Involvement of α5β1 integrins in interleukin 8 production induced by oral viridans streptococcal protein I/IIf in cultured endothelial cells

Using human endothelial cells, we define a mechanism that accounts for the induction of interleukin 8 (IL-8) by protein I/IIf, an adhesin from Streptococcus mutans serotype f. We report that protein I/IIf interactions with endothelial cells increased the tyrosine phosphorylation of three cellular components with relative mass of 145 000, 125 000 and 70 000 in endothelial cells. These proteins were identified as phospholipase C gamma (PLC gamma), focal adhesion kinase (FAK) and paxillin after immunoprecipitation with monoclonal antibodies (mAbs) and immunoblotting with antiphosphotyrosine mAbs. These results suggested that beta 1 integrins could be one of the components implicated in the modulin activity of protein I/IIf. By incubating protein I/IIf with either purified alpha 5 beta 1 integrins or with alpha 5 beta 1 integrins overexpressing CHO cells, we demonstrated that alpha 5 beta 1 integrins act as cell receptors for protein I/IIf. We also showed that protein I/IIf interactions with alpha 5 beta 1 integrins lead to IL-8 secretion. Using specific inhibitors, we demonstrated that protein I/IIf-induced IL-8 release involves mitogen-activated protein kinases (MAPKs), and that PLC gamma and PKC also seem to contribute to protein I/IIf stimulation. However, PI-3K activation is not involved in IL-8 release. Altogether, these results indicate that, after binding to alpha 5 beta 1 integrins, protein I/IIf induces IL-8 release by activating the MAPKs signalling pathways.