title: Toxoplasma gondii resides in a vacuole that avoids fusion with host cell endocytic and exocytic vesicular trafficking pathways.
abstract: Toxoplasma gondii actively penetrates its vertebrate host cell to establish a nonfusigenic compartment called the parasitophorous vacuole (PV) that has previously been characterized primarily in phagocytic cells. To determine the fate of this unique compartment in nonphagocytic cells, we examined the trafficking of host cell proteins and lipids in Toxoplasma-infected fibroblasts using quantitative immunofluorescence and immunoelectron microscopy. Toxoplasma-containing vacuoles remained segregated from all levels of the endocytic pathway, as shown by the absence of delivery of transferrin receptors, mannose phosphate receptors, and the lysosomal-associated protein LAMP1 to the vacuole. The PV was also inaccessible to lipids (DiIC16, and GM1) that were internalized from the plasma membrane via the endocytic system. In contrast, vacuoles containing dead parasites or zymosan sequentially acquired both endosomal and lysosomal protein markers and host lipids, reflecting the competency of fibroblasts to process phagocytic vacuoles. The mature PV often lies adjacent to the host cell Golgi, suggesting that it may intersect with vesicles from the exocytic pathway. Despite this proximity, the PV was inaccessible to nitrobenzadiazole-labeled sphingolipids exported from the Golgi and did not contain the host protein markers AP1 or beta-COP. Our results demonstrate that Toxoplasma resides in a compartment that excludes delivery of protein and lipid components from the host cell endocytic and exocytic pathways.
authors.affiliation: Department of Molecular Microbiology, Washington University School of Medicine, St. Louis, Missouri, 63110, USA.
authors.forename: D G
authors.initials: DG
authors.lastname: Mordue
authors.forename: S
authors.initials: S
authors.lastname: Håkansson
authors.forename: I
authors.initials: I
authors.lastname: Niesman
authors.forename: L D
authors.initials: LD
authors.lastname: Sibley
mesh_terms: D016475:3T3 Cells; D033961:Adaptor Protein Complex 1; D033965:Adaptor Protein Complex alpha Subunits; D033942:Adaptor Proteins, Vesicular Transport; D000818:Animals; D015703:Antigens, CD / Q000032:analysis; D002462:Cell Membrane / Q000378:metabolism; D002966:Clathrin / Q000032:analysis; D004705:Endocytosis; D005089:Exocytosis; D005347:Fibroblasts / Q000469:parasitology* / Q000648:ultrastructure; D005455:Fluorescent Antibody Technique; D006056:Golgi Apparatus / Q000378:metabolism; D006790:Host-Parasite Interactions; D006801:Humans; D052118:Lysosomal-Associated Membrane Protein 1; D051907:Lysosomal Membrane Proteins; D008562:Membrane Glycoproteins / Q000032:analysis; D008563:Membrane Lipids / Q000378:metabolism; D008565:Membrane Proteins / Q000032:analysis; D051379:Mice; D016253:Microscopy, Immunoelectron; D010587:Phagocytosis; D017527:Receptor, IGF Type 2 / Q000032:analysis; D011990:Receptors, Transferrin / Q000032:analysis; D014122:Toxoplasma / Q000502:physiology*; D014617:Vacuoles / Q000469:parasitology*; D015054:Zymosan / Q000276:immunology
chemical_list: D033961:Adaptor Protein Complex 1; D033965:Adaptor Protein Complex alpha Subunits; D033942:Adaptor Proteins, Vesicular Transport; D015703:Antigens, CD; D002966:Clathrin; D052118:Lysosomal-Associated Membrane Protein 1; D051907:Lysosomal Membrane Proteins; D008562:Membrane Glycoproteins; D008563:Membrane Lipids; D008565:Membrane Proteins; D017527:Receptor, IGF Type 2; D011990:Receptors, Transferrin; D015054:Zymosan