title: Protection against CD95-induced apoptosis by chlamydial infection at a mitochondrial step.
abstract: Chlamydiae are obligate intracellular bacteria that infect human epithelial and myeloid cells. Previous work has established that chlamydiae are able to protect a cell against apoptosis induced by certain experimentally applied stimuli. Here we provide an analysis of this protective activity against the signal transduction during CD95-induced apoptosis. In HeLa cells overexpressing CD95, infection with Chlamydia trachomatis inhibited the appearance of apoptotic morphology, effector caspase activity, the activation of caspase-9 and -3, and the release of cytochrome c from mitochondria. However, caspase-8-processing and activity (measured as cleavage of Bid) were unaffected by the chlamydial infection. Similarly, infection with the species C. pneumoniae did not prevent the activation of caspase-8 but inhibited the appearance of effector caspase activity upon signaling through CD95. Furthermore, infection with C. trachomatis was able to inhibit CD95-induced apoptosis in Jurkat lymphoid cells, where a mitochondrial contribution is required, but not in SKW6.4 lymphoid cells, where caspase-8 directly activates caspase-3. Taken together, these data show that chlamydial infection can protect cells against CD95-induced apoptosis but only where a mitochondrial signaling step is necessary for apoptotic signal transduction.
authors.affiliation: Institute for Medical Microbiology, Technische Universität München, D-81675 Munich, Germany.
authors.forename: Silke F
authors.initials: SF
authors.lastname: Fischer
authors.forename: Thomas
authors.initials: T
authors.lastname: Harlander
authors.forename: Juliane
authors.initials: J
authors.lastname: Vier
authors.forename: Georg
authors.initials: G
authors.lastname: Häcker
mesh_terms: D017209:Apoptosis; D051023:BH3 Interacting Domain Death Agonist Protein; D002352:Carrier Proteins / Q000378:metabolism; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases / Q000378:metabolism; D002460:Cell Line; D002692:Chlamydia trachomatis / Q000502:physiology*; D045304:Cytochromes c / Q000378:metabolism; D019610:Cytoprotection; D006801:Humans; D008928:Mitochondria / Q000502:physiology*; D015398:Signal Transduction; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology; D019014:fas Receptor / Q000502:physiology*
chemical_list: D051023:BH3 Interacting Domain Death Agonist Protein; C494814:BID protein, human; D002352:Carrier Proteins; D019014:fas Receptor; D045304:Cytochromes c; C505407:CASP3 protein, human; C506433:CASP9 protein, human; D053148:Caspase 3; D053453:Caspase 9; D020169:Caspases