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alpha-Toxin is a mediator of Staphylococcus aureus-induced cell death and activates caspases via the intrinsic death pathway independently of death receptor signaling.

Bantel H, Sinha B, Domschke W, Peters G, Schulze-Osthoff K, Jänicke RU - J. Cell Biol. (2001)

Bottom Line: Furthermore, alpha-toxin-induced caspase activation in CD95-resistant Jurkat sublines lacking CD95, Fas-activated death domain, or caspase-8 but not in cells stably expressing the antiapoptotic protein Bcl-2.Together with our finding that alpha-toxin induces cytochrome c release in intact cells and, interestingly, also from isolated mitochondria in a Bcl-2-controlled manner, our results demonstrate that S. aureus alpha-toxin triggers caspase activation via the intrinsic death pathway independently of death receptors.Hence, our findings clearly define a signaling pathway used in S. aureus-induced cytotoxicity and may provide a molecular rationale for future therapeutic interventions in bacterial infections.

View Article: PubMed Central - PubMed

Affiliation: Department of Immunology and Cell Biology, University of Münster, 48149 Münster, Germany.

ABSTRACT
Infections with Staphylococcus aureus, a common inducer of septic and toxic shock, often result in tissue damage and death of various cell types. Although S. aureus was suggested to induce apoptosis, the underlying signal transduction pathways remained elusive. We show that caspase activation and DNA fragmentation were induced not only when Jurkat T cells were infected with intact bacteria, but also after treatment with supernatants of various S. aureus strains. We also demonstrate that S. aureus-induced cell death and caspase activation were mediated by alpha-toxin, a major cytotoxin of S. aureus, since both events were abrogated by two different anti-alpha-toxin antibodies and could not be induced with supernatants of an alpha-toxin-deficient S. aureus strain. Furthermore, alpha-toxin-induced caspase activation in CD95-resistant Jurkat sublines lacking CD95, Fas-activated death domain, or caspase-8 but not in cells stably expressing the antiapoptotic protein Bcl-2. Together with our finding that alpha-toxin induces cytochrome c release in intact cells and, interestingly, also from isolated mitochondria in a Bcl-2-controlled manner, our results demonstrate that S. aureus alpha-toxin triggers caspase activation via the intrinsic death pathway independently of death receptors. Hence, our findings clearly define a signaling pathway used in S. aureus-induced cytotoxicity and may provide a molecular rationale for future therapeutic interventions in bacterial infections.

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S. aureusα-toxin induces cytochrome c release in intact cells and isolated mitochondria in a Bcl-2–controlled manner. (A) Western blot analysis of cytosolic cytochrome c in Jurkat cells treated for the indicated times with 0.03 μg/ml α-toxin or for 8 h with 1 μg/ml staurosporine (Stauro). (B) Effect of α-toxin on isolated mitochondria. Isolated mitochondria from Jurkat (lanes 1–7) or from Bcl-2–overexpressing Jurkat cells (lanes 8–14) were incubated for 30 min with a buffer control (lanes 2 and 9), 10 μg/ml betulinic acid (lanes 3 and 10), or the indicated concentrations of α-toxin (lanes 4–7 and 11–14). The release of cytochrome c was detected by immunoblotting. Lanes 1 and 8 (total mitos) represent the complete amount of cytochrome c present in mitochondria from Jurkat and Jurkat Bcl-2 cells, respectively. (C) Measurement of the mitochondrial transmembrane potential (ΔΨm) in untreated (Control) Jurkat and Jurkat Bcl-2 cells or in cells treated for 4 h with etoposide or the indicated concentrations of α-toxin.
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fig9: S. aureusα-toxin induces cytochrome c release in intact cells and isolated mitochondria in a Bcl-2–controlled manner. (A) Western blot analysis of cytosolic cytochrome c in Jurkat cells treated for the indicated times with 0.03 μg/ml α-toxin or for 8 h with 1 μg/ml staurosporine (Stauro). (B) Effect of α-toxin on isolated mitochondria. Isolated mitochondria from Jurkat (lanes 1–7) or from Bcl-2–overexpressing Jurkat cells (lanes 8–14) were incubated for 30 min with a buffer control (lanes 2 and 9), 10 μg/ml betulinic acid (lanes 3 and 10), or the indicated concentrations of α-toxin (lanes 4–7 and 11–14). The release of cytochrome c was detected by immunoblotting. Lanes 1 and 8 (total mitos) represent the complete amount of cytochrome c present in mitochondria from Jurkat and Jurkat Bcl-2 cells, respectively. (C) Measurement of the mitochondrial transmembrane potential (ΔΨm) in untreated (Control) Jurkat and Jurkat Bcl-2 cells or in cells treated for 4 h with etoposide or the indicated concentrations of α-toxin.

Mentions: To further examine the S. aureus–induced caspase activation pathway, we monitored the release of mitochondrial cytochrome c from Jurkat cells incubated for various times with α-toxin. Western blot analysis showed a time-dependent increase of cytochrome c release, which was first, although only marginally, visible after a 2-h exposure of the cells to α-toxin (Fig. 9 A). Nevertheless, continuous exposure of the cells to α-toxin resulted in increasing cytosolic cytochrome c levels that were comparable to those released after an 8-h treatment of cells with the kinase inhibitor staurosporine.


alpha-Toxin is a mediator of Staphylococcus aureus-induced cell death and activates caspases via the intrinsic death pathway independently of death receptor signaling.

Bantel H, Sinha B, Domschke W, Peters G, Schulze-Osthoff K, Jänicke RU - J. Cell Biol. (2001)

S. aureusα-toxin induces cytochrome c release in intact cells and isolated mitochondria in a Bcl-2–controlled manner. (A) Western blot analysis of cytosolic cytochrome c in Jurkat cells treated for the indicated times with 0.03 μg/ml α-toxin or for 8 h with 1 μg/ml staurosporine (Stauro). (B) Effect of α-toxin on isolated mitochondria. Isolated mitochondria from Jurkat (lanes 1–7) or from Bcl-2–overexpressing Jurkat cells (lanes 8–14) were incubated for 30 min with a buffer control (lanes 2 and 9), 10 μg/ml betulinic acid (lanes 3 and 10), or the indicated concentrations of α-toxin (lanes 4–7 and 11–14). The release of cytochrome c was detected by immunoblotting. Lanes 1 and 8 (total mitos) represent the complete amount of cytochrome c present in mitochondria from Jurkat and Jurkat Bcl-2 cells, respectively. (C) Measurement of the mitochondrial transmembrane potential (ΔΨm) in untreated (Control) Jurkat and Jurkat Bcl-2 cells or in cells treated for 4 h with etoposide or the indicated concentrations of α-toxin.
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Related In: Results  -  Collection

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fig9: S. aureusα-toxin induces cytochrome c release in intact cells and isolated mitochondria in a Bcl-2–controlled manner. (A) Western blot analysis of cytosolic cytochrome c in Jurkat cells treated for the indicated times with 0.03 μg/ml α-toxin or for 8 h with 1 μg/ml staurosporine (Stauro). (B) Effect of α-toxin on isolated mitochondria. Isolated mitochondria from Jurkat (lanes 1–7) or from Bcl-2–overexpressing Jurkat cells (lanes 8–14) were incubated for 30 min with a buffer control (lanes 2 and 9), 10 μg/ml betulinic acid (lanes 3 and 10), or the indicated concentrations of α-toxin (lanes 4–7 and 11–14). The release of cytochrome c was detected by immunoblotting. Lanes 1 and 8 (total mitos) represent the complete amount of cytochrome c present in mitochondria from Jurkat and Jurkat Bcl-2 cells, respectively. (C) Measurement of the mitochondrial transmembrane potential (ΔΨm) in untreated (Control) Jurkat and Jurkat Bcl-2 cells or in cells treated for 4 h with etoposide or the indicated concentrations of α-toxin.
Mentions: To further examine the S. aureus–induced caspase activation pathway, we monitored the release of mitochondrial cytochrome c from Jurkat cells incubated for various times with α-toxin. Western blot analysis showed a time-dependent increase of cytochrome c release, which was first, although only marginally, visible after a 2-h exposure of the cells to α-toxin (Fig. 9 A). Nevertheless, continuous exposure of the cells to α-toxin resulted in increasing cytosolic cytochrome c levels that were comparable to those released after an 8-h treatment of cells with the kinase inhibitor staurosporine.

Bottom Line: Furthermore, alpha-toxin-induced caspase activation in CD95-resistant Jurkat sublines lacking CD95, Fas-activated death domain, or caspase-8 but not in cells stably expressing the antiapoptotic protein Bcl-2.Together with our finding that alpha-toxin induces cytochrome c release in intact cells and, interestingly, also from isolated mitochondria in a Bcl-2-controlled manner, our results demonstrate that S. aureus alpha-toxin triggers caspase activation via the intrinsic death pathway independently of death receptors.Hence, our findings clearly define a signaling pathway used in S. aureus-induced cytotoxicity and may provide a molecular rationale for future therapeutic interventions in bacterial infections.

View Article: PubMed Central - PubMed

Affiliation: Department of Immunology and Cell Biology, University of Münster, 48149 Münster, Germany.

ABSTRACT
Infections with Staphylococcus aureus, a common inducer of septic and toxic shock, often result in tissue damage and death of various cell types. Although S. aureus was suggested to induce apoptosis, the underlying signal transduction pathways remained elusive. We show that caspase activation and DNA fragmentation were induced not only when Jurkat T cells were infected with intact bacteria, but also after treatment with supernatants of various S. aureus strains. We also demonstrate that S. aureus-induced cell death and caspase activation were mediated by alpha-toxin, a major cytotoxin of S. aureus, since both events were abrogated by two different anti-alpha-toxin antibodies and could not be induced with supernatants of an alpha-toxin-deficient S. aureus strain. Furthermore, alpha-toxin-induced caspase activation in CD95-resistant Jurkat sublines lacking CD95, Fas-activated death domain, or caspase-8 but not in cells stably expressing the antiapoptotic protein Bcl-2. Together with our finding that alpha-toxin induces cytochrome c release in intact cells and, interestingly, also from isolated mitochondria in a Bcl-2-controlled manner, our results demonstrate that S. aureus alpha-toxin triggers caspase activation via the intrinsic death pathway independently of death receptors. Hence, our findings clearly define a signaling pathway used in S. aureus-induced cytotoxicity and may provide a molecular rationale for future therapeutic interventions in bacterial infections.

Show MeSH
Related in: MedlinePlus