B-234. Mechanisms of Interferon-Induced Resistance to Staphylococcal Alpha-Toxin

T. O. Yarovinsky1, P. J. Sims2, M. Husmann3;
1Yale Univ., New Haven, CT, 2Univ. of Rochester Med. Ctr., Rochester, NY, 3Inst. of Med. Microbiology and Hygiene, Johannes Gutenberg-Univ. Main, Mainz, GERMANY.

BACKGROUND. Staphylococcal α-toxin contributes to the pathogenesis of staphylococcal infections by inducing necrotic cell death and excessive inflammation. We have recently found that pretreatment with interferons (IFNs) decreases α-toxin-induced cell death and production of pro-inflammatory cytokines. Although the protective effects of IFNs were not dependent on MAP-kinase or caspase-1 activities, inhibition of fatty acid synthase activity with cerulenin sensitized cells to α-toxin and negated IFN-induced protection. In this study, we explored the role of turnover of plasma membrane phospholipids in IFN-induced resistance to staphylococcal α-toxin. METHODS. In vitro cell cultures of human mononuclear phagocytes (THP-1 cells) were used to evaluate the role of candidate lipogenic genes in IFN-induced protection from α-toxin. Intracellular potassium efflux following α-toxin exposure was measured using cell permeable potassium indicator PBFI-AM and fluorimetry. Altered distribution of membrane phospholipids was analyzed by annexin V binding and flow cytometry. RESULTS. We found that pretreatment with IFNα had no effect on α-toxin binding and oligomerization. However, IFNα-treated cells showed decreased efflux of intracellular potassium through α-toxin pores in the plasma membrane. IFNα induced phospholipid scramblase 1 and disrupted plasma membrane asymmetry as evidenced by increased annexin V binding to non-apoptotic cells. IFNα-induced protection from α-toxin was not dependent on activation of sterol response element binding proteins, sphingomyelinase activity or serum-derived factors, such as low-density lipoproteins, but required extracellular calcium. CONCLUSIONS. Our data suggest that IFN-induced protection from α-toxin is mediated, at least in part, by induction of phospholipids scramblase 1, which is involved in calcium-dependent translocation of membrane phospholipids.