Disease relevance of Phagosomes

• Here we show that Toll-like receptor 2 is recruited specifically to macrophage phagosomes containing yeast, and that a point mutation in the receptor abrogates inflammatory responses to yeast and Gram-positive bacteria, but not to Gram-negative bacteria [1].
• The human macrophage mannose receptor directs Mycobacterium tuberculosis lipoarabinomannan-mediated phagosome biogenesis [2].
• Class II MHC molecules were present in a tubulo-vesicular lysosome compartment, which appeared to fuse with phagosomes, as well as in the resulting phagolysosomes containing internalized Listeria; these compartments were all positive for Lamp 1 and cathepsin D and lacked 46-kD mannose-6-phosphate receptors [3].
• Here we show that compartments of the late endocytic pathway, bearing the tetanus neurotoxin-insensitive vesicle-associated membrane protein (TI-VAMP/VAMP7), are recruited upon particle binding and undergo exocytosis before phagosome sealing in macrophages during Fc receptor (FcR)-mediated phagocytosis [4].
• Salmonella typhimurium activates virulence gene transcription within acidified macrophage phagosomes [5].

High impact information on Phagosomes

• Autophagy stimulation increased phagosomal colocalization with Beclin-1, a subunit of the phosphatidylinositol 3-kinase hVPS34, necessary for autophagy and a target for mycobacterial phagosome maturation arrest [6].
• We have identified a WD repeat host protein that was recruited to and actively retained on phagosomes by living, but not dead, mycobacteria [7].
• A fusion of coronin with green fluorescent protein (GFP) accumulates in the cups within less than 1 min upon attachment of a particle and is gradually released from the phagosome within 1 min after engulfment is completed [8].
• Immunocytochemical studies using antibodies against purified TC-TOX showed that the protein was localized to the luminal space of parasite-containing phagosomes [9].
• Here we show that M. tuberculosis phagosomes are secluded from the cytosolic MHC-I processing pathway and that mycobacteria-infected cells lose their antigen-presenting capacity [10].

Chemical compound and disease context of Phagosomes

• Previous studies have shown that the ability of Mycobacterium tuberculosis to block a Ca(2+) flux is an important step in its capacity to halt phagosome maturation [11].
• Rac1 may act via Arp2/3, phosphatidylinositol 4,5-bisphosphate and capping-proteins in the formation of nascent phagosomes during Yersinia uptake [12].
• In contrast, more than 70% of phagosomes that contained Escherichia coli, polystyrene beads, or exponential phase (E) L. pneumophila matured to phagolysosomes, as judged by co-localization with LAMP-1, cathepsin D and fluorescent endosomal probes [13].
• Furthermore, (iii) mycobacteria were not killed in auto-phagolysosomes, and (iv) cholesterol replenishment enabled mycobacterium to rescue itself from autophagic phagolysosomes to again reside individually in phagosomes which no longer fused with lysosomes [14].
• Modulation of cellular phosphatidylinositol 3-phosphate levels in primary macrophages affects heat-killed but not viable Mycobacterium avium's transport through the phagosome maturation process [15].

Biological context of Phagosomes

• Using this mutant organism as a relevant biological probe, we demonstrate here that the calcium concentration in Y. pestis-containing phagolysosomes is sufficiently low to permit virulence gene expression; this resolves the question of where Y. pestis might express its Ca2+-regulated genes in vivo [16].
• Immunocytochemistry shows that early during phagocytosis of zymosan, adenosine 3',5'-monophosphate (cyclic AMP) appears on the cell surface before the phagosome is internalized [17].
• Acid phosphatase cytochemistry revealed that phagosomes containing live L. pneumophila did not fuse with either primary or secondary lysosomes [18].
• Natural resistance to infection with intracellular pathogens: the Nramp1 protein is recruited to the membrane of the phagosome [19].
• Focal exocytosis of VAMP3-containing vesicles at sites of phagosome formation [20].

Anatomical context of Phagosomes

• Bacteria phagocytosed by leukocytes are killed and degraded by toxic oxygen metabolites produced in the phagosome via an NADPH oxidase [21].
• Nramp1 codes for an integral membrane protein expressed in the lysosomal compartment of macrophages, and is recruited to the membrane of phagosomes soon after the completion of phagocytosis [22].
• One such mechanism involves the fusion of the endoplasmic reticulum (ER) with the endosomal-phagosomal system, in which the machinery required for peptide loading of MHC class I molecules is introduced directly into the phagosome [23].
• The targeting of Nramp1 from endocytic vesicles to the phagosomal membrane supports the hypothesis that Nramp1 controls the replication of intracellular parasites by altering the intravacuolar environment of the microbe-containing phagosome [19].
• Thus, in two independent models of phagocytosis human neutrophils convert L-tyrosine to 3-chlorotyrosine, indicating that a Cl2-like oxidant is generated in the phagolysosome [24].

Associations of Phagosomes with chemical compounds

• Live S. cerevisiae cells isolated from the phagolysosome are induced for genes of the glyoxylate cycle, a metabolic pathway that permits the use of two-carbon compounds as carbon sources [25].
• Recent advances in phagosome biology have been made possible largely by a model system that uses inert latex beads [26].
• During ingestion of COZ, punctate structures rich in F-actin, vinculin, alpha-actinin, paxillin, and phosphotyrosine-containing proteins are distributed over the phagosome surface [27].
• Phagosomes from Nramp1(+/+) mice extrude Mn(2+) faster than their Nramp(-/-) counterparts [22].
• Furthermore, the delivery of active proteases to the phagosome is significantly reduced after the activation of DCs with lipopolysaccharide [28].

Gene context of Phagosomes

• The Toll-like receptor 2 is recruited to macrophage phagosomes and discriminates between pathogens [1].
• Dynamin 2 is enriched on early phagosomes, and expression of a dominant-negative mutant of dynamin 2 significantly inhibits particle internalization at the stage of membrane extension around the particle [29].
• We used fluorescent chimeric proteins to monitor the dynamics of association of actin and active Cdc42 and Rac1 with the forming phagosome [30].
• Although actin was found to disappear from the base of the forming phagosome before sealing was complete, Rac1/Cdc42 activity persisted, suggesting that termination of GTPase activity is not the main determinant of actin disassembly [30].
• The smaller subpopulation of afipiae whose phagosomes will be part of the endocytic system enters into an EEA1-positive compartment, which also subsequently acquires LAMP-1 [31].

Analytical, diagnostic and therapeutic context of Phagosomes

• Double immunofluorescence studies and direct purification of latex bead-containing phagosomes demonstrated that upon phagocytosis, Nramp1 is recruited to the membrane of the phagosome and remains associated with this structure during its maturation to phagolysosome [19].
• Flow organellometry and Western blot analysis showed that MTB phagosomes acquired lysosome-associated membrane protein-1 (LAMP-1), MHC-II, and H2-DM [32].
• Discharge of lactoferrin, a secondary granule marker into the phagosome was verified by immunostaining using standard epifluorescence, confocal laser scanning and electron microscopy [33].
• Proteins from 131I/lactoperoxidase-labeled phagolysosomes, phagolysosomes derived from 131I/lactoperoxidase-labeled cells, and phagolysosomes prepared from [35S]methionine metabolically labeled cells were analyzed by high-resolution two-dimensional gel electrophoresis [34].
• Colocalization of F-actin, p57, and p47phox on phagosomes was confirmed by immunoblotting [35].

References