INTERACTION OF IPA PROTEINS OF SHIGELLA-FLEXNERI WITH ALPHA(5)BETA(1)INTEGRIN PROMOTES ENTRY OF THE BACTERIA INTO MAMMALIAN-CELLS

Shigella is a genus of highly adapted bacterial pathogens that cause b acillary dysentery in humans. Bacteria reaching the colon invade intes tinal epithelial cells by a process of bacterial-directed endocytosis mediated by the Ipa proteins: IpaB, IpaC, and IpaD of Shigella. The in vasion of epithelial cells is thought to be a receptor-mediated phenom enon, although the cellular components of the host that interact with the Ipa proteins have not yet been identified. We report here that in a Shigella flexneri invasive system and Chinese hamster ovary (CHO) ce ll monolayers, the Ipa proteins were capable of interacting directly w ith alpha(5) beta(1) integrin. The invasive capacity of S. flexneri fo r CHO cells increased as levels of alpha(5) beta(1) integrin were elev ated. When CHO cells were infected with S. flexneri, the tyrosine phos phorylation both of pp 125(FAK), an integrin-regulated 125 K focal adh esion kinase, and of paxillin was stimulated. In contrast, an isogenic strain of S. flexneri that was defective in invasion owing to a mutat ion in its spa32 gene failed to induce such phosphorylation. Under in vitro and in vivo conditions, the released IpaB, IpaC, and IpaD protei ns bound to alpha(5) beta(1) integrin in a manner different from that of soluble fibronectin but similar to that of the tissue form of fibro nectin. At the site of attachment of S. flexneri to CHO cells, alpha(5 ) beta(1) integrin converged with polymerization of actin. These data thus suggest that the capacity of Ipa proteins to interact with alpha( 5) beta(1) integrin may be an important Shigella factor in triggering the reorganization of actin cytoskeletons.