Autophagy is a rapidly expanding field in the sense that our knowledge about the molecular mechanism and its connections to a wide range of physiological processes has increased substantially in the past decade. Similarly, the vocabulary associated with autophagy has grown concomitantly. This fact makes it difficult for readers, even those who work in the field, to keep up with the ever-expanding terminology associated with the various autophagy-related processes. Accordingly, we have developed a comprehensive glossary of autophagy-related terms that is meant to provide a quick reference for researchers who need a brief reminder of the regulatory effects of transcription factors or chemical agents that induce or inhibit autophagy, the function of the autophagy-related proteins, or the role of accessory machinery or structures that are associated with autophagy.
autophagy; definitions; glossary; lexicon; terms
Great progress has been made toward understanding the pathogenesis of Parkinson’s disease (PD) during the past two decades, mainly as a consequence of the discovery of specific gene mutations contributing to the onset of PD. Recently, dysregulation of the autophagy pathway has been observed in the brains of PD patients and in animal models of PD, indicating the emerging role of autophagy in this disease. Indeed, autophagy is increasingly implicated in a number of pathophysiologies, including various neurodegenerative diseases. This article will lead you through the connection between autophagy and PD by introducing the concept and physiological function of autophagy, and the proteins related to autosomal dominant and autosomal recessive PD, particularly α-synuclein and PINK1-PARKIN, as they pertain to autophagy.
Proteins associated with inherited forms of Parkinson’s disease (PD) (e.g., α-synuclein) are involved in autophagy. Basal, constitutive autophagy may be essential for neuronal survival; its dysregulation may lead to neurodegeneration.
From today's perspective, it is obvious that macroautophagy (hereafter autophagy) is an important pathway that is connected to a range of developmental and physiological processes. This viewpoint, however, is relatively recent, coinciding with the molecular identification of autophagy-related (Atg) components that function as the protein machinery that drives the dynamic membrane events of autophagy. It may be difficult, especially for scientists new to this area of research, to appreciate that the field of autophagy long existed as a “backwater” topic that attracted little interest or attention. Paralleling the development of the autophagy field was the identification and analysis of the cytoplasm-to-vacuole targeting (Cvt) pathway, the only characterized biosynthetic route that utilizes the Atg proteins. Here, we relate some of the initial history, including some never-before-revealed facts, of the analysis of the Cvt pathway and the convergence of those studies with autophagy.
The process of macroautophagy (referred to hereafter as autophagy), is generally characterized by the prominent formation of autophagic vesicles in the cytoplasm. In the past decades, studies of autophagy have been vastly expanded. As an essential process to maintain cellular homeostasis and functions, autophagy is responsible for the lysosome-mediated degradation of damaged proteins and organelles, and thus misregulation of autophagy can result in a variety of pathological conditions in human beings. Although our understanding of regulatory pathways that control autophagy is still limited, an increasing number of studies have shed light on the importance of autophagy in a wide range of physiological processes and human diseases. The goal of the reviews in the current issue is to provide a general overview of current knowledge on autophagy. The machinery and regulation of autophagy were outlined with special attention to its role in diabetes, neurodegenerative disorders, infectious diseases and cancer.
autophagy; disease; physiology
Autophagy is an evolutionarily conserved intracellular process by which bulk cytoplasm is enveloped inside a double-membraned vesicle and shuttled to lysosomes for degradation. Within the last 15 years, the genes necessary for the execution of autophagy have been identified and the number of tools for studying this process has grown. Autophagy is essential for tissue homeostasis and development and defective autophagy is associated with a number of diseases. As intracellular parasites, during the course of an infection, viruses encounter autophagy and interact with the proteins that execute this process. Autophagy and/or autophagy genes likely play both anti-viral and proviral roles in the life cycles and pathogenesis of many different virus families. With respect to anti-viral roles, the autophagy proteins function in targeting viral components or virions for lysosomal degradation in a process termed xenophagy, and they also play a role in the initiation of innate and adaptive immune system responses to viral infections. Consistent with this anti-viral role of host autophagy, some viruses encode virulence factors that interact with the host autophagy machinery and block the execution of autophagy. In contrast, other viruses appear to utilise components of the autophagic machinery to foster their own intracellular growth or non-lytic cellular egress. As the details of the role(s) of autophagy in viral pathogenesis become clearer, new anti-viral therapies could be developed to inhibit the beneficial and enhance the destructive aspects of autophagy on the viral life cycle.
A repertoire of mechanisms in the autophagy system combats viral infections.
Autophagy is an evolutionarily ancient process eukaryotic cells utilize to remove and recycle intracellular material in order to maintain cellular homeostasis. In metazoans, the autophagy machinery not only functions in this capacity but also has evolved to perform a diverse repertoire of intracellular transport and regulatory functions. In response to virus infections, the autophagy machinery degrades viruses, shuttles viral pathogen-associated molecular patterns to endosomes containing Toll-like receptors, facilitates viral-antigen processing for major histocompatibility complex presentation and transports antiviral proteins to viral replication sites. This is accomplished through canonical autophagy or through processes involving distinct subsets of the autophagy-related genes (Atgs). Herein, we discuss how the variable components of the autophagy machinery contribute to antiviral defense and highlight three emerging themes: first, autophagy delivers viral cytosolic components to several distinct endolysosomal compartments; second, Atg proteins act alone, as subgroups or collectively; and third, the specificity of autophagy and the autophagy machinery is achieved by recognition of triggers and selective targeting by adaptors.
autophagy; dendritic cells; innate immunity; T-cell responses; virus infection
Autophagy is an evolutionarily conserved process of cellular self-digestion that serves as a mechanism to clear damaged organelles and recycle nutrients. Since autophagy can promote cell survival as well as cell death, it has been linked to different human pathologies, including cancer. Although mono-allelic deletion of autophagy-related gene BECN1 in breast tumors originally indicated a tumor suppressive role for autophagy in breast cancer, the intense research during the last decade suggests a role for autophagy in tumor progression. It is now recognized that tumor cells often utilize autophagy to survive various stresses, such as oncogene-induced transformation, hypoxia, endoplasmic reticulum (ER) stress and extracellular matrix detachment. Induction of autophagy by tumor cells may also contribute to tumor dormancy and resistance to anticancer therapies, thus making autophagy inhibitors promising drug candidates for breast cancer treatment. The scientific endeavors continue to define a precise role for autophagy in breast cancer. In this article, we review the current literature on the role of autophagy during the development and progression of breast cancer, and discuss the potential of autophagy modulators for breast cancer treatment.
Autophagy; breast cancer; transformation; hypoxia; ER stress; tumor microenvironment; metabolism; metastasis; apoptosis; cancer therapy
Autophagy is an evolutionarily conserved process of cellular self-eating and is a major pathway for degradation of cytoplasmic material by the lysosomal machinery. Autophagy functions as a cellular response in nutrient starvation, but it is also associated with the removal of protein aggregates and damaged organelles and therefore plays an important role in the quality control of proteins and organelles. Although it was initially believed that autophagy occurs randomly in the cell, during the last years, there is growing evidence that sequestration and degradation of cytoplasmic material by autophagy can be selective. Given the important role of autophagy and selective autophagy in several disease-related processes such as neurodegeneration, infections, and tumorigenesis, it is important to understand the molecular mechanisms of selective autophagy, especially at the organismal level. Drosophila is an excellent genetically modifiable model organism exhibiting high conservation in the autophagic machinery. However, the regulation and mechanisms of selective autophagy in Drosophila have been largely unexplored. In this paper, I will present an overview of the current knowledge about selective autophagy in Drosophila.
Autophagy is a cell autonomous process allowing each individual cell to fight intracellular pathogens. Autophagy can destroy pathogens within the cytosol, and can elicit innate and adaptive immune responses against microorganisms. Nevertheless, numerous pathogens have developed molecular strategies enabling them to avoid or even exploit autophagy for their own benefit. IRGM (immunity-related GTPase family M) is a human protein recently highlighted for its contribution to autophagy upon infections. The physical association of IRGM with mitochondria and different autophagy-regulating proteins, ATG5, ATG10, SH3GLB1, and LC3, contribute to explain how IRGM could regulate autophagy. Whereas IRGM is involved in autophagy-mediated immunity against bacteria, certain viruses seem to have developed strategies to manipulate autophagy through the selective targeting of this protein. Furthermore, irgm variants are linked to infection-associated human pathologies such as the inflammatory Crohn’s disease. Here, we discuss how IRGM might contribute to human autophagy upon viral infection, and why its targeting might be beneficial to virus replication.
autophagy; IRGM; virus; infection; immunity; interferon
Autophagy is a cell self-digestion process via lysosomes that clears “cellular waste”, including aberrantly modified proteins or protein aggregates and damaged organelles. Therefore, autophagy is considered a protein and organelle quality control mechanism that maintains normal cellular homeostasis. Dysfunctional autophagy has been observed in ageing tissues and several ageing-associated diseases. Lifespan of model organisms such as yeast, worms, flies, and mice can be extended through promoting autophagy, either by genetic manipulations such as over-expression of Sirtuin 1, or by administrations of rapamycin, resveratrol or spermidine. The evidence supports that autophagy may play an important role in delaying ageing or extending lifespan. In this review, we summarize the current knowledge about autophagy and its regulation, outline recent developments ie the genetic and pharmacological manipulations of autophagy that affects the lifespan, and discuss the role of autophagy in the ageing-related diseases.
autophagy; ageing; ageing-associated diseases; cancer; neurodegenerative diseases; Sirtuin 1; p53; rapamycin; resveratrol; spermidine
Autophagy is a process of self-degradation that maintains cellular viability during periods of metabolic stress. Although autophagy is considered a survival mechanism when faced with cellular stress, extensive autophagy can also lead to cell death. Aberrations in autophagy are associated with several diseases, including cancer. Therapeutic exploitation of this process requires a clear understanding of its regulation. Although the core molecular components involved in the execution of autophagy are well studied there is limited information on how cellular signaling pathways, particularly kinases, regulate this complex process. Protein kinases are integral to the autophagy process. Atg1, the first autophagy-related protein identified, is a serine/threonine kinase and it is regulated by another serine/threonine kinase mTOR. Emerging studies suggest the participation of many different kinases in regulating various components/steps of this catabolic process. This review focuses on the regulation of autophagy by several kinases with particular emphasis on serine/threonine protein kinases such as mTOR, AMP-activated protein kinase, Akt, mitogen-activated protein kinase (ERK, p38 and JNK) and protein kinase C that are often deregulated in cancer and are important therapeutic targets.
autophagy; protein kinase; mTOR; p70S6K; AMPK; PI3K; Akt; MAPK; PKC
Background/Aim. Autophagy, a cellular degradation process, has paradoxical roles in tumorigenesis and the progression of human cancers. The aim of this study was to investigate the expression levels of autophagy-related proteins in colorectal cancer (CRC) and to evaluate their prognostic significance. Methods. This study is a retrospective review of immunohistochemical and clinicopathological data. All specimens evaluated were obtained from 263 patients with colorectal cancer who had undergone surgery between November 1996 and August 2007. The primary outcomes measured were the expression levels of three autophagy-related proteins (ATG5, BECN1/Beclin 1, and Microtubule-associated protein 1 light chain 3B (LC3B)) by immunohistochemistry and its association in clinicopathological parameters and patient survival. Results. The autophagy-related protein expression frequencies were 65.1% (151/232) for ATG5, 71.3% (174/244) for BECN1, and 74.7% (186/249) for LC3B for the 263 patients. Correlation between the expression of autophagy-related proteins was significant for all protein pairs. Multivariate analysis showed that negative LC3B expression and absence of autophagy-related proteins expression were independently associated with poor prognosis. Conclusion. Absence of autophagy-related proteins expression is associated with poor clinical outcome in CRC, suggesting that these proteins have potential uses as novel prognostic markers.
Autophagy is an intracellular degradative process with a number of roles, one of which can be the protection of eukaryotic cells from invading microbes. Microtubule-associated protein light-chain 3 (LC3) is a key autophagy-related protein that is recruited to the double-membrane autophagosome responsible for sequestering material intended for delivery to lysosomes. GFP-LC3 is widely used as a marker of autophagosome formation as denoted by the formation of green puncta when viewed by fluorescence microscopy. Recently, it has been demonstrated that LC3 can be recruited to other membranes including single-membrane phagosomes, in a process termed LC3-associated phagocytosis (LAP). Thus, the observation of green puncta in cells can no longer, by itself, be taken as evidence of autophagy. This review will clarify those features of LAP which serve to distinguish it from autophagy and that make connections with host autophagic responses in terms of infection by microbial pathogens. More specifically, it will refer to concurrent studies of the mechanism by which LAP is triggered in comparison to autophagy.
autophagosome; autophagy; LC3; phagocytosis; LC3-associated phagocytosis (LAP)
Nutrient deprivation is a stimulus shared by both autophagy and the formation of primary cilia. The recently discovered role of primary cilia in nutrient sensing and signaling motivated us to explore the possible functional interactions between this signaling hub and autophagy. Here we show that part of the molecular machinery involved in ciliogenesis also participates in the early steps of the autophagic process. Signaling from the cilia, such as that from the Hedgehog pathway, induces autophagy by acting directly on essential autophagy-related proteins strategically located in the base of the cilium by ciliary trafficking proteins. While abrogation of ciliogenesis partially inhibits autophagy, blockage of autophagy enhances primary cilia growth and cilia-associated signaling during normal nutritional conditions. We propose that basal autophagy regulates ciliary growth through the degradation of proteins required for intraflagellar transport. Compromised ability to activate the autophagic response may underlie the basis of some common ciliopathies.
primary cilia; intraflagellar transport proteins; lysosomes; autophagosomes; vesicular trafficking
(Macro)autophagy is a cellular membrane trafficking process that serves to deliver cytoplasmic constituents to lysosomes for degradation. At basal levels, it is critical for maintaining cytoplasmic as well as genomic integrity and is therefore key to maintaining cellular homeostasis. Autophagy is also highly adaptable and can be modified to digest specific cargoes to bring about selective effects in response to numerous forms of intracellular and extracellular stress. It is not a surprise, therefore, that autophagy has a fundamental role in cancer and that perturbations in autophagy can contribute to malignant disease. We review here the roles of autophagy in various aspects of tumor suppression including the response of cells to nutrient and hypoxic stress, the control of programmed cell death, and the connection to tumor-associated immune responses.
In healthy cells, autophagy protects against malignant disease by maintaining cellular homeostasis. However, upon transformation, activation of autophagy can promote and suppress cancer progression.
Toll-like receptor (TLR) signaling is linked to autophagy that facilitates elimination of intracellular pathogens. However, it is largely unknown whether autophagy controls TLR signaling. Here, we report that poly(I:C) stimulation induces selective autophagic degradation of the TLR adaptor molecule TRIF and the signaling molecule TRAF6, which is revealed by gene silencing of the ubiquitin-editing enzyme A20. This type of autophagy induced formation of autophagosomes and could be suppressed by an autophagy inhibitor and lysosomal inhibitors. However, this autophagy was not associated with canonical autophagic processes, including involvement of Beclin-1 and conversion of LC3-I to LC3-II. Through screening of TRIF-interacting ‘autophagy receptors’ in human cells, we identified that NDP52 mediated the selective autophagic degradation of TRIF and TRAF6 but not TRAF3. NDP52 was polyubiquitinated by TRAF6 and was involved in aggregation of TRAF6, which may result in the selective degradation. Intriguingly, only under the condition of A20 silencing, NDP52 could effectively suppress poly(I:C)-induced proinflammatory gene expression. Thus, this study clarifies a selective autophagic mechanism mediated by NDP52 that works downstream of TRIF–TRAF6. Furthermore, although A20 is known as a signaling fine-tuner to prevent excess TLR signaling, it paradoxically downregulates the fine-tuning effect of NDP52 on TLR signaling.
Electronic supplementary material
The online version of this article (doi:10.1007/s00018-011-0819-y) contains supplementary material, which is available to authorized users.
Autophagy; A20; NDP52; Signal transduction; Toll-like receptor (TLR)
PKA puts the brakes on autophagy by inhibiting LC3 recruitment to autophagosomes.
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 is a highly conserved housekeeping pathway that plays a critical role in the removal of aged or damaged intracellular organelles and their delivery to lysosomes for degradation.1,2 Autophagy begins with the formation of membranes arising in part from the endoplasmic reticulum, that elongate and fuse engulfing cytoplasmic constituents into a classic double-membrane bound nascent autophagosome. These early autophagosomes undergo a stepwise maturation process to form the late autophagosome or amphisome that ultimately fuses with a lysosome. Efficient autophagy is dependent on an equilibrium between the formation and elimination of autophagosomes; thus, a deficit in any part of this pathway will cause autophagic dysfunction. Autophagy plays a role in aging and age-related diseases. 1,2,7 However, few studies of autophagy in retinal disease have been reported.
Recent studies show that autophagy and changes in lysosomal activity are associated with both retinal aging and age-related macular degeneration (AMD).3,4 This article describes methods which employ the target protein LC3 to monitor autophagic flux in retinal pigment epithelial cells. During autophagy, the cytosolic form of LC3 (LC3-I) is processed and recruited to the phagophore where it undergoes site specific proteolysis and lipidation near the C terminus to form LC3-II.5 Monitoring the formation of cellular autophagosome puncta containing LC3 and measuring the ratio of LC3-II to LC3-I provides the ability to monitor autophagy flux in the retina.
autophagy flux; LC3; retinal pigment epithelium; lysosomes; age-related macular degeneration; aging
Autophagy is a vesicular trafficking process responsible for the degradation of long-lived, misfolded or abnormal proteins, as well as damaged or surplus organelles. Abnormalities of the autophagic activity may result in the accumulation of protein aggregates, organelle dysfunction, and autophagy disorders were associated with various diseases. Hence, mechanisms of autophagy regulation are under exploration.
Over-expression of hsa-miR-376a1 (shortly MIR376A) was performed to evaluate its effects on autophagy. Autophagy-related targets of the miRNA were predicted using Microcosm Targets and MIRanda bioinformatics tools and experimentally validated. Endogenous miRNA was blocked using antagomirs and the effects on target expression and autophagy were analyzed. Luciferase tests were performed to confirm that 3′ UTR sequences in target genes were functional. Differential expression of MIR376A and the related MIR376B was compared using TaqMan quantitative PCR.
Here, we demonstrated that, a microRNA (miRNA) from the DLK1/GTL2 gene cluster, MIR376A, played an important role in autophagy regulation. We showed that, amino acid and serum starvation-induced autophagy was blocked by MIR376A overexpression in MCF-7 and Huh7 cells. MIR376A shared the same seed sequence and had overlapping targets with MIR376B, and similarly blocked the expression of key autophagy proteins ATG4C and BECN1 (Beclin 1). Indeed, 3′ UTR sequences in the mRNA of these autophagy proteins were responsive to MIR376A in luciferase assays. Antagomir tests showed that, endogenous MIR376A was participating to the control of ATG4C and BECN1 transcript and protein levels. Moreover, blockage of endogenous MIR376A accelerated starvation-induced autophagic activity. Interestingly, MIR376A and MIR376B levels were increased with different kinetics in response to starvation stress and tissue-specific level differences were also observed, pointing out to an overlapping but miRNA-specific biological role.
Our findings underline the importance of miRNAs encoded by the DLK1/GTL2 gene cluster in stress-response control mechanisms, and introduce MIR376A as a new regulator of autophagy.
Autophagy is a cell biological process, enabling cells to autodigest their own cytosol when starved, remove cytoplasmic protein aggregates too large for proteasomal degradation, eliminate aberrant or over-proliferated organelles, and sanitize the cytoplasm by killing intracellular microbes. The role of autophagy has been expanded in recent years to include diverse immunological effector and regulatory functions. In this review, we summarize the multiple immunological roles of autophagy uncovered to date and focus primarily on details of induction of autophagy by pattern recognition receptors, as a newly established Toll-like receptor output. Taken together with other links between autophagy and innate and adaptive immunity processes, this cell-autonomous antimicrobial defense may be evolutionarily positioned at the root of immunity with the multiple innate and adaptive immunity connections uncovered to date reflecting a co-evolution of this ancient cell-defense mechanism and more advanced immunological systems in metazoans.
autophagy; TLR; immunity; inflammation
Autophagy is a fundamental eukaryotic process with multiple cytoplasmic homeostatic roles, recently expanded to include unique standalone immunological functions and interactions with nearly all parts of the immune system. Here, we review this growing repertoire of autophagy roles in innate and adaptive immunity and inflammation. Its unique functions include cell-autonomous elimination of intracellular microbes facilitated by specific receptors. Other intersections of autophagy with immune processes encompass effects on inflammasome activation and secretion of its substrates including IL-1β, effector and regulatory interactions with Toll-like and Nod-like receptors, antigen presentation, naïve T cell repertoire selection, and mature T cell development and homeostasis. Genome wide association studies in human populations strongly implicate autophagy in chronic inflammatory disease and autoimmune disorders. Collectively, the unique features of autophagy as an immunological process and its contributions to other arms of the immune system represent a new immunological paradigm.
Autophagy is intimately associated with eukaryotic cell death and apoptosis. Indeed in some cases the same proteins control both autophagy and apoptosis. Apoptotic signaling can regulate autophagy and conversely autophagy can regulate apoptosis (and most likely other cell death mechanisms). However the molecular connections between autophagy and cell death are complicated and, in different contexts, autophagy may promote or inhibit cell death. Surprisingly, although we know that, at its core, autophagy involves degradation of sequestered cytoplasmic material, and therefore presumably must be mediating its effects on cell death by degrading something, in most cases we have little idea what is being degraded to promote autophagy’s pro- or anti-death activities. Because autophagy is known to play important roles in health and many diseases, it is critical to understand the mechanisms by which autophagy interacts with and affects the cell death machinery since this will perhaps allow new ways to prevent or treat disease. In this chapter we discuss the current state of understanding of these processes.
Apoptosis; caspase; autophagic cell death; TRAIL; BCL proteins; autophagy-mediated protection; ATG protein function
Autophagy is a cellular process that is highly conserved among eukaryotes and permits the degradation of cellular material. Autophagy is involved in multiple survival-promoting processes. It not only facilitates the maintenance of cell homeostasis by degrading long-lived proteins and damaged organelles, but it also plays a role in cell differentiation and cell development. Equally important is its function for survival in stress-related conditions such as recycling of proteins and organelles during nutrient starvation. Protozoan parasites have complex life cycles and face dramatically changing environmental conditions; whether autophagy represents a critical coping mechanism throughout these changes remains poorly documented. To investigate this in Toxoplasma gondii, we have used TgAtg8 as an autophagosome marker and showed that autophagy and the associated cellular machinery are present and functional in the parasite. In extracellular T. gondii tachyzoites, autophagosomes were induced in response to amino acid starvation, but they could also be observed in culture during the normal intracellular development of the parasites. Moreover, we generated a conditional T. gondii mutant lacking the orthologue of Atg3, a key autophagy protein. TgAtg3-depleted parasites were unable to regulate the conjugation of TgAtg8 to the autophagosomal membrane. The mutant parasites also exhibited a pronounced fragmentation of their mitochondrion and a drastic growth phenotype. Overall, our results show that TgAtg3-dependent autophagy might be regulating mitochondrial homeostasis during cell division and is essential for the normal development of T. gondii tachyzoites.
Autophagy is a catabolic process involved in maintaining cellular homeostasis in eukaryotic cells, while coping with their changing environmental conditions. Mechanistically, it is also a process of considerable complexity involving multiple protein factors and implying numerous protein-protein and protein-membrane interactions. The cellular material to be degraded by autophagy is contained in a membrane-bound compartment called the autophagosome. We have characterised the formation of autophagosomes in the protozoan parasite Toxoplasma gondii by following the relocalisation of autophagosome-bound TgAtg8. Thus, exploiting GFP-TgAtg8 as a marker, we showed that it is a process that is regulated and can be induced artificially by amino acid starvation. Autophagic vesicles were also observed in normally dividing intracellular parasites. Depleting Toxoplasma of the TgAtg3 autophagy protein led to an impairment of TgAtg8 conjugation to the autophagosomal membrane and, at the cellular level, to a fragmentation of the single mitochondrion of the parasite and to a severe growth arrest. We have thus found that TgAtg3-dependent autophagy is essential for normal intracellular development of T. gondii tachyzoites.
Autophagy is an evolutionarily conserved lysosomal self-digestion process involved in degradation of long-lived proteins and damaged organelles. In recent years, increasing evidence indicates that autophagy is associated with a number of pathological processes, including cancer. In this review, we focus on the recent studies of the evolutionarily conserved autophagy-related genes (ATGs) that are implicated in autophagosome formation and the pathways involved. We discuss several key autophagic mediators (eg, Beclin-1, UVRAG, Bcl-2, Class III and I PI3K, mTOR, and p53) that play pivotal roles in autophagic signaling networks in cancer. We discuss the Janus roles of autophagy in cancer and highlighted their relationship to tumor suppression and tumor progression. We also present some examples of targeting ATGs and several protein kinases as anticancer strategy, and discuss some autophagy-modulating agents as antitumor agents. A better understanding of the relationship between autophagy and cancer would ultimately allow us to harness autophagic pathways as new targets for drug discovery in cancer therapeutics.
autophagy; cancer; autophagy-related gene (ATG); Beclin-1; Bcl-2; Class III and I PI3K; mTOR; p53
Autophagy is the regulated catabolic process for recycling damaged or unnecessary organelles, which plays crucial roles in cell survival during nutrient deficiency, and innate immune defense against pathogenic microorganisms. Autophagy has been also reported to be involved in various conditions including inflammatory diseases. IRGM (human immunity-related GTPase) has an important function in eliminating Mycobacterium tuberculosis from host cells via autophagy. We examined the association between genetic polymorphism and clinical course/outcome in severely septic patients.
The study included 125 patients with severe sepsis/septic shock (SS) and 104 non-sepsis patients who were admitted to the intensive care unit (ICU) of Chiba University Hospital between October 2001 and September 2008 (discovery cohort) and 268 SS patients and 454 non-sepsis patients who were admitted to ICUs of five Japanese institutions including Chiba University Hospital between October 2008 and September 2012 (multi-center validation cohort). Three hundred forty seven healthy volunteers who consented to this study were also included. Genotyping was performed for a single-nucleotide polymorphism (SNP) within the coding region of IRGM, IRGM(+313) (rs10065172). Lipopolysaccharide challenge of whole blood from randomly selected healthy volunteers (n = 70) was performed for comparison of IRGM mRNA expression among different genotypes.
No significant difference in genotypic distributions (CC/CT/TT) at the IRGM(+313) locus was observed among the three subject groups (SS, non-sepsis, and healthy volunteers) in either cohort. When mortality were compared, no significant difference was observed in the non-sepsis group, while TT homozygotes exhibited a significantly higher mortality than the CC+CT genotype category in the SS group for both cohorts (P = 0.043, 0.037). Lipopolysaccharide challenge to whole blood showed a significant suppression of IRGM mRNA expression in TT compared with the CC+CT genotype category (P = 0.019).
The data suggest that the IRGM(+313), an autophagy-related polymorphic locus, influences outcome in severely septic patients, with the possible involvement of autophagy in sepsis exacerbation.