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Current Opinion in Chemical Biology Feb 2019Phagosomes are highly dynamic organelles formed by the uptake of particles through phagocytic innate immune cells such as macrophages. Their key roles in microbe... (Review)
Review
Phagosomes are highly dynamic organelles formed by the uptake of particles through phagocytic innate immune cells such as macrophages. Their key roles in microbe elimination and antigen presentation make them essential for innate and adaptive immunity. However, phagosomes are also important for tissue homeostasis as even in healthy individuals billions of dead cells are phagocytosed each day. In this short review, we highlight how the use of latex beads as inert baits for phagocytosis and subsequent analysis by proteomics has changed our understanding of the phagosome. We further discuss recent data on post-translational modifications such as phosphorylation and ubiquitylation that regulate phagosome functions and demonstrate that the phagosome is not only a 'degradative organelle' but also serves as a subcellular signalling platform.
Topics: Animals; Humans; Phagosomes; Phosphorylation; Protein Processing, Post-Translational; Proteins; Proteomics; Signal Transduction; Ubiquitination
PubMed: 30481638
DOI: 10.1016/j.cbpa.2018.11.001 -
Frontiers in Immunology 2022Phagocytes, such as macrophages and dendritic cells, possess the ability to ingest large quantities of exogenous material into membrane-bound endocytic organelles such... (Review)
Review
Phagocytes, such as macrophages and dendritic cells, possess the ability to ingest large quantities of exogenous material into membrane-bound endocytic organelles such as macropinosomes and phagosomes. Typically, the ingested material, which consists of diverse macromolecules such as proteins and nucleic acids, is delivered to lysosomes where it is digested into smaller molecules like amino acids and nucleosides. These smaller molecules can then be exported out of the lysosomes by transmembrane transporters for incorporation into the cell's metabolic pathways or for export from the cell. There are, however, exceptional instances when undigested macromolecules escape degradation and are instead delivered across the membrane of endocytic organelles into the cytosol of the phagocyte. For example, double stranded DNA, a damage associated molecular pattern shed by necrotic tumor cells, is endocytosed by phagocytes in the tumor microenvironment and delivered to the cytosol for detection by the cytosolic "danger" sensor cGAS. Other macromolecular "danger" signals including lipopolysaccharide, intact proteins, and peptidoglycans can also be actively transferred from within endocytic organelles to the cytosol. Despite the obvious biological importance of these processes, we know relatively little of how macromolecular "danger" signals are transferred across endocytic organelle membranes for detection by cytosolic sensors. Here we review the emerging evidence for the active cytosolic transfer of diverse macromolecular "danger" signals across endocytic organelle membranes. We will highlight developing trends and discuss the potential molecular mechanisms driving this emerging phenomenon.
Topics: Cytosol; Endocytosis; Endosomes; Macromolecular Substances; Macrophages; Phagosomes
PubMed: 35911757
DOI: 10.3389/fimmu.2022.944142 -
Fungal Biology Sep 2023Many species of medically important fungi are prolific in the formation of asexual spores. Spores undergo a process of active swelling and cell wall remodelling before a...
Many species of medically important fungi are prolific in the formation of asexual spores. Spores undergo a process of active swelling and cell wall remodelling before a germ tube is formed and filamentous growth ensues. Highly elongated germ tubes are known to be difficult to phagocytose and pose particular challenges for immune phagocytes. However, the significance of the earliest stages of spore germination during immune cell interactions has not been investigated and yet this is likely to be important for defence against sporogenous fungal pathogens. We show here that macrophages restrict the early phases of the spore germination process of Aspergillus fumigatus and Mucor circinelloides including the initial phase of spore swelling, spore germination and early polarised growth. Macrophages are therefore adept at retarding germination as well as subsequent vegetative growth which is likely to be critical for immune surveillance and protection against sporulating fungi.
Topics: Spores, Fungal; Germination; Macrophages; Phagocytes; Phagosomes
PubMed: 37821151
DOI: 10.1016/j.funbio.2023.08.002 -
Immunological Reviews Sep 2016Phagocytosis, the regulated uptake of large particles (>0.5 μm in diameter), is essential for tissue homeostasis and is also an early, critical component of the innate... (Review)
Review
Phagocytosis, the regulated uptake of large particles (>0.5 μm in diameter), is essential for tissue homeostasis and is also an early, critical component of the innate immune response. Phagocytosis can be conceptually divided into three stages: phagosome, formation, maturation, and resolution. Each of these involves multiple reactions that require exquisite spatial and temporal orchestration. The molecular events underlying these stages are being unraveled and the current state of knowledge is briefly summarized in this article.
Topics: Animals; Homeostasis; Humans; Immunity, Innate; Phagocytosis; Phagosomes
PubMed: 27558334
DOI: 10.1111/imr.12439 -
MBio Sep 2014Group A Streptococcus (GAS, Streptococcus pyogenes) is an ongoing threat to human health as the agent of streptococcal pharyngitis, skin and soft tissue infections, and...
UNLABELLED
Group A Streptococcus (GAS, Streptococcus pyogenes) is an ongoing threat to human health as the agent of streptococcal pharyngitis, skin and soft tissue infections, and life-threatening conditions such as necrotizing fasciitis and streptococcal toxic shock syndrome. In animal models of infection, macrophages have been shown to contribute to host defense against GAS infection. However, as GAS can resist killing by macrophages in vitro and induce macrophage cell death, it has been suggested that GAS intracellular survival in macrophages may enable persistent infection. Using isogenic mutants, we now show that the GAS pore-forming toxin streptolysin O (SLO) and its cotoxin NAD-glycohydrolase (NADase) mediate GAS intracellular survival and cytotoxicity for macrophages. Unexpectedly, the two toxins did not inhibit fusion of GAS-containing phagosomes with lysosomes but rather prevented phagolysosome acidification. SLO served two essential functions, poration of the phagolysosomal membrane and translocation of NADase into the macrophage cytosol, both of which were necessary for maximal GAS intracellular survival. Whereas NADase delivery to epithelial cells is mediated by SLO secreted from GAS bound to the cell surface, in macrophages, the source of SLO and NADase is GAS contained within phagolysosomes. We found that transfer of NADase from the phagolysosome to the macrophage cytosol occurs not by simple diffusion through SLO pores but rather by a specific translocation mechanism that requires the N-terminal translocation domain of NADase. These results illuminate the mechanisms through which SLO and NADase enable GAS to defeat macrophage-mediated killing and provide new insight into the virulence of a major human pathogen.
IMPORTANCE
Macrophages constitute an important element of the innate immune response to mucosal pathogens. They ingest and kill microbes by phagocytosis and secrete inflammatory cytokines to recruit and activate other effector cells. Group A Streptococcus (GAS, Streptococcus pyogenes), an important cause of pharyngitis and invasive infections, has been shown to resist killing by macrophages. We find that GAS resistance to macrophage killing depends on the GAS pore-forming toxin streptolysin O (SLO) and its cotoxin NAD-glycohydrolase (NADase). GAS bacteria are internalized by macrophage phagocytosis but resist killing by secreting SLO, which damages the phagolysosome membrane, prevents phagolysosome acidification, and translocates NADase from the phagolysosome into the macrophage cytosol. NADase augments SLO-mediated cytotoxicity by depleting cellular energy stores. These findings may explain the nearly universal production of SLO by GAS clinical isolates and the association of NADase with the global spread of a GAS clone implicated in invasive infections.
Topics: Bacterial Proteins; Cell Line; Cloning, Molecular; Cytosol; Epithelial Cells; Humans; Intracellular Membranes; Macrophages; Microscopy, Confocal; NAD+ Nucleosidase; Phagocytosis; Phagosomes; Streptococcus pyogenes; Streptolysins
PubMed: 25227466
DOI: 10.1128/mBio.01690-14 -
Frontiers in Cellular and Infection... 2021Cells of the innate immune system continuously patrol the extracellular environment for potential microbial threats that are to be neutralized by phagocytosis and... (Review)
Review
Cells of the innate immune system continuously patrol the extracellular environment for potential microbial threats that are to be neutralized by phagocytosis and delivery to lysosomes. In addition, phagocytes employ autophagy as an innate immune mechanism against pathogens that succeed to escape the phagolysosomal pathway and invade the cytosol. In recent years, LC3-associated phagocytosis (LAP) has emerged as an intermediate between phagocytosis and autophagy. During LAP, phagocytes target extracellular microbes while using parts of the autophagic machinery to label the cargo-containing phagosomes for lysosomal degradation. LAP contributes greatly to host immunity against a multitude of bacterial pathogens. In the pursuit of survival, bacteria have developed elaborate strategies to disarm or circumvent the LAP process. In this review, we will outline the nature of the LAP mechanism and discuss recent insights into its interplay with bacterial pathogens.
Topics: Autophagy; Bacteria; Microtubule-Associated Proteins; Phagocytosis; Phagosomes
PubMed: 35047422
DOI: 10.3389/fcimb.2021.809121 -
International Journal of Medical... Jan 2018The mature phagosome of macrophages is a hostile environment for the vast majority of phagocytosed microbes. In addition to active destruction of the engulfed microbes... (Review)
Review
The mature phagosome of macrophages is a hostile environment for the vast majority of phagocytosed microbes. In addition to active destruction of the engulfed microbes by antimicrobial compounds, restriction of essential nutrients in the phagosomal compartment contributes to microbial growth inhibition and killing. However, some pathogenic microorganisms have not only developed various strategies to efficiently withstand or counteract antimicrobial activities, but also to acquire nutrients within macrophages for intracellular replication. Successful intracellular pathogens are able to utilize host-derived amino acids, carbohydrates and lipids as well as trace metals and vitamins during intracellular growth. This requires sophisticated strategies such as phagosome modification or escape, efficient nutrient transporters and metabolic adaptation. In this review, we discuss the metabolic adaptation of facultative intracellular bacteria and fungi to the intracellular lifestyle inside macrophages.
Topics: Adaptation, Physiological; Animals; Bacteria; Biological Transport; Cytosol; Fungi; Humans; Macrophages; Nutrients; Phagosomes
PubMed: 29150190
DOI: 10.1016/j.ijmm.2017.11.001 -
Autophagy May 2016The macroautophagy (hereafter autophagy) process involves de novo formation of double-membrane autophagosomes; after sequestering cytoplasm these transient organelles... (Review)
Review
The macroautophagy (hereafter autophagy) process involves de novo formation of double-membrane autophagosomes; after sequestering cytoplasm these transient organelles fuse with the vacuole/lysosome. Genetic studies in yeasts have characterized more than 40 autophagy-related (Atg) proteins required for autophagy, and the majority of these proteins play roles in autophagosome formation. The fusion of autophagosomes with the vacuole is mediated by the Rab GTPase Ypt7, its guanine nucleotide exchange factor Mon1-Ccz1, and soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) proteins. However, these factors are not autophagosome-vacuole fusion specific. We recently showed that 2 autophagy scaffold proteins, the Atg17-Atg31-Atg29 complex and Atg11, regulate autophagosome-vacuole fusion by recruiting the vacuolar SNARE Vam7 to the phagophore assembly site (PAS), where an autophagosome forms in yeast.
Topics: Animals; Autophagosomes; Autophagy; Autophagy-Related Proteins; Carrier Proteins; Humans; Phagosomes; Vacuoles
PubMed: 26986547
DOI: 10.1080/15548627.2016.1162364 -
Virulence Dec 2019Autophagy is a well-conserved process of self-digestion of intracellular components. is a protozoan parasite with a complex life-cycle that involves insect vectors and... (Review)
Review
Autophagy is a well-conserved process of self-digestion of intracellular components. is a protozoan parasite with a complex life-cycle that involves insect vectors and mammalian hosts. Like other eukaryotic organisms, possesses an autophagic pathway that is activated during metacyclogenesis, the process that generates the infective forms of parasites. In addition, it has been demonstrated that mammalian autophagy has a role during host cell invasion by , and that can modulate this process to its own benefit. This review describes the latest findings concerning the participation of autophagy in both the differentiation processes and during the interaction of parasites within the host cells. Data to date suggest parasite autophagy is important for parasite survival and differentiation, which offers interesting prospects for therapeutic strategies. Additionally, the interruption of mammalian autophagy reduces the parasite infectivity, interfering with the intracellular cycle of inside the host. However, the impact on other stages of development, such as the intracellular replication of parasites is still not clearly understood. Further studies in this matter are necessaries to define the integral effect of autophagy on infection with both and approaches.
Topics: Animals; Autophagy; Chagas Disease; Host-Parasite Interactions; Humans; Life Cycle Stages; Mice; Phagosomes; Trypanosoma cruzi
PubMed: 30489206
DOI: 10.1080/21505594.2018.1543517 -
Cell Death and Differentiation Mar 2019Autophagy is a conserved intracellular degradation pathway essential for protein homeostasis, survival and development. Defects in autophagic pathways have been... (Review)
Review
Autophagy is a conserved intracellular degradation pathway essential for protein homeostasis, survival and development. Defects in autophagic pathways have been connected to a variety of human diseases, including cancer and neurodegeneration. In the process of macroautophagy, cytoplasmic cargo is enclosed in a double-membrane structure and fused to the lysosome to allow for digestion and recycling of material. Autophagosome formation is primed by the ULK complex, which enables the downstream production of PI(3)P, a key lipid signalling molecule, on the phagophore membrane. The PI(3)P is generated by the PI3 kinase (PI3K) complex, consisting of the core components VPS34, VPS15 and Beclin 1. Beclin 1 is a central player in autophagy and constitutes a molecular platform for the regulation of autophagosome formation and maturation. Post-translational modifications of Beclin 1 affect its stability, interactions and ability to regulate PI3K activity, providing the cell with a plethora of strategies to fine-tune the levels of autophagy. Being such an important regulator, Beclin 1 is a potential target for therapeutic intervention and interfering with the post-translational regulation of Beclin 1 could be one way of manipulating the levels of autophagy. In this review, we provide an overview of the known post-translational modifications of Beclin 1 that govern its role in autophagy and how these modifications are maintained by input from several upstream signalling pathways. ▓.
Topics: Animals; Autophagy; Autophagy-Related Proteins; Beclin-1; Class III Phosphatidylinositol 3-Kinases; Humans; Phagosomes; Phosphatidylinositol 3-Kinases; Phosphatidylinositol Phosphates; Phosphorylation; Protein Processing, Post-Translational; Signal Transduction; Ubiquitination
PubMed: 30546075
DOI: 10.1038/s41418-018-0254-9