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Decreased glycogen synthase kinase 3-beta levels and related physiological changes in Bacillus anthracis lethal
Amy E Tucker1, Isabelle I Salles, Daniel E Voth
1Department of Botany and Microbiology, The University of Oklahoma, Norman 73019, USA.
Abstract:
The lethal factor (LF) component of Bacillus anthracis lethal toxin (LeTx) cleaves mitogen activated protein kinase kinases (MAPKKs) in a variety of different cell types, yet only macrophages are rapidly killed by this toxin. The reason for this selective killing is unclear, but suggests other factors may also be involved in LeTx intoxication. In the current study, DNA membrane arrays were used to identify broad changes in macrophage physiology after treatment with LeTx. Expression of genes regulated by MAPKK activity did not change significantly, yet a series of genes under glycogen synthase kinase-3-beta (GSK-3beta) regulation changed expression following LeTx treatment. Correlating with these transcriptional changes GSK-3beta was found to be below detectable levels in toxin-treated cells and an inhibitor of GSK-3beta, LiCl, sensitized resistant IC-21 macrophages to LeTx. In addition, zebrafish embryos treated with LeTx showed signs of delayed pigmentation and cardiac hypertrophy; both processes are subject to regulation by GSK-3beta. A putative compensatory response to loss of GSK-3beta was indicated by differential expression of three motor proteins following toxin treatment and Kif1C, a motor protein involved in sensitivity to LeTx, increased expression in toxin-sensitive cells yet decreased in resistant cells following toxin treatment. Differential expression of microtubule-associating proteins and a decrease in the level of cellular tubulin were detected in LeTx-treated cells, both of which can result from loss of GSK-3beta activity. These data provide new information on LeTx's overall influence on macrophage physiology and suggest loss of GSK-3beta contributes to cytotoxicity.
Insights
Bacillus anthracis lethal toxin (LeTx) selectively kills macrophages by targeting glycogen synthase kinase-3-beta (GSK-3beta). Loss of GSK-3beta activity contributes to LeTx cytotoxicity, impacting cellular processes and motor protein regulation.
Area of Science:
- Cellular Biology
- Toxicology
- Molecular Biology
Background:
- Bacillus anthracis lethal toxin (LeTx) contains a lethal factor (LF) that cleaves mitogen-activated protein kinase kinases (MAPKKs).
- While LeTx affects many cell types, only macrophages are rapidly killed, indicating unknown factors contribute to its selective toxicity.
Purpose of the Study:
- To investigate broad physiological changes in macrophages following LeTx treatment.
- To identify specific cellular pathways and factors involved in LeTx-induced macrophage cytotoxicity.
Main Methods:
- DNA membrane arrays were employed to analyze global gene expression changes in macrophages post-LeTx exposure.
- Levels of glycogen synthase kinase-3-beta (GSK-3beta) were measured in treated and untreated cells.
- The effect of a GSK-3beta inhibitor (LiCl) on LeTx sensitivity was assessed.
- Phenotypic changes in zebrafish embryos exposed to LeTx were observed.
Main Results:
- LeTx treatment did not significantly alter genes regulated by MAPKKs but induced changes in genes regulated by GSK-3beta.
- GSK-3beta levels decreased significantly in LeTx-treated macrophages.
- Inhibition of GSK-3beta sensitized resistant macrophages to LeTx.
- Zebrafish embryos exhibited delayed pigmentation and cardiac hypertrophy, processes regulated by GSK-3beta.
- Differential expression of motor proteins, including Kif1C, and changes in microtubule-associated proteins and tubulin levels were observed.
Conclusions:
- Loss of GSK-3beta activity is a key factor contributing to LeTx-induced macrophage cytotoxicity.
- LeTx intoxication involves broader cellular dysregulation beyond MAPKK cleavage, including GSK-3beta pathways.
- GSK-3beta plays a significant role in macrophage physiology and response to LeTx, influencing motor protein function and cellular integrity.