Showing papers in "Cell Death and Disease in 2012"

Necrostatin-1 analogues: critical issues on the specificity, activity and in vivo use in experimental disease models.

Abstract: Necrostatin-1 (Nec-1) is widely used in disease models to examine the contribution of receptor-interacting protein kinase (RIPK) 1 in cell death and inflammation. We studied three Nec-1 analogs: Nec-1, the active inhibitor of RIPK1, Nec-1 inactive (Nec-1i), its inactive variant, and Nec-1 stable (Nec-1s), its more stable variant. We report that Nec-1 is identical to methyl-thiohydantoin-tryptophan, an inhibitor of the potent immunomodulatory enzyme indoleamine 2,3-dioxygenase (IDO). Both Nec-1 and Nec-1i inhibited human IDO, but Nec-1s did not, as predicted by molecular modeling. Therefore, Nec-1s is a more specific RIPK1 inhibitor lacking the IDO-targeting effect. Next, although Nec-1i was ∼100 × less effective than Nec-1 in inhibiting human RIPK1 kinase activity in vitro, it was only 10 times less potent than Nec-1 and Nec-1s in a mouse necroptosis assay and became even equipotent at high concentrations. Along the same line, in vivo, high doses of Nec-1, Nec-1i and Nec-1s prevented tumor necrosis factor (TNF)-induced mortality equally well, excluding the use of Nec-1i as an inactive control. Paradoxically, low doses of Nec-1 or Nec-1i, but not Nec -1s, even sensitized mice to TNF-induced mortality. Importantly, Nec-1s did not exhibit this low dose toxicity, stressing again the preferred use of Nec-1s in vivo. Our findings have important implications for the interpretation of Nec-1-based data in experimental disease models.

JC-1: alternative excitation wavelengths facilitate mitochondrial membrane potential cytometry.

Abstract: Mitochondrial membrane potential provides a valuable indicator of cells’ health and functional status. Cytometry- and microscopy-based analyses, in combination with fluorescent probes, are widely used to study mitochondrial behavior related to cellular pathways, most notably – apoptosis. The cyanine dye JC-1 (5,5′,6,6′-tetrachloro-1,1′,3,3′-tetraethylbenzimi- dazolylcarbocyanine iodide) facilitates discrimination of energized and deenergized mitochondria because the normally green fluorescent dye forms red fluorescent aggregates when concentrated in energized mitochondria in response to their higher membrane potential. JC-1 fluorescence is usually excited by the 488 nm laser wavelength common in flow cytometers. In this study, we show that in practice this approach is not optimal for monitoring mitochondrial behavior. Investigation of fluorescence of JC-1 in solution and in cells using spectrofluorimetry, microscopy and flow cytometry reveals that excitation at 405 nm wavelength, now available on standard instruments, produces signals from aggregate fluorescence with considerably less spillover from dye monomer fluorescence than can be obtained using 488 nm excitation. The improved data are more accurate and eliminate the necessity for fluorescence compensation, making the use of the alternative excitation wavelengths beneficial for mitochondria-related biological and biomedial research.

Cancer metabolism: current perspectives and future directions.

Abstract: Cellular metabolism influences life and death decisions. An emerging theme in cancer biology is that metabolic regulation is intricately linked to cancer progression. In part, this is due to the fact that proliferation is tightly regulated by availability of nutrients. Mitogenic signals promote nutrient uptake and synthesis of DNA, RNA, proteins and lipids. Therefore, it seems straight-forward that oncogenes, that often promote proliferation, also promote metabolic changes. In this review we summarize our current understanding of how ‘metabolic transformation' is linked to oncogenic transformation, and why inhibition of metabolism may prove a cancer′s ‘Achilles' heel'. On one hand, mutation of metabolic enzymes and metabolic stress sensors confers synthetic lethality with inhibitors of metabolism. On the other hand, hyperactivation of oncogenic pathways makes tumors more susceptible to metabolic inhibition. Conversely, an adequate nutrient supply and active metabolism regulates Bcl-2 family proteins and inhibits susceptibility to apoptosis. Here, we provide an overview of the metabolic pathways that represent anti-cancer targets and the cell death pathways engaged by metabolic inhibitors. Additionally, we will detail the similarities between metabolism of cancer cells and metabolism of proliferating cells.

Targeting ATR in vivo using the novel inhibitor VE-822 results in selective sensitization of pancreatic tumors to radiation

Abstract: Combined radiochemotherapy is the currently used therapy for locally advanced pancreatic ductal adenocarcinoma (PDAC), but normal tissue toxicity limits its application. Here we test the hypothesis that inhibition of ATR (ATM-Rad3-related) could increase the sensitivity of the cancer cells to radiation or chemotherapy without affecting normal cells. We tested VE-822, an ATR inhibitor, for in vitro and in vivo radiosensitization. Chk1 phosphorylation was used to indicate ATR activity, γH2AX and 53BP1 foci as evidence of DNA damage and Rad51 foci for homologous recombination activity. Sensitivity to radiation (XRT) and gemcitabine was measured with clonogenic assays in vitro and tumor growth delay in vivo. Murine intestinal damage was evaluated after abdominal XRT. VE-822 inhibited ATR in vitro and in vivo. VE-822 decreased maintenance of cell-cycle checkpoints, increased persistent DNA damage and decreased homologous recombination in irradiated cancer cells. VE-822 decreased survival of pancreatic cancer cells but not normal cells in response to XRT or gemcitabine. VE-822 markedly prolonged growth delay of pancreatic cancer xenografts after XRT and gemcitabine-based chemoradiation without augmenting normal cell or tissue toxicity. These findings support ATR inhibition as a promising new approach to improve the therapeutic ration of radiochemotherapy for patients with PDAC.

ER stress activates the NLRP3 inflammasome via an UPR-independent pathway

Abstract: Uncontrolled endoplasmic reticulum (ER) stress responses are proposed to contribute to the pathology of chronic inflammatory diseases such as type 2 diabetes or atherosclerosis. However, the connection between ER stress and inflammation remains largely unexplored. Here, we show that ER stress causes activation of the NLRP3 inflammasome, with subsequent release of the pro-inflammatory cytokine interleukin-1β. This ER-triggered proinflammatory signal shares the same requirement for reactive oxygen species production and potassium efflux compared with other known NLRP3 inflammasome activators, but is independent of the classical unfolded protein response (UPR). We thus propose that the NLRP3 inflammasome senses and responds to ER stress downstream of a previously uncharacterized ER stress response signaling pathway distinct from the UPR, thus providing mechanistic insight to the link between ER stress and chronic inflammatory diseases.

Therapeutic metformin/AMPK activation blocked lymphoma cell growth via inhibition of mTOR pathway and induction of autophagy.

Abstract: Adenosine monophosphate-activated protein kinase (AMPK) acts as a major sensor of cellular energy status in cancers and is critically involved in cell sensitivity to anticancer agents. Here, we showed that AMPK was inactivated in lymphoma and related to the upregulation of the mammalian target of rapamycin (mTOR) pathway. AMPK activator metformin potentially inhibited the growth of B- and T-lymphoma cells. Strong antitumor effect was also observed on primary lymphoma cells while sparing normal hematopoiesis ex vivo. Metformin-induced AMPK activation was associated with the inhibition of the mTOR signaling without involving AKT. Moreover, lymphoma cell response to the chemotherapeutic agent doxorubicin and mTOR inhibitor temsirolimus was significantly enhanced when co-treated with metformin. Pharmacologic and molecular knock-down of AMPK attenuated metformin-mediated lymphoma cell growth inhibition and drug sensitization. In vivo, metformin induced AMPK activation, mTOR inhibition and remarkably blocked tumor growth in murine lymphoma xenografts. Of note, metformin was equally effective when given orally. Combined treatment of oral metformin with doxorubicin or temsirolimus triggered lymphoma cell autophagy and functioned more efficiently than either agent alone. Taken together, these data provided first evidence for the growth-inhibitory and drug-sensitizing effect of metformin on lymphoma. Selectively targeting mTOR pathway through AMPK activation may thus represent a promising new strategy to improve treatment of lymphoma patients.

Mitosis-targeted anti-cancer therapies: where they stand

Abstract: The strategy of clinically targeting cancerous cells at their most vulnerable state during mitosis has instigated numerous studies into the mitotic cell death (MCD) pathway. As the hallmark of cancer revolves around cell-cycle deregulation, it is not surprising that antimitotic therapies are effective against the abnormal proliferation of transformed cells. Moreover, these antimitotic drugs are also highly selective and sensitive. Despite the robust rate of discovery and the development of mitosis-selective inhibitors, the unpredictable complexities of the human body's response to these drugs still herald the biggest challenge towards clinical success. Undoubtedly, the need to bridge the gap between promising preclinical trials and effective translational bedside treatment prompts further investigations towards mapping out the mechanistic pathways of MCD, understanding how these drugs work as medicine in the body and more comprehensive target validations. In this review, current antimitotic agents are summarized with particular emphasis on the evaluation of their clinical efficacy as well as their limitations. In addition, we discuss the basis behind the lack of activity of these inhibitors in human trials and the potential and future directions of mitotic anticancer strategies.

Alpha-synuclein: from secretion to dysfunction and death

Abstract: The aggregation, deposition, and dysfunction of alpha-synuclein (aSyn) are common events in neurodegenerative disorders known as synucleinopathies. These include Parkinson's disease, dementia with Lewy bodies, and multiple system atrophy. A growing body of knowledge on the biology of aSyn is emerging and enabling novel hypotheses to be tested. In particular, the hypothesis that aSyn is secreted from neurons, thus contributing to the spreading of pathology not only in the brain but also in other organs, is gaining momentum. Nevertheless, the precise mechanism(s) of secretion, as well as the consequences of extracellular aSyn species for neighboring cells are still unclear. Here, we review the current literature and integrate existing data in order to propose possible mechanisms of secretion, cell dysfunction, and death. Ultimately, the complete understanding of these processes might open novel avenues for the development of new therapeutic strategies.

Caspase-1: is IL-1 just the tip of the ICEberg?

Abstract: Caspase-1, formerly known as interleukin (IL)-1-converting enzyme is best established as the protease responsible for the processing of the key pro-inflammatory cytokine IL-1β from an inactive precursor to an active, secreted molecule. Thus, caspase-1 is regarded as a key mediator of inflammatory processes, and has become synonymous with inflammation. In addition to the processing of IL-1β, caspase-1 also executes a rapid programme of cell death, termed pyroptosis, in macrophages in response to intracellular bacteria. Pyroptosis is also regarded as a host response to remove the niche of the bacteria and to hasten their demise. These processes are generally accepted as the main roles of caspase-1. However, there is also a wealth of literature supporting a direct role for caspase-1 in non-infectious cell death processes. This is true in mammals, but also in non-mammalian vertebrates where caspase-1-dependent processing of IL-1β is absent because of the lack of appropriate caspase-1 cleavage sites. This literature is most prevalent in the brain where caspase-1 may directly regulate neuronal cell death in response to diverse insults. We attempt here to summarise the evidence for caspase-1 as a cell death enzyme and propose that, in addition to the processing of IL-1β, caspase-1 has an important and a conserved role as a cell death protease.

DNA damage induces reactive oxygen species generation through the H2AX-Nox1/Rac1 pathway.

Abstract: The DNA damage response (DDR) cascade and ROS (reactive oxygen species) signaling are both involved in the induction of cell death after DNA damage, but a mechanistic link between these two pathways has not been clearly elucidated. This study demonstrates that ROS induction after treatment of cells with neocarzinostatin (NCS), an ionizing radiation mimetic, is at least partly mediated by increasing histone H2AX. Increased levels of ROS and cell death induced by H2AX overexpression alone or DNA damage leading to H2AX accumulation are reduced by treating cells with the antioxidant N-Acetyl-L-Cysteine (NAC), the NADP(H) oxidase (Nox) inhibitor DPI, expression of Rac1N17, and knockdown of Nox1, but not Nox4, indicating that induction of ROS by H2AX is mediated through Nox1 and Rac1 GTPase. H2AX increases Nox1 activity partly by reducing the interaction between a Nox1 activator NOXA1 and its inhibitor 14-3-3zeta. These results point to a novel role of histone H2AX that regulates Nox1-mediated ROS generation after DNA damage.

ATP release and purinergic signaling: a common pathway for particle-mediated inflammasome activation.

Abstract: Deposition of uric acid crystals in joints causes the acute and chronic inflammatory disease known as gout and prolonged airway exposure to silica crystals leads to the development of silicosis, an irreversible fibrotic pulmonary disease. Aluminum salt (Alum) crystals are frequently used as vaccine adjuvant. The mechanisms by which crystals activate innate immunity through the Nlrp3 inflammasome are not well understood. Here, we show that uric acid, silica and Alum crystals trigger the extracellular delivery of endogenous ATP, which just precedes the secretion of mature interleukin-1β (IL-1β) by macrophages, both events depending on purinergic receptors and connexin/pannexin channels. Interestingly, not only ATP but also ADP and UTP are involved in IL-1β production upon these Nlrp3 inflammasome activators through multiple purinergic receptor signaling. These findings support a pivotal role for nucleotides as danger signals and provide a new molecular mechanism to explain how chemically and structurally diverse stimuli can activate the Nlrp3 inflammasome.

Autophagy as a new therapeutic target in Duchenne muscular dystrophy

Abstract: A resolutive therapy for Duchene muscular dystrophy, a severe degenerative disease of the skeletal muscle, is still lacking. Because autophagy has been shown to be crucial in clearing dysfunctional organelles and in preventing tissue damage, we investigated its pathogenic role and its suitability as a target for new therapeutic interventions in Duchenne muscular dystrophy (DMD). Here we demonstrate that autophagy is severely impaired in muscles from patients affected by DMD and mdx mice, a model of the disease, with accumulation of damaged organelles. The defect in autophagy was accompanied by persistent activation via phosphorylation of Akt, mammalian target of rapamycin (mTOR) and of the autophagy-inhibiting pathways dependent on them, including the translation-initiation factor 4E-binding protein 1 and the ribosomal protein S6, and downregulation of the autophagy-inducing genes LC3, Atg12, Gabarapl1 and Bnip3. The defective autophagy was rescued in mdx mice by long-term exposure to a low-protein diet. The treatment led to normalisation of Akt and mTOR signalling; it also reduced significantly muscle inflammation, fibrosis and myofibre damage, leading to recovery of muscle function. This study highlights novel pathogenic aspects of DMD and suggests autophagy as a new effective therapeutic target. The treatment we propose can be safely applied and immediately tested for efficacy in humans.

A novel role for RIP1 kinase in mediating TNFα production

Abstract: Receptor-interacting protein 1 (RIP1) is a Ser/Thr kinase with both kinase-dependent and kinase-independent roles in death receptor signaling. The kinase activity of RIP1 is required for necroptosis, a caspase-independent pathway of programmed cell death. In some cell types, the inhibition of caspases leads to autocrine production of TNFα, which then activates necroptosis. Here, we describe a novel role for RIP1 kinase in regulating TNFα production after caspase inhibition. Caspase inhibitors activate RIP1 kinase and another protein, EDD, to mediate JNK signaling, which stimulates Sp1-dependent transcription of TNFα. This pathway is independent of nuclear factor κB and also occurs after Smac mimetic/IAP antagonist treatment or the loss of TNF receptor-associated factor 2 (Traf2). These findings implicate cIAP1/2 and Traf2 as negative regulators of this RIP1 kinase-dependent TNFα production pathway and suggest a novel role for RIP1 kinase in mediating TNFα production under certain conditions.

miR-204 targets Bcl-2 expression and enhances responsiveness of gastric cancer

Abstract: Micro RNAs (miRs) are small non-coding RNAs aberrantly expressed in human tumors. Here, we aim to identify miRs whose deregulated expression leads to the activation of oncogenic pathways in human gastric cancers (GCs). Thirty nine out of 123 tumoral and matched uninvolved peritumoral gastric specimens from three independent European subsets of patients were analyzed for the expression of 851 human miRs using Agilent Platform. The remaining 84 samples were used to validate miRs differentially expressed between tumoral and matched peritumoral specimens by qPCR. miR-204 falls into a group of eight miRs differentially expressed between tumoral and peritumoral samples. Downregulation of miR-204 has prognostic value and correlates with increased staining of Bcl-2 protein in tumoral specimens. Ectopic expression of miR-204 inhibited colony forming ability, migration and tumor engraftment of GC cells. miR-204 targeted Bcl-2 messenger RNA and increased responsiveness of GC cells to 5-fluorouracil and oxaliplatin treatment. Ectopic expression of Bcl-2 protein counteracted miR-204 pro-apoptotic activity in response to 5-fluorouracil. Altogether, these findings suggest that modulation of aberrant expression of miR-204, which in turn releases oncogenic Bcl-2 protein activity might hold promise for preventive and therapeutic strategies of GC.

Exosome-mediated shuttling of microRNA-29 regulates HIV Tat and morphine-mediated Neuronal dysfunction

Abstract: Neuronal damage is a hallmark feature of HIV-associated neurological disorders (HANDs). Opiate drug abuse accelerates the incidence and progression of HAND; however, the mechanisms underlying the potentiation of neuropathogenesis by these drugs remain elusive. Opiates such as morphine have been shown to enhance HIV transactivation protein Tat-mediated toxicity in both human neurons and neuroblastoma cells. In the present study, we demonstrate reduced expression of the tropic factor platelet-derived growth factor (PDGF)-B with a concomitant increase in miR-29b in the basal ganglia region of the brains of morphine-dependent simian immunodeficiency virus (SIV)-infected macaques compared with the SIV-infected controls. In vitro relevance of these findings was corroborated in cultures of astrocytes exposed to morphine and HIV Tat that led to increased release of miR-29b in exosomes. Subsequent treatment of neuronal SH-SY5Y cell line with exosomes from treated astrocytes resulted in decreased expression of PDGF-B, with a concomitant decrease in viability of neurons. Furthermore, it was shown that PDGF-B was a target for miR-29b as evidenced by the fact that binding of miR-29 to the 3′-untranslated region of PDGF-B mRNA resulted in its translational repression in SH-SY5Y cells. Understanding the regulation of PDGF-B expression may provide insights into the development of potential therapeutic targets for neuronal loss in HIV-1-infected opiate abusers.

Paclitaxel resistance is associated with switch from apoptotic to autophagic cell death in MCF-7 breast cancer cells

Abstract: Taxanes remain first line chemotherapy in management of metastatic breast cancer and have a key role in epithelial ovarian cancer, with increasingly common use of weekly paclitaxel dosing regimens. However, their clinical utility is limited by the development of chemoresistance. To address this, we modelled in vitro paclitaxel resistance in MCF-7 cells. We show that at clinically relevant drug doses, emerging paclitaxel resistance is associated with profound changes in cell death responses and a switch from apoptosis to autophagy as the principal mechanism of drug-induced cytotoxicity. This was characterised by a complete absence of caspase-mediated apoptotic cell death (using the pan-caspase-inhibitor Z-VAD) in paclitaxel-resistant MCF-7TaxR cells, compared with parent MCF-7 or MDA-MB-231 cell lines on paclitaxel challenge, downregulation of caspase-7, caspase-9 and BCl2-interacting mediator of cell death (BIM) expression. Silencing with small interfering RNA to BIM in MCF-7 parental cells was sufficient to confer paclitaxel resistance, inferring the significance in downregulation of this protein in contributing to the resistant phenotype of the MCF-7TaxR cell line. Conversely, there was an increased autophagic response in the MCF-7TaxR cell line with reduced phospho-mTOR and relative resistance to the mTOR inhibitors rapamycin and RAD001. In conclusion, we show for the first time that paclitaxel resistance is associated with profound changes in cell death response with deletion of multiple apoptotic factors balanced by upregulation of the autophagic pathway and collateral sensitivity to platinum.

Selective modulation of subtype III IP₃R by Akt regulates ER Ca²⁺ release and apoptosis.

Abstract: Ca2+ transfer from endoplasmic reticulum (ER) to mitochondria can trigger apoptotic pathways by inducing release of mitochondrial pro-apoptotic factors. Three different types of inositol 1,4,5-trisphosphate receptor (IP3R) serve to discharge Ca2+ from ER, but possess some peculiarities, especially in apoptosis induction. The anti-apoptotic protein Akt can phosphorylate all IP3R isoforms and protect cells from apoptosis, reducing ER Ca2+ release. However, it has not been elucidated which IP3R subtypes mediate these effects. Here, we show that Akt activation in COS7 cells, which lack of IP3R I, strongly suppresses IP3-mediated Ca2+ release and apoptosis. Conversely, in SH-SY 5Y cells, which are type III-deficient, Akt is unable to modulate ER Ca2+ flux, losing its anti-apoptotic activity. In SH-SY 5Y-expressing subtype III, Akt recovers its protective function on cell death, by reduction of Ca2+ release. Moreover, regulating Ca2+ flux to mitochondria, Akt maintains the mitochondrial integrity and delays the trigger of apoptosis, in a type III-dependent mechanism. These results demonstrate a specific activity of Akt on IP3R III, leading to diminished Ca2+ transfer to mitochondria and protection from apoptosis, suggesting an additional level of cell death regulation mediated by Akt.

miR-29b sensitizes multiple myeloma cells to bortezomib-induced apoptosis through the activation of a feedback loop with the transcription factor Sp1

Abstract: MicroRNAs (miRNAs) with tumor-suppressor potential might have therapeutic applications in multiple myeloma (MM) through the modulation of still undiscovered molecular pathways. Here, we investigated the effects of enforced expression of miR-29b on the apoptotic occurrence in MM and highlighted its role in the context of a new transcriptional loop that is finely tuned by the proteasome inhibitor bortezomib. In details, in vitro growth inhibition and apoptosis of MM cells was induced by either transient expression of synthetic miR-29b or its stable lentivirus-enforced expression. We identified Sp1, a transcription factor endowed with oncogenic activity, as a negative regulator of miR-29b expression in MM cells. Since Sp1 expression and functions are regulated via the 26S proteasome, we investigated the effects of bortezomib on miR-29b-Sp1 loop, showing that miR-29b levels were indeed upregulated by the drug. At the same time, the bortezomib/miR-29b combination produced significant pro-apoptotic effects. We also demonstrated that the PI3K/AKT pathway plays a major role in the regulation of miR-29b-Sp1 loop and induction of apoptosis in MM cells. Finally, MM xenografts constitutively expressing miR-29b showed significant reduction of their tumorigenic potential. Our findings indicate that miR-29b is involved in a regulatory loop amenable of pharmacologic intervention and modulates the anti-MM activity of bortezomib in MM cells.

JNK modulates FOXO3a for the expression of the mitochondrial death and mitophagy marker BNIP3 in pathological hypertrophy and in heart failure

Abstract: Bcl-2 E1B 19-KDa interacting protein 3 (BNIP3) is a mitochondrial death and mitophagy marker, which is involved in inducing cardiac remodeling post myocardial infarction. In this study, we show that BNIP3 expression increases in stressed cardiomyocytes in vitro and in response to pressure overload in vivo, and that its transcription is directly related to JNK activity. BNIP3 expression gradually increased in the first weeks after pressure overload and peaked at the heart failure stage. Ultrastructurally, the mitochondrial area was inversely proportional to BNIP3 expression. Both JNK and AKT activities increased with pressure overload; however, JNK signaling dominated over AKT signaling for the activation of the transcription factor FOXO3a and for the transcription of its effector, BNIP3. 3-methyladenine attenuated JNK signaling and significantly decreased BNIP3 expression and reversed cardiac remodeling in heart failure. Ultrastructurally, the mitochondrial area was significantly increased in the 3-methyladenine group compared with placebo. Moreover, adenoviral gene delivery of dominant negative JNK in a rat model of pressure overload hypertrophy abolished the increase in BNIP3 expression in response to pressure overload. These results suggest that JNK signaling is a critical modulator of the transcription factor FOXO3a driving the expression of its effector, BNIP3, in heart failure and that JNK, through BNIP3, induces mitochondrial apoptosis and mitophagy.

Activation of the unfolded protein response enhances motor recovery after spinal cord injury

Abstract: Spinal cord injury (SCI) is a major cause of paralysis, and involves multiple cellular and tissular responses including demyelination, inflammation, cell death and axonal degeneration. Recent evidence suggests that perturbation on the homeostasis of the endoplasmic reticulum (ER) is observed in different SCI models; however, the functional contribution of this pathway to this pathology is not known. Here we demonstrate that SCI triggers a fast ER stress reaction (1-3 h) involving the upregulation of key components of the unfolded protein response (UPR), a process that propagates through the spinal cord. Ablation of X-box-binding protein 1 (XBP1) or activating transcription factor 4 (ATF4) expression, two major UPR transcription factors, leads to a reduced locomotor recovery after experimental SCI. The effects of UPR inactivation were associated with a significant increase in the number of damaged axons and reduced amount of oligodendrocytes surrounding the injury zone. In addition, altered microglial activation and pro-inflammatory cytokine expression were observed in ATF4 deficient mice after SCI. Local expression of active XBP1 into the spinal cord using adeno-associated viruses enhanced locomotor recovery after SCI, and was associated with an increased number of oligodendrocytes. Altogether, our results demonstrate a functional role of the UPR in SCI, offering novel therapeutic targets to treat this invalidating condition.

Senescence-associated secretory phenotype favors the emergence of cancer stem-like cells

Abstract: The molecular mechanisms underlying cancer resistance remain elusive. One possible explanation is that cancer stem cells (CSCs) elude drug treatment, emerge and reproduce a tumor. Using multiple myeloma as a paradigm, we showed that cancer stem-like cells (CSLCs) appear after genotoxic stress because of their intrinsic properties. However, these properties do not drive the emergence of the CSLCs. Following genotoxic stress, remaining DNA damages lead to a senescence-associated secretory phenotype (SASP). Senescent cells, which are the non-CSLCs, secrete chemokines contributing to the emergence, maintenance and migration of CSLCs. Downregulation of checkpoint protein 2, a key player of SASP, significantly reduced the emergence of CSLCs. Our results unravel a novel molecular mechanism by which SASP might promote malignancy, underlining the dual role of senescence in tumorigenesis. This mechanism, based on mutual cooperation among tumor cells, illustrates how cancer may relapse; its targeting could represent new therapeutic opportunities.

Activation of autophagy induces retinal ganglion cell death in a chronic hypertensive glaucoma model.

Abstract: Autophagy is reported to have important roles in relation to regulated cell death pathways and neurodegeneration. This study used chronic hypertensive glaucoma rat model to investigate whether the autophagy pathway has a role in the apoptosis of retinal ganglion cells (RGCs) after chronic intraocular pressure (IOP) elevation. Under electron microscopy, autophagosomes were markedly accumulated in the dendrites and cytoplasm of RGCs after IOP elevation. Western blot analysis showed that LC3-II/LC3-I and beclin-1 were upregulated throughout the 8-weeks period after IOP elevation. The pattern of LC3 immunostaining showed autophagy activation in the cytoplasm of RGCs to increase and peak at 4 weeks after IOP elevation. Most of these LC3B-positive RGCs underwent apoptosis by terminal deoxynucleotidyltransferase-mediated biotinylated UTP nick end labeling, and inhibition of autophagy with 3-methyladenine decreased RGC apoptosis. The activated pattern shows that autophagy is initially activated in the dendrites of the RGCs, but, thereafter autophagy is mainly activated in the cytoplasm of RGCs. This may show that autophagy is differently regulated in different compartments of the neuron. This present study showed that autophgy is activated in RGCs and has a role in autophagic cell death after chronic IOP elevation.

Targeting Cullin-RING ligases by MLN4924 induces autophagy via modulating the HIF1-REDD1-TSC1-mTORC1-DEPTOR axis.

Abstract: MLN4924, a newly discovered small molecule inhibitor of NEDD8-activating enzyme (NAE), inactivates Cullin-RING E3 ubiquitin Ligases (CRLs) by blocking cullin neddylation As a result, MLN4924 causes accumulation of several key substrates of CRLs and effectively suppresses tumor cell growth by inducing apoptosis and senescence However, the role of MLN4924 in induction of autophagy and its biological significance are totally unknown Here we showed that MLN4924 effectively induces autophagy in both time- and dose-dependent manners in multiple human cancer lines, indicating a general phenomenon Mechanistically, by inactivating CRLs, MLN4924 causes accumulation of DEPTOR and HIF1α The siRNA knockdown and gene KO studies showed that DEPTOR and the HIF1-REDD1-TSC1 axis are responsible for MLN4924-induced autophagy via inhibiting mTORC1 Biologically, autophagy is a survival signal to tumor cells, and blockage of autophagy via siRNA knockdown, gene KO and small molecule inhibitor remarkably enhanced MLN4924-induced apoptosis Our study reveals an uncharacterized mechanism of MLN4924 action and provides the proof-of-concept evidence for strategic drug combination of MLN4924 with an autophagy inhibitor for maximal killing of tumor cells via enhancing apoptosis

MicroRNA-10b pleiotropically regulates invasion, angiogenicity and apoptosis of tumor cells resembling mesenchymal subtype of glioblastoma multiforme

Abstract: Glioblastoma multiforme (GBM) is a heterogeneous disease despite its seemingly uniform pathology. Deconvolution of The Cancer Genome Atlas’s GBM gene expression data has unveiled the existence of distinct gene expression signature underlying discrete GBM subtypes. Recent conflicting findings proposed that microRNA (miRNA)-10b exclusively regulates glioma growth or invasion but not both. We showed that silencing of miRNA-10b by baculoviral decoy vectors in a glioma cell line resembling the mesenchymal subtype of GBM reduces its growth, invasion and angiogenesis while promoting apoptosis in vitro. In an orthotopic human glioma mouse model, inhibition of miRNA-10b diminishes the invasiveness, angiogenicity and growth of the mesenchymal subtype-like glioma cells in the brain and significantly prolonged survival of glioma-bearing mice. We demonstrated that the pleiotropic nature of miRNA-10b was due to its suppression of multiple tumor suppressors, including TP53, FOXO3, CYLD, PAX6, PTCH1, HOXD10 and NOTCH1. In particular, siRNA-mediated knockdown experiments identified TP53, PAX6, NOTCH1 and HOXD10 as invasion regulatory genes in our mesenchymal subtype-like glioma cells. By interrogating the REMBRANDT, we noted that dysregulation of many direct targets of miRNA-10b was associated with significantly poorer patient survival. Thus, our study uncovers a novel role for miRNA-10b in regulating angiogenesis and suggests that miRNA-10b may be a pleiotropic regulator of gliomagenesis.

BMP2 sensitizes glioblastoma stem-like cells to Temozolomide by affecting HIF-1α stability and MGMT expression

Abstract: Glioblastoma multiforme (GBM) is the most common brain tumour, characterized by a central and partially necrotic (i.e., hypoxic) core enriched in cancer stem cells (CSCs). We previously showed that the most hypoxic and immature (i.e., CSCs) GBM cells were resistant to Temozolomide (TMZ) in vitro, owing to a particularly high expression of O6-methylguanine-DNA-methyltransferase (MGMT), the most important factor associated to therapy resistance in GBM. Bone morphogenetic proteins (BMPs), and in particular BMP2, are known to promote differentiation and growth inhibition in GBM cells. For this reason, we investigated whether a BMP2-based treatment would increase TMZ response in hypoxic drug-resistant GBM-derived cells. Here we show that BMP2 induced strong differentiation of GBM stem-like cells and subsequent addition of TMZ caused dramatic increase of apoptosis. Importantly, we correlated these effects to a BMP2-induced downregulation of both hypoxia-inducible factor-1α (HIF-1α) and MGMT. We report here a novel mechanism involving the HIF-1α-dependent regulation of MGMT, highlighting the existence of a HIF-1α/MGMT axis supporting GBM resistance to therapy. As confirmed from this evidence, over-stabilization of HIF-1α in TMZ-sensitive GBM cells abolished their responsiveness to it. In conclusion, we describe a HIF-1α-dependent regulation of MGMT and suggest that BMP2, by down-modulating the HIF-1α/MGMT axis, should increase GBM responsiveness to chemotherapy, thus opening the way to the development of future strategies for GBM treatment.

The P2X7 receptor is a key modulator of aerobic glycolysis.

Abstract: Ability to adapt to conditions of limited nutrient supply requires a reorganization of the metabolic pathways to balance energy generation and production of biosynthetic intermediates. Several fast-growing cells overexpress the P2X7 receptor (P2X7R) for extracellular ATP. A feature of this receptor is to allow growth in the absence of serum. We show here that transfection of P2X7R allows proliferation of P2X7R-transfected HEK293 (HEK293-P2X7) cells not only in the absence of serum but also in low (4 mM) glucose, and increases lactate output compared with mock-transfected HEK293 (HEK293-mock) cells. In HEK293-P2X7, lactate output is further stimulated upon addition of exogenous ATP or the mitochondrial uncoupler carbonylcyanide p-trifluoromethoxyphenylhydrazone (FCCP). In the human neuroblastoma cell line ACN, lactate output is also dependent on P2X7R function. P2X7R-expressing cells upregulate (a) the glucose transporter Glut1, (b) the glycolytic enzymes glyceraldehyde 3-phosphate dehydrogenase (G3PDH), (c) phosphofructokinase (PFK), (d) pyruvate kinase M2 (PKM2) and (e) pyruvate dehydrogenase kinase 1 (PDHK1); furthermore, P2X7R expression (a) inhibits pyruvate dehydrogenase (PDH) activity, (b) increases phosphorylated Akt/PKB and hypoxia-inducible factor 1α (HIF-1α) expression and (c) enhances intracellular glycogen stores. In HEK293-P2X7 cells, glucose deprivation increases lactate production, expression of glycolytic enzymes and ph-Akt/PKB level. These data show that the P2X7R has an intrinsic ability to reprogram cell metabolism to meet the needs imposed by adverse environmental conditions.

Cannabidiol protects oligodendrocyte progenitor cells from inflammation-induced apoptosis by attenuating endoplasmic reticulum stress.

Abstract: Cannabidiol (CBD) is the most abundant cannabinoid in Cannabis sativa that has no psychoactive properties. CBD has been approved to treat inflammation, pain and spasticity associated with multiple sclerosis (MS), of which demyelination and oligodendrocyte loss are hallmarks. Thus, we investigated the protective effects of CBD against the damage to oligodendrocyte progenitor cells (OPCs) mediated by the immune system. Doses of 1lM CBD protect OPCs from oxidative stress by decreasing the production of reactive oxygen species. CBD also protects OPCs from apoptosis induced by LPS/IFNc through the decrease of caspase 3 induction via mechanisms that do not involve CB1, CB2, TRPV1 or PPARc receptors. Tunicamycin-induced OPC death was attenuated by CBD, suggesting a role of endoplasmic reticulum (ER) stress in the mode of action of CBD. This protection against ER stress-induced apoptosis was associated with reduced phosphorylation of eiF2a, one of the initiators of the ER stress pathway. Indeed, CBD diminished the phosphorylation of PKR and eiF2a induced by LPS/IFNc. The pro-survival effects of CBD in OPCs were accompanied by decreases in the expression of ER apoptotic effectors (CHOP, Bax and caspase 12), and increased expression of the anti-apoptotic Bcl-2. These findings suggest that attenuation of the ER stress pathway is involved in the ‘oligoprotective’ effects of CBD during inflammation. Cell Death and Disease (2012) 3, e331; doi:10.1038/cddis.2012.71; published online 28 June 2012 Subject Category: Neuroscience Cannabidiol (CBD) is the most abundant cannabinoid in Cannabis sativa that is devoid of psychoactive properties. CBD exerts anti-inflammatory, antioxidant and neuroprotective effects, 1 and it has been approved for the treatment of inflammation, pain and spasticity associated with multiple sclerosis (MS). 2 Studies in an animal model of EAE have shown that CBD ameliorates the severity of the disease by attenuating neuroinflammation and axonal damage. 3 Oligodendrocyte progenitor cells (OPCs) are relatively quiescent cells derived from precursors of the perinatal CNS that make up around 5‐8% of the glial cell population in the adult; in the injured CNS, they can divideand are thought to differentiate to new myelinating oligodendroytes that replace those that have beenlost in demyelinating areas. 4 OPCs are highlyvulnerable to inflammation and oxidative stress as they have a high metabolic rate, high intracellular iron, and low concentrations of the antioxidative glutathione; they also express an arsenal of molecules rendering them susceptible to inflammatory cytokines or high calcium levels among others. 5 It is known

Inhibition of Casein kinase-2 induces p53-dependent cell cycle arrest and sensitizes glioblastoma cells to tumor necrosis factor (TNFα)-induced apoptosis through SIRT1 inhibition

Abstract: Glioblastoma multiforme (GBM) are resistant to TNFα-induced apoptosis and blockade of TNFα-induced NF-κB activation sensitizes glioma cells to apoptosis. As Casein kinase-2 (CK2) induces aberrant NF-κB activation and as we observed elevated CK2 levels in GBM tumors, we investigated the potential of CK2 inhibitors (CK2-Is) - DRB and Apigenin in sensitizing glioma cells to TNFα-induced apoptosis. CK2-Is and CK2 small interfering RNA (siRNA) reduced glioma cell viability, inhibited TNFα-mediated NF-κB activation, and sensitized cell to TNFα-induced apoptosis. Importantly, CK2-Is activated p53 function in wild-type but not in p53 mutant cells. Activation of p53 function involved its increased transcriptional activation, DNA-binding ability, increased expression of p53 target genes associated with cell cycle progression and apoptosis. Moreover, CK2-Is decreased telomerase activity and increased senescence in a p53-dependent manner. Apoptotic gene profiling indicated that CK2-Is differentially affect p53 and TNFα targets in p53 wild-type and mutant glioma cells. CK2-I decreased MDM2-p53 association and p53 ubiquitination to enhance p53 levels. Interestingly, CK2-Is downregulated SIRT1 activity and over-expression of SIRT1 decreased p53 transcriptional activity and rescued cells from CK2-I-induced apoptosis. This ability of CK2-Is to sensitize glioma to TNFα-induced death via multiple mechanisms involving abrogation of NF-κB activation, reactivation of wild-type p53 function and SIRT1 inhibition warrants investigation.

Apoptosis, autophagy and ER stress in mevalonate cascade inhibition-induced cell death of human atrial fibroblasts

Abstract: 3-hydroxy-3-methyl-glutaryl-CoA reductase inhibitors (statins) are cholesterol-lowering drugs that exert other cellular effects and underlie their beneficial health effects, including those associated with myocardial remodeling. We recently demonstrated that statins induces apoptosis and autophagy in human lung mesenchymal cells. Here, we extend our knowledge showing that statins simultaneously induces activation of the apoptosis, autophagy and the unfolded protein response (UPR) in primary human atrial fibroblasts (hATF). Thus we tested the degree to which coordination exists between signaling from mitochondria, endoplasmic reticulum and lysosomes during response to simvastatin exposure. Pharmacologic blockade of the activation of ER-dependent cysteine-dependent aspartate-directed protease (caspase)-4 and lysosomal cathepsin-B and -L significantly decreased simvastatin-induced cell death. Simvastatin altered total abundance and the mitochondrial fraction of proapoptotic and antiapoptotic proteins, while c-Jun N-terminal kinase/stress-activated protein kinase mediated effects on B-cell lymphoma 2 expression. Chemical inhibition of autophagy flux with bafilomycin-A1 augmented simvastatin-induced caspase activation, UPR and cell death. In mouse embryonic fibroblasts that are deficient in autophagy protein 5 and refractory to autophagy induction, caspase-7 and UPR were hyper-induced upon treatment with simvastatin. These data demonstrate that mevalonate cascade inhibition-induced death of hATF manifests from a complex mechanism involving co-regulation of apoptosis, autophagy and UPR. Furthermore, autophagy has a crucial role in determining the extent of ER stress, UPR and permissiveness of hATF to cell death induced by statins.

Non-small cell lung cancer stem/progenitor cells are enriched in multiple distinct phenotypic subpopulations and exhibit plasticity

Abstract: Cancer stem cells (CSCs) represent a population of cancer cells that possess unique self-renewal and differentiation characteristics required for tumorigenesis and are resistant to chemotherapy-induced apoptosis Lung CSCs can be enriched by several markers including drug-resistant side population (SP), CD133pos and ALDHhigh Using human non-small cell lung adenocarcinoma cell lines and patient-derived primary tumor cells, we demonstrate that SP cells represent a subpopulation distinct from other cancer stem/progenitor cell (CS/PC) populations marked by CD133pos or ALDHhigh The non-CS/PCs and CS/PCs of each subpopulation are interconvertible Epithelial-mesenchymal transition (EMT) promotes the formation of CD133pos and ALDHhigh CS/PC subpopulations while suppressing the SP CS/PC subpopulation Rac1 GTPase activity is significantly increased in cells that have undergone EMT, and targeting Rac1 is effective in inhibiting the dynamic conversion of non-CS/PCs to CS/PCs, as well as the CS/PC activity These results imply that various subpopulations of CS/PCs and non-CS/PCs may achieve a stochastic equilibrium in a defined microenvironment, and eliminating multiple subpopulations of CS/PCs and effectively blocking non-CS/PC to CS/PC transition, by an approach such as targeting Rac1, can be a more effective therapy