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Induction of mycobacterial proteins during phagocytosis and heat shock: a time interval analysis
1Department of Microbiology and Immunology, George Washington University, Washington, DC.
Abstract:
Mycobacterium tuberculosis survives macrophage bactericidal activities by mechanisms that may include induction of stress proteins. We sought to determine whether the synthesis of any mycobacterial proteins is increased during phagocytosis and whether any of these proteins are also up-regulated during heat shock. Protein synthesis by M. tuberculosis H37Ra during phagocytosis by the mouse macrophage cell line IC-21, and during heat shock at 45 and 48 degrees C, was monitored at various time intervals using 35S-labeled methionine/cysteine and sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Our data suggest the existence of certain common elements in the stress response of mycobacteria to the three stress stimuli. This apparent similarity was best characterized by the up-regulation of a 25-kDa protein after exposure to each of the stress conditions. Furthermore, this 25-kDa protein and a 37-kDa protein that was also synthesized during phagocytosis appeared to be extracellular because they were preferentially solubilized when infected macrophages were lysed with 0.5% NP-40.
Insights
Mycobacterium tuberculosis increases synthesis of specific proteins, including a 25-kDa protein, when encountering macrophage stress or heat shock. These stress proteins may aid bacterial survival within macrophages.
Area of Science:
- Microbiology
- Immunology
- Molecular Biology
Background:
- Mycobacterium tuberculosis evades host immune defenses, particularly macrophage bactericidal activity.
- Induction of stress proteins is a potential mechanism for Mycobacterium tuberculosis survival.
- Understanding stress responses is crucial for developing novel therapeutic strategies.
Purpose of the Study:
- To investigate if Mycobacterium tuberculosis protein synthesis is upregulated during macrophage phagocytosis.
- To determine if these upregulated proteins are also induced by heat shock.
- To identify common stress response elements in Mycobacterium tuberculosis.
Main Methods:
- Utilized Mycobacterium tuberculosis H37Ra and mouse macrophage cell line IC-21.
- Monitored protein synthesis using 35S-labeled methionine/cysteine during phagocytosis and heat shock (45°C and 48°C).
- Analyzed protein expression via sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE).
Main Results:
- Identified a common stress response element characterized by the upregulation of a 25-kDa protein under phagocytosis and heat shock.
- Observed increased synthesis of a 37-kDa protein during phagocytosis.
- Both the 25-kDa and 37-kDa proteins were preferentially solubilized after NP-40 lysis, suggesting extracellular localization.
Conclusions:
- Mycobacterium tuberculosis exhibits common protein synthesis responses to phagocytosis and heat shock.
- A 25-kDa protein is significantly upregulated under these stress conditions, potentially contributing to bacterial survival.
- The extracellular nature of the 25-kDa and 37-kDa proteins suggests roles in host-pathogen interactions.
