THE SECRETED ALPHA-HEMOLYSIN OF S. aureus ACTIVATES THE AUTOPHAGIC RESPONSE IN THE HOST CELL

MESTRE MB; FADER CM; SOLA C; COLOMBO MI

Sede del Gobierno, Universidad Nacional de Rosario, Rosario, Argentina

Congreso; XLIV Reunión Anual SAIB; 2008

Sociedad Argentina de Investigación Bioquímica y Biología Celular

S. aureus induces a caspase-independent cell death, with the participation of autophagy. This involves the sequestration of cytosolic components, organelles and microorganisms in a vacuole, the autophagosome, which finally fuses with the lysosome. Our purpose was to identify the factor(s) and the signalling pathway that participates in the activation of the autophagic response caused by S. aureus."-Hemolysin is a pore forming toxin secreted by S. aureus.CHO cells over-expressing GFP-LC3 (an autophagosome marker) were incubated with the toxin. This caused a marked activation of autophagy in a concentration-dependent manner. In order to address if the toxin is the only secreted factor responsible for the activation of autophagy, CHO GFP-LC3 cells were infected with the following S. aureus strains: wt, a mutant deficient for "-Hemolysin (Hla-) and the Hla (-) mutant expressing an "-Hemolysin plasmid. S. aureus wt as well as the mutant expressing the plasmid stimulated autophagy upon infection. In contrast, the Hla(-) mutant was unable of activating this pathway. In addition, we demonstrated that autophagy activation was calcium dependent, since this was hampered by the intracellular calcium chelator BAPTA-AM. Interestingly, the toxin effect was not prevented by the classical autophagy inhibitors 3-MA and Wortmannin, suggesting that the action of "-Hemolysin is independent of PI3K