Streptococcus mutans antigen I/II binds to α5β1 integrins via its A-domain and increases β1 integrins expression on periodontal ligament fibroblast cells

The cell wall anchored protein I/II of Streptococcus mutans plays a significant role in colonizing the dental structures and induces the synthesis of proinflammatory cytokines after binding to α5β1 integrins of host cells. Whilst the signalling pathways triggered by bound protein I/II and leading to the release of proinflammatory cytokines has been extensively studied, the molecular mechanisms of binding of protein I/II to this host cell factor remain more elusive. Using a panel of purified recombinant polypeptides corresponding to defined domains of the streptococcal protein I/II, we aimed to better characterize protein I/II-α5β1 integrins interaction. Our results show that the A region plays a major role in binding of protein I/II to α5β1 integrin. Using specific inhibitors, we demonstrated that this interaction requires β subunits of the integrin and that the glycosylated residues of the integrin interact with the V-region of the protein I/IIf. Periodontal fibroblasts (PDL-Fb) express β1-integrins on their cell membrane. Stimulation with protein I/II increases the expression of β1-integrins. These data suggest a modulatory effect of the streptococcal protein I/II on expression of integrins by PDL-Fb. This might have important implication for understanding the role of PDL-Fb cells in periradicular inflammation.