Table of Contents

Volume 5, Issue 7

  October 1, 2009

  Pages 925 - 1074

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 Issue Catalogue (MARC XML)

REVIEW

Open Access Article

Autophagy in food biotechnology

Hagai Abeliovich and Ramon Gonzalez
Pages 925 - 929
http://dx.doi.org/10.4161/auto.5.7.9213
Abstract | PDF

The purpose of this review is not to explain autophagy (as clearly there are a plethora of reviews and research papers on the topic) but to provide the autophagy-savvy reader with an overview of the impact of autophagy research on a number of current topics in food biotechnology.  To understand this connection, we need to remember that autophagy is, at the end of the day, a type of stress response. Since as humans we are heterotrophic eukaryotic organisms, our cells, and the cells of those organisms that we consume, use autophagy as part of the day-to-day business of living. Thus, a number of food biotechnology processes such as brewing and winemaking employ eukaryotic organisms under autophagy-inducing conditions, as noted below. In addition, food spoilage processes also involve eukayotic organisms and these processes also involve physiological aspects that impinge on autophagy. Finally, the recently introduced concept of “functional foods” introduces the possibility of engineering foodstuff for the induction or inhibition of autophagy in the consumer, with a potential promise of health benefits that merits further research.


In this review, we will provide a perspective on the current literature in these three areas, their relationship to current basic research in autophagy, and their future applicative potential.




CLINICAL BRIEF REPORTS

Open Access Article

The prognostic role of Beclin 1 protein expression in high-grade gliomas

Luigi Pirtoli, Gabriele Cevenini, Paolo Tini, Marta Vannini, Giuseppe Oliveri, Stefania Marsili, Vasileios Mourmouras, Giovanni Rubino and Clelia Miracco
Pages 930 - 936
http://dx.doi.org/10.4161/auto.5.7.9227
Abstract | PDF

High Grade Gliomas (HGG) have a poor outcome, however, prognostic sub-groups of patients may be individuated by some clinico-biological parameters. It was recently demonstrated that the main response of HGG to therapy is autophagic death. Autophagy is involved in tumor suppression, and is defective in HGG, in which we previously found an underexpression of beclin 1 autophagic gene protein product. Underexpression of Beclin 1 protein has been correlated to poor patient outcome in other tumor types. In this paper, the prognostic role of beclin 1 expression in HGG patients was investigated. We firstly evaluated the tumor cell cytoplasmic expression of Beclin 1 protein (BPCE), in a sample of 76 HGG by immunohistochemistry, and compared it with cell proliferation and apoptosis. We found high BPCE score positively correlated with apoptosis, and negatively with cell proliferation (p < 0,05). We then correlated BPCE score with survival and other prognostic parameters (histological grading , MGMT gene methylation status, age, patient performance status according to the Karnofski classification (KPS), extent of surgery, radiation therapy (RT) modality, temozolomide chemotherapy (TMZ CHT), and optimal/suboptimal post-surgical treatment). Forty-seven (61.8%) and twenty-nine (38.2%) patients showed high and low BPCE scores, respectively. BPCE showed statistically significant correlations with survival both at the univariate (p = 0.03) and multivariate analysis (p = 0.037). High BPCE was also positively correlated  with high KPS values (p = 0.023), and with the accomplishment of an optimal post-operative therapy (p = 0.037). Furthermore, among patients showing a MGMT methylated gene, survival was significantly higher in cases with a higher BPCE score. BPCE score might be added to pathological evaluation of HGG for prognostic purposes.

Open Access Article

Knockdown of autophagy-related gene decreases the production of infectious Hepatitis C virus particles

Isei Tanida, Masayoshi Fukasawa, Takashi Ueno, Eiki Kominami, Takaji Wakita and Kentaro Hanada
Pages 937 - 945
http://dx.doi.org/10.4161/auto.5.7.9243
Abstract | PDF

Hepatitis C virus (HCV) is a positive strand RNA virus, and classified within the Flaviridae family.  It has been reported that Atg7-knockdown decreases the amount of HCV replicon RNA, when HCV JFH1 RNA and HCV subgenomic replicon were transfected into Huh7.5 cells.  However, when infectious naïve HCV particles are directly infected into Huh7.5.1 cells, it is still unclear whether Atg7-knockdown decreases the production of intracellular HCV-related proteins, HCV mRNA and infectious HCV particles.  When Atg7 protein in HCV-infected Huh7.5.1 cells was knocked down by RNA-interference, the levels of intracellular HCV core, NS3, NS5A proteins, HCV mRNA, and secreted albumin remained unchanged compared with those in the control HCV-infected cells.  However, the level of infectious HCV particles released in the medium was decreased by the Atg7-knockdown.  The similar results were obtained, when beclin1 was knocked down by RNA-interference.  The colocalization of endogenous LC3-puncta with HCV core, HS5A proteins, and lipid droplets was also investigated.  However, little endogenous LC3-puncta colocalized with HCV core, NS5A proteins or lipid droplets.  These results suggested that autophagy contributed to the effective production of HCV particles, but little to the intracellular production of HCV-related proteins, HCV mRNA, and secretory pathway, in naïve HCV particles-infection system.




BASIC RESEARCH PAPERS

Open Access Article

MgAtg9 trafficking in Magnaporthe oryzae

Bo Dong, Xiao-Hong Liu, Jian-Ping Lu, Fu-Sheng Zhang, Hui-Min Gao, Hong-Kai Wang and Fu-Cheng Lin
Pages 946 - 953
http://dx.doi.org/10.4161/auto.5.7.9161
Abstract | PDF

Autophagy is a vacuolar/lysosomal cytoplasmic recycling system in eukaryotic cells. ScATG9 is indispensable for autophagy in Saccharomyces cerevisiae. Here, we deleted MgATG9, the orthologue of ScATG9, via targeted gene replacement in the phytopathogenic filamentous fungus Magnaporthe oryzae, and then analyzed the cellular distribution pattern of EGFP-MgAtg9 in the Mgatg9∆ mutant. We detected an expression profile of multiple green dots in the conidial cell inoculated in rich media and in the appressoria differentiated from the conidia in H₂O. Concurrent with the punctation, we found some fluorescent signals localized on the central vacuole of the submerged hyphae from the conidia cultured in rich media. Next, we introduced DsRed2-MgAtg8 into the Mgatg9∆ mutant expressing EGFP-MgAtg9 and observed partial overlap at multiple sites in the conidial cell, reminiscent of that in the mammalian system. Our findings further led to the postulation that the multiple sites where the two fusions colocalized tend to merge as a central structure in the conidial cell. Finally, we tested the expression of EGFP-MgAtg9 in null mutants of MgATG1, 2, 13 and 18, respectively. We speculate that MgAtg1, 2 and 18, but not MgAtg13, is required for MgAtg9 cycling through the multiple colocalization sites to its storage pools in the conidial cell of M. oryzae, and fusion of these colocalization sites into a central structure could be governed through other unidentified mechanisms.

Open Access Article

Autophagy is required for tolerance of drought and salt stress in plants

Yimo Liu, Yan Xiong and Diane C. Bassham
Pages 954 - 963
http://dx.doi.org/10.4161/auto.5.7.9290
Abstract | PDF

Autophagy is a protein degradation process in which cells recycle cytoplasmic contents when subjected to environmental stress conditions or during certain stages of development. Upon the induction of autophagy, a double membrane autophagosome forms around cytoplasmic components and delivers them to the vacuole or lysosome for degradation. In plants, autophagy has been shown previously to be induced during abiotic stresses including nutrient starvation and oxidative stress. In this paper, we demonstrate the induction of autophagy in high salt and osmotic stress conditions, concomitant with the upregulation of expression of an Arabidopsis thaliana autophagy-related gene AtATG18a. Autophagy-defective RNAi-AtATG18a plants are more sensitive to salt and drought conditions than wild-type plants, demonstrating a role for autophagy in the response to these stresses. NADPH oxidase inhibitors block autophagy induction upon nutrient starvation and salt stress, but not during osmotic stress, indicating that autophagy can be activated by NADPH oxidase-dependent or -independent pathways. Together our results indicate that diverse environmental stresses can induce autophagy and that autophagy is regulated by distinct signaling pathways in different conditions.

Open Access Article

Autophagy is not universally required for phosphatidyl-serine exposure and apoptotic cell engulfment during neural development

María A. Mellén, Enrique J. de la Rosa and Patricia Boya
Pages 964 - 972
http://dx.doi.org/10.4161/auto.5.7.9292
Abstract | PDF

Apoptosis and autophagy are physiological processes implicated in the maintenance of cell and tissue homeostasis. We took advantage of the existence of multiple phases of
developmental cell death in the embryonic chick retina and of the availability of shortterm organotypic retinal cultures to approach the possible relationship between
apoptosis and autophagy during neural development. We examined retinas at embryonic day 5, an early stage at which cell death is related to eye morphogenesis and to retinal
ganglion cell generation, as well as at embryonic day 9, when cell death is associated with neurotrophic support of the retinal ganglion cells. Exposure to 3-methyl-adenine, a
classical inhibitor of autophagy, elicited a selective accumulation of apoptotic bodies in the dorsotemporal area of embryonic day 5 retinas where neurogenesis is taking place.
This accumulation was correlated with a blockage of phosphatidyl-serine presentation and, consequently, with a lack of engulfment of the dying cells by their neighbors. In
striking contrast, none of these phenomena were observed in association with cell death in the optic nerve and optic fissure at embryonic day 5, or in embryonic day 9 retinas.
Our data suggest that autophagy is essential for phosphatidyl-serine presentation by apoptotic cells during the phase of cell death associated to neurogenesis, but this is not a
universal requirement for all phases of cell death occurring during retinal development.

Open Access Article

Atg101, a novel mammalian autophagy protein interacting with Atg13

Nao Hosokawa, Takahiro Sasaki, Shun-ichiro Iemura, Tohru Natsume, Taichi Hara and Noboru Mizushima
Pages 973 - 979
http://dx.doi.org/10.4161/auto.5.7.9296
Abstract | PDF

Autophagy is a major route, by which cytoplasmic contents are delivered to the lysosome for degradation. Many autophagy-related (ATG) genes have been identified in yeast. Although most of them are conserved in human, the molecular composition of the Atg1 complex appears to differ between yeast and mammals. In yeast, Atg1 forms a complex with Atg11, Atg13, Atg17, Atg29 and Atg31, whereas mammalian Atg1 (ULK1/2) interacts with Atg13 and FIP200. Here, we identify a novel mammalian Atg13 binding protein, named Atg101. Atg101 shows no homology with other Atg proteins, and is conserved in various eukaryotes, but not in Saccharomyces cerevisiae. Atg101 associates with the ULK-Atg13-FIP200 complex, most likely through direct interaction with Atg13. In Atg13 siRNA-treated cells, Atg101 is present solely as a monomer. Interaction between Atg101 and the ULK-Atg13-FIP200 complex is stable, and is not regulated by nutrient conditions. GFP-Atg101 localizes to the isolation membrane/phagophore. GFP-LC3 dot formation is suppressed and endogenous LC3-I accumulate in Atg101 siRNA-treated cells suggesting that Atg101 is a critical factor for autophagy. Furthermore, Atg101 is important for the stability and basal phosphorylation of Atg13 and ULK1. These data suggest that Atg101 is a novel Atg protein that functions together with ULK, Atg13 and FIP200.

Open Access Article

A combined proteomic and genetic analysis identifies a role for the lipid desaturase Desat1 in starvation-induced autophagy in Drosophila

Katja Köhler, Erich Brunner, Xue Li Guan, Karin Boucke, Urs F. Greber, Sonali Mohanty, Julia M.I. Barth, Markus R. Wenk and Ernst Hafen
Pages 980 - 990
http://dx.doi.org/10.4161/auto.5.7.9325
Abstract | PDF

Autophagy is a lysosomal-mediated degradation process that promotes cell survival during nutrient-limiting conditions. However, excessive autophagy results in cell death. In Drosophila, autophagy is regulated nutritionally, hormonally and developmentally in several tissues, including the fat body, a nutrient-storage organ. Here, we use a proteomics approach to identify components of starvation-induced autophagic responses in the Drosophila fat body. Using cICAT^TM labeling and mass spectrometry, differences in protein expression levels of normal compared to starved fat bodies were determined. Candidates were analyzed genetically for their involvement in autophagy in fat bodies deficient for the respective genes. One of these genes, Desat1, encodes a lipid desaturase. Desat1 mutant cells fail to induce autophagy upon starvation. The desat1 protein localizes to autophagic structures after nutrient depletion and is required for fly development. Lipid analyses revealed that Desat1 regulates the composition of lipids in Drosophila. We propose that Desat1 exerts its role in autophagy by controlling lipid biosynthesis and/or signaling necessary for autophagic responses.

Open Access Article

Granulosa cell subtypes respond by autophagy or cell death to oxLDL-dependent activation of the oxidized lipoprotein receptor 1 and toll-like 4 receptor

Heike Serke, Constanze Vilser, Marcin Nowicki, Fayez A. Hmeidan, Verona Blumenauer, Katja Hummitzsch, Andreas Lösche and Katharina Spanel-Borowski
Pages 991 - 1003
http://dx.doi.org/10.4161/auto.5.7.9507
Abstract | PDF

Autophagic cell death has been observed in granulosa cell cultures via the oxLDL-dependent activation of lectin-like oxidized low density lipoprotein receptor 1 (LOX-1). This activation might differ for cytokeratin-positive (CK⁺) and CK^- granulosa cells. In particular, LOX-1 and Toll-like receptor 4 (TLR4), one of the pattern recognition receptors of innate immunity, might be diversely regulated. Granulosa cell subtype cultures were established from the follicle harvests of patients undergoing in vitro fertilization (IVF) therapy. In response to oxLDL treatment, the fibroblast-like CK- cells upregulated LOX-1 and exhibited reparative autophagy, which could be blocked with anti-LOX-1 antibody. The epithelioid-like CK⁺ cells did not regulate LOX-1 expression upon oxLDL application, but the expression of TLR4 and CD14 increased between 0 and 36 h of oxLDL/nDL treatment. This up-regulation was associated with non-apoptotic cell death based on the absence of cleaved caspase-3. Reactive oxygen species (ROS) increased with 12 h oxLDL application and steroidogenic acute regulatory (StAR) protein expression was negligible. In CK^- cells, the inhibition of TLR4 downregulated LOX-1 and induced apoptosis. We concluded that CK- granulosa cells are protected against oxLDL-dependent apoptosis by TLR4, whereas, in CK⁺ cells, oxLDL-induced TLR4 activation triggers non-apoptotic cell death. The CK⁺ cells might represent immune-like granulosa cells involved in ovarian remodeling processes.

Open Access Article

Sexual dimorphism of autophagy in Syrian hamster Harderian gland culminates in a holocrine secretion in female glands

Ignacio Vega-Naredo, Beatriz Caballero, Verónica Sierra, Covadonga Huidobro-Fernández, David de Gonzalo-Calvo, Marina García-Macia, Delio Tolivia, María Josefa Rodríguez-Colunga and Ana Coto-Montes
Pages 1004 - 1017
http://dx.doi.org/10.4161/auto.5.7.9610
Abstract | PDF

The Syrian hamster Harderian gland (HG) has a large porphyrin metabolism with a sexual dimorphism, showing male HGs much lower porphyrin concentrations than female glands. Damage derived from this production of porphyrins, displayed by reactive oxygen species, forces the gland to develop morphological changes that must have a physiological significance. Thus, oxidative stress is present in two states: mild oxidative stress in male HGs and extreme oxidative stress in female HGs. Cathepsins data gave indirect indications about the presence of programmed cell death affecting the lysosomal pathway, especially in female HGs, which showed an accumulation of autophagic bodies. Our results showed different degrees of autophagy in Syrian hamster HGs depending on sex and probably controlled by the redox-sensitive transcription factors: NF-kappaB and p53. The discovery of these sexual dimorphisms in redox signaling and in autophagy corroborates previous findings and underlines the key role of reactive oxygen species in the regulation of autophagy. In addition, in this paper we propose a physiological significance for these phenomena: male HGs develop a survival autophagy, while in female HGs, autophagy culminates in a detachment-derived cell death that plays a central role in its secretory activity, leading to a massive glandular secretion.




TOOLBOX

Open Access Article

Identification of novel autophagy regulators by a luciferase-based assay for the kinetics of autophagic flux

Thomas Farkas, Maria Høyer-Hansen and Marja Jäättelä
Pages 1018 - 1025
http://dx.doi.org/10.4161/auto.5.7.9443
Abstract | PDF

Macroautophagy (hereafter referred to as autophagy) has recently emerged as an attractive target for the treatment of various degenerative diseases and cancer. The discovery of effective pharmaceutical regulators of autophagy has, however, been hindered by a lack of feasible assay systems for autophagic flux. Here, we present a luciferase-based reporter assay that measures autophagic flux in real time in living cells and demonstrate that this assay system is apt for the detection of dose- and stimulus-dependent differences in autophagy kinetics. Furthermore, by screening a small molecule kinase inhibitor library containing 80 compounds we identified 12 compounds as inducers of autophagic flux. Importantly, six inhibitors of the class I phosphoinositide 3-kinase – protein kinase B – mammalian target of rapamycin complex 1 axis, the central signaling pathway repressing autophagy, scored as autophagy inducers adequately validating the screen. We conclude that the assay system presented here allows easy and rapid monitoring of autophagy kinetics and is suitable for screening of small molecule libraries.




ARTICLE ADDENDA

Open Access Article

Nuclear membrane-derived autophagy, a novel process that participates in the presentation of endogenous viral antigens during HSV-1 infection

Luc English, Magali Chemali and Michel Desjardins
Pages 1026 - 1029
http://dx.doi.org/10.4161/auto.5.7.9163
Abstract | PDF

Complex membrane trafficking events are involved in the regulation of antigen processing and presentation of both endogenous and exogenous antigens.  While these processes were believed to involve mainly organelles along the endo/phagocytic and the biosynthetic pathways, recent studies have shown that autophagy also participates actively in both innate and adaptive immunity.  We have shown recently that, in macrophages infected with the Herpes simplex type 1 virus, autophagy plays a key role in the targeting of viral proteins to hydrolytic compartments, and their processing for presentation on MHC class I molecules.  This pathway involves a novel type of autophagosomes formed by coiling of the nuclear membrane where viral proteins are highly enriched.  The ability to enhance the contribution of autophagy to antigen presentation in various conditions suggests that this pathway could be used to boost the immune response against viral infection and develop new vaccines.

Open Access Article

Inhibition of p38α unveils an AMPK-FoxO3A axis linking autophagy to cancer-specific metabolism

Fulvio Chiacchiera and Cristiano Simone
Pages 1030 - 1033
http://dx.doi.org/10.4161/auto.5.7.9252
Abstract | PDF

Autophagy is an essential process for the maintenance of cellular and metabolic homeostasis. Indeed, it is required for the recovery of ATP-generating substrates in cells subjected to different types of stress insults. Thus, the activity of the autophagic machinery strongly depends on the metabolic status of the cell.¹ It has been proposed that this principle applies not only to normal, but also to cancer cells,² despite the profound differences in their metabolism. Cancer cells predominantly produce ATP through the constitutive activation of aerobic glycolysis, a process that generally relies on the stabilization and activation of the transcription factor HIF1α, which regulates the expression of glycolytic genes.³ We recently showed that p38α is required to sustain the expression of HIF1α target genes, and that its inhibition causes a rapid drop in ATP levels in colorectal cancer cells (CRCs). This acute energy need triggers AMPK-dependent nuclear accumulation of FoxO3A and subsequent activation of its transcriptional program, leading to sequential induction of autophagy, cell cycle arrest and cell death. In vivo, pharmacological blockade of p38α has both a cytostatic and cytotoxic effect on colorectal neoplasms, associated with nuclear enrichment of FoxO3A and expression of its target genes p21 and PTEN.⁴ Our data suggest that CRCs impaired in their glycolytic metabolism trigger autophagy as a reversible recovery mechanism and undergo cell cycle arrest; however, the persistence of the stress insults inevitably leads to cell death.

Open Access Article

Autophagy maintains cardiac function in the starved adult

Genzou Takemura, Hiromitsu Kanamori, Kazuko Goto, Rumi Maruyama, Akiko Tsujimoto, Hisayoshi Fujiwara, Mitsuru Seishima and Shinya Minatoguchi
Pages 1034 - 1036
http://dx.doi.org/10.4161/auto.5.7.9297
Abstract | PDF

To examine the functional significance and detailed morphological characteristics of starvation-induced autophagy in the adult heart, we starved green fluorescent protein (GFP)-microtubule-associated protein 1 light chain 3 (LC3) transgenic mice for up to 3 days.  Electron microscopy revealed that, after as little as 12 hours of starvation, round and homogenously electron-dense lipid droplet-like vacuoles appeared in cardiomyocytes.  These were determined to be lysosomes based on cathepsin D immunopositivity and acid phosphatase activity.  The numbers of these lysosomes increased with starvation time, and typical autolysosomes with intracellular organelles destined for degradation appeared and increased in number at later times during the starvation period.  Myocardial expression of the autophagy-related proteins LC3-II, cathepsin D, and ubiquitin increased, while myocardial ATP content decreased, as the starvation interval proceeded.  Treatment with bafilomycin A1, an autophagy inhibitor, did not affect cardiac function in normally fed mice, but it significantly depressed cardiac function and caused significant left ventricular dilatation in the mice starved for 3 days.  Cardiomyocytes from starved mice treated with bafilomycin A1 showed marked accumulation of lysosomes, and the myocardial amino acid content, which increased during starvation in normally fed mice, as well as the myocardial ATP content, were severely reduced, which likely contributed to the cardiac dysfunction.  The present findings suggest autophagy plays a critical role in the maintenance of cardiac function during starvation in the adult.




AUTOPHAGIC PUNCTA

Open Access Article

Protein turnover and inclusion body formation

Siddhartha Mitra, Andrey S. Tsvetkov and Steven Finkbeiner
Pages 1037 - 1038
http://dx.doi.org/10.4161/auto.5.7.9291
Abstract | PDF

In a recent study, we investigated the relationship between inclusion body (IB) formation and the activity of the ubiquitin-
proteasome system (UPS) in a primary neuron model of Huntington disease. We followed individual neurons over the
course of days and monitored the level of mutant huntingtin (htt) (which causes Huntington disease), IB formation, UPS function,
and neuronal toxicity. The accumulation of UPS substrates and neuronal toxicity increased with increasing levels of proteasome
inhibition. The UPS was more impaired in neurons that subsequently formed IBs than in those that did not; however, after IBs
formed, UPS function improved. These findings suggest that IB formation is a protective cellular response mediated in part by
increased degradation of intracellular protein.

Open Access Article

Morphological homeostasis by autophagy

Daniel Lingwood, Sebastian Schuck, Charles Ferguson, Mathias Gerl and Kai Simons
Pages 1039 - 1040
http://dx.doi.org/10.4161/auto.5.7.9314
Abstract | PDF

With cellular organelles coming in all shapes and sizes, the principle ‘form follows function’ is readily discernible through the cytologist’s lens. Architecturally, one might ask whether there is feedback in this organization. Does a cell ‘know’ when it has constructed membrane into the stacks of the Golgi, the cisternae of the mitochondria or the tubules of the endoplasmic reticulum? Proofreading can occur in vivo as both errors in nucleic acids and misfolds in proteins are recognized by the cell. Are there analogous systems which maintain/regulate the architectural integrity of organelles? Our recent paper entitled “Generation of cubic membranes from controlled homotypic interactions of membrane proteins in the endoplasmic reticulum” suggests that autophagy may play such a role.

Open Access Article

Atg26-mediated pexophagy and fungal phytopathogenicity

Yoshitaka Takano, Makoto Asakura and Yasuyoshi Sakai
Pages 1041 - 1042
http://dx.doi.org/10.4161/auto.5.7.9316
Abstract | PDF

Colletotrichum orbiculare is a plant pathogenic fungus that causes disease on cucumber plants.  A homologue of ATG26 (CoATG26) was identified as the gene involved in pathogenesis.  The peroxisomes are degraded via pexophagy during formation of an infection structure called the appressorium of C. orbiculare.  The Coatg26 mutant developed appressoria but exhibited a specific defect in the subsequent host invasion step.  Importantly, the autophagic degradation of peroxisomes was significantly delayed in the appressoria of the Coatg26 mutant.  Domain and localization analysis of CoAtg26 also demonstrated a strong correlation of functional pexophagy with pathogenicity. Furthermore, in contrast to the Coatg26 mutant, the Coatg8 mutant, defective in the entire autophagic pathway, could not form normal appressoria in the earlier steps of morphogenesis.  These results indicate that CoAtg26-mediated pexophagy plays critical roles in host plant invasion.

Open Access Article

Cisd2 mediates mitochondrial integrity and life span in mammals

Yi-Fan Chen, Cheng-Heng Kao, Ralph Kirby and Ting-Fen Tsai
Pages 1043 - 1045
http://dx.doi.org/10.4161/auto.5.7.9351
Abstract | PDF

CISD2, the causative gene for Wolfram syndrome 2 (WFS2), is a previously uncharacterized novel gene. Using a mouse genetic approach, this work demonstrated for the first time that Cisd2 is involved in mammalian life span control. Cisd2 deficiency in mice leads to mitochondrial breakdown and dysfunction; this is accompanied by cell death with autophagic features and these events precede the two earliest manifestations of nerve and muscle degeneration. Together, they lead to a panel of phenotypic features suggestive of premature aging. This work effectively links Cisd2 gene function, mitochondrial integrity and aging in mammals.

Open Access Article

Autophagy facilitates oncogene-induced senescence

Masako Narita, Andrew R.J. Young and Masashi Narita
Pages 1046 - 1047
http://dx.doi.org/10.4161/auto.5.7.9444
Abstract | PDF

Oncogenic stress triggers a range of intracellular protective responses including DNA damage checkpoints, senescence and apoptosis, depending on the cell type and the severity of the particular stress. Senescent cells are metabolically viable but are stably arrested. Senescence is a collective phenotype, however, that is comprised of various signaling pathways and effector mechanisms. Thus, to understand and manipulate the senescence phenotype, it is critical to find its effector mechanisms and determine the relationships between them. We have recently found that autophagy is activated upon acute induction of senescence and facilitates another effector mechanism: the senescence associated secretory phenotype (SASP).

Open Access Article

TRB3 links ER stress to autophagy in cannabinoid antitumoral action

María Salazar, Arkaitz Carracedo, Íñigo J. Salanueva, Sonia Hernández-Tiedra, Ainara Egia, Mar Lorente, Patricia Vázquez, Sofia Torres, Juan L. Iovanna, Manuel Guzmán, Patricia Boya and Guillermo Velasco
Pages 1048 - 1049
http://dx.doi.org/10.4161/auto.5.7.9508
Abstract | PDF

Δ⁹-tetrahydrocannabinol (THC), the main active component of marijuana, is being investigated as a potential anti-tumoral agent. We find that THC stimulates an endoplasmic reticulum (ER) stress-related signaling pathway, which activates autophagy via inhibition of the Akt/mTORC1 axis. We also show that autophagy is upstream of apoptosis in cannabinoid-induced cancer cell death and that activation of this pathway is necessary for the anti-tumoral action of cannabinoids in vivo.

Open Access Article

Targeted therapies and autophagy: new insights from chronic myeloid leukemia

Paolo Salomoni and Bruno Calabretta
Pages 1050 - 1051
http://dx.doi.org/10.4161/auto.5.7.9509
Abstract | PDF

Patients who develop chronic myeloid leukemia (CML) are currently treated with tyrosine kinase inhibitors (TKIs), which inhibit the function of the oncogene BCR/Abl. Most CML cells undergo apoptosis when BCR/Abl tyrosine kinase activity is suppressed by TKIs. Cells surviving drug treatment are either stem cells (CML in early phase) or cells with BCR/Abl-dependent or -independent mechanisms of drug resistance (CML in advanced phase).  Since survival of these cells is thought to be responsible for disease recurrence, it is critical to find ways to fully eradicate CML stem cells. We have recently shown that when CML cells, including stem cells, are exposed to TKI they activate an autophagic program, which relies on intracellular calcium and is not inhibited by Bcl-2. Pharmacological or RNAi-mediated inhibition of autophagy potentiates the effect of TKI in inducing death of CML cells, including the stem cells. These data strongly suggest that inhibition of autophagy may improve the therapeutic effects of TKIs in the treatment of CML. In addition, they give credence to the idea that in cancer cells autophagy is part of a stereotypic response to stress and specifically to abrogation of their main oncogenic signal(s).

Open Access Article

Starving to succeed

Emma Davenport, Lauren I. Aronson and Faith E. Davies
Pages 1052 - 1054
http://dx.doi.org/10.4161/auto.5.7.9510
Abstract | PDF

Cancer cells rely on the efficient and effective turnover of cell signaling molecules to ensure their continued survival, and hence depend on specific amino acids (AAs) for their growth and metastatic capabilities.  This dependence has been exploited by the recent, successful development of the proteasome inhibitor, bortezomib, which inhibits the degradation of proteins; and suggests that inhibitors of other essential steps in the mechanisms of cellular protein turnover may provide novel therapeutic targets.  The provision of free AAs within cancer cells is controlled by aminopeptidases which are responsible for the cleavage of AAs from the amino terminus of proteins or peptides.  Recent studies have demonstrated that the expression of aminopeptidases is upregulated in cancer cells compared to normal cells, providing a rationale for further study and development of clinical grade aminopeptidase inhibitors.

Open Access Article

Autophagy and the pancreatic beta-cell in human type 2 diabetes

Piero Marchetti and Matilde Masini
Pages 1055 - 1056
http://dx.doi.org/10.4161/auto.5.7.9511
Abstract | PDF

Pancreatic beta-cell dysfunction is central to the development and worsening of type 2 diabetes. Whereas beta-cell apoptosis plays a major role in reducing beta-cell mass in diabetes, alterations of autophagy can also lead to beta-cell death, as recently demonstrated in type 2 diabetic subjects. In addition, several studies with cell lines and rodent models have shown the importance of autophagy in regulating beta-cell survival and function. Although most of the underlying molecular mechanisms remain to be elucidated, this growing evidence raises interest in the role of autophagy in beta-cell pathophysiology and suggests the possibility of exploring autophagic processes to develop tools for protection of the pancreatic beta-cell in type 2 diabetes.

Open Access Article

Atg4D at the interface between autophagy and apoptosis

Virginie M.S. Betin and Jon D. Lane
Pages 1057 - 1059
http://dx.doi.org/10.4161/auto.5.7.9684
Abstract | PDF

The Atg4 family of endopeptidases regulates autophagosome biogenesis by priming newly synthesised Atg8 to enable covalent attachment of phosphatidylethanolamine, and by delipidating Atg8 at the lysosomal fusion step. Control of Atg4 activity is therefore crucial, although little is known about how these molecules are regulated in living cells. We have found that one human Atg4 family member (Atg4D) is cleaved at DEVD63K by caspase-3 during apoptosis. Importantly, our studies suggest that native Atg4D is enzymatically inactive, but gains GABARAP-L1 priming/delipidation activity following caspase cleavage. Caspase-cleaved Atg4D is also highly cytotoxic; however, toxicity is not due to enhanced autophagy, but is mediated by a putative C-terminal BH3 domain, and is associated with transient recruitment of Atg4D to mitochondria.

Open Access Article

Targeting autophagy to prevent neonatal stroke damage

Julien Puyal and Peter G.H. Clarke
Pages 1060 - 1061
http://dx.doi.org/10.4161/auto.5.7.9728
Abstract | PDF

Cell death due to cerebral ischemia has been attributed to necrosis and apoptosis, but autophagic mechanisms have recently been implicated as well. Using rats exposed to neonatal focal cerebral ischemia, we have shown that lysosomal and autophagic activities are increased in ischemic neurons, and have obtained strong neuroprotection by post-ischemic inhibition of autophagy.

Open Access Article

VSV infection is sensed by Drosophila, attenuates nutrient signaling, and thereby activates antiviral autophagy

Sara Cherry
Pages 1062 - 1063
http://dx.doi.org/10.4161/auto.5.7.9730
Abstract | PDF

Innate immune mechanisms are the first line of defense against pathogens including viruses. This work identifies autophagy, an innate intracellular degradative pathway, as antiviral against Vesicular Stomatitis Virus (VSV) in Drosophila. VSV is sensed by cells via the surface glycoprotein leading to the attenuation of the nutrient signaling pathway thereby activating an antiviral autophagic program.

Open Access Article

Autophagy-dependent and -independent mechanisms of mitochondrial clearance during reticulocyte maturation

Ji Zhang and Paul Ney
Pages 1064 - 1065
http://dx.doi.org/10.4161/auto.5.7.9749
Abstract | PDF

Erythrocyte formation involves the elimination of mitochondria at the reticulocyte stage of development.  Nix-/- reticulocytes fail to eliminate their mitochondria at this step due to a defect in the targeting of mitochondria to autophagosomes.  To determine the role of autophagy in this process, we generated Atg7-/- transplant mice.  Atg7-/- reticulocytes exhibit a partial defect in mitochondrial clearance, demonstrating that there are both autophagy-dependent and -independent mechanisms of mitochondrial clearance.  We used Atg7-/- autophagy-defective reticulocytes to study temporal events in mitochondrial clearance.  Mitochondrial depolarization precedes elimination, but in Atg7-/- reticulocytes the depolarization event is markedly delayed.  Since Atg7 regulates autophagosome formation, we infer that mitochondrial depolarization occurs downstream of autophagosome formation in reticulocytes.  We propose that there are two mechanisms of mitochondrial clearance: one that is triggered by mitochondrial depolarization, and a second NIX-dependent mechanism, which is not.  The NIX-dependent mechanism remains to be elucidated.

Open Access Article

Tamoxifen and AEBS ligands induced apoptosis and autophagy in breast cancer cells through the stimulation of sterol accumulation

Philippe de Medina, Sandrine Silvente-Poirot and Marc Poirot
Pages 1066 - 1067
http://dx.doi.org/10.4161/auto.5.7.9820
Abstract | PDF

Tamoxifen (Tx) interacts with high affinity to the microsomal antiestrogen binding site (AEBS) which is a hetero-oligomeric complex involved in cholesterol metabolism. We established that Tx and other AEBS ligands induce breast cancer cell differentiation, apoptosis and autophagy through the induction of sterol accumulation. We determined that cell death is sterol- and ROS-dependent and is prevented by the antioxidant vitamin E. Macroautophagy is characterized by the accumulation of autophagic vacuoles, an increase in the expression of Beclin 1 and the stimulation of autophagic flux. We established that macroautophagy is sterol-dependent and is associated with cell survival rather than cytotoxicity, since blockage of macroautophagy sensitizes cells to AEBS ligands. These results show that the accumulation of sterols by AEBS ligands in MCF-7 cells induces both apoptosis and macroautophagy. Collectively, these data support a therapeutic potential for selective AEBS ligands in breast cancer management and reveal a mechanism that explains the induction of autophagy in MCF-7 cells by Tx and other selective estrogen receptor modulators. Moreover these data give pharmacological clues to improve the apoptotic efficacy of AEBS ligands.

Open Access Article

Growth factor signaling permits hypoxia-induced autophagy by a HIF1α-dependent, BNIP3/3L-independent transcriptional program in human cancer cells

Simon Wilkinson and Kevin M. Ryan
Pages 1068 - 1069
http://dx.doi.org/10.4161/auto.5.7.9821
Abstract | PDF

Several recent reports have demonstrated that autophagy is induced in response to hypoxia in cultured cells. However, the mechanism and consequence of hypoxia-induced autophagy remains unclear as there is no consensus between these studies. In our recent report we show that, in human cancer cells, hypoxia cooperates with growth factor signaling to facilitate a HIF1α-driven transcriptional response that promotes autophagy. Here we summarize these findings and set them in context of the findings of other groups, concluding that there are likely multiple routes to different forms of autophagy that serve different purposes downstream of hypoxia, depending upon the degree of stress and cellular context.

Open Access Article

Autophagy defects contribute to neurodegeneration induced by dysfunctional ESCRT-III

Jin-A Lee, Lei Liu and Fen-Biao Gao
Pages 1070 - 1072
http://dx.doi.org/10.4161/auto.5.7.9823
Abstract | PDF

The endosomal sorting complex required for transport (ESCRT) machinery is involved in multiple cellular processes, including autophagy (macroautophagy). Autophagy is an important intracellular pathway that involves the formation and maturation of autophagosomes and their fusion with lysosomes for bulk degradation of cytoplasmic contents and organelles. In flies and cultured mammalian cells, autophagosomes accumulate when ESCRT-III is rendered dysfunctional by reduced activity of its subunits or by ectopic expression of mutant CHMP2B associated with frontotemporal dementia linked to chromosome 3 (FTD3). Compromised ESCRT-III function results in eventual neuronal cell loss; however, the mechanism of this form of neurodegeneration is largely unknown. Recently, we found that inhibiting autophagy induction in cultured cortical neurons, either by small-molecule inhibitors of phosphatidylinositol 3-kinases (PtdIns3K) or by loss of atg5 or atg7 activity, delays but does not completely suppress neuronal cell loss caused by dysfunctional ESCRT-III. These findings indicate that excess accumulation of autophagosomes is detrimental to neuronal survival, and dysfunctional ESCRT-III appears to cause neurodegeneration through multiple mechanisms.

Open Access Article

The complexity in regulation of MEF2D by chaperone-mediated autophagy

Qian Yang and Zixu Mao
Pages 1073 - 1074
http://dx.doi.org/10.4161/auto.5.7.9824
Abstract | PDF

Chaperone mediated autophagy (CMA) targets specific cytoplasmic proteins for degradation by lysosomes and has been implicated to play a role in neurodegeneration.  Our recent studies identify neuronal survival factor MEF2D as a direct substrate of CMA and show that dysregulation of this process may contribute to the pathogenesis of Parkinson disease.  One interesting finding presented in our study is the apparent loss of DNA binding capacity by the accumulated MEF2D following inhibition of CMA. The possibilities and implication of this finding are discussed.