Death of HT29 adenocarcinoma cells induced by TNF family receptor activation is caspase-independent and displays features of both apoptosis and necrosis

Human CD4 cytotoxic T lymphocytes mediate potent tumor control in humanized immune system mice

Efficacy of immune checkpoint inhibitors in cancers can be limited by CD8 T cell dysfunction or HLA-I down-regulation. Tumor control mechanisms independent of CD8/HLA-I axis would overcome these limitations. Here, we report potent CD4 T cell-mediated tumor regression and memory responses in humanized immune system (HIS) mice implanted with HT-29 colorectal tumors. The regressing tumors showed increased CD4 cytotoxic T lymphocyte (CTL) infiltration and enhanced tumor HLA-II expression compared to progressing tumors. The intratumoral CD4 T cell subset associated with tumor regression expressed multiple cytotoxic markers and exhibited clonal expansion. Notably, tumor control was abrogated by depletion of CD4 but not CD8 T cells. CD4 T cells derived from tumor-regressing mice exhibited HLA-II-dependent and tumor-specific killing ex vivo. Taken together, our study demonstrates a critical role of human CD4 CTLs in mediating tumor clearance independent of CD8 T cells and provides a platform to study human anti-tumor immunity in vivo.

Antibody–drug conjugates harboring a kinesin spindle protein inhibitor with immunostimulatory properties

Antibody–drug conjugates (ADCs) are used to target cancer cells by means of antibodies directed to tumor-associated antigens, causing the incorporation of a cytotoxic payload into target cells. Here, we characterized the mode of action of ADC costing of a TWEAKR-specific monoclonal antibody conjugated to a small molecule kinesin spindle protein (KSP) inhibitor (KSPi). These TWEAKR-KSPi-ADCs showed strong efficacy in a TWEAKR expressing CT26 colon cancer model in mice. TWEAKR-KSPi-ADCs controlled the growth of CT26 colon cancers in immunodeficient as well as in immunocompetent mice. However, when treated with suboptimal doses, TWEAKR-KSPi-ADCs were still active in immunocompetent but not in immunodeficient mice, indicating that TWEAKR-KSPi-ADCs act – in addition to the cytotoxic mode of action – through an immunological mechanism. Indeed, in vitro experiments performed with a cell-permeable small molecule KSPi closely related to the active payload released from the TWEAKR-KSPi-ADCs revealed that KSPi was capable of stimulating several hallmarks of immunogenic cell death (ICD) on three different human cancer cell lines: cellular release of adenosine triphosphate (ATP) and high mobility group B1 protein (HMGB1), exposure of calreticulin on the cell surface as well as a transcriptional type-I interferon response. Further, in vivo experiments confirmed that treatment with TWEAKR-KSPi-ADCs activated immune responses via enhancing the infiltration of CD4⁺ and CD8⁺ T lymphocytes in tumors and the local production of interferon-γ, interleukin-2, and tumor necrosis factor-α. In conclusion, the antineoplastic effects of TWEAKR-KSPi-ADCs can partly be attributed to its ICD-stimulatory properties.

SMYD2 targets RIPK1 and restricts TNF-induced apoptosis and necroptosis to support colon tumor growth

SMYD2 is a histone methyltransferase, which methylates both histone H3K4 as well as a number of non-histone proteins. Dysregulation of SMYD2 has been associated with several diseases including cancer. In the present study, we investigated whether and how SMYD2 might contribute to colorectal cancer. Increased expression levels of SMYD2 were detected in human and murine colon tumor tissues compared to tumor-free tissues. SMYD2 deficiency in colonic tumor cells strongly decreased tumor growth in two independent experimental cancer models. On a molecular level, SMYD2 deficiency sensitized colonic tumor cells to TNF-induced apoptosis and necroptosis without affecting cell proliferation. Moreover, we found that SMYD2 targeted RIPK1 and inhibited the phosphorylation of RIPK1. Finally, in a translational approach, pharmacological inhibition of SMYD2 attenuated colonic tumor growth. Collectively, our data show that SMYD2 is crucial for colon tumor growth and inhibits TNF-induced apoptosis and necroptosis.

Virtual Screening for Biomimetic Anti-Cancer Peptides from Cordyceps militaris Putative Pepsinized Peptidome and Validation on Colon Cancer Cell Line

Colorectal cancer is one of the leading causes of cancer-related death in Thailand and many other countries. The standard practice for curing this cancer is surgery with an adjuvant chemotherapy treatment. However, the unfavorable side effects of chemotherapeutic drugs are undeniable. Recently, protein hydrolysates and anticancer peptides have become popular alternative options for colon cancer treatment. Therefore, we aimed to screen and select the anticancer peptide candidates from the in silico pepsin hydrolysate of a Cordyceps militaris (CM) proteome using machine-learning-based prediction servers for anticancer prediction, i.e., AntiCP, iACP, and MLACP. The selected CM-anticancer peptide candidates could be an alternative treatment or co-treatment agent for colorectal cancer, reducing the use of chemotherapeutic drugs. To ensure the anticancer properties, an in vitro assay was performed with "CM-biomimetic peptides" on the non-metastatic colon cancer cell line (HT-29). According to the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay results from peptide candidate treatments at 0-400 µM, the IC₅₀ doses of the CM-biomimetic peptide with no toxic and cancer-cell-penetrating ability, original C. militaris biomimetic peptide (C-ori), against the HT-29 cell line were 114.9 µM at 72 hours. The effects of C-ori compared to the doxorubicin, a conventional chemotherapeutic drug for colon cancer treatment, and the combination effects of both the CM-anticancer peptide and doxorubicin were observed. The results showed that C-ori increased the overall efficiency in the combination treatment with doxorubicin. According to the acridine orange/propidium iodine (AO/PI) staining assay, C-ori can induce apoptosis in HT-29 cells significantly, confirmed by chromatin condensation, membrane blebbing, apoptotic bodies, and late apoptosis which were observed under a fluorescence microscope.

Metabolic activation and colitis pathogenesis is prevented by lymphotoxin β receptor expression in neutrophils

Inflammatory bowel disease is characterized by an exacerbated intestinal immune response, but the critical mechanisms regulating immune activation remain incompletely understood. We previously reported that the TNF-superfamily molecule TNFSF14 (LIGHT) is required for preventing severe disease in mouse models of colitis. In addition, deletion of lymphotoxin beta receptor (LTβR), which binds LIGHT, also led to aggravated colitis pathogenesis. Here, we aimed to determine the cell type(s) requiring LTβR and the mechanism critical for exacerbation of colitis. Specific deletion of LTβR in neutrophils (LTβRΔN), but not in several other cell types, was sufficient to induce aggravated colitis and colonic neutrophil accumulation. Mechanistically, RNA-Seq analysis revealed LIGHT-induced suppression of cellular metabolism, and mitochondrial function, that was dependent on LTβR. Functional studies confirmed increased mitochondrial mass and activity, associated with excessive mitochondrial ROS production and elevated glycolysis at steady-state and during colitis. Targeting these metabolic changes rescued exacerbated disease severity. Our results demonstrate that LIGHT signals to LTβR on neutrophils to suppress metabolic activation and thereby prevents exacerbated immune pathogenesis during colitis.

Caspase-Independent Regulated Necrosis Pathways as Potential Targets in Cancer Management

Regulated necrosis is an emerging type of cell death independent of caspase. Recently, with increasing findings of regulated necrosis in the field of biochemistry and genetics, the underlying molecular mechanisms and signaling pathways of regulated necrosis are gradually understood. Nowadays, there are several modes of regulated necrosis that are tightly related to cancer initiation and development, including necroptosis, ferroptosis, parthanatos, pyroptosis, and so on. What’s more, accumulating evidence shows that various compounds can exhibit the anti-cancer effect via inducing regulated necrosis in cancer cells, which indicates that caspase-independent regulated necrosis pathways are potential targets in cancer management. In this review, we expand the molecular mechanisms as well as signaling pathways of multiple modes of regulated necrosis. We also elaborate on the roles they play in tumorigenesis and discuss how each of the regulated necrosis pathways could be therapeutically targeted.

Altered mitochondrial calcium handling and cell death by necroptosis: An emerging paradigm

The classical necroptosis signaling is mediated by death receptors (DRs) that work in synergy with traditional caspase inhibitory signals. Currently, potential therapeutic molecules are in various phases of clinical trials for a spectrum of pathological conditions associated with necroptosis. However, a non-classical model of necroptosis has also emerged over the last decade with a relatively unexplored molecular mechanism. Although in vitro studies and preclinical models have shown its close association with mitochondrial dysfunction (mito-dysfunction), contradictory reports have emerged which complicate its definitiveness. Though impaired mitochondrial calcium ([Ca²⁺]_m) handling is established in necrotic cell death, how this interplay regulates necroptosis is yet to be elucidated. Taking these questions into consideration, we have discussed various molecular aspects of necroptosis with the emerging role of mito-dysfunction. Based on the central role of altered [Ca²⁺]_m handling in mito-dysfunction mediated necroptosis, we have provided a comprehensive molecular insight into this emerging paradigm. Potential reasons for the contradictory findings regarding the role of mito-dysfunction in necroptosis in general and mitochondrial-dependent necroptosis in specific are discussed. We also provide insights into the current understanding of how [Ca²⁺]_m can be a critical determinant in deciding the cell fate under certain pathological conditions, while under others it may be dispensable. Lastly, we have highlighted the key molecular targets which have a direct implication for therapeutic intervention in conditions that are associated with impaired [Ca²⁺]_m handling and cell death by necroptosis.

The molecular mechanisms of MLKL-dependent and MLKL-independent necrosis

Necrosis, a type of unwanted and passive cell demise, usually occurs under the excessive external stress and is considered to be unregulated. However, under some special conditions such as caspase inhibition, necrosis is regulable in a well-orchestrated way. The term 'regulated necrosis' has been proposed to describe such programed necrosis. Recently, several forms of necrosis, including necroptosis, pyroptosis, ferroptosis, parthanatos, oxytosis, NETosis, and Na+/K+-ATPase-mediated necrosis, have been identified, and some crucial regulators governing regulated necrosis have also been discovered. Mixed lineage kinase domain-like pseudokinase (MLKL), a core regulator in necroptosis, acts as an executioner in response to ligands of death receptor family. Its activation requires the receptor-interacting protein kinases, RIP1 and RIP3. However, MLKL is only involved in necroptosis, i.e. MLKL is dispensable for necrosis. Therefore, this review is aimed at summarizing the molecular mechanisms of MLKL-dependent and MLKL-independent necrosis.

Nerolidol Mitigates Colonic Inflammation: An Experimental Study Using both In Vivo and In Vitro Models

Nerolidol (NED) is a naturally occurring sesquiterpene alcohol present in various plants with potent anti-inflammatory effects. In the current study, we investigated NED as a putative anti-inflammatory compound in an experimental model of colonic inflammation. C57BL/6J male black mice (C57BL/6J) were administered 3% dextran sodium sulfate (DSS) in drinking water for 7 days to induce colitis. Six groups received either vehicle alone or DSS alone or DSS with oral NED (50, 100, and 150 mg/kg body weight/day by oral gavage) or DSS with sulfasalazine. Disease activity index (DAI), colonic histology, and biochemical parameters were measured. TNF-α-treated HT-29 cells were used as in vitro model of colonic inflammation to study NED (25 µM and 50 µM). NED significantly decreased the DAI and reduced the inflammation-associated changes in colon length as well as macroscopic and microscopic architecture of the colon. Changes in tissue Myeloperoxidase (MPO) concentrations, neutrophil and macrophage mRNA expression (CXCL2 and CCL2), and proinflammatory cytokine content (IL-1β, IL-6, and TNF-α) both at the protein and mRNA level were significantly reduced by NED. The increase in content of the proinflammatory enzymes, COX-2 and iNOS induced by DSS were also significantly inhibited by NED along with tissue nitrate levels. NED promoted Nrf2 nuclear translocation dose dependently. NED significantly increased antioxidant enzymes activity (Superoxide dismutase (SOD) and Catalase (CAT)), Hemeoxygenase-1 (HO-1), and SOD3 mRNA levels. NED treatment in TNF-α-challenged HT-29 cells significantly decreased proinflammatory chemokines (CXCL1, IL-8, CCL2) and COX-2 mRNA levels. NED supplementation attenuates colon inflammation through its potent antioxidant and anti-inflammatory activity both in in vivo and in vitro models of colonic inflammation.

Necroptosis, ADAM proteases and intestinal (dys)function

Recently, an unexpected connection between necroptosis and members of the a disintegrin and metalloproteinase (ADAM) protease family has been reported. Necroptosis represents an important cell death routine which helps to protect from viral, bacterial, fungal and parasitic infections, maintains adult T cell homeostasis and contributes to the elimination of potentially defective organisms before parturition. Equally important for organismal homeostasis, ADAM proteases control cellular processes such as development and differentiation, immune responses or tissue regeneration. Notably, necroptosis as well as ADAM proteases have been implicated in the control of inflammatory responses in the intestine. In this review, we therefore provide an overview of the physiology and pathophysiology of necroptosis, ADAM proteases and intestinal (dys)function, discuss the contribution of necroptosis and ADAMs to intestinal (dys)function, and review the current knowledge on the role of ADAMs in necroptotic signaling.

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.

Genome-wide screen identifies a novel prognostic signature for breast cancer survival

Large genomic datasets in combination with clinical data can be used as an unbiased tool to identify genes important in patient survival and discover potential therapeutic targets. We used a genome-wide screen to identify 587 genes significantly and robustly deregulated across four independent breast cancer (BC) datasets compared to normal breast tissue. Gene expression of 381 genes was significantly associated with relapse-free survival (RFS) in BC patients. We used a gene co-expression network approach to visualize the genetic architecture in normal breast and BCs. In normal breast tissue, co-expression cliques were identified enriched for cell cycle, gene transcription, cell adhesion, cytoskeletal organization and metabolism. In contrast, in BC, only two major co-expression cliques were identified enriched for cell cycle-related processes or blood vessel development, cell adhesion and mammary gland development processes. Interestingly, gene expression levels of 7 genes were found to be negatively correlated with many cell cycle related genes, highlighting these genes as potential tumor suppressors and novel therapeutic targets. A forward-conditional Cox regression analysis was used to identify a 12-gene signature associated with RFS. A prognostic scoring system was created based on the 12-gene signature. This scoring system robustly predicted BC patient RFS in 60 sampling test sets and was further validated in TCGA and METABRIC BC data. Our integrated study identified a 12-gene prognostic signature that could guide adjuvant therapy for BC patients and includes novel potential molecular targets for therapy.

Enavatuzumab, a Humanized Anti-TWEAK Receptor Monoclonal Antibody, Exerts Antitumor Activity through Attracting and Activating Innate Immune Effector Cells

Enavatuzumab is a humanized IgG1 anti-TWEAK receptor monoclonal antibody that was evaluated in a phase I clinical study for the treatment of solid malignancies. The current study was to determine whether and how myeloid effector cells were involved in postulated mechanisms for its potent antitumor activity in xenograft models. The initial evidence for a role of effector cells was obtained in a subset of tumor xenograft mouse models whose response to enavatuzumab relied on the binding of Fc of the antibody to Fcγ receptor. The involvement of effector cells was further confirmed by immunohistochemistry, which revealed strong infiltration of CD45⁺ effector cells into tumor xenografts in responding models, but minimal infiltration in nonresponders. Consistent with the xenograft studies, human effector cells preferentially migrated toward in vivo-responsive tumor cells treated by enavatuzumab in vitro, with the majority of migratory cells being monocytes. Conditioned media from enavatuzumab-treated tumor cells contained elevated levels of chemokines, which might be responsible for enavatuzumab-triggered effector cell migration. These preclinical studies demonstrate that enavatuzumab can exert its potent antitumor activity by actively recruiting and activating myeloid effectors to kill tumor cells. Enavatuzumab-induced chemokines warrant further evaluation in clinical studies as potential biomarkers for such activity.

Autophagy of metallothioneins prevents TNF-induced oxidative stress and toxicity in hepatoma cells

Lysosomal membrane permeabilization (LMP) induced by oxidative stress has recently emerged as a prominent mechanism behind TNF cytotoxicity. This pathway relies on diffusion of hydrogen peroxide into lysosomes containing redox-active iron, accumulated by breakdown of iron-containing proteins and subcellular organelles. Upon oxidative lysosomal damage, LMP allows relocation to the cytoplasm of low mass iron and acidic hydrolases that contribute to DNA and mitochondrial damage, resulting in death by apoptosis or necrosis. Here we investigate the role of lysosomes and free iron in death of HTC cells, a rat hepatoma line, exposed to TNF following metallothionein (MT) upregulation. Iron-binding MT does not normally occur in HTC cells in significant amounts. Intracellular iron chelation attenuates TNF and cycloheximide (CHX)-induced LMP and cell death, demonstrating the critical role of this transition metal in mediating cytokine lethality. MT upregulation, combined with starvation-activated MT autophagy almost completely suppresses TNF and CHX toxicity, while impairment of both autophagy and MT upregulation by silencing of Atg7, and Mt1a and/or Mt2a, respectively, abrogates protection. Interestingly, MT upregulation by itself has little effect, while stimulated autophagy alone depresses cytokine toxicity to some degree. These results provide evidence that intralysosomal iron-catalyzed redox reactions play a key role in TNF and CHX-induced LMP and toxicity. The finding that chelation of intralysosomal iron achieved by autophagic delivery of MT, and to some degree probably of other iron-binding proteins as well, into the lysosomal compartment is highly protective provides a putative mechanism to explain autophagy-related suppression of death by TNF and CHX.

An outline of necrosome triggers

Necroptosis was initially identified as a backup cell death program when apoptosis is blocked. However, it is now recognized as a cellular defense mechanism against infections and is presumed to be a detrimental factor in several pathologies driven by cell death. Necroptosis is a prototypic form of regulated necrosis that depends on activation of the necrosome, which is a protein complex in which receptor interacting protein kinase (RIPK) 3 is activated. The RIP homotypic interaction motif (RHIM) is the core domain that regulates activation of the necrosome. To date, three RHIM-containing proteins have been reported to activate the kinase activity of RIPK3 within the necrosome: RIPK1, Toll/IL-1 receptor domain-containing adaptor inducing IFN-β (TRIF), and DNA-dependent activator of interferon regulatory factors (DAI). Here, we review and discuss commonalities and differences of the increasing number of activators of the necrosome. Since the discovery that activation of mixed lineage kinase domain-like (MLKL) by RIPK3 kinase activity is crucial in necroptosis, interest has increased in monitoring and therapeutically targeting their activation. The availability of new phospho-specific antibodies, pharmacologic inhibitors, and transgenic models will allow us to further document the role of necroptosis in degenerative, inflammatory and infectious diseases.

Context-dependent roles for lymphotoxin-β receptor signaling in cancer development

The LTα1β2 and LIGHT TNF superfamily cytokines exert pleiotropic physiological functions through the activation of their cognate lymphotoxin-β receptor (LTβR). Interestingly, since the discovery of these proteins, accumulating evidence has pinpointed a role for LTβR signaling in carcinogenesis. Early studies have shown a potential anti-tumoral role in a subset of solid cancers either by triggering apoptosis in malignant cells or by eliciting an anti-tumor immune response. However, more recent studies provided robust evidence that LTβR signaling is also involved in diverse cell-intrinsic and microenvironment-dependent pro-oncogenic mechanisms, affecting several solid and hematological malignancies. Consequently, the usefulness of LTβR signaling axis blockade has been investigated as a potential therapeutic approach for cancer. Considering the seemingly opposite roles of LTβR signaling in diverse cancer types and their key implications for therapy, we here extensively review the different mechanisms by which LTβR activation affects carcinogenesis, focusing on the diverse contexts and different models assessed.

Autophagy in acute kidney injury

Autophagy is a conserved multistep pathway that degrades and recycles damaged organelles and macromolecules to maintain intracellular homeostasis. The autophagy pathway is upregulated under stress conditions including cell starvation, hypoxia, nutrient and growth-factor deprivation, endoplasmic reticulum stress, and oxidant injury, most of which are involved in the pathogenesis of acute kidney injury (AKI). Recent studies demonstrate that basal autophagy in the kidney is vital for the normal homeostasis of the proximal tubules. Deletion of key autophagy proteins impaired renal function and increased p62 levels and oxidative stress. In models of AKI, autophagy deletion in proximal tubules worsened tubular injury and renal function, highlighting that autophagy is renoprotective in models of AKI. In addition to nonselective sequestration of autophagic cargo, autophagy can facilitate selective degradation of damaged organelles, particularly mitochondrial degradation through the process of mitophagy. Damaged mitochondria accumulate in autophagy-deficient kidneys of mice subjected to ischemia-reperfusion injury, but the precise mechanisms of regulation of mitophagy in AKI are not yet elucidated. Recent progress in identifying the interplay of autophagy, apoptosis, and regulated necrosis has revived interest in examining shared pathways/molecules in this crosstalk during the pathogenesis of AKI. Autophagy and its associated pathways pose potentially unique targets for therapeutic interventions in AKI.

Pan-Bcl-2 inhibitor Obatoclax is a potent late stage autophagy inhibitor in colorectal cancer cells independent of canonical autophagy signaling

BACKGROUND

Colorectal cancer is the third most common malignancy in humans and novel therapeutic approaches are urgently needed. Autophagy is an evolutionarily highly conserved cellular process by which cells collect unnecessary organelles or misfolded proteins and subsequently degrade them in vesicular structures in order to refuel cells with energy. Dysregulation of the complex autophagy signaling network has been shown to contribute to the onset and progression of cancer in various models. The Bcl-2 family of proteins comprises central regulators of apoptosis signaling and has been linked to processes involved in autophagy. The antiapoptotic members of the Bcl-2 family of proteins have been identified as promising anticancer drug targets and small molecules inhibiting those proteins are in clinical trials.

METHODS

Flow cytometry and colorimetric assays were used to assess cell growth and cell death. Long term 3D cell culture was used to assess autophagy in a tissue mimicking environment in vitro. RNA interference was applied to modulate autophagy signaling. Immunoblotting and q-RT PCR were used to investigate autophagy signaling. Immunohistochemistry and fluorescence microscopy were used to detect autophagosome formation and autophagy flux.

RESULTS

This study demonstrates that autophagy inhibition by obatoclax induces cell death in colorectal cancer (CRC) cells in an autophagy prone environment. Here, we demonstrate that pan-Bcl-2 inhibition by obatoclax causes a striking, late stage inhibition of autophagy in CRC cells. In contrast, ABT-737, a Mcl-1 sparing Bcl-2 inhibitor, failed to interfere with autophagy signaling. Accumulation of p62 as well as Light Chain 3 (LC3) was observed in cells treated with obatoclax. Autophagy inhibition caused by obatoclax is further augmented in stressful conditions such as starvation. Furthermore, our data demonstrate that inhibition of autophagy caused by obatoclax is independent of the essential pro-autophagy proteins Beclin-1, Atg7 and Atg12.

CONCLUSIONS

The objective of this study was to dissect the contribution of Bcl-2 proteins to autophagy in CRC cells and to explore the potential of Bcl-2 inhibitors for autophagy modulation. Collectively, our data argue for a Beclin-1 independent autophagy inhibition by obatoclax. Based on this study, we recommend the concept of autophagy inhibition as therapeutic strategy for CRC.

24(S)-Hydroxycholesterol induces RIPK1-dependent but MLKL-independent cell death in the absence of caspase-8

24(S)-Hydroxycholesterol (24S-OHC), which is enzymatically produced in the brain, is known to play an important role in maintaining brain cholesterol homeostasis. We have previously reported that 24S-OHC induces a type of non-apoptotic programmed necrosis in neuronal cells expressing little caspase-8. Necroptosis has been characterized as a type of programmed necrosis in which activation of receptor-interacting protein kinase 1 (RIPK1), RIPK3, and mixed lineage kinase domain-like (MLKL) is involved in the signaling pathway. In the present study, we investigated the involvement of these three proteins in 24S-OHC-induced cell death. We found that RIPK1 but neither RIPK3 nor MLKL was expressed in human neuroblastoma SH-SY5Y cells, while all three proteins were expressed in human T lymphoma caspase-8-deficient Jurkat (Jurkat(Cas8-/-)) cells. In Jurkat(Cas8-/-) cells, tumor necrosis factor α (TNFα)-induced cell death was significantly suppressed by treatment with respective inhibitors of RIPK1, RIPK3, and MLKL. In contrast, only RIPK1 inhibitor showed significant suppression of 24S-OHC-induced cell death, and even this was less prominent than was observed in TNFα-induced cell death. In Jurkat(Cas8-/-) cells, knockdown of either RIPK1 or RIPK3 caused moderate but significant suppression of 24S-OHC-induced cell death, but no such effect was observed as a result of knockdown of MLKL. Collectively, these results suggest that, for both SH-SY5Y cells and Jurkat(Cas8-/-) cells, 24S-OHC-induced cell death is dependent on RIPK1 but not on MLKL. We therefore conclude that, in the absence of caspase-8 activity, 24S-OHC induces a necroptosis-like cell death which is RIPK1-dependent but MLKL-independent.

Amorfrutins Are Natural PPARγ Agonists with Potent Anti-inflammatory Properties

Amorfrutins are isoprenoid-substituted benzoic acid derivatives, which were found in Amorpha fruticosa L. (bastard indigo) and in Glycyrrhiza foetida Desf. (licorice). Recently, amorfrutins were shown to be selective activators of the nuclear receptor PPARγ. Here, we investigated the effects and PPARγ-based mechanisms of reducing inflammation in colon cells by treatment with amorfrutins. In TNF-α-stimulated colon cells amorfrutin A (1) reduced significantly the expression and secretion of several inflammation mediators, in part due to interaction with PPARγ. These results support the hypothesis that amorfrutins may have the potential to treat inflammation disorders such as chronic inflammatory bowel diseases.

The molecular relationships between apoptosis, autophagy and necroptosis

Cells are constantly subjected to a vast range of potentially lethal insults, which may activate specific molecular pathways that have evolved to kill the cell. Cell death pathways are defined partly by their morphology, and more specifically by the molecules that regulate and enact them. As these pathways become more thoroughly characterized, interesting molecular links between them have emerged, some still controversial and others hinting at the physiological and pathophysiological roles these death pathways play. We describe specific molecular programs controlling cell death, with a focus on some of the distinct features of the pathways and the molecular links between them.

Necroptosis, in vivo detection in experimental disease models

Over the last decade, our picture of cell death signals involved in experimental disease models totally shifted. Indeed, in addition to apoptosis, multiple forms of regulated necrosis have been associated with an increasing number of pathologies such as ischemia-reperfusion injury in brain, heart and kidney, inflammatory diseases, sepsis, retinal disorders, neurodegenerative diseases and infectious disorders. Especially necroptosis is currently attracting the attention of the scientific community. However, the in vivo identification of ongoing necroptosis in experimental disease conditions remains troublesome, mainly due to the lack of specific biomarkers. Initially, Receptor-Interacting Protein Kinase 1 (RIPK1) and RIPK3 kinase activity were uniquely associated with induction of necroptosis, however recent evidence suggests pleiotropic functions in cell death, inflammation and survival, obscuring a clear picture. In this review, we will present the last methodological advances for in vivo necroptosis identification and discuss past and recent data to provide an update of the so-called "necroptosis-associated pathologies".

Therapeutic exploitation of necroptosis for cancer therapy

Evasion of programmed cell death represents one of the hallmarks of cancers that contributes to tumor initiation, progression and treatment resistance. This calls for novel therapeutic concepts to reactivate cell death programs in human malignancies. Since necroptosis represents a regulated form of necrosis that is under the control of defined signal transduction pathways, it offers molecular targets for rational therapeutic intervention. Indeed, there is mounting evidence showing that many currently used anticancer agents can engage necroptotic signaling pathways and thereby elicit cell death in malignant cells. A better understanding of the signaling networks regulating necroptosis in cancer cells is expected to speed up the development of anticancer drugs for therapeutic exploitation of necroptosis for cancer therapy.

Benzo(a)pyrene-7,8-diol-9,10-epoxide induced p53-independent necrosis via the mitochondria-associated pathway involving Bax and Bak activation

Benzo(a)pyrene-7,8-diol-9,10-epoxide (BPDE) is a highly reactive DNA damage agent and can induce cell death through both p53-independent and -dependent pathways. However, little is known about the molecular mechanisms of p53-independent pathways in BPDE-induced cell death. To understand the p53-independent mechanisms, we have now examined BPDE-induced cytotoxicity in p53-deficient baby mouse kidney (BMK) cells. The results showed that BPDE could induce Bax and Bak activation, cytochrome c release, caspases activation, and necrotic cell death in the BMK cells. Bax and Bak, two key molecules of mitochondrial permeability transition pore, were interdependently activated by BPDE, with Bax and Bak translocation to and Bax/Bak homo-oligomerization in mitochondria, release of cytochrome c was induced. Importantly, cytochrome c release and necrotic cell death were diminished in BMK cells (Bax−/−), BMK cells (Bak−/−), and BMK cells (Bax−/−/Bak−/−). Furthermore, overexpression of Bcl-2 could ameliorate BPDE-induced cytochrome c release and necrosis. Together the findings suggested that BPDE-induced necrosis was modulated by the p53-independent pathway, which was related to the translocation of Bax and Bak to mitochondria, release of cytochrome c, and activation of caspases.

Effects of siRNA on RET/PTC3 junction oncogene in papillary thyroid carcinoma: from molecular and cellular studies to preclinical investigations

RET/PTC3 junction oncogene is typical of radiation-induced childhood papillary thyroid carcinoma (PTC) with a short latency period. Since, RET/PTC3 is only present in the tumour cells, thus represents an interesting target for specific therapy by small interfering RNA (siRNA). Our aim is to demonstrate in vitro and in vivo molecular and cellular effects of siRNA on RET/PTC3 knockdown for therapeutic application.First, we established a novel cell line stably expressing RET/PTC3 junction oncogene, named RP3 which was found tumorigenic in nude mice compared to NIH/3T3 mouse fibroblasts. Among four siRNAs and five concentrations tested against RET/PTC3, an efficient siRNA RET/PTC3 and an appropriate dose (50 nM) were selected which showed significant inhibition (p<0.001) of gene (RT-qPCR) and protein (Western blot) expressions. This siRNA was found efficient in RP3 cells (harbouring RET/PTC3) but non-efficient in BHP10-3 SCmice cell line (harbouring RET/PTC1) showing that a specific siRNA against fusion sequence is required to target the junction oncogene. In vitro siRNA RET/PTC3 showed significant (p<0.001) inhibitory effects on RP3 cell viability (MTT assay) and on invasion/migration (IncuCyte scratch test) with blockage of cell cycle at G0/G1 phase (flow cytometry) and induced apoptosis by caspase-3 and PARP1 cleavage (WB). After intravenous injection in nude mice, respective squalene (SQ) nanoparticles (NPs) of siRNA RET/PTC3 significantly (p<0.001) reduced RP3 tumour growth, oncogene and oncoprotein expressions, induced apoptosis and partially restored differentiation (decrease in Ki67). Hence, our findings highly support the use of siRNA RET/PTC3-SQ NPs as a new promising treatment for patients affected by PTC expressing RET/PTC3.

Regulated necrosis: the expanding network of non-apoptotic cell death pathways

Cell death research was revitalized by the understanding that necrosis can occur in a highly regulated and genetically controlled manner. Although RIPK1 (receptor-interacting protein kinase 1)- and RIPK3-MLKL (mixed lineage kinase domain-like)-mediated necroptosis is the most understood form of regulated necrosis, other examples of this process are emerging, including cell death mechanisms known as parthanatos, oxytosis, ferroptosis, NETosis, pyronecrosis and pyroptosis. Elucidating how these pathways of regulated necrosis are interconnected at the molecular level should enable this process to be therapeutically targeted.

Concerted action of Nrf2-ARE pathway, MRN complex, HMGB1 and inflammatory cytokines - implication in modification of radiation damage

Whole body exposure to low linear energy transfer (LET) ionizing radiations (IRs) damages vital intracellular bio-molecules leading to multiple cellular and tissue injuries as well as pathophysiologies such as inflammation, immunosuppression etc. Nearly 70% of damage is caused indirectly by radiolysis of intracellular water leading to formation of reactive oxygen species (ROS) and free radicals and producing a state of oxidative stress. The damage is also caused by direct ionization of biomolecules. The type of radiation injuries is dependent on the absorbed radiation dose. Sub-lethal IR dose produces more of DNA base damages, whereas higher doses produce more DNA single strand break (SSBs), and double strand breaks (DSBs). The Nrf2-ARE pathway is an important oxidative stress regulating pathway. The DNA DSBs repair regulated by MRN complex, immunomodulation and inflammation regulated by HMGB1 and various types of cytokines are some of the key pathways which interact with each other in a complex manner and modify the radiation response. Because the majority of radiation damage is via oxidative stress, it is essential to gain in depth understanding of the mechanisms of Nrf2-ARE pathway and understand its interactions with MRN complex, HMGB1 and cytokines to increase our understanding on the radiation responses. Such information is of tremendous help in development of medical radiation countermeasures, radioprotective drugs and therapeutics. Till date no approved and safe countermeasure is available for human use. This study reviews the Nrf2-ARE pathway and its crosstalk with MRN-complex, HMGB1 and cytokines (TNF-a, IL-6, IFN-? etc.). An attempt is also made to review the modification of some of these pathways in presence of selected antioxidant radioprotective compounds or herbal extracts.

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Exposure to low linear energy transfer (LET) ionizing radiation (IR) causes intracellular oxidative stress and activate the Nrf2-ARE antioxidant pathway.

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Irradiation also causes inflammation and DNA damage which affect other pathways related to MRN complex and HMGB1 proteins.

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The antioxidant Keap1-Nrf2-ARE pathway most importantly regulates intracellular oxidative stress.

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The interaction of Keap1-Nrf2-ARE pathway with HMGB1 regulated inflammation; MRN complex regulated DNA repair is reviewed.

Membrane-bound TRAIL supplements natural killer cell cytotoxicity against neuroblastoma cells

Neuroblastoma cells have been reported to be resistant to death induced by soluble, recombinant forms of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) (CD253/TNFSF10) because of low or absent expression of caspase-8 and/or TRAIL-receptor 2 (TRAIL-R2/DR5/CD262/TNFRSF10b). However, their sensitivity to membrane-bound TRAIL on natural killer (NK) cells is not known. Comparing microarray gene expression and response to NK cell-mediated cytotoxicity, we observed a correlation between TRAIL-R2 expression and the sensitivity of 14 neuroblastoma cell lines to the cytotoxicity of NK cells activated with interleukin (IL)-2 plus IL-15. Even though most NK cytotoxicity was dependent upon perforin, the cytotoxicity was supplemented by TRAIL in 14 of 17 (82%) neuroblastoma cell lines as demonstrated using an anti-TRAIL neutralizing antibody. Similarly, a recently developed NK cell expansion system employing IL-2 plus lethally irradiated K562 feeder cells constitutively expressing membrane-bound IL-21 (K562 clone 9.mbIL21) resulted in activated NK cells derived from normal healthy donors and neuroblastoma patients that also utilized TRAIL to supplement cytotoxicity. Exogenous interferon-γ upregulated expression of caspase-8 in 3 of 4 neuroblastoma cell lines and increased the contribution of TRAIL to NK cytotoxicity against 2 of the 3 lines; however, relatively little inhibition of cytotoxicity was observed when activated NK cells were treated with an anti-interferon-γ neutralizing antibody. Constraining the binding of anti-TRAIL neutralizing antibody to membrane-bound TRAIL but not soluble TRAIL indicated that membrane-bound TRAIL alone was responsible for essentially all of the supplemental cytotoxicity. Together, these findings support a role for membrane-bound TRAIL in the cytotoxicity of NK cells against neuroblastoma cells.

The mechanism of necroptosis in normal and cancer cells

Programmed cell death is a basic cellular process that is critical to maintain tissue homeostasis. Besides apoptosis, necroptosis has more recently been discovered as another form of regulated cell death. Necroptosis plays a pivotal role during normal development and has also been implicated in the pathogenesis of a variety of human diseases. The control of necroptosis by defined signal transduction pathways offers the opportunity to target this cellular process for therapeutic purposes. For example, in cancer necroptosis is often impaired during tumorigenesis and can be engaged by targeted pharmacological approaches. Further insights into the signaling networks involved in the regulation of necroptosis will likely have important implications for the exploitation of this form of programmed cell death for the diagnosis or treatment of many diseases.

Tumor necrosis factor-like weak inducer of apoptosis and its receptor fibroblast growth factor-inducible 14 are expressed in urticarial vasculitis

Tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK), a member of the TNF family, has been implicated as a pro-inflammatory cytokine in many types of autoimmune and infectious diseases. However, information about TWEAK in dermatological diseases is limited. To date, no studies have investigated the roles of TWEAK in patients with urticarial vasculitis (UV). This study aimed to assess serum TWEAK levels, together with TWEAK and fibroblast growth factor-inducible 14 (Fn14) expressions of skin lesions in patients with UV. Serum TWEAK levels in patients with UV, together with patients with cutaneous leukocytoclastic angiitis (CLA) and healthy controls were detected by enzyme-linked immunosorbent assay; TWEAK and Fn14 expressions of skin lesions were analyzed by immunohistochemistry. Results showed that TWEAK and Fn14 were abundantly expressed in the dermal vessel wall of lesional skin in patients with UV but not healthy controls. Serum TWEAK levels in the acute stage in patients with UV were significantly higher than those in the convalescent stage and healthy controls. Serum TWEAK levels were elevated significantly in patients with CLA compared with those in healthy controls. Our previous study indicated that TWEAK may be an important mediator for the development of vascular inflammation in skin. In addition, we also found that TWEAK blockade substantially reduced vascular damage and perivascular leukocyte infiltrates in lipopolysaccharide-induced cutaneous vasculitis. Our study shows that TWEAK may be associated with the pathogenesis of UV; it is therefore suggested that TWEAK may be a potential therapeutic target for UV and other types of cutaneous vasculitis.

Functional expression of TWEAK and the receptor Fn14 in human malignant ovarian tumors: possible implication for ovarian tumor intervention

The aim of this current study was to investigate the expression of the tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) and its receptor fibroblast growth factor-inducible 14 (Fn14) in human malignant ovarian tumors, and test TWEAK’s potential role on tumor progression in cell models in-vitro. Using immunohistochemistry (IHC), we found that TWEAK and its receptor Fn14 were expressed in human malignant ovarian tumors, but not in normal ovarian tissues or in borderline/benign epithelial ovarian tumors. High levels of TWEAK expression was detected in the majority of malignant tumors (36 out of 41, 87.80%). Similarly, 35 out of 41 (85.37%) malignant ovarian tumors were Fn14 positive. In these malignant ovarian tumors, however, TWEAK/Fn14 expression was not corrected with patients’ clinical subtype/stages or pathological features. In vitro, we demonstrated that TWEAK only inhibited ovarian cancer HO-8910PM cell proliferation in combination with tumor necrosis factor-α (TNF-α), whereas either TWEAK or TNF-α alone didn’t affect HO-8910PM cell growth. TWEAK promoted TNF-α production in cultured THP-1 macrophages. Meanwhile, conditioned media from TWEAK-activated macrophages inhibited cultured HO-8910PM cell proliferation and invasion. Further, TWEAK increased monocyte chemoattractant protein-1 (MCP-1) production in cultured HO-8910PM cells to possibly recruit macrophages. Our results suggest that TWEAK/Fn14, by activating macrophages, could be ovarian tumor suppressors. The unique expression of TWEAK/Fn14 in malignant tumors indicates that it might be detected as a malignant ovarian tumor marker.

Restoration of ASC expression sensitizes colorectal cancer cells to genotoxic stress-induced caspase-independent cell death

Apoptosis-associated speck-like protein containing a caspase recruitment domain (ASC), an essential component of the inflammasome complex, is frequently silenced by epigenetic methylation in many tumor cells. Here, we demonstrate that restoration of ASC expression in human colorectal cancer DLD-1 cells, in which ASC is silenced by aberrant methylation, potentiated cell death mediated by DNA damaging agent. Contrarily, ASC knockdown in HT-29 cells rendered cells less susceptible to etoposide toxicity. The increased susceptibility of ASC-expressing DLD-1 cells to genotoxic stress was independent of inflammasome or caspase activation, but partially dependent on mitochondrial ROS production and JNK activation. Thus, our data suggest that ASC expression in cancer cells is an important factor in determining their susceptibility to chemotherapy.

TWEAK signals through JAK-STAT to induce tumor cell apoptosis

The TWEAK receptor Fn14 (TNFRSF12), a member of the TNF Receptor superfamily, can mediate many processes, including apoptosis. Fn14 agonists have therefore been the subject of interest as potential cancer therapeutics. In cell culture experiments, interferon gamma (IFNγ) is typically required for induction of apoptotic activity by either TWEAK or Fn14 agonistic antibodies in most cell lines. We have investigated the mechanism of IFNγ signaling and the role of JAK-STAT signaling in TWEAK/Fn14-mediated tumor cell killing. We found that IFNγ-mediated enhancement of tumor cell killing is JAK-STAT dependent, as JAK inhibitors block IFNγ-dependent TWEAK induced apoptosis. Exposure of tumor cells to IFNγ results in an increase in Fn14 expression on the cell surface, which may be a mechanism by which IFNγ induces sensitivity to TWEAK. In a reciprocal fashion, we observed that IFNγ receptor levels increase in response to TWEAK treatment in WiDr cells. Significantly, we found that TWEAK alone can induce STAT1 phosphorylation in WiDr tumor cells. Moreover, TWEAK induction of tumor cell apoptosis in WiDr cells in the absence of IFNγ is mediated by the JAK-STAT pathway. Correspondingly, we show that treatment of tumor bearing mice with mBIIB036, an Fn14 agonistic antibody, results in STAT1 phosphorylation in the tumors. Notably, the level of STAT1 phosphorylation appears to correlate with the degree of tumor growth inhibition by BIIB036 in vivo. Additionally, in WiDr cells, TWEAK induces a soluble factor, which we have identified as IFNβ, capable of independently inducing STAT1 phosphorylation when transferred to naïve cells. Finally, either IFNα or IFNβ can partially substitute for IFNγ in sensitizing tumor cells to Fn14 agonists. In summary, we show that TWEAK/Fn14 can signal through the JAK-STAT pathway to induce IFNβ, and that the ability of TWEAK to induce tumor cell apoptosis is mediated by JAK-STAT signaling. We also demonstrate that IFNγ enhancement of TWEAK/FN14-mediated tumor cell death is JAK-dependent and may occur by IFNγ-dependent upregulation of Fn14 on tumor cells. These findings may have implications for the appropriately targeted clinical development of Fn14 agonists as anti-cancer therapy.

Alpha-fetoprotein acts as a novel signal molecule and mediates transcription of Fn14 in human hepatocellular carcinoma

BACKGROUND & AIMS

The function of cytoplasmic AFP as a regulatory factor in the growth of tumor cells has been well defined. However, its precise mechanism of action and its clinical significance remain to be worked out.

METHODS

Specimens from HCC patients were analyzed by using immunohistochemistry, co-immunoprecipitation (CoIP), and chromatin immunoprecipitation (ChIP) assays to evaluate the role of AFP in RAR signaling-mediated carcinogenesis. Quantitative real-time reverse transcription PCR, Western blotting, confocal microscopy, CoIP, GST pull-down, siRNA, gene transfection, and ChIP assays were also used for analysis of cell lines.

RESULTS

RAR is able to interact with cytoplasmic AFP and binds to the element of the regulatory region of the Fn14 gene in the neoplastic tissue of HCC patients. An assay of hepatocyte cell lines of differing AFP expression showed that cytoplasmic AFP is able to block ATRA-induced nuclear translocation of RAR and expression of the Fn14 gene. Knockdown of AFP in siRNA-transfected HepG2 and Bel7402 cells led to greater binding of RAR to its response element. The expression of the Fn14 gene was therefore up regulated as reflected by increases in mRNA and protein levels. Conversely, transfection of HLE and L02 cells (AFP negative) with the afp gene resulted in apparent reduction of RAR binding to DNA and Fn14 protein.

CONCLUSIONS

Demonstration of the involvement of cytoplasmic AFP in RAR-mediated expression of the Fn14 gene strongly indicates AFP plays a signal molecule-like role in the regulation of hepatocellular carcinoma growth.

The anti-Fn14 antibody BIIB036 inhibits tumor growth in xenografts and patient derived primary tumor models and enhances efficacy of chemotherapeutic agents in multiple xenograft models

Agonistic antibodies targeting Fn14, the receptor for TWEAK, have demonstrated anti-tumor activity in xenograft models. Herein, we further explore the therapeutic potential of the humanized anti-Fn14 agonistic antibody, BIIB036, as a single agent and in combination with standard of care cancer therapeutics. Pharmacokinetic studies of BIIB036 in tumor-bearing mice revealed a half-life of approximately three days suggesting twice a week dosing would be necessary to maintain efficacy. However, in multiple xenograft models, BIIB036 treatment resulted in extended tumor growth inhibition up to 40-50 d following cessation of dosing, suggesting that frequent administration of BIIB036 may not be necessary to maintain prolonged anti-tumor activity. Subsequent xenograft studies revealed that maximal efficacy was achieved with BIIB036 dosing once every two weeks, by either intraperitoneal or subcutaneous administration. Xenograft tumors that were initially treated with BIBI036 and then re-grew up to 1000 mm³ following cessation of the first cycle of treatment remained sensitive to a second cycle of treatment. BIIB036 was also evaluated in patient derived primary colon tumor models, where efficacy compared favorably with a standard of care agent. Lastly, BIIB036 enhanced the efficacy of several standard of care chemotherapeutics, including paclitaxel in MDA-MBA-231 breast tumor xenografts, paclitaxel or carboplatin in HOP62 non-small cell lung xenografts, and 5-FU in NCI-N87 gastric xenografts, with no overlapping toxicities. These studies thus establish BIIB036 as a promising therapeutic agent with durable anti-tumor activity in human xenografts as well as patient derived primary tumor models, and enhanced activity and tolerability in combination with standard of care chemotherapeutics. Taken together, the data presented herein suggest that BIIB036 warrants evaluation in the clinic.

TWEAK affects keratinocyte G2/M growth arrest and induces apoptosis through the translocation of the AIF protein to the nucleus

The soluble TNF-like weak inducer of apoptosis (TWEAK, TNFSF12) binds to the fibroblast growth factor-inducible 14 receptor (FN14, TNFRSF12A) on the cell membrane and induces multiple biological responses, such as proliferation, migration, differentiation, angiogenesis and apoptosis. Previous reports show that TWEAK, which does not contain a death domain in its cytoplasmic tail, induces the apoptosis of tumor cell lines through the induction of TNFα secretion. TWEAK induces apoptosis in human keratinocytes. Our experiments clearly demonstrate that TWEAK does not induce the secretion of TNFα or TRAIL proteins. The use of specific inhibitors and the absence of procaspase-3 cleavage suggest that the apoptosis of keratinocytes follows a caspase- and cathepsin B-independent pathway. Further investigation showed that TWEAK induces a decrease in the mitochondrial membrane potential of keratinocytes. Confocal microscopy showed that TWEAK induces the cleavage and the translocation of apoptosis inducing factor (AIF) from the mitochondria to the nucleus, thus initiating caspase-independent apoptosis. Moreover, TWEAK induces FOXO3 and GADD45 expression, cdc2 phosphorylation and cdc2 and cyclinB1 degradation, resulting in the arrest of cell growth at the G2/M phase. Finally, we report that TWEAK and FN14 are normally expressed in the basal layer of the physiological epidermis and are greatly enhanced in benign (psoriasis) and malignant (squamous cell carcinoma) skin pathologies that are characterized by an inflammatory component. TWEAK might play an essential role in skin homeostasis and pathology.

Many stimuli pull the necrotic trigger, an overview

The lab of Jürg Tschopp was the first to report on the crucial role of receptor-interacting protein kinase 1 (RIPK1) in caspase-independent cell death. Because of this pioneer finding, regulated necrosis and in particular RIPK1/RIPK3 kinase-mediated necrosis, referred to as necroptosis, has become an intensively studied form of regulated cell death. Although necrosis was identified initially as a backup cell death program when apoptosis is blocked, it is now recognized as a cellular defense mechanism against viral infections and as being critically involved in ischemia-reperfusion damage. The observation that RIPK3 ablation rescues embryonic lethality in mice deficient in caspase-8 or Fas-associated-protein-via-a-death-domain demonstrates the crucial role of this apoptotic platform in the negative control of necroptosis during development. Here, we review and discuss commonalities and differences of the increasing list of inducers of regulated necrosis ranging from cytokines, pathogen-associated molecular patterns, to several forms of physicochemical cellular stress. Since the discovery of the crucial role of RIPK1 and RIPK3 in necroptosis, these kinases have become potential therapeutic targets. The availability of new pharmacological inhibitors and transgenic models will allow us to further document the important role of this form of cell death in degenerative, inflammatory and infectious diseases.

Studies of binding of tumor necrosis factor (TNF)-like weak inducer of apoptosis (TWEAK) to fibroblast growth factor inducible 14 (Fn14)

To perform highly sensitive cellular binding studies with TNF-like weak inducer of apoptosis (TWEAK), we developed a bioluminescent variant of soluble TWEAK (GpL-FLAG-TNC-TWEAK) by fusing it genetically to the C terminus of the luciferase of Gaussia princeps (GpL). Equilibrium binding studies on human (HT1080 and HT29) and murine (Renca and B16) cell lines at 37 °C revealed high affinities of human TWEAK from 53 to 112 pm. The dissociation rate constant of the TWEAK-Fn14 interaction was between 0.48×10(-3) s(-1) (HT29) and 0.58×10(-3) s(-1) (HT1080) for the human molecules, and the association rate constant obtained was 3.3×10(6) m(-1) s(-1) for both cell lines. It has been shown previously that oligomerization of soluble TWEAK trimers results in enhanced Fn14-mediated activation of the classical NFκB pathway. Binding studies with GpL-FLAG-TNC-TWEAK trimers oligomerized by help of a FLAG tag-specific antibody gave no evidence for a major increase in Fn14 occupancy by oligomerized ligand despite strongly enhanced induction of the NFκB target IL8. Thus, aggregated complexes of soluble TWEAK and Fn14 have a higher intrinsic activity to stimulate the classical NFκB pathway and qualitatively differ from isolated trimeric TWEAK-Fn14 complexes. Furthermore, determination of IL8 induction as a function of occupied activated receptors revealed that the intrinsic capability of TNFR1 to stimulate the classical NFκB pathway and IL8 production was ∼100-fold higher than Fn14. Thus, although ∼25 activated TNFR1 trimers were sufficient to trigger half-maximal IL8 production, more than 2500 cell-bound oligomerized TWEAK trimers were required to elicit a similar response.

Inhibition of TNF-induced IL-6 by the TWEAK-Fn14 interaction in rheumatoid arthritis fibroblast like synoviocytes

OBJECTIVES

TNF-like weak inducer of apoptosis (TWEAK), a member of the TNF superfamily, has been shown to increase cytokine production by rheumatoid arthritis (RA) fibroblast-like synoviocytes (FLS). In this study, we determined the effect of interaction between TWEAK and its receptor fibroblast growth factor-inducible-14 (Fn14) on cytokine expression in RAFLS.

METHODS

RAFLS were obtained from surgical synovial specimens and used at passage 5-10. Cytokine protein and mRNA expression were measured with ELISA and real time-PCR, respectively. Apoptotic cells were detected by TUNEL assay. RelB activation was detected by Western blot analysis.

RESULTS

TWEAK inhibited IL-6 production from total synovial cells from RA. TWEAK weakly induced FLS IL-6 and IL-8, but in contrast TWEAK dose-dependently inhibited IL-6 and IL-8 production by TNFα-activated FLS. TWEAK did not induce apoptosis in FLS but inhibited proliferation of TNFα-activated FLS. TWEAK induced RelB activation and suppressed IL-6 mRNA expression in TNFα-activated FLS and both of these phenomenon were abolished by inhibition of new protein synthesis with cycloheximide.

CONCLUSIONS

TWEAK has a previously unsuspected inhibitory effect on cytokine production by TNFα-activated RAFLS. This observation suggests that the effects of TWEAK on cytokine expression varies with the pro-inflammatory context, and that in TNFα-activated states such as RA TWEAK may have a net inhibitory effect.

Development of an Fn14 agonistic antibody as an anti-tumor agent

TWEAK, a TNF family ligand with pleiotropic cellular functions, was originally described as capable of inducing tumor cell death in vitro. TWEAK functions by binding its receptor, Fn14, which is up-regulated on many human solid tumors. Herein, we show that intratumoral administration of TWEAK, delivered either by an adenoviral vector or in an immunoglobulin Fc-fusion form, results in significant inhibition of tumor growth in a breast xenograft model. To exploit the TWEAK-Fn14 pathway as a therapeutic target in oncology, we developed an anti-Fn14 agonistic antibody, BIIB036. Studies described herein show that BIIB036 binds specifically to Fn14 but not other members of the TNF receptor family, induces Fn14 signaling, and promotes tumor cell apoptosis in vitro. In vivo, BIIB036 effectively inhibits growth of tumors in multiple xenograft models, including colon (WiDr), breast (MDA-MB-231), and gastric (NCI-N87) tumors, regardless of tumor cell growth inhibition response observed to BIIB036 in vitro. The anti-tumor activity in these cell lines is not TNF-dependent. Increasing the antigen-binding valency of BIB036 significantly enhances its anti-tumor effect, suggesting the contribution of higher order cross-linking of the Fn14 receptor. Full Fc effector function is required for maximal activity of BIIB036 in vivo, likely due to the cross-linking effect and/or ADCC mediated tumor killing activity. Taken together, the anti-tumor properties of BIIB036 validate Fn14 as a promising target in oncology and demonstrate its potential therapeutic utility in multiple solid tumor indications.

Death ligand TRAIL, secreted by CD1a+ and CD14+ cells in blister fluids, is involved in killing keratinocytes in toxic epidermal necrolysis

Toxic epidermal necrolysis (TEN) is characterized by an acute detachment and destruction of keratinocytes, affecting large areas of the skin. It is often related to adverse drug reactions. Previous studies have shown that effector CD8+ T cells, which accumulate in the blister fluid, are functionally cytotoxic and act through a classical perforin/granzyme B pathway. It has recently been shown that these cytotoxic T cells also secrete granulysin peptide, which is lethal to keratinocytes. These cytotoxic T cells exert their killer activity against autologous keratinocytes in the presence of the drug. However, they are unlikely to be the only effectors of TEN. We therefore searched for soluble death factors in the blister fluids that might kill keratinocytes. We found that the amounts of interferon-γ, TRAIL and TNF-α proteins were significantly greater in TEN blister fluids than in all controls (normal sera, TEN sera, burns and Eosinophilic pustular folliculitis blister fluids) and TNF-like weak inducer of apoptosis (TWEAK) amounts are also greater in all controls except burns. We showed that these proteins acted in synergy to induce the death of keratinocytes in vitro. We also found that TRAIL and TWEAK were secreted by CD1a+ and CD14+ cells present in the blister fluids. Thus, in addition to MHC class I-restricted cytotoxic T lymphocytes (CTLs), which lyse keratinocytes, ligands secreted by non-lymphoid cells capable of inducing keratinocyte death in an MHC class I-independent manner, also seem to be present in the blister fluids of patients with TEN.

zVAD-induced autophagic cell death requires c-Src-dependent ERK and JNK activation and reactive oxygen species generation

The treatment of L929 fibrosarcoma cells with zVAD has been shown to induce necroptosis. However, whether autophagy is involved or not in this event remains controversial. In this study, we re-examined the role of autophagy in zVAD-induced cell death in L929 cells and further elucidated the signaling pathways triggered by caspase inhibition and contributing to autophagic death. First, we found that zVAD can stimulate LC3-II formation, autophagosome and autolysosome formation, and ROS accumulation. Antioxidants, beclin 1 or Atg5 silencing, and class III PtdIns3K inhibitors all effectively blocked ROS production and cell death, suggesting ROS accumulation downstream of autophagy contributes to cell necrosis. zVAD also stimulated PARP activation, and the PARP inhibitor DPQ can reduce zVAD-induced cell death, but did not affect ROS production, suggesting the increased ROS leads to PARP activation and cell death. Notably, our data also indicated the involvement of Src-dependent JNK and ERK in zVAD-induced ROS production and autophagic death. We found caspase 8 is associated with c-Src at the resting state, and upon zVAD treatment this association was decreased and accompanied by c-Src activation. In conclusion, we confirm the autophagic death in zVAD-treated L929 cells, and define a new molecular pathway in which Src-dependent ERK and JNK activation can link a signal from caspase inhibition to autophagy, which in turn induce ROS production and PARP activation, eventually leading to necroptosis. Thus, in addition to initiating proteolytic activity for cell apoptosis, inactivated caspase 8 also functions as a signaling molecule for autophagic death.

Nuclear factor of activated T cells (NFAT) signaling regulates PTEN expression and intestinal cell differentiation

Previously we demonstrated that overexpression of PTEN enhanced intestinal cell differentiation. In this study we provide evidence showing that NFATc1 and NFATc4 are regulators of PTEN expression. Importantly, our results suggest that NFATc1 and NFATc4 regulation of intestinal cell differentiation may be through PTEN regulation.

The nuclear factor of activated T cell (NFAT) proteins are a family of transcription factors (NFATc1–c4) involved in the regulation of cell differentiation and adaptation. Previously we demonstrated that inhibition of phosphatidylinositol 3-kinase or overexpression of PTEN enhanced intestinal cell differentiation. Here we show that treatment of intestinal-derived cells with the differentiating agent sodium butyrate (NaBT) increased PTEN expression, NFAT binding activity, and NFAT mRNA expression, whereas pretreatment with the NFAT signaling inhibitor cyclosporine A (CsA) blocked NaBT-mediated PTEN induction. Moreover, knockdown of NFATc1 or NFATc4, but not NFATc2 or NFATc3, attenuated NaBT-induced PTEN expression. Knockdown of NFATc1 decreased PTEN expression and increased the phosphorylation levels of Akt and downstream targets Foxo1 and GSK-3α/β. Furthermore, overexpression of NFATc1 or the NFATc4 active mutant increased PTEN and p27^kip1 expression and decreased Akt phosphorylation. In addition, pretreatment with CsA blocked NaBT-mediated induction of intestinal alkaline phosphatase (IAP) activity and villin and p27^kip1 expression; knockdown of either NFATc1 or NFATc4 attenuated NaBT-induced IAP activity. We provide evidence showing that NFATc1 and NFATc4 are regulators of PTEN expression. Importantly, our results suggest that NFATc1 and NFATc4 regulation of intestinal cell differentiation may be through PTEN regulation.

TNF-alpha-induced mitochondrial alterations in human T cells requires FADD and caspase-8 activation but not RIP and caspase-3 activation

Although much is known about how TNF-alpha induces apoptosis in the presence of inhibitors of protein synthesis, little is known about how it induces apoptosis without these inhibitors. In this report we investigated temporal sequence of events induced by TNF-alpha in the absence of protein synthesis. Regardless of whether we measured the effects by plasma membrane phosphotidylserine accumulation, by DNA strand breaks, or activation of caspases, significant changes were observed only between 12-24 h of TNF-alpha treatment. One of the earliest changes observed after TNF-alpha treatment was mitochondrial swelling at 10 min; followed by cytochrome c and Smac release at 10-30 min, and then heterochromatin clumping occurred at 60 min. While genetic deletion of receptor-interaction protein (RIP) had no effect on TNF-alpha-induced mitochondrial damage, deletion of Fas-associated death domain (FADD) abolished the TNF-induced mitochondrial swelling. Since pan-caspase inhibitor z-VAD-fmk abolished the TNF-alpha-induced mitochondrial changes, z-DEVD-fmk, an inhibitor of caspase-3 had no effect, suggesting that TNF-alpha-induced mitochondrial changes or cytochrome c and Smac release requires caspase-8 but not caspase-3 activation. Overall, our results indicated that mitochondrial changes are early events in TNF-alpha-induced apoptosis and that these mitochondrial changes require recruitment of FADD and caspase-8 activation, but not caspase-3 activation or RIP recruitment.

Combating apoptosis and multidrug resistant cancers by targeting lysosomes

Acquired therapy resistance is one of the prime obstacles for successful cancer treatment. Partial resistance is often acquired already during an early face of tumor development when genetic changes causing defects in classical caspase-dependent apoptosis pathway provide transformed cells with a growth advantage by protecting them against various apoptosis inducing stimuli including transforming oncogenes themselves and host immune system. Apoptosis defective cells are further selected during tumor progression and finally by apoptosis inducing treatments. Another form of resistance, multidrug resistance, arises during cancer treatment when cancer cells with effective efflux of cytotoxic agents escape the therapy. Remarkably, induction of lysosomal membrane permeabilization has recently emerged as an effective way to kill apoptosis resistant cancer cells and some lysosome targeting drugs can also re-sensitize multidrug resistant cells to classical chemotherapy. In this review, we highlight recent data on lysosomal cell death pathways and their implications for the future treatment of apoptosis defective and multidrug resistant aggressive tumors.

TWEAK/Fn14 promotes apoptosis of human endometrial cancer cells via caspase pathway

Tumor necrosis factor-like weak inducer of apoptosis (TWEAK) and its receptor fibroblast growth factor-inducible immediate-early response protein 14 (Fn14) have been detected in several human tumors, and demonstrated to regulate multiple cellular responses, including proliferation, survival, migration, apoptosis and differentiation, suggesting roles in cancer. The objective of this study was to clarify the role of TWEAK/Fn14 in the development of human endometrial cancer. We found that TWEAK gene expression was down-regulated and Fn14 gene expression was up-regulated in human endometrial cancer specimens compared with that in normal endometrial specimens; TWEAK acting on Fn14 decreased cell viability by inducing apoptosis through caspase pathways in endometrial cancer cells. Our results suggest that Fn14 expression is high in endometrial cancers whereas local produced TWEAK may be low. TWEAK/Fn14 pathway activation may promote cancer cell apoptosis, which provides a new therapeutic target for human endometrial cancer treatment.

Metronomic PDT and cell death pathways

The term "metronomic" was recently introduced to describe continuous low-dose administration of chemotherapeutics following the discovery that this causes minimal side effects (Hanahan et al. 2000, J Clin Invest, 105(8), 1045-1047; Bisland et al. 2004, Photochem Photobiol, 80, 22-30). Metronomic dosing in PDT is proposed by analogy and the rationale is as a means to improve the tumor-specific response through cell death by apoptosis. We investigated the molecular mechanisms associated with apoptosis following ALA-PDT treatment in two brain glioma cell lines, namely U87 (human) and CNS-1 (rat) cells. We used the high energy of light at a short time (acute PDT) and the low energy of light at a long time of exposure (metronomic PDT) to treat both cell lines. To identify potential cell death pathways associated with metronomic PDT, microarray analysis of gene expression was conducted on RNA from glioblastoma cells with metronomic ALA-PDT. The apoptosis mechanism for metronomic ALA-PDT occurred via the inhibition of LTbetaR and the transcription factor NF-kappaB. This inhibition was ALA concentration dependent.