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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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Both intact S. aureus cells and bacterial supernatants induce T cell apoptosis. Jurkat cells were incubated with live washed bacteria (A) or sterile-filtered supernatants of the same bacterial cultures (B). After the indicated times, the proportion of apoptotic cells was determined by flow cytometry. (A) Fresh suspensions of the indicated bacterial strains were added to Jurkat cells, resulting in a MOI of 30 (low) and 120 (high). Cells were incubated on ice for 2 h to allow sedimentation and then shifted to 37°C. Lysostaphin (20 μg/ml) was added to lyse and kill staphylococci. Lysostaphin without bacteria served as a negative control, whereas agonistic anti-CD95 was used as a positive control. (B) Fresh bacterial supernatants were added to Jurkat cells, resulting in a final concentration (vol/vol) of 0.1% (low) and 1% (high).
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fig1: Both intact S. aureus cells and bacterial supernatants induce T cell apoptosis. Jurkat cells were incubated with live washed bacteria (A) or sterile-filtered supernatants of the same bacterial cultures (B). After the indicated times, the proportion of apoptotic cells was determined by flow cytometry. (A) Fresh suspensions of the indicated bacterial strains were added to Jurkat cells, resulting in a MOI of 30 (low) and 120 (high). Cells were incubated on ice for 2 h to allow sedimentation and then shifted to 37°C. Lysostaphin (20 μg/ml) was added to lyse and kill staphylococci. Lysostaphin without bacteria served as a negative control, whereas agonistic anti-CD95 was used as a positive control. (B) Fresh bacterial supernatants were added to Jurkat cells, resulting in a final concentration (vol/vol) of 0.1% (low) and 1% (high).

Mentions: To assess the cytotoxic potential of different S. aureus strains and investigate whether intact bacteria are required for this process, Jurkat leukemic T cells were incubated with various cytotoxic or noncytotoxic S. aureus strains or with their respective culture supernatants. As measured by the formation of hypodiploid DNA, both washed whole bacteria (Fig. 1 A) of the cytotoxic and hemolytic S. aureus strains 6850 and RN6390 and their respective supernatants (Fig. 1 B) efficiently induced apoptosis of Jurkat cells in a dose- and time-dependent manner. Remarkably, cell death induction by either supernatants or intact bacteria was achieved to a similar extent and with similar kinetics as with an agonistic anti-CD95 antibody. In contrast, the noncytotoxic and nonhemolytic S. aureus strain Cowan I and the nonpathogenic S. carnosus strain TM300 did not induce cell death.


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)

Both intact S. aureus cells and bacterial supernatants induce T cell apoptosis. Jurkat cells were incubated with live washed bacteria (A) or sterile-filtered supernatants of the same bacterial cultures (B). After the indicated times, the proportion of apoptotic cells was determined by flow cytometry. (A) Fresh suspensions of the indicated bacterial strains were added to Jurkat cells, resulting in a MOI of 30 (low) and 120 (high). Cells were incubated on ice for 2 h to allow sedimentation and then shifted to 37°C. Lysostaphin (20 μg/ml) was added to lyse and kill staphylococci. Lysostaphin without bacteria served as a negative control, whereas agonistic anti-CD95 was used as a positive control. (B) Fresh bacterial supernatants were added to Jurkat cells, resulting in a final concentration (vol/vol) of 0.1% (low) and 1% (high).
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Related In: Results  -  Collection

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getmorefigures.php?uid=PMC2198876&req=5

fig1: Both intact S. aureus cells and bacterial supernatants induce T cell apoptosis. Jurkat cells were incubated with live washed bacteria (A) or sterile-filtered supernatants of the same bacterial cultures (B). After the indicated times, the proportion of apoptotic cells was determined by flow cytometry. (A) Fresh suspensions of the indicated bacterial strains were added to Jurkat cells, resulting in a MOI of 30 (low) and 120 (high). Cells were incubated on ice for 2 h to allow sedimentation and then shifted to 37°C. Lysostaphin (20 μg/ml) was added to lyse and kill staphylococci. Lysostaphin without bacteria served as a negative control, whereas agonistic anti-CD95 was used as a positive control. (B) Fresh bacterial supernatants were added to Jurkat cells, resulting in a final concentration (vol/vol) of 0.1% (low) and 1% (high).
Mentions: To assess the cytotoxic potential of different S. aureus strains and investigate whether intact bacteria are required for this process, Jurkat leukemic T cells were incubated with various cytotoxic or noncytotoxic S. aureus strains or with their respective culture supernatants. As measured by the formation of hypodiploid DNA, both washed whole bacteria (Fig. 1 A) of the cytotoxic and hemolytic S. aureus strains 6850 and RN6390 and their respective supernatants (Fig. 1 B) efficiently induced apoptosis of Jurkat cells in a dose- and time-dependent manner. Remarkably, cell death induction by either supernatants or intact bacteria was achieved to a similar extent and with similar kinetics as with an agonistic anti-CD95 antibody. In contrast, the noncytotoxic and nonhemolytic S. aureus strain Cowan I and the nonpathogenic S. carnosus strain TM300 did not induce cell death.

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