Table of Contents

Volume 8, Issue 7

  July 2012

  Pages 1003 - 1163

View covers archive

 Issue Catalogue (MARC XML)

EDITOR'S CORNER

The autophagy community

Daniel J. Klionsky
Page 1003
http://dx.doi.org/10.4161/auto.20666
Abstract | Full Text | PDF

There are various definitions of community. A definition that I found in one of my dictionaries is the following: “A social, religious, occupational, or other group sharing common characteristics or interests and perceived or perceiving itself as distinct in some respect from the larger society within which it exists.” Thus, I think it is fair to say that there is a worldwide autophagy community. That is, there is a group of researchers (our occupation), whose members share an interest in autophagy (our common characteristic), and that group is distinct from the larger society (I do not want to begin describing the many ways this applies). But do we feel like a community, and do we need a community? I suggest that a community is indeed beneficial, and I propose one mechanism for enhancing the development of the autophagy community.




AUTOPHAGIC FLUX

Highlights from this issue

Andriy Nemchenko
Pages 1004 - 1005
http://dx.doi.org/10.4161/auto.21310
Full Text | PDF




AUTOPHAGY COMMUNITY

Autophagy Researchers


Pages 1006 - 1008
http://dx.doi.org/10.4161/auto.20667
Full Text | PDF




REVIEW

Emerging role of autophagy in kidney function, diseases and aging

Tobias B. Huber, Charles L. Edelstein, Björn Hartleben, Ken Inoki, Zheng Dong, Daisuke Koya, Shinji Kume, Wilfred Lieberthal, Nicolas Pallet, Alejandro Quiroga, Kameswaran Ravichandran, Katalin Susztak, Sei Yoshida and Zheng Dong
Pages 1009 - 1031
http://dx.doi.org/10.4161/auto.19821
Abstract | Full Text | PDF

Autophagy is a highly conserved process that degrades cellular long-lived proteins and organelles. Accumulating evidence indicates that autophagy plays a critical role in kidney maintenance, diseases and aging. Ischemic, toxic, immunological, and oxidative insults can cause an induction of autophagy in renal epithelial cells modifying the course of various kidney diseases. This review summarizes recent insights on the role of autophagy in kidney physiology and diseases alluding to possible novel intervention strategies for treating specific kidney disorders by modifying autophagy.




BASIC RESEARCH PAPERS

Suppression of basal autophagy reduces lung cancer cell proliferation and enhances caspase-dependent and -independent apoptosis by stimulating ROS formation

Vitaliy O. Kaminskyy, Tatiana Piskunova, Irina B. Zborovskaya, Elena M. Tchevkina and Boris Zhivotovsky
Pages 1032 - 1044
http://dx.doi.org/10.4161/auto.20123
Abstract | Full Text | PDF

Autophagy is a catabolic process involved in the turnover of organelles and macromolecules which, depending on conditions, may lead to cell death or preserve cell survival. We found that some lung cancer cell lines and tumor samples are characterized by increased levels of lipidated LC3. Inhibition of autophagy sensitized non-small cell lung carcinoma (NSCLC) cells to cisplatin-induced apoptosis; however, such response was attenuated in cells treated with etoposide. Inhibition of autophagy stimulated ROS formation and treatment with cisplatin had a synergistic effect on ROS accumulation. Using genetically encoded hydrogen peroxide probes directed to intracellular compartments we found that autophagy inhibition facilitated formation of hydrogen peroxide in the cytosol and mitochondria of cisplatin-treated cells. The enhancement of cell death under conditions of inhibited autophagy was partially dependent on caspases, however, antioxidant NAC or hydroxyl radical scavengers, but not the scavengers of superoxide or a MnSOD mimetic, reduced the release of cytochrome c and abolished the sensitization of the cells to cisplatin-induced apoptosis. Such inhibition of ROS prevented the processing and release of AIF (apoptosis-inducing factor) and HTRA2 from mitochondria. Furthermore, suppression of autophagy in NSCLC cells with active basal autophagy reduced their proliferation without significant effect on the cell-cycle distribution. Inhibition of cell proliferation delayed accumulation of cells in the S phase upon treatment with etoposide that could attenuate the execution stage of etoposide-induced apoptosis. These findings suggest that autophagy suppression leads to inhibition of NSCLC cell proliferation and sensitizes them to cisplatin-induced caspase-dependent and -independent apoptosis by stimulation of ROS formation.

Open Access Article

Compromised autophagy by MIR30B benefits the intracellular survival of Helicobacter pylori

Bin Tang, Na Luo, Jiang Gu, Yuan Zhuang, Qian Li, Hai-Guang Wang, Yao Fang, Bo Yu, Jin-Yu Zhang, Qing-Hua Xie, Li Chen, Xue-Jun Jiang, Bin Xiao, Quan-Ming Zou and Xu-Hu Mao
Pages 1045 - 1057
http://dx.doi.org/10.4161/auto.20159
Abstract | Full Text | PDF

Helicobacter pylori evade immune responses and achieve persistent colonization in the stomach. However, the mechanism by which H. pylori infections persist is not clear. In this study, we showed that MIR30B is upregulated during H. pylori infection of an AGS cell line and human gastric tissues. Upregulation of MIR30B benefited bacterial replication by compromising the process of autophagy during the H. pylori infection. As a potential mechanistic explanation for this observation, we demonstrate that MIR30B directly targets ATG12 and BECN1, which are important proteins involved in autophagy. These results suggest that compromise of autophagy by MIR30B allows intracellular H. pylori to evade autophagic clearance, thereby contributing to the persistence of H. pylori infections.

Sorting nexin Snx41 is essential for conidiation and mediates glutathione-based antioxidant defense during invasive growth in Magnaporthe oryzae

Yi Zhen Deng, Ziwei Qu, Yunlong He and Naweed I. Naqvi
Pages 1058 - 1070
http://dx.doi.org/10.4161/auto.20217
Abstract | Full Text | PDF

The sorting nexins Atg20/Snx42 and Snx41 regulate membrane traffic and endosomal protein sorting and are essential for Cvt and/or pexophagy in yeast. Previously, we showed that macroautophagy is necessary for conidiation in the rice-blast fungus Magnaporthe oryzae. Here, we analyzed the physiological function(s) of selective autophagy in Magnaporthe through targeted deletion of MGG_12832, an ortholog of yeast SNX41 and ATG20/SNX42. Loss of MGG_12832 (hereafter SNX41) abolished conidia formation and pathogenesis in M. oryzae. Snx41-GFP localized as dynamic puncta or short tubules that are partially associated with autophagosomes and/or autophagic vacuoles. PX domain, but not macroautophagy per se, was required for such localization of Snx41-GFP in Magnaporthe. Although not required for nonselective autophagy, Snx41 was essential for pexophagy in Magnaporthe. We identified Oxp1, an ATP-dependent oxoprolinase in the gamma-glutamyl cycle, as a binding partner and potential retrieval target of Snx41-dependent protein sorting. The substrate of Oxp1, 5-oxoproline, could partially restore conidiation in the snx41Δ. Exogenous glutathione, a product of the gamma-glutamyl cycle, significantly restored pathogenicity in the snx41Δ mutant, likely through counteracting the oxidative stress imposed by the host. We propose that the gamma-glutamyl cycle and glutathione biosynthesis are subject to regulation by Snx41-dependent vesicular trafficking, and mediate antioxidant defense crucial for in planta growth and pathogenic differentiation of Magnaporthe at the onset of blast disease in rice.

Autophagy is induced through the ROS-TP53-DRAM1 pathway in response to mitochondrial protein synthesis inhibition

Xiaolei Xie, Li Le, Yanxin Fan, Lin Lv and Junjie Zhang
Pages 1071 - 1084
http://dx.doi.org/10.4161/auto.20250
Abstract | Full Text | PDF

Mitoribosome in mammalian cells is responsible for synthesis of 13 mtDNA-encoded proteins, which are integral parts of four mitochondrial respiratory chain complexes (I, III, IV and V). ERAL1 is a nuclear-encoded GTPase important for the formation of the 28S small mitoribosomal subunit. Here, we demonstrate that knockdown of ERAL1 by RNA interference inhibits mitochondrial protein synthesis and promotes reactive oxygen species (ROS) generation, leading to autophagic vacuolization in HeLa cells. Cells that lack ERAL1 expression showed a significant conversion of LC3-I to LC3-II and an enhanced accumulation of autophagic vacuoles carrying the LC3 marker, all of which were blocked by the autophagy inhibitor 3-MA as well as by the ROS scavenger NAC. Inhibition of mitochondrial protein synthesis either by ERAL1 siRNA or chloramphenicol (CAP), a specific inhibitor of mitoribosomes, induced autophagy in HTC-116 TP53^+/+ cells, but not in HTC-116 TP53^−/− cells, indicating that tumor protein 53 (TP53) is essential for the autophagy induction. The ROS elevation resulting from mitochondrial protein synthesis inhibition induced TP53 expression at transcriptional levels by enhancing TP53 promoter activity, and increased TP53 protein stability by suppressing TP53 ubiquitination through MAPK14/p38 MAPK-mediated TP53 phosphorylation. Upregulation of TP53 and its downstream target gene DRAM1, but not CDKN1A/p21, was required for the autophagy induction in ERAL1 siRNA or CAP-treated cells. Altogether, these data indicate that autophagy is induced through the ROS-TP53-DRAM1 pathway in response to mitochondrial protein synthesis inhibition.

Dimethyl sulfoxide reduces hepatocellular lipid accumulation through autophagy induction

Young Mi Song, Sun-Ok Song, Yong-Keun Jung, Eun-Seok Kang, Bong Soo Cha, Hyun Chul Lee and Byung-Wan Lee
Pages 1085 - 1097
http://dx.doi.org/10.4161/auto.20260
Abstract | Full Text | PDF

Induction of autophagy is known not only to regulate cellular homeostasis but also to decrease triglyceride accumulation in hepatocytes. The aim of this study is to investigate whether DMSO (dimethyl sulfoxide) has a beneficial role in free fatty acid-induced hepatic fat accumulation.

In HepG2 cells, treatment with 0.5 mM palmitate for six hours significantly increased lipid and triglyceride (TG) accumulation, assessed by Oil-red O staining and TG quantification assay. Treatment with 0.01% DMSO for 16 h statistically reduced palmitate-induced TG contents. Pretreatment of 10 mM 3-methyladenine (3MA) for 2 h restored hepatocellular lipid contents, which were attenuated by treatment with DMSO. DMSO increased LC3-II conversion and decreased SQSTM1/p62 expression in a time and dose-dependent manner. In addition, the number of autophagosomes and autolysosomes, as seen under an electron microscopy, as well as the percentage of RFP-LAMP1 colocalized with GFP-LC3 dots in cells transfected with both GFP-LC3 and RFP-LAMP1, as seen under a fluorescent microscopy, also increased in DMSO-treated HepG2 cells. DMSO also suppressed p-eIF2α/p-EIF2S1, ATF4, p-AKT1, p-MTOR and p-p70s6k/p-RPS6KB2 expression as assessed by western blotting. Knockdown of ATF4 expression using siRNA suppressed ATF4 expression and phosphorylation of AKT1, MTOR and RPS6KB2, but increased LC3-II conversion. DMSO reduced not only soluble but also insoluble mtHTT (mutant huntingtin aggregates) expressions, which were masked in the presence of autophagy inhibitor. DMSO, a kind of chemical chaperone, activated autophagy by suppressing ATF4 expression and might play a protective role in the development of fatty acid-induced hepatosteatosis.

MAPK14/p38α confers irinotecan resistance to TP53-defective cells by inducing survival autophagy

Salome Paillas, Annick Causse, Laetitia Marzi, Philippe de Medina, Marc Poirot, Vincent Denis, Nadia Vezzio-Vie, Lucile Espert, Hayat Arzouk, Arnaud Coquelle, Pierre Martineau, Maguy Del Rio, Sophie Pattingre and Céline Gongora
Pages 1098 - 1112
http://dx.doi.org/10.4161/auto.20268
Abstract | Full Text | PDF

Recently we have shown that the mitogen-activated protein kinase (MAPK) MAPK14/p38α is involved in resistance of colon cancer cells to camptothecin-related drugs. Here we further investigated the cellular mechanisms involved in such drug resistance and showed that, in HCT116 human colorectal adenocarcinoma cells in which TP53 was genetically ablated (HCT116-TP53KO), overexpression of constitutively active MAPK14/p38α decreases cell sensitivity to SN-38 (the active metabolite of irinotecan), inhibits cell proliferation and induces survival-autophagy. Since autophagy is known to facilitate cancer cell resistance to chemotherapy and radiation treatment, we then investigated the relationship between MAPK14/p38α, autophagy and resistance to irinotecan. We demonstrated that induction of autophagy by SN38 is dependent on MAPK14/p38α activation. Finally, we showed that inhibition of MAPK14/p38α or autophagy both sensitizes HCT116-TP53KO cells to drug therapy. Our data proved that the two effects are interrelated, since the role of autophagy in drug resistance required the MAPK14/p38α. Our results highlight the existence of a new mechanism of resistance to camptothecin-related drugs: upon SN38 induction, MAPK14/p38α is activated and triggers survival-promoting autophagy to protect tumor cells against the cytotoxic effects of the drug. Colon cancer cells could thus be sensitized to drug therapy by inhibiting either MAPK14/p38 or autophagy.

Open Access Article

Macroautophagy is deregulated in murine and human lupus T lymphocytes

Frédéric Gros, Johan Arnold, Nicolas Page, Marion Décossas, Anne-Sophie Korganow, Thierry Martin and Sylviane Muller
Pages 1113 - 1123
http://dx.doi.org/10.4161/auto.20275
Abstract | Full Text | PDF

Macroautophagy was recently shown to regulate both lymphocyte biology and innate immunity. In this study we sought to determine whether a deregulation of autophagy was linked to the development of autoimmunity. Genome-wide association studies have pointed out nucleotide polymorphisms that can be associated with systemic lupus erythematosus, but the potential role of autophagy in the initiation and/or development of this syndrome is still unknown. Here, we provide first clues of macroautophagy deregulation in lupus. By the use of LC3 conversion assays and electron microscopy experiments, we observed that T cells from two distinct lupus-prone mouse models, i.e., MRL^lpr/lpr and (NZB/NZW)F1, exhibit high loads of autophagic compartments compared with nonpathologic control CBA/J and BALB/c mice. Unlike normal mice, autophagy increases with age in murine lupus. In vivo lipopolysaccharide stimulation in CBA/J control mice efficiently activates T lymphocytes but fails to upregulate formation of autophagic compartments in these cells. This argues against a deregulation of autophagy in lupus T cells solely resulting from an acute inflammation injury. Autophagic vacuoles quantified by electron microscopy are also found to be significantly more frequent in T cells from lupus patients compared with healthy controls and patients with non-lupus autoimmune diseases. This elevated number of autophagic structures is not distributed homogeneously and appears to be more pronounced in certain T cells. These results suggest that autophagy could regulate the survival of autoreactive T cell during lupus, and could thus lead to design new therapeutic options for lupus.




RESOURCE

Open Access Article

Loss of the starvation-induced gene Rack1 leads to glycogen deficiency and impaired autophagic responses in Drosophila

Balázs Érdi, Péter Nagy, Ágnes Zvara, Ágnes Varga, Karolina Pircs, Dalma Ménesi, László G. Puskás and Gábor Juhász
Pages 1124 - 1135
http://dx.doi.org/10.4161/auto.20069
Abstract | Full Text | PDF

Autophagy delivers cytoplasmic material for lysosomal degradation in eukaryotic cells. Starvation induces high levels of autophagy to promote survival in the lack of nutrients. We compared genome-wide transcriptional profiles of fed and starved control, autophagy-deficient Atg7 and Atg1 null mutant Drosophila larvae to search for novel regulators of autophagy. Genes involved in catabolic processes including autophagy were transcriptionally upregulated in all cases. We also detected repression of genes involved in DNA replication in autophagy mutants compared with control animals. The expression of Rack1 (receptor of activated protein kinase C 1) increased 4.1- to 5.5-fold during nutrient deprivation in all three genotypes. The scaffold protein Rack1 plays a role in a wide range of processes including translation, cell adhesion and migration, cell survival and cancer. Loss of Rack1 led to attenuated autophagic response to starvation, and glycogen stores were decreased 11.8-fold in Rack1 mutant cells. Endogenous Rack1 partially colocalized with GFP-Atg8a and early autophagic structures on the ultrastructural level, suggesting its involvement in autophagosome formation. Endogenous Rack1 also showed a high degree of colocalization with glycogen particles in the larval fat body, and with Shaggy, the Drosophila homolog of glycogen synthase kinase 3B (GSK-3B). Our results, for the first time, demonstrated the fundamental role of Rack1 in autophagy and glycogen synthesis.




AUTOPHAGIC PUNCTA

Autophagy and RNA virus interactomes reveal IRGM as a common target

Isabel Pombo Grégoire, Chantal Rabourdin-Combe and Mathias Faure
Pages 1136 - 1137
http://dx.doi.org/10.4161/auto.20339
Abstract | Full Text | PDF

Several intracellular pathogens have the ability to avoid or exploit the otherwise destructive process of autophagy. RNA viruses are constantly confronted with cellular autophagy, and several of them hijack autophagy during the infectious cycle to improve their own replication. Nevertheless, our knowledge of viral molecular strategies used to manipulate autophagy remains limited. Our study allowed the identification of molecular interactions between 44 autophagy-associated proteins and 83 viral proteins belonging to five different RNA virus families. This interactome revealed that the autophagy network machinery is highly targeted by RNA viruses. Interestingly, whereas some autophagy-associated proteins are targeted by only one RNA virus family, others are recurrent targets of several families. Among them, we found IRGM as the most targeted autophagy-associated protein. Downregulation of IRGM expression prevents autophagy induction by measles virus, HCV and HIV-1, and compromises viral replication. Our work combined interactomic and analytical approaches to identify potential pathogen virulence factors targeting autophagy.

Open Access Article

Viral subversion of autophagy impairs oncogene-induced senescence

Andrew M. Leidal, Patrick W.K. Lee and Craig McCormick
Pages 1138 - 1140
http://dx.doi.org/10.4161/auto.20340
Abstract | Full Text | PDF

Many viruses have evolved elegant strategies to co-opt cellular autophagic responses to facilitate viral propagation and evasion of immune surveillance. Kaposi’s sarcoma-associated herpesvirus (KSHV) establishes a life-long persistent infection in its human host, and is etiologically linked to several cancers. KSHV gene products have been shown to modulate autophagy but their contribution to pathogenesis remains unclear. Our recent study demonstrated that KSHV subversion of autophagy promotes bypass of oncogene-induced senescence (OIS), an important host barrier to tumor initiation. These findings suggest that KSHV has evolved to subvert autophagy, at least in part, to establish an optimal niche for infection, concurrently dampening host antiviral defenses and allowing the ongoing proliferation of infected cells.

Proper macrophagic differentiation requires both autophagy and caspase activation

Arnaud Jacquel, Sandrine Obba, Eric Solary and Patrick Auberger
Pages 1141 - 1143
http://dx.doi.org/10.4161/auto.20367
Abstract | Full Text | PDF

Autophagy allows the elimination of superfluous or damaged macromolecules or organelles. Genetic evidence indicates that autophagy plays essential functions during differentiation. The differentiation of human blood monocytes into macrophages is a caspase-dependent process triggered by colony stimulating factor1 (CSF1/CSF-1). We have established, using pharmacological inhibitors, siRNA approaches and Atg7^−/− mice, that autophagy is required for proper CSF1/CSF-1-driven differentiation of human and murine monocytes and acquisition of phagocytic functions. Collectively, these findings highlight an essential role of autophagy during monocyte differentiation and acquisition of macrophage functions. Deciphering the complex interplay between caspase and autophagy that occurs during this process will undoubtedly bring new insights in our understanding of monocyte differentiation.

Open Access Article

The downward spiral of tau and autolysosomes: A new hypothesis in neurodegeneration

Suren S. Ambegaokar and George R. Jackson
Pages 1144 - 1145
http://dx.doi.org/10.4161/auto.20515
Abstract | Full Text | PDF

A growing body of research has connected autophagy to neurodegenerative diseases such as Alzheimer disease (AD). In autopsied AD brain, large multivesicular bodies accumulate in neurons. Knockout mice deficient for key autophagy genes demonstrate age-dependent neurodegeneration. Most neurodegenerative diseases are characterized by accumulation of insoluble protein species; the type of protein and the location of aggregates within the nervous system help to define the type of disorder. It has been hypothesized that the inability to degrade such aggregates is a major causative factor in neuronal dysfunction and eventual neuronal death. As neurons are postmitotic and thus cannot regenerate themselves, mechanisms of protein clearance have received much attention in the field. The function of the ubiquitin-proteasome system (UPS) is impaired in models of neurodegeneration, and overexpression of chaperone proteins, such as those in the HSP70 family, leads to beneficial effects in many models of proteinopathies. Recently, studies of the effects of autophagy as a clearance mechanism have uncovered compelling evidence that inducing autophagy can alleviate many pathogenic and behavioral symptoms in animal and cellular models of neurodegeneration.

LC3 as a potential therapeutic target in hypoxia-induced pulmonary hypertension

Tim Lahm and Irina Petrache
Pages 1146 - 1147
http://dx.doi.org/10.4161/auto.20520
Abstract | Full Text | PDF

Recent research suggests that microtubule-associated protein 1 light chain 3B (LC3B) confers protection against hypoxia-induced pulmonary hypertension (HPH) by inhibiting proliferation of pulmonary artery (PA) wall cells. We recently demonstrated that 17β-estradiol (E2), a sex hormone with known protective properties in HPH, increases lung LC3-II expression in chronically hypoxic male Sprague-Dawley rats. Stimulatory E2 effects on LC3-II were recapitulated in isolated hypoxic (1% O₂ for 48 h), but not room air-exposed primary rat PA endothelial cells (PAECs), and were accompanied by hypoxia-specific inhibitory effects on other parameters involved in proproliferative signaling (MAPK3/ERK1-MAPK1/ERK2 activation, VEGF secretion), as well as inhibitory effects on PAEC proliferation. Taken together, these results suggest that E2 mediates hypoxia-specific antiproliferative effects in PAECs, and that stimulation of autophagy may be one of the underlying mechanisms of E2-mediated protection in HPH. Viewed in the context of previously published data, these results indicate that LC3 1) exerts protective effects in the pathogenesis of HPH, and 2) may represent a potential target for future therapeutic interventions in HPH.

Autophagy in intra-hepatic cholangiocarcinoma

Jing Li Huang and Aram F. Hezel
Pages 1148 - 1149
http://dx.doi.org/10.4161/auto.20647
Abstract | Full Text | PDF

Intra-hepatic cholangiocarcinoma (IHCC) is a primary cancer of the liver that shares histological features with the hepatic bile ducts from which it is thought to arise. The incidence of this disease is increasing, possibly related to increased inflammatory liver diseases such as viral hepatitis and steatohepatitis (commonly called “fatty liver”), induced by obesity, diabetes, and other metabolic derangements. Its prognosis is generally poor with early metastasis and presently there are limited effective treatments. A basic understanding of the disease has long been hampered by limited tumor cell lines and good model systems. Similarly, such limitations have obstructed new therapeutic inroads.

The ins and outs of human reticulocyte maturation: Autophagy and the endosome/exosome pathway

Rebecca E. Griffiths, Sabine Kupzig, Nicola Cogan, Tosti J. Mankelow, Virginie M.S. Betin, Kongtana Trakarnsanga, Edwin J. Massey, Stephen F. Parsons, David J. Anstee and Jon D. Lane
Pages 1150 - 1151
http://dx.doi.org/10.4161/auto.20648
Abstract | Full Text | PDF

The maturation of reticulocytes into functional erythrocytes is a complex process requiring extensive cytoplasmic and plasma membrane remodeling, cytoskeletal rearrangements and changes to cellular architecture. Autophagy is implicated in the sequential removal of erythroid organelles during erythropoiesis, although how this is regulated during late stages of erythroid differentiation, and the potential contribution of autophagy during reticulocyte maturation, remain unclear. Using an optimized ex vivo differentiation system for human erythropoiesis, we have observed that maturing reticulocytes are characterized by the presence of one or few large vacuolar compartments. These label strongly for glycophorin A (GYPA/GPA) which is internalized from the plasma membrane; however, they also contain organellar remnants (ER, Golgi, mitochondria) and stain strongly for LC3, suggesting that they are endocytic/autophagic hybrid structures. Interestingly, we observed the release of these vacuoles by exocytosis in maturing reticulocytes, and speculate that autophagy is needed to concentrate the final remnants of the reticulocyte endomembrane system in autophagosome/endosome hybrid compartments that are primed to undergo exocytosis.

Dietary lipids and aging compromise chaperone-mediated autophagy by similar mechanisms

Jose Antonio Rodriguez-Navarro and Ana Maria Cuervo
Pages 1152 - 1154
http://dx.doi.org/10.4161/auto.20649
Abstract | Full Text | PDF

Chaperone-mediated autophagy (CMA) is a selective form of autophagy whose distinctive feature is the fact that substrate proteins are translocated directly from the cytosol across the lysosomal membrane for degradation inside lysosomes. CMA substrates are cytosolic proteins bearing a pentapeptide motif in their sequence that, when recognized by the cytosolic chaperone HSPA8/HSC70, targets them to the surface of the lysosomes. Once there, substrate proteins bind to the lysosome-associated membrane protein type 2 isoform A (LAMP2A), inducing assembly of this receptor protein into a higher molecular weight protein complex that is used by the substrate proteins to reach the lysosomal lumen. CMA is constitutively active in most cells but it is maximally activated under conditions of stress.

Not all autophagy is equal

Maria F. Czyzyk-Krzeska, Jarek Meller and David R. Plas
Pages 1155 - 1156
http://dx.doi.org/10.4161/auto.20650
Abstract | Full Text | PDF

Autophagy is an important mechanism in cancer cell survival and tumor growth and plays both pro- and anti-oncogenic roles. However, the biochemical basis for these diverse functions is not well understood. Our work provides new evidence for the existence of two separate autophagic programs regulated in an opposite manner by the von Hippel-Lindau tumor suppressor (VHL). These programs, marked by differential requirements for LC3B vs. LC3C, play tumor-promoting and tumor-suppressing roles in renal cancer.

Defective mitophagy in human Niemann-Pick Type C1 neurons is due to abnormal autophagy activation

Maria Paulina Ordonez
Pages 1157 - 1158
http://dx.doi.org/10.4161/auto.20668
Abstract | Full Text | PDF

Although traditionally regarded as a cellular adaptive process triggered by nutrient deprivation, autophagy in neurons appears to provide an important neuroprotective mechanism. Neurons in the brain are protected from starvation, and neuronal autophagy serves a critical role in the turnover of abnormal proteins and damaged organelles. As post-mitotic, highly polarized cells with active protein trafficking, neurons rely heavily on an efficient autophagic pathway. Using human embryonic stem cell-derived neurons engineered to mimic the cholesterol lysosomal storage disease Niemann Pick type C1 (NPC1), we have shown that excessive activation and impaired progression of the autophagic pathway conspire to cause abnormal mitochondrial clearance. Defective mitophagy is exceptionally severe in human NPC1 neurons, as compared with patient fibroblasts, and may explain the selective neuronal failure observed in NPC1 and related neurodegenerative disorders.




VIEWS AND COMMENTARIES

Autophagy across the eukaryotes: Is S. cerevisiae the odd one out?

Jason S. King
Pages 1159 - 1162
http://dx.doi.org/10.4161/auto.20527
Abstract | Full Text | PDF

Autophagy is conserved throughout the eukaryotes and for many years, work in Saccharomyces cerevisiae has been at the forefront of autophagy research. However as our knowledge of the autophagic machinery has increased, differences between S. cerevisiae and mammalian cells have become apparent. Recent work in other organisms, such as the amoeba Dictyostelium discoideum, indicate an autophagic pathway much more similar to mammalian cells than S. cerevisiae, despite its earlier evolutionary divergence. S. cerevisiae therefore appear to have significantly specialized, and the autophagic pathway in mammals is much more ancient than previously appreciated, which has implications for how we interpret data from organisms throughout the eukaryotic tree.




ERRATUM

Erratum to: Knecht E, Criado-García O, Aguado C, Gayarre J, Duran-Trio L, Garcia-Cabrero AM, et al. Malin knockout mice support a primary role of autophagy in the pathogenesis of Lafora disease. Autophagy 2012; 8:701–3

Erwin Knecht, Olga Criado-García, Carmen Aguado, Javier Gayarre, Lara Duran-Trio, Ana M. Garcia-Cabrero, Santiago Vernia, Beatriz San Millán, Miguel Heredia, Carlos Romá-Mateo, Silvana Mouron, Lucía Juana-López, Mercedes Domínguez, Carmen Navarro, Jose M. Serratosa, Marina Sanchez, Pascual Sanz, Paola Bovolenta and Santiago Rodríguez de Córdoba
Page 1163
http://dx.doi.org/10.4161/auto.21428
Full Text | PDF