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Published on: September 18, 2020
Identification of macrophage and stress-induced proteins of Mycobacterium tuberculosis
1Department of Medicine, School of Medicine, University of California, Los Angeles 90095, USA.
Abstract:
Using phosphorimager technology to quantitate differences in protein expression, we have investigated the modulation of protein synthesis by Mycobacterium tuberculosis in response to intracellular residence in human macrophages and, for comparison, in response to various stress conditions during extracellular growth. Proteins of M. tuberculosis growing intracellularly in human THP-1 cells and extracellularly in broth were labeled with [35S]methionine; during intracellular growth, host cell protein synthesis was inhibited with cycloheximide. The metabolically labeled proteins were separated by two-dimensional gel electrophoresis and quantitatively analyzed. Intracellular residence in macrophages induced a profound change in the overall phenotype of M. tuberculosis. The expression of at least 16 M. tuberculosis proteins was induced (at least a twofold increase compared with growth in broth) and 28 proteins repressed (at least a twofold decrease). Many of the phenotypic changes in protein expression induced during intracellular growth occurred during extracellular growth in response to stress conditions including heat-shock, low pH, and H2O2. However, the pattern of induced and repressed proteins was unique to each stress condition. Of the 16 macrophage-induced proteins, 6 were absent during extracellular growth under both normal and stress conditions. Such proteins are potential virulence determinants and/or they may be important in the cell-mediated and protective immune response to M. tuberculosis infection.
Insights
Mycobacterium tuberculosis significantly alters protein expression within human macrophages, with some induced proteins unique to the intracellular environment. These unique proteins may be crucial for virulence and immune response during tuberculosis infection.
Area of Science:
- Microbiology
- Immunology
- Molecular Biology
Background:
- Mycobacterium tuberculosis (M. tuberculosis) is a pathogen that resides within human macrophages.
- Understanding M. tuberculosis protein expression changes during intracellular residence is crucial for identifying virulence factors and host immune response mechanisms.
Purpose of the Study:
- To investigate the modulation of M. tuberculosis protein synthesis in response to intracellular residence in human macrophages.
- To compare these changes with those induced by various stress conditions during extracellular growth.
Main Methods:
- Proteins of M. tuberculosis were metabolically labeled with [35S]methionine during intracellular growth in THP-1 cells and extracellular broth.
- Host cell protein synthesis was inhibited with cycloheximide during intracellular growth.
- Labeled proteins were separated by two-dimensional gel electrophoresis and quantitatively analyzed using phosphorimager technology.
Main Results:
- Intracellular residence induced significant changes in M. tuberculosis protein expression: 16 proteins were induced (≥2-fold increase) and 28 were repressed (≥2-fold decrease) compared to broth growth.
- Many stress-induced protein expression changes observed during extracellular growth mirrored those during intracellular growth, but stress-specific patterns emerged.
- Six of the 16 macrophage-induced proteins were not detected during extracellular growth under normal or stress conditions.
Conclusions:
- Intracellular residence profoundly alters the M. tuberculosis phenotype.
- The unique proteins induced during macrophage residence are potential virulence determinants.
- These unique proteins may also play a significant role in the cell-mediated and protective immune response to M. tuberculosis infection.
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