Bim inhibits autophagy by recruiting Beclin 1 to microtubules

Emerging Mechanisms in Initiating and Terminating Autophagy

Autophagy is a major degradative process activated in a rapid and transient manner to cope with stress conditions. Whether autophagy is beneficial or detrimental depends upon the rate of induction and the appropriateness of the duration. Alterations in both autophagy initiation and termination predispose the cell to death, and affect the execution of other inducible processes such as inflammation. In this review we discuss how stress signaling pathways dynamically control the activity of the autophagy machinery by mediating post-translational modifications and regulatory protein interactions. In particular, we highlight the emerging role of TRIM and CULLIN families of ubiquitin ligases which play opposite roles in the autophagy response by promoting or inhibiting, respectively, the activity of the autophagy initiation complex.

Sexual divergence in microtubule function: the novel intranasal microtubule targeting SKIP normalizes axonal transport and enhances memory

Activity-dependent neuroprotective protein (ADNP), essential for brain formation, is a frequent autism spectrum disorder (ASD)-mutated gene. ADNP associates with microtubule end-binding proteins (EBs) through its SxIP motif, to regulate dendritic spine formation and brain plasticity. Here, we reveal SKIP, a novel four-amino-acid peptide representing an EB-binding site, as a replacement therapy in an outbred Adnp-deficient mouse model. We discovered, for the first time, axonal transport deficits in Adnp(+/-) mice (measured by manganese-enhanced magnetic resonance imaging), with significant male-female differences. RNA sequencing evaluations showed major age, sex and genotype differences. Function enrichment and focus on major gene expression changes further implicated channel/transporter function and the cytoskeleton. In particular, a significant maturation change (1 month-five months) was observed in beta1 tubulin (Tubb1) mRNA, only in Adnp(+/+) males, and sex-dependent increase in calcium channel mRNA (Cacna1e) in Adnp(+/+) males compared with females. At the protein level, the Adnp(+/-) mice exhibited impaired hippocampal expression of the calcium channel (voltage-dependent calcium channel, Cacnb1) as well as other key ASD-linked genes including the serotonin transporter (Slc6a4), and the autophagy regulator, BECN1 (Beclin1), in a sex-dependent manner. Intranasal SKIP treatment normalized social memory in 8- to 9-month-old Adnp(+/-)-treated mice to placebo-control levels, while protecting axonal transport and ameliorating changes in ASD-like gene expression. The control, all d-amino analog D-SKIP, did not mimic SKIP activity. SKIP presents a novel prototype for potential ASD drug development, a prevalent unmet medical need.

Conformational flexibility of BECN1: Essential to its key role in autophagy and beyond

BECN1 (Beclin 1), a highly conserved eukaryotic protein, is a key regulator of autophagy, a cellular homeostasis pathway, and also participates in vacuolar protein sorting, endocytic trafficking, and apoptosis. BECN1 is important for embryonic development, the innate immune response, tumor suppression, and protection against neurodegenerative disorders, diabetes, and heart disease. BECN1 mediates autophagy as a core component of the class III phosphatidylinositol 3-kinase complexes. However, the exact mechanism by which it regulates the activity of these complexes, or mediates its other diverse functions is unclear. BECN1 interacts with several diverse protein partners, perhaps serving as a scaffold or interaction hub for autophagy. Based on extensive structural, biophysical and bioinformatics analyses, BECN1 consists of an intrinsically disordered region (IDR), which includes a BH3 homology domain (BH3D); a flexible helical domain (FHD); a coiled-coil domain (CCD); and a β-α-repeated autophagy-specific domain (BARAD). Each of these BECN1 domains mediates multiple diverse interactions that involve concomitant conformational changes. Thus, BECN1 conformational flexibility likely plays a key role in facilitating diverse protein interactions. Further, BECN1 conformation and interactions are also modulated by numerous post-translational modifications. A better structure-based understanding of the interplay between different BECN1 conformational and binding states, and the impact of post-translational modifications will be essential to elucidating the mechanism of its multiple biological roles.

BH3 mimetic Obatoclax (GX15-070) mediates mitochondrial stress predominantly via MCL-1 inhibition and induces autophagy-dependent necroptosis in human oral cancer cells

We have previously reported overexpression of antiapoptotic MCL-1 protein in human oral cancers and its association with therapy resistance and poor prognosis, implying it to be a potential therapeutic target. Hence, we investigated the efficacy and mechanism of action of Obatoclax, a BH3 mimetic pan BCL-2 inhibitor in human oral cancer cell lines. All cell lines exhibited high sensitivity to Obatoclax with complete clonogenic inhibition at 200-400 nM concentration which correlated with their MCL-1 expression. Mechanistic insights revealed that Obatoclax induced a caspase-independent cell death primarily by induction of a defective autophagy. Suppression of autophagy by ATG5 downregulation significantly blocked Obatoclax-induced cell death. Further, Obatoclax induced interaction of p62 with key components of the necrosome RIP1K and RIP3K. Necrostatin-1 mediated inhibition of RIP1K significantly protected the cells from Obatoclax induced cell death. Moreover, Obatoclax caused extensive mitochondrial stress leading to their dysfunction. Interestingly, MCL-1 downregulation alone caused mitochondrial stress, highlighting its importance for mitochondrial homeostasis. We also demonstrated in vivo efficacy of Obatoclax against oral cancer xenografts and its synergism with ionizing radiation in vitro. Our studies thus suggest that Obatoclax induces autophagy-dependent necroptosis in oral cancer cells and holds a great promise in the improved management of oral cancer patients.

Functional links between microtubules, autophagy and leaf starch degradation in plants

Mounting evidence suggests that microtubules play important roles in several aspects of autophagy in mammalian cells, such as autophagosome biogenesis, autophagosome trafficking and autolysosome formation. However, little research attention has been paid to the engagement of microtubules in plant autophagy. Recently, we reported novel findings in Nicotiana benthamiana that disruption of microtubules reduces autophagosome formation during upregulation of macroautophagy and triggers a specific type of chloroplast autophagy (SEX chlorophagy), which is closely associated with the starch-excess phenotype of leaves. These findings reveal important functional links between microtubules, autophagy and leaf starch degradation in plants.

Preoperative overnight parenteral nutrition (TPN) improves skeletal muscle protein metabolism indicated by microarray algorithm analyses in a randomized trial

Loss of muscle mass is associated with increased risk of morbidity and mortality in hospitalized patients. Uncertainties of treatment efficiency by short‐term artificial nutrition remain, specifically improvement of protein balance in skeletal muscles. In this study, algorithmic microarray analysis was applied to map cellular changes related to muscle protein metabolism in human skeletal muscle tissue during provision of overnight preoperative total parenteral nutrition (TPN). Twenty‐two patients (11/group) scheduled for upper GI surgery due to malignant or benign disease received a continuous peripheral all‐in‐one TPN infusion (30 kcal/kg/day, 0.16 gN/kg/day) or saline infusion for 12 h prior operation. Biopsies from the rectus abdominis muscle were taken at the start of operation for isolation of muscle RNA. RNA expression microarray analyses were performed with Agilent Sureprint G3, 8 × 60K arrays using one‐color labeling. 447 mRNAs were differently expressed between study and control patients (P < 0.1). mRNAs related to ribosomal biogenesis, mRNA processing, and translation were upregulated during overnight nutrition; particularly anabolic signaling S6K1 (P < 0.01–0.1). Transcripts of genes associated with lysosomal degradation showed consistently lower expression during TPN while mRNAs for ubiquitin‐mediated degradation of proteins as well as transcripts related to intracellular signaling pathways, PI3 kinase/MAPkinase, were either increased or decreased. In conclusion, muscle mRNA alterations during overnight standard TPN infusions at constant rate altered mRNAs associated with mTOR signaling; increased initiation of protein translation; and suppressed autophagy/lysosomal degradation of proteins. This indicates that overnight preoperative parenteral nutrition is effective to promote muscle protein metabolism.

Suppression of Bim by microRNA-19a may protect cardiomyocytes against hypoxia-induced cell death via autophagy activation

Microvascular obstruction (MO), one of unfavorable complications of percutaneous coronary intervention (PCI), is responsible for the lost benefit of reperfusion therapy. Determination of microRNA-19a, a member of the miR-17-92 cluster, using quantitative real-time polymerase chain reaction (PCR) revealed notably down-regulated microRNA-19a, in myocardium with MO. Nonetheless, the role of miR-19a in MO and the underlying mechanism remains to be elucidated. To this end, an in vitro microembolization model in cardiomyocytes was used. Our data revealed that hypoxic exposure prompted cardiomyocyte apoptosis in a time-dependent manner accompanied by reduced miR-19a. miR-19a overexpression clearly ameliorated hypoxia-induced cell death (necrosis and apoptosis), at least in part, through switching on autophagy. Further dual-luciferase reporter assay and immunoblotting studies demonstrated that miR-19a-induced cytoprotection might be achieved in part through modulation of the specific target Bcl-2 interacting mediator of cell death, Bim, an apoptotic activator. Bim sufficiently interfered with miR-19a-induced LC3 conversion and increased cardiomyocyte apoptosis under hypoxia. Moreover, cardiomyocytes pretreated with 3-methyladenine conferred resistance to the cytoprotective effect of miR-19a and displayed notably increased TUNEL staining and caspase-3 activity. In conclusion, miR-19a protected cardiomyocytes against hypoxia-induced lethality at least in part via Bim suppression and subsequently autophagy activation.

Nuclear DNA damage signalling to mitochondria in ageing

Mitochondrial dysfunction is a hallmark of ageing, and mitochondrial maintenance may lead to increased healthspan. Emerging evidence suggests a crucial role for signalling from the nucleus to mitochondria (NM signalling) in regulating mitochondrial function and ageing. An important initiator of NM signalling is nuclear DNA damage, which accumulates with age and may contribute to the development of age-associated diseases. DNA damage-dependent NM signalling constitutes a network that includes nuclear sirtuins and controls genomic stability and mitochondrial integrity. Pharmacological modulation of NM signalling is a promising novel approach for the prevention and treatment of age-associated diseases.

Autophagy and Apoptotic Crosstalk: Mechanism of Therapeutic Resistance in HER2-Positive Breast Cancer

While breast cancer patients benefit from the use of HER2 inhibitors, many fail therapy and become resistant to treatment, indicating a critical need to prevent treatment failure. A number of studies have emerged that highlight the catabolic process of autophagy in breast cancer as a mechanism of resistance to chemotherapy and targeted inhibitors. Furthermore, recent research has begun to dissect how autophagy signaling crosstalks with apoptotic signaling. Thus, a possible strategy in fighting resistance is to couple targeting of apoptotic and autophagy signaling pathways. In this review, we discuss how cellular response by autophagy circumvents cell death to promote resistance of breast cancers to HER2 inhibitors, as well as the potential avenues of therapeutic intervention.

Mammalian Autophagy: How Does It Work?

Autophagy is a conserved intracellular pathway that delivers cytoplasmic contents to lysosomes for degradation via double-membrane autophagosomes. Autophagy substrates include organelles such as mitochondria, aggregate-prone proteins that cause neurodegeneration and various pathogens. Thus, this pathway appears to be relevant to the pathogenesis of diverse diseases, and its modulation may have therapeutic value. Here, we focus on the cell and molecular biology of mammalian autophagy and review the key proteins that regulate the process by discussing their roles and how these may be modulated by posttranslational modifications. We consider the membrane-trafficking events that impact autophagy and the questions relating to the sources of autophagosome membrane(s). Finally, we discuss data from structural studies and some of the insights these have provided.

Chronic heart failure: Ca(2+), catabolism, and catastrophic cell death

Robust successes have been achieved in recent years in conquering the acutely lethal manifestations of heart disease. Many patients who previously would have died now survive to enjoy happy and productive lives. Nevertheless, the devastating impact of heart disease continues unabated, as the spectrum of disease has evolved with new manifestations. In light of this ever-evolving challenge, insights that culminate in novel therapeutic targets are urgently needed. Here, we review fundamental mechanisms of heart failure, both with reduced (HFrEF) and preserved (HFpEF) ejection fraction. We discuss pathways that regulate cardiomyocyte remodeling and turnover, focusing on Ca(2+) signaling, autophagy, and apoptosis. In particular, we highlight recent insights pointing to novel connections among these events. We also explore mechanisms whereby potential therapeutic approaches targeting these processes may improve morbidity and mortality in the devastating syndrome of heart failure.

BIM-EL localization: The key to understanding anoikis resistance in inflammatory breast cancer cells

Inflammatory breast cancer (IBC) is a highly metastatic and rare type of breast cancer, accounting for 2-6% of newly diagnosed breast cancer cases each year. The highly metastatic nature of IBC cells remains poorly understood. Here we describe our recent data regarding the ability of IBC cells to overcome anoikis.

New horizons in schizophrenia treatment: autophagy protection is coupled with behavioral improvements in a mouse model of schizophrenia

Autophagy plays a key role in the pathophysiology of schizophrenia as manifested by a 40% decrease in BECN1/Beclin 1 mRNA in postmortem hippocampal tissues relative to controls. This decrease was coupled with the deregulation of the essential ADNP (activity-dependent neuroprotector homeobox), a binding partner of MAP1LC3B/LC3B (microtubule-associated protein 1 light chain 3 β) another major constituent of autophagy. The drug candidate NAP (davunetide), a peptide fragment from ADNP, enhanced the ADNP-LC3B interaction. Parallel genetic studies have linked allelic variation in the gene encoding MAP6/STOP (microtubule-associated protein 6) to schizophrenia, along with altered MAP6/STOP protein expression in the schizophrenic brain and schizophrenic-like behaviors in Map6-deficient mice. In this study, for the first time, we reveal significant decreases in hippocampal Becn1 mRNA and reversal by NAP but not by the antipsychotic clozapine (CLZ) in Map6-deficient (Map6(+/-)) mice. Normalization of Becn1 expression by NAP was coupled with behavioral protection against hyperlocomotion and cognitive deficits measured in the object recognition test. CLZ reduced hyperlocomotion below control levels and did not significantly affect object recognition. The combination of CLZ and NAP resulted in normalized outcome behaviors. Phase II clinical studies have shown NAP-dependent augmentation of functional activities of daily living coupled with brain protection. The current studies provide a new mechanistic pathway and a novel avenue for drug development.

Regulation of autophagy by Beclin 1 in the heart

Dysregulation of autophagy in cardiomyocytes is implicated in various heart disease conditions. Beclin 1, a mammalian ortholog of yeast Atg6 and a core component of the autophagy machinery, plays a central role in the regulation of autophagy through activation of Vps34. Beclin 1's ability to activate Vps34 is tightly regulated via transcriptional regulation, miRNA, post-translational modification, and interaction with Beclin 1 binding proteins. Of these mechanisms, binding of Beclin 1 with Bcl-2 family proteins (Bcl-2/XL) that negatively regulate autophagy activity has been shown to be both positively and negatively regulated by various kinases, including DAPK, ROCK1, Mst1 and JNK1, in response to external stimuli. Beclin 1's interaction with Bcl-2/XL also secondarily affects apoptosis through regulation of pro-apoptotic BH3 domain containing proteins. Thus, modulation of Beclin 1 significantly influences both autophagy and apoptosis, thereby deeply affecting the survival and death of cardiomyocytes in the heart. In this review, we discuss the signaling mechanism of autophagy modulation through Beclin 1 and therapeutic potential of Beclin 1 in heart diseases.

Regulation of Bim in Health and Disease

The BH3-only Bim protein is a major determinant for initiating the intrinsic apoptotic pathway under both physiological and pathophysiological conditions. Tight regulation of its expression and activity at the transcriptional, translational and post-translational levels together with the induction of alternatively spliced isoforms with different pro-apoptotic potential, ensure timely activation of Bim. Under physiological conditions, Bim is essential for shaping immune responses where its absence promotes autoimmunity, while too early Bim induction eliminates cytotoxic T cells prematurely, resulting in chronic inflammation and tumor progression. Enhanced Bim induction in neurons causes neurodegenerative disorders including Alzheimer's, Parkinson's and Huntington's diseases. Moreover, type I diabetes is promoted by genetically predisposed elevation of Bim in β-cells. On the contrary, cancer cells have developed mechanisms that suppress Bim expression necessary for tumor progression and metastasis. This review focuses on the intricate network regulating Bim activity and its involvement in physiological and pathophysiological processes.

Local anesthetics induce autophagy in young permanent tooth pulp cells

Pulp cells are essential for tooth development, and dentin repair and regeneration. In addition these cells have been identified as an important stem cell source. Local anesthetics are widely used in dental clinics, as well as the other clinical disciplines and have been suggested to interfere with human permanent tooth development and induce tooth agenesis through unknown mechanisms. Using pig model and human young permanent tooth pulp cells, our research has identified that the local anesthetics commonly used in clinics can affect cell proliferation. Molecular pathway profiling suggested that LC3II is one of the earliest molecules induced by the agents and p62 is the only common downstream target identified for all the drugs tested. The effect of the drugs could be partially recovered by V-ATPase inhibitor only if early intervention is performed. Our results provide novel evidence that local anesthetics could affect tooth cell growth that potentially can have impacts on tooth development.

Beclin 1 biology and its role in heart disease

Macroautophagy (hereafter termed autophagy) is a highly evolutionarily conserved pathway that degrades intracellular components such as damaged organelles in lysosome. Autophagy occurs at low basal levels in virtually all types of cells, which is required for the maintenance of cellular homeostasis. Beclin 1 protein, encoded by the beclin 1 gene, plays a central role in the regulation of autophagy. Beclin 1 primarily functions as a scaffolding protein assembling Beclin 1 interactome to regulate Class III PI3K/VPS34 activity, which in turn, tightly controls autophagy at multiple stages. In addition to autophagy, Beclin 1 participates in the regulation of other biological processes such as endocytosis, apoptosis and phagocytosis. Fine-tuning of Beclin 1 protein levels, intracellular localization and the assembly of its interactome is pivotal for the proper execution of these biological functions. Deregulation of Beclin 1 contributes to the pathogenesis of a variety of human diseases. In this review, we summarize biology of Beclin 1 and its role in human pathology, with an emphasis on heart disease.

Autophagic activity in neuronal cell death

As post-mitotic cells with great energy demands, neurons depend upon the homeostatic and waste-recycling functions provided by autophagy. In addition, autophagy also promotes survival during periods of harsh stress and targets aggregate-prone proteins associated with neurodegeneration for degradation. Despite this, autophagy has also been controversially described as a mechanism of programmed cell death. Instances of autophagic cell death are typically associated with elevated numbers of cytoplasmic autophagosomes, which have been assumed to lead to excessive degradation of cellular components. Due to the high activity and reliance on autophagy in neurons, these cells may be particularly susceptible to autophagic death. In this review, we summarize and assess current evidence in support of autophagic cell death in neurons, as well as how the dysregulation of autophagy commonly seen in neurodegeneration can contribute to neuron loss. From here, we discuss potential treatment strategies relevant to such cell-death pathways.

MiR-124 Regulates Apoptosis and Autophagy Process in MPTP Model of Parkinson's Disease by Targeting to Bim

Parkinson's disease (PD) is the most prevalent movement disorder characterized by selective loss of midbrain dopaminergic (DA) neurons. MicroRNA-124 (miR-124) is abundantly expressed in the DA neurons and its expression level decreases in the 1-methyl-4-pheny-1, 2, 3, 6-tetrahydropyridine (MPTP) model of PD. However, whether the upregulation of miR-124 could attenuate neurodegeneration remains unknown. Here, we employed miR-124 agomir and miR-124 mimics to upregulate miR-124 expression in MPTP-treated mice and MPP(+) -intoxicated SH-SY5Y cells, respectively. We found that loss of DA neurons and striatal dopamine in MPTP-treated mice was significantly reduced by upregulating miR-124. In addition, we identified a target of miR-124, Bim that mediated the neuroprotection of miR-124. Indeed, treatment of miR-124 agomir in MPTP-treated mice inhibited Bim expression, thus suppressing Bax translocation to mitochondria. Moreover, impaired autophagy process in MPTP-treated mice and MPP(+) -intoxicated SH-SY5Y cells characterized as autophagosomes (AP) accumulation and lysosomal depletion were alleviated by the upregulation of miR-124. Taken together, these results indicate that upregulation of miR-124 could regulate apoptosis and impaired autophagy process in the MPTP model of PD, thus reducing the loss of DA neurons.

Beclin orthologs: integrative hubs of cell signaling, membrane trafficking, and physiology

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Beclin orthologs are crucial regulators of autophagy and related membrane-trafficking pathways.

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Multiple signaling pathways converge on Beclin 1 to regulate cellular stress responses, membrane trafficking, and physiology.

The Beclin family, including yeast Atg6 (autophagy related gene 6), its orthologs in higher eukaryotic species, and the more recently characterized mammalian-specific Beclin 2, are essential molecules in autophagy and other membrane-trafficking events. Extensive studies of Beclin orthologs have provided considerable insights into the regulation of autophagy, the diverse roles of autophagy in physiology and disease, and potential new strategies to modulate autophagy in a variety of clinical diseases. In this review we discuss the functions of Beclin orthologs, the regulation of such functions by diverse cellular signaling pathways, and the effects of such regulation on downstream cellular processes including tumor suppression and metabolism. These findings suggest that Beclin orthologs serve as crucial molecules that integrate diverse environmental signals with membrane trafficking events to ensure optimal responses of the cell to stressful stimuli.

BECN1 is involved in the initiation of mitophagy: it facilitates PARK2 translocation to mitochondria

The autophagy protein BECN1/Beclin 1 is known to play a central role in autophagosome formation and maturation. The results presented here demonstrate that BECN1 interacts with the Parkinson disease-related protein PARK2. This interaction does not require PARK2 translocation to mitochondria and occurs mostly in cytosol. However, our results suggest that BECN1 is involved in PARK2 translocation to mitochondria because loss of BECN1 inhibits CCCP- or PINK1 overexpression-induced PARK2 translocation. Our results also demonstrate that the observed PARK2-BECN1 interaction is functionally important. Measurements of the level of MFN2 (mitofusin 2), a PARK2 substrate, demonstrate that depletion of BECN1 prevents PARK2 translocation-induced MFN2 ubiquitination and loss. BECN1 depletion also rescues the MFN2 loss-induced suppression of mitochondrial fusion. In sum, our results demonstrate that BECN1 interacts with PARK2 and regulates PARK2 translocation to mitochondria as well as PARK2-induced mitophagy prior to autophagosome formation.

Die another way--non-apoptotic mechanisms of cell death

Regulated, programmed cell death is crucial for all multicellular organisms. Cell death is essential in many processes, including tissue sculpting during embryogenesis, development of the immune system and destruction of damaged cells. The best-studied form of programmed cell death is apoptosis, a process that requires activation of caspase proteases. Recently it has been appreciated that various non-apoptotic forms of cell death also exist, such as necroptosis and pyroptosis. These non-apoptotic cell death modalities can be either triggered independently of apoptosis or are engaged should apoptosis fail to execute. In this Commentary, we discuss several regulated non-apoptotic forms of cell death including necroptosis, autophagic cell death, pyroptosis and caspase-independent cell death. We outline what we know about their mechanism, potential roles in vivo and define outstanding questions. Finally, we review data arguing that the means by which a cell dies actually matters, focusing our discussion on inflammatory aspects of cell death.

Autophagy and apoptosis: where do they meet?

Autophagy and apoptosis are two important cellular processes with complex and intersecting protein networks; as such, they have been the subjects of intense investigation. Recent advances have elucidated the key players and their molecular circuitry. For instance, the discovery of Beclin-1's interacting partners has resulted in the identification of Bcl-2 as a central regulator of autophagy and apoptosis, which functions by interacting with both Beclin-1 and Bax/Bak respectively. When localized to the endoplasmic reticulum and mitochondria, Bcl-2 inhibits autophagy. Cellular stress causes the displacement of Bcl-2 from Beclin-1 and Bax, thereby triggering autophagy and apoptosis, respectively. The induction of autophagy or apoptosis results in disruption of complexes by BH3-only proteins and through post-translational modification. The mechanisms linking autophagy and apoptosis are not fully defined; however, recent discoveries have revealed that several apoptotic proteins (e.g., PUMA, Noxa, Nix, Bax, XIAP, and Bim) modulate autophagy. Moreover, autophagic proteins that control nucleation and elongation regulate intrinsic apoptosis through calpain- and caspase-mediated cleavage of autophagy-related proteins, which switches the cellular program from autophagy to apoptosis. Similarly, several autophagic proteins are implicated in extrinsic apoptosis. This highlights a dual cellular role for autophagy. On one hand, autophagy degrades damaged mitochondria and caspases, and on the other hand, it provides a membrane-based intracellular platform for caspase processing in the regulation of apoptosis. In this review, we highlight the crucial factors governing the crosstalk between autophagy and apoptosis and describe the mechanisms controlling cell survival and cell death.

Connecting autophagy: AMBRA1 and its network of regulation

During autophagy, a double-membraned vesicle called the autophagosome is responsible for the degradation of long-lived proteins and damaged/old organelles, thus contributing to the maintenance of cellular homeostasis. Physiological stimuli and stressors enhance autophagy in order to accomplish important processes such as cell differentiation or as a cytoprotective response. In line with this, numerous studies have demonstrated the relevance of proper autophagy regulation to health. Autophagy defects are associated with the insurgence of neurological/neurodegenerative diseases and cancer. Moreover, the autophagy pathway is often potentiated in cancer cells to increase cell survival. Increased knowledge of the molecular mechanisms underlying autophagy regulation and their interplay with other cellular pathways would provide advances in cancer treatment. In this context, post-translational modifications, protein-protein interactions, and regulative feedback loops offer promising insights. In this review, we focus on AMBRA1, a proautophagic protein that was recently demonstrated to participate in numerous crucial regulative mechanisms of the autophagy process.

Involvement of autophagy inhibition in Brucea javanica oil emulsion-induced colon cancer cell death

Brucea javanica oil emulsion (BJOE), the petroleum ether extract of B. javanica emulsified by phospholipid, is widely used in China as an anticancer agent. The extracts from B. javanica induce cancer cell death by various mechanisms; however, it is not known whether these mechanisms involve autophagy, which is an important process in cancer development and treatment. Thus, the current study aimed to investigate whether BJOE modulates autophagy in HCT116 human colon cancer cells and whether modulation of autophagy is an anticancer mechanism of BJOE. Immunoblotting was employed to analyze the protein expression levels of microtubule-associated protein light-chain 3 (LC3), a specific protein marker of autophagy, in HCT116 cancer cells following exposure to BJOE. The apoptosis rate of the HCT116 cancer cells was detected by performing an Annexin V-fluorescein isothiocyanate/propidium iodide assay. According to the effect of BJOE administration on autophagy in the HCT116 cancer cells (induction or suppression), a functionally opposite agent (autophagy suppressor or inducer) was applied to counteract this effect, and the apoptosis rate of the cancer cells was detected again. The role of autophagy (pro-survival or pro-death) was demonstrated by comparing the rates of apoptotic cancer cells prior to and following the counteraction. The results revealed that BJOE suppressed the protein expression levels of LC3, including the LC3-I and LC3-II forms, and induced apoptosis in the HCT116 cancer cells with a high level of basal LC3. The apoptosis-inducing activity of BJOE was significantly attenuated when autophagy was induced by the administration of trehalose, an autophagy inducer. The data indicates that autophagy inhibition is involved in BJOE-induced cancer cell death, and that this inhibition may be a potential anticancer mechanism of BJOE.

RIPK1 regulates survival of human melanoma cells upon endoplasmic reticulum stress through autophagy

Although RIPK1 (receptor [TNFRSF]-interacting protein kinase 1) is emerging as a critical determinant of cell fate in response to cellular stress resulting from activation of death receptors and DNA damage, its potential role in cell response to endoplasmic reticulum (ER) stress remains undefined. Here we report that RIPK1 functions as an important prosurvival mechanism in melanoma cells undergoing pharmacological ER stress induced by tunicamycin (TM) or thapsigargin (TG) through activation of autophagy. While treatment with TM or TG upregulated RIPK1 and triggered autophagy in melanoma cells, knockdown of RIPK1 inhibited autophagy and rendered the cells sensitive to killing by TM or TG, recapitulating the effect of inhibition of autophagy. Consistently, overexpression of RIPK1 enhanced induction of autophagy and conferred resistance of melanoma cells to TM- or TG-induced cell death. Activation of MAPK8/JNK1 or MAPK9/JNK2, which phosphorylated BCL2L11/BIM leading to its dissociation from BECN1/Beclin 1, was involved in TM- or TG-induced, RIPK1-mediated activation of autophagy; whereas, activation of the transcription factor HSF1 (heat shock factor protein 1) downstream of the ERN1/IRE1-XBP1 axis of the unfolded protein response was responsible for the increase in RIPK1 in melanoma cells undergoing pharmacological ER stress. Collectively, these results identify upregulation of RIPK1 as an important resistance mechanism of melanoma cells to TM- or TG-induced ER stress by protecting against cell death through activation of autophagy, and suggest that targeting the autophagy-activating mechanism of RIPK1 may be a useful strategy to enhance sensitivity of melanoma cells to therapeutic agents that induce ER stress.

Anoikis evasion in inflammatory breast cancer cells is mediated by Bim-EL sequestration

Inflammatory breast cancer (IBC) is a rare and highly invasive type of breast cancer, and patients diagnosed with IBC often face a very poor prognosis. IBC is characterized by the lack of primary tumor formation and the rapid accumulation of cancerous epithelial cells in the dermal lymphatic vessels. Given that normal epithelial cells require attachment to the extracellular matrix (ECM) for survival, a comprehensive examination of the molecular mechanisms underlying IBC cell survival in the lymphatic vessels is of paramount importance to our understanding of IBC pathogenesis. Here we demonstrate that, in contrast to normal mammary epithelial cells, IBC cells evade ECM-detachment-induced apoptosis (anoikis). ErbB2 and EGFR knockdown in KPL-4 and SUM149 cells, respectively, causes decreased colony growth in soft agar and increased caspase activation following ECM detachment. ERK/MAPK signaling was found to operate downstream of ErbB2 and EGFR to protect cells from anoikis by facilitating the formation of a protein complex containing Bim-EL, LC8, and Beclin-1. This complex forms as a result of Bim-EL phosphorylation on serine 59, and thus Bim-EL cannot localize to the mitochondria and cause anoikis. These results reveal a novel mechanism that could be targeted with innovative therapeutics to induce anoikis in IBC cells.

Autophagy and mitophagy in the myocardium: therapeutic potential and concerns

The autophagic-lysosomal degradation pathway is critical for cardiac homeostasis, and defects in this pathway are associated with development of cardiomyopathy. Autophagy is responsible for the normal turnover of organelles and long-lived proteins. Autophagy is also rapidly up-regulated in response to stress, where it rapidly clears dysfunctional organelles and cytotoxic protein aggregates in the cell. Autophagy is also important in clearing dysfunctional mitochondria before they can cause harm to the cell. This quality control mechanism is particularly important in cardiac myocytes, which contain a very high volume of mitochondria. The degradation of proteins and organelles also generates free fatty acids and amino acids, which help maintain energy levels in myocytes during stress conditions. Increases in autophagy have been observed in various cardiovascular diseases, but a major question that remains to be answered is whether enhanced autophagy is an adaptive or maladaptive response to stress. This review discusses the regulation and role of autophagy in the myocardium under baseline conditions and in various aetiologies of heart disease. It also discusses whether this pathway represents a new therapeutic target to treat or prevent cardiovascular disease and the concerns associated with modulating autophagy.

Dynein function and protein clearance changes in tumor cells induced by a Kunitz-type molecule, Amblyomin-X

Amblyomin-X is a Kunitz-type recombinant protein identified from the transcriptome of the salivary glands of the tick Amblyomma cajennense and has anti-coagulant and antitumoral activity. The supposed primary target of this molecule is the proteasome system. Herein, we elucidated intracellular events that are triggered by Amblyomin-X treatment in an attempt to provide new insight into how this serine protease inhibitor, acting on the proteasome, could be comparable with known proteasome inhibitors. The collective results showed aggresome formation after proteasome inhibition that appeared to occur via the non-exclusive ubiquitin pathway. Additionally, Amblyomin-X increased the expression of various chains of the molecular motor dynein in tumor cells, modulated specific ubiquitin linkage signaling and inhibited autophagy activation by modulating mTOR, LC3 and AMBRA1 with probable dynein involvement. Interestingly, one possible role for dynein in the mechanism of action of Amblyomin-X was in the apoptotic response and its crosstalk with autophagy, which involved the factor Bim; however, we observed no changes in the apoptotic response related to dynein in the experiments performed. The characteristics shared among Amblyomin-X and known proteasome inhibitors included NF-κB blockage and nascent polypeptide-dependent aggresome formation. Therefore, our study describes a Kunitz-type protein that acts on the proteasome to trigger distinct intracellular events compared to classic known proteasome inhibitors that are small-cell-permeable molecules. In investigating the experiments and literature on Amblyomin-X and the known proteasome inhibitors, we also found differences in the structures of the molecules, intracellular events, dynein involvement and tumor cell type effects. These findings also reveal a possible new target for Amblyomin-X, i.e., dynein, and may serve as a tool for investigating tumor cell death associated with proteasome inhibition.

Mending a broken heart: the role of mitophagy in cardioprotection

The heart is highly energy dependent with most of its energy provided by mitochondrial oxidative phosphorylation. Mitochondria also play a role in many other essential cellular processes including metabolite synthesis and calcium storage. Therefore, maintaining a functional population of mitochondria is critical for cardiac function. Efficient degradation and replacement of dysfunctional mitochondria ensures cell survival, particularly in terminally differentiated cells such as cardiac myocytes. Mitochondria are eliminated via mitochondrial autophagy or mitophagy. In the heart, mitophagy is an essential housekeeping process and required for cardiac homeostasis. Reduced autophagy and accumulation of impaired mitochondria have been linked to progression of heart failure and aging. In this review, we discuss the pathways that regulate mitophagy in cells and highlight the cardioprotective role of mitophagy in response to stress and aging. We also discuss the therapeutic potential of targeting mitophagy and directions for future investigation.

A Bim-targeting strategy overcomes adaptive bortezomib resistance in myeloma through a novel link between autophagy and apoptosis

Bim contributes to resistance to various standard and novel agents. Here we demonstrate that Bim plays a functional role in bortezomib resistance in multiple myeloma (MM) cells and that targeting Bim by combining histone deacetylase inhibitors (HDACIs) with BH3 mimetics (eg, ABT-737) overcomes bortezomib resistance. BH3-only protein profiling revealed high Bim levels (Bim(hi)) in most MM cell lines and primary CD138(+) MM samples. Whereas short hairpin RNA Bim knockdown conferred bortezomib resistance in Bim(hi) cells, adaptive bortezomib-resistant cells displayed marked Bim downregulation. HDACI upregulated Bim and, when combined with ABT-737, which released Bim from Bcl-2/Bcl-xL, potently killed bortezomib-resistant cells. These events were correlated with Bim-associated autophagy attenuation, whereas Bim knockdown sharply increased autophagy in Bim(hi) cells. In Bim(low) cells, autophagy disruption by chloroquine (CQ) was required for HDACI/ABT-737 to induce Bim expression and lethality. CQ also further enhanced HDACI/ABT-737 lethality in bortezomib-resistant cells. Finally, HDACI failed to diminish autophagy or potentiate ABT-737-induced apoptosis in bim(-/-) mouse embryonic fibroblasts. Thus, Bim deficiency represents a novel mechanism of adaptive bortezomib resistance in MM cells, and Bim-targeting strategies combining HDACIs (which upregulate Bim) and BH3 mimetics (which unleash Bim from antiapoptotic proteins) overcomes such resistance, in part by disabling cytoprotective autophagy.

Artesunate induces necrotic cell death in schwannoma cells

Established as a potent anti-malaria medicine, artemisinin-based drugs have been suggested to have anti-tumour activity in some cancers. Although the mechanism is poorly understood, it has been suggested that artemisinin induces apoptotic cell death. Here, we show that the artemisinin analogue artesunate (ART) effectively induces cell death in RT4 schwannoma cells and human primary schwannoma cells. Interestingly, our data indicate for first time that the cell death induced by ART is largely dependent on necroptosis. ART appears to inhibit autophagy, which may also contribute to the cell death. Our data in human schwannoma cells show that ART can be combined with the autophagy inhibitor chloroquine (CQ) to potentiate the cell death. Thus, this study suggests that artemisinin-based drugs may be used in certain tumours where cells are necroptosis competent, and the drugs may act in synergy with apoptosis inducers or autophagy inhibitors to enhance their anti-tumour activity.

Autosis and autophagic cell death: the dark side of autophagy

It is controversial whether cells truly die via autophagy or whether — in dying cells — autophagy is merely an innocent bystander or a well-intentioned ‘Good Samaritan' trying to prevent inevitable cellular demise. However, there is increasing evidence that the genetic machinery of autophagy may be essential for cell death in certain settings. We recently identified a novel form of autophagy gene-dependent cell death, termed autosis, which is mediated by the Na⁺,K⁺-ATPase pump and has unique morphological features. High levels of cellular autophagy, as occurs with treatment with autophagy-inducing peptides, starvation, or in vivo during certain types of ischemia, can trigger autosis. These findings provide insights into the mechanisms and strategies for prevention of cell death during extreme stress conditions.

Cell biology. Metabolic control of cell death

Beyond their contribution to basic metabolism, the major cellular organelles, in particular mitochondria, can determine whether cells respond to stress in an adaptive or suicidal manner. Thus, mitochondria can continuously adapt their shape to changing bioenergetic demands as they are subjected to quality control by autophagy, or they can undergo a lethal permeabilization process that initiates apoptosis. Along similar lines, multiple proteins involved in metabolic circuitries, including oxidative phosphorylation and transport of metabolites across membranes, may participate in the regulated or catastrophic dismantling of organelles. Many factors that were initially characterized as cell death regulators are now known to physically or functionally interact with metabolic enzymes. Thus, several metabolic cues regulate the propensity of cells to activate self-destructive programs, in part by acting on nutrient sensors. This suggests the existence of "metabolic checkpoints" that dictate cell fate in response to metabolic fluctuations. Here, we discuss recent insights into the intersection between metabolism and cell death regulation that have major implications for the comprehension and manipulation of unwarranted cell loss.

Regulating cell death at, on, and in membranes

Bcl-2 family proteins are central regulators of apoptosis. Various family members are located in the cytoplasm, endoplasmic reticulum, and mitochondrial outer membrane in healthy cells. However during apoptosis most of the interactions between family members that determine the fate of the cell occur at the membranes of intracellular organelles. It has become evident that interactions with membranes play an active role in the regulation of Bcl-2 family protein interactions. Here we provide an overview of various models proposed to explain how the Bcl-2 family regulates apoptosis and discuss how membrane binding affects the structure and function of each of the three categories of Bcl-2 proteins (pro-apoptotic, pore-forming, and anti-apoptotic). We also examine how the Bcl-2 family regulates other aspects of mitochondrial and ER physiology relevant to cell death.

Small molecules, big effects: the role of microRNAs in regulation of cardiomyocyte death

MicroRNAs (miRNAs) are a class of small non-coding RNAs involved in posttranscriptional regulation of gene expression, and exerting regulatory roles in plethora of biological processes. In recent years, miRNAs have received increased attention for their crucial role in health and disease, including in cardiovascular disease. This review summarizes the role of miRNAs in regulation of cardiac cell death/cell survival pathways, including apoptosis, autophagy and necrosis. It is envisaged that these miRNAs may explain the mechanisms behind the pathogenesis of many cardiac diseases, and, most importantly, may provide new avenues for therapeutic intervention that will limit cardiomyocyte cell death before it irreversibly affects cardiac function. Through an in-depth literature analysis coupled with integrative bioinformatics (pathway and synergy analysis), we dissect here the landscape of complex relationships between the apoptosis-regulating miRNAs in the context of cardiomyocyte cell death (including regulation of autophagy–apoptosis cross talk), and examine the gaps in our current understanding that will guide future investigations.

Microtubules and their role in cellular stress in cancer

Microtubules are highly dynamic structures, which consist of α- and β-tubulin heterodimers, and are involved in cell movement, intracellular trafficking, and mitosis. In the context of cancer, the tubulin family of proteins is recognized as the target of the tubulin-binding chemotherapeutics, which suppress the dynamics of the mitotic spindle to cause mitotic arrest and cell death. Importantly, changes in microtubule stability and the expression of different tubulin isotypes as well as altered post-translational modifications have been reported for a range of cancers. These changes have been correlated with poor prognosis and chemotherapy resistance in solid and hematological cancers. However, the mechanisms underlying these observations have remained poorly understood. Emerging evidence suggests that tubulins and microtubule-associated proteins may play a role in a range of cellular stress responses, thus conferring survival advantage to cancer cells. This review will focus on the importance of the microtubule-protein network in regulating critical cellular processes in response to stress. Understanding the role of microtubules in this context may offer novel therapeutic approaches for the treatment of cancer.

Autophagy and cell death

Autophagy is intimately associated with eukaryotic cell death and apoptosis. Indeed, in some cases the same proteins control both autophagy and apoptosis. Apoptotic signalling can regulate autophagy and conversely autophagy can regulate apoptosis (and most likely other cell death mechanisms). However, the molecular connections between autophagy and cell death are complicated and, in different contexts, autophagy may promote or inhibit cell death. Surprisingly, although we know that, at its core, autophagy involves degradation of sequestered cytoplasmic material, and therefore presumably must be mediating its effects on cell death by degrading something, in most cases we have little idea of what is being degraded to promote autophagy's pro- or anti-death activities. Because autophagy is known to play important roles in health and many diseases, it is critical to understand the mechanisms by which autophagy interacts with and affects the cell death machinery since this will perhaps allow new ways to prevent or treat disease. In the present chapter, we discuss the current state of understanding of these processes.

Regulation of autophagy by mTOR-dependent and mTOR-independent pathways: autophagy dysfunction in neurodegenerative diseases and therapeutic application of autophagy enhancers

Autophagy is an intracellular degradation pathway essential for cellular and energy homoeostasis. It functions in the clearance of misfolded proteins and damaged organelles, as well as recycling of cytosolic components during starvation to compensate for nutrient deprivation. This process is regulated by mTOR (mammalian target of rapamycin)-dependent and mTOR-independent pathways that are amenable to chemical perturbations. Several small molecules modulating autophagy have been identified that have potential therapeutic application in diverse human diseases, including neurodegeneration. Neurodegeneration-associated aggregation-prone proteins are predominantly degraded by autophagy and therefore stimulating this process with chemical inducers is beneficial in a wide range of transgenic disease models. Emerging evidence indicates that compromised autophagy contributes to the aetiology of various neurodegenerative diseases related to protein conformational disorders by causing the accumulation of mutant proteins and cellular toxicity. Combining the knowledge of autophagy dysfunction and the mechanism of drug action may thus be rational for designing targeted therapy. The present review describes the cellular signalling pathways regulating mammalian autophagy and highlights the potential therapeutic application of autophagy inducers in neurodegenerative disorders.

Autophagy: regulation and role in development

Autophagy is an evolutionarily conserved cellular process through which long-lived proteins and damaged organelles are recycled to maintain energy homeostasis. These proteins and organelles are sequestered into a double-membrane structure, or autophagosome, which subsequently fuses with a lysosome in order to degrade the cargo. Although originally classified as a type of programmed cell death, autophagy is more widely viewed as a basic cell survival mechanism to combat environmental stressors. Autophagy genes were initially identified in yeast and were found to be necessary to circumvent nutrient stress and starvation. Subsequent elucidation of mammalian gene counterparts has highlighted the importance of this process to normal development. This review provides an overview of autophagy, the types of autophagy, its regulation and its known impact on development gleaned primarily from murine models.

Autophagy controls the kinetics and extent of mitochondrial apoptosis by regulating PUMA levels

Macroautophagy is thought to protect against apoptosis; however, underlying mechanisms are poorly understood. We examined how autophagy affects canonical death receptor-induced mitochondrial outer membrane permeabilization (MOMP) and apoptosis. MOMP occurs at variable times in a population of cells, and this is delayed by autophagy. Additionally, autophagy leads to inefficient MOMP, after which some cells die through a slower process than typical apoptosis and, surprisingly, can recover and divide afterward. These effects are associated with p62/SQSTM1-dependent selective autophagy causing PUMA levels to be kept low through an indirect mechanism whereby autophagy affects constitutive levels of PUMA mRNA. PUMA depletion is sufficient to prevent the sensitization to apoptosis that occurs when autophagy is blocked. Autophagy can therefore control apoptosis via a key regulator that makes MOMP faster and more efficient, thus ensuring rapid completion of apoptosis. This identifies a molecular mechanism whereby cell-fate decisions can be determined by autophagy.

The role of cell signalling in the crosstalk between autophagy and apoptosis

Not surprisingly, the death of a cell is a complex and well controlled process. For several decades, apoptosis, the first genetically programmed death process to be identified has taken centre stage as the principal mechanism of programmed cell death (type I cell death) in mammalian tissues. Apoptosis has been extensively studied and its contribution to the pathogenesis of disease well documented. However, apoptosis does not function alone in determining the fate of a cell. More recently, autophagy, a process in which de novo formed membrane enclosed vesicles engulf and consume cellular components, has been shown to engage in complex interplay with apoptosis. As a result, cell death has been subdivided into the categories apoptosis (Type I), autophagic cell death (Type II), and necrosis (Type III). The boundary between Type I and II cell death is not completely clear and as we will discuss in this review and perhaps a discrete difference does not exist, due to intrinsic factors among different cell types and crosstalk among organelles within each cell type. Apoptosis may begin with autophagy and autophagy can often end with apoptosis, inhibition or a blockade of caspase activity may lead a cell to default into Type II cell death from Type I.

Self-consumption: the interplay of autophagy and apoptosis

Autophagy and apoptosis control the turnover of organelles and proteins within cells, and of cells within organisms, respectively, and many stress pathways sequentially elicit autophagy, and apoptosis within the same cell. Generally autophagy blocks the induction of apoptosis, and apoptosis-associated caspase activation shuts off the autophagic process. However, in special cases, autophagy or autophagy-relevant proteins may help to induce apoptosis or necrosis, and autophagy has been shown to degrade the cytoplasm excessively, leading to 'autophagic cell death'. The dialogue between autophagy and cell death pathways influences the normal clearance of dying cells, as well as immune recognition of dead cell antigens. Therefore, the disruption of the relationship between autophagy and apoptosis has important pathophysiological consequences.

V-ATPase inhibition regulates anoikis resistance and metastasis of cancer cells

Fighting metastasis is a major challenge in cancer therapy and novel therapeutic targets and drugs are highly appreciated. Resistance of invasive cells to anoikis, a particular type of apoptosis induced by loss of cell-matrix contact, is a major prerequisite for their metastatic spread. Inducing anoikis in metastatic cancer cells is therefore a promising therapeutic approach. The vacuolar-ATPase (V-ATPase), a proton pump located at the membrane of acidic organelles, has recently come to focus as an antimetastatic cancer target. As V-ATPase inhibitors have shown to prevent invasion of tumor cells and are able to induce apoptosis, we proposed that V-ATPase inhibition induces anoikis-related pathways in invasive cancer cells. We used the V-ATPase inhibitor archazolid to investigate the mechanism of anoikis induction in various metastatic cancer cells (T24, MDA-MB-231, 4T1, 5637) in vitro. Anoikis induction by archazolid was characterized by decreased c-FLIP expression and caspase-8 activation as well as reduction of active integrin-β1 and an early increase of the proapoptotic protein BIM. However, we observed that archazolid also induces mechanisms opposing anoikis such as degradation of BIM mediated by extracellular signal-regulated kinase (ERK), Akt and Src kinases at later time points and induction of reactive oxygen species. Still, intravenous injection of archazolid-treated 4T1-Luc2 mouse breast cancer cells resulted in reduced metastasis in mouse lungs. Thus, V-ATPase inhibition is not only an interesting option to reduce cancer metastasis, but also to better understand anoikis resistance and to find choices to fight against it.

Modulation of apoptosis sensitivity through the interplay with autophagic and proteasomal degradation pathways

Autophagic and proteasomal degradation constitute the major cellular proteolysis pathways. Their physiological and pathophysiological adaptation and perturbation modulates the relative abundance of apoptosis-transducing proteins and thereby can positively or negatively adjust cell death susceptibility. In addition to balancing protein expression amounts, components of the autophagic and proteasomal degradation machineries directly interact with and co-regulate apoptosis signal transduction. The influence of autophagic and proteasomal activity on apoptosis susceptibility is now rapidly gaining more attention as a significant modulator of cell death signalling in the context of human health and disease. Here we present a concise and critical overview of the latest knowledge on the molecular interplay between apoptosis signalling, autophagy and proteasomal protein degradation. We highlight that these three pathways constitute an intricate signalling triangle that can govern and modulate cell fate decisions between death and survival. Owing to rapid research progress in recent years, it is now possible to provide detailed insight into the mechanisms of pathway crosstalk, common signalling nodes and the role of multi-functional proteins in co-regulating both protein degradation and cell death.

Self-consumption: the interplay of autophagy and apoptosis

Autophagy and apoptosis control the turnover of organelles and proteins within cells, and of cells within organisms, respectively, and many stress pathways sequentially elicit autophagy, and apoptosis within the same cell. Generally autophagy blocks the induction of apoptosis, and apoptosis-associated caspase activation shuts off the autophagic process. However, in special cases, autophagy or autophagy-relevant proteins may help to induce apoptosis or necrosis, and autophagy has been shown to degrade the cytoplasm excessively, leading to 'autophagic cell death'. The dialogue between autophagy and cell death pathways influences the normal clearance of dying cells, as well as immune recognition of dead cell antigens. Therefore, the disruption of the relationship between autophagy and apoptosis has important pathophysiological consequences.

p38 and JNK MAPK pathways control the balance of apoptosis and autophagy in response to chemotherapeutic agents

The Mitogen Activated Protein Kinase (MAPK) signaling plays a critical role in the outcome and the sensitivity to anticancer therapies. Activated MAPK can transmit extracellular signals to regulate cell growth, proliferation, differentiation, migration, apoptosis and so on. Apoptosis as well as macroautophagy (hereafter referred to as autophagy) can be induced by extracellular stimuli such the treatment of chemotherapeutic agents, resulting in different cell response to these drugs. However, the molecular mechanisms mediating these two cellular processes remain largely unknown. Recently, several studies provide new insights into p38 and JNK MAPK pathways function in the control of the balance of autophagy and apoptosis in response to genotoxic stress. Our increased understanding of the role of p38 and JNK MAPK pathways in regulating the balance of autophagy and apoptosis will hopefully provide prospective strategies for cancer therapy.

Autophagy variation within a cell population determines cell fate through selective degradation of Fap-1

Autophagy regulates cell death both positively and negatively, but the molecular basis for this paradox remains inadequately characterized. We demonstrate here that transient cell-to-cell variations in autophagy can either promote cell death or survival depending on the stimulus and cell type. By separating cells with high and low basal autophagy by flow cytometry, we demonstrate that autophagy determines which cells live or die in response to death receptor activation. We have determined that selective autophagic degradation of the phosphatase Fap-1 promotes Fas apoptosis in Type I cells. Conversely, autophagy inhibits apoptosis in Type II cells or upon treatment with TRAIL in either Type I or II cells. These data illustrate that differences in autophagy in a cell population determine cell fate in a stimulus- and cell type-specific manner. This example of selective autophagy of an apoptosis regulator may represent a general mechanism for context-specific regulation of cell fate by autophagy.

Beclin 1 deficiency correlated with lymph node metastasis, predicts a distinct outcome in intrahepatic and extrahepatic cholangiocarcinoma

Autophagy can be tumor suppressive as well as promotive in regulation of tumorigenesis and disease progression. Accordingly, the prognostic significance of autophagy key regulator Beclin 1 was varied among different tumors. Here, we detected the clinicopathological and prognostic effect of Beclin 1 in the subtypes of intrahepatic cholangiocarcinoma (ICC) and extrahepatic cholangiocarcinoma (ECC). Beclin 1 expression level was detected by immunohistochemistry staining in 106 ICC and 74 ECC patients. We found that Beclin 1 was lowly expressed in 126 (70%) cholangiocarcinoma patients, consist of 72 ICC and 54 ECC. Moreover, the cholangiocarcinoma patients with lymph node metastasis (N1) had a lower Beclin 1 level than that of N0 subgroup (P=0.012). However, we did not detect any correlations between Beclin 1 and other clinicopathological features, including tumor subtypes, vascular invasion, HBV infection, liver cirrhosis, cholecystolithiasis and TNM stage. Survival analysis showed that, compared with the high expression subset, Beclin 1 low expression was correlated with a poorer 3-year progression-free survival (PFS, 69.1% VS 46.8%, P=041) for cholangiocarcinoma. Importantly, our stratified univariate and multivariate analysis confirmed that Beclin 1 lowly expressed ICC had an inferior PFS as well as overall survival than ECC, particularly than that of Beclin 1 highly expressed ECC patients. Thus, our study demonstrated that Beclin 1low expression, correlated with lymph node metastasis, and might be a negative prognostic biomarker for cholangiocarcinoma. Combined Beclin 1 level with the anatomical location might lead to refined prognosis for the subtypes of ICC and ECC.