gobiocypris rarus, was cloned and analyzed. To investigate the possible role of itgb1b on grass carp reovirus (GCRV) infection, we generated an ITGB1b-deficient rare minnow (ITGB1b^-/-) using the CRISPR/Cas9 system. Following stimulation with GCRV, the survival time of the -ITGB1b^-/- rare minnows was extended in comparison to the wild-type minnows. Moreover, the relative copy number of GCRV and the level of clathrin-mediated endocytosis-associated and apoptosis-related gene expression in the ITGB1b^-/- rare minnows was significantly lower than that of the wild-type minnows. These results suggested that the absence of itgb1b reduced viral entry efficiency and the expression of apoptosis-related genes. Moreover, the data suggested that itgb1b played an important role in mediating the entry of viruses into the cells via clathrin. Therefore, these findings provide novel insight into the function of itgb1b in the process of GCRV infection.

Going (Reo)Viral: Factors Promoting Successful Reoviral Oncolytic Infection

Oncolytic viruses show intriguing potential as cancer therapeutic agents. These viruses are capable of selectively targeting and killing cancerous cells while leaving healthy cells largely unaffected. The use of oncolytic viruses for cancer treatments in selected circumstances has recently been approved by the Food and Drug Administration (FDA) of the US and work is progressing on engineering viral vectors for enhanced selectivity, efficacy and safety. However, a better fundamental understanding of tumour and viral biology is essential for the continued advancement of the oncolytic field. This knowledge will not only help to engineer more potent and effective viruses but may also contribute to the identification of biomarkers that can determine which patients will benefit most from this treatment. A mechanistic understanding of the overlapping activity of viral and standard chemotherapeutics will enable the development of better combinational approaches to improve patient outcomes. In this review, we will examine each of the factors that contribute to productive viral infections in cancerous cells versus healthy cells. Special attention will be paid to reovirus as it is a well-studied virus and the only wild-type virus to have received orphan drug designation by the FDA. Although considerable insight into reoviral biology exists, there remain numerous deficiencies in our understanding of the factors regulating its successful oncolytic infection. Here we will discuss what is known to regulate infection as well as speculate about potential new mechanisms that may enhance successful replication. A joint appreciation of both tumour and viral biology will drive innovation for the next generation of reoviral mediated oncolytic therapy.

Current understanding of reovirus oncolysis mechanisms

Mammalian orthoreovirus (reovirus) is under development as a cancer virotherapy. Clinical trials demonstrate that reovirus-based therapies are safe and tolerated in patients with a wide variety of cancers. Although reovirus monotherapy has proven largely ineffective, reovirus sensitizes cancer cells to existing chemotherapeutic agents and radiation. Clinical trials are underway to test the efficacy of reovirus in combination with chemotherapeutic and radiation regimens and to evaluate the effectiveness of reovirus in conjunction with immunotherapies. Central to the use of reovirus to treat cancer is its capacity to directly kill cancer cells and alter the cellular environment to augment other therapies. Apoptotic cell death is a prominent mechanism of reovirus cancer cell killing. However, reoviruses can also kill cancer cells through nonapoptotic mechanisms. Here, we describe mechanisms of reovirus cancer cell killing, highlight how reovirus is used in combination with existing cancer treatments, and discuss what is known as to how reovirus modulates cancer immunotherapy.

Reactive oxygen species-induced parthanatos of immunocytes by human cytomegalovirus-associated substance

Previous studies have examined various immune evasion strategies of human cytomegalovirus (HCMV) to gain understanding of its pathogenesis. Although the mechanism that underlies immunocyte destruction near HCMV‐infected lesions has yet to be established, it is here shown that substances produced by HCMV‐infected cells induce death in several types of immunocytes, but not in fibroblasts or astrocytomas. These substances contain HCMV proteins and were termed HCMV‐associated insoluble substance (HCMVAIS). The mechanism by which HCMVAIS induces cell death was characterized to improve understanding the death of immunocytes near HCMV‐infected lesions. HCMVAIS were found to trigger production of intracellular nicotinamide adenine dinucleotide phosphate oxidase‐derived reactive oxygen species (ROS), resulting in cell death, this effect being reversed following treatment with ROS inhibitors. Cell death was not induced in splenocytes from NOX‐2 knockout mice. It was hypothesized that DNA damage induced by oxidative stress initiates poly ADP‐ribose polymerase‐1 (PARP‐1)‐mediated cell death, or parthanatos. HCMVAIS‐induced cell death is accompanied by PARP‐1 activation in a caspase‐independent manner, nuclear translocation of apoptosis‐inducing factor (AIF), and DNA fragmentation, which are typical features of parthanatos. Treatment with an AIF inhibitor decreased the rate of HCMVAIS‐induced cell death, this being confirmed by hematoxylin and eosin staining; cell death in most HCMV‐positive foci in serial section samples of a large intestine with HCMV infection was TUNEL‐positive, cleaved caspase 3‐negative and CD45‐positive. Taken together, these data suggest that HCMV inhibits local immune responses via direct killing of immunocytes near HCMV‐infected cells through ROS‐induced parthanatos by HCMVAIS.

Anti-tumor efficacy of oncolytic reovirus against gastrointestinal stromal tumor cells

Imatinib, a multitargeted receptor tyrosine kinase inhibitor, is used as the standard initial therapy against inoperable gastrointestinal stromal tumor (GIST). However, GIST can acquire resistance to imatinib within several years of therapy. The development of oncolytic reovirus as an anticancer agent has expanded to many clinical trials for various tumors. Here, we investigated whether reovirus has antitumor activity against GIST cells in the setting of imatinib sensitivity in vitro and in vivo. Cell proliferation and apoptosis assays were performed using a human GIST cell line, GIST-T1, and imatinib-resistant GIST (GIST-IR) cells that we established. The molecular pathways responsible for cell damage by reovirus were explored using PCR-arrays and Western blots. Reovirus significantly induced apoptotic cell death in GIST-T1 and GIST-IR cells in vitro, despite differences in the activation of receptor tyrosine kinase pathways between GIST-T1 and GIST-IR. Molecular assays indicated the possibility that reovirus induces apoptotic cell death via Fas signaling. Furthermore, in vivo mouse tumor xenograft models demonstrated a significant anti-tumor effect of reovirus on both GIST-T1 and GIST-IR cells. Our results demonstrate the therapeutic potential of reovirus against GIST.

Sclerosing and obstructive cholangiopathy in biliary atresia: mechanisms and association with biliary innate immunity

Biliary atresia (BA) is histologically characterized by a progressive, sclerosing cholangitis and the obstruction of extrahepatic bile ducts. In terms of the etiology and pathogenesis of BA, several viral infections consisting of dsRNA, including Reoviridae, have been implicated. Human biliary epithelial cells (BECs) possess an innate immune system consisting of Toll-like receptors (TLRs). BECs have negative regulatory mechanisms of TLR tolerance to avoid an excessive inflammatory response to lipopolysaccharide (LPS), a TLR4 ligand; however, they lack the tolerance to poly(I:C) (a synthetic analog of viral dsRNA), a TLR3 ligand. Treatment with poly(I:C) induces the expression of the apoptosis-inducer TNF-related apoptosis-inducing ligand (TRAIL), along with the antiviral molecule IFN-β1, and reduces the viability of BECs by enhancing apoptosis. In response, surviving BECs increase their expression of various markers, including basic FGF [an epithelial-mesenchymal transition (EMT)-inducer], S100A4 (a mesenchymal marker), and Snail (a transcriptional factor), and decrease that of epithelial markers such as CK19 and E-cadherin before undergoing EMT. Extrahepatic bile ducts in BA infants frequently show a lack of epithelial markers and an aberrant expression of vimentin, in addition to the enhancement of TRAIL and apoptosis. dsRNA viruses may directly induce apoptosis and EMT in human BECs as a result of the biliary innate immune response, supporting the notion that Reoviridae infections may be directly associated with the pathogenesis of cholangiopathies in BA.

Virus Infection and Death Receptor-Mediated Apoptosis

Virus infection can trigger extrinsic apoptosis. Cell-surface death receptors of the tumor necrosis factor family mediate this process. They either assist persistent viral infection or elicit the elimination of infected cells by the host. Death receptor-mediated apoptosis plays an important role in viral pathogenesis and the host antiviral response. Many viruses have acquired the capability to subvert death receptor-mediated apoptosis and evade the host immune response, mainly by virally encoded gene products that suppress death receptor-mediated apoptosis. In this review, we summarize the current information on virus infection and death receptor-mediated apoptosis, particularly focusing on the viral proteins that modulate death receptor-mediated apoptosis.

Fas Ligand-mediated cytotoxicity of CD4+ T cells during chronic retrovirus infection

CD4+ helper T cells and cytotoxic CD8+ T cells are key players for adaptive immune responses against acute infections with retroviruses. Similar to textbook knowledge the most important function of CD4+ T cells during an acute retrovirus infection seems to be their helper function for other immune cells. Whereas there was no direct anti-viral activity of CD4+ T cells during acute Friend Virus (FV) infection, they were absolutely required for the control of chronic infection. During chronic FV infection a population of activated FV-specific CD4+ T cells did not express cytotoxic molecules, but Fas Ligand that can induce Fas-induced apoptosis in target cells. Using an MHC II-restricted in vivo CTL assay we demonstrated that FV-specific CD4+ T cells indeed mediated cytotoxic effects against FV epitope peptide loaded targets. CD4 + CTL killing was also detected in FV-infected granzyme B knockout mice confirming that the exocytosis pathway was not involved. However, killing could be blocked by antibodies against FasL, which identified the Fas/FasL pathway as critical cytotoxic mechanism during chronic FV infection. Interestingly, targeting the co-stimulatory receptor CD137 with an agonistic antibody enhanced CD4+ T cell cytotoxicity. This immunotherapy may be an interesting new approach for the treatment of chronic viral infections.

Bid-deficient fish delay grass carp reovirus (GCRV) replication and attenuate GCRV-triggered apoptosis

Bid, BH3-interacting domain death agonist, is a pro-apoptotic BH3-only member of Bcl-2 family, playing an important role in apoptosis. In the study, Bid genes from grass carp (Ctenopharyngodon idellus) and rare minnow (Gobiocypris rarus), named CiBid and GrBid, were cloned and analyzed. Bid was constitutively expressed in all examined tissues of grass carp, but the expression level varied in different tissues. Following grass carp reovirus (GCRV) stimulation in vivo, Bid and apoptosis related genes Caspase-9 and Caspase-3 was up-regulated significantly at the late stage of infection. Moreover, we generated a Bid-deficient rare minnow (Bid^-/-) to investigate the possible role of Bid in GCRV-triggered apoptosis. We found that the survival time of Bid^-/- rare minnow after GCRV infection was extended when compared with wild-type fish, the relative copy number of GCRV in Bid^-/- rare minnow was lower than that in wild-type fish, and the expression level of Caspase-9 and Caspase-3 in Bid^-/- rare minnow were significantly lower than that in the wild-type fish. Collectively, the current data revealed the important role of Bid during virus-induced apoptosis in teleost fish. Our study would provide new insight into understanding the GCRV induced apoptosis and may provide a target gene for virus-resistant breeding in grass carp.

Cloning and characterization of Bax1 and Bax2 genes of Ctenopharyngodon idellus and evaluation of transcript expression in response to grass carp reovirus infection

Multidomain proapoptotic Bcl-2-associated X (Bax) protein is an essential effector responsible for mitochondrial outer membrane permeabilization, resulting in cell death via apoptosis. In this study, two Bax genes of grass carp (Ctenopharyngodon idellus), designated as CiBax1 and CiBax2, were isolated and analyzed. The obtained CiBax1 cDNA is 2058 bp long, with a 579 bp open reading frame (ORF) coding a protein of 192 amino acid residues. The full-length cDNA of CiBax2 is 1161 bp, with a 618 bp ORF coding 205 amino acids. Both CiBax1 and CiBax2 are typical members of Bcl-2 family containing conserved Bcl and C-terminal domains, and they share conserved synteny with zebrafish Bax genes despite the grass carp Bax mapping to different linkage groups. Phylogenetic analysis showed that CiBax1 was clustered with Bax from most teleost fish, and CiBax2 was close to Bax2 from teleost fish but far separated from that of Salmo salar. Quantitative real-time PCR analysis revealed broad expression of CiBax1 and CiBax2 in tissues from healthy grass carp, but the relative expression level differed. The mRNA expression of CiBax1 and CiBax2 was both upregulated significantly and peaked in all examined tissues at days 5 or 6 post-infection with grass carp reovirus. Subcellular localization indicated that CiBax1 protein was localized in both nucleus and cytosol, while CiBax2 protein only in cytosol. Moreover, CiBax2, but not CiBax1 was colocalized with mitochondrion under normal condition. Taken together, the findings would be helpful for further understanding of the function of Bax in teleost fish.

Viruses and the Diversity of Cell Death

Cell death is a common outcome of virus infection. In some cases, cell death curbs virus replication. In others, cell death enhances virus dissemination and contributes to tissue injury, exacerbating viral disease. Three forms of cell death are observed following virus infection-apoptosis, necroptosis, and pyroptosis. In this review, I describe the core machinery needed for each of these forms of cell death. Using representative viruses, I highlight how distinct stages of virus replication initiate signaling pathways that elicit these forms of cell death. I also discuss viral strategies to overcome the deleterious effects of cell death on virus propagation and the consequences of cell death for host physiology.

Repurposing Sunitinib with Oncolytic Reovirus as a Novel Immunotherapeutic Strategy for Renal Cell Carcinoma

PURPOSE

In addition to their direct cytopathic effects, oncolytic viruses are capable of priming antitumor immune responses. However, strategies to enhance the immunotherapeutic potential of these agents are lacking. Here, we investigated the ability of the multi-tyrosine kinase inhibitor and first-line metastatic renal cell carcinoma (RCC) agent, sunitinib, to augment the antitumor immune response generated by oncolytic reovirus.

EXPERIMENTAL DESIGN

In vitro, oncolysis and chemokine production were assessed in a panel of human and murine RCC cell lines after exposure to reovirus, sunitinib, or their combination. In vivo, the RENCA syngeneic murine model of RCC was employed to determine therapeutic and tumor-specific immune responses after treatment with reovirus (intratumoral), sunitinib, or their combination. Parallel investigations employing the KLN205 syngeneic murine model of lung squamous cell carcinoma (NSCLC) were conducted for further validation.

RESULTS

Reovirus-mediated oncolysis and chemokine production was observed following RCC infection. Reovirus monotherapy reduced tumor burden and was capable of generating a systemic adaptive antitumor immune response evidenced by increased numbers of tumor-specific CD8⁺ IFNγ-producing cells. Coadministration of sunitinib with reovirus further reduced tumor burden resulting in improved survival, decreased accumulation of immune suppressor cells, and the establishment of protective immunity upon tumor rechallenge. Similar results were observed for KLN205 tumor-bearing mice, highlighting the potential broad applicability of this approach.

CONCLUSIONS

The ability to repurpose sunitinib for augmentation of reovirus' immunotherapeutic efficacy positions this novel combination therapy as an attractive strategy ready for clinical testing against a range of histologies, including RCC and NSCLC. Clin Cancer Res; 22(23); 5839-50. ©2016 AACR.

N-Myc expression enhances the oncolytic effects of vesicular stomatitis virus in human neuroblastoma cells

N-myc oncogene amplification is associated but not present in all cases of high-risk neuroblastoma (NB). Since oncogene expression could often modulate sensitivity to oncolytic viruses, we wanted to examine if N-myc expression status would determine virotherapy efficacy to high-risk NB. We showed that induction of exogenous N-myc in a non-N-myc-amplified cell line background (TET-21N) increased susceptibility to oncolytic vesicular stomatitis virus (mutant VSVΔM51) and alleviated the type I IFN-induced antiviral state. Cells with basal N-myc, on the other hand, were less susceptible to virus-induced oncolysis and established a robust IFN-mediated antiviral state. The same effects were also observed in NB cell lines with and without N-myc amplification. Microarray analysis showed that N-myc overexpression in TET-21N cells downregulated IFN-stimulated genes (ISGs) with known antiviral functions. Furthermore, virus infection caused significant changes in global gene expression in TET-21N cells overexpressing N-myc. Such changes involved ISGs with various functions. Therefore, the present study showed that augmented susceptibility to VSVΔM51 by N-myc at least involves downregulation of ISGs with antiviral functions and alleviation of the IFN-stimulated antiviral state. Our studies suggest the potential utility of N-myc amplification/overexpression as a predictive biomarker of virotherapy response for high-risk NB using IFN-sensitive oncolytic viruses.

Distinct roles of TNF-related apoptosis-inducing ligand (TRAIL) in viral and bacterial infections: from pathogenesis to pathogen clearance

INTRODUCTION

Apoptotic death of different cells observed during infection is thought to limit overwhelming inflammation in response to microbial challenge. However, the underlying apoptotic death mechanisms have not been well defined. Tumor necrosis factor (TNF) related apoptosis-inducing ligand (TRAIL) is a type II transmembrane protein belonging to the TNF superfamily, which is involved not only in tumor growth suppression but in infection control and also in the regulation of both innate and adaptive immune responses.

FINDINGS

In this review, we have summarized data of recent studies on the influence of the TRAIL/TRAIL receptor (TRAIL-R) system on the development of viral and bacterial infections. TRAIL may have a dual function in the immune system being able to kill infected cells and also to participate in the pathogenesis of multiple infections. Moreover, many pathogens have evolved mechanisms to manipulate TRAIL signaling thus increasing pathogen replication.

CONCLUSION

Present data highlight an essential role for the TRAIL/TRAIL-R system in the regulation and modulation of apoptosis and show that TRAIL has distinct roles in pathogenesis and pathogen elimination. Knowledge of the factors that determine whether TRAIL is helpful or harmful supposes its potential therapeutic implications that are only beginning to be explored.

Exploring Reovirus Plasticity for Improving Its Use as Oncolytic Virus

Reoviruses are non-enveloped viruses with a segmented double stranded RNA genome. In humans, they are not associated with serious disease. Human reoviruses exhibit an inherent preference to replicate in tumor cells, which makes them ideally suited for use in oncolytic virotherapies. Their use as anti-cancer agent has been evaluated in several clinical trials, which revealed that intra-tumoral and systemic delivery of reoviruses are well tolerated. Despite evidence of anti-tumor effects, the efficacy of reovirus in anti-cancer monotherapy needs to be further enhanced. The opportunity to treat both the primary tumor as well as metastases makes systemic delivery a preferred administration route. Several pre-clinical studies have been conducted to address the various hurdles connected to systemic delivery of reoviruses. The majority of those studies have been done in tumor-bearing immune-deficient murine models. This thwarts studies on the impact of the contribution of the immune system to the tumor cell eradication. This review focuses on key aspects of the reovirus/host-cell interactions and the methods that are available to modify the virus to alter these interactions. These aspects are discussed with a focus on improving the reovirus' antitumor efficacy.

Evidence for Oncolytic Virotherapy: Where Have We Got to and Where Are We Going?

The last few years have seen an increased interest in immunotherapy in the treatment of malignant disease. In particular, there has been significant enthusiasm for oncolytic virotherapy, with a large amount of pre-clinical data showing promise in animal models in a wide range of tumour types. How do we move forward into the clinical setting and translate something which has such potential into meaningful clinical outcomes? Here, we review how the field of oncolytic virotherapy has developed thus far and what the future may hold.

Expression pattern and transcriptional regulatory mechanism of noxa gene in grass carp (Ctenopharyngodon idella)

Noxa, a pro-apoptotic protein, plays an important role in cell apoptosis. The researches about noxa gene were concentrated in mammalians, whereas the role and transcriptional regulatory mechanism of noxa in fish were still unclear. In this study, the expression pattern and transcriptional regulatory mechanism of noxa gene in grass carp were analyzed. Noxa was constitutively expressed in all the examined tissues but the relative expression level differed. After exposure to grass carp reovirus (GCRV), mRNA expression level of noxa was down-regulated at the early phase whereas up-regulated at the late phase of infection. Luciferase assays showed that the promoter region -867 ∼ +107 of noxa had high activity and the region -678 ∼ -603 was important in the response to GCRV infection. By deleting the predicted transcription factor binding sites, transcription factors FOXO1 and CEBPβ were found important for noxa in response to GCRV infection. Moreover, the noxa promoter was biotin-labeled and incubated with nuclear extracts from GCRV infected cells. Mass spectrometry analysis showed that transcription factors FOXO1 and CEBPβ were also enriched in the combined proteins. Therefore, the results suggested that transcription factors FOXO1 and CEBPβ may play an important role in the regulation of noxa. Our study would provide new insight into the transcriptional regulatory mechanism of noxa in teleost fish.

Proteomics informed by transcriptomics reveals Hendra virus sensitizes bat cells to TRAIL-mediated apoptosis

BACKGROUND

Bats are a major reservoir of emerging infectious viruses. Many of these viruses are highly pathogenic to humans however bats remain asymptomatic. The mechanism by which bats control viral replication is unknown. Here we utilize an integrated approach of proteomics informed by transcriptomics to compare the response of immortalized bat and human cells following infection with the highly pathogenic bat-borne Hendra virus (HeV).

RESULTS

The host response between the cell lines was significantly different at both the mRNA and protein levels. Human cells demonstrated minimal response eight hours post infection, followed by a global suppression of mRNA and protein abundance. Bat cells demonstrated a robust immune response eight hours post infection, which led to the up-regulation of apoptosis pathways, mediated through the tumor necrosis factor-related apoptosis inducing ligand (TRAIL). HeV sensitized bat cells to TRAIL-mediated apoptosis, by up-regulating death receptor transcripts. At 48 and 72 hours post infection, bat cells demonstrated a significant increase in apoptotic cell death.

CONCLUSIONS

This is the first study to comprehensively compare the response of bat and human cells to a highly pathogenic zoonotic virus. An early induction of innate immune processes followed by apoptosis of virally infected bat cells highlights the possible involvement of programmed cell death in the host response. Our study shows for the first time a side-by-side high-throughput analysis of a dangerous zoonotic virus in cell lines derived from humans and the natural bat host. This enables a way to search for divergent mechanisms at a molecular level that may influence host pathogenesis.

Proteomics informed by transcriptomics reveals Hendra virus sensitizes bat cells to TRAIL-mediated apoptosis

Background

Bats are a major reservoir of emerging infectious viruses. Many of these viruses are highly pathogenic to humans however bats remain asymptomatic. The mechanism by which bats control viral replication is unknown. Here we utilize an integrated approach of proteomics informed by transcriptomics to compare the response of immortalized bat and human cells following infection with the highly pathogenic bat-borne Hendra virus (HeV).

Results

The host response between the cell lines was significantly different at both the mRNA and protein levels. Human cells demonstrated minimal response eight hours post infection, followed by a global suppression of mRNA and protein abundance. Bat cells demonstrated a robust immune response eight hours post infection, which led to the up-regulation of apoptosis pathways, mediated through the tumor necrosis factor-related apoptosis inducing ligand (TRAIL). HeV sensitized bat cells to TRAIL-mediated apoptosis, by up-regulating death receptor transcripts. At 48 and 72 hours post infection, bat cells demonstrated a significant increase in apoptotic cell death.

Conclusions

This is the first study to comprehensively compare the response of bat and human cells to a highly pathogenic zoonotic virus. An early induction of innate immune processes followed by apoptosis of virally infected bat cells highlights the possible involvement of programmed cell death in the host response. Our study shows for the first time a side-by-side high-throughput analysis of a dangerous zoonotic virus in cell lines derived from humans and the natural bat host. This enables a way to search for divergent mechanisms at a molecular level that may influence host pathogenesis.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-014-0532-x) contains supplementary material, which is available to authorized users.

Evolutionary evidence of tumor necrosis factor super family members in the Japanese pufferfish (Takifugu rubripes): Comprehensive genomic identification and expression analysis

Tumor necrosis factor (TNF) and its superfamily (TNFSF) members are important inflammatory cytokines. Although fish have fourteen TNFSF genes, their genomic location and existence are yet to be described and confirmed in the Japanese pufferfish (Fugu) (Takifugu rubripes). Therefore, we conducted in silico identification, synteny analysis of TNFSF genes from Fugu with that of zebrafish and human TNFSF loci and their expression analysis in various tissues. We identified ten novel TNFSF genes, viz. TNFSF5 (CD40L), TNFSF6 (FasL), three TNFSF10 (TRAIL) (-1, 2 and 3), TNFSF11 (RANKlg), TNFSF12 (TWEAK), two TNFSF13B (BAFF) (1 and 2) and TNFSF14 (LIGHT) belonging to seven TNFSFs in Fugu. Several features such as existence of TNF family signature, conservation of genes in TNF loci with human and zebrafish chromosomes and phylogenetic clustering with other teleost TNFSF orthologs confirmed their identity. Fugu TNFSF genes were constitutively expressed in all eight different tissues with most of them expressed highly in liver. Fugu TNFSF10 gene has three homologs present on chromosomes 10 (TNFSF10-1), 8 (TNFSF10-2) and 2 (TNFSF10-3). Moreover, a phylogenetic analysis containing all available vertebrate (mammals, birds, reptiles, amphibians and fish) TNFSF10 orthologs showed that Fugu TNFSF10-1 and 10-3 are present in all vertebrates, whereas TNFSF10-2 was not related to any mammalian and avian orthologs. Viral double-stranded RNA mimic poly (I:C) caused an elevated expression of three Fugu TNFSF10 genes in head kidney cells at 4h indicating probable role of these genes to induce apoptosis in virus-infected cells. In conclusion, Fugu possesses genes belonging to nine TNFSFs including the newly identified seven and previously reported two, TNFSF New (TNF-N) and TNFSF2 (TNF-α). Our findings would add up information to TNFSF evolution among vertebrates.

The oncolytic virus, pelareorep, as a novel anticancer agent: a review

Pelareorep (REOLYSIN®) is an investigational new drug, a proprietary formulation consisting of a live, replication-competent, naturally occurring Reovirus Type 3 Dearing strain. Through several preclinical studies it was determined that reovirus can exhibit profound cytotoxic effects on cancer cells predominantly with an activated RAS-signalling pathway. Moreover, it was discovered that reoviruses can "hitchhike" on peripheral blood mononuclear cells and dendritic cells, thereby evading neutralizing antibodies of the host immune system. Cell carriage, targeted delivery, triggering host immune response and other inherent characteristics of the reovirus led to its further advancement into cancer therapy. When injected into Sprague-Dawley rats, the viral routes of clearance, predominantly through the spleen and liver, remained consistent with earlier studies. Toxicology findings were considered incidental and not associated with pelareorep when tested in animal models. Pelareorep demonstrated a high level of homogeneity at the amino acid level and genetic stability when compared to the master and working virus banks. The drug is manufactured in a 100 L bioreactor after which it is purified and formulated for use in pre-clinical, clinical and research studies. Over the past few decades, we have witnessed a paradigm shift from conventional therapy to the conceivable use of oncolytic viruses for the treatment of cancer. This review will detail pre-clinical evidence of anticancer activity of pelareorep that has led to extensive clinical development. Several Phase I-II clinical trials have been completed or are ongoing in cancer patients on a broad spectrum of solid tumors and hematologic malignancies.

Oncolytic reovirus combined with trastuzumab enhances antitumor efficacy through TRAIL signaling in human HER2-positive gastric cancer cells

The human epidermal growth factor receptor 2 (HER2)-targeting agent, trastuzumab, is effective for HER2-overexpressing gastric cancer therapy. As oncolytic reovirus is currently undergoing clinical trials internationally, we wanted to explore whether combination therapy using trastuzumab and reovirus might provide a novel, more effective therapeutic option for gastric cancer. Cell proliferation and cell apoptosis were examined in vitro, while molecular analysis of pathways responsible for cell damage was examined using polymerase chain reaction array. Activation of the proteins related to apoptosis, cell growth and survival was detected by Western blotting. Mouse tumor xenograft models were used to examine antitumor activity in vivo. Reovirus sensitized HER2-overexpressing gastric cancer cells to undergo apoptosis. Both in vitro and in vivo studies provided evidence that the combination therapy is a more powerful modality against HER2-overexpressing gastric cancer cells than treatment using a single agent. Molecular analysis indicated that combination therapy induced significantly higher levels of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) in cancer cells. Antibody against TRAIL strongly inhibited cell toxicity caused by the combined treatment. These data suggest that reovirus may augment trastuzumab-induced cytotoxicity in gastric cancer cells.

Activated ras signaling pathways and reovirus oncolysis: an update on the mechanism of preferential reovirus replication in cancer cells

The development of wild-type, unmodified Type 3 Dearing strain reovirus as an anticancer agent has currently expanded to 32 clinical trials (both completed and ongoing) involving reovirus in the treatment of cancer. It has been more than 30 years since the potential of reovirus as an anticancer agent was first identified in studies that demonstrated the preferential replication of reovirus in transformed cell lines but not in normal cells. Later investigations have revealed the involvement of activated Ras signaling pathways (both upstream and downstream) and key steps of the reovirus infectious cycle in promoting preferential replication in cancer cells with reovirus-induced cancer cell death occurring through necrotic, apoptotic, and autophagic pathways. There is increasing evidence that reovirus-induced antitumor immunity involving both innate and adaptive responses also contributes to therapeutic efficacy though this discussion is beyond the scope of this article. Here, we review our current understanding of the mechanism of oncolysis contributing to the broad anticancer activity of reovirus. Further understanding of reovirus oncolysis is critical in enhancing the clinical development and efficacy of reovirus.

Oncolytic Immunotherapy: Dying the Right Way is a Key to Eliciting Potent Antitumor Immunity

Oncolytic viruses (OVs) are novel immunotherapeutic agents whose anticancer effects come from both oncolysis and elicited antitumor immunity. OVs induce mostly immunogenic cancer cell death (ICD), including immunogenic apoptosis, necrosis/necroptosis, pyroptosis, and autophagic cell death, leading to exposure of calreticulin and heat-shock proteins to the cell surface, and/or released ATP, high-mobility group box 1, uric acid, and other damage-associated molecular patterns as well as pathogen-associated molecular patterns as danger signals, along with tumor-associated antigens, to activate dendritic cells and elicit adaptive antitumor immunity. Dying the right way may greatly potentiate adaptive antitumor immunity. The mode of cancer cell death may be modulated by individual OVs and cancer cells as they often encode and express genes that inhibit/promote apoptosis, necroptosis, or autophagic cell death. We can genetically engineer OVs with death-pathway-modulating genes and thus skew the infected cancer cells toward certain death pathways for the enhanced immunogenicity. Strategies combining with some standard therapeutic regimens may also change the immunological consequence of cancer cell death. In this review, we discuss recent advances in our understanding of danger signals, modes of cancer cell death induced by OVs, the induced danger signals and functions in eliciting subsequent antitumor immunity. We also discuss potential combination strategies to target cells into specific modes of ICD and enhance cancer immunogenicity, including blockade of immune checkpoints, in order to break immune tolerance, improve antitumor immunity, and thus the overall therapeutic efficacy.

The interplay of reovirus with autophagy

Autophagy participates in multiple fundamental physiological processes, including survival, differentiation, development, and cellular homeostasis. It eliminates cytoplasmic protein aggregates and damaged organelles by triggering a series of events: sequestering the protein substrates into double-membrane vesicles, fusing the vesicles with lysosomes, and then degrading the autophagic contents. This degradation pathway is also involved in various disorders, for instance, cancers and infectious diseases. This paper provides an overview of modulation of autophagy in the course of reovirus infection and also the interplay of autophagy and reovirus.

Nonstructural protein σ1s mediates reovirus-induced cell cycle arrest and apoptosis

Reovirus nonstructural protein σ1s is implicated in cell cycle arrest at the G2/M boundary and induction of apoptosis. However, the contribution of σ1s to these effects in an otherwise isogenic viral background has not been defined. To evaluate the role of σ1s in cell cycle arrest and apoptosis, we used reverse genetics to generate a σ1s-null reovirus. Following infection with wild-type virus, we observed an increase in the percentage of cells in G2/M, whereas the proportion of cells in G2/M following infection with the σ1s-null mutant was unaffected. Similarly, we found that the wild-type virus induced substantially greater levels of apoptosis than the σ1s-null mutant. These data indicate that σ1s is required for both reovirus-induced cell cycle arrest and apoptosis. To define sequences in σ1s that mediate these effects, we engineered viruses encoding C-terminal σ1s truncations by introducing stop codons in the σ1s open reading frame. We also generated viruses in which charged residues near the σ1s amino terminus were replaced individually or as a cluster with nonpolar residues. Analysis of these mutants revealed that amino acids 1 to 59 and the amino-terminal basic cluster are required for induction of both cell cycle arrest and apoptosis. Remarkably, viruses that fail to induce cell cycle arrest and apoptosis also are attenuated in vivo. Thus, identical sequences in σ1s are required for reovirus-induced cell cycle arrest, apoptosis, and pathogenesis. Collectively, these findings provide evidence that the σ1s-mediated properties are genetically linked and suggest that these effects are mechanistically related.

Induction of apoptosis in MCF-7 cells by the hemagglutinin-neuraminidase glycoprotein of Newcastle disease virus Malaysian strain AF2240

Newcastle disease virus (NDV) exerts its naturally occurring oncolysis possibly through the induction of apoptosis. We hypothesized that the binding of the virus to the cell via the hemagglutinin-neuraminidase (HN) glycoprotein may be sufficient to not only induce apoptosis but to induce a higher apoptosis level than the parental NDV AF2240 virus. NDV AF2240 induction of apoptosis in MCF-7 human breast cancer cells was analyzed and quantified. In addition, the complete HN gene of NDV strain AF2240 was amplified, sequenced and cloned into the pDisplay eukaryotic expression vector. HN gene expression was first detected at the cell surface membrane of the transfected MCF-7 cells. HN induction of apoptosis in transfected MCF-7 cells was analyzed and quantified. The expression of the HN gene alone was able to induce apoptosis in MCF-7 cells but it was a less potent apoptosis inducer compared to the parental NDV AF2240 strain. In conclusion, the NDV AF2240 strain is a more suitable antitumor candidate agent than its recombinant HN gene unless the latter is further improved by additional modifications.

Cloning and preliminary functional studies of the JAM-A gene in grass carp (Ctenopharyngodon idellus)

Grass carp (Ctenopharyngodon idellus) is a very important aquaculture species in China and other South-East Asian countries; however, disease outbreaks in this species are frequent, resulting in huge economic losses. Grass carp hemorrhage caused by grass carp reovirus (GCRV) is one of the most serious diseases. Junction adhesion molecule A (JAM-A) is the mammalian receptor for reovirus, and has been well studied. However, the JAM-A gene in grass carp has not been studied so far. In this study, we cloned and elucidated the structure of the JAM-A gene in grass carp (GcJAM-A) and then studied its functions during grass carp hemorrhage. GcJAM-A is composed of 10 exons and 9 introns, and its full-length cDNA is 1833 bp long, with an 888 bp open reading frame (ORF) that encodes a 295 amino acid protein. The GcJAM-A protein is predicted to contain a typical transmembrane domain. Maternal expression pattern of GcJAM-A is observed during early embryogenesis, while zygote expression occurs at 8 h after hatching. GcJAM-A is expressed strongly in the gill, liver, intestine and kidney, while it is expressed poorly in the blood, brain, spleen and head kidney. Moreover, lower expression is observed in the gill, liver, intestine, brain, spleen and kidney of 30-month-old individuals, compared with 6-month-old. In a GcJAM-A-knockdown cell line (CIK) infected with GCRV, the expression of genes involved in the interferon and apoptosis pathways was significantly inhibited. These results suggest that GcJAM-A could be a receptor for GCRV. We have therefore managed to characterize the GcJAM-A gene and provide evidence for its role as a receptor for GCRV.

Reovirus activates a caspase-independent cell death pathway

Virus-induced apoptosis is thought to be the primary mechanism of cell death following reovirus infection. Induction of cell death following reovirus infection is initiated by the incoming viral capsid proteins during cell entry and occurs via NF-κB-dependent activation of classical apoptotic pathways. Prototype reovirus strain T3D displays a higher cell-killing potential than strain T1L. To investigate how signaling pathways initiated by T3D and T1L differ, we methodically analyzed cell death pathways activated by these two viruses in L929 cells. We found that T3D activates NF-κB, initiator caspases, and effector caspases to a significantly greater extent than T1L. Surprisingly, blockade of NF-κB or caspases did not affect T3D-induced cell death. Cell death following T3D infection resulted in a reduction in cellular ATP levels and was sensitive to inhibition of the kinase activity of receptor interacting protein 1 (RIP1). Furthermore, membranes of T3D-infected cells were compromised. Based on the dispensability of caspases, a requirement for RIP1 kinase function, and the physiological status of infected cells, we conclude that reovirus can also induce an alternate, necrotic form of cell death described as necroptosis. We also found that induction of necroptosis requires synthesis of viral RNA or proteins, a step distinct from that necessary for the induction of apoptosis. Thus, our studies reveal that two different events in the reovirus replication cycle can injure host cells by distinct mechanisms.

Virus-induced cell death is a determinant of pathogenesis. Mammalian reovirus is a versatile experimental model for identifying viral and host intermediaries that contribute to cell death and for examining how these factors influence viral disease. In this study, we identified that in addition to apoptosis, a regulated form of cell death, reovirus is capable of inducing an alternate form of controlled cell death known as necroptosis. Death by this pathway perturbs the integrity of host membranes and likely triggers inflammation. We also found that apoptosis and necroptosis following viral infection are activated by distinct mechanisms. Our results suggest that host cells can detect different stages of viral infection and attempt to limit viral replication through different forms of cellular suicide. While these death responses may aid in curbing viral spread, they can also exacerbate tissue injury and disease following infection.

Soluble TRAIL in normal pregnancy and acute pyelonephritis: a potential explanation for the susceptibility of pregnant women to microbial products and infection

OBJECTIVE

Pregnancy is characterized by activation of the innate immune response demonstrated by phenotypic and metabolic changes in granulocytes and monocytes. This state of activation has been implicated in the pathophysiology of multiorgan dysfunction of pregnant women with acute viral or bacterial infection. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) is one of the mediators responsible for neutrophil apoptosis. Gene deletion of TRAIL results in delayed neutrophil apoptosis and resolution of inflammation after the administration of bacterial endotoxin. The aim of this study was to determine whether maternal plasma concentrations of the soluble form of TRAIL (sTRAIL) differ in women with uncomplicated pregnancy and those with acute pyelonephritis.

METHOD

A cross-sectional study was conducted to include women in the following groups: (1) non-pregnant (n = 23); (2) uncomplicated pregnancies (n = 93) and (3) pregnancies with acute pyelonephritis (n = 23). Plasma concentrations of sTRAIL were determined by enzyme-linked immunoassay.

RESULTS

(1) Women with uncomplicated pregnancies had a lower mean plasma sTRAIL concentration (pg/mL) than non-pregnant women (31.5 ± 10.1 versus 53.3 ± 12.5; p < 0.001); (2) plasma sTRAIL concentrations did not change as a function of gestational age (Pearson correlation = -0.1; p = 0.4); (3) the mean plasma sTRAIL concentration (pg/mL) was significantly lower in pregnant women with acute pyelonephritis than in those with uncomplicated pregnancies (20.5 ± 6.6 versus 31.5 ± 10.1; p < 0.001) and (4) among patients with acute pyelonephritis, patients with bacteremia had a significantly lower mean plasma concentration of sTRAIL (pg/mL) than those without bacteremia (15.1 ± 4.8 versus 24.7 ± 4.6; p < 0.001).

CONCLUSION

Women with uncomplicated pregnancies are associated with a significantly lower mean maternal plasma concentration of sTRAIL than that observed in non-pregnant women. Moreover, a further decrease in plasma sTRAIL concentration was observed in pregnant women with acute pyelonephritis, and this could account, at least in part, for the exaggerated intravascular inflammatory response previously reported in pyelonephritis during pregnancy.

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.

Reovirus receptors, cell entry, and proapoptotic signaling

Mammalian orthoreoviruses (reoviruses) are members of the Reoviridae. Reoviruses contain 10 double-stranded (ds) RNA gene segments enclosed in two concentric protein shells, called outer capsid and core. These viruses serve as a versatile experimental system for studies of viral replication events at the virus-cell interface, including engagement of cell-surface receptors, internalization and disassembly, and activation of the innate immune response, including NF-κB-dependent cellular signaling pathways. Reoviruses also provide a model system for studies of virus-induced apoptosis and organ-specific disease in vivo.Reoviruses attach to host cells via the filamentous attachment protein, σ1. The σ1 protein of all reovirus serotypes engages junctional adhesion molecule-A (JAM-A), an integral component of intercellular tight junctions. The σ1 protein also binds to cell-surface carbohydrate, with the type of carbohydrate bound varying by serotype. Following attachment to JAM-A and carbohydrate, reovirus internalization is mediated by β1 integrins, most likely via clathrin-dependent endocytosis. In the endocytic compartment, reovirus outer-capsid protein σ3 is removed by acid-dependent cysteine proteases in most cell types. Removal of σ3 results in the exposure of a hydrophobic conformer of the viral membrane-penetration protein, μ1, which pierces the endosomal membrane and delivers transcriptionally active reovirus core particles into the cytoplasm.Reoviruses induce apoptosis in both cultured cells and infected mice. Perturbation of reovirus disassembly using inhibitors of endosomal acidification or protease activity abrogates apoptosis. The μ1-encoding M2 gene is genetically linked to strain-specific differences in apoptosis-inducing capacity, suggesting a function for μ1 in induction of death signaling. Reovirus disassembly leads to activation of transcription factor NF-κB, which modulates apoptotic signaling in numerous types of cells. Inhibition of NF-κB nuclear translocation using either pharmacologic agents or expression of transdominant forms of IκB blocks reovirus-induced apoptosis, suggesting an essential role for NF-κB activation in the death response. Multiple effector pathway s downstream of NF-κB-directed gene expression execute reovirus-induced cell death. This chapter will focus on the mechanisms by which reovirus attachment and disassembly activate NF-κB and stimulate the cellular proapoptotic machinery.

Quantification of the host response proteome after mammalian reovirus T1L infection

All viruses are dependent upon host cells for replication. Infection can induce profound changes within cells, including apoptosis, morphological changes, and activation of signaling pathways. Many of these alterations have been analyzed by gene arrays to measure the cellular "transcriptome." We used SILAC (stable isotope labeling by amino acids in cell culture), combined with high-throughput 2-D HPLC/mass spectrometry, to determine relative quantitative differences in host proteins at 6 and 24 hours after infecting HEK293 cells with reovirus serotype 1 Lang (T1L). 3,076 host proteins were detected at 6 hpi, of which 132 and 68 proteins were significantly up or down regulated, respectively. 2,992 cellular proteins, of which 104 and 49 were up or down regulated, respectively, were identified at 24 hpi. IPA and DAVID analyses indicated proteins involved in cell death, cell growth factors, oxygen transport, cell structure organization and inflammatory defense response to virus were up-regulated, whereas proteins involved in apoptosis, isomerase activity, and metabolism were down-regulated. These proteins and pathways may be suitable targets for intervention to either attenuate virus infection or enhance oncolytic potential.

Reovirus: a targeted therapeutic--progress and potential

Medical therapy of patients with malignancy requires a paradigm shift through development of new drugs with a good safety record and novel mechanisms of activity. While there is no dearth of such molecules, one particular agent, "reovirus" is promising by its ability to target cancer cells with aberrant signaling pathways. This double-stranded RNA virus has been therapeutically formulated and has rapidly progressed from preclinical validation of anticancer activity to a phase III registration study in platinum refractory metastatic squamous cell carcinoma of the head and neck. During this process, reovirus has shown safety both as a single agent when administered intratumorally and intravenously, as well as in combination therapy, with multiple chemotherapeutics such as gemcitabine, carboplatin/paclitaxel, and docetaxel; and similarly with radiation. The scientific rationale for its development as an anticancer agent stems from the fact that it preferentially replicates in and induces lyses of cells with an activated Kras pathway. As documented in many previous studies, the initial observation of greater tropism in Kras-compromised situation might certainly not be the sole and possibly not even the predominant reason for enhanced virulence. All the same, scientists have emphasized on Kras optimistically due to its high prevalence in various types of cancers. Incidence of Kras mutation has been found to be highest in pancreatic cancer (85%-90%) followed by colorectal (35-45%) and lung (25-30%). Reovirus, in fact has the potential not only as a therapy but also as a tool to unravel the aberrant cellular pathway leading to carcinogenicity.

Reovirus as a viable therapeutic option for the treatment of multiple myeloma

PURPOSE

Despite the recent advances made in the treatment of multiple myeloma, the disease still remains incurable. The oncolytic potential of reovirus has previously been shown and is currently in phase III clinical trials for solid tumors. We tested the hypothesis that reovirus can successfully target human multiple myeloma in vitro, ex vivo, and in vivo without affecting human hematopoietic stem cell (HHSC) re-population/differentiation in a murine model that partially recapitulates human multiple myeloma.

EXPERIMENTAL DESIGN

Human myeloma cell lines and ex vivo tumor specimens were exposed to reovirus and oncolysis and mechanisms of cell death were assessed. RPMI 8226(GFP+) cells were injected intravenously to non-obese diabetic/severe combined immune deficient (NOD/SCID) mice and treated with live reovirus (LV) or dead virus (DV). Multiple myeloma disease progression was evaluated via whole-body fluorescence and bone marrow infiltration. HHSCs exposed to LV/DV were injected to NOD/SCID mice and re-population/differentiation was monitored.

RESULTS

A total of six of seven myeloma cell lines and five of seven patient tumor specimens exposed to reovirus showed significant in vitro sensitivity. Tumor response of multiple myeloma by LV, but not DV, was confirmed by comparison of total tumor weights (P = 0.05), and bone marrow infiltration (1/6, LV; 5/6, DV). Mice injected with LV- or DV-exposed HHSCs maintained in vivo re-population/lineage differentiation showing a lack of viral effect on the stem cell compartment. Reovirus oncolysis was mediated primarily by activation of the apoptotic pathways.

CONCLUSIONS

The unique ability of reovirus to selectively kill multiple myeloma while sparing HHSCs places it as a promising systemic multiple myeloma therapeutic for clinical testing.

Transmissible gastroenteritis virus infection induces apoptosis through FasL- and mitochondria-mediated pathways

Transmissible gastroenteritis virus (TGEV) has been reported to induce apoptosis in swine testis (ST) cells. However, the mechanisms underlying TGEV-induced apoptosis are still unclear. In this study we observed that TGEV infection induced apoptosis in porcine kidney (PK-15) cells in a time- and dose-dependent manner. TGEV infection up-regulated FasL, activated FasL-mediated apoptotic pathway, leading to activation of caspase-8 and cleavage of Bid. In addition, TGEV infection down-regulated Bcl-2, up-regulated Bax expression, promoted translocation of Bax to mitochondria, activated mitochondria-mediated apoptotic pathway, which in turn caused the release of cytochrome c and the activation of caspase-9. Both extrinsic and intrinsic pathways activated downstream effector caspase-3, followed by the cleavage of PARP, resulting in cell apoptosis. Moreover, TGEV infection did not induce significant DNA fragmentation in ammonium chloride (NH₄Cl) pretreated PK-15 cells or cells infected with UV-inactivated TGEV. In turn, block of caspases activation also did not affect TGEV replication. Taken together, this study demonstrates that TGEV-induced apoptosis is dependent on viral replication in PK-15 cells and occurs through activation of FasL- and mitochondria-mediated apoptotic pathways.