Molecular definitions of cell death subroutines: recommendations of the Nomenclature Committee on Cell Death 2012

Multimodal immunogenic cancer cell death as a consequence of anticancer cytotoxic treatments

Apoptotic cell death generally characterized by a morphologically homogenous entity has been considered to be essentially non-immunogenic. However, apoptotic cancer cell death, also known as type 1 programmed cell death (PCD), was recently found to be immunogenic after treatment with several chemotherapeutic agents and oncolytic viruses through the emission of various danger-associated molecular patterns (DAMPs). Extensive studies have revealed that two different types of immunogenic cell death (ICD) inducers, recently classified by their distinct actions in endoplasmic reticulum (ER) stress, can reinitiate immune responses suppressed by the tumor microenvironment. Indeed, recent clinical studies have shown that several immunotherapeutic modalities including therapeutic cancer vaccines and oncolytic viruses, but not conventional chemotherapies, culminate in beneficial outcomes, probably because of their different mechanisms of ICD induction. Furthermore, interests in PCD of cancer cells have shifted from its classical form to novel forms involving autophagic cell death (ACD), programmed necrotic cell death (necroptosis), and pyroptosis, some of which entail immunogenicity after anticancer treatments. In this review, we provide a brief outline of the well-characterized DAMPs such as calreticulin (CRT) exposure, high-mobility group protein B1 (HMGB1), and adenosine triphosphate (ATP) release, which are induced by the morphologically distinct types of cell death. In the latter part, our review focuses on how emerging oncolytic viruses induce different forms of cell death and the combinations of oncolytic virotherapies with further immunomodulation by cyclophosphamide and other immunotherapeutic modalities foster dendritic cell (DC)-mediated induction of antitumor immunity. Accordingly, it is increasingly important to fully understand how and which ICD inducers cause multimodal ICD, which should aid the design of reasonably multifaceted anticancer modalities to maximize ICD-triggered antitumor immunity and eliminate residual or metastasized tumors while sparing autoimmune diseases.

Rapamycin regulates biochemical metabolites

The mammalian target of rapamycin (mTOR) kinase is a master regulator of protein synthesis that couples nutrient sensing to cell growth, and deregulation of this pathway is associated with tumorigenesis. p53, and its less investigated family member p73, have been shown to interact closely with mTOR pathways through the transcriptional regulation of different target genes. To investigate the metabolic changes that occur upon inhibition of the mTOR pathway and the role of p73 in this response primary mouse embryonic fibroblast from control and TAp73(-/-) were treated with the macrocyclic lactone rapamycin. Extensive gas chromatography/mass spectrometry (GC/MS) and liquid chromatography/mass spectrometry (LC/MS/MS) analysis were used to obtain a rapamycin-dependent global metabolome profile from control or TAp73(-/-) cells. In total 289 metabolites involved in selective pathways were identified; 39 biochemical metabolites were found to be significantly altered, many of which are known to be associated with the cellular stress response.

Genistein promotes cell death of ethanol-stressed HeLa cells through the continuation of apoptosis or secondary necrosis

Background

Apoptosis is a major target and treatment effect of multiple chemotherapeutical agents in cancer. A soybean isoflavone, genistein, is a well-studied chemopreventive agent and has been reported to potentiate the anticancer effect of some chemotherapeutics. However, its mechanistic basis of chemo-enhancement effect remains to be fully elucidated.

Methods

Apoptotic features of low concentration stressed cancer cells were studied by microscopic method, western blot, immunostaining and annexin V/PI assay. Genistein’s effects on unstressed cells and recovering cells were investigated using MTT cell viability assay and LDH cytotoxicity assay. Quantitative real-time PCR was employed to analyze the possible gene targets involved in the recovery and genistein’s effect.

Results

Low-concentration ethanol stressed cancer cells showed apoptotic features and could recover after stress removal. In stressed cells, genistein at sub-toxic dosage promoted the cell death. Quantitative real-time PCR revealed the up-regulation of anti-apoptotic genes MDM2 and XIAP during the recovery process in HeLa cells, and genistein treatment suppressed their expression. The application of genistein, MDM2 inhibitor and XIAP inhibitor to the recovering HeLa cells caused persistent caspase activity and enhanced cell death. Flow cytometry study indicated that genistein treatment could lead to persistent phosphatidylserine (PS) externalization and necrotic events in the recovering HeLa cells. Caspase activity inhibition shifted the major effect of genistein to necrosis.

Conclusions

These results suggested two possible mechanisms through which genistein promoted cell death in stressed cancer cells. Genistein could maintain the existing apoptotic signal to enhance apoptotic cell death. It could also disrupt the recovering process in caspase-independent manner, which lead to necrotic events. These effects may be related to the enhanced antitumor effect of chemotherapeutic drugs when they were combined with genistein.

Curcumin induces apoptosis in gallbladder carcinoma cell line GBC-SD cells

Background

Gallbladder carcinoma is a malignant tumor with a very low 5-year survival rate because of the difficulty with its early diagnosis and the very poor prognosis of the advanced cancer state. The aims of this study were to determine whether curcumin could induce the apoptosis of a gallbladder carcinoma cell line, GBC-SD, and to clarify its related mechanism.

Methods

First, the anti-proliferative activities of curcumin-treated and untreated GBC-SD cells were determined using the MTT and colony formation assays. Then, the early apoptosis of cells was detected by the annexin V/propidium iodide double-staining assay and Hoechst 33342 staining assay. Detection of mitochondrial membrane potential was used to validate the ability of curcumin on inducing apoptosis in GBC-SD cells. Cell cycle changes were detected by flow cytometric analysis. Finally, the expressions of the apoptosis-related proteins or genes caspase-3, PARP, Bcl-2, and Bax were analyzed by western blot and quantitative real time PCR assay. Statistical analyses were performed using the Student’s t-test for comparison of the results obtained from cells with or without curcumin treatment.

Results

The MTT assay revealed that curcumin had induced a dose- and a time-dependent decrease in cell viability. Colony counting indicated that curcumin had induced a dose-dependent decrease in the colony formation ability in GBC-SD cells. Cells treated with curcumin were arrested at the S phase, according to the flow cytometric analysis. A significant induction of both the early and late phases of apoptosis was shown by the annexin V-FITC and PI staining. Morphological changes in apoptotic cells were also found by the Hoechst 33342 staining. After treatment with curcumin fluorescence shifted from red to green as ΔΨm decreased. Furthermore, western blot and quantitative real time PCR assays demonstrated that the curcumin induced apoptosis in GBC-SD cells by regulating the ratio of Bcl-2/Bax and activating the expression of cleaved caspase-3.

Conclusions

Taken together, the results indicate that curcumin may be a potential agent for the treatment of gallbladder cancer.

Macrophages and recently identified forms of cell death

Recent advances in cell death biology have uncovered an ever increasing range of cell death forms. Macrophages have a bidirectional relationship with cell death that modulates the immune response. Thus, macrophages engulf apoptotic cells and secrete cytokines that may promote cell death in parenchymal cells. Furthermore, the presence of apoptotic or necrotic dead cells in the microenvironment elicits differential macrophage responses. Apoptotic cells elicit anti-inflammatory responses in macrophages. By contrast macrophages may undergo a proinflammatory form of cell death (pyroptosis) in response to damage-associated molecular patterns (DAMPs) released from necrotic cells and also in response to pathogen-associated molecular patterns (PAMPs). Pyroptosis is a recently identified form of cell death that occurs predominantly in subsets of inflammatory macrophages and is associated to the release of interleukin-1β (IL-1β) and IL-18. Deregulation of these processes may result in disease. Thus, failure of macrophages to engulf apoptotic cells may be a source of autoantigens in autoimmune diseases, excessive macrophage release of proapoptotic factors or sterile pyroptosis may contribute to tissue injury and failure of pathogen-induced pyroptosis may contribute to pathogen survival. Ongoing research is exploring the therapeutic opportunities resulting this new knowledge.

Cisplatin resistance associated with PARP hyperactivation

Non-small cell lung carcinoma patients are frequently treated with cisplatin (CDDP), most often yielding temporary clinical responses. Here, we show that PARP1 is highly expressed and constitutively hyperactivated in a majority of human CDDP-resistant cancer cells of distinct histologic origin. Cells manifesting elevated intracellular levels of poly(ADP-ribosyl)ated proteins (PAR(high)) responded to pharmacologic PARP inhibitors as well as to PARP1-targeting siRNAs by initiating a DNA damage response that translated into cell death following the activation of the intrinsic pathway of apoptosis. Moreover, PARP1-overexpressing tumor cells and xenografts displayed elevated levels of PAR, which predicted the response to PARP inhibitors in vitro and in vivo more accurately than PARP1 expression itself. Thus, a majority of CDDP-resistant cancer cells appear to develop a dependency to PARP1, becoming susceptible to PARP inhibitor-induced apoptosis.

Role of helicase-like transcription factor (hltf) in the G2/m transition and apoptosis in brain

HLTF participates in transcription, chromatin remodeling, DNA damage repair, and tumor suppression. Aside from being expressed in mouse brain during embryonic and postnatal development, little is known about Hltf's functional importance. Splice variant quantification of wild-type neonatal (6-8 hour postpartum) brain gave a ratio of 5:1 for Hltf isoform 1 (exons 1-25) to isoform 2 (exons 1-21 with exon 21 extended via a partial intron retention event). Western analysis showed a close correlation between mRNA and protein expression. Complete loss of Hltf caused encephalomalacia with increased apoptosis, and reduced viability. Sixty-four percent of Hltf null mice died, 48% within 12-24 hours of birth. An RNA-Seq snapshot of the neonatal brain transcriptome showed 341 of 20,000 transcripts were altered (p < 0.05) - 95 up regulated and 246 down regulated. MetaCore^TM enrichment pathway analysis revealed Hltf regulates cell cycle, cell adhesion, and TGF-beta receptor signaling. Hltf's most important role is in the G2/M transition of the cell cycle (p  =  4.672e-7) with an emphasis on transcript availability of major components in chromosome cohesion and condensation. Hltf null brains have reduced transcript levels for Rad21/Scc1, histone H3.3, Cap-E/Smc2, Cap-G/G2, and Aurora B kinase. The loss of Hltf in its yeast Rad5-like role in DNA damage repair is accompanied by down regulation of Cflar, a critical inhibitor of TNFRSF6-mediated apoptosis, and increased (p<0.0001) active caspase-3, an indicator of intrinsic triggering of apoptosis in null brains. Hltf also regulates Smad7/Bambi/Tgf-beta/Bmp5/Wnt10b signaling in brain. ChIP confirmed Hltf binding to consensus sequences in predicted (promoter Scgb3a1 gene) and previously unidentified (P-element on chromosome 7) targets. This study is the first to provide a comprehensive view of Hltf targets in brain. Moreover, it reveals how silencing Hltf disrupts cell cycle progression, and attenuates DNA damage repair.

Histone deacetylase inhibitors modulate miRNA and mRNA expression, block metaphase, and induce apoptosis in inflammatory breast cancer cells

To develop new therapies for inflammatory breast cancer (IBC) we have compared the effects of two hydroxamic acid-based histone deacetylase (HDAC) inhibitors, CG-1521 and Trichostatin A (TSA) on the biology of two IBC cell lines: SUM149PT and SUM190PT. CG-1521 and TSA induce dose (0−10 µM) and time-dependent (0−96 h) increases in the proportion of cells undergoing cell cycle arrest and apoptosis in the presence or absence of 17β-estradiol. In SUM 149PT cells, both CG-1521 and TSA increase the levels of acetylated α-tubulin; however the morphological effects are different: CG-1521 blocks mitotic spindle formation and prevents abscission during cytokinesis while TSA results in an increase in cell size. In SUM190PT cells CG-1521 does not cause an increase in acetylated-α-tubulin and even though TSA significantly increases the levels of acetylated tubulin, neither inhibitor alters the morphology of the cells. Microarray analysis demonstrates that CG-1521 modulates the expression of 876 mRNAs and 63 miRNAs in SUM149PT cells, and 1227 mRNAs and 35 miRNAs in SUM190PT cells. Only 9% of the genes are commonly modulated in both cell lines, suggesting that CG-1521 and TSA target different biological processes in the two cell lines most likely though the inhibition of different HDACs in these cell lines. Gene ontology (GO) analysis reveals that CG-1521 affects the expression of mRNAs that encode proteins associated with the spindle assembly checkpoint, chromosome segregation, and microtubule-based processes in both cell lines and has cell-type specific effects on lipid biosynthesis, response to DNA damage, and cell death.

Distinct and atypical intrinsic and extrinsic cell death pathways between photoreceptor cell types upon specific ablation of Ranbp2 in cone photoreceptors

Non-autonomous cell-death is a cardinal feature of the disintegration of neural networks in neurodegenerative diseases, but the molecular bases of this process are poorly understood. The neural retina comprises a mosaic of rod and cone photoreceptors. Cone and rod photoreceptors degenerate upon rod-specific expression of heterogeneous mutations in functionally distinct genes, whereas cone-specific mutations are thought to cause only cone demise. Here we show that conditional ablation in cone photoreceptors of Ran-binding protein-2 (Ranbp2), a cell context-dependent pleiotropic protein linked to neuroprotection, familial necrotic encephalopathies, acute transverse myelitis and tumor-suppression, promotes early electrophysiological deficits, subcellular erosive destruction and non-apoptotic death of cones, whereas rod photoreceptors undergo cone-dependent non-autonomous apoptosis. Cone-specific Ranbp2 ablation causes the temporal activation of a cone-intrinsic molecular cascade highlighted by the early activation of metalloproteinase 11/stromelysin-3 and up-regulation of Crx and CoREST, followed by the down-modulation of cone-specific phototransduction genes, transient up-regulation of regulatory/survival genes and activation of caspase-7 without apoptosis. Conversely, PARP1⁺-apoptotic rods develop upon sequential activation of caspase-9 and caspase-3 and loss of membrane permeability. Rod photoreceptor demise ceases upon cone degeneration. These findings reveal novel roles of Ranbp2 in the modulation of intrinsic and extrinsic cell death mechanisms and pathways. They also unveil a novel spatiotemporal paradigm of progression of neurodegeneration upon cell-specific genetic damage whereby a cone to rod non-autonomous death pathway with intrinsically distinct cell-type death manifestations is triggered by cell-specific loss of Ranbp2. Finally, this study casts new light onto cell-death mechanisms that may be shared by human dystrophies with distinct retinal spatial signatures as well as with other etiologically distinct neurodegenerative disorders.

The secondary demise of healthy neurons upon the degeneration of neurons harboring primary genetic defect(s) is hallmark to neurodegenerative diseases. However, the factors and mechanisms driving these cell-death processes are not understood, a severe limitation which has hampered the therapeutic development of neuroprotective approaches. The neuroretina is comprised of two main types of photoreceptor neurons, rods and cones. These undergo degeneration upon heterogeneous mutations or environmental stressors and the underlying diseases present conspicuous spatiotemporal pathological signatures whose molecular bases are not understood. We employed the multifunctional protein, Ran-binding protein-2 (Ranbp2), which is implicated in cell-type and stress-dependent clinical manifestations, to examine its role(s) in primary and secondary photoreceptor death mechanisms upon its specific loss in cones. Contrary to prior findings, we found that dying cones can trigger the loss of healthy rods. This process arises by the immediate activation of novel Ranbp2-responsive factors and downstream cascade events in cones that promote extrinsically the demise of rods. The mechanisms of rod and cone demise are molecularly distinct. Collectively, the data uncover distinct Ranbp2 roles in intrinsic and extrinsic cell-death and will likely contribute to our understanding of the spatiotemporal onset and progression of diseases affecting photoreceptor mosaics and other neural networks.

Plk1 is upregulated in androgen-insensitive prostate cancer cells and its inhibition leads to necroptosis

Castration-resistant prostate cancer (PCa) is refractory to hormone therapy and new strategies for treatment are urgently needed. We found that androgen-insensitive (AI) PCa cells, LNCaP-AI, are reprogrammed to upregulate the mitotic kinase Plk1 (Polo-like kinase 1) and other M-phase cell-cycle proteins, which may underlie AI PCa growth. In androgen-depleted media, LNCaP-AI cells showed exquisite sensitivity to growth inhibition by subnanomolar concentrations of a small molecule inhibitor of Plk1, BI2536, suggesting that these cells are dependent on Plk1 for growth. In contrast, the androgen-responsive parental LNCaP cells showed negligible responses to BI2536 treatment under the same condition. BI2536 treatment of LNCaP-AI cells resulted in an increase in cell death marker PARP-1 (polymerase-1) but did not activate caspase-3, an apoptosis marker, suggesting that the observed cell death was caspase-independent. BI2536-treated LNCaP-AI cells formed multinucleated giant cells that contain clusters of nuclear vesicles indicative of mitotic catastrophe. Live-cell time-lapse imaging revealed that BI2536-treated giant LNCaP-AI cells underwent necroptosis, as evidenced by 'explosive' cell death and partial reversal of cell death by a necroptosis inhibitor. Our studies suggest that LNCaP-AI cells underwent reprogramming in both their cell growth and cell death pathways, rendering them highly sensitive to Plk1 inhibition that induces necroptosis. Harnessing necroptosis through Plk1 inhibition may be explored for therapeutic intervention of castration-resistant PCa.

The transcription factor IRF3 triggers "defensive suicide" necrosis in response to viral and bacterial pathogens

Although molecular components that execute noninflammatory apoptotic cell death are well defined, molecular pathways that trigger necrotic cell death remain poorly characterized. Here, we show that in response to infection with adenovirus or Listeria monocytogenes, macrophages in vivo undergo rapid proinflammatory necrotic death that is controlled by interferon-regulatory factor 3 (IRF3). The transcriptional activity of IRF3 is, surprisingly, not required for the induction of necrosis, and it proceeds normally in mice deficient in all known regulators of necrotic death or IRF3 activation, including RIPK3, caspases 1, 8, or 11, STING, and IPS1/MAVS. Although L. monocytogenes triggers necrosis to promote the infection, IRF3-dependent necrosis is required for reducing pathogen burden in the models of disseminated infection with adenovirus. Therefore, our studies implicate IRF3 as a principal and nonredundant component of a physiologically regulated necrotic cell-death pathway that operates as an effective innate immune mechanism of host protection against disseminated virus infection.

The transcription factor IRF3 triggers "defensive suicide" necrosis in response to viral and bacterial pathogens

Although molecular components that execute noninflammatory apoptotic cell death are well defined, molecular pathways that trigger necrotic cell death remain poorly characterized. Here, we show that in response to infection with adenovirus or Listeria monocytogenes, macrophages in vivo undergo rapid proinflammatory necrotic death that is controlled by interferon-regulatory factor 3 (IRF3). The transcriptional activity of IRF3 is, surprisingly, not required for the induction of necrosis, and it proceeds normally in mice deficient in all known regulators of necrotic death or IRF3 activation, including RIPK3, caspases 1, 8, or 11, STING, and IPS1/MAVS. Although L. monocytogenes triggers necrosis to promote the infection, IRF3-dependent necrosis is required for reducing pathogen burden in the models of disseminated infection with adenovirus. Therefore, our studies implicate IRF3 as a principal and nonredundant component of a physiologically regulated necrotic cell-death pathway that operates as an effective innate immune mechanism of host protection against disseminated virus infection.

Prostate apoptosis response-4 is involved in the apoptosis response to docetaxel in MCF-7 breast cancer cells

Experimental evidence indicates that prostate apoptosis response-4 (Par-4, also known as PAWR) is a key regulator of cancer cell survival and may be a target for cancer-selective targeted therapeutics. Par-4 was first identified in prostate cancer cells undergoing apoptosis. Both intracellular and extracellular Par-4 have been implicated in apoptosis. Relatively little is known about the role of Par-4 in breast cancer cell apoptosis. In this study, we sought to investigate the effects of Par-4 expression on cell proliferation, apoptosis and drug sensitivity in breast cancer cells. MCF-7 cells were stably transfected with expression vectors for Par-4, or transiently transfected with siRNA for Par-4 knockdown. Cell proliferation assays were performed using MTT and apoptosis was evaluated using acridine orange staining, fluorescence microscopy and flow cytometry. Par-4 overexpression reduced MCF-7 proliferation rates. Conversely, Par-4 knockdown led to increased MCF-7 proliferation. Par-4 downregulation also led to increased BCL-2 and reduced BID expression. Par-4 overexpression did not affect the cell cycle profile. However, MCF-7 cells with increased Par-4 expression showed reduced ERK phosphorylation, suggesting that the inhibition of cell proliferation promoted by Par-4 may be mediated by the MAPK/ERK1/2 pathway. MCF-7 cells with increased Par-4 expression showed a marginal increase in early apoptotic cells. Importantly, we found that Par-4 expression modulates apoptosis in response to docetaxel in MCF7 breast cancer cells. Par-4 exerts growth inhibitory effects on breast cancer cells and chemosensitizes them to docetaxel.

Nutrient availability links mitochondria, apoptosis, and obesity

Mitochondria are the dominant source of the cellular energy requirements through oxidative phosphorylation, but they are also central players in apoptosis. Nutrient availability may have been the main evolutionary driving force behind these opposite mitochondrial functions: production of energy to sustain life and release of apoptotic proteins to trigger cell death. Here, we explore the link between nutrients, mitochondria and apoptosis with known and potential implications for age-related decline and metabolic syndromes.

The omega-3 polyunsaturated fatty acid DHA induces simultaneous apoptosis and autophagy via mitochondrial ROS-mediated Akt-mTOR signaling in prostate cancer cells expressing mutant p53

Docosahexaenoic acid (DHA) induces autophagy-associated apoptotic cell death in wild-type p53 cancer cells via regulation of p53. The present study investigated the effects of DHA on PC3 and DU145 prostate cancer cell lines harboring mutant p53. Results show that, in addition to apoptosis, DHA increased the expression levels of lipidated form LC3B and potently stimulated the autophagic flux, suggesting that DHA induces both autophagy and apoptosis in cancer cells expressing mutant p53. DHA led to the generation of mitochondrial reactive oxygen species (ROS), as shown by the mitochondrial ROS-specific probe mitoSOX. Similarly, pretreatment with the antioxidant N-acetyl-cysteine (NAC) markedly inhibited both the autophagy and the apoptosis triggered by DHA, indicating that mitochondrial ROS mediate the cytotoxicity of DHA in mutant p53 cells. Further, DHA reduced the levels of phospho-Akt and phospho-mTOR in a concentration-dependent manner, while NAC almost completely blocked that effect. Collectively, these findings present a novel mechanism of ROS-regulated apoptosis and autophagy that involves Akt-mTOR signaling in prostate cancer cells with mutant p53 exposed to DHA.

Obatoclax (GX15-070) triggers necroptosis by promoting the assembly of the necrosome on autophagosomal membranes

Obatoclax (GX15-070), a small-molecule inhibitor of antiapoptotic Bcl-2 proteins, has been reported to trigger cell death via autophagy. However, the underlying molecular mechanisms have remained elusive. Here, we identify GX15-070-stimulated assembly of the necrosome on autophagosomal membranes as a key event that connects GX15-070-stimulated autophagy to necroptosis. GX15-070 predominately induces a non-apoptotic form of cell death in rhabdomyosarcoma cells, as evident by lack of typical apoptotic features such as DNA fragmentation or caspase activation and by insensitivity to the broad-range caspase inhibitor zVAD.fmk. Instead, GX15-070 triggers massive accumulation of autophagosomes, which are required for GX15-070-induced cell death, as blockade of autophagosome formation by silencing of Atg5 or Atg7 abolishes GX15-070-mediated cell death. Co-immunoprecipitation studies reveal that GX15-070 stimulates the interaction of Atg5, a constituent of autophagosomal membranes, with components of the necrosome such as FADD, RIP1 and RIP3. This GX15-070-induced assembly of the necrosome on autophagosomes occurs in a Atg5-dependent manner, as knockdown of Atg5 abrogates formation of this complex. RIP1 is necessary for GX15-070-induced cell death, as both genetic and pharmacological inhibition of RIP1 by shRNA-mediated knockdown or by the RIP1 inhibitor necrostatin-1 blocks GX15-070-induced cell death. Similarly, RIP3 knockdown rescues GX15-070-mediated cell death and suppression of clonogenic survival. Interestingly, RIP1 or RIP3 silencing has no effect on GX15-070-stimulated autophagosome formation, underlining that RIP1 and RIP3 mediate cell death downstream of autophagy induction. Of note, GX15-070 significantly suppresses tumor growth in a RIP1-dependent manner in the chorioallantoic membrane model in vivo. In conclusion, GX15-070 triggers necroptosis by promoting the assembly of the necrosome on autophagosomes. These findings provide novel insights into the molecular mechanisms of GX15-070-induced non-apoptotic cell death.

An antimitotic and antivascular agent BPR0L075 overcomes multidrug resistance and induces mitotic catastrophe in paclitaxel-resistant ovarian cancer cells

Paclitaxel plays a major role in the treatment of ovarian cancer; however, resistance to paclitaxel is frequently observed. Thus, new therapy that can overcome paclitaxel resistance will be of significant clinical importance. We evaluated antiproliferative effects of an antimitotic and antivascular agent BPR0L075 in paclitaxel-resistant ovarian cancer cells. BPR0L075 displays potent and broad-spectrum cytotoxicity at low nanomolar concentrations (IC₅₀ = 2–7 nM) against both parental ovarian cancer cells (OVCAR-3, SKOV-3, and A2780-1A9) and paclitaxel-resistant sublines (OVCAR-3-TR, SKOV-3-TR, 1A9-PTX10), regardless of the expression levels of the multidrug resistance transporter P-gp and class III β-tubulin or mutation of β-tubulin. BPR0L075 blocks cell cycle at the G2/M phase in paclitaxel-resistant cells while equal concentration of paclitaxel treatment was ineffective. BPR0L075 induces cell death by a dual mechanism in parental and paclitaxel-resistant ovarian cancer cells. In the parental cells (OVCAR-3 and SKOV-3), BPR0L075 induced apoptosis, evidenced by poly(ADP-ribose) polymerase (PARP) cleavage and DNA ladder formation. BPR0L075 induced cell death in paclitaxel-resistant ovarian cancer cells (OVCAR-3-TR and SKOV-3-TR) is primarily due to mitotic catastrophe, evidenced by formation of giant, multinucleated cells and absence of PARP cleavage. Immunoblotting analysis shows that BPR0L075 treatment induced up-regulation of cyclin B1, BubR1, MPM-2, and survivin protein levels and Bcl-XL phosphorylation in parental cells; however, in resistant cells, the endogenous expressions of BubR1 and survivin were depleted, BPR0L075 treatment failed to induce MPM-2 expression and phosphorylation of Bcl-XL. BPR0L075 induced cell death in both parental and paclitaxel-resistant ovarian cancer cells proceed through caspase-3 independent mechanisms. In conclusion, BPR0L075 displays potent cytotoxic effects in ovarian cancer cells with a potential to overcome paclitaxel resistance by bypassing efflux transporters and inducing mitotic catastrophe. BPR0L075 represents a novel microtubule therapeutic to overcome multidrug resistance and trigger alternative cell death by mitotic catastrophe in ovarian cancer cells that are apoptosis-resistant.

The antiviral cytokines IFN-α and IFN-β modulate parietal epithelial cells and promote podocyte loss: implications for IFN toxicity, viral glomerulonephritis, and glomerular regeneration

Interferon (IFN)-α and IFN-β are the central regulators of antiviral immunity but little is known about their roles in viral glomerulonephritis (eg, HIV nephropathy). We hypothesized that IFN-α and IFN-β would trigger local inflammation and podocyte loss. We found that both IFNs consistently activated human and mouse podocytes and parietal epithelial cells to express numerous IFN-stimulated genes. However, only IFN-β significantly induced podocyte death and increased the permeability of podocyte monolayers. In contrast, only IFN-α caused cell-cycle arrest and inhibited the migration of parietal epithelial cells. Both IFNs suppressed renal progenitor differentiation into mature podocytes. In Adriamycin nephropathy, injections with either IFN-α or IFN-β aggravated proteinuria, macrophage influx, and glomerulosclerosis. A detailed analysis showed that only IFN-β induced podocyte mitosis. This did not, however, lead to proliferation, but was associated with podocyte loss via podocyte detachment and/or mitotic podocyte death (mitotic catastrophe). We did not detect TUNEL-positive podocytes. Thus, IFN-α and IFN-β have both common and differential effects on podocytes and parietal epithelial cells, which together promote glomerulosclerosis by enhancing podocyte loss while suppressing podocyte regeneration from local progenitors.

Osteocyte apoptosis

Apoptotic death of osteocytes was recognized over 15 years ago, but its significance for bone homeostasis has remained elusive. A new paradigm has emerged that invokes osteocyte apoptosis as a critical event in the recruitment of osteoclasts to a specific site in response to skeletal unloading, fatigue damage, estrogen deficiency and perhaps in other states where bone must be removed. This is accomplished by yet to be defined signals emanating from dying osteocytes, which stimulate neighboring viable osteocytes to produce osteoclastogenic cytokines. The osteocyte apoptosis caused by chronic glucocorticoid administration does not increase osteoclasts; however, it does negatively impact maintenance of bone hydration, vascularity, and strength.

RIP1 expression is necessary for CD30-mediated cell death induction in anaplastic large-cell lymphoma cells

CD30, a member of the tumor necrosis factor receptor (TNFR) superfamily, is consistently expressed by tumor cells of anaplastic large-cell lymphoma (ALCL). CD30 stimulation induces massive caspase-dependent cell death of ALCL cells in case of canonical NFκB inhibition or proteasome inhibition. However, CD30, a TNFR lacking a death domain (DD), is unable to recruit a death inducing complex containing TRADD (TNFR1-associated DD-protein) or FADD (FAS-associated DD-domain protein) together with the receptor-interacting protein 1 (RIP1) and caspase-8. Thus, the mechanism explaining CD30-induced cell death of lymphocytes remains obscure. Here, we demonstrate that blockage of RIP1 by siRNA or pharmacological inhibition of RIP1 by Necrostatin-1 almost completely prevented CD30-induced cell death. In addition, we revealed CD30-induced accumulation of RIP1 at the cytoplasma membrane of NFκB-inhibited ALCL cells by confocal laser scanning microscopy. Finally, primary ALCL cases can be subdivided into two groups based on the presence or absence of RIP1 as revealed by immunohistology. Taken together, our study identified RIP1 as a crucial mediator of CD30-induced cell death that bears features of apoptosis as well as necroptosis. RIP1 expression in ALCL tumor cells might eligible for the therapeutic application of CD30 antibodies in combination with NFκB/proteasome inhibitors that should result in CD30-induced cell death.

Temporal and spatial evolution of therapy-induced tumor apoptosis detected by caspase-3-selective molecular imaging

PURPOSE

Induction of apoptosis in tumors is considered a desired goal of anticancer therapy. We investigated whether the dynamic temporal and spatial evolution of apoptosis in response to cytotoxic and mechanism-based therapeutics could be detected noninvasively by the caspase-3 radiotracer [(18)F]ICMT-11 and positron emission tomography (PET).

EXPERIMENTAL DESIGN

The effects of a single dose of the alkylating agent cyclophosphamide (CPA or 4-hydroperoxycyclophosphamide), or the mechanism-based small molecule SMAC mimetic birinapant on caspase-3 activation was assessed in vitro and by [(18)F]ICMT-11-PET in mice bearing 38C13 B-cell lymphoma, HCT116 colon carcinoma, or MDA-MB-231 breast adenocarcinoma tumors. Ex vivo analysis of caspase-3 was compared to the in vivo PET imaging data.

RESULTS

Drug treatment increased the mean [(18)F]ICMT-11 tumor uptake with a peak at 24 hours for CPA (40 mg/kg; AUC40-60: 8.04 ± 1.33 and 16.05 ± 3.35 %ID/mL × min at baseline and 24 hours, respectively) and 6 hours for birinapant (15 mg/kg; AUC40-60: 20.29 ± 0.82 and 31.07 ± 5.66 %ID/mL × min, at baseline and 6 hours, respectively). Voxel-based spatiotemporal analysis of tumor-intrinsic heterogeneity suggested that discrete pockets of caspase-3 activation could be detected by [(18)F]ICMT-11. Increased tumor [(18)F]ICMT-11 uptake was associated with caspase-3 activation measured ex vivo, and early radiotracer uptake predicted apoptosis, distinct from the glucose metabolism with [(18)F]fluorodeoxyglucose-PET, which depicted continuous loss of cell viability.

CONCLUSION

The proapoptotic effects of CPA and birinapant resulted in a time-dependent increase in [(18)F]ICMT-11 uptake detected by PET. [(18)F]ICMT-11-PET holds promise as a noninvasive pharmacodynamic biomarker of caspase-3-associated apoptosis in tumors.

Regulation of autophagy by stress-responsive transcription factors

Autophagy is an evolutionarily conserved process that promotes the lysosomal degradation of intracellular components including organelles and portions of the cytoplasm. Besides operating as a quality control mechanism in steady-state conditions, autophagy is upregulated in response to a variety of homeostatic perturbations. In this setting, autophagy mediates prominent cytoprotective effects as it sustains energetic homeostasis and contributes to the removal of cytotoxic stimuli, thus orchestrating a cell-wide, multipronged adaptive response to stress. In line with the critical role of autophagy in health and disease, defects in the autophagic machinery as well as in autophagy-regulatory signaling pathways have been associated with multiple human pathologies, including neurodegenerative disorders, autoimmune conditions and cancer. Accumulating evidence indicates that the autophagic response to stress may proceed in two phases. Thus, a rapid increase in the autophagic flux, which occurs within minutes or hours of exposure to stressful conditions and is entirely mediated by post-translational protein modifications, is generally followed by a delayed and protracted autophagic response that relies on the activation of specific transcriptional programs. Stress-responsive transcription factors including p53, NF-κB and STAT3 have recently been shown to play a major role in the regulation of both these phases of the autophagic response. Here, we will discuss the molecular mechanisms whereby autophagy is orchestrated by stress-responsive transcription factors.

Dietary ω -3 polyunsaturated fatty acid DHA: a potential adjuvant in the treatment of cancer

ω-3 Polyunsaturated fatty acids (PUFAs), mainly present in fish oil, are part of the human diet. Among PUFAs, docosahexaenoic acid (DHA) has received particular attention for its anti-inflammatory, antiproliferative, proapoptotic, antiangiogenetic, anti-invasion, and antimetastatic properties. These data suggest that DHA can exert antitumor activity potentially representing an effective adjuvant in cancer chemotherapy. This review is focused on current knowledge supporting the potential use of DHA for the enhancement of the efficacy of anticancer treatments in relation to its ability to enhance the uptake of anticancer drugs, regulate the oxidative status of tumor cells, and inhibit tumor cell invasion and metastasis.

Caspase-1 is a novel target of p63 in tumor suppression

p63 is a p53 family transcription factor, which besides unique roles in epithelial development, shares tumor suppressive activity with its homolog p53. The p63 gene has different transcriptional start sites, which generate two N-terminal isoforms (transactivation domain (TA)p63 and amino terminal truncated protein(ΔN)p63); in addition alternative splicing at the 5′-end give rise to at least five C-terminal isoforms. This complexity of gene structure has probably fostered the debate and controversy on p63 function in cancer, with TP63-harboring two distinctive promoters, codifying for the TAp63 and ΔNp63 isoforms, and having discrete functions. However, ΔNp63 also drives expression of target genes that have a relevant role in cancer and metastasis. In this study, we identified a novel p63 transcriptional target, caspase-1. Caspase-1 is proinflammatory caspase, which functions in tumor suppression. We show that both p63 isoforms promote caspase-1 expression by physical binding to its promoter. Consistent with our in vitro findings, we also identified a direct correlation between p63 and caspase-1 expression in human cancer data sets. In addition, survival estimation analysis demonstrated that functional interaction between p63 and caspase-1 represents a predictor of positive survival outcome in human cancers. Overall, our data report a novel p63 target gene involved in tumor suppression, and the clinical analysis underlines the biological relevance of this finding and suggests a further clinically predictive biomarker.

Synthetic lethal interaction between PI3K/Akt/mTOR and Ras/MEK/ERK pathway inhibition in rhabdomyosarcoma

Rhabdomyosarcoma (RMS) frequently exhibits concomitant activation of the PI3K/Akt/mTOR and the Ras/MEK/ERK pathways. Therefore, we investigated whether pharmacological cotargeting of these two key survival pathways suppresses RMS growth. Here, we identify a synthetic lethal interaction between PI3K/Akt/mTOR and Ras/MEK/ERK pathway inhibition in RMS. The dual PI3K/mTOR inhibitor PI103 and the MEK inhibitor UO126 synergize to trigger apoptosis in several RMS cell lines in a highly synergistic manner (combination index <0.1), whereas either agent alone induces minimal cell death. Similarly, genetic knockdown of p110α and MEK1/2 cooperates to induce apoptosis. Molecular studies reveal that cotreatment with PI103/UO126 cooperates to suppress PI3K/Akt/mTOR and Ras/MEK/ERK signaling, whereas either compound alone is not only less effective to inhibit signaling, but even cross-activates the other pathway. Accordingly, PI103 alone increases ERK phosphorylation, while UO126 enhances Akt phosphorylation, consistent with negative crosstalks between these two signaling pathways. Furthermore, PI103/UO126 cotreatment causes downregulation of several antiapoptotic proteins such as XIAP, Bcl-xL and Mcl-1 as well as increased expression and decreased phosphorylation of the proapoptotic protein BimEL, thus shifting the balance towards apoptosis. Consistently, PI103/UO126 cotreatment cooperates to trigger Bax activation, loss of mitochondrial membrane potential, caspase activation and caspase-dependent apoptosis. This identification of a synthetic lethal interaction between PI3K/mTOR and MEK inhibitors has important implications for the development of novel treatment strategies in RMS.

Reovirus activates a caspase-independent cell death pathway

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

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

Genetic disruption of Abl nuclear import reduces renal apoptosis in a mouse model of cisplatin-induced nephrotoxicity

DNA damage activates nuclear Abl tyrosine kinase to stimulate intrinsic apoptosis in cancer cell lines and mouse embryonic stem cells. To examine the in vivo function of nuclear Abl in apoptosis, we generated Abl-μNLS (μ, mutated in nuclear localization signals) mice. We show here that cisplatin-induced apoptosis is defective in the renal proximal tubule cells (RPTC) from the Abl^μ/μ mice. When injected with cisplatin, we found similar levels of platinum in the Abl^+/+ and the Abl^μ/μ kidneys, as well as similar initial inductions of p53 and PUMAα expression. However, the accumulation of p53 and PUMAα could not be sustained in the Abl^μ/μ kidneys, leading to reductions in renal apoptosis and tubule damage. Co-treatment of cisplatin with the Abl kinase inhibitor, imatinib, reduced the accumulation of p53 and PUMAα in the Abl^+/+ but not in the Abl^μ/μ kidneys. The residual apoptosis in the Abl^μ/μ mice was not further reduced in the Abl^μ/μ; p53^−/− double-mutant mice, suggesting that nuclear Abl and p53 are epistatic to each other in this apoptosis response. Although apoptosis and tubule damage were reduced, cisplatin-induced increases in phospho-Stat-1 and blood urea nitrogen were similar between the Abl^+/+ and the Abl^μ/μ kidneys, indicating that RPTC apoptosis is not the only factor in cisplatin-induced nephrotoxicity. These results provide in vivo evidence for the pro-apoptotic function of Abl, and show that its nuclear localization and tyrosine kinase activity are both required for the sustained expression of p53 and PUMAα in cisplatin-induced renal apoptosis.

Assessing main death pathways in T lymphocytes from HIV infected individuals

Increased lymphocyte death is a hallmark of human immunodeficiency virus (HIV) infection. Although virological factors have been linked to this phenomenon, increased cell death rates are still observed in treated individuals in which viral replication is halted. To understand the nature of this remaining altered cell death, we have developed a simple and fast assay to assess major cell death pathways in lymphocytes isolated from HIV-infected individuals. The combination of three factors: (i) antibody staining to identify CD3(+) CD4(+) and CD3(+) CD8(+) cells, (ii) assessment of mitochondrial and plasma membrane function using DiOC6(3) or JC-1 probes and vital dyes, and (iii) caspase inhibition, allowed for the quantification of caspase-independent and -dependent cell death in CD4 and CD8 T cells. The latter mechanism was divided in intrinsic and extrinsic apoptotic pathways according to the sensitivity of the dissipation of mitochondrial membrane potential to Z-VAD-fmk or Q-VD-oPH treatment. Our data show similar results for both caspase inhibitors in treated infected individuals, whereas Q-VD-oPH showed a more potent inhibition in viremic individuals, yielding lower levels of intrinsic apoptosis. Comparison of DiOC6(3) and JC-1 probes yielded similar results in CD4 T cells, allowing for a clear definition of death mechanism in these cells. However, in CD8 T-cells, JC-1 showed heterogeneous staining and detected significantly lower levels of cell death with a higher contribution of intrinsic apoptosis. In conclusion, we provide a simple method to assess CD4 T-cell death mechanisms in HIV-infected individuals. The reasons and consequences of mitochondrial heterogeneity in CD8 T-cells require further evaluation.

Cyclophilin D modulates cell death transition from early apoptosis to programmed necrosis induced by honokiol

Honokiol is a pharmacologically active small molecule with multifunctional antitumor effects. Although plenty of literature is available on honokiol-triggered apoptosis and programmed necrosis, few studies have investigated the potential existence of death mode transition from apoptosis to programmed necrosis. In the current study, we demonstrated that the necrotic cell population (PI-positive) gradually increased and the early-stage apoptotic cell population (PI-negative and AV-positive) decreased in a dose- and time-dependent manner following honokiol treatment. Furthermore, we demonstrated that these PI-positive cells were under necrotic cell death, since no late-apoptosis characteristics including conspicuous chromatin condensation or DNA ladder patterns were detected. These results demonstrated that cells suffered death mode transition from early-stage apoptosis to programmed necrosis with the increase of honokiol dose or treatment time. The protein expression of RIP3 markedly increased in parallel with HNK-triggered death mode transition, while the expression of RIP1 decreased. Cyclophilin D expression increased during cell death mode transition, and inhibition of cyclophilin D by cyclosporin A clearly blocked HNK-triggered programmed necrosis. These data indicated that honokiol-induced programmed necrosis and death mode transition are potentially RIP3‑dependent, cyclophilin D-regulated. Further results showed that blocked cyclophilin D by cyclosporin A inhibited HNK-induced necrosis, but did not affect HNK-induced RIP3 overexpression. This indicated that cyclophilin D was a potential modulator at downstream of RIP3. In conclusion, honokiol triggers a potential RIP3-dependent cell death mode transition from early-stage apoptosis to programmed necrosis, which is highly regulated by cyclophilin D.

Bendamustine overcomes resistance to melphalan in myeloma cell lines by inducing cell death through mitotic catastrophe

Melphalan has been a mainstay of multiple myeloma (MM) therapy for many years. However, following treatment with this alkylator, malignant plasma cells usually escape both apoptosis and cell cycle control, and acquire drug-resistance resulting in tumor progression. Bendamustine is being used in MM patients refractory to conventional DNA-damaging agents, although the mechanisms driving this lack of cross-resistance are still undefined. Here, we investigated the molecular pathway of bendamustine-induced cell death in melphalan-sensitive and melphalan-resistant MM cell lines. Bendamustine affected cell survival resulting in secondary necrosis, and prompted cell death primarily through caspase-2 activation. Also, bendamustine blocked the cell cycle in the G2/M phase and induced micronucleation, erratic chromosome spreading and mitotic spindle perturbations in melphalan-resistant MM cells. In these cells, both Aurora kinase A (AURKA) and Polo-like kinase-1 (PLK-1), key components of the spindle-assembly checkpoint, were down-regulated following incubation with bendamustine, whereas levels of Cyclin B1 increased as a consequence of the prolonged mitotic arrest induced by the drug. These findings indicate that, at least in vitro, bendamustine drives cell death by promoting mitotic catastrophe in melphalan-resistant MM cells. Hence, activation of this alternative pathway of cell death may be a novel approach to the treatment of apoptosis-resistant myelomas.

Down-regulation of wild-type p53-induced phosphatase 1 (Wip1) plays a critical role in regulating several p53-dependent functions in premature senescent tumor cells

Premature or drug-induced senescence is a major cellular response to chemotherapy in solid tumors. The senescent phenotype develops slowly and is associated with chronic DNA damage response. We found that expression of wild-type p53-induced phosphatase 1 (Wip1) is markedly down-regulated during persistent DNA damage and after drug release during the acquisition of the senescent phenotype in carcinoma cells. We demonstrate that down-regulation of Wip1 is required for maintenance of permanent G2 arrest. In fact, we show that forced expression of Wip1 in premature senescent tumor cells induces inappropriate re-initiation of mitosis, uncontrolled polyploid progression, and cell death by mitotic failure. Most of the effects of Wip1 may be attributed to its ability to dephosphorylate p53 at Ser(15) and to inhibit DNA damage response. However, we also uncover a regulatory pathway whereby suppression of p53 Ser(15) phosphorylation is associated with enhanced phosphorylation at Ser(46), increased p53 protein levels, and induction of Noxa expression. On the whole, our data indicate that down-regulation of Wip1 expression during premature senescence plays a pivotal role in regulating several p53-dependent aspects of the senescent phenotype.

Survival function of the FADD-CASPASE-8-cFLIP(L) complex

Caspase-8, the initiator caspase of the death receptor pathway of apoptosis, its adapter molecule, FADD, required for caspase-8 activation, and cFLIPL, a caspase-8-like protein that lacks a catalytic site and blocks caspase-8-mediated apoptosis, are each essential for embryonic development. Animals deficient in any of these genes present with E10.5 embryonic lethality. Recent studies have shown that development in caspase-8-deficient mice is rescued by ablation of RIPK3, a kinase that promotes a form of programmed, necrotic cell death. Here, we show that FADD, RIPK3 double-knockout mice develop normally but that the lethal effects of cFLIP deletion are not rescued by RIPK3 deficiency. Remarkably, in mice lacking FADD, cFLIP, and RIPK3, embryonic development is normal. This can be explained by the convergence of two cell processes: the enzymatic activity of the FADD-caspase-8-cFLIPL complex blocks RIPK3-dependent signaling (including necrosis), whereas cFLIPL blocks RIPK3-independent apoptosis promoted by the FADD-caspase-8 complex.

Trial watch: Oncolytic viruses for cancer therapy

Oncolytic virotherapy is emerging as a promising approach for the treatment of several neoplasms. The term "oncolytic viruses" is generally employed to indicate naturally occurring or genetically engineered attenuated viral particles that cause the demise of malignant cells while sparing their non-transformed counterparts. From a conceptual standpoint, oncolytic viruses differ from so-called "oncotropic viruses" in that only the former are able to kill cancer cells, even though both display a preferential tropism for malignant tissues. Of note, such a specificity can originate at several different steps of the viral cycle, including the entry of virions (transductional specificity) as well as their intracellular survival and replication (post-transcriptional and transcriptional specificity). During the past two decades, a large array of replication-competent and replication-incompetent oncolytic viruses has been developed and engineered to express gene products that would specifically promote the death of infected (cancer) cells. However, contrarily to long-standing beliefs, the antineoplastic activity of oncolytic viruses is not a mere consequence of the cytopathic effect, i.e., the lethal outcome of an intense, productive viral infection, but rather involves the elicitation of an antitumor immune response. In line with this notion, oncolytic viruses genetically modified to drive the local production of immunostimulatory cytokines exert more robust therapeutic effects than their non-engineered counterparts. Moreover, the efficacy of oncolytic virotherapy is significantly improved by some extent of initial immunosuppression (facilitating viral replication and spread) followed by the administration of immunostimulatory molecules (boosting antitumor immune responses). In this Trial Watch, we will discuss the results of recent clinical trials that have evaluated/are evaluating the safety and antineoplastic potential of oncolytic virotherapy.

Control of autophagic cell death by caspase-10 in multiple myeloma

We performed a loss-of-function RNA interference screen to define therapeutic targets in multiple myeloma, a genetically diverse plasma cell malignancy. Unexpectedly, we discovered that all myeloma lines require caspase-10 for survival irrespective of their genetic abnormalities. The transcription factor IRF4 induces both caspase-10 and its associated protein cFLIPL in myeloma, generating a protease that does not induce apoptosis but rather blocks an autophagy-dependent cell death pathway. Caspase-10 inhibits autophagy by cleaving the BCL2-interacting protein BCLAF1, itself a strong inducer of autophagy that acts by displacing beclin-1 from BCL2. While myeloma cells require a basal level of autophagy for survival, caspase-10 tempers this response to avoid cell death. Drugs that disrupt this vital balance may have therapeutic potential in myeloma.

Necroptosis: the release of damage-associated molecular patterns and its physiological relevance

Regulated necrosis, termed necroptosis, is negatively regulated by caspase-8 and is dependent on the kinase activity of RIPK1 and RIPK3. Necroptosis leads to rapid plasma membrane permeabilization and to the release of cell contents and exposure of damage-associated molecular patterns (DAMPs). We are only beginning to identify the necroptotic DAMPs, their modifications, and their potential role in the regulation of inflammation. In this review, we discuss the physiological relevance of necroptosis and its role in the modulation of inflammation. For example, during viral infection, RIPK3-mediated necroptosis acts as a backup mechanism to clear pathogens. Necroptosis is also involved in apparently immunologically silent maintenance of T cell homeostasis. In contrast, the induction of necroptosis in skin, intestine, systemic inflammatory response syndrome, and ischemia reperfusion injury provoke a strong inflammatory response, which might be triggered by emission of DAMPs from necroptotic cells, showing the detrimental side of necroptosis.

Cell death proteomics database: consolidating proteomics data on cell death

Programmed cell death is a ubiquitous process of utmost importance for the development and maintenance of multicellular organisms. More than 10 different types of programmed cell death forms have been discovered. Several proteomics analyses have been performed to gain insight in proteins involved in the different forms of programmed cell death. To consolidate these studies, we have developed the cell death proteomics (CDP) database, which comprehends data from apoptosis, autophagy, cytotoxic granule-mediated cell death, excitotoxicity, mitotic catastrophe, paraptosis, pyroptosis, and Wallerian degeneration. The CDP database is available as a web-based database to compare protein identifications and quantitative information across different experimental setups. The proteomics data of 73 publications were integrated and unified with protein annotations from UniProt-KB and gene ontology (GO). Currently, more than 6,500 records of more than 3,700 proteins are included in the CDP. Comparing apoptosis and autophagy using overrepresentation analysis of GO terms, the majority of enriched processes were found in both, but also some clear differences were perceived. Furthermore, the analysis revealed differences and similarities of the proteome between autophagosomal and overall autophagy. The CDP database represents a useful tool to consolidate data from proteome analyses of programmed cell death and is available at http://celldeathproteomics.uio.no.

Multiple interacting cell death mechanisms in the mediation of excitotoxicity and ischemic brain damage: a challenge for neuroprotection

There is currently no approved neuroprotective pharmacotherapy for acute conditions such as stroke and cerebral asphyxia. One of the reasons for this may be the multiplicity of cell death mechanisms, because inhibition of a particular mechanism leaves the brain vulnerable to alternative ones. It is therefore essential to understand the different cell death mechanisms and their interactions. We here review the multiple signaling pathways underlying each of the three main morphological types of cell death--apoptosis, autophagic cell death and necrosis--emphasizing their importance in the neuronal death that occurs during cerebral ischemia and hypoxia-ischemia, and we analyze the interactions between the different mechanisms. Finally, we discuss the implications of the multiplicity of cell death mechanisms for the design of neuroprotective strategies.

Heterogeneity of cell death

Cell death constitutes a number of heterogeneous processes. Despite the dynamic nature of cell death, studies of cell death have primarily focused on apoptosis, and cell death has often been viewed as static events occurring in linear pathways. In this article we review cell death heterogeneity with specific focus on 4 aspects of cell death: the type of cell death; how it is induced; its mechanism(s); the results of cell death, and the implications of cell death heterogeneity for both basic and clinical research. This specifically reveals that cell death occurs in multiple overlapping forms that simultaneously occur within a population. Network and pathway heterogeneity in cell death is also discussed. Failure to integrate cell death heterogeneity within analyses can lead to inaccurate predictions of the amount of cell death that takes place in a tumor. Similarly, many molecular methods employed in cell death studies homogenize a population removing heterogeneity between individual cells and can be deceiving. Finally, and most importantly, cell death heterogeneity is linked to the formation of new genome systems through induction of aneuploidy and genome chaos (rapid genome reorganization).

Mitochondria and cell signalling

Mitochondria have long been considered as crucial organelles, primarily for their roles in biosynthetic reactions such as ATP synthesis. However, it is becoming increasingly apparent that mitochondria are intimately involved in cell signalling pathways. Mitochondria perform various signalling functions, serving as platforms to initiate cell signalling, as well as acting as transducers and effectors in multiple processes. Here, we discuss the active roles that mitochondria have in cell death signalling, innate immunity and autophagy. Common themes of mitochondrial regulation emerge from these diverse but interconnected processes. These include: the outer mitochondrial membrane serving as a major signalling platform, and regulation of cell signalling through mitochondrial dynamics and by mitochondrial metabolites, including ATP and reactive oxygen species. Importantly, defects in mitochondrial control of cell signalling and in the regulation of mitochondrial homeostasis might underpin many diseases, in particular age-related pathologies.

How many ways can a podocyte die?

Podocytes are highly specialized epithelial cells that line the urinary surface of the glomerular capillary tuft. To maintain kidney filtration, podocytes oppose the high intraglomerular hydrostatic pressure, form a molecular sieve, secrete soluble factors to regulate other glomerular cell types, and provide synthesis and maintenance of the glomerular basement membrane. Impairment of any of these functions after podocyte injury results in proteinuria and possibly renal failure. Loss of glomerular podocytes is a key feature for the progression of renal diseases, and detached podocytes can be retrieved in the urine of patients with progressive glomerular diseases. Thus, the concept of podocyte loss as a hallmark of progressive glomerular disease has been widely accepted. However, the nature of events that promote podocyte detachment and whether detachment is preceded by any kind of podocyte cell death, such as apoptosis, necroptosis, or necrosis, still remains unclear and is discussed in this review.

The selective BH4-domain biology of Bcl-2-family members: IP3Rs and beyond

Anti-apoptotic Bcl-2-family members not only neutralize pro-apoptotic proteins but also directly regulate intracellular Ca(2+) signaling from the endoplasmic reticulum (ER), critically controlling cellular health, survival, and death initiation. Furthermore, distinct Bcl-2-family members may selectively regulate inositol 1,4,5-trisphosphate receptor (IP3R): Bcl-2 likely acts as an endogenous inhibitor of the IP3R, preventing pro-apoptotic Ca(2+) transients, while Bcl-XL likely acts as an endogenous IP3R-sensitizing protein promoting pro-survival Ca(2+) oscillations. Furthermore, distinct functional domains in Bcl-2 and Bcl-XL may underlie the divergence in IP3R regulation. The Bcl-2 homology (BH) 4 domain, which targets the central modulatory domain of the IP3R, is likely to be Bcl-2's determining factor. In contrast, the hydrophobic cleft targets the C-terminal Ca(2+)-channel tail and might be more crucial for Bcl-XL's function. Furthermore, one amino acid critically different in the sequence of Bcl-2's and Bcl-XL's BH4 domains underpins their selective effect on Ca(2+) signaling and distinct biological properties of Bcl-2 versus Bcl-XL. This difference is evolutionary conserved across five classes of vertebrates and may represent a fundamental divergence in their biological function. Moreover, these insights open novel avenues to selectively suppress malignant Bcl-2 function in cancer cells by targeting its BH4 domain, while maintaining essential Bcl-XL functions in normal cells. Thus, IP3R-derived molecules that mimic the BH4 domain's binding site on the IP3R may function synergistically with BH3-mimetic molecules selectivity suppressing Bcl-2's proto-oncogenic activity. Finally, a more general role for the BH4 domain on IP3Rs, rather than solely anti-apoptotic, may not be excluded as part of a complex network of molecular interactions.

The oncogene metadherin modulates the apoptotic pathway based on the tumor necrosis factor superfamily member TRAIL (Tumor Necrosis Factor-related Apoptosis-inducing Ligand) in breast cancer

Metadherin (MTDH), the newly discovered gene, is overexpressed in more than 40% of breast cancers. Recent studies have revealed that MTDH favors an oncogenic course and chemoresistance. With a number of breast cancer cell lines and breast tumor samples, we found that the relative expression of MTDH correlated with tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) sensitivity in breast cancer. In this study, we found that knockdown of endogenous MTDH cells sensitized the MDA-MB-231 cells to TRAIL-induced apoptosis both in vitro and in vivo. Conversely, stable overexpression of MTDH in MCF-7 cells enhanced cell survival with TRAIL treatment. Mechanically, MTDH down-regulated caspase-8, decreased caspase-8 recruitment into the TRAIL death-inducing signaling complex, decreased caspase-3 and poly(ADP-ribose) polymerase-2 processing, increased Bcl-2 expression, and stimulated TRAIL-induced Akt phosphorylation, without altering death receptor status. In MDA-MB-231 breast cancer cells, sensitization to TRAIL upon MTDH down-regulation was inhibited by the caspase inhibitor Z-VAD-fmk (benzyloxycarbonyl-VAD-fluoromethyl ketone), suggesting that MTDH depletion stimulates activation of caspases. In MCF-7 breast cancer cells, resistance to TRAIL upon MTDH overexpression was abrogated by depletion of Bcl-2, suggesting that MTDH-induced Bcl-2 expression contributes to TRAIL resistance. We further confirmed that MTDH may control Bcl-2 expression partly by suppressing miR-16. Collectively, our results point to a protective function of MTDH against TRAIL-induced death, whereby it inhibits the intrinsic apoptosis pathway through miR-16-mediated Bcl-2 up-regulation and the extrinsic apoptosis pathway through caspase-8 down-regulation.