Inhibition of death receptor signals by cellular FLIP

Protein Kinase-Mediated Decision Between the Life and Death

Protein kinases are intracellular signaling enzymes that catalyze the phosphorylation of specific residues in their target substrate proteins. They play important role for regulation of life and death decisions. The complexity of the relationship between death receptors and protein kinases' cell death decision-making mechanisms create many difficulties in the treatment of various diseases. The most of fifteen different cell death pathways, which are reported by Nomenclature Committee on Cell Death (NCCD) are protein kinase signal transduction-mediated negative or positive selections. Tumor necrosis factor (TNF) as a main player of death pathways is a dual-functioning molecule in that it can promote both cell survival or cell death. All apoptotic and necrotic signal transductions are conveyed through death domain-containing death receptors, which are expressed on the surface of nearly all human cells. In humans, eight members of the death receptor family have been identified. While the interaction of TNF with TNF Receptor 1 (TNFR1) activates various signal transduction pathways, different death receptors activate three main signal transduction pathways: nuclear factor kappa B (NF-ĸB)-mediated differentiation or pro-inflammatory cytokine synthesis, mitogen-activated protein kinase (MAPK)-mediated stress response and caspase-mediated apoptosis. The link between the NF-ĸB and the c-Jun NH₂-terminal kinase (JNK) pathways comprise another check-point to regulate cell death. TNF-α also promotes the "receptor-interacting serine/threonine protein kinase 1" (RIPK1)/RIPK3/ mixed lineage kinase domain-like pseudokinase (MLKL)-dependent necrosis. Thus, necrosome is mainly comprised of MLKL, RIPK3 and, in some cases, RIPK1. In fact, RIPK1 is at the crossroad between life and death, downstream of various receptors as a regulator of endoplasmic reticulum stress-induced death. TNFR1 signaling complex (TNF-RSC), which contains multiple kinase activities, promotes phosphorylation of transforming growth factor β-activated kinase 1 (TAK1), inhibitor of nuclear transcription factor κB (IκB) kinase (IKK) α/IKKβ, IκBα, and NF-κB. IKKs affect cell-survival pathways in NF-κB-independent manner. Toll-like receptor (TLR) stimulation triggers various signaling pathways dependent on myeloid differentiation factor-88 (MyD88), Interleukin-1 receptor (IL-1R)-associated kinase (IRAK1), IRAK2 and IRAK4, lead to post-translational activation of nucleotide and oligomerization domain (NLRP3). Thereby, cell fate decisions following TLR signaling is parallel with death receptor signaling. Inhibition of IKKα/IKKβ or its upstream activators sensitize cells to death by inducing RIPK1-dependent apoptosis or necroptosis. During apoptosis, several kinases of the NF-κB pathway, including IKK1 and NF-κB essential modulator (NEMO), are cleaved by cellular caspases. This event can terminate the NF-κB-derived survival signals. In both canonical and non-canonical pathways, IKK is key to NF-κB activation. Whereas, the activation process of IKK, the functions of NEMO ubiquitination, IKK-related non-canonical pathway and the nuclear transportation of NEMO and functions of IKKα are still debated in cell death. In addition, cluster of differentiation 95 (CD95)-mediated non-apoptotic signaling and CD95- death-inducing signaling complex (DISC) interactions are waiting for clarification.

TRAIL of Hope Meeting Resistance in Cancer

Tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) induces apoptosis selectively via its interaction with the death receptors TRAILR1/DR4 and TRAILR2/DR5 in a wide range of cancers, while sparing normal cells. Despite its tremendous potential for cancer therapeutics, the translation of TRAIL into the clinic has been confounded by TRAIL-resistant cancer populations. We discuss different molecular mechanisms underlying TRAIL-mediated apoptosis and resistance to TRAIL. We also discuss the successes and failures of recent preclinical and clinical studies of TRAIL-induced apoptosis, and current attempts to overcome TRAIL resistance, and we provide a perspective for improving the prospects of future clinical implementation.

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.

Designed ferritin nanocages displaying trimeric TRAIL and tumor-targeting peptides confer superior anti-tumor efficacy

TRAIL is considered a promising target for cancer therapy because it mediates activation of the extrinsic apoptosis pathway in a tumor-specific manner by binding to and trimerizing its functional receptors, DR4 or DR5. Although recombinant human TRAIL has shown high potency and specificity for killing cancer cells in preclinical studies, it has failed in multiple clinical trials for several reasons, including a very short half-life mainly caused by instability of the monomeric form of TRAIL and rapid renal clearance of the off-targeted TRAIL. To overcome such obstacles, we developed a TRAIL-active trimer nanocage (TRAIL-ATNC) that presents the TRAIL ligand in its trimer-like conformation by connecting it to a triple helix sequence that links to the threefold axis of the ferritin nanocage. We also ligated the tumor-targeting peptide, IL4rP, to TRAIL-ATNC to enhance tumor targeting. The developed TRAIL-ATNCIL4rP showed enhanced agonistic activity compared with monomeric TRAIL. The in vivo serum half-life of TRAIL-ATNCIL4rP was ~ 16-times longer than that of native TRAIL. As a consequence of these properties, TRAIL-ATNCIL4rP exhibited efficacy as an anti-tumor agent in vivo against xenograft breast cancer as well as orthotopic pancreatic cancer models, highlighting the promise of this system for development as novel therapeutics against cancer.

Innate Lymphoid Cells in Crohn's Disease

Innate lymphoid cells (ILCs) are a large family of cells of the immune system that performs various functions in immune defense, inflammation, and tissue remodeling. As a part of the innate immune system, ILCs are a distinct form of lymphocytes different from T and B cells. ILCs can provide host defense against the source of infection and initiate the repair and remodeling processes to restore and maintain host body homeostasis. The number of patients with Crohn’s disease (CD) worldwide has continued to increase in recent years and this disease has brought sickness and death to many families. Numerous studies have found that ILCs also undergo a series of alternations during the development of CD and contribute to this disease. Despite this, the pathogenesis of CD is still not fully explained. So, we keep researching and exploring. In this review, we have closely linked the latest progress on ILCs and CD, and introduced, in detail, the specific roles of four different types of ILCs in CD. We also describe new progress in the pathogenesis of CD, with particular emphasis on the plasticity of ILC3s in this disease. These new studies and findings may provide new insights and breakthrough points for the treatment of CD.

Caspase-8-dependent gasdermin D cleavage promotes antimicrobial defense but confers susceptibility to TNF-induced lethality

Gasdermin D (GSDMD) is a pore-forming protein that promotes pyroptosis and release of proinflammatory cytokines. Recent studies revealed that apoptotic caspase-8 directly cleaves GSDMD to trigger pyroptosis. However, the molecular requirements for caspase-8-dependent GSDMD cleavage and the physiological impact of this signaling axis are unresolved. Here, we report that caspase-8-dependent GSDMD cleavage confers susceptibility to tumor necrosis factor (TNF)-induced lethality independently of caspase-1 and that GSDMD activation provides host defense against Yersinia infection. We further demonstrate that GSDMD inactivation by apoptotic caspases at aspartate 88 (D88) suppresses TNF-induced lethality but promotes anti-Yersinia defense. Last, we show that caspase-8 dimerization and autoprocessing are required for GSDMD cleavage, and provide evidence that the caspase-8 autoprocessing and activity on various complexes correlate with its ability to directly cleave GSDMD. These findings reveal GSDMD as a potential therapeutic target to reduce inflammation associated with mutations in the death receptor signaling machinery.

TRAIL receptor agonists convert the response of breast cancer cells to ONC201 from anti-proliferative to apoptotic

ONC201 was initially identified as an inducer of cell death through the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) pathway. The compound is currently being tested in patients with hematological malignancies and solid tumors, including those of the breast. We investigated strategies to convert the response of breast cancers to ONC201 from anti-proliferative to apoptotic. ONC201 treatment upregulates TRAIL and primes TRAIL-resistant non-triple negative breast cancer (TNBC) cells to undergo cell death through the extrinsic pathway. Remarkably, the addition of exogenous recombinant human TRAIL (rhTRAIL) converts the response of TRAIL-resistant non-TNBC cells to ONC201 from anti-proliferative to apoptotic in a death receptor 5 (DR5)-dependent manner in vitro. Importantly, normal fibroblasts do not undergo apoptosis following rhTRAIL plus ONC201. In vivo, MDA-MB-361 tumor growth rate is significantly reduced following treatment with a combination of ONC201 and rhTRAIL as compared to control tumors. Natural killer (NK) cells which use TRAIL to kill DR5-expressing cancer cells, exhibit greater cytotoxicity against ONC201-treated breast cancer cells compared to controls. rhTRAIL also converts the response of cells from other tumor types to ONC201 from anti-proliferative to apoptotic. A monoclonal DR5-agonistic antibody converts the response of non-TNBC cells to ONC201 from anti-proliferative to apoptotic. Our findings describe a novel therapeutic strategy that potently converts the response of a cancer cell to ONC201 from anti-proliferative to apoptotic. This approach may be clinically relevant and has potential to induce tumor regression of patient tumors with relative resistance to ONC201 monotherapy.

Backbone and side-chain chemical shift assignments of a cellular FLICE-inhibitory protein (c-FLIPS)

Cellular FLICE-inhibitory protein (c-FLIP), which is involved in regulating the apoptosis of the extrinsic cell death pathway contains two death effector domains (DED). There are several splicing variants including short-form (c-FLIP_S) and long-form (c-FLIP_L). The death-inducing signaling complex (DISC) initiates apoptosis and programmed necrosis, DISC assembly and activation are regulated by c-FLIP. Here we report the NMR chemical shift assignments of c-FLIPs, which pave the way for investigating the molecular basis of the anti-apoptotic function of c-FLIP_S.

Targeting NF-κB pathway for the therapy of diseases: mechanism and clinical study

NF-κB pathway consists of canonical and non-canonical pathways. The canonical NF-κB is activated by various stimuli, transducing a quick but transient transcriptional activity, to regulate the expression of various proinflammatory genes and also serve as the critical mediator for inflammatory response. Meanwhile, the activation of the non-canonical NF-κB pathway occurs through a handful of TNF receptor superfamily members. Since the activation of this pathway involves protein synthesis, the kinetics of non-canonical NF-κB activation is slow but persistent, in concordance with its biological functions in the development of immune cell and lymphoid organ, immune homeostasis and immune response. The activation of the canonical and non-canonical NF-κB pathway is tightly controlled, highlighting the vital roles of ubiquitination in these pathways. Emerging studies indicate that dysregulated NF-κB activity causes inflammation-related diseases as well as cancers, and NF-κB has been long proposed as the potential target for therapy of diseases. This review attempts to summarize our current knowledge and updates on the mechanisms of NF-κB pathway regulation and the potential therapeutic application of inhibition of NF-κB signaling in cancer and inflammatory diseases.

TRAIL therapy and prospective developments for cancer treatment

Tumor Necrosis Factor (TNF) Related Apoptosis-Inducing Ligand (TRAIL), an immune cytokine of TNF-family, has received much attention in late 1990s as a potential cancer therapeutics due to its selective ability to induce apoptosis in cancer cells. TRAIL binds to cell surface death receptors, TRAIL-R1 (DR4) and TRAIL-R2 (DR5) and facilitates formation of death-inducing signaling complex (DISC), eventually activating the p53-independent apoptotic cascade. This unique mechanism makes the TRAIL a potential anticancer therapeutic especially for p53-mutated tumors. However, recombinant human TRAIL protein (rhTRAIL) and TRAIL-R agonist monoclonal antibodies (mAb) failed to exert robust anticancer activities due to inherent and/or acquired resistance, poor pharmacokinetics and weak potencies for apoptosis induction. To get TRAIL back on track as a cancer therapeutic, multiple strategies including protein modification, combinatorial approach and TRAIL gene therapy are being extensively explored. These strategies aim to enhance the half-life and bioavailability of TRAIL and synergize with TRAIL action ultimately sensitizing the resistant and non-responsive cells. We summarize emerging strategies for enhanced TRAIL therapy in this review and cover a wide range of recent technologies that will provide impetus to rejuvenate the TRAIL therapeutics in the clinical realm.

Targeting apoptosis in cancer therapy

For over three decades, a mainstay and goal of clinical oncology has been the development of therapies promoting the effective elimination of cancer cells by apoptosis. This programmed cell death process is mediated by several signalling pathways (referred to as intrinsic and extrinsic) triggered by multiple factors, including cellular stress, DNA damage and immune surveillance. The interaction of apoptosis pathways with other signalling mechanisms can also affect cell death. The clinical translation of effective pro-apoptotic agents involves drug discovery studies (addressing the bioavailability, stability, tumour penetration, toxicity profile in non-malignant tissues, drug interactions and off-target effects) as well as an understanding of tumour biology (including heterogeneity and evolution of resistant clones). While tumour cell death can result in response to therapy, the selection, growth and dissemination of resistant cells can ultimately be fatal. In this Review, we present the main apoptosis pathways and other signalling pathways that interact with them, and discuss actionable molecular targets, therapeutic agents in clinical translation and known mechanisms of resistance to these agents.

The NLRP3 Inflammasome as a Critical Actor in the Inflammaging Process

As a consequence of the considerable increase in the human lifespan over the last century, we are experiencing the appearance and impact of new age-related diseases. The causal relationships between aging and an enhanced susceptibility of suffering from a broad spectrum of diseases need to be better understood. However, one specific shared feature seems to be of capital relevance for most of these conditions: the low-grade chronic inflammatory state inherently associated with aging, i.e., inflammaging. Here, we review the molecular and cellular mechanisms that link aging and inflammaging, focusing on the role of the innate immunity and more concretely on the nucleotide-binding oligomerization domain (NOD)-like receptor family pyrin domain containing 3 (NLRP3) inflammasome, as well as how the chronic activation of this inflammasome has a detrimental effect on different age-related disorders.

Multiple roles of caspase-8 in cell death, inflammation, and innate immunity

Caspase-8 is an apical caspase involved in the programmed form of cell death called apoptosis that is critically important for mammalian development and immunity. Apoptosis was historically described as immunologically silent in contrast to other types of programmed cell death such as necroptosis or pyroptosis. Recent reports suggest considerable crosstalk between these different forms of cell death. It is becoming increasingly clear that caspase-8 has many non-apoptotic roles, participating in multiple processes including regulation of necroptosis (mediated by receptor-interacting serine/threonine kinases, RIPK1-RIPK3), inflammatory cytokine expression, inflammasome activation, and cleavage of IL-1β and gasdermin D, and protection against shock and microbial infection. In this review, we discuss the involvement of caspase-8 in cell death and inflammation and highlight its role in innate immune responses and in the relationship between different forms of cell death. Caspase-8 is one of the central components in this type of crosstalk.

Caspase-8-Dependent Inflammatory Responses Are Controlled by Its Adaptor, FADD, and Necroptosis

Cell death pathways regulate various homeostatic processes. Autoimmune lymphoproliferative syndrome (ALPS) in humans and lymphoproliferative (LPR) disease in mice result from abrogated CD95-induced apoptosis. Because caspase-8 mediates CD95 signaling, we applied genetic approaches to dissect the roles of caspase-8 in cell death and inflammation. Here, we describe oligomerization-deficient Caspase-8^{F122GL123G/F122GL123G} and non-cleavable Caspase-8^D387A/D387A mutant mice with defective caspase-8-mediated apoptosis. Although neither mouse developed LPR disease, removal of the necroptosis effector Mlkl from Caspase-8^D387A/D387A mice revealed an inflammatory role of caspase-8. Ablation of one allele of Fasl, Fadd, or Ripk1 prevented the pathology of Casp8^D387A/D387AMlkl^-/- animals. Removing both Fadd alleles from these mice resulted in early lethality prior to post-natal day 15 (P15), which was prevented by co-ablation of either Ripk1 or Caspase-1. Our results suggest an in vivo role of the inflammatory RIPK1-caspase-8-FADD (FADDosome) complex and reveal a FADD-independent inflammatory role of caspase-8 that involves activation of an inflammasome.

Modulation of Cell Death and Promotion of Chondrogenic Differentiation by Fas/FasL in Human Dental Pulp Stem Cells (hDPSCs)

Human dental pulp stem cells (hDPSCs) are characterized by high proliferation rate, the multi-differentiation ability and, notably, low immunogenicity and immunomodulatory properties exerted through different mechanisms including Fas/FasL pathway. Despite their multipotency, hDPSCs require particular conditions to achieve chondrogenic differentiation. This might be due to the perivascular localization and the expression of angiogenic marker under standard culture conditions. FasL stimulation was able to promote the early induction of chondrogenic commitment and to lead the differentiation at later times. Interestingly, the expression of angiogenic marker was reduced by FasL stimulation without activating the extrinsic apoptotic pathway in standard culture conditions. In conclusion, these findings highlight the peculiar embryological origin of hDPSCs and provide further insights on their biological properties. Therefore, Fas/FasL pathway not only is involved in determining the immunomodulatory properties, but also is implicated in supporting the chondrogenic commitment of hDPSCs.

Potency and Selectivity of SMAC/DIABLO Mimetics in Solid Tumor Therapy

Aiming to promote cancer cell apoptosis is a mainstream strategy of cancer therapy. The second mitochondria-derived activator of caspase (SMAC)/direct inhibitor of apoptosis protein (IAP)-binding protein with low pI (DIABLO) protein is an essential and endogenous antagonist of inhibitor of apoptosis proteins (IAPs). SMAC mimetics (SMs) are a series of synthetically chemical compounds. Via database analysis and literature searching, we summarize the potential mechanisms of endogenous SMAC inefficiency, degradation, mutation, releasing blockage, and depression. We review the development of SMs, as well as preclinical and clinical outcomes of SMs in solid tumor treatment, and we analyze their strengths, weaknesses, opportunities, and threats from our point of view. We also highlight several questions in need of further investigation.

Importance of TNF-alpha and its alterations in the development of cancers

TNF-alpha is involved in many physiologic and pathologic cellular pathways, including cellular proliferation, differentiation, and death, regulation of immunologic reactions to different cells and molecules, local and vascular invasion of neoplasms, and destruction of tumor vasculature. It is obvious that because of integrated functions of TNF-alpha inside different physiologic systems, it cannot be used as a single-agent therapy for neoplasms; however, long-term investigation of its different cellular pathways has led to recognition of a variety of subsequent molecules with more specific interactions, and therefore, might be suitable as prognostic and therapeutic factors for neoplasms. Here, we will review different aspects of the TNF-alpha as a cytokine involved in both physiologic functions of cells and pathologic abnormalities, most importantly, cancers.

FLIP(L): the pseudo-caspase

Possessing structural homology with their active enzyme counterparts but lacking catalytic activity, pseudoenzymes have been identified for all major enzyme groups. Caspases are a family of cysteine‐dependent aspartate‐directed proteases that play essential roles in regulating cell death and inflammation. Here, we discuss the only human pseudo‐caspase, FLIP(L), a paralog of the apoptosis‐initiating caspases, caspase‐8 and caspase‐10. FLIP(L) has been shown to play a key role in regulating the processing and activity of caspase‐8, thereby modulating apoptotic signaling mediated by death receptors (such as TRAIL‐R1/R2), TNF receptor‐1 (TNFR1), and Toll‐like receptors. In this review, these canonical roles of FLIP(L) are discussed. Additionally, a range of nonclassical pseudoenzyme roles are described, in which FLIP(L) functions independently of caspase‐8. These nonclassical pseudoenzyme functions enable FLIP(L) to play key roles in the regulation of a wide range of biological processes beyond its canonical roles as a modulator of cell death.

Multitasking Kinase RIPK1 Regulates Cell Death and Inflammation

Receptor-interacting serine threonine kinase 1 (RIPK1) is a widely expressed kinase that is essential for limiting inflammation in both mice and humans. Mice lacking RIPK1 die at birth from multiorgan inflammation and aberrant cell death, whereas humans lacking RIPK1 are immunodeficient and develop very early-onset inflammatory bowel disease. In contrast to complete loss of RIPK1, inhibiting the kinase activity of RIPK1 genetically or pharmacologically prevents cell death and inflammation in several mouse disease models. Indeed, small molecule inhibitors of RIPK1 are in phase I clinical trials for amyotrophic lateral sclerosis, and phase II clinical trials for psoriasis, rheumatoid arthritis, and ulcerative colitis. This review focuses on which signaling pathways use RIPK1, how activation of RIPK1 is regulated, and when activation of RIPK1 appears to be an important driver of inflammation.

Fas Ligand (FasL) in Association with Tumor-Infiltrating Lymphocytes (TILs) in Early Stage Cervical Cancer

OBJECTIVE

To date, little is known about the roles of FasL and TILs in cervical cancer. This study aims to determine the correlation between FasL expression and TILs presence in cervical cancer.

METHODS

In this study, we analysed the FasL and TIL presence in 32 squamous cell carcinoma or adenocarcinoma that were obtained from early stage (≤ IIA2) cervical cancer patients using immunohistochemistry. The level of FasL and TIL was assessed qualitatively, and then quantified with the H-Score system.

RESULTS

Most of the patients were between 30 to 50 years old (59,4%), and had never taken pap smear examination before (96,9%). Based on the Pearson analysis of FasL and TIL presence, we found that FasL was inversely correlated with CD45 or TIL number when the level of FasL is above 140 and the CD45 is below 160. Based on Chi-Square test of FasL and TIL classification, there was a nine-fold odds ratio (OR) of lower TILs classification in high expression of FasL classification (OR 9, p=0.01).

CONCLUSION

An inverse correlation between FasL expression and TILs level, that might indicate FasL-induced TILs apoptosis in tumor tissue, was observed. The strong inverse correlation between FasL and TILs presence showed some insight about the interactions between cancer cells and its surroundings inside of the cervical cancer tissue. This might also be further developed to tailor a prognostic marker that can predict the outcome of therapy in patients, not only in cervical cancer, but generally in all cancer.

c-FLIP is crucial for IL-7/IL-15-dependent NKp46+ ILC development and protection from intestinal inflammation in mice

NKp46⁺ innate lymphoid cells (ILC) modulate tissue homeostasis and anti-microbial immune responses. ILC development and function are regulated by cytokines such as Interleukin (IL)-7 and IL-15. However, the ILC-intrinsic pathways translating cytokine signals into developmental programs are largely unknown. Here we show that the anti-apoptotic molecule cellular FLICE-like inhibitory protein (c-FLIP) is crucial for the generation of IL-7/IL-15-dependent NKp46⁺ ILC1, including conventional natural killer (cNK) cells, and ILC3. Cytokine-induced phosphorylation of signal transducer and activator of transcription 5 (STAT5) precedes up-regulation of c-FLIP, which protects developing NKp46⁺ ILC from TNF-induced apoptosis. NKp46⁺ ILC-specific inactivation of c-FLIP leads to the loss of all IL-7/IL-15-dependent NKp46⁺ ILC, thereby inducing early-onset chronic colitis and subsequently microbial dysbiosis; meanwhile, the depletion of cNK, but not NKp46⁺ ILC1/3, aggravates experimental colitis. In summary, our data demonstrate a non-redundant function of c-FLIP for the generation of NKp46⁺ ILC, which protect T/B lymphocyte-sufficient mice from intestinal inflammation.

Viral FLIP blocks Caspase-8 driven apoptosis in the gut in vivo

A strict cell death control in the intestinal epithelium is indispensable to maintain barrier integrity and homeostasis. In order to achieve a balance between cell proliferation and cell death, a tight regulation of Caspase-8, which is a key player in controlling apoptosis, is required. Caspase-8 activity is regulated by cellular FLIP proteins. These proteins are expressed in different isoforms (cFLIP_long and cFLIP_short) which determine cell death and survival. Interestingly, several viruses encode FLIP proteins, homologous to cFLIP_short, which are described to regulate Caspase-8 and the host cell death machinery. In the current study a mouse model was generated to show the impact of viral FLIP (vFLIP) from Kaposi’s Sarcoma-associated Herpesvirus (KSHV)/ Human Herpesvirus-8 (HHV-8) on cell death regulation in the gut. Our results demonstrate that expression of vFlip in intestinal epithelial cells suppressed cFlip expression, but protected mice from lethality, tissue damage and excessive apoptotic cell death induced by genetic cFlip deletion. Finally, our model shows that vFlip expression decreases cFlip mediated Caspase-8 activation in intestinal epithelial cells. In conclusion, our data suggests that viral FLIP neutralizes and compensates for cellular FLIP, efficiently counteracting host cell death induction and facilitating further propagation in the host organism.

Chidamide induces necroptosis via regulation of c‑FLIPL expression in Jurkat and HUT‑78 cells

T‑cell acute lymphoblastic leukemia (T‑ALL) is a hematopoietic malignancy, which is associated with a poor prognosis. It is difficult to achieve complete remission or long‑term survival with conventional chemotherapy, partly due to decreased apoptosis. However, necroptosis can serve as an alternative pathway to induce cell death. The present study investigated whether the selective histone deacetylase (HDAC) inhibitor chidamide exerted a therapeutic effect on T‑ALL and explored the underlying mechanism. The results revealed that HDAC expression was increased in Jurkat and HUT‑78 cells treated compared with the control cell line (H9), and was accompanied by elevated cellular Fas‑associated death domain‑like interleukin‑1β converting enzyme inhibitory protein long form (c‑FLIPL) levels. Chidamide treatment (2 µmol/l) also induced mitochondrial dysfunction, necroptosis and apoptosis in T‑ALL cells in vitro. Furthermore, necroptosis was increased when apoptosis was blocked in T‑ALL cells. Additionally, chidamide (2 µmol/l) downregulated c‑FLIPL, HDAC1 and HDAC3 expression, and increased receptor‑interacting protein kinase 3 expression and the phosphorylation of mixed lineage kinase domain‑like pseudokinase in Jurkat and HUT‑78 cells. The results obtained in the present study revealed that chidamide may induce necroptosis via regulation of c‑FLIPL expression when apoptosis is inhibited in Jurkat and HUT‑78 cells.

miR-125b suppresses cellular proliferation by targeting c-FLIP in gallbladder carcinoma

Gallbladder carcinoma (GBC) is the most common malignant tumor of the biliary tract. The incidence rate of gallbladder cancer ranks sixth among gastrointestinal types of cancer, and its incidence is increasing each year. Further clarification of the pathogenesis of GBC is essential, and identification of novel effective treatments is required. It has been previously demonstrated that high expression of the anti-apoptotic protein cellular Fas-associated death domain-like interleukin-1-converting enzyme inhibitory protein (c-FLIP) in GBC inhibited apoptosis in gallbladder cancer cells. In subsequent experiments, it was observed that microRNA (miR)-125b could target c-FLIP and inhibit the protein expression of c-FLIP by binding to the 3'untranslated regions of c-FLIP mRNA. In addition, the expression of miR-125b in GBC was significantly decreased, and the growth of gallbladder cancer cells was inhibited by the overexpression of miR-125b. The present study demonstrated that miR-125b could suppress the proliferation of gallbladder cancer cells by targeting c-FLIP. c-FLIP enriched the target gene pathway of miR-125b and may serve as a novel target for the treatment of GBC.

IFN‑β sensitizes TRAIL‑induced apoptosis by upregulation of death receptor 5 in malignant glioma cells

Tumor necrosis factor‑related apoptosis‑inducing ligand (TRAIL), a member of the tumor necrosis factor (TNF) family, induces apoptosis in cancer cells by binding to its receptors, death receptor 4 (DR4) and DR5, without affecting normal cells, and is therefore considered to be a promising antitumor agent for use in cancer treatment. However, several studies have indicated that most glioma cell lines display resistance to TRAIL‑induced apoptosis. To overcome such resistance and to improve the efficacy of TRAIL‑based therapies, identification of ideal agents for combinational treatment is important for achieving rational clinical treatment in glioblastoma patients. The main aim of this study was to investigate whether interferon‑β (IFN‑β) (with its pleiotropic antitumor activities) could sensitize malignant glioma cells to TRAIL‑induced apoptosis using glioma cell lines. TRAIL exhibited a dose‑dependent antitumor effect in all of the 7 types of malignant glioma cell lines, although the intensity of the effect varied among the cell lines. In addition, combined treatment with TRAIL (low clinical dose: 1 ng/ml) and IFN‑β (clinically relevant concentration: 10 IU/ml) in A‑172, AM‑38, T98G, U‑138MG and U‑251MG demonstrated a more marked antitumor effect than TRAIL alone. Furthermore, the antitumor effect of the combined treatment with TRAIL and IFN‑β may be enhanced via an extrinsic apoptotic system, and upregulation of DR5 was revealed to play an important role in this process in U‑138MG cells. These findings provide an experimental basis to suggest that combined treatment with TRAIL and IFN‑β may offer a new therapeutic strategy for malignant gliomas.

Dual-Responsive DNA Nanodevice for the Available Imaging of an Apoptotic Signaling Pathway in Situ

Fluorescence imaging tools enable the in situ visualization of those molecules involved in various cell signaling pathways, but directly describing these pathways instead of the separate mediators in situ is much more meaningful and still full of challenges. In this work, a dual-responsive DNA nanodevice that allows the available imaging of an apoptotic signaling pathway in living cells has been developed. The nanodevice is constructed through assembling an elaborately designed Y-shaped DNA (Y-DNA) layer on gold nanoparticles (AuNPs). Only if an apoptotic signaling pathway involving the manganese superoxide dismutase (MnSOD) mRNA and downstream cytochrome c (Cyt c) is presented to serve as the input, the nanodevice can perform an "AND" logic gate operation, disassembling the Y-DNA from the AuNP surface and thereafter outputting a fluorescence signal. In comparison with the fluorescence imaging methods that target individual specific molecules, our strategy allows direct profiling of a specific signaling pathway by connected characterization of two correlative targets. The programmable feature of this strategy also shows the potential for the profiling of other signaling pathways. The concept of studying the line connecting two points will contribute to the systematic interrogation on the signaling networks in situ as the networks are composed of lines instead of individual points.

Molecular Insights into the Mechanism of Necroptosis: The Necrosome As a Potential Therapeutic Target

Necroptosis, or regulated necrosis, is an important type of programmed cell death in addition to apoptosis. Necroptosis induction leads to cell membrane disruption, inflammation and vascularization. It plays important roles in various pathological processes, including neurodegeneration, inflammatory diseases, multiple cancers, and kidney injury. The molecular regulation of necroptotic pathway has been intensively studied in recent years. Necroptosis can be triggered by multiple stimuli and this pathway is regulated through activation of receptor-interacting protein kinase 1 (RIPK1), RIPK3 and pseudokinase mixed lineage kinase domain-like (MLKL). A better understanding of the mechanism of regulation of necroptosis will further aid to the development of novel drugs for necroptosis-associated human diseases. In this review, we focus on new insights in the regulatory machinery of necroptosis. We further discuss the role of necroptosis in different pathologies, its potential as a therapeutic target and the current status of clinical development of drugs interfering in the necroptotic pathway.

Fundamental Mechanisms of Regulated Cell Death and Implications for Heart Disease

Twelve regulated cell death programs have been described. We review in detail the basic biology of nine including death receptor-mediated apoptosis, death receptor-mediated necrosis (necroptosis), mitochondrial-mediated apoptosis, mitochondrial-mediated necrosis, autophagy-dependent cell death, ferroptosis, pyroptosis, parthanatos, and immunogenic cell death. This is followed by a dissection of the roles of these cell death programs in the major cardiac syndromes: myocardial infarction and heart failure. The most important conclusion relevant to heart disease is that regulated forms of cardiomyocyte death play important roles in both myocardial infarction with reperfusion (ischemia/reperfusion) and heart failure. While a role for apoptosis in ischemia/reperfusion cannot be excluded, regulated forms of necrosis, through both death receptor and mitochondrial pathways, are critical. Ferroptosis and parthanatos are also likely important in ischemia/reperfusion, although it is unclear if these entities are functioning as independent death programs or as amplification mechanisms for necrotic cell death. Pyroptosis may also contribute to ischemia/reperfusion injury, but potentially through effects in non-cardiomyocytes. Cardiomyocyte loss through apoptosis and necrosis is also an important component in the pathogenesis of heart failure and is mediated by both death receptor and mitochondrial signaling. Roles for immunogenic cell death in cardiac disease remain to be defined but merit study in this era of immune checkpoint cancer therapy. Biology-based approaches to inhibit cell death in the various cardiac syndromes are also discussed.

Expression of DR5 and c‑FLIP proteins as novel prognostic biomarkers for non‑small cell lung cancer patients treated with surgical resection and chemotherapy

TRAIL-R2 (DR5), one of the death receptors, can activate the extrinsic apoptosis pathway, while cellular FLICE-inhibitory protein (c-FLIP) can inhibit this pathway. Both of them play important roles in the occurrence and development of most tumors. To date, there is no relevant report concerning the relationship between expression of DR5 and c-FLIP protein and clinicopathological/prognostic implications in patients with non-small cell lung cancer (NSCLC) treated with surgical resection and chemotherapy. Thus, the aim of the present study was to investigate the potential prognostic significance of DR5 and c-FLIP in NSCLC patients and their predictive roles in the chemotherapeutic response. In the present study, DR5 and c-FLIP were detected by immunohistochemistry (IHC) in tissue microarrays of NSCLC. The results showed that the expression levels of DR5 and c-FLIP were significantly higher in lung squamous cell carcinoma (SCC) and lung adenocarcinoma (ADC) tissues compared with levels noted in the non-cancerous control lung tissues (all P<0.05). In addition, DR5 expression was significantly increased in lung ADC (P<0.001), whereas, c-FLIP was higher in lung SCC (P<0.001) and smoker patients with clinical stage III (P=0.019, P=0.016, respectively). In addition, NSCLC patients with overexpression of DR5 and loss of c-FLIP expression exhibited a higher overall survival (OS) rate as determined by Kaplan-Meier analysis (P=0.029, P=0.038, respectively). Multivariate analysis confirmed that high expression of DR5 and loss of c-FLIP expression were independent favorable prognostic factors for NSCLC patients (P=0.016, P=0.035, respectively). In conclusion, overexpression of DR5 and loss of c-FLIP expression may serve as novel favorable prognostic biomarkers for NSCLC patients treated with chemotherapy after radical resection and used as predictors for tumor response to chemotherapy drugs.

CD19-positive antibody-secreting cells provide immune memory

Long-lived antibody-secreting cells (ASCs) are critical for the maintenance of humoral immunity through the continued production of antibodies specific for previously encountered pathogen or vaccine antigens. Recent reports describing humoral immune memory have suggested the importance of long-lived CD19^- bone marrow (BM) ASCs, which secrete antibodies recognizing previously encountered vaccine antigens. However, these reports do not agree upon the unique contribution of the CD19⁺ BM ASC subset toward humoral immunity. Here, we found both CD19⁺ and negative ASCs from human BM were similar in functional capacity to react to a number of vaccine antigens via ELISpot assays. The CD19⁺ cells were the predominant ASC population found in lymphoid tissues, and unlike the CD19^- ASCs, which were found only in spleen and BM, the CD19⁺ ASCs were found in tonsil and blood. CD19⁺ ASCs from the BM, spleen, and tonsil were capable of recognizing polio vaccine antigens, indicating the CD19⁺ ASC cells play a novel role in long-lasting immune defense. Comparative gene expression analysis indicated CD19⁺ and negative BM ASCs differed significantly by only 14 distinct messenger RNAs and exhibited similar gene expression for cell cycle, autophagy, and apoptosis control necessary for long life. In addition, we show identical CDR-H3 sequences found on both BM ASC subsets, indicating a shared developmental path. Together, these results provide novel insight for the distribution, function, genetic regulation, and development of long-lived ASCs and may not only impact improved cell therapies but also enhance strategies for vaccine development.

The Molecular Links between Cell Death and Inflammasome

Programmed cell death pathways and inflammasome activation pathways can be genetically and functionally separated. Inflammasomes are specialized protein complexes that process pro-inflammatory cytokines, interleukin-1β (IL-1β), and IL-18 to bioactive forms for protection from a wide range of pathogens, as well as environmental and host-derived danger molecules. Programmed cell death has been extensively studied, and its role in the development, homeostasis, and control of infection and danger is widely appreciated. Apoptosis and the recently recognized necroptosis are the best-characterized forms of programmed death, and the interplay between them through death receptor signaling is also being studied. Moreover, growing evidence suggests that many of the signaling molecules known to regulate programmed cell death can also modulate inflammasome activation in a cell-intrinsic manner. Therefore, in this review, we will discuss the current knowledge concerning the role of the signaling molecules originally associated with programmed cell death in the activation of inflammasome and IL-1β processing.

PI3K/AKT inhibitors aggravate death receptor-mediated hepatocyte apoptosis and liver injury

The PI3K/AKT signaling pathway is one of the most frequently activated signaling networks in human cancers and has become a valuable target in anticancer therapy. However, accumulating reports suggest that adverse effects such as severe liver injury and inflammation may accompany treatment with pan-PI3K and pan-AKT inhibitors. Our prior work has demonstrated that activation of the PI3K/AKT pathway has a protective role in Fas- or TNFα-induced hepatocytic cell death and liver injury. We postulated that PI3K or AKT inhibitors may exacerbate liver damage via the death factor-mediated hepatocyte apoptosis. In this study we found that several drugs targeting PI3K/AKT either clinically used or in clinical trials sensitized hepatocytes to agonistic anti-Fas antibody- or TNFα-induced apoptosis and significantly shortened the survival of mice in in vivo liver damage models. The PI3K or AKT inhibitors promoted Fas aggregation, inhibited the expression of cellular FLICE-inhibitory protein S and L (FLIP_L/S), and enhanced procaspase-8 activation. Conversely, cotreatment with the AKT specific activator SC79 reversed these effects. Taken together, these findings suggest that PI3K or AKT inhibitors may render hepatocytes hypersensitive to Fas- or TNFα-induced apoptosis and liver injury.

Cellular demolition: Proteins as molecular players of programmed cell death

Apoptosis, a well-characterized and regulated cell death programme in eukaryotes plays a fundamental role in developing or later-life periods to dispose of unwanted cells to maintain typical tissue architecture, homeostasis in a spatiotemporal manner. This silent cellular death occurs without affecting any neighboring cells/tissue and avoids triggering of immunological response. Furthermore, diminished forms of apoptosis result in cancer and autoimmune diseases, whereas unregulated apoptosis may also lead to the development of a myriad of neurodegenerative diseases. Unraveling the mechanistic events in depth will provide new insights into understanding physiological control of apoptosis, pathological consequences of abnormal apoptosis and development of novel therapeutics for diseases. Here we provide a brief overview of molecular players of programmed cell death with discussion on the role of caspases, modifications, ubiquitylation in apoptosis, removal of the apoptotic body and its relevance to diseases.

Apoptotic signalling targets the post-endocytic sorting machinery of the death receptor Fas/CD95

Fas plays a major role in regulating ligand-induced apoptosis in many cell types. It is well known that several cancers demonstrate reduced cell surface levels of Fas and thus escape a potential control system via ligand-induced apoptosis, although underlying mechanisms are unclear. Here we report that the endosome associated trafficking regulator 1 (ENTR1), controls cell surface levels of Fas and Fas-mediated apoptotic signalling. ENTR1 regulates, via binding to the coiled coil domain protein Dysbindin, the delivery of Fas from endosomes to lysosomes thereby controlling termination of Fas signal transduction. We demonstrate that ENTR1 is cleaved during Fas-induced apoptosis in a caspase-dependent manner revealing an unexpected interplay of apoptotic signalling and regulation of endolysosomal trafficking resulting in a positive feedback signalling-loop. Our data provide insights into the molecular mechanism of Fas post-endocytic trafficking and signalling, opening possible explanations on how cancer cells regulate cell surface levels of death receptors.

Fas is a death receptor that regulates apoptosis in many cell types and is downregulated on the cell surface in many cancers. Here, Sharma et al. show that endosome associated trafficking regulator ENTR1 regulates delivery of Fas to lysosomes, thereby controlling its degradation and signalling.

The combination of TPL2 knockdown and TNFα causes synthetic lethality via caspase-8 activation in human carcinoma cell lines

Most normal and tumor cells are protected from tumor necrosis factor α (TNFα)-induced apoptosis. Here, we identify the MAP3 kinase tumor progression locus-2 (TPL2) as a player contributing to the protection of a subset of tumor cell lines. The combination of TPL2 knockdown and TNFα gives rise to a synthetic lethality phenotype via receptor-interacting serine/threonine-protein kinase 1 (RIPK1)-dependent and -independent mechanisms. Whereas wild-type TPL2 rescues the phenotype, its kinase-dead mutant does not. Comparison of the molecular events initiated by small interfering RNA for TPL2 (siTPL2) ± TNFα in treatment-sensitive and -resistant lines revealed that the activation of caspase-8, downstream of miR-21-5p and cFLIP, is the dominant TPL2-dependent event. More important, comparison of the gene expression profiles of all of the tested cell lines results in the clustering of sensitive and resistant lines into distinct groups, providing proof of principle for the feasibility of generating a predictive tool for treatment sensitivity.

Epigenetic Regulation of TRAIL Signaling: Implication for Cancer Therapy

One of the main characteristics of carcinogenesis relies on genetic alterations in DNA and epigenetic changes in histone and non-histone proteins. At the chromatin level, gene expression is tightly controlled by DNA methyl transferases, histone acetyltransferases (HATs), histone deacetylases (HDACs), and acetyl-binding proteins. In particular, the expression level and function of several tumor suppressor genes, or oncogenes such as c-Myc, p53 or TRAIL, have been found to be regulated by acetylation. For example, HATs are a group of enzymes, which are responsible for the acetylation of histone proteins, resulting in chromatin relaxation and transcriptional activation, whereas HDACs by deacetylating histones lead to chromatin compaction and the subsequent transcriptional repression of tumor suppressor genes. Direct acetylation of suppressor genes or oncogenes can affect their stability or function. Histone deacetylase inhibitors (HDACi) have thus been developed as a promising therapeutic target in oncology. While these inhibitors display anticancer properties in preclinical models, and despite the fact that some of them have been approved by the FDA, HDACi still have limited therapeutic efficacy in clinical terms. Nonetheless, combined with a wide range of structurally and functionally diverse chemical compounds or immune therapies, HDACi have been reported to work in synergy to induce tumor regression. In this review, the role of HDACs in cancer etiology and recent advances in the development of HDACi will be presented and put into perspective as potential drugs synergizing with TRAIL's pro-apoptotic potential.

CD95/Fas and metastatic disease: What does not kill you makes you stronger

CD95 (also known as Fas) is the prototype of death receptors; however, evidence suggests that this receptor mainly implements non-apoptotic signaling pathways such as NF-κB, MAPK, and PI3K that are involved in cell migration, differentiation, survival, and cytokine secretion. At least two different forms of CD95 L exist. The multi-aggregated transmembrane ligand (m-CD95 L) is cleaved by metalloproteases to release a homotrimeric soluble ligand (s-CD95 L). Unlike m-CD95 L, the interaction between s-CD95 L and its receptor CD95 fails to trigger apoptosis, but instead promotes calcium-dependent cell migration, which contributes to the accumulation of inflammatory Th17 cells in damaged organs of lupus patients and favors cancer cell invasiveness. Novel inhibitors targeting the pro-inflammatory roles of CD95/CD95 L may provide attractive therapeutic options for patients with chronic inflammatory disorders or cancer. This review discusses the roles of the CD95/CD95 L pair in cell migration and metastasis.

Caspase-8 promotes c-Rel-dependent inflammatory cytokine expression and resistance against Toxoplasma gondii

Caspase-8 is a key integrator of cell survival and cell death decisions during infection and inflammation. Following engagement of tumor necrosis factor superfamily receptors or certain Toll-like receptors (TLRs), caspase-8 initiates cell-extrinsic apoptosis while inhibiting RIPK3-dependent programmed necrosis. In addition, caspase-8 has an important, albeit less well understood, role in cell-intrinsic inflammatory gene expression. Macrophages lacking caspase-8 or the adaptor FADD have defective inflammatory cytokine expression and inflammasome priming in response to bacterial infection or TLR stimulation. How caspase-8 regulates cytokine gene expression, and whether caspase-8-mediated gene regulation has a physiological role during infection, remain poorly defined. Here we demonstrate that both caspase-8 enzymatic activity and scaffolding functions contribute to inflammatory cytokine gene expression. Caspase-8 enzymatic activity was necessary for maximal expression of Il1b and Il12b, but caspase-8 deficient cells exhibited a further decrease in expression of these genes. Furthermore, the ability of TLR stimuli to induce optimal IκB kinase phosphorylation and nuclear translocation of the nuclear factor kappa light chain enhancer of activated B cells family member c-Rel required caspase activity. Interestingly, overexpression of c-Rel was sufficient to restore expression of IL-12 and IL-1β in caspase-8-deficient cells. Moreover, Ripk3 ^-/- Casp8 ^-/- mice were unable to control infection by the intracellular parasite Toxoplasma gondii, which corresponded to defects in monocyte recruitment to the peritoneal cavity, and exogenous IL-12 restored monocyte recruitment and protection of caspase-8-deficient mice during acute toxoplasmosis. These findings provide insight into how caspase-8 controls inflammatory gene expression and identify a critical role for caspase-8 in host defense against eukaryotic pathogens.

c-FLIP and CD95 signaling are essential for survival of renal cell carcinoma

Clear cell renal cell carcinoma (ccRCC) is the most-prominent tumor type of kidney cancers. Resistance of renal cell carcinoma (RCC) against tumor therapy is often owing to apoptosis resistance, e.g., by overexpression of anti-apoptotic proteins. However, little is known about the role of the apoptosis inhibitor c-FLIP and its potential impact on death receptor-induced apoptosis in ccRCC cells. In this study, we demonstrate that c-FLIP is crucial for resistance against CD95L-induced apoptosis in four ccRCC cell lines. Strikingly, downregulation of c-FLIP expression by short hairpin RNA (shRNA)interference led to spontaneous caspase activation and apoptotic cell death. Of note, knockdown of all c-FLIP splice variants was required to induce apoptosis. Stimulation of ccRCC cells with CD95L induced NF-κB and MAP kinase survival pathways as revealed by phosphorylation of RelA/p65 and Erk1/2. Interestingly, CD95L surface expression was high in all cell lines analyzed, and CD95 but not TNF-R1 clustered at cell contact sites. Downstream of CD95, inhibition of the NF-κB pathway led to spontaneous cell death. Surprisingly, knockdown experiments revealed that c-FLIP inhibits NF-κB activation in the context of CD95 signaling. Thus, c-FLIP inhibits apoptosis and dampens NF-κB downstream of CD95 but allows NF-κB activation to a level sufficient for ccRCC cell survival. In summary, we demonstrate a complex CD95-FLIP-NF-κB-signaling circuit, in which CD95-CD95L interactions mediate a paracrine survival signal in ccRCC cells with c-FLIP and NF-κB both being required for inhibiting cell death and ensuring survival. Our findings might lead to novel therapeutic approaches of RCC by circumventing apoptosis resistance.

In Vivo Models of Oncoproteins Encoded by Kaposi's Sarcoma-Associated Herpesvirus

Kaposi's sarcoma-associated herpesvirus (KSHV) is a human oncogenic virus. KSHV utilizes its proteins to modify the cellular environment to promote viral replication and persistence. Some of these proteins are oncogenic, modulating cell proliferation, apoptosis, angiogenesis, genome stability, and immune responses, among other cancer hallmarks. These changes can lead to the development of KSHV-associated malignancies. In this Gem, we focus on animal models of oncogenic KSHV proteins that were developed to enable better understanding of KSHV tumorigenesis.

Countering TRAIL Resistance in Melanoma

Melanoma of the skin has become a prime example for demonstrating the success of targeted cancer therapy. Nevertheless, high mortality has remained, mainly related to tumor heterogeneity and inducible therapy resistance. But the development of new therapeutic strategies and combinations has raised hope of finally defeating this deadly disease. TNF-related apoptosis-inducing ligand (TRAIL) represents a promising antitumor strategy. The principal sensitivity of melanoma cells for TRAIL was demonstrated in previous studies; however, inducible resistance appeared as a major problem. To address this issue, combination strategies were tested, and survival pathway inhibitors were shown to sensitize melanoma cells for TRAIL-induced apoptosis. Finally, cell cycle inhibition was identified as a common principle of TRAIL sensitization in melanoma cells. Mitochondrial apoptosis pathways, pro- and antiapoptotic Bcl-2 proteins as well as the rheostat consisted of Smac (Second mitochondria-derived activator of caspase) and XIAP (X-linked inhibitor of apoptosis protein) appeared to be of particular importance. Furthermore, the role of reactive oxygen species (ROS) was recognized in this setting. Inducible TRAIL resistance in melanoma can be explained by (i) high levels of antiapoptotic Bcl-2 proteins, (ii) high levels of XIAP, and (iii) suppressed Bax activity. These hurdles have to be overcome to enable the use of TRAIL in melanoma therapy. Several strategies appear as particularly promising, including new TRAIL receptor agonists, Smac and BH3 mimetics, as well as selective kinase inhibitors.

Fas ligand and nitric oxide combination to control smooth muscle growth while sparing endothelium

Metallic stents cause vascular wall damage with subsequent smooth muscle cell (SMC) proliferation, neointimal hyperplasia, and treatment failure. To combat in-stent restenosis, drug-eluting stents (DES) delivering mTOR inhibitors such as sirolimus or everolimus have become standard for coronary stenting. However, the relatively non-specific action of mTOR inhibitors prevents efficient endothelium recovery and mandates dual antiplatelet therapy to prevent thrombosis. Unfortunately, long-term dual antiplatelet therapy leads to increased risk of bleeding/stroke and, paradoxically, myocardial infarction. Here, we took advantage of the fact that nitric oxide (NO) increases Fas receptors on the SMC surface. Fas forms a death-inducing complex upon binding to Fas ligand (FasL), while endothelial cells (ECs) are relatively resistant to this pathway. Selected doses of FasL and NO donor synergistically increased SMC apoptosis and inhibited SMC growth more potently than did everolimus or sirolimus, while having no significant effect on EC viability and proliferation. This differential effect was corroborated in ex vivo pig coronaries, where the neointimal formation was inhibited by the drug combination, but endothelial viability was retained. We also deployed FasL-NO donor-releasing ethylene-vinyl acetate copolymer (EVAc)-coated stents into pig coronary arteries, and cultured them in perfusion bioreactors for one week. FasL and NO donor, released from the stent coating, killed SMCs close to the stent struts, even in the presence of flow rates mimicking those of native arteries. Thus, the FasL-NO donor-combination has a potential to prevent intimal hyperplasia and in-stent restenosis, without harming endothelial restoration, and hence may be a superior drug delivery strategy for DES.

MC159 of Molluscum Contagiosum Virus Suppresses Autophagy by Recruiting Cellular SH3BP4 via an SH3 Domain-Mediated Interaction

MC159 is a viral FLIP (FLICE inhibitory protein) encoded by the molluscum contagiosum virus (MCV) enabling MCV to evade antiviral immunity and to establish persistent infections in humans. Here, we show that MC159 contains a functional SH3 binding motif, which mediates avid and selective binding to SH3BP4, a signaling protein known to regulate endocytic trafficking and suppress cellular autophagy. The capacity to bind SH3BP4 was dispensable for regulation of NF-κB-mediated transcription and suppression of proapoptotic caspase activation but contributed to inhibition of amino acid starvation-induced autophagy by MC159. These results provide new insights into the cellular functions of MC159 and reveal SH3BP4 as a novel host cell factor targeted by a viral immune evasion protein.IMPORTANCE After the eradication of smallpox, molluscum contagiosum virus (MCV) is the only poxvirus restricted to infecting humans. MCV infection is common and causes benign skin lesions that usually resolve spontaneously but may persist for years and grow large, especially in immunocompromised individuals. While not life threatening, MCV infections pose a significant global health burden. No vaccine or specific anti-MCV therapy is available. MCV encodes several proteins that enable it to evade antiviral immunity, a notable example of which is the MC159 protein. In this study, we describe a novel mechanism of action for MC159 involving hijacking of a host cell protein called SH3BP4 to suppress autophagy, a cellular recycling mechanism important for antiviral immunity. This study contributes to our understanding of the host cell interactions of MCV and the molecular function of MC159.

c-FLIP, a Novel Biomarker for Cancer Prognosis, Immunosuppression, Alzheimer's Disease, Chronic Obstructive Pulmonary Disease (COPD), and a Rationale Therapeutic Target

Dysregulation of c-FLIP (cellular FADD-like IL-1β-converting enzyme inhibitory protein) has been shown in several diseases including cancer, Alzheimer's disease, and chronic obstructive pulmonary disease (COPD). c-FLIP is a critical anti-cell death protein often overexpressed in tumors and hematological malignancies and its increased expression is often associated with a poor prognosis. c-FLIP frequently exists as long (c-FLIPL) and short (c-FLIPS) isoforms, regulates its anti-cell death functions through binding to FADD (FAS associated death domain protein), an adaptor protein known to activate caspases-8 and -10 and links c-FLIP to several cell death regulating complexes including the death-inducing signaling complex (DISC) formed by various death receptors. c-FLIP also plays a critical role in necroptosis and autophagy. Furthermore, c-FLIP is able to activate several pathways involved in cytoprotection, proliferation, and survival of cancer cells through various critical signaling proteins. Additionally, c-FLIP can inhibit cell death induced by several chemotherapeutics, anti-cancer small molecule inhibitors, and ionizing radiation. Moreover, c-FLIP plays major roles in aiding the survival of immunosuppressive tumor-promoting immune cells and functions in inflammation, Alzheimer's disease (AD), and chronic obstructive pulmonary disease (COPD). Therefore, c-FLIP can serve as a versatile biomarker for cancer prognosis, a diagnostic marker for several diseases, and an effective therapeutic target. In this article, we review the functions of c-FLIP as an anti-apoptotic protein and negative prognostic factor in human cancers, and its roles in resistance to anticancer drugs, necroptosis and autophagy, immunosuppression, Alzheimer's disease, and COPD.

A Novel AKT Activator, SC79, Prevents Acute Hepatic Failure Induced by Fas-Mediated Apoptosis of Hepatocytes

Acute liver failure is a serious clinical problem of which the underlying pathogenesis remains unclear and for which effective therapies are lacking. The Fas receptor/ligand system, which is negatively regulated by AKT, is known to play a prominent role in hepatocytic cell death. We hypothesized that AKT activation may represent a strategy to alleviate Fas-induced fulminant liver failure. We report here that a novel AKT activator, SC79, protects hepatocytes from apoptosis induced by agonistic anti-Fas antibody CH11 (for humans) or Jo2 (for mice) and significantly prolongs the survival of mice given a lethal dose of Jo2. Under Fas-signaling stimulation, SC79 inhibited Fas aggregation, prevented the recruitment of the adaptor molecule Fas-associated death domain (FADD) and procaspase-8 [or FADD-like IL-1β-converting enzyme (FLICE)] into the death-inducing signaling complex (DISC), but SC79 enhanced the recruitment of the long and short isoforms of cellular FLICE-inhibitory protein at the DISC. All of the SC79-induced hepatoprotective and DISC-interruptive effects were confirmed to have been reversed by the Akt inhibitor LY294002. These results strongly indicate that SC79 protects hepatocytes from Fas-induced fatal hepatic apoptosis. The potent alleviation of Fas-mediated hepatotoxicity by the relatively safe drug SC79 highlights the potential of our findings for immediate hepatoprotective translation.

Tumour Necrosis Factor Alpha in Intestinal Homeostasis and Gut Related Diseases

The intestinal epithelium constitutes an indispensable single-layered barrier to protect the body from invading pathogens, antigens or toxins. At the same time, beneficial nutrients and water have to be absorbed by the epithelium. To prevent development of intestinal inflammation or tumour formation, intestinal homeostasis has to be tightly controlled and therefore a strict balance between cell death and proliferation has to be maintained. The proinflammatory cytokine tumour necrosis factor alpha (TNFα) was shown to play a striking role for the regulation of this balance in the gut. Depending on the cellular conditions, on the one hand TNFα is able to mediate cell survival by activating NFκB signalling. On the other hand, TNFα might trigger cell death, in particular caspase-dependent apoptosis but also caspase-independent programmed necrosis. By regulating these cell death and survival mechanisms, TNFα exerts a variety of beneficial functions in the intestine. However, TNFα signalling is also supposed to play a critical role for the pathogenesis of inflammatory bowel disease (IBD), infectious diseases, intestinal wound healing and tumour formation. Here we review the literature about the physiological and pathophysiological role of TNFα signalling for the maintenance of intestinal homeostasis and the benefits and difficulties of anti-TNFα treatment during IBD.

Up-regulation of tumor necrosis factor-α pathway survival genes and of the receptor TNFR2 in gastric cancer

BACKGROUND

Gastric carcinogenesis can be induced by chronic inflammation triggered by Helicobacter pylori (H. pylori) infection. Tumor necrosis factor (TNF)-α and its receptors (TNFR1 and TNFR2) regulate important cellular processes, such as apoptosis and cell survival, and the disruption of which can lead to cancer. This signaling pathway is also modulated by microRNAs (miRNAs), altering gene expression.

AIM

To evaluate the mRNA and miRNAs expression involved in the TNF-α signaling pathway in gastric cancer (GC) tissues and its relationship.

METHODS

Quantitative polymerase chain reaction (qPCR) by TaqMan^® assay was used to quantify the RNA transcript levels of TNF-α signaling pathway (TNF, TNFR1, TNFR2, TRADD, TRAF2, CFLIP, NFKB1, NFKB2, CASP8, CASP3) and miRNAs that targets genes from this pathway (miR-19a, miR-34a, miR-103a, miR-130a, miR-181c) in 30 GC fresh tissue samples. Molecular diagnosis of H. pylori was performed by nested PCR for gene HSP60. A miRNA:mRNA interaction network was construct using Cytoscape v3.1.1 from the in silico analysis performed using public databases.

RESULTS

Up-regulation of cellular survival genes as TNF, TNFR2, TRADD, TRAF2, CFLIP, and NFKB2, besides CASP8 and miR-34a was observed in GC tissues, whereas mediators of apoptosis such as TNFR1 and CASP3 were down-regulated. When the samples were stratified by histological type, the expression of miR-103a and miR-130a was significantly increased in the diffuse-type of GC compared to the intestinal-type. However, no influence of H. pylori infection was observed on the expression levels of mRNA and miRNAs analyzed. Moreover, the miRNA:mRNA interaction network showed several interrelations between the miRNAs and their target genes, highlighting miR-19a and miR-103a, which has as predicted or validated target a large number of genes in the TNF-α pathway, including TNF, TNFR1, TNFR2, CFLIP, TRADD, CASP3 and CASP8.

CONCLUSION

Our findings show that cell survival genes mediated by TNF/TNFR2 binding is up-regulated in GC favoring its pro-tumoral effect, while pro-apoptotic genes as CASP3 and TNFR1 are down-regulated, indicating disbalance between apoptosis and cell proliferation processes in this neoplasm. This process can also be influenced by an intricate regulatory network of miRNA:mRNA.

TRAILblazing Strategies for Cancer Treatment

In the late 1990s, tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), a member of the TNF-family, started receiving much attention for its potential in cancer therapy, due to its capacity to induce apoptosis selectively in tumour cells in vivo. TRAIL binds to its membrane-bound death receptors TRAIL-R1 (DR4) and TRAIL-R2 (DR5) inducing the formation of a death-inducing signalling complex (DISC) thereby activating the apoptotic cascade. The ability of TRAIL to also induce apoptosis independently of p53 makes TRAIL a promising anticancer agent, especially in p53-mutated tumour entities. Thus, several so-called TRAIL receptor agonists (TRAs) were developed. Unfortunately, clinical testing of these TRAs did not reveal any significant anticancer activity, presumably due to inherent or acquired TRAIL resistance of most primary tumour cells. Since the potential power of TRAIL-based therapies still lies in TRAIL's explicit cancer cell-selectivity, a desirable approach going forward for TRAIL-based cancer therapy is the identification of substances that sensitise tumour cells for TRAIL-induced apoptosis while sparing normal cells. Numerous of such TRAIL-sensitising strategies have been identified within the last decades. However, many of these approaches have not been verified in animal models, and therefore potential toxicity of these approaches has not been taken into consideration. Here, we critically summarise and discuss the status quo of TRAIL signalling in cancer cells and strategies to force tumour cells into undergoing apoptosis triggered by TRAIL as a cancer therapeutic approach. Moreover, we provide an overview and outlook on innovative and promising future TRAIL-based therapeutic strategies.

How patients with an intact immune system develop head and neck cancer

Although the adaptive immune system can detect and eliminate malignant cells, patients with intact and fully functional immune systems develop head and neck cancer. How is this paradox explained? Manuscripts published in the English language from 1975 to 2018 were reviewed using search inputs related to tumor cell antigenicity and immunogenicity, immunodominance, cancer immunoediting and genomic alterations present within carcinomas. Early in tumor development, T cell responses to immunodominant antigens may lead to the elimination of cancer cells expressing these antigens and a tumor composed to tumor cells expressing only immunorecessive antigens. Conversely, other tumor cells may acquire genomic or epigenetic alterations that result in an antigen processing or presentation defect or other inability to be detected or killed by T cells. Such T cell insensitive tumor cells may also be selected for in a progressing tumor. Tumors harboring subpopulations of cells that cannot be eliminated by T cells may require non-T cell-based treatments, such as NK cell immunotherapies. Recognition of such tumor cell populations within a heterogeneous cancer may inform the selection of treatment for HNSCC in the future.