title: Nramp1 modifies the fusion of Salmonella typhimurium-containing vacuoles with cellular endomembranes in macrophages.
abstract: Salmonella survive and replicate within mammalian cells by becoming secluded within specialized membrane-bound vacuoles inaccessible to the host defense mechanisms. Delayed acidification of the vacuole and its incomplete fusion with lysosomes have been implicated in intracellular Salmonella survival. Nramp1 confers to macrophages resistance to a variety of intracellular pathogens, including Salmonella, but its precise mode of action is not understood. We investigated whether Nramp1 affects the maturation and acidification of Salmonella-containing vacuoles (SCV). A mouse-derived macrophage line (RAW/Nramp1(-)) devoid of Nramp1 and therefore susceptible to infection was compared with isogenic clones stably transfected with Nramp1 (RAW/Nramp1(+)). Intravacuolar pH, measured in situ, was similar in Nramp1-expressing and -deficient cells. SCV acquired LAMP1 and fused with preloaded fluid-phase markers in both cell types. In contrast, although few vacuoles in RAW/Nramp1(-) acquired mannose 6-phosphate receptor, many more contained M6PR in RAW/Nramp1(+) cells. Shortly after closure, SCV in RAW/Nramp1(-) became inaccessible to extracellular markers, suggesting inability to fuse with newly formed endosomes. Expression of Nramp1 markedly increased the access to extracellularly added markers. We propose that Nramp1 counteracts the ability of Salmonella to become secluded in a compartment that limits access of bactericidal agents, allowing the normal degradative pathway of the macrophage to proceed.
authors.affiliation: Division of Cell Biology, Hospital for Sick Children, Toronto M5G 1X8, Ontario, Canada.
authors.forename: Patricia
authors.initials: P
authors.lastname: Cuellar-Mata
authors.forename: Nada
authors.initials: N
authors.lastname: Jabado
authors.forename: Jun
authors.initials: J
authors.lastname: Liu
authors.forename: Wendy
authors.initials: W
authors.lastname: Furuya
authors.forename: B Brett
authors.initials: BB
authors.lastname: Finlay
authors.forename: Philippe
authors.initials: P
authors.lastname: Gros
authors.forename: Sergio
authors.initials: S
authors.lastname: Grinstein
mesh_terms: D000818:Animals; D027682:Cation Transport Proteins / Q000502:physiology*; D002461:Cell Line, Transformed; D006863:Hydrogen-Ion Concentration; D007425:Intracellular Membranes / Q000382:microbiology; D008264:Macrophages / Q000382:microbiology* / Q000648:ultrastructure; D051379:Mice; D017527:Receptor, IGF Type 2 / Q000378:metabolism; D012486:Salmonella typhimurium / Q000502:physiology*; D014617:Vacuoles / Q000382:microbiology*; D000099173:Natural Resistance-associated Macrophage Protein 1
chemical_list: D027682:Cation Transport Proteins; D017527:Receptor, IGF Type 2; D000099173:Natural Resistance-associated Macrophage Protein 1