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A bacterial invasin induces macrophage apoptosis by binding directly to ICE
Y Chen1, M R Smith, K Thirumalai
1Skirball Institute, Department of Microbiology and Kaplan Cancer Center, New York University School of Medicine, 540 First Avenue, New York, NY 10016, USA.
Abstract:
Shigella, the etiological agent of dysentery, kills macrophages by inducing apoptosis. Deletion mutants in the invasion invasion plasmid antigen B (ipaB) of Shigella flexneri are not cytotoxic. Here, we localized IpaB to the cytoplasm of macrophages infected with S. flexneri. Purified IpaB induced apoptosis when microinjected into macrophages, indicating that IpaB is sufficient to induce apoptosis. Using a GST-IpaB fusion protein as a ligand in affinity purification, we isolated four IpaB binding proteins from macrophages which were identified as the precursor and the mature polypeptides of interleukin-1beta converting enzyme (ICE) or a highly homologous protease. We found that IpaB binds directly to ICE and this enzyme is activated during S. flexneri infection. Furthermore, specific inhibitors of ICE prevented Shigella-induced apoptosis.
Insights
Shigella bacteria kill immune cells by triggering apoptosis. The study found that Shigella's invasion plasmid antigen B (IpaB) directly interacts with interleukin-1beta converting enzyme (ICE), leading to macrophage cell death.
Area of Science:
- Microbiology
- Immunology
- Cell Biology
Background:
- Shigella flexneri causes dysentery by inducing macrophage apoptosis.
- Invasion plasmid antigen B (IpaB) is crucial for Shigella's cytotoxic effects.
- The precise mechanism by which IpaB induces apoptosis is not fully understood.
Purpose of the Study:
- To investigate the role of IpaB in Shigella-induced macrophage apoptosis.
- To identify host cell proteins that interact with IpaB.
- To elucidate the molecular pathway linking IpaB to apoptosis.
Main Methods:
- Localization of IpaB within infected macrophages.
- Microinjection of purified IpaB into macrophages to assess its apoptotic potential.
- Affinity purification using a GST-IpaB fusion protein to identify binding partners.
- Enzyme activity assays and inhibition studies targeting interleukin-1beta converting enzyme (ICE).
Main Results:
- IpaB was localized to the cytoplasm of S. flexneri-infected macrophages.
- Purified IpaB alone was sufficient to induce macrophage apoptosis.
- Four IpaB-binding proteins were identified, including interleukin-1beta converting enzyme (ICE).
- IpaB directly binds to and activates ICE during infection.
- Inhibitors of ICE blocked Shigella-induced apoptosis.
Conclusions:
- IpaB is a key virulence factor that directly induces macrophage apoptosis.
- The interaction between IpaB and ICE is critical for Shigella pathogenesis.
- Targeting the IpaB-ICE interaction may offer therapeutic strategies against Shigella infections.