Interaction of Ipa proteins of Shigella flexneri with α5β1 integrin promotes entry of the bacteria into mammalian cells

Abstract

Shigella is a genus of highly adapted bacterial pathogens that cause bacillary dysentery in humans. Bacteria reaching the colon invade intestinal epithelial cells by a process of bacterial-directed endocytosis mediated by the Ipa proteins: IpaB, IpaC, and IpaD of Shigella. The invasion of epithelial cells is though to be a receptor-mediated phenomenon, 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) cell monolayers, the Ipa proteins were capable of interacting directly with α5β1 integrin. The invasive capacity of S. flexneri for CHO cells increased as levels of α5β1 integrin were elevated. When CHO cells were infected with S. flexneri, the tyrosine phosphorylation both of pp 125(LAK), an integrin-regulated 125 K focal adhesion kinase, and of paxillin was stimulated. In contrast, and isogenic strain of S. flexneri that was defective in invasion owing to a mutation in its spa32 gene failed to induce such phosphorylation. Under in vitro and in vivo conditions, the released IpaB, IpaC, and IpaD proteins bound to α5β1 integrin in a manner different from that of solution fibronectin but similar to that of the tissue form of fibronectin. At the site of attachment of S. flexneri to CHO cells, α5β1 integrin converged with polymerization of actin. These data thus suggest that the capacity of Ipa proteins to interact with α5β1 integrin may be an important Shigella factor in triggering the reorganization of actin cytoskeletons.