toxins Article Major Determinants of Airway Epithelial Cell Sensitivity to S. aureus Alpha-Toxin: Disposal of Toxin Heptamers by Extracellular Vesicle Formation and Lysosomal Degradation Nils Möller 1,* , Sabine Ziesemer 1, Christian Hentschker 2, Uwe Völker 2 and Jan-Peter Hildebrandt 1 1 Animal Physiology and Biochemistry, University of Greifswald, Felix Hausdorff-Strasse 1, D-17489 Greifswald, Germany;
[email protected] (S.Z.);
[email protected] (J.-P.H.) 2 Department of Functional Genomics, Interfaculty Institute for Genetics and Functional Genomics, University Medicine Greifswald, Felix Hausdorff-Strasse 8, D-17475 Greifswald, Germany;
[email protected] (C.H.);
[email protected] (U.V.) * Correspondence:
[email protected] Abstract: Alpha-toxin is a major virulence factor of Staphylococcus aureus. Monomer binding to host cell membranes results in the formation of heptameric transmembrane pores. Among human model airway epithelial cell lines, A549 cells were most sensitive toward the toxin followed by 16HBE14o- and S9 cells. In this study we investigated the processes of internalization of pore-containing plasma membrane areas as well as potential pathways for heptamer degradation (lysosomal, proteasomal) or disposal (formation of exosomes/micro-vesicles). The abundance of toxin heptamers upon applying an alpha-toxin pulse to the cells declined both in extracts of whole cells and of cellular membranes of Citation: Möller, N.; Ziesemer, S.; S9 cells, but not in those of 16HBE14o- or A549 cells. Comparisons of heptamer degradation rates un- Hentschker, C.; Völker, U.; der inhibition of lysosomal or proteasomal degradation revealed that an important route of heptamer Hildebrandt, J.-P.