@article{KronesRuehlingBeckeretal.2021,
  author    = {Krones, David and R{\"u}hling, Marcel and Becker, Katrin Anne and Kunz, Tobias C. and Sehl, Carolin and Paprotka, Kerstin and Gulbins, Erich and Fraunholz, Martin},
  title     = {Staphylococcus aureus α-Toxin Induces Acid Sphingomyelinase Release From a Human Endothelial Cell Line},
  series = {Frontiers in Microbiology},
  volume    = {12},
  journal   = {Frontiers in Microbiology},
  issn      = {1664-302X},
  doi       = {10.3389/fmicb.2021.694489},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-244843},
  year      = {2021},
  abstract  = {Staphylococcus aureus (S. aureus) is well known to express a plethora of toxins of which the pore-forming hemolysin A (α-toxin) is the best-studied cytolysin. Pore-forming toxins (PFT) permeabilize host membranes during infection thereby causing concentration-dependent effects in host cell membranes ranging from disordered ion fluxes to cytolysis. Host cells possess defense mechanisms against PFT attack, resulting in endocytosis of the breached membrane area and delivery of repair vesicles to the insulted plasma membrane as well as a concurrent release of membrane repair enzymes. Since PFTs from several pathogens have been shown to recruit membrane repair components, we here investigated whether staphylococcal α-toxin is able to induce these mechanisms in endothelial cells. We show that S. aureus α-toxin induced increase in cytosolic Ca2+ in endothelial cells, which was accompanied by p38 MAPK phosphorylation. Toxin challenge led to increased endocytosis of an extracellular fluid phase marker as well as increased externalization of LAMP1-positive membranes suggesting that peripheral lysosomes are recruited to the insulted plasma membrane. We further observed that thereby the lysosomal protein acid sphingomyelinase (ASM) was released into the cell culture medium. Thus, our results show that staphylococcal α-toxin triggers mechanisms in endothelial cells, which have been implicated in membrane repair after damage of other cell types by different toxins.},
  language  = {en}
}
@article{MaGulbinsEdwardsetal.2017,
  author    = {Ma, Jie and Gulbins, Erich and Edwards, Michael J. and Caldwell, Charles C. and Fraunholz, Martin and Becker, Katrin Anne},
  title     = {Staphylococcus aureus α-toxin induces inflammatory cytokines via lysosomal acid sphingomyelinase and ceramides},
  series = {Cellular Physiology and Biochemistry},
  volume    = {43},
  journal   = {Cellular Physiology and Biochemistry},
  number    = {6},
  doi       = {10.1159/000484296},
  url       = {http://nbn-resolving.de/urn:nbn:de:bvb:20-opus-181481},
  pages     = {2170-2184},
  year      = {2017},
  abstract  = {Staphylococcus aureus (S. aureus) infections are a major clinical problem and range from mild skin and soft-tissue infections to severe and even lethal infections such as pneumonia, endocarditis, sepsis, osteomyelitis, and toxic shock syndrome. Toxins that are released from S. aureus mediate many of these effects. Here, we aimed to identify molecular mechanisms how α-toxin, a major S. aureus toxin, induces inflammation. Methods: Macrophages were isolated from the bone marrow of wildtype and acid sphingomyelinase-deficient mice, stimulated with S. aureus α-toxin and activation of the acid sphingomyelinase was quantified. The subcellular formation of ceramides was determined by confocal microscopy. Release of cathepsins from lysosomes, activation of inflammasome proteins and formation of Interleukin-1β (IL-1β) and Tumor Necrosis Factor-α (TNF-α) were analyzed by western blotting, confocal microscopy and ELISA. Results: We demonstrate that S. aureus α-toxin activates the acid sphingomyelinase in ex vivo macrophages and triggers a release of ceramides. Ceramides induced by S. aureus α-toxin localize to lysosomes and mediate a release of cathepsin B and D from lysosomes into the cytoplasm. Cytosolic cathepsin B forms a complex with Nlrc4. Treatment of macrophages with α-toxin induces the formation of IL-1β and TNF-α. These events are reduced or abrogated, respectively, in cells lacking the acid sphingomyelinase and upon treatment of macrophages with amitriptyline, a functional inhibitor of acid sphingomyelinase. Pharmacological inhibition of cathepsin B prevented activation of the inflammasome measured as release of IL-1β, while the formation of TNF-α was independent of cathepsin B. Conclusion: We demonstrate a novel mechanism how bacterial toxins activate the inflammasome and mediate the formation and release of cytokines: S. aureus α-toxin triggers an activation of the acid sphingomyelinase and a release of ceramides resulting in the release of lysosomal cathepsin B and formation of pro-inflammatory cytokines.},
  language  = {en}
}