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Pseudomonas aeruginosa mediated apoptosis requires the ADP-ribosylating activity of exoS
Melissa R Kaufman1, Jinghua Jia2,1, Lin Zeng2,1
1Department of Microbiology and Immunology, University of Arkansas for Medical Sciences, Little Rock, AR 72205, USA1.
Abstract:
Pseudomonas aeruginosa is an opportunistic bacterial pathogen that primarily infects immunocompromised individuals and patients with cystic fibrosis. Using a tissue culture system, invasive strains of P. aeruginosa were discovered to induce apoptosis at high frequency in HeLa and other epithelial and fibroblast cell lines. This apoptotic phenotype in the infected cells was determined by several criteria including (i) visual changes in cell morphology, (ii) induction of chromatin condensation and nuclear marginalization, (iii) the presence of a high percentage of cells with subG1 DNA content, and (iv) activation of caspase-3 activity. Induction of the type III secretion machinery, but not invasion of P. aeruginosa is required for induction of apoptosis. The apoptosis phenotype is independent of the cytoskeletal rearrangements that occur in the host cell early after infection. Mutants in P. aeruginosa exoS fail to induce apoptosis and complementation with wild-type exoS restored the apoptosis-inducing capacity, demonstrating that ExoS is the effector molecule. Analysis of exoS activity mutants shows that the ADP-ribosylating capacity of ExoS is essential for inducing the apoptotic pathway.
Insights
Pseudomonas aeruginosa infection triggers programmed cell death (apoptosis) in host cells. The bacterial protein ExoS, through its ADP-ribosylating activity, is essential for inducing this apoptotic response.
Area of Science:
- Microbiology
- Cell Biology
- Pathogenesis
Background:
- Pseudomonas aeruginosa is an opportunistic pathogen affecting immunocompromised individuals and cystic fibrosis patients.
- Apoptosis, or programmed cell death, is a critical cellular process.
- Understanding bacterial mechanisms inducing apoptosis is key to developing treatments.
Purpose of the Study:
- To investigate the mechanism by which Pseudomonas aeruginosa induces apoptosis in host cells.
- To identify the specific bacterial factors responsible for triggering this cellular response.
Main Methods:
- Utilized a tissue culture system with HeLa and other epithelial/fibroblast cell lines.
- Assessed apoptosis through morphological changes, chromatin condensation, DNA content analysis (subG1), and caspase-3 activity.
- Employed P. aeruginosa mutants deficient in type III secretion and the ExoS protein.
Main Results:
- P. aeruginosa efficiently induced apoptosis in host cells, characterized by specific cellular and molecular markers.
- Type III secretion machinery, not bacterial invasion, was required for apoptosis induction.
- Mutations in the bacterial ExoS protein abolished apoptosis induction, while complementation restored it.
- The ADP-ribosylating activity of ExoS was essential for its ability to induce apoptosis.
Conclusions:
- ExoS is the primary Pseudomonas aeruginosa effector molecule responsible for inducing host cell apoptosis.
- The ADP-ribosylating function of ExoS is critical for initiating the apoptotic pathway.
- This study elucidates a key mechanism of P. aeruginosa pathogenesis.