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IAP-IAP complexes required for apoptosis resistance of C. trachomatis-infected cells.

ABSTRACT: Host cells infected with obligate intracellular bacteria Chlamydia trachomatis are profoundly resistant to diverse apoptotic stimuli. The molecular mechanisms underlying the block in apoptotic signaling of infected cells is not well understood. Here we investigated the molecular mechanism by which apoptosis induced via the tumor necrosis factor (TNF) receptor is prevented in infected epithelial cells. Infection with C. trachomatis leads to the up-regulation of cellular inhibitor of apoptosis (cIAP)-2, and interfering with cIAP-2 up-regulation sensitized infected cells for TNF-induced apoptosis. Interestingly, besides cIAP-2, cIAP-1 and X-linked IAP, although not differentially regulated by infection, are required to maintain apoptosis resistance in infected cells. We detected that IAPs are constitutively organized in heteromeric complexes and small interfering RNA-mediated silencing of one of these IAPs affects the stability of another IAP. In particular, the stability of cIAP-2 is modulated by the presence of X-linked IAP and their interaction is stabilized in infected cells. Our observations suggest that IAPs are functional and stable as heteromers, a thus far undiscovered mechanism of IAP regulation and its role in modulation of apoptosis.

SUBMITTER: Rajalingam K

PROVIDER: S-EPMC1626104 | biostudies-literature | 2006 Oct

REPOSITORIES: biostudies-literature

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IAP-IAP complexes required for apoptosis resistance of C. trachomatis-infected cells.

Rajalingam Krishnaraj K Sharma Manu M Paland Nicole N Hurwitz Robert R Thieck Oliver O Oswald Monique M Machuy Nikolaus N Rudel Thomas T

PLoS pathogens 20061001 10

Host cells infected with obligate intracellular bacteria Chlamydia trachomatis are profoundly resistant to diverse apoptotic stimuli. The molecular mechanisms underlying the block in apoptotic signaling of infected cells is not well understood. Here we investigated the molecular mechanism by which apoptosis induced via the tumor necrosis factor (TNF) receptor is prevented in infected epithelial cells. Infection with C. trachomatis leads to the up-regulation of cellular inhibitor of apoptosis (cI ...[more]

PMID: 17069460

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Project description:The sexually transmitted pathogen Chlamydia trachomatis (CT) is able to replicate and survive in human intestinal epithelial cells, being the gastro-intestinal tract a suitable site of residence for this microorganism. In this context, no detailed information about the mechanisms of cell death in intestinal cell lines after a chlamydial infection is available. The aim of this study was to compare the effect of two different CT serovars (D and L2) on the survival/death of different intestinal cell lines (Caco-2 and COLO-205), using endocervical cells (HeLa) as a reference model of genital infection. Seventy two hours after chlamydial infection at different multiplicity of infection (MOI) levels, the viability of HeLa, Caco-2 and COLO 205 cells was evaluated through dose-response experiments by means of a MTS-based assay. To get deeper insights in the mechanisms of cell death induced by CT, cell viability was assessed in presence of different inhibitors (i.e. pan-caspase inhibitor Z-VAD, necroptosis inhibitor Necrostatin-1, hydrogen peroxide scavenger catalase, caspase-1 inhibitor Ac-YVAD-cmk). Moreover, the activation of effector caspases and the presence of cellular apoptotic/necrotic changes were evaluated at different time points after CT infection. Our results demonstrated that, for both chlamydial serovars, intestinal cell lines are more resistant to CT-induced cell death compared to HeLa, thus representing a suitable 'niche' for chlamydial residence and replication. In literature, apoptosis has been widely described to be the main cell death mechanism elicited by chlamydia infection. However, our data demonstrate that necroptosis plays a relevant role, proceeding in parallel with apoptosis. The protective effect of catalase suggests the involvement of oxidative stress in triggering both cell death pathways. Moreover, we demonstrated that caspase-1 is involved in CT-induced cell death, potentially contributing to host inflammatory response and tissue damage. Cells infected by L2 serovar displayed a higher activation of effector caspases compared to cells infected with serovar D, suggesting a serovar-specific activation of apoptotic pathways and potentially explaining the greater virulence of L serovars. Finally, we found that Chlamydia elicits the early externalization of phosphatidylserine on the external leaflet of plasma membrane independently of caspase activation.

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IAP-IAP complexes required for apoptosis resistance of C. trachomatis-infected cells.

Publications

IAP-IAP complexes required for apoptosis resistance of C. trachomatis-infected cells.

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