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Inhibition of macromolecular synthesis in cultured macrophages by Pseudomonas pseudomallei exotoxin
1Department of Biochemistry, Life Science Faculty, Universiti Kebangsaan Malaysia, Selangor.
Abstract:
Pseudomonas pseudomallei exotoxin was found to be a potent inhibitor of protein and DNA synthesis in cultured macrophages. Inhibition of DNA synthesis occurred at toxin concentrations as low as 1-2 micrograms/ml and inhibition of 3H-thymidine uptake was almost complete at concentrations of 8 micrograms/ml or more. A close correlation between cell damage and inhibition by DNA synthesis was observed. For protein synthesis, inhibition was obtained at much lower doses (0.06-2.0 micrograms/ml) of the toxin. At similar toxin concentrations, DNA synthesis was marginally affected. Further, it was shown that protein synthesis inhibition occurred almost immediately after incubation, reaching its maximal inhibitory effect of 70% after 6 hr. DNA synthesis, however, was minimally affected by a similar toxin concentration even after 10 hr of incubation. The inhibition of macromolecular synthesis in macrophages by P. pseudomallei exotoxin may be relevant to its modulatory effect on the host defense mechanism.
Insights
Pseudomonas pseudomallei exotoxin strongly inhibits protein and DNA synthesis in macrophages. Protein synthesis is affected at lower doses and faster than DNA synthesis, impacting host defense mechanisms.
Area of Science:
- Microbiology
- Cell Biology
- Toxicology
Background:
- Pseudomonas pseudomallei exotoxin is a virulence factor.
- Understanding its cellular targets is crucial for elucidating its pathogenicity.
Purpose of the Study:
- To investigate the effects of P. pseudomallei exotoxin on protein and DNA synthesis in cultured macrophages.
- To determine the dose- and time-dependency of the exotoxin's inhibitory effects.
Main Methods:
- Cultured macrophages were incubated with varying concentrations of P. pseudomallei exotoxin.
- Inhibition of protein synthesis was measured by [3H]-leucine incorporation.
- Inhibition of DNA synthesis was measured by [3H]-thymidine uptake.
Main Results:
- P. pseudomallei exotoxin potently inhibited both protein and DNA synthesis in macrophages.
- Protein synthesis inhibition occurred at significantly lower toxin concentrations (0.06-2.0 µg/ml) and faster than DNA synthesis inhibition.
- Maximal protein synthesis inhibition (70%) was observed after 6 hours, while DNA synthesis was minimally affected even after 10 hours.
- A correlation between cell damage and DNA synthesis inhibition was noted.
Conclusions:
- P. pseudomallei exotoxin differentially affects macromolecular synthesis in macrophages, with a more pronounced and rapid effect on protein synthesis.
- These findings suggest a mechanism by which the exotoxin may modulate the host defense response.