title: Birc1e/Naip5 rapidly antagonizes modulation of phagosome maturation by Legionella pneumophila.
abstract: Legionella survives intracellularly by preventing fusion with lysosomes, due to phagosome escape from the endocytic pathway at an early stage of phagosome maturation, and by creating a replicative organelle that acquires endoplasmic reticulum (ER) characteristics through sustained interactions and fusion with the ER. Intracellular replication of Legionella pneumophila in mouse macrophages is controlled by the Lgn1 locus. Functional complementation in vivo has identified the Birc1e/Naip5 gene as being responsible for the Lgn1 effect. To understand the function and temporal site of action of Birc1e/Naip5 in susceptibility to L. pneumophila, we examined the biogenesis of Legionella-containing vacuoles (LCVs) formed in permissive A/J macrophages and in their Birc1e/Naip5 transgenic non-permissive counterpart. Birc1e/Naip5 effects on acquisition of lysosomal and ER markers were evident within 1-2 h following infection. A significantly higher proportion of LCVs formed in Birc1e/Naip5 transgenic macrophages had acquired the lysosomal markers cathepsin D and Lamp1 by 2 h post infection, whereas a significantly higher proportion of LCVs formed in permissive macrophages were positively stained for the ER markers BAP31 and calnexin, 6 h post infection. Likewise, studies by electron microscopy showed acquisition of lysosomal contents (horseradish peroxidase), within the first hour following phagocytic uptake, by LCVs formed in Birc1e/Naip5 transgenic macrophages and delivery of the ER marker glucose 6-phosphatase (G6Pase) only to the lumen of LCVs formed in A/J macrophages. Finally, a larger proportion of LCVs formed in A/J macrophages were studded with ribosomes 24 h post infection, compared with LCVs formed in Birc1e/Naip5 transgenic macrophages. These results suggest that sensing of L. pneumophila products by Birc1e/Naip5 in macrophages occurs rapidly following phagocytosis, a process that antagonizes the ability of L. pneumophila to remodel its phagosome into a specialized vacuole with ER characteristics.
authors.affiliation: Department of Biochemistry, Centre for the Study of Host Resistance, McGill University, Montreal, Quebec, Canada.
authors.forename: Anne
authors.initials: A
authors.lastname: Fortier
authors.forename: Chantal
authors.initials: C
authors.lastname: de Chastellier
authors.forename: Stéphanie
authors.initials: S
authors.lastname: Balor
authors.forename: Philippe
authors.initials: P
authors.lastname: Gros
mesh_terms: D000818:Animals; D037281:Calnexin / Q000378:metabolism; D002402:Cathepsin D / Q000378:metabolism; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000378:metabolism / Q000648:ultrastructure; D005952:Glucose-6-Phosphatase / Q000378:metabolism; D016952:Legionella pneumophila / Q000254:growth & development*; D052118:Lysosomal-Associated Membrane Protein 1 / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism / Q000648:ultrastructure; D008264:Macrophages / Q000378:metabolism* / Q000382:microbiology / Q000648:ultrastructure; D008565:Membrane Proteins / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains; D008822:Mice, Transgenic; D046529:Microscopy, Electron, Transmission; D008856:Microscopy, Fluorescence; D051616:Neuronal Apoptosis-Inhibitory Protein / Q000235:genetics / Q000378:metabolism / Q000502:physiology*; D010588:Phagosomes / Q000378:metabolism* / Q000648:ultrastructure; D013997:Time Factors
chemical_list: C489642:Bcap31 protein, mouse; D052118:Lysosomal-Associated Membrane Protein 1; D008565:Membrane Proteins; C496806:Naip5 protein, mouse; D051616:Neuronal Apoptosis-Inhibitory Protein; D037281:Calnexin; D005952:Glucose-6-Phosphatase; D002402:Cathepsin D