title: Host cell autophagy is induced by Toxoplasma gondii and contributes to parasite growth.
abstract: Autophagy has been shown to contribute to defense against intracellular bacteria and parasites. In comparison, the ability of such pathogens to manipulate host cell autophagy to their advantage has not been examined. Here we present evidence that infection by Toxoplasma gondii, an intracellular protozoan parasite, induces host cell autophagy in both HeLa cells and primary fibroblasts, via a mechanism dependent on host Atg5 but independent of host mammalian target of rapamycin suppression. Infection led to the conversion of LC3 to the autophagosome-associated form LC3-II, to the accumulation of LC3-containing vesicles near the parasitophorous vacuole, and to the relocalization toward the vacuole of structures labeled by the phosphatidylinositol 3-phosphate indicator YFP-2xFYVE. The autophagy regulator beclin 1 was concentrated in the vicinity of the parasitophorous vacuole in infected cells. Inhibitor studies indicated that parasite-induced autophagy is dependent on calcium signaling and on abscisic acid. At physiologically relevant amino acid levels, parasite growth became defective in Atg5-deficient cells, indicating a role for host cell autophagy in parasite recovery of host cell nutrients. A flow cytometric analysis of cell size as a function of parasite content revealed that autophagy-dependent parasite growth correlates with autophagy-dependent consumption of host cell mass that is dependent on parasite progression. These findings indicate a new role for autophagy as a pathway by which parasites may effectively compete with the host cell for limiting anabolic resources.
authors.affiliation: Department of Pathology, Albert Einstein College of Medicine, Bronx, New York 10461, USA.
authors.forename: Yubao
authors.initials: Y
authors.lastname: Wang
authors.forename: Louis M
authors.initials: LM
authors.lastname: Weiss
authors.forename: Amos
authors.initials: A
authors.lastname: Orlofsky
mesh_terms: D000040:Abscisic Acid / Q000276:immunology / Q000378:metabolism; D000818:Animals; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D001343:Autophagy / Q000187:drug effects / Q000276:immunology*; D000071187:Autophagy-Related Protein 5; D000071186:Beclin-1; D020013:Calcium Signaling / Q000187:drug effects / Q000276:immunology; D002352:Carrier Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D008565:Membrane Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D051379:Mice; D008869:Microtubule-Associated Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D010588:Phagosomes / Q000235:genetics / Q000276:immunology / Q000378:metabolism / Q000469:parasitology; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D011506:Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D058570:TOR Serine-Threonine Kinases; D014122:Toxoplasma / Q000276:immunology* / Q000378:metabolism; D014123:Toxoplasmosis / Q000235:genetics / Q000276:immunology* / Q000378:metabolism
chemical_list: C502778:ATG5 protein, human; D051017:Apoptosis Regulatory Proteins; C495773:Atg5 protein, mouse; D000071187:Autophagy-Related Protein 5; C491997:BECN1 protein, human; D000071186:Beclin-1; C115010:Becn1 protein, mouse; D002352:Carrier Proteins; C477012:MAP1LC3A protein, human; C480860:Map1lc3b protein, mouse; D008565:Membrane Proteins; D008869:Microtubule-Associated Proteins; D011506:Proteins; D000040:Abscisic Acid; D017853:Phosphotransferases (Alcohol Group Acceptor); C546842:MTOR protein, human; C546843:mTOR protein, mouse; D058570:TOR Serine-Threonine Kinases