TRUNDD, a new member of the TRAIL receptor family that antagonizes TRAIL signalling

TNF-Related Apoptosis-Inducing Ligand: Non-Apoptotic Signalling

TNF-related apoptosis-inducing ligand (TRAIL or Apo2 or TNFSF10) belongs to the TNF superfamily. When bound to its agonistic receptors, TRAIL can induce apoptosis in tumour cells, while sparing healthy cells. Over the last three decades, this tumour selectivity has prompted many studies aiming at evaluating the anti-tumoral potential of TRAIL or its derivatives. Although most of these attempts have failed, so far, novel formulations are still being evaluated. However, emerging evidence indicates that TRAIL can also trigger a non-canonical signal transduction pathway that is likely to be detrimental for its use in oncology. Likewise, an increasing number of studies suggest that in some circumstances TRAIL can induce, via Death receptor 5 (DR5), tumour cell motility, potentially leading to and contributing to tumour metastasis. While the pro-apoptotic signal transduction machinery of TRAIL is well known from a mechanistic point of view, that of the non-canonical pathway is less understood. In this study, we the current state of knowledge of TRAIL non-canonical signalling.

TRAIL and its receptors in cardiac diseases

Cardiovascular disease is a leading cause of death worldwide. Loss of cardiomyocytes that occurs during many types of damage to the heart such as ischemic injury and stress caused by pressure overload, diminishes cardiac function due to their limited regenerative capacity and promotes remodeling, which further damages the heart. Cardiomyocyte death occurs through two primary mechanisms, necrosis and apoptosis. Apoptosis is a highly regulated form of cell death that can occur through intrinsic (mitochondrial) or extrinsic (receptor mediated) pathways. Extrinsic apoptosis occurs through a subset of Tumor Necrosis Receptor (TNF) family receptors termed "Death Receptors." While some ligands for death receptors have been extensively studied in the heart, such as TNF-α, others have been virtually unstudied. One poorly characterized cardiac TNF related ligand is TNF-Related Apoptosis Inducing Ligand (TRAIL). TRAIL binds to two apoptosis-inducing receptors, Death Receptor (DR) 4 and DR5. There are also three decoy TRAIL receptors, Decoy Receptor (DcR) 1, DcR2 and osteoprotegerin (OPG). While TRAIL has been extensively studied in the cancer field due to its ability to selectively induce apoptosis in transformed cell types, emerging clinical evidence points towards a role for TRAIL and its receptors in cardiac pathology. This article will highlight our current understanding of TRAIL and its receptors in normal and pathological conditions in the heart.

Nicotinamide mononucleotide (NMN) alleviates the poly(I:C)-induced inflammatory response in human primary cell cultures

NMN is the direct precursor of nicotinamide adenine dinucleotide (NAD+) and is considered as a key factor for increasing NAD+ levels and mitochondrial activity in cells. In this study, based on transcriptome analysis, we showed that NMN alleviates the poly(I:C)-induced inflammatory response in cultures of two types of human primary cells, human pulmonary microvascular endothelial cells (HPMECs) and human coronary artery endothelial cells (HCAECs). Major inflammatory mediators, including IL6 and PARP family members, were grouped into coexpressed gene modules and significantly downregulated under NMN exposure in poly(I:C)-activated conditions in both cell types. The Bayesian network analysis of module hub genes predicted common genes, including eukaryotic translation initiation factor 4B (EIF4B), and distinct genes, such as platelet-derived growth factor binding molecules, in HCAECs, which potentially regulate the identified inflammation modules. These results suggest a robust regulatory mechanism by which NMN alleviates inflammatory pathway activation, which may open up the possibility of a new role for NMN replenishment in the treatment of chronic or acute inflammation.

RNA-seq and Single-Cell Transcriptome Analyses of TRAIL Receptors Gene Expression in Human Osteosarcoma Cells and Tissues

Osteosarcoma (OS) is the most common primary cancer in the skeletal system, characterized by a high incidence of lung metastasis, local recurrence and death. Systemic treatment of this aggressive cancer has not improved significantly since the introduction of chemotherapy regimens, underscoring a critical need for new treatment strategies. TRAIL receptors have long been proposed to be therapeutic targets for cancer treatment, but their role in osteosarcoma remains unclear. In this study, we investigated the expression profile of four TRAIL receptors in human OS cells using total RNA-seq and single-cell RNA-seq (scRNA-seq). The results revealed that TNFRSF10B and TNFRSF10D but not TNFRSF10A and TNFRSF10C are differentially expressed in human OS cells as compared to normal cells. At the single cell level by scRNA-seq analyses, TNFRSF10B, TNFRSF10D, TNFRSF10A and TNFRSF10C are most abundantly expressed in endothelial cells of OS tissues among nine distinct cell clusters. Notably, in osteoblastic OS cells, TNFRSF10B is most abundantly expressed, followed by TNFRSF10D, TNFRSF10A and TNFRSF10C. Similarly, in an OS cell line U2-OS using RNA-seq, TNFRSF10B is most abundantly expressed, followed by TNFRSF10D, TNFRSF10A and TNFRSF10C. According to the TARGET online database, poor patient outcomes were associated with low expression of TNFRSF10C. These results could provide a new perspective to design novel therapeutic targets of TRAIL receptors for the diagnosis, prognosis and treatment of OS and other cancers.

Targeting TRAIL Death Receptors in Triple-Negative Breast Cancers: Challenges and Strategies for Cancer Therapy

The tumor necrosis factor (TNF) superfamily member TNF-related apoptosis-inducing ligand (TRAIL) induces apoptosis in cancer cells via death receptor (DR) activation with little toxicity to normal cells or tissues. The selectivity for activating apoptosis in cancer cells confers an ideal therapeutic characteristic to TRAIL, which has led to the development and clinical testing of many DR agonists. However, TRAIL/DR targeting therapies have been widely ineffective in clinical trials of various malignancies for reasons that remain poorly understood. Triple negative breast cancer (TNBC) has the worst prognosis among breast cancers. Targeting the TRAIL DR pathway has shown notable efficacy in a subset of TNBC in preclinical models but again has not shown appreciable activity in clinical trials. In this review, we will discuss the signaling components and mechanisms governing TRAIL pathway activation and clinical trial findings discussed with a focus on TNBC. Challenges and potential solutions for using DR agonists in the clinic are also discussed, including consideration of the pharmacokinetic and pharmacodynamic properties of DR agonists, patient selection by predictive biomarkers, and potential combination therapies. Moreover, recent findings on the impact of TRAIL treatment on the immune response, as well as novel strategies to address those challenges, are discussed.

Escaping cell death via TRAIL decoy receptors: a systematic review of their roles and expressions in colorectal cancer

The development of targeted therapy such as tumour necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-based therapy has gained increasing attention as a promising new approach in cancer therapy. TRAIL specifically targets cancer cells while sparing the normal cells, thus, limiting the known side effects of the majority anti-cancer therapies. As more extensive research and clinical trials are conducted, resistance to TRAIL molecule has become one of the significant issues associated with the failure of TRAIL in treating colorectal cancer (CRC). To date, the exact mechanism by which TRAIL resistance may have occurred remains unknown. Interestingly, recent studies have revealed the critical role of the TRAIL decoy receptor family; consisting of decoy receptor 1 (DcR1; also known as TRAIL-R3), decoy receptor 2 (DcR2; also known as TRAIL-R4), and osteoprotegerin (OPG) in driving TRAIL resistance. This review highlights the expression of the decoy receptors in CRC and its possible association with the reduction in sensitivity towards TRAIL treatment based on the currently available in vitro, in vivo, and human studies. Additionally, discrepancies between the outcomes from different research groups are discussed, and essential areas are highlighted for future investigation of the roles of decoy receptors in modulating TRAIL-induced apoptosis. Overcoming TRAIL resistance through modulating the expression(s) and elucidating the role(s) of TRAIL decoy receptors hold great promise for TRAIL-based therapies to be extensively explored in treating human cancers including CRC.

Endogenous TRAIL-R4 critically impacts apoptotic and non-apoptotic TRAIL-induced signaling in cancer cells

Binding of TRAIL to its death domain-containing receptors TRAIL-R1 and TRAIL-R2 can induce cell death and/or pro-inflammatory signaling. The importance of TRAIL and TRAIL-R1/R2 in tumor immune surveillance and cancer biology has meanwhile been well documented. In addition, TRAIL has been shown to preferentially kill tumor cells, raising hope for the development of targeted anti-cancer therapies. Apart from death-inducing receptors, TRAIL also binds to TRAIL-R3 and TRAIL-R4. Whereas TRAIL-R3 is lacking an intracellular domain entirely, TRAIL-R4 contains a truncated death domain but still a signaling-competent intracellular part. It is assumed that these receptors have anti-apoptotic, yet still not well understood regulatory functions.

To analyze the significance of the endogenous levels of TRAIL-R4 for TRAIL-induced signaling in cancer cells, we stably knocked down this receptor in Colo357 and MDA-MB-231 cells and analyzed the activation of apoptotic and non-apoptotic pathways in response to treatment with TRAIL.

We found that TRAIL-R4 affects a plethora of signaling pathways, partly in an opposite way. While knockdown of TRAIL-R4 in Colo357 strongly increased apoptosis and reduced clonogenic survival, it inhibited cell death and improved clonogenic survival of MDA-MB-231 cells after TRAIL treatment. Furthermore, TRAIL-R4 turned out to be an important regulator of the expression of a variety of anti-apoptotic proteins in MDA-MB-231 cells since TRAIL-R4-KD reduced the cellular levels of FLIPs, XIAP and cIAP2 but upregulated the levels of Bcl-xL. By inhibiting Bcl-xL with Navitoclax, we could finally show that this protein mainly accounts for the acquired resistance of MDA-MB-231 TRAIL-R4-KD cells to TRAIL-induced apoptosis. Analyses of non-apoptotic signaling pathways revealed that in both cell lines TRAIL-R4-KD resulted in a constitutively increased activity of AKT and ERK, while it reduced AKT activity after TRAIL treatment. Furthermore, TRAIL-R4-KD potentiated TRAIL-induced activation of ERK and p38 in Colo357, and NF-κB in MDA-MB-231 cells. Importantly, in both cell lines the activity of AKT, ERK, p38 and NF-κB after TRAIL treatment was higher in TRAIL-R4-KD cells than in respective control cells.

Thus, our data provide evidence for the important regulatory functions of endogenous TRAIL-R4 in cancer cells and improve our understanding of the very complex human TRAIL/TRAIL-R system.

Hypermethylation of tumor necrosis factor decoy receptor gene in non-small cell lung cancer

Abnormal methylation of the TNFRSF10C and TNFRSF10D genes has been observed in numerous types of cancer; however, no studies have investigated the methylation of these genes in non-small cell lung cancer (NSCLC). The aim of the present study was to investigate the association between TNFRSF10C and TNFRSF10D methylation and NSCLC. Methylation levels of 44 pairs of NSCLC tumor tissues and distant non-tumor tissues were analyzed using quantitative methylation specific PCR and methylation reference percentage values (PMR). The methylation levels of the TNFRSF10C gene in NSCLC tumor tissue samples were significantly higher compared with those in the distant non-tumor tissues (median PMR, 2.73% vs. 0.75%; P=0.013). Subgroup analysis demonstrated that the methylation levels of TNFRSF10C in tumor tissues from male patients were significantly higher compared with those in distant non-tumor tissues (median PMR, 2.73% vs. 0.75%; P=0.041). The levels of TNFRSF10C methylation were also higher in the tumor tissues of patients who were non-smokers compared with their distant non-tumor tissues (median PMR, 2.50% vs. 0.63%; P=0.013). TNFRSF10C methylation levels were higher in the tumor tissues from male patients compared with those from female patients (median PMR, 2.50% vs. 0.63%; P=0.031). However, no significant differences in the methylation levels of the TNFRSF10D gene were observed between the sexes. Using the cBioPortal and The Cancer Genome Atlas lung cancer data, it was demonstrated that TNFRSF10C methylation levels were inversely correlated with TNFRSF10C mRNA expression levels (r=-0.379; P=0.008). In addition, demethylation of lung cancer cell lines A549 and NCI-H1299 using 5'-aza-deoxycytidine further confirmed that TNFRSF10C hypomethylation was associated with significant upregulation of TNFRSF10C mRNA expression levels [A549 fold-change (FC)=8; P=1.0×10^-4; NCI-H1299 FC=3.163; P=1.143×10^-5]. A dual luciferase reporter gene assay was also performed with the insert of TNFRSF10C promoter region, and the results revealed that the TNFRSF10C gene fragment significantly enhanced the transcriptional activity of the reporter gene compared with that in the control group (FC=1.570; P=0.032). Overall, the results of the present study demonstrated that hypermethylation of TNFRSF10C was associated with NSCLC.

Adaptive archaic introgression of copy number variants and the discovery of previously unknown human genes

Copy number variants (CNVs) are subject to stronger selective pressure than single-nucleotide variants, but their roles in archaic introgression and adaptation have not been systematically investigated. We show that stratified CNVs are significantly associated with signatures of positive selection in Melanesians and provide evidence for adaptive introgression of large CNVs at chromosomes 16p11.2 and 8p21.3 from Denisovans and Neanderthals, respectively. Using long-read sequence data, we reconstruct the structure and complex evolutionary history of these polymorphisms and show that both encode positively selected genes absent from most human populations. Our results collectively suggest that large CNVs originating in archaic hominins and introgressed into modern humans have played an important role in local population adaptation and represent an insufficiently studied source of large-scale genetic variation.

TRAIL receptor signaling: From the basics of canonical signal transduction toward its entanglement with ER stress and the unfolded protein response

The cytokine tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the large TNF superfamily that can trigger apoptosis in transformed or infected cells by binding and activating two receptors, TRAIL receptor 1 (TRAILR1) and TRAIL receptor 2 (TRAILR2). Compared to other death ligands of the same family, TRAIL induces apoptosis preferentially in malignant cells while sparing normal tissue and has therefore been extensively investigated for its suitability as an anti-cancer agent. Recently, it was noticed that TRAIL receptor signaling is also linked to endoplasmic reticulum (ER) stress and the unfolded protein response (UPR). The role of TRAIL receptors in regulating cellular apoptosis susceptibility therefore is broader than previously thought. Here, we provide an overview of TRAIL-induced signaling, covering the core signal transduction during extrinsic apoptosis as well as its link to alternative outcomes, such as necroptosis or NF-κB activation. We discuss how environmental factors, transcriptional regulators, and genetic or epigenetic alterations regulate TRAIL receptors and thus alter cellular TRAIL susceptibility. Finally, we provide insight into the role of TRAIL receptors in signaling scenarios that engage the unfolded protein response and discuss how these findings might be translated into new combination therapies for cancer treatment.

Interactions of Tumor Necrosis Factor-Related Apoptosis-Inducing Ligand (TRAIL) with the Immune System: Implications for Inflammation and Cancer

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) is a member of the TNF superfamily. TRAIL has historically been distinct from the Fas ligand and TNFα in terms of selective apoptosis induction in tumor cells and has a nearly non-existent systemic toxicity. Consequently, in the search for an ideal drug for tumor therapy, TRAIL rapidly drew interest, promising effective tumor control with minimal side effects. However, euphoria gave way to disillusionment as it turned out that carcinoma cells possess or can acquire resistance to TRAIL-induced apoptosis. Additionally, studies on models of inflammation and autoimmunity revealed that TRAIL can influence immune cells in many different ways. While TRAIL was initially found to be an important player in tumor defense by natural killer cells or cytotoxic T cells, additional effects of TRAIL on regulatory T cells and effector T cells, as well as on neutrophilic granulocytes and antigen-presenting cells, became focuses of interest. The tumor-promoting effects of these interactions become particularly important for consideration in cases where tumors are resistant to TRAIL-induced apoptosis. Consequently, murine models have shown that TRAIL can impair the tumor microenvironment toward a more immunosuppressive type, thereby promoting tumor growth. This review summarizes the current state of knowledge on TRAIL’s interactions with the immune system in the context of cancer.

Novel Apoptosis-Inducing Agents for the Treatment of Cancer, a New Arsenal in the Toolbox

Evasion from apoptosis is an important hallmark of cancer cells. Alterations of apoptosis pathways are especially critical as they confer resistance to conventional anti-cancer therapeutics, e.g., chemotherapy, radiotherapy, and targeted therapeutics. Thus, successful induction of apoptosis using novel therapeutics may be a key strategy for preventing recurrence and metastasis. Inhibitors of anti-apoptotic molecules and enhancers of pro-apoptotic molecules are being actively developed for hematologic malignancies and solid tumors in particular over the last decade. However, due to the complicated apoptosis process caused by a multifaceted connection with cross-talk pathways, protein–protein interaction, and diverse resistance mechanisms, drug development within the category has been extremely challenging. Careful design and development of clinical trials incorporating predictive biomarkers along with novel apoptosis-inducing agents based on rational combination strategies are needed to ensure the successful development of these molecules. Here, we review the landscape of currently available direct apoptosis-targeting agents in clinical development for cancer treatment and update the related biomarker advancement to detect and validate the efficacy of apoptosis-targeted therapies, along with strategies to combine them with other agents.

Small molecule ONC201 inhibits HIV-1 replication in macrophages via FOXO3a and TRAIL

Despite the success of antiretroviral therapy (ART), eradication of HIV-1 from brain reservoirs remains elusive. HIV-1 brain reservoirs include perivascular macrophages that are behind the blood-brain barrier and difficult to access by ART. Macrophages express transcription factor FOXO3a and the TNF superfamily cytokine TRAIL, which are known to target HIV-1-infected macrophages for viral inhibition. ONC201 is a novel and potent FOXO3a activator capable of inducing TRAIL. It can cross the blood-brain barrier, and has shown antitumor effects in clinical trials. We hypothesized that activation of FOXO3a/TRAIL by ONC201 will inhibit HIV-1 replication in macrophages. Using primary human monocyte-derived macrophages, we demonstrated that ONC201 dose-dependently decreased replication levels of both HIV-1 laboratory strain and primary strains as determined by HIV-1 reverse transcriptase activity assay. Consistent with data on HIV-1 replication, ONC201 also reduced intracellular and extracellular p24, viral RNA, and integrated HIV-1 DNA in infected macrophages. Blocking TRAIL or knockdown of FOXO3a with siRNA reversed ONC201-mediated HIV-1 suppression, suggesting that ONC201 inhibits HIV-1 through FOXO3a and TRAIL. The anti-HIV-1 effect of ONC201 was further validated in vivo in NOD/scid-IL-2Rgcnull mice. After intracranial injection of HIV-1-infected macrophages into the basal ganglia, we treated the mice daily with ONC201 through intraperitoneal injection for six days. ONC201 significantly decreased p24 levels in both the macrophages and the brain tissues, suggesting that ONC201 suppresses HIV-1 in vivo. Therefore, ONC201 can be a promising drug candidate to combat persistent HIV-1 infection in the brain.

Apoptosis of tumor-infiltrating T lymphocytes: a new immune checkpoint mechanism

Immunotherapy based on checkpoint inhibitors is providing substantial clinical benefit, but only to a minority of cancer patients. The current priority is to understand why the majority of patients fail to respond. Besides T-cell dysfunction, T-cell apoptosis was reported in several recent studies as a relevant mechanism of tumoral immune resistance. Several death receptors (Fas, DR3, DR4, DR5, TNFR1) can trigger apoptosis when activated by their respective ligands. In this review, we discuss the immunomodulatory role of the main death receptors and how these are shaping the tumor microenvironment, with a focus on Fas and its ligand. Fas-mediated apoptosis of T cells has long been known as a mechanism allowing the contraction of T-cell responses to prevent immunopathology, a phenomenon known as activation-induced cell death, which is triggered by induction of Fas ligand (FasL) expression on T cells themselves and qualifies as an immune checkpoint mechanism. Recent evidence indicates that other cells in the tumor microenvironment can express FasL and trigger apoptosis of tumor-infiltrating lymphocytes (TIL), including endothelial cells and myeloid-derived suppressor cells. The resulting disappearance of TIL prevents anti-tumor immunity and may in fact contribute to the absence of TIL that is typical of "cold" tumors that fail to respond to immunotherapy. Interfering with the Fas-FasL pathway in the tumor microenvironment has the potential to increase the efficacy of cancer immunotherapy.

Interview: a conversation with Vishva M Dixit on his journey from remote African village to apoptosis, necroptosis and the inflammasome

Vishva M. Dixit, M.D., Vice President of Physiological Chemistry at Genentech, Inc. has made many contributions to biomedicine, and his early work on apoptosis is prominent in introductory textbooks of biology and medicine.

He is a member of the National Academy of Sciences, the National Academy of Medicine, the American Academy of Arts and Sciences, and a Foreign Member, European Molecular Biology Organization.

Additionally, he serves on the Boards of the Gates Foundation, Howard Hughes Medical Institute, and Keystone Symposia.

Divergent Roles for TRAIL in Lung Diseases

The tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) is a widely expressed cytokine that can bind five different receptors. TRAIL has been of particular interest for its proposed ability to selectively induce apoptosis in tumour cells. However, it has also been found to regulate a wide variety of non-canonical cellular effects including survival, migration and proliferation via kinase signalling pathways. Lung diseases represent a wide range of conditions affecting multiple tissues. TRAIL has been implicated in several biological processes underlying lung diseases, including angiogenesis, inflammation, and immune regulation. For example, TRAIL is detrimental in pulmonary arterial hypertension—it is upregulated in patient serum and lungs, and drives the underlying proliferative pulmonary vascular remodelling in rodent models. However, TRAIL protects against pulmonary fibrosis in mice models—by inducing apoptosis of neutrophils—and reduced serum TRAIL is found in patients. Conversely, in the airways TRAIL positively regulates inflammation and immune response. In COPD patients and asthmatic patients challenged with antigen, TRAIL and its death receptors are upregulated in serum and airways. Furthermore, TRAIL-deleted mouse models have reduced airway inflammation and remodelling. In the context of respiratory infections, TRAIL assists in immune response, e.g., via T-cell toxicity in influenza infection, and neutrophil killing in S. pneumoniae infection. In this mini-review, we examine the functions of TRAIL and highlight the diverse roles TRAIL has in diseases affecting the lung. Disentangling the facets of TRAIL signalling in lung diseases could help in understanding their pathogenic processes and targeting novel treatments.

Regulation of TNF-Related Apoptosis-Inducing Ligand Signaling by Glycosylation

Tumor necrosis-factor related apoptosis-inducing ligand, also known as TRAIL or APO2L (Apo-2 ligand), is a cytokine of the TNF superfamily acknowledged for its ability to trigger selective apoptosis in tumor cells while being relatively safe towards normal cells. Its binding to its cognate agonist receptors, namely death receptor 4 (DR4) and/or DR5, can induce the formation of a membrane-bound macromolecular complex, coined DISC (death-signaling inducing complex), necessary and sufficient to engage the apoptotic machinery. At the very proximal level, TRAIL DISC formation and activation of apoptosis is regulated both by antagonist receptors and by glycosylation. Remarkably, though, despite the fact that all membrane-bound TRAIL receptors harbor putative glycosylation sites, only pro-apoptotic signaling through DR4 and DR5 has, so far, been found to be regulated by N- and O-glycosylation, respectively. Because putative N-glycosylation sequons and O-glycosylation sites are also found and conserved in all these receptors throughout all animal species (in which these receptors have been identified), glycosylation is likely to play a more prominent role than anticipated in regulating receptor/receptor interactions or trafficking, ultimately defining cell fate through TRAIL stimulation. This review aims to present and discuss these emerging concepts, the comprehension of which is likely to lead to innovative anticancer therapies.

ZIKV infection effects changes in gene splicing, isoform composition and lncRNA expression in human neural progenitor cells

BACKGROUND

The Zika virus (ZIKV) is a mosquito-borne flavivirus that causes microcephaly and Guillain-Barré syndrome in infected individuals. To obtain insights into the mechanism of ZIKV infection and pathogenesis, we analyzed the transcriptome of ZIKV infected human neural progenitor cells (hNPCs) for changes in alternative splicing (AS), gene isoform (ISO) composition and long noncoding RNAs (lncRNAs) expression.

METHODS

We analyzed differentially expressed lncRNAs, AS, ISO from RNA-seq data in ZIKV infected hNPCs.

RESULTS

We obtained 149 differentially expressed lncRNAs, including potential viral targets to modulate cellular processes such as cell cycle, apoptosis and immune response. The infection induced 262 cases of AS occurring in 229 genes, which were enriched in cell death, RNA processing, transport, and neuron development. Among 691 differentially expressed ISOs, upregulated ISOs were enriched in signaling, regulation of transcription, and amino acid biosynthesis, while downregulated ISOs were mostly enriched in cell cycle. Importantly, these analyses revealed specific links between ZIKV induced changes in cellular pathways and the type of changes in the host transcriptome, suggesting important regulatory mechanisms.

CONCLUSIONS

Our analyses revealed candidate lncRNAs, AS events and ISOs which may function in ZIKV infection induced cell cycle disruption, apoptosis and attenuation of neurogenesis, and shed light on the roles of lncRNAs, AS and ISOs in virus-host interactions, and would facilitate future studies of ZIKV infection and pathogenesis.

ONC201 activates ER stress to inhibit the growth of triple-negative breast cancer cells

ONC201 was previously identified as a first-in-class antitumor agent and small-molecule inducer of the TRAIL (tumor necrosis factor-related apoptosis-inducing ligand) gene that induces apoptosis in cancer cells. ONC201 has a safety profile and is currently in phase II clinical trials for the treatment of various malignancies. In the current study, we examine the effect of ONC201 on triple-negative breast cancer cells (TNBC), a subtype of breast cancer that is sensitive to TRAIL. We find that ONC201 inhibits the growth of TNBC cells including TNBC cells that have developed acquired TRAIL resistance. However, TNBC cells that have developed acquired ONC201 resistance are cross-resistant to TRAIL. Mechanistically, ONC201 triggers an integrated stress response (ISR) involving the activation of the transcription factor ATF4. Knockdown of ATF4 impairs ONC201-induced apoptosis of TNBC cells. Importantly, the activation of ATF4 is compromised in ONC201-resistant TNBC cells. Thus, our results indicate that ONC201 induces an ISR to cause TNBC cell death and suggest that TNBC patients may benefit from ONC201-based therapies.

Decoy TRAIL receptor CD264: a cell surface marker of cellular aging for human bone marrow-derived mesenchymal stem cells

BACKGROUND

Mesenchymal stem cells (MSCs) are a mixture of progenitors that are heterogeneous in their regenerative potential. Development of MSC therapies with consistent efficacy is hindered by the absence of an immunophenotype of MSC heterogeneity. This study evaluates decoy TRAIL receptor CD264 as potentially the first surface marker to detect cellular aging in heterogeneous MSC cultures.

METHODS

CD264 surface expression, regenerative potential, and metrics of cellular aging were assessed in vitro for marrow MSCs from 12 donors ages 20-60 years old. Male and female donors were age matched. Expression of CD264 was compared with that of p16, p21, and p53 during serial passage of MSCs.

RESULTS

When CD264⁺ cell content was 20% to 35%, MSC cultures from young (ages 20-40 years) and older (ages 45-60 years) donors proliferated rapidly and differentiated extensively. Older donor MSCs containing < 35% CD264⁺ cells had a small size and negligible senescence despite the donor's advanced chronological age. Above the 35% threshold, CD264 expression inversely correlated with proliferation and differentiation potential. When CD264⁺ cell content was 75%, MSCs were enlarged and mostly senescent with severely compromised regenerative potential. There was no correlation of the older donors' chronological age to either CD264⁺ cell content or the regenerative potential of the donor MSCs. CD264 was upregulated after p53 and had a similar expression profile to that of p21 during serial passage of MSCs. No sex-linked differences were detected in this study.

CONCLUSIONS

These results suggest that CD264 is a surface marker of cellular age for MSCs, not the chronological age of the MSC donor. CD264 is first upregulated in MSCs at an intermediate stage of cellular aging and remains upregulated as aging progresses towards senescence. The strong inverse correlation of CD264⁺ cell content to the regenerative potential of MSCs has possible application to assess the therapeutic potential of patient MSCs, standardize the composition and efficacy of MSC therapies, and facilitate aging research on MSCs.

The hemagglutinin-neuramidinase protein of Newcastle disease virus upregulates expression of the TRAIL gene in murine natural killer cells through the activation of Syk and NF-κB

Newcastle disease virus (NDV) is responsible for tumoricidal activity in vitro and in vivo. However, the mechanisms that lead to this activity are unclear. Natural killer cells are able to induce apoptosis of tumor cells through multiple pathways, including the tumor necrosis factor-related apoptosis-inducing ligand-death receptor pathway. We previously showed that exposure of NK and T cells to NDV resulted in enhanced tumoricidal activity that was mediated by upregulated expression of the TRAIL gene, via an interferon gamma -dependent pathway. Other pathways involved in the upregulated expression of TRAIL are yet to be identified. In the current study, we used mice in which the IFN-γ receptor one gene was inactivated functionally. We identified an IFN-γ-independent TRAIL pathway in the NDV-stimulated NK cells. Hemagglutinin-neuramidinase induced expression of the TRAIL gene in IFN-R1-/- NK cells by binding to the NKp46 receptor. This upregulation was inhibited by pretreatment of NDV with a neutralizing monoclonal antibody against HN, or desialylation of NK cells. Phosphorylation of spleen tryosine kinases and IκBα was increased in HN-induced IFN-R1-/- NK cells. Treatment with the HN neutralizing monoclonal antibody, pharmacological disialylation, or a Syk inhibitor decreased Syk and IκBα phosphorylation levels. We concluded that killer activation receptors pathway is involved in the IFN-γ-independent TRAIL expression of NDV-stimulated NK cells, and these are activated by Syk and NF-κB.

Mechanisms of immunomodulation by mammalian and viral decoy receptors: insights from structures

Immune responses are regulated by effector cytokines and chemokines that signal through cell surface receptors. Mammalian decoy receptors - which are typically soluble or inactive versions of cell surface receptors or soluble protein modules termed binding proteins - modulate and antagonize signalling by canonical effector-receptor complexes. Viruses have developed a diverse array of molecular decoys to evade host immune responses; these include viral homologues of host cytokines, chemokines and chemokine receptors; variants of host receptors with new functions; and novel decoy receptors that do not have host counterparts. Over the past decade, the number of known mammalian and viral decoy receptors has increased considerably, yet a comprehensive curation of the corresponding structure-mechanism relationships has not been carried out. In this Review, we provide a comprehensive resource on this topic with a view to better understanding the roles and evolutionary relationships of mammalian and viral decoy receptors, and the opportunities for leveraging their therapeutic potential.

Effect of vitamin E succinate on the expression of the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor in gastric cancer cells and CD4(+) T cells

Gastric malignancy, which shows poor prognosis, is one of the most frequent causes of cancer-associated deaths. Vitamin E succinate (VES) inhibits cell proliferation and induces apoptosis in a concentration- and time-dependent manner. We explored the effect of VES on the expression of the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor in gastric cancer cells and CD4(+) T cells. On one hand, VES dose-dependently regulated the expression of the TRAIL receptor in gastric cancer cells. Moreover, the activation of the TRAIL receptor, death receptor 4 (DR4), and death receptor 5 (DR5) in gastric cancer cells increased for up to 12 h. On the other hand, the expression of TRAIL protein in human CD4(+) T cells was obviously upregulated in the presence of VES. On the basis of these findings, we combined VES and human CD4(+) T cells to induce apoptosis of MKN28 human gastric cancer cells. The results showed that VES induced higher gastric cancer cell apoptosis when combined with human CD4(+) T cells than when applied alone. We conclude that VES can induce the expression of TRAIL receptor in gastric cancer cells, as well as the expression of TRAIL in CD4(+) T cells. Overall, our results provide a theoretical basis for future immunotherapy studies.

Target and resistance-related proteins of recombinant mutant human tumor necrosis factor-related apoptosis-inducing ligand on myeloma cell lines

Recombinant mutant human tumor necrosis factor-related apoptosis-inducing ligand (rmhTRAIL) has become a potential therapeutic drug for multiple myeloma (MM). However, the exact targets and resistance mechanisms of rmhTRAIL on MM cells remain to be elucidated. The present study aimed to investigate the target and resistance-related proteins of rmhTRAIL on myeloma cell lines. A TRAIL-sensitive myeloma cell line, RPMI 8226, and a TRAIL-resistance one, U266, were chosen and the differentially expressed proteins between the two cell lines were analyzed prior and subsequent to rmhTRAIL administration by a liquid chromatography-tandem mass spectrometry method. The results showed that following TRAIL treatment, 6 apoptosis-related proteins, calpain small subunit 1 (CPNS1), peflin (PEF1), B-cell receptor-associated protein 31 (BAP31), apoptosis-associated speck-like protein containing CARD (ASC), BAG family molecular chaperone regulator 2 (BAG2) and chromobox protein homolog 3 (CBX3), were upregulated in RPMI 8226 cells while no change was identified in the U266 cells. Furthermore, small ubiquitin-related modifier 1 and several other ubiquitin proteasome pathway (UPP)-related proteins expressed higher levels in TRAIL-resistant cells U266 compared to the RPMI-8226 cells prior and subsequent to rmhTRAIL treatment. These results suggested that CPNS1, PEF1, BAP31, ASC, BAG2 and CBX3 were possibly target proteins of rmhTRAIL on RPMI 8226 cells, while UPP may have a vital role in mediating TRAIL-resistance in U266 cells.

TRAIL-CM4 fusion protein shows in vitro antibacterial activity and a stronger antitumor activity than solo TRAIL protein

A TRAIL-CM4 fusion protein in soluble form with tumor selective apoptosis and antibacterial functions was expressed in the Escherichia coli expression system and isolated through dialysis refolding and histidine-tag Nickel-affinity purification. Fresh Jurkat cells were treated with the TRAIL-CM4 fusion protein. Trypan blue staining and MTT analyses showed that, similar to a TRAIL positive control, Jurkat cell proliferation was significantly inhibited. Flow cytometry analyses using Annexin V-fluorescein revealed that Jurkat cells treated with the TRAIL-CM4 fusion protein exhibited increased apoptosis. Laser confocal microscopy showed that APB-CM4 and the fusion protein TRAIL-CM4 can bind to Jurkat cell membranes and initiate their destruction. ABP-CM4 enhances the antitumor activity of TRAIL by targeting and damaging the tumor cell membrane. In antibacterial experiments, agar well diffusion and bacterial growth inhibition curve assays revealed concentration-dependent TRAIL-CM4 antibacterial activity against Escherichia coli K12D31. The expressed TRAIL-CM4 fusion protein exhibited enhanced antitumor and antibacterial activities. Fusion protein expression allowed the two different proteins to function in combination.

Poly-ADP-ribosylation of HMGB1 regulates TNFSF10/TRAIL resistance through autophagy

Both apoptosis ("self-killing") and autophagy ("self-eating") are evolutionarily conserved processes, and their crosstalk influences anticancer drug sensitivity and cell death. However, the underlying mechanism remains unclear. Here, we demonstrated that HMGB1 (high mobility group box 1), normally a nuclear protein, is a crucial regulator of TNFSF10/TRAIL (tumor necrosis factor [ligand] superfamily, member 10)-induced cancer cell death. Activation of PARP1 (poly [ADP-ribose] polymerase 1) was required for TNFSF10-induced ADP-ribosylation of HMGB1 in cancer cells. Moreover, pharmacological inhibition of PARP1 activity or knockdown of PARP1 gene expression significantly inhibited TNFSF10-induced HMGB1 cytoplasmic translocation and subsequent HMGB1-BECN1 complex formation. Furthermore, suppression of the PARP1-HMGB1 pathway diminished autophagy, increased apoptosis, and enhanced the anticancer activity of TNFSF10 in vitro and in a subcutaneous tumor model. These results indicate that PARP1 acts as a prominent upstream regulator of HMGB1-mediated autophagy and maintains a homeostatic balance between apoptosis and autophagy, which provides new insight into the mechanism of TNFSF10 resistance.

Triptolide enhances the tumoricidal activity of TRAIL against renal cell carcinoma

Renal cell carcinoma (RCC) is resistant to traditional cancer therapies, and metastatic RCC (mRCC) is incurable. The shortcomings in current therapeutic options for patients with mRCC provide the rationale for the development of novel treatment protocols. Tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has proven to be a potent inducer of tumor cell death in vitro and in vivo, and a number of TRAIL death receptor agonists (recombinant TRAIL or TRAIL death receptor-specific mAb) have been developed and tested clinically. Unfortunately the clinical efficacy of TRAIL has been underwhelming and is likely due to a number of possible mechanisms that render tumors resistant to TRAIL, prompting the search for drugs that increase tumor cell susceptibility to TRAIL. The objective of this study was to determine the effectiveness of combining the diterpene triepoxide triptolide, or its water-soluble prodrug, Minnelide, with TRAIL receptor agonists against RCC in vitro or in vivo, respectively. TRAIL-induced apoptotic death of human RCC cells was increased in the presence of triptolide. The triptolide-induced sensitization was accompanied by increased TRAIL-R2 (DR5) and decreased heat shock protein 70 expression. In vivo treatment of mice bearing orthotopic RCC (Renca) tumors showed the combination of Minnelide and agonistic anti-DR5 mAb significantly decreased tumor burden and increased animal survival compared to either therapy alone. Our data suggest triptolide/Minnelide sensitizes RCC cells to TRAIL-induced apoptosis through altered TRAIL death receptor and heat shock protein expression.

Therapeutic applications of TRAIL receptor agonists in cancer and beyond

TRAIL/Apo-2L is a member of the TNF superfamily first described as an apoptosis-inducing cytokine in 1995. Similar to TNF and Fas ligand, TRAIL induces apoptosis in caspase-dependent manner following TRAIL death receptor trimerization. Because tumor cells were shown to be particularly sensitive to this cytokine while normal cells/tissues proved to be resistant along with being able to synthesize and release TRAIL, it was rapidly appreciated that TRAIL likely served as one of our major physiologic weapons against cancer. In line with this, a number of research laboratories and pharmaceutical companies have attempted to exploit the ability of TRAIL to kill cancer cells by developing recombinant forms of TRAIL or TRAIL receptor agonists (e.g., receptor-specific mAb) for therapeutic purposes. In this review article we will describe the biochemical pathways used by TRAIL to induce different cell death programs. We will also summarize the clinical trials related to this pathway and discuss possible novel uses of TRAIL-related therapies. In recent years, the physiological importance of TRAIL has expanded beyond being a tumoricidal molecule to one critical for a number of clinical settings - ranging from infectious disease and autoimmunity to cardiovascular anomalies. We will also highlight some of these conditions where modulation of the TRAIL/TRAIL receptor system may be targeted in the future.

Activation of tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) receptor gene expression following DNA demethylation in placental choriocarcinoma and transformed cell lines

We characterised DNA methylation and gene expression of four tumour necrosis factor-related apoptosis-inducing ligand (TRAIL) receptors DR4, DR5, DcR1 and DcR2 in three choriocarcinoma (JAR, JEG-3, BeWo) and two transformed (HTR-8/SVneo and HPT-8) cell lines. DR4 mRNA was detected in JAR, JEG-3, BeWo and HTR-8/SVneo cells, whereas DR5 was present in all detected cells. DcR1 transcripts were expressed only in JAR, JEG-3 and BeWo cells, whereas DcR2 transcripts were detected only in HTR-8/SVneo and HPT-8 cells. Hypermethylated DR4 promoter was observed in JAR, JEG-3, BeWo and HTR-8/SVneo cells, hypermethylated DcR1 promoter in HTR-8/SVneo and HPT-8 cells and hypermethylated DcR2 promoter in JAR, JEG-3 and BeWo cells. Restoration of DR4, DcR1 and DcR2 expression with decreased DNA methylation of these genes was induced by the DNA demethylation agent 5-aza-2'-deoxycytidine (5-aza-CdR) in trophoblast cells, whereas DR5 expression did not exhibit any change. Significant negative correlation between the expression and DNA methylation of these genes was also observed. In all tested cell lines, only HPT-8 demonstrated sensitivity to TRAIL-induced apoptosis. Combined treatment with 5-aza-CdR and TRAIL resulted in apoptosis in JAR, JEG-3, BeWo and HTR-8/SVneo cells but not in HPT-8 cells. The results indicate that DNA methylation is associated with TRAIL receptor expression and might be involved in trophoblast apoptosis.

The role of the osteoprotegerin/tumor necrosis factor related apoptosis-inducing ligand axis in the pathogenesis of pulmonary arterial hypertension

Pulmonary arterial hypertension (PAH) is a fatal condition driven by a progressive remodelling of the small pulmonary arteries through sustained vasoconstriction, and vascular cell proliferation. This process causes a substantial reduction in luminal area increasing pulmonary vascular resistance and blood pressure leading to right heart failure. Current medical therapies can alleviate some symptoms and reduce the vasoconstrictive aspects of disease but new treatments are required that target the vascular cell proliferation if we are to develop new therapies. Expression of the tumour necrosis factor related apoptosis-inducing ligand (TRAIL) and osteoprotegerin (OPG) proteins are increased in IPAH. Specifically OPG is increased within the serum of patients with idiopathic pulmonary arterial hypertension (IPAH) and has prognostic utility, and both OPG and TRAIL are increased within pulmonary vascular lesions of patients with IPAH, and are mitogens for pulmonary artery smooth muscle cells in vitro. We have demonstrated that genetic deletion, or antibody blockade of TRAIL prevents, and critically reverses the development of PAH in multiple rodent models. The role OPG plays in this process both through interacting with TRAIL, and indirectly through other mechanisms is currently unclear these but data highlight the critical importance of this pathway in PAH pathogenesis, and its potential for future therapies.

Osteoblasts display different responsiveness to TRAIL-induced apoptosis during their differentiation process

Apoptosis can occur throughout the life span of osteoblasts (OBs), beginning from the early stages of differentiation and continuing throughout all stages of their working life. Here, we investigated the effects of tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) on normal human OBs showing for the first time that the expression of TRAIL receptors is modulated during OB differentiation. In particular, the TRAIL receptor ratio was in favor of the deaths because of the low expression of DcR2 in undifferentiated OBs, differently it was shifted toward the decoys in differentiated ones. Undifferentiated OBs treated with TRAIL showed reduced cell viability, whereas differentiated OBs displayed TRAIL resistance. The OB sensitiveness to TRAIL was due to the up-regulation of DR5 and the down-regulation of DcR2. The main death receptor involved in TRAIL-reduced OB viability was DR5 as demonstrated by the rescue of cell viability observed in the presence of anti-DR5 neutralizing antibody. Besides the ratio of TRAIL receptors, the sensitivity of undifferentiated OBs to TRAIL-cytotoxic effect was also associated with low mRNA levels of intracellular anti-apoptotic proteins, such as cFLIP, the activation of caspase-8 and -3, as well as the DNA fragmentation. This study suggests that apoptotic effect exerted by TRAIL/TRAIL-receptor system on normal human OB is strictly dependent upon cell differentiation status.

CCT327 enhances TRAIL-induced apoptosis through the induction of death receptors and downregulation of cell survival proteins in TRAIL-resistant human leukemia cells

Tumor necrosis factor-related apoptosis‑inducing ligand (TRAIL) has potential application in cancer therapy and it has the ability to selectively kill cancer cells without affecting normal cells. However, the development of resistance to TRAIL in cancer cells cannot be avoided. This study investigated the effects of 2-(5-methylselenophen‑2‑yl)‑6,7‑methylenedioxyquinolin‑4-one (CCT327), an analogue of quinolin-4-one, on the sensitization of cancer cells to TRAIL and on TRAIL‑induced apoptosis in TRAIL‑resistance human leukemia cells (HL60‑TR). We found that CCT327 enhanced TRAIL‑induced apoptosis through upregulation of death receptors DR4 and DR5. In addition to upregulating DRs (death receptors), CCT327 suppressed the expression of decoy receptor DcR1 and DcR2. CCT327 significantly downregulated the expression of FLICE inhibitory protein (cFLIP) and other antiapoptotic proteins. We also demonstrated that CCT327 could activate p38 and JNK. Moreover, CCT327-induced induction of DR5 and DR4 was mediated by reactive oxygen species (ROS), and N-acetylcysteine (NAC) blocked the induction of DRs by CCT327. Taken together, these results showed that CCT327 combined with TRAIL treatment may provide an effective therapeutic strategy for cancer.

Getting TRAIL back on track for cancer therapy

Unlike other members of the TNF superfamily, the TNF-related apoptosis-inducing ligand (TRAIL, also known as Apo2L) possesses the unique capacity to induce apoptosis selectively in cancer cells in vitro and in vivo. This exciting discovery provided the basis for the development of TRAIL-receptor agonists (TRAs), which have demonstrated robust anticancer activity in a number of preclinical studies. Subsequently initiated clinical trials testing TRAs demonstrated, on the one hand, broad tolerability but revealed, on the other, that therapeutic benefit was rather limited. Several factors that are likely to account for TRAs' sobering clinical performance have since been identified. First, because of initial concerns over potential hepatotoxicity, TRAs with relatively weak agonistic activity were selected to enter clinical trials. Second, although TRAIL can induce apoptosis in several cancer cell lines, it has now emerged that many others, and importantly, most primary cancer cells are resistant to TRAIL monotherapy. Third, so far patients enrolled in TRA-employing clinical trials were not selected for likelihood of benefitting from a TRA-comprising therapy on the basis of a valid(ated) biomarker. This review summarizes and discusses the results achieved so far in TRA-employing clinical trials in the light of these three shortcomings. By integrating recent insight on apoptotic and non-apoptotic TRAIL signaling in cancer cells, we propose approaches to introduce novel, revised TRAIL-based therapeutic concepts into the cancer clinic. These include (i) the use of recently developed highly active TRAs, (ii) the addition of efficient, but cancer-cell-selective TRAIL-sensitizing agents to overcome TRAIL resistance and (iii) employing proteomic profiling to uncover resistance mechanisms. We envisage that this shall enable the design of effective TRA-comprising therapeutic concepts for individual cancer patients in the future.

TWEAK-Fn14 Cytokine-Receptor Axis: A New Player of Myocardial Remodeling and Cardiac Failure

Tumor necrosis factor (TNF) has been firmly established as a pathogenic factor in heart failure, a significant socio-economic burden. In this review, we will explore the role of other members of the TNF/TNF receptor superfamily (TNFSF/TNFRSF) in cardiovascular diseases (CVDs) focusing on TWEAK and its receptor Fn14, new players in myocardial remodeling and heart failure. The TWEAK/Fn14 pathway controls a variety of cellular activities such as proliferation, differentiation, and apoptosis and has diverse biological functions in pathological mechanisms like inflammation and fibrosis that are associated with CVDs. Furthermore, it has recently been shown that the TWEAK/Fn14 axis is a positive regulator of cardiac hypertrophy and that deletion of Fn14 receptor protects from right heart fibrosis and dysfunction. We discuss the potential use of the TWEAK/Fn14 axis as biomarker for CVDs as well as therapeutic target for future treatment of human heart failure based on supporting data from animal models and in vitro studies. Collectively, existing data strongly suggest the TWEAK/Fn14 axis as a potential new therapeutic target for achieving cardiac protection in patients with CVDs.

Apoptosis-associated uncoupling of bone formation and resorption in osteomyelitis

The mechanisms underlying the destruction of bone tissue in osteomyelitis are only now being elucidated. While some of the tissue damage associated with osteomyelitis likely results from the direct actions of bacteria and infiltrating leukocytes, perhaps exacerbated by bacterial manipulation of leukocyte survival pathways, infection-induced bone loss predominantly results from an uncoupling of the activities of osteoblasts and osteoclasts. Bacteria or their products can directly increase osteoclast formation and activity, and the inflammatory milieu at sites of infection can further promote bone resorption. In addition, osteoclast activity is critically regulated by osteoblasts that can respond to bacterial pathogens and foster both inflammation and osteoclastogenesis. Importantly, bone loss during osteomyelitis is also brought about by a decline in new bone deposition due to decreased bone matrix synthesis and by increased rates of osteoblast apoptosis. Extracellular bacterial components may be sufficient to reduce osteoblast viability, but the causative agents of osteomyelitis are also capable of inducing continuous apoptosis of these cells by activating intrinsic and extrinsic cell death pathways to further uncouple bone formation and resorption. Interestingly, bacterial internalization appears to be required for maximal osteoblast apoptosis, and cytosolic inflammasome activation may act in concert with autocrine/paracrine death receptor-ligand signaling to induce cell death. The manipulation of apoptotic pathways in infected bone cells could be an attractive new means to limit inflammatory damage in osteomyelitis. However, the mechanism that is the most important in bacterium-induced bone loss has not yet been identified. Furthermore, it remains to be determined whether the host would be best served by preventing osteoblast cell death or by promoting apoptosis in infected cells.

Regulation of the Src-PP2A interaction in tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL)-induced apoptosis

TNF-related apoptosis-inducing ligand (TRAIL) selectively induces apoptosis in transformed and tumor cells but not in normal cells, making it a promising agent for cancer therapy. However, many cancer cells are resistant to TRAIL, and the underlying mechanisms are not fully understood. Here, we show that the regulation of the PP2A and Src interaction plays a critical role in TRAIL resistance. Specifically, we show that TRAIL treatment activates the tyrosine kinase Src, which subsequently phosphorylates caspase-8 at tyrosine 380, leading to the inhibition of caspase-8 activation. We also show that upon TRAIL treatment, Src, caspase-8, and PP2A/C (a catalytic subunit of the PP2A phosphatase) are redistributed into lipid rafts, a microdomain of the plasma membrane enriched with cholesterol, where PP2A dephosphorylates Src at tyrosine 418 and in turn inhibits caspase-8 phosphorylation. Furthermore, we find that TRAIL treatment causes PP2A/C degradation. These data suggest that the balance between Src-mediated caspase-8 phosphorylation and the inactivation of Src-mediated caspase-8 phosphorylation by PP2A determines the outcome of TRAIL treatment in breast cancer cells. Therefore, this work identifies a novel mechanism by which the interaction between PP2A and Src in the context of caspase-8 activation modulates TRAIL sensitivity in cancer cells.

The TRAIL of oncogenes to apoptosis

Despite the significant advances in clinical research, surgical resection, radiotherapy and chemotherapy are still used as the primary method for cancer treatment. As compared to conventional therapies that often induce systemic toxicity and eventually contribute to tumor resistance, the TNF-related apoptosis-inducing ligand (TRAIL) is a promising anticancer agent that selectively triggers apoptosis in various cancer cells by interacting with its proapoptotic receptors DR4 and KILLER/DR5, while sparing the normal surrounding tissue. The intensive studies of TRAIL signaling pathways over the past decade have provided clues for understanding the molecular mechanisms of TRAIL-induced apoptosis in carcinogenesis and identified an array of therapeutic responses elicited by TRAIL and its receptor agonists. Analysis of its activity at the molecular level has shown that TRAIL improves survival either as monotherapies or combinatorial therapies with other mediators of apoptosis or anticancer chemotherapy. Combinatorial treatments amplify the activities of anticancer agents and widen the therapeutic window by overcoming tumor resistance to apoptosis and driving cancer cells to self-destruction. Although TRAIL sensitivity varies widely depending on the cell type, nontransformed cells are largely resistant to death mediated by TRAIL Death Receptors (DRs). Genetic alterations in cancer can contribute in tumor progression and often play an important role in evasion of apoptosis by tumor cells. Remarkably, RAS, MYC and HER2 oncogenes have been shown to sensitise tumor cells to TRAIL induced cell death. Here, we summarise the cross-talk of oncogenic and apoptotic pathways and how they can be exploited toward efficient combinatorial therapeutic protocols.

Inhibition of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) reverses experimental pulmonary hypertension

Genetic deletion of TRAIL or antibody blockade prevents the development of pulmonary arterial hypertension and can reverse vascular remodeling in established disease.

Pulmonary arterial hypertension (PAH) is a life-threatening disease characterized by the progressive narrowing and occlusion of small pulmonary arteries. Current therapies fail to fully reverse this vascular remodeling. Identifying key pathways in disease pathogenesis is therefore required for the development of new-targeted therapeutics. We have previously reported tumor necrosis factor–related apoptosis-inducing ligand (TRAIL) immunoreactivity within pulmonary vascular lesions from patients with idiopathic PAH and animal models. Because TRAIL can induce both endothelial cell apoptosis and smooth muscle cell proliferation in the systemic circulation, we hypothesized that TRAIL is an important mediator in the pathogenesis of PAH. We demonstrate for the first time that TRAIL is a potent stimulus for pulmonary vascular remodeling in human cells and rodent models. Furthermore, antibody blockade or genetic deletion of TRAIL prevents the development of PAH in three independent rodent models. Finally, anti-TRAIL antibody treatment of rodents with established PAH reverses pulmonary vascular remodeling by reducing proliferation and inducing apoptosis, improves hemodynamic indices, and significantly increases survival. These preclinical investigations are the first to demonstrate the importance of TRAIL in PAH pathogenesis and highlight its potential as a novel therapeutic target to direct future translational therapies.

The tumor necrosis factor superfamily in heart failure

Numerous clinical studies have established that tumor necrosis factor (TNF)-alpha may play a pathogenic role in the development and progression of heart failure (HF). Recent reports suggest that other ligands in the TNF superfamily could also play a pathogenic role in chronic HF. TNF superfamily ligands are expressed predominantly by cells in the immune system, while the TNF receptor superfamily are expressed by a wide variety of cells, including myocardial cells. Several pathways are activated by ligand-receptor interactions, but of particular importance is the nuclear factor (NF)-kappaB pathway which is activated in the failing human heart. All ligands in the TNF superfamily have the potential to activate NF-kappaB, leading to transcription of genes involved in apoptosis, cell survival, proliferation, inflammation and hypertrophic signaling in cardiomyocytes. Among several TNF superfamily members that are activated in HF, the authors' have recentlyshown that CD40L-CD40 and OPG-RANK-RANKL interactions may be implicated in the pathogenesis of HF through different mechanisms, possibly representing new targets for therapy in this disorder.

Regulation of the human TRAIL gene

TRAIL is a member of the TNF superfamily that induces tumor-selective cell death by engaging the pro-apoptotic death receptors DR4 and DR5. The antitumor potential of the TRAIL pathway has been targeted by several therapeutic approaches including recombinant TRAIL and TRAIL-receptor agonist antibodies among others. Interest in sensitizing tumor cells to TRAIL-mediated apoptosis has driven investigations of TRAIL-receptor gene regulation, though regulation of the TRAIL gene has been less studied. Physiologically, TRAIL serves as a pro-apoptotic effector molecule in the immune surveillance of cancer that is conditionally expressed by immune cells upon stimulation via an interferon-response element that was identified in early studies of the TRAIL gene promoter. Here, we map the TRAIL gene promoter and review studies of TRAIL gene regulation that involve several modalities of gene regulation including transcription factors, epigenetics, single-nucleotide polymorphisms and functionally distinct isoforms.

Structural basis of LaDR5, a novel agonistic anti-death receptor 5 (DR5) monoclonal antibody, to inhibit DR5/TRAIL complex formation

Background

As a member of the TNF superfamily, TRAIL could induce human tumor cell apoptosis through its cognate death receptors DR4 or DR5, which can induce formation of the death inducing signaling complex (DISC) and activation of the membrane proximal caspases (caspase-8 or caspase-10) and mitochondrial pathway. Some monoclonal antibodies against DR4 or DR5 have been reported to have anti-tumor activity.

Results

In this study, we reported a novel mouse anti-human DR5 monoclonal antibody, named as LaDR5, which could compete with TRAIL to bind DR5 and induce the apoptosis of Jurkat cells in the absence of second cross-linking in vitro. Using computer-guided molecular modeling method, the 3-D structure of LaDR5 Fv fragment was constructed. According to the crystal structure of DR5, the 3-D complex structure of DR5 and LaDR5 was modeled using molecular docking method. Based on distance geometry method and intermolecular hydrogen bonding analysis, the key functional domain in DR5 was predicted and the DR5 mutants were designed. And then, three mutants of DR5 was expressed in prokaryotic system and purified by affinity chromatograph to determine the epitope of DR5 identified by LaDR5, which was consistent with the theoretical results of computer-aided analysis.

Conclusions

Our results demonstrated the specific epitope located in DR5 that plays a crucial role in antibody binding and even antineoplastic bioactivity. Meanwhile, revealed structural features of DR5 may be important to design or screen novel drugs agonist DR5.

Down-regulation of DcR2 sensitizes androgen-dependent prostate cancer LNCaP cells to TRAIL-induced apoptosis

Background

Dysregulation of many apoptotic related genes and androgens are critical in the development, progression, and treatment of prostate cancer. The differential sensitivity of tumour cells to TRAIL-induced apoptosis can be mediated by the modulation of surface TRAIL receptor expression related to androgen concentration. Our previous results led to the hypothesis that downregulation of TRAIL-decoy receptor DcR2 expression following androgen deprivation would leave hormone sensitive normal prostate cells vulnerable to the cell death signal generated by TRAIL via its pro-apoptotic receptors. We tested this hypothesis under pathological conditions by exploring the regulation of TRAIL-induced apoptosis related to their death and decoy receptor expression, as also to hormonal concentrations in androgen-sensitive human prostate cancer, LNCaP, cells.

Results

In contrast to androgen-insensitive PC3 cells, decoy (DcR2) and death (DR5) receptor protein expression was correlated with hormone concentrations and TRAIL-induced apoptosis in LNCaP cells. Silencing of androgen-sensitive DcR2 protein expression by siRNA led to a significant increase in TRAIL-mediated apoptosis related to androgen concentration in LNCaP cells.

Conclusions

The data support the hypothesis that hormone modulation of DcR2 expression regulates TRAIL-induced apoptosis in LNCaP cells, giving insight into cell death induction in apoptosis-resistant hormone-sensitive tumour cells from prostate cancer. TRAIL action and DcR2 expression modulation are potentially of clinical value in advanced tumour treatment.

Sensitization of human bladder tumor cells to TNF-related apoptosis-inducing ligand (TRAIL)-induced apoptosis with a small molecule IAP antagonist

Urothelial carcinoma of the bladder accounts for approximately 5% of all cancer deaths in humans. The large majority of bladder tumors are non-muscle invasive at diagnosis, but even after local surgical therapy there is a high rate of local tumor recurrence and progression. Current treatments extend time to recurrence but do not significantly alter disease survival. The objective of the present study was to investigate the tumoricidal potential of combining the apoptosis-inducing protein TNF-related apoptosis-inducing ligand (TRAIL) with a small molecule inhibitor of apoptosis proteins (IAP) antagonist to interfere with intracellular regulators of apoptosis in human bladder tumor cells. Our results demonstrate that the IAP antagonist Compound A exhibits high binding affinity to the XIAP BIR3 domain. When Compound A was used at nontoxic concentrations in combination with TRAIL, there was a significant increase in the sensitivity of TRAIL-sensitive and TRAIL-resistant bladder tumor lines to TRAIL-mediated apoptosis. In addition, modulation of TRAIL sensitivity in the TRAIL-resistant bladder tumor cell line T24 with Compound A was reciprocated by XIAP small interfering RNA-mediated suppression of XIAP expression, suggesting the importance of XIAP-mediated resistance to TRAIL in these cells. These results suggest the potential of combining Compound A with TRAIL as an alternative therapy for bladder cancer.

Therapeutic effect of neural stem cells expressing TRAIL and bortezomib in mice with glioma xenografts

Treatment of glioblastoma remains a challenge in neuro-oncology. We investigated if treatment with neural stem cells engineered to express membrane-bound TRAIL (NSCs-mTRAIL) alone or in combination with proteasome inhibitors is a feasible therapeutic approach for experimental glioma. Glioma cells showed resistance to soluble TRAIL and proteasome inhibitors alone, but responded well to their combined treatment. In co-culture with NSCs-mTRAIL, glioma cells appeared to be more prone to apoptosis than to treatment with soluble TRAIL, which was enhanced by proteasome inhibitor bortezomib. In vivo, the survival of animals bearing intracranial glial xenografts was significantly improved by NSCs-mTRAIL. The addition of bortezomib further enhanced the efficacy of NSCs-TRAIL treated group in one of examined tumor models. These data demonstrate that therapy with NSCs-mTRAIL is a potent cell based approach for treatment of glioma. Such an approach warrants further search for therapeutics capable of increasing sensitivity of glioma cells to mTRAIL in vivo.

Advances in Viral Vector-Based TRAIL Gene Therapy for Cancer

Numerous biologic approaches are being investigated as anti-cancer therapies in an attempt to induce tumor regression while circumventing the toxic side effects associated with standard chemo- or radiotherapies. Among these, tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) has shown particular promise in pre-clinical and early clinical trials, due to its preferential ability to induce apoptotic cell death in cancer cells and its minimal toxicity. One limitation of TRAIL use is the fact that many tumor types display an inherent resistance to TRAIL-induced apoptosis. To circumvent this problem, researchers have explored a number of strategies to optimize TRAIL delivery and to improve its efficacy via co-administration with other anti-cancer agents. In this review, we will focus on TRAIL-based gene therapy approaches for the treatment of malignancies. We will discuss the main viral vectors that are being used for TRAIL gene therapy and the strategies that are currently being attempted to improve the efficacy of TRAIL as an anti-cancer therapeutic.