title: Proliferation of Toxoplasma gondii suppresses host cell autophagy.
abstract: Autophagy is a process of cytoplasmic degradation of endogenous proteins and organelles. Although its primary role is protective, it can also contribute to cell death. Recently, autophagy was found to play a role in the activation of host defense against intracellular pathogens. The aims of our study was to investigate whether host cell autophagy influences Toxoplasma gondii proliferation and whether autophagy inhibitors modulate cell survival. HeLa cells were infected with T. gondii with and without rapamycin treatment to induce autophagy. Lactate dehydrogenase assays showed that cell death was extensive at 36-48 hr after infection in cells treated with T. gondii with or without rapamycin. The autophagic markers, LC3 II and Beclin 1, were strongly expressed at 18-24 hr after exposure as shown by Western blotting and RT-PCR. However, the subsequent T. gondii proliferation suppressed autophagy at 36 hr post-infection. Pre-treatment with the autophagy inhibitor, 3-methyladenine (3-MA), down-regulated LC3 II and Beclin 1. The latter was also down-regulated by calpeptin, a calpain inhibitor. Monodansyl cadaverine (MDC) staining detected numerous autophagic vacuoles (AVs) at 18 hr post-infection. Ultrastructural observations showed T. gondii proliferation in parasitophorous vacuoles (PVs) coinciding with a decline in the numbers of AVs by 18 hr. FACS analysis failed to confirm the presence of cell apoptosis after exposure to T. gondii and rapamycin. We concluded that T. gondii proliferation may inhibit host cell autophagy and has an impact on cell survival.
authors.affiliation: Department of Environmental Biology and Medical Parasitology, Hanyang University College of Medicine, Seoul 133-791, Korea.
authors.forename: Youn-Jin
authors.initials: YJ
authors.lastname: Lee
authors.forename: Hyun-Ouk
authors.initials: HO
authors.lastname: Song
authors.forename: Young-Ha
authors.initials: YH
authors.lastname: Lee
authors.forename: Jae-Sook
authors.initials: JS
authors.lastname: Ryu
authors.forename: Myoung-Hee
authors.initials: MH
authors.lastname: Ahn
mesh_terms: D000900:Anti-Bacterial Agents / Q000494:pharmacology; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology; D001343:Autophagy / Q000187:drug effects; D006367:HeLa Cells; D006801:Humans; D020123:Sirolimus / Q000494:pharmacology; D014122:Toxoplasma / Q000166:cytology* / Q000502:physiology*
chemical_list: D000900:Anti-Bacterial Agents; D020123:Sirolimus
keywords: Beclin 1; LC3 II; Toxoplasma gondii; autophagy; rapamycin