α-Hemolysin enhancesStaphylococcus aureusinternalization and survival within mast cells by modulating the expression of β1 integrin

Mast cells (MCs) are important sentinels of the host defence against invading pathogens. We previously reported that Staphylococcus aureus evaded the extracellular antimicrobial activities of MCs by promoting its internalization within these cells via β1 integrins. Here, we investigated the molecular mechanisms governing this process. We found that S. aureus responded to the antimicrobial mediators released by MCs by up-regulating the expression of α-hemolysin (Hla), fibronectin-binding protein A and several regulatory systems. We also found that S. aureus induced the up-regulation of β1 integrin expression on MCs and that this effect was mediated by Hla-ADAM10 (a disintegrin and metalloproteinase 10) interaction. Thus, deletion of Hla or inhibition of Hla-ADAM10 interaction significantly impaired S. aureus internalization within MCs. Furthermore, purified Hla but not the inactive HlaH35L induced up-regulation of β1 integrin expression in MCs in a dose-dependent manner. Our data support a model in which S. aureus counter-reacts the extracellular microbicidal mechanisms of MCs by increasing expression of fibronectin-binding proteins and by inducing Hla-ADAM10-mediated up-regulation of β1 integrin in MCs. The up-regulation of bacterial fibronectin-binding proteins, concomitantly with the increased expression of its receptor β1 integrin on the MCs, resulted in enhanced S. aureus internalization through the binding of fibronectin-binding proteins to integrin β1 via fibronectin.