Role of non-canonical Beclin 1-independent autophagy in cell death induced by resveratrol in human breast cancer cells

The Beclin 1 network regulates autophagy and apoptosis

Beclin 1, the mammalian orthologue of yeast Atg6, has a central role in autophagy, a process of programmed cell survival, which is increased during periods of cell stress and extinguished during the cell cycle. It interacts with several cofactors (Atg14L, UVRAG, Bif-1, Rubicon, Ambra1, HMGB1, nPIST, VMP1, SLAM, IP(3)R, PINK and survivin) to regulate the lipid kinase Vps-34 protein and promote formation of Beclin 1-Vps34-Vps15 core complexes, thereby inducing autophagy. In contrast, the BH3 domain of Beclin 1 is bound to, and inhibited by Bcl-2 or Bcl-XL. This interaction can be disrupted by phosphorylation of Bcl-2 and Beclin 1, or ubiquitination of Beclin 1. Interestingly, caspase-mediated cleavage of Beclin 1 promotes crosstalk between apoptosis and autophagy. Beclin 1 dysfunction has been implicated in many disorders, including cancer and neurodegeneration. Here, we summarize new findings regarding the organization and function of the Beclin 1 network in cellular homeostasis, focusing on the cross-regulation between apoptosis and autophagy.

Diversity in the regulation of autophagy and mitophagy: lessons from Parkinson's disease

Selective mitochondrial degradation through autophagy (mitophagy) has emerged as an important homeostatic mechanism in a variety of organisms and contexts. Complete clearance of mitochondria can be observed during normal maturation of certain mammalian cell types, and during certain forms of neuronal cell death. In recent years, autophagy dysregulation has been implicated in toxin-injured dopaminergic neurons as well as in major genetic models of Parkinson's disease (PD), including α-synuclein, leucine-rich repeat kinase 2 (LRRK2), parkin, PTEN-induced kinase 1 (PINK1), and DJ-1. Indeed, PINK1-parkin interactions may form the basis of a mechanism by which dissipation of the inner mitochondrial membrane potential can trigger selective mitochondrial targeting for autophagy. Multiple signals are likely to exist, however, depending upon the trigger for mitophagy. Similarly, the regulation of basal or injury-induced autophagy does not always follow canonical pathways described for nutrient deprivation. Implications of this regulatory diversity are discussed in the context of neuronal function and survival. Further studies are needed to address whether alterations in autophagy regulation play a directly injurious role in PD pathogenesis, or if the observed changes reflect impaired, appropriate, or excessive autophagic responses to other forms of cellular injury.

Microtubule-associated protein 1S (MAP1S) bridges autophagic components with microtubules and mitochondria to affect autophagosomal biogenesis and degradation

The ubiquitously distributed MAP1S is a homologue of the exclusively neuronal distributed microtubule-associated protein 1A and 1B (MAP1A/B). They give rise to multiple isoforms through similar post-translational modification. Isoforms of MAP1S have been implicated in microtubule dynamics and mitotic abnormalities and mitotic cell death. Here we show that ablation of the Map1s gene in mice caused reduction in the B-cell CLL/lymphoma 2 or xL (Bcl-2/xL) and cyclin-dependent kinase inhibitor 1B (P27) protein levels, accumulation of defective mitochondria, and severe defects in response to nutritive stress, suggesting defects in autophagosomal biogenesis and clearance. Furthermore, MAP1S isoforms interacted with the autophagosome-associated light chain 3 of MAP1A/B (LC3), a homologue of yeast autophagy-related gene 8 (ATG8), and recruited it to stable microtubules in a MAP1S and LC3 isoform-dependent mode. In addition, MAP1S interacted with mitochondrion-associated leucine-rich PPR-motif containing protein (LRPPRC) that interacts with the mitophagy initiator and Parkinson disease-related protein Parkin. The three-way interactions of MAP1S isoforms with LC3 and microtubules as well as the interaction of MAP1S with LRPPRC suggest that MAP1S isoforms may play positive roles in integration of autophagic components with microtubules and mitochondria in both autophagosomal biogenesis and degradation. For the first time, our results clarify roles of MAP1S in bridging microtubules and mitochondria with autophagic and mitophagic initiation, maturation, trafficking, and lysosomal clearance. Defects in the MAP1S-regulated autophagy may impact heart disease, cancers, neurodegenerative diseases, and a wide range of other diseases.

A role for autophagic protein beclin 1 early in lymphocyte development

Autophagy is a highly regulated and evolutionarily conserved process of cellular self-digestion. Recent evidence suggests that this process plays an important role in regulating T cell homeostasis. In this study, we used Rag1(-/-) (recombination activating gene 1(-/-)) blastocyst complementation and in vitro embryonic stem cell differentiation to address the role of Beclin 1, one of the key autophagic proteins, in lymphocyte development. Beclin 1-deficient Rag1(-/-) chimeras displayed a dramatic reduction in thymic cellularity compared with control mice. Using embryonic stem cell differentiation in vitro, we found that the inability to maintain normal thymic cellularity is likely caused by impaired maintenance of thymocyte progenitors. Interestingly, despite drastically reduced thymocyte numbers, the peripheral T cell compartment of Beclin 1-deficient Rag1(-/-) chimeras is largely normal. Peripheral T cells displayed normal in vitro proliferation despite significantly reduced numbers of autophagosomes. In addition, these chimeras had greatly reduced numbers of early B cells in the bone marrow compared with controls. However, the peripheral B cell compartment was not dramatically impacted by Beclin 1 deficiency. Collectively, our results suggest that Beclin 1 is required for maintenance of undifferentiated/early lymphocyte progenitor populations. In contrast, Beclin 1 is largely dispensable for the initial generation and function of the peripheral T and B cell compartments. This indicates that normal lymphocyte development involves Beclin 1-dependent, early-stage and distinct, Beclin 1-independent, late-stage processes.

Multifaceted approach to resveratrol bioactivity: Focus on antioxidant action, cell signaling and safety

Resveratrol (RVT) is a naturally occurring trihydroxy stilbene that displays a wide spectrum of physiological activity. Its ability to behave therapeutically as a component of red wine has attracted wide attention. The phenol acts as a protective agent involving various body constituents. Most attention has been given to beneficial effects in insults involving cancer, aging, cardiovascular system, inflammation and the central nervous system. One of the principal modes of action appears to be as antioxidant. Other mechanistic pathways entail cell signaling, apoptosis and gene expression. There is an intriguing dichotomy in relation to pro-oxidant property. Also discussed are metabolism, receptor binding, rationale for safety and suggestions for future work. This is the first comprehensive review of RVT based on a broad, unifying mechanism.

Arachidin-1, a peanut stilbenoid, induces programmed cell death in human leukemia HL-60 cells

The stilbenoids, arachidin-1 (Ara-1), arachidin-3, isopentadienylresveratrol, and resveratrol, have been isolated from germinating peanut kernels and characterized as antioxidant and anti-inflammatory agents. Resveratrol possesses anticancer activity, and studies have indicated that it induces programmed cell death (PCD) in human leukemia HL-60 cells. In this study, the anticancer activity of these stilbenoids was determined in HL-60 cells. Ara-1 had the highest efficacy in inducing PCD in HL-60 cells, with an approximately 4-fold lower EC50 than resveratrol. Ara-1 treatment caused mitochondrial membrane damage, activation of caspases, and nuclear translocation of apoptosis-inducing factor, resulting in chromosome degradation and cell death. Therefore, Ara-1 induces PCD in HL-60 cells through caspase-dependent and caspase-independent pathways. Ara-1 demonstrates its efficacy as an anticancer agent by inducing caspase-independent cell death, which is an alternative death pathway of cancer cells with mutations in key apoptotic genes. These findings indicate the merits of screening other peanut stilbenoids for anticancer activity.

Arsenic trioxide induces a beclin-1-independent autophagic pathway via modulation of SnoN/SkiL expression in ovarian carcinoma cells

Arsenic trioxide (As(2)O(3)), used to treat promyelocytic leukemia, triggers cell death through unknown mechanisms. To further our understanding of As(2)O(3)-induced death, we analyzed its effects on transforming growth factor-β (TGFβ) signaling mediators in ovarian cells. Dysregulated TGFβ signaling is a characteristic of ovarian cancers. As(2)O(3) reduced the protein expression of EVI1, TAK1, SMAD2/3, and TGFβRII while increasing SnoN/SkiL. EVI1 protein was modulated by treatment with the proteasome inhibitors, MG132 and PS-341/Velcade, suggesting that degradation occurs through the ubiquitin-proteasome pathway. The sensitivity of ovarian cells to As(2)O(3)-induced apoptosis correlated with expression of multidrug resistance protein 1. Interestingly, expression of SnoN was similar to LC3-II (autophagy marker), which increased with induction of cytoplasmic vacuolation preceding apoptosis. These vesicles were identified as autophagosomes based on transmission electron microscopy and immunofluorescence staining with EGFP-LC3. The addition of N-acetyl-L-cysteine (ROS scavenger) to As(2)O(3)-treated cells reversed changes in SnoN protein and the autophagic/apoptotic response. In contrast to beclin-1 knockdown, siRNA targeting ATG5, ATG7, and hVps34 markedly reduced autophagy in As(2)O(3)-treated ovarian carcinoma cells. Further, treatment with SnoN siRNA markedly decreased LC3-II levels and increased PARP degradation (an apoptosis marker). Collectively, these findings suggest that As(2)O(3) induces a beclin-1-independent autophagic pathway in ovarian carcinoma cells and implicates SnoN in promoting As(2)O(3)-mediated autophagic cell survival.

Hydrogen peroxide induces Beclin 1-independent autophagic cell death by suppressing the mTOR pathway via promoting the ubiquitination and degradation of Rheb in GSH-depleted RAW 264.7 cells

A novel mechanism for H₂O₂-induced autophagic cell death in GSH-depleted RAW 264.7 cells, a murine macrophage cell line, is proposed. Under GSH-depleted conditions, H₂O₂-induced autophagic cell, characterized by an increased LC3-II/I ratio, a decreased level of p62 and the formation of autophagic vacuoles, was inhibited by bafilomycin A1 and by Atg5 siRNA transfection, whereas the cell death was not inhibited by zVAD-fmk, by PI3K inhibitors or by Beclin 1 siRNA transfection. In addition, H₂O₂ treatment reduced the activity of mTOR and promoted the ubiquitination and degradation of Rheb, a key upstream activator of mTOR. Furthermore, proteasome inhibition with MG132 restored the expression of Rheb and increased mTOR activity, resulting in an increased viability of H₂O₂-treated cells. Collectively, these findings demonstrate that H₂O₂ induces Beclin 1-independent autophagic cell death by suppressing the mTOR pathway via promoting the ubiquitination and degradation of Rheb in GSH-depleted RAW 264.7 cells.

Can autophagy promote longevity?

Organismal lifespan can be extended by genetic manipulation of cellular processes such as histone acetylation, the insulin/IGF-1 (insulin-like growth factor 1) pathway or the p53 system. Longevity-promoting regimens, including caloric restriction and inhibition of TOR with rapamycin, resveratrol or the natural polyamine spermidine, have been associated with autophagy (a cytoprotective self-digestive process) and in some cases were reported to require autophagy for their effects. We summarize recent developments that outline these links and hypothesize that clearing cellular damage by autophagy is a common denominator of many lifespan-extending manipulations.

Resveratrol arrests cell cycle and induces apoptosis in human hepatocellular carcinoma Huh-7 cells

Resveratrol has been shown to possess anticancer, anti-aging, anti-inflammatory, antimicrobial, and neuroprotective activities. In this study, we examined the antiproliferative properties of resveratrol and its molecular mechanism(s) of action in Huh-7 cells, a new human hepatoma cell line system for hepatitis C virus. Results showed that resveratrol significantly inhibited Huh-7 cell proliferation (50% inhibitory concentration = 22.4 μg/mL) and effectively induced cell cycle arrest and apoptosis. It up-regulated p21/WAF1 expression in a p53-independent manner, but the expressions of cyclin E, cyclin A, and cyclin-dependent kinase 2 were down-regulated. It also caused an increase in the ratio of pro-apoptotic/anti-apoptotic protein, which was associated with the mitochondrial membrane depolarization and the increase in caspase activity. Resveratrol showed no effect on Fas, Fas ligand, extracellular signal regulated kinase (ERK) 1/2, and p38 expression but down-regulated phospho-ERK and phospho-p38 expression. In addition, resveratrol was noted to trigger autophagic cell death through the increased expression of autophagy-related Atg5, Atg7, Atg9, and Atg12 proteins. These results suggest that resveratrol could be an important chemoprevention agent for hepatoma of hepatitis C virus infection.

The elimination of accumulated and aggregated proteins: a role for aggrephagy in neurodegeneration

The presence of ubiquitinated protein inclusions is a hallmark of most adult onset neurodegenerative disorders. Although the toxicity of these structures remains controversial, their prolonged presence in neurons is indicative of some failure in fundamental cellular processes. It therefore may be possible that driving the elimination of inclusions can help re-establish normal cellular function. There is growing evidence that macroautophagy has two roles; first, as a non-selective degradative response to cellular stress such as starvation, and the other as a highly selective quality control mechanism whose basal levels are important to maintain cellular health. One particular form of macroautophagy, aggrephagy, may have particular relevance in neurodegeneration, as it is responsible for the selective elimination of accumulated and aggregated ubiquitinated proteins. In this review, we will discuss the molecular mechanisms and role of protein aggregation in neurodegeneration, as well as the molecular mechanism of aggrephagy and how it may impact disease. This article is part of a Special Issue entitled "Autophagy and protein degradation in neurological diseases."

Regulation of the autophagy protein LC3 by phosphorylation

Macroautophagy is a major catabolic pathway that impacts cell survival, differentiation, tumorigenesis, and neurodegeneration. Although bulk degradation sustains carbon sources during starvation, autophagy contributes to shrinkage of differentiated neuronal processes. Identification of autophagy-related genes has spurred rapid advances in understanding the recruitment of microtubule-associated protein 1 light chain 3 (LC3) in autophagy induction, although braking mechanisms remain less understood. Using mass spectrometry, we identified a direct protein kinase A (PKA) phosphorylation site on LC3 that regulates its participation in autophagy. Both metabolic (rapamycin) and pathological (MPP(+)) inducers of autophagy caused dephosphorylation of endogenous LC3. The pseudophosphorylated LC3 mutant showed reduced recruitment to autophagosomes, whereas the nonphosphorylatable mutant exhibited enhanced puncta formation. Finally, autophagy-dependent neurite shortening induced by expression of a Parkinson disease-associated G2019S mutation in leucine-rich repeat kinase 2 was inhibited by dibutyryl-cyclic adenosine monophosphate, cytoplasmic expression of the PKA catalytic subunit, or the LC3 phosphorylation mimic. These data demonstrate a role for phosphorylation in regulating LC3 activity.

Autophagy gone awry in neurodegenerative diseases

Autophagy is essential for neuronal homeostasis, and its dysfunction has been directly linked to a growing number of neurodegenerative disorders. The reasons behind autophagic failure in degenerating neurons can be very diverse because of the different steps required for autophagy and the characterization of the molecular players involved in each of them. Understanding the step(s) affected in the autophagic process in each disorder could explain differences in the course of these pathologies and will be essential to developing targeted therapeutic approaches for each disease based on modulation of autophagy. Here we present examples of different types of autophagic dysfunction described in common neurodegenerative disorders and discuss the prospect of exploring some of the recently identified autophagic variants and the interactions among autophagic and non-autophagic proteolytic systems as possible future therapeutic targets.

Autophagy-active beclin-1 correlates with favourable clinical outcome in non-Hodgkin lymphomas

The expression of beclin-1, an oncosuppressor monoallelically deleted in >60% epithelial cancers, has been shown to be developmentally regulated in T and B lymphocytes. By interacting with either bcl-2 or class III phosphatidyl-inositol-3-phosphate kinase, beclin-1 regulates apoptosis and autophagy, two processes crucial for lymphatic tissue homeostasis. We analyzed the potential link between beclin-1-mediated autophagy and the malignant behaviour of lymphomas. The tissue expression of beclin-1 was analyzed in a large series of non-Hodgkin lymphomas and correlated with patient's clinical outcome. By immunofluorescence, beclin-1 staining showed faintly detectable and diffusely distributed in the cytoplasm (regarded as negative) or confined to the perinuclear region as large and brilliant puncta suggestive of macro-aggregate reactivity (regarded as positive). The positive expression of beclin-1 well correlated with the presence of LC3-positive autophagic vacuoles and was inversely correlated with the expression of bcl-2. Non-Hodgkin lymphomas in which > or =20% of tumour cells expressed high level of beclin-1 aggregates were associated with a complete (57%) or partial (35%) remission. The 5-year overall survival probability, calculated by the Kaplan-Meier method, was 92% and 42% in beclin-1-expressing non-Hodgkin lymphomas with > or =20% and <20% positive cells, respectively (log-rank test, P<0.000.1). In Cox multivariate analysis, the level of beclin-1 expression, adjusted for patient's age and pathologic stage, revealed to be significantly correlated with patient's survival (P<0.0001). This is the first demonstration of the involvement of beclin-1 and autophagy in the clinical behaviour of non-Hodgkin lymphomas. The present data are compatible with the hypothesis that non-Hodgkin lymphomas with upregulated autophagy are more responsive to chemotherapy and indicate that beclin-1 could be a valuable independent prognostic factor in this heterogeneous group of tumours.

The Bcl-2 homology domain 3 mimetic gossypol induces both Beclin 1-dependent and Beclin 1-independent cytoprotective autophagy in cancer cells

Gossypol, a natural Bcl-2 homology domain 3 mimetic compound isolated from cottonseeds, is currently being evaluated in clinical trials. Here, we provide evidence that gossypol induces autophagy followed by apoptotic cell death in both the MCF-7 human breast adenocarcinoma and HeLa cell lines. We first show that knockdown of the Bcl-2 homology domain 3-only protein Beclin 1 reduces gossypol-induced autophagy in MCF-7 cells, but not in HeLa cells. Gossypol inhibits the interaction between Beclin 1 and Bcl-2 (B-cell leukemia/lymphoma 2), antagonizes the inhibition of autophagy by Bcl-2, and hence stimulates autophagy. We then show that knockdown of Vps34 reduces gossypol-induced autophagy in both cell lines, and consistent with this, the phosphatidylinositol 3-phosphate-binding protein WIPI-1 is recruited to autophagosomal membranes. Further, Atg5 knockdown also reduces gossypol-mediated autophagy. We conclude that gossypol induces autophagy in both a canonical and a noncanonical manner. Notably, we found that gossypol-mediated apoptotic cell death was potentiated by treatment with the autophagy inhibitor wortmannin or with small interfering RNA against essential autophagy genes (Vps34, Beclin 1, and Atg5). Our findings support the notion that gossypol-induced autophagy is cytoprotective and not part of the cell death process induced by this compound.

The PEA-15 protein regulates autophagy via activation of JNK

PEA-15/PED (phosphoprotein enriched in astrocytes 15 kDa/phosphoprotein enriched in diabetes) is a death effector domain-containing protein which is known to modulate apoptotic cell death. The mechanism by which PEA-15 inhibits caspase activation and increases ERK (extracellular-regulated kinase) activity is well characterized. Here, we demonstrate that PEA-15 is not only pivotal in the activation of the ERK pathway but also modulates JNK (c-Jun N-terminal kinase) signaling. Upon overexpression of PEA-15 in malignant glioma cells, JNK is potently activated. The PEA-15-induced JNK activation depends on the phosphorylation of PEA-15 at both phosphorylation sites (serine 104 and serine 116). The activation of JNK is substantially inhibited by siRNA-mediated down-regulation of endogenous PEA-15. Moreover, we demonstrate that glioma cells overexpressing PEA-15 show increased signs of autophagy in response to classical autophagic stimuli such as ionizing irradiation, serum deprivation, or rapamycin treatment. In contrast, the non-phosphorylatable mutants of PEA-15 are not capable of promoting autophagy. The inhibition of JNK abrogates the PEA-15-mediated increase in autophagy. In conclusion, our data show that PEA-15 promotes autophagy in glioma cells in a JNK-dependent manner. This might render glioma cells more resistant to adverse stimuli such as starvation or ionizing irradiation.

Resveratrol enhances perforin expression and NK cell cytotoxicity through NKG2D-dependent pathways

In a previous report, we showed that the in vivo cytotoxic activity of the natural killer (NK) cells isolated from resveratrol-pretreated rats is significantly enhanced compared with that of the non-pretreated rats; however, the underlying mechanism remains unclear. In the present study, we use cultured NK92 cell line to examine the possible signaling pathways underlying the resveratrol-induced activation. Using cultured K562, HepG2, and A549 cells as targets, we show that resveratrol pretreatment increases NK cell cytotoxicity in a dose-dependent manner. The enhanced cytotoxic effect is accompanied by increases in JNK and ERK-1/2 MAP kinase activity and perforin expression. Moreover, the expression of NKG2D, an upstream signaling molecule of the MAP kinases pathway, is also enhanced. Resveratrol-enhanced perforin expression and cytotoxic activity are effectively inhibited by pretreatment with the inhibitors of JNK (SP600125), ERK-1/2 (PD98059), or by siRNAs against JNK-1 and ERK-2. However, the inhibitors or siRNA to p38 exhibits no effect. Since IL-2 has been shown to induce NKG2D expression and perforin release, we therefore, examined whether IL-2 and resveratrol act in parallel. We show that IL-2 also stimulates perforin expression, however, when treated together with resveratrol, they exhibit no additive effect. The results suggest that in NK92 cells, resveratrol may act via a similar or overlapping pathway as that of IL-2, to enhance perforin expression and cytotoxic activity. Data presented strongly indicate that resveratrol act via NKG2D-dependent JNK and ERK-1/2 pathways.

A pivotal role for PINK1 and autophagy in mitochondrial quality control: implications for Parkinson disease

The PTEN-induced putative kinase 1 (PINK1) is a mitochondrially targeted serine-threonine kinase, which is linked to autosomal recessive familial parkinsonism. Current literature implicates PINK1 as a pivotal regulator of mitochondrial quality control, promoting maintenance of respiring mitochondrial networks through cristae stabilization, phosphorylation of chaperones and possibly regulation of mitochondrial transport or autophagy. Pulse-chase studies indicate that PINK1 is rapidly processed into at least two shorter forms, which are distributed in both mitochondrial and cytosolic compartments. Through indirect regulation of mitochondrial proteases and Drp1, PINK1 may act to facilitate localized repair and fusion in response to minor mitochondrial stress. With severe mitochondrial damage, PINK1 facilitates aggregation and clearance of depolarized mitochondria through interactions with Parkin and possibly Beclin1. This switch in function most probably involves altered processing, post-translational modification and/or localization of PINK1, as overexpression of full-length PINK1 is required for mitochondrial Parkin recruitment. Under conditions of PINK1 deficiency, dysregulation of reactive oxygen species, electron transport chain function and calcium homeostasis trigger altered mitochondrial dynamics, indicating compromise of mitochondrial quality control mechanisms. Nevertheless, Parkin- and Beclin1-regulated mitochondrial autophagy remains effective at recycling PINK1-deficient mitochondria; failure of this final tier of mitochondrial quality control contributes to cell death. Thus, PINK1 plays a pivotal, multifactorial role in mitochondrial homeostasis. As autophagic recycling represents the final tier of mitochondrial quality control, whether PINK1 levels are enhanced or reduced, strategies to promote selective mitophagy and mitochondrial biogenesis may prove effective for multiple forms of Parkinson's disease.

Simultaneous induction of non-canonical autophagy and apoptosis in cancer cells by ROS-dependent ERK and JNK activation

Background

Chemotherapy-induced reduction in tumor load is a function of apoptotic cell death, orchestrated by intracellular caspases. However, the effectiveness of these therapies is compromised by mutations affecting specific genes, controlling and/or regulating apoptotic signaling. Therefore, it is desirable to identify novel pathways of cell death, which could function in tandem with or in the absence of efficient apoptotic machinery. In this regard, recent evidence supports the existence of a novel cell death pathway termed autophagy, which is activated upon growth factor deprivation or exposure to genotoxic compounds. The functional relevance of this pathway in terms of its ability to serve as a stress response or a truly death effector mechanism is still in question; however, reports indicate that autophagy is a specialized form of cell death under certain conditions.

Methodology/Principal Findings

We report here the simultaneous induction of non-canonical autophagy and apoptosis in human cancer cells upon exposure to a small molecule compound that triggers intracellular hydrogen peroxide (H₂O₂) production. Whereas, silencing of beclin1 neither inhibited the hallmarks of autophagy nor the induction of cell death, Atg 7 or Ulk1 knockdown significantly abrogated drug-induced H₂O₂-mediated autophagy. Furthermore, we provide evidence that activated extracellular regulated kinase (ERK) and c-Jun N-terminal kinase (JNK) are upstream effectors controlling both autophagy and apoptosis in response to elevated intracellular H₂O₂. Interestingly, inhibition of JNK activity reversed the increase in Atg7 expression in this system, thus indicating that JNK may regulate autophagy by activating Atg7. Of note, the small molecule compound triggered autophagy and apoptosis in primary cells derived from patients with lymphoma, but not in non-transformed cells.

Conclusions/Significance

Considering that loss of tumor suppressor beclin 1 is associated with neoplasia, the ability of this small molecule compound to engage both autophagic and apoptotic machineries via ROS production and subsequent activation of ERK and JNK could have potential translational implications.

Review: autophagy and neurodegeneration: survival at a cost?

Protein aggregation, mitochondrial impairment and oxidative stress are common to multiple neurodegenerative diseases. Homeostasis is regulated by a balanced set of anabolic and catabolic responses, which govern removal and repair of damaged proteins and organelles. Macroautophagy is an evolutionarily conserved pathway for the degradation of long-lived proteins, effete organelles and protein aggregates. Aberrations in macroautophagy have been observed in Alzheimer, Huntington, Parkinson, motor neuron and prion diseases. In this review, we will discuss the divergent roles of macroautophagy in neurodegenerative diseases and suggest a potential regulatory mechanism that could determine cell death or survival outcomes. We also highlight emerging data on neurite morphology and synaptic remodelling that indicate the possibility of detrimental functional trade-offs in the face of neuronal cell survival, particularly if the need for elevated macroautophagy is sustained.

Resveratrol promotes autophagic cell death in chronic myelogenous leukemia cells via JNK-mediated p62/SQSTM1 expression and AMPK activation

Autophagy that is induced by starvation or cellular stress can enable cancer cell survival by sustaining energy homeostasis and eliminating damaged organelles and proteins. In response to stress, cancer cells have been reported to accumulate the protein p62/SQSTM1 (p62), but its role in the regulation of autophagy is controversial. Here, we report that the plant phytoalexin resveratrol (RSV) triggers autophagy in imatinib-sensitive and imatinib-resistant chronic myelogenous leukemia (CML) cells via JNK-dependent accumulation of p62. JNK inhibition or p62 knockdown prevented RSV-mediated autophagy and antileukemic effects. RSV also stimulated AMPK, thereby inhibiting the mTOR pathway. AMPK knockdown or mTOR overexpression impaired RSV-induced autophagy but not JNK activation. Lastly, p62 expression and autophagy in CD34+ progenitors from patients with CML was induced by RSV, and disrupting autophagy protected CD34+ CML cells from RSV-mediated cell death. We concluded that RSV triggered autophagic cell death in CML cells via both JNK-mediated p62 overexpression and AMPK activation. Our findings show that the JNK and AMPK pathways can cooperate to eliminate CML cells via autophagy.

Autophagy in health and disease. 1. Regulation and significance of autophagy: an overview

Macroautophagy is a vacuolar degradation pathway that terminates in the lysosomal compartment after formation of a cytoplasmic vacuole or autophagosome that engulfs macromolecules and organelles. The identification of ATG (autophagy-related) genes that are involved in the formation of autophagosomes has greatly increased our knowledge of the molecular basis of macroautophagy, and its roles in cell function, which extend far beyond degradation and quality control of the cytoplasm. Macroautophagy, which plays a major role in tissue homeostasis, is now recognized as contributing to innate and adaptive immune responses. Recently, several mediators of apoptosis have been shown to control macroautophagy. Deciphering the cross talk between macroautophagy and apoptosis probably should help increase understanding of the role of macroautophagy in human disease and is likely to be of therapeutic importance.

Autophagy mediates pharmacological lifespan extension by spermidine and resveratrol

Although autophagy has widely been conceived as a self-destructive mechanism that causes cell death, accumulating evidence suggests that autophagy usually mediates cytoprotection, thereby avoiding the apoptotic or necrotic demise of stressed cells. Recent evidence produced by our groups demonstrates that autophagy is also involved in pharmacological manipulations that increase longevity. Exogenous supply of the polyamine spermidine can prolong the lifespan of (while inducing autophagy in) yeast, nematodes and flies. Similarly, resveratrol can trigger autophagy in cells from different organisms, extend lifespan in nematodes, and ameliorate the fitness of human cells undergoing metabolic stress. These beneficial effects are lost when essential autophagy modulators are genetically or pharmacologically inactivated, indicating that autophagy is required for the cytoprotective and/or anti-aging effects of spermidine and resveratrol. Genetic and functional studies indicate that spermidine inhibits histone acetylases, while resveratrol activates the histone deacetylase Sirtuin 1 to confer cytoprotection/longevity. Although it remains elusive whether the same histones (or perhaps other nuclear or cytoplasmic proteins) act as the downstream targets of spermidine and resveratrol, these results point to an essential role of protein hypoacetylation in autophagy control and in the regulation of longevity.

TOR-dependent control of autophagy: biting the hand that feeds

Induction of autophagy in response to starvation is a highly conserved ability of eukaryotic cells, indicating a crucial and ancient role of this process in adapting to nutrient conditions. The target of rapamycin (TOR) pathway is major conduit for such signals, and in most cell types TOR activity is necessary and sufficient to suppress autophagy under favorable growth conditions. Recent studies have begun to reveal how TOR activity is regulated in response to nutritional cues, and are shedding new light on the mechanisms by which TOR controls the autophagic machinery. In addition, a variety of signals, stressors and pharmacological agents that induce autophagy independent of nutrient conditions have been identified. In some cases these signals appear to have been spliced into the core TOR pathway, whereas others are able to bypass the control mechanisms regulated by TOR. Increasing evidence is pointing to an important role for both positive and negative feedback loops in controlling this pathway, leading to an emerging view that TOR signaling not only regulates autophagy but is also highly sensitive to cellular rates of autophagy and other TOR-dependent processes.

Cardioprotection by resveratrol: a novel mechanism via autophagy involving the mTORC2 pathway

AIMS

On the basis of our previous reports that cardioprotection induced by ischaemic preconditioning induces autophagy and that resveratrol, a polyphenolic antioxidant present in grapes and red wine induces preconditioning-like effects, we sought to determine if resveratrol could induce autophagy.

METHODS AND RESULTS

Resveratrol at lower doses (0.1 and 1 microM in H9c2 cardiac myoblast cells and 2.5 mg/kg/day in rats) induced cardiac autophagy shown by enhanced formation of autophagosomes and its component LC3-II after hypoxia-reoxygenation or ischaemia-reperfusion. The autophagy was attenuated with the higher dose of resveratrol. The induction of autophagy was correlated with enhanced cell survival and decreased apoptosis. Treatment with rapamycin (100 nM), a known inducer of autophagy, did not further increase autophagy compared with resveratrol alone. Autophagic inhibitors, wortmannin (2 microM) and 3-methyladenine (10 mM), significantly attenuated the resveratrol-induced autophagy and induced cell death. The activation of mammalian target of rapamycin (mTOR) was differentially regulated by low-dose resveratrol, i.e. the phosphorylation of mTOR at serine 2448 was inhibited, whereas the phosphorylation of mTOR at serine 2481 was increased, which was attenuated with a higher dose of resveratrol. Although resveratrol attenuated the activation of mTOR complex 1, low-dose resveratrol significantly induced the expression of Rictor, a component of mTOR complex 2, and activated its downstream survival kinase Akt (Ser 473). Resveratrol-induced Rictor was found to bind with mTOR. Furthermore, treatment with Rictor siRNA attenuated the resveratrol-induced autophagy.

CONCLUSION

Our results indicate that at lower dose, resveratrol-mediated cell survival is, in part, mediated through the induction of autophagy involving the mTOR-Rictor survival pathway.

Resveratrol: its biologic targets and functional activity

The polyphenolic phytoalexin resveratrol (RSV) and its analogues have received tremendous attention over the past couple of decades because of a number of reports highlighting their benefits in vitro and in vivo in a variety of human disease models, including cardio- and neuroprotection, immune regulation, and cancer chemoprevention. These studies have underscored the high degree of diversity in terms of the signaling networks and cellular effector mechanisms that are affected by RSV. The activity of RSV has been linked to cell-surface receptors, membrane signaling pathways, intracellular signal-transduction machinery, nuclear receptors, gene transcription, and metabolic pathways. The promise shown by RSV has prompted heightened interest in studies aimed at translating these observations to clinical settings. In this review, we present a comprehensive account of the basic chemistry of RSV, its bioavailability, and its multiple intracellular target proteins and signaling pathways.

Anticancer and cancer chemopreventive potential of grape seed extract and other grape-based products

With emerging trends in the incidence of cancer of various organ sites, additional approaches are needed to control human malignancies. Intervention or prevention of cancer by dietary constituents, a strategy defined as chemoprevention, holds great promise in our conquest to control cancer, because it can be implemented on a broader population base with less economic burden. Consistent with this, several epidemiological studies have shown that populations that consume diets rich in fruits and vegetables have an overall lower cancer incidence. Based on these encouraging observations, research efforts from across the globe have focused on identifying, characterizing, and providing scientific basis to the efficacy of various phytonutrients in an effort to develop effective strategy to control various human malignancies. Cancer induction, growth, and progression are multi-step events and numerous studies have demonstrated that various dietary agents interfere with these stages of cancer, thus blocking malignancy. Fruits and vegetables represent untapped reservoir of various nutritive and nonnutritive phytochemicals with potential cancer chemopreventive activity. Grapes and grape-based products are one such class of dietary products that have shown cancer chemopreventive potential and are also known to improve overall human health. This review focuses on recent advancements in cancer chemopreventive and anticancer efficacy of grape seed extract and other grape-based products. Overall, completed studies from various scientific groups conclude that both grapes and grape-based products are excellent sources of various anticancer agents and their regular consumption should thus be beneficial to the general population.

Regulation of autophagy by a beclin 1-targeted microRNA, miR-30a, in cancer cells

beclin 1, the mammalian homologue of the yeast Atg6, is a key autophagy-promoting gene that plays a critical role in the regulation of cell death and survival of various types of cells. However, recent studies have observed that the expression of beclin 1 is altered in certain diseases including cancers. The causes underlying the aberrant expression of beclin 1 remain largely unknown. We report here that microRNAs (miRNAs), a class of endogenous, 22-24 nucleotide noncoding RNA molecules able to affect stability and translation of mRNA, may represent a previously unrecognized mechanism for regulating beclin 1 expression and autophagy. We demonstrated that beclin 1 is a potential target for miRNA miR-30a, and this miRNA could negatively regulate beclin 1 expression resulting in decreased autophagic activity. Treatment of tumor cells with the miR-30a mimic decreased, and with the antagomir increased, the expression of beclin 1 mRNA and protein. Dual luciferase reporter assay confirmed that the miR-30a binding sequences in the 3'-UTR of beclin 1 contribute to the modulation of beclin 1 expression by miR-30a. Furthermore, inhibition of beclin 1 expression by the miR-30a mimic blunted activation of autophagy induced by rapamycin. Our study of the role of miR-30a in regulating beclin 1 expression and autophagy reveals a novel function for miRNA in a critical cellular event with significant impacts in cancer development, progression and treatment, and in other diseases.

Autophagy as an antimicrobial strategy

Autophagy is a process of lysosomal degradation that was originally described as a cellular response to adapt to a lack of nutrients and to enable the elimination of damaged organelles. Autophagy is increasingly recognized as a process that is also involved in innate and adaptive immune responses against pathogens. Studies on the regulation of autophagy have uncovered components of the autophagic cascade that can be manipulated pharmacologically. Approaches to modulate autophagy may result in novel strategies for the treatment and prevention of various infections.

Intracellular protein degradation in mammalian cells: recent developments

In higher organisms, dietary proteins are broken down into amino acids within the digestive tract but outside the cells, which incorporate the resulting amino acids into their metabolism. However, under certain conditions, an organism loses more nitrogen than is assimilated in the diet. This additional loss was found in the past century to come from intracellular proteins and started an intensive research that produced an enormous expansion of the field and a dispersed literature. Therefore, our purpose is to provide an updated summary of the current knowledge on the proteolytic machinery involved in intracellular protein degradation and its physiological and pathological relevance, especially addressed to newcomers in the field who may find further details in more specialized reviews. However, even providing a general overview, this is an extremely wide field and, therefore, we mainly focus on mammalian cells, while other cells will be mentioned only for comparison purposes.

Dihydroceramide intracellular increase in response to resveratrol treatment mediates autophagy in gastric cancer cells

Resveratrol has both apoptosis and autophagy-promoting activities in different cancer cells. Dihydroceramide is the immediate precursor of the apoptotic mediator ceramide in the de novo sphingolipid synthesis pathway. Here we demonstrate that resveratrol induces autophagy in HGC-27 cells, with no sign of cell death. Autophagy occurs after an increase in dihydroceramides by inhibition of dihydroceramide desaturase. The effects of resveratrol are mimicked by a dihydroceramide desaturase inhibitor. These results demonstrate that resveratrol-induced autophagy occurs with a rise in intracellular dihydroceramide levels as the result of inhibition of dihydroceramide desaturases activity and that dihydroceramide accumulation is responsible for autophagy promotion.

Life and death partners: apoptosis, autophagy and the cross-talk between them

It is not surprising that the demise of a cell is a complex well-controlled process. Apoptosis, the first genetically programmed death process identified, has been extensively studied and its contribution to the pathogenesis of disease well documented. Yet, apoptosis does not function alone to determine a cell's fate. More recently, autophagy, a process in which de novo-formed membrane-enclosed vesicles engulf and consume cellular components, has been shown to engage in a complex interplay with apoptosis. In some cellular settings, it can serve as a cell survival pathway, suppressing apoptosis, and in others, it can lead to death itself, either in collaboration with apoptosis or as a back-up mechanism when the former is defective. The molecular regulators of both pathways are inter-connected; numerous death stimuli are capable of activating either pathway, and both pathways share several genes that are critical for their respective execution. The cross-talk between apoptosis and autophagy is therefore quite complex, and sometimes contradictory, but surely critical to the overall fate of the cell. Furthermore, the cross-talk is a key factor in the outcome of death-related pathologies such as cancer, its development and treatment.

p65/RelA modulates BECN1 transcription and autophagy

Recently, autophagy has emerged as a critical process in the control of T-cell homeostasis. Given the pivotal role of NF-kappaB in the signaling events of T cells, we have analyzed and unveiled a conserved NF-kappaB binding site in the promoter of the murine and human BECN1 autophagic gene (Atg6). Accordingly, we demonstrate that the NF-kappaB family member p65/RelA upregulates BECN1 mRNA and protein levels in different cellular systems. Moreover, p65-mediated upregulation of BECN1 is coupled to increased autophagy. The newly identified kappaB site in the BECN1 promoter specifically interacts with p65 both in vitro and in living Jurkat cells upon phorbol myristate acetate (PMA)-ionomycin stimulation, where p65 induction is coupled to BECN1 upregulation and autophagy induction. Finally, anti-CD3- and PMA-ionomycin-mediated activation of T-cell receptor signaling in peripheral T cells from lymph nodes of healthy mice results in an upregulation of BECN1 expression that can be blocked by the NF-kappaB inhibitor BAY 11-7082. Altogether, these data suggest that autophagy could represent a novel route modulated by p65 to regulate cell survival and control T-cell homeostasis.

Macroautophagy: the key ingredient to a healthy diet?

Dietary compounds can influence the risk of cancer and other diseases through diverse mechanisms which include the activation or inhibition of macroautophagy. Macroautophagy is a catabolic process for the lysosomal degradation and recycling of cytoplasmic constituents which has been implicated in several pathologies, including cancer and neurodegeneration. In some instances, macroautophagy acts to suppress tumor formation and neural degeneration. Thus, it may be feasible to design diets, supplements or therapeutics that can alter the level of macroautophagy within cells to prevent or treat disease. While critical questions still need to be answered before we can safely and effectively implement such a strategy, we provide here a review of the literature regarding dietary constituents that have a demonstrated macroautophagy-modulating function.

Novel roles for protein kinase Cdelta-dependent signaling pathways in acute hypoxic stress-induced autophagy

Macroautophagy, a tightly orchestrated intracellular process for bulk degradation of cytoplasmic proteins or organelles, is believed to be essential for cell survival or death in response to stress conditions. Recent observations indicate that autophagy is an adaptive response in cells subjected to prolonged hypoxia. However, the signaling mechanisms that activate autophagy under acute hypoxic stress are not clearly understood. In this study, we show that acute hypoxic stress by treatment with 1% O(2) or desferroxamine, a hypoxia-mimetic agent, of cells renders a rapid induction of LC3-II level changes and green fluorescent protein-LC3 puncta accumulation, hallmarks of autophagic processing, and that this process involves protein kinase Cdelta (PKCdelta), and occurs prior to the induction of BNIP3 (Bcl-2/adenovirus E1B 19-kDa interacting protein 3). Interestingly, hypoxic stress leads to a rapid and transient activation of JNK in Pa-4 or mouse embryo fibroblast cells. Acute hypoxic stress-induced changes in LC3-II level and JNK activation are attenuated in Pa-4 cells by dominant negative PKCdeltaKD or in mouse embryo fibroblast/PKCdelta-null cells. Intriguingly, the requirement of PKCdelta is not apparent for starvation-induced autophagy. The importance of PKCdelta in hypoxic stress-induced adaptive responses is further supported by our findings that inhibition of PKCdelta-facilitated autophagy by 3-methyladenine or Atg5 knock-out renders a greater prevalence of cell death following prolonged desferroxamine treatment, whereas PKCdelta- or JNK1-deficient cells exhibit resistance to extended hypoxic exposure. These results uncover dual roles of PKCdelta-dependent signaling in the cell fate determination upon hypoxic exposure.

Autophagic cell death: the story of a misnomer

Dying cells often display a large-scale accumulation of autophagosomes and hence adopt a morphology called autophagic cell death. In many cases, it is agreed that this autophagic cell death is cell death with autophagy rather than cell death by autophagy. Here, we evaluate the accumulating body of literature that argues that cell death occurs by autophagy. We also list the caveats that must be considered when deciding whether or not autophagy is an important effector mechanism of cell death.

Autophagic cell death: the story of a misnomer

Dying cells often display a large-scale accumulation of autophagosomes and hence adopt a morphology called autophagic cell death. In many cases, it is agreed that this autophagic cell death is cell death with autophagy rather than cell death by autophagy. Here, we evaluate the accumulating body of literature that argues that cell death occurs by autophagy. We also list the caveats that must be considered when deciding whether or not autophagy is an important effector mechanism of cell death.

Does autophagy have a license to kill mammalian cells?

Macroautophagy is an evolutionarily conserved vacuolar, self-digesting mechanism for cellular components, which end up in the lysosomal compartment. In mammalian cells, macroautophagy is cytoprotective, and protects the cells against the accumulation of damaged organelles or protein aggregates, the loss of interaction with the extracellular matrix, and the toxicity of cancer therapies. During periods of nutrient starvation, stimulating macroautophagy provides the fuel required to maintain an active metabolism and the production of ATP. Macroautophagy can inhibit the induction of several forms of cell death, such as apoptosis and necrosis. However, it can also be part of the cascades of events that lead to cell death, either by collaborating with other cell death mechanisms or by causing cell death on its own. Loss of the regulation of bulk macroautophagy can prime self-destruction by cells, and some forms of selective autophagy and non-canonical forms of macroautophagy have been shown to be associated with cell demise. There is now mounting evidence that autophagy and apoptosis share several common regulatory elements that are crucial in any attempt to understand the dual role of autophagy in cell survival and cell death.