The autophagic pathway is actively modulated by phase II Coxiella burnetii to efficiently replicate in the host cell.
TL;DR: It is proposed that C.’burnetii transits through the normal endo/phagocytic pathway but actively interacts with autophagosomes at early times after infection, possibly favouring the intracellular differentiation and survival of the bacteria.
Abstract: The etiologic agent of Q fever Coxiella burnetii, is an intracellular obligate parasite that develops large vacuoles with phagolysosomal characteristics, containing multiple replicating bacteria. We have previously shown that Phase II C. burnetii replicative vacuoles generated after 24-48 h post infection are decorated with the autophagic protein LC3. The aim of the present study was to examine, at earlier stages of infection, the distribution and roles of the small GTPases Rab5 and Rab7, markers of early and late endosomes respectively, as well as of the protein LC3 on C. burnetii trafficking. Our results indicate that: (i) Coxiella phagosomes (Cph) acquire the two Rab proteins sequentially during infection; (ii) overexpression of a dominant negative mutant form of Rab5, but not of Rab7, impaired Coxiella entry, whereas both Rab5 and Rab7 dominant negative mutants inhibited vacuole formation; (iii) Cph colocalized with the protein LC3 as early as 5 min after infection; acquisition of this protein appeared to be a bacterially driven process, because it was inhibited by the bacteriostatic antibiotic chloramphenicol and (iv) C. burnetii delayed the arrival of the typical lysosomal protease cathepsin D to the Cph, which delay is further increased by starvation-induced autophagy. Based on our results we propose that C. burnetii transits through the normal endo/phagocytic pathway but actively interacts with autophagosomes at early times after infection. This intersection with the autophagic pathway delays fusion with the lysosomal compartment possibly favouring the intracellular differentiation and survival of the bacteria.
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TL;DR: Current understanding of the cellular events that occur during parasitism of host cells by Coxiella, including deployment of a type IV secretion system to deliver effector proteins to the host cytosol is summarized.
Abstract: Summary
Most intracellular parasites employ sophisticated mechanisms to direct biogenesis of a vacuolar replicative niche that circumvents default maturation through the endolysosomal cascade. However, this is not the case of the Q fever bacterium, Coxiella burnetii. This hardy, obligate intracellular pathogen has evolved to not only survive, but to thrive, in the harshest of intracellular compartments: the phagolysosome. Following internalization, the nascent Coxiella phagosome ultimately develops into a large and spacious parasitophorous vacuole (PV) that acquires lysosomal characteristics such as acidic pH, acid hydrolases and cationic peptides, defences designed to rid the host of intruders. However, transit of Coxiella to this environment is initially stalled, a process that is apparently modulated by interactions with the autophagic pathway. Coxiella actively participates in biogenesis of its PV by synthesizing proteins that mediate phagosome stalling, autophagic interactions, and development and maintenance of the mature vacuole. Among the potential mechanisms mediating these processes is deployment of a type IV secretion system to deliver effector proteins to the host cytosol. Here we summarize our current understanding of the cellular events that occur during parasitism of host cells by Coxiella.
1,004 citations
Cites background from "The autophagic pathway is actively ..."
...However, fusion with lysosomes, as indicated by the presence of the lysosomal enzymes acid phosphatase (Howe and Mallavia, 2000) and cathepsin D (Romano et al., 2007), takes approximately 2 h, which is significantly slower than phagosomes harbouring inert particles such as latex beads that acquire…...
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...Early autophagosome interactions and delayed lysosomal hydrolase delivery are reliant on Coxiella protein synthesis (Howe and Mallavia, 2000; Romano et al., 2007), indicating these are pathogen-directed processes....
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..., 2002) and CHO (Chinese hamster ovary fibroblast) (Romano et al., 2007) cells....
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...…2007), three lysosomal glycoproteins [LAMP-1 and LAMP-2 and LAMP-3 (CD63)] (Heinzen et al., 1996; Ghigo et al., 2002; Sauer et al., 2005; Shannon et al., 2005), flotillin 1 and 2 (Howe and Heinzen, 2006), and the autophagosome markers LC3 (Romano et al., 2007) and Rab24 (Gutierrez et al., 2005)....
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..., 2005), flotillin 1 and 2 (Howe and Heinzen, 2006), and the autophagosome markers LC3 (Romano et al., 2007) and Rab24 (Gutierrez et al....
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TL;DR: An overview of the antimicrobial defences of the host cell is presented, with emphasis on macrophages, for which phagocytosis has been studied most extensively and some of the evasive strategies used by bacteria are described.
Abstract: Professional phagocytes have a vast and sophisticated arsenal of microbicidal features. They are capable of ingesting and destroying invading organisms, and can present microbial antigens on their surface, eliciting acquired immune responses. To survive this hostile response, certain bacterial species have developed evasive strategies that often involve the secretion of effectors to co-opt the cellular machinery of the host. In this Review, we present an overview of the antimicrobial defences of the host cell, with emphasis on macrophages, for which phagocytosis has been studied most extensively. In addition, using Mycobacterium tuberculosis, Listeria monocytogenes, Legionella pneumophila and Coxiella burnetii as examples, we describe some of the evasive strategies used by bacteria.
849 citations
TL;DR: In mammals, autophagy has been implicated in either the pathogenesis or response to a wide variety of diseases, including neurodegenerative disease, chronic bacterial and viral infections, atherosclerosis, and cancer.
Abstract: Autophagy is a process by which cytoplasmic components are sequestered in double membrane vesicles and degraded upon fusion with lysosomal compartments. In yeast, autophagy is activated in response to changes in the extracellular milieu. Depending upon the stimulus, autophagy can degrade cytoplasmic contents nonspecifically or can target the degradation of specific cellular components. Both of these have been adopted in higher eukaryotes and account for the expanding role of autophagy in various cellular processes, as well as contribute to the variation in cellular outcomes after induction of autophagy. In some cases, autophagy appears to be an adaptive response, whereas under other circumstances it is involved in cell death. In mammals, autophagy has been implicated in either the pathogenesis or response to a wide variety of diseases, including neurodegenerative disease, chronic bacterial and viral infections, atherosclerosis, and cancer. As the basic molecular pathways that regulate autophagy are elucidated, the relationship of autophagy to the pathogenesis of various disease states emerges.
529 citations
TL;DR: This work has suggested that a machinery that is distinct from receptor-mediated endocytosis is used in phagosome maturation, and a subset of these candidate proteins makes up the first pathway to be identified for the maturation of apoptotic cell-containing phagosomes.
Abstract: Phagosome maturation is the process by which internalized particles (such as bacteria and apoptotic cells) are trafficked into a series of increasingly acidified membrane-bound structures, leading to particle degradation. The characterization of the phagosomal proteome and studies in model organisms and mammals have led to the identification of numerous candidate proteins that cooperate to control the maturation of phagosomes containing different particles. A subset of these candidate proteins makes up the first pathway to be identified for the maturation of apoptotic cell-containing phagosomes. This suggests that a machinery that is distinct from receptor-mediated endocytosis is used in phagosome maturation.
485 citations
TL;DR: In this article, the authors discuss canonical and non-canonical autophagy pathways and their current knowledge of antibacterial auto-pathway, with a focus on the interplay between bacterial factors and autophag components.
Abstract: Autophagy is a cellular process that targets proteins, lipids and organelles to lysosomes for degradation, but it has also been shown to combat infection with various pathogenic bacteria. In turn, bacteria have developed diverse strategies to avoid autophagy by interfering with autophagy signalling or the autophagy machinery and, in some cases, they even exploit autophagy for their growth. In this Review, we discuss canonical and non-canonical autophagy pathways and our current knowledge of antibacterial autophagy, with a focus on the interplay between bacterial factors and autophagy components.
449 citations
References
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TL;DR: It is demonstrated that the rat microtubule‐associated protein 1 light chain 3 (LC3), a homologue of Apg8p essential for autophagy in yeast, is associated to the autophagosome membranes after processing.
Abstract: Little is known about the protein constituents of autophagosome membranes in mammalian cells. Here we demonstrate that the rat microtubule-associated protein 1 light chain 3 (LC3), a homologue of Apg8p essential for autophagy in yeast, is associated to the autophagosome membranes after processing. Two forms of LC3, called LC3-I and -II, were produced post-translationally in various cells. LC3-I is cytosolic, whereas LC3-II is membrane bound. The autophagic vacuole fraction prepared from starved rat liver was enriched with LC3-II. Immunoelectron microscopy on LC3 revealed specific labelling of autophagosome membranes in addition to the cytoplasmic labelling. LC3-II was present both inside and outside of autophagosomes. Mutational analyses suggest that LC3-I is formed by the removal of the C-terminal 22 amino acids from newly synthesized LC3, followed by the conversion of a fraction of LC3-I into LC3-II. The amount of LC3-II is correlated with the extent of autophagosome formation. LC3-II is the first mammalian protein identified that specifically associates with autophagosome membranes.
6,244 citations
"The autophagic pathway is actively ..." refers background in this paper
...LC3 is a mammalian homologue of the yeast Atg8 and is targeted to autophagosomal membranes after a posttranslational processing that involves the conjugation with the lipid phosphatidylethanolamine (Kabeya et al., 2000)....
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TL;DR: The core protein machinery that is necessary to drive formation and consumption of intermediates in the macroautophagy pathway includes a ubiquitin-like protein conjugation system and a protein complex that directs membrane docking and fusion at the lysosome or vacuole.
Abstract: Macroautophagy is a dynamic process involving the rearrangement of subcellular membranes to sequester cytoplasm and organelles for delivery to the lysosome or vacuole where the sequestered cargo is degraded and recycled. This process takes place in all eukaryotic cells. It is highly regulated through the action of various kinases, phosphatases, and guanosine triphosphatases (GTPases). The core protein machinery that is necessary to drive formation and consumption of intermediates in the macroautophagy pathway includes a ubiquitin-like protein conjugation system and a protein complex that directs membrane docking and fusion at the lysosome or vacuole. Macroautophagy plays an important role in developmental processes, human disease, and cellular response to nutrient deprivation.
3,398 citations
"The autophagic pathway is actively ..." refers background in this paper
...Autophagy is a physiological process required for the removal of aged organelles and cytosolic components (reviewed by Klionsky and Emr, 2000; Yoshimori, 2004)....
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TL;DR: Cellular organelles in the exocytic and endocytic pathways have a distinctive spatial distribution and communicate through an elaborate system of vesiculo-tubular transport.
Abstract: Cellular organelles in the exocytic and endocytic pathways have a distinctive spatial distribution and communicate through an elaborate system of vesiculo-tubular transport. Rab proteins and their effectors coordinate consecutive stages of transport, such as vesicle formation, vesicle and organelle motility, and tethering of vesicles to their target compartment. These molecules are highly compartmentalized in organelle membranes, making them excellent candidates for determining transport specificity and organelle identity.
3,373 citations
"The autophagic pathway is actively ..." refers background in this paper
...The family of small GTPases Rab plays a crucial role in membrane trafficking of eukaryotic cells, regulating tethering, docking and fusion events among different compartments (Zerial and McBride, 2001)....
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TL;DR: The results on the apg mutants suggest that autophagy via autophagic bodies is indispensable for protein degradation in the vacuoles under starvation conditions, and that at least 15 APG genes are involved inAutophagy in yeast.
1,653 citations
"The autophagic pathway is actively ..." refers background in this paper
...Different groups have identified many molecules involved in the autophagy process in both yeast and mammalian cells (Tsukada and Ohsumi, 1993; Thumm et al., 1994; Mizushima et al., 2001)....
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TL;DR: This work found that the level of Rab 5 dynamically fluctuates on individual early endosomes, linked by fusion and fission events into a network in time, and suggested Rab conversion as the mechanism of cargo progression between early and late endosome.
1,549 citations
"The autophagic pathway is actively ..." refers background or result in this paper
...Published work has established comparable endocytic marker conversion kinetics in epithelial cells, in both the endocytic (Rink et al., 2005) and phagocytic process (Vieira et al., 2003)....
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...Published work has established comparable endocytic marker conversion kinetics in epithelial cells, in both the endocytic (Rink et al., 2005) and phagocytic process (Vieira et al....
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