title: Toxoplasma gondiiinhibits cytochromec-induced caspase activation in its host cell by interference with holo-apoptosome assembly.
abstract: Inhibition of programmed cell death pathways of mammalian cells often facilitates the sustained survival of intracellular microorganisms. The apicomplexan parasiteToxoplasma gondiiis a master regulator of host cell apoptotic pathways. Here, we have characterized a novel anti-apoptotic activity ofT. gondii. Using a cell-free cytosolic extract model, we show thatT. gondiiinterferes with the activities of caspase 9 and caspase 3/7 which have been induced by exogenous cytochromecand dATP. Proteolytic cleavage of caspases 9 and 3 is also diminished suggesting inhibition of holo-apoptosome function. Parasite infection of Jurkat T cells and subsequent triggering of apoptosome formation by exogenous cytochromecin vitroandin vivoindicated thatT. gondiialso interferes with caspase activation in infected cells. Importantly, parasite inhibition of cytochromec-induced caspase activation considerably contributes to the overall anti-apoptotic activity ofT. gondiias observed in staurosporine-treated cells. Co-immunoprecipitation showed thatT. gondiiabolishes binding of caspase 9 to Apaf-1 whereas the interaction of cytochromecwith Apaf-1 remains unchanged. Finally,T. gondiilysate mimics the effect of viable parasites and prevents holo-apoptosome functionality in a reconstitutedin vitrosystem comprising recombinant Apaf-1 and caspase 9. Beside inhibition of cytochromecrelease from host cell mitochondria,T. gondiithus also targets the holo-apoptosome assembly as a second mean to efficiently inhibit the caspase-dependent intrinsic cell death pathway.
authors.affiliation: Institute for Medical Microbiology, Georg-August-University, Göttingen, Germany. ; Present address: In den Brühlwiesen 12, 61352 Bad Homburg, Germany.
authors.forename: Kristin
authors.initials: K
authors.lastname: Graumann
authors.affiliation: Institute for Medical Microbiology, Georg-August-University, Göttingen, Germany. ; Present address: Institute for Medical Microbiology, University Hospital Münster, Domagkstraße 10, 48149 Münster, Germany.
authors.forename: Frieder
authors.initials: F
authors.lastname: Schaumburg
authors.affiliation: Institute for Biophysical Chemistry, Hannover Medical School, Hannover, Germany.
authors.forename: Thomas F
authors.initials: TF
authors.lastname: Reubold
authors.affiliation: Institute for Medical Microbiology, Georg-August-University, Göttingen, Germany.
authors.forename: Diana
authors.initials: D
authors.lastname: Hippe
authors.affiliation: Institute for Biophysical Chemistry, Hannover Medical School, Hannover, Germany.
authors.forename: Susanne
authors.initials: S
authors.lastname: Eschenburg
authors.affiliation: Institute for Medical Microbiology, Georg-August-University, Göttingen, Germany.
authors.forename: Carsten G K
authors.initials: CG
authors.lastname: Lüder
keywords: Apaf-1; Toxoplasma gondii; apoptosis; apoptosome; caspase activation; intrinsic pathway; pathogen-host interaction