SOLUBLE INVASION PLASMID ANTIGEN-C (IPAC) FROM SHIGELLA-FLEXNERI ELICITS EPITHELIAL-CELL RESPONSES RELATED TO PATHOGEN INVASION

Shigella flexneri invades colonic epithelial cells by pathogen-induced phagocytosis, The three proposed effecters of S. flexneri internaliza tion are invasion plasmid antigens B (IpaB), IpaC, and IpaD, which are encoded on the pathogen's 230-kb virulence plasmid and translocated t o the extracellular milieu via the Mxi-Spa translocon. To date, there are no definitive functional data for any purified Ipa protein, Here, we describe the first characterization of highly purified recombinant IpaC, which elicits numerous epithelial cell responses related to even ts that take place during pathogen invasion, I-125-labeled IpaC binds cultured Henle 407 intestinal cells with an apparent dissociation cons tant in the low micromolar range, Moreover, incubation of epithelial c ells with IpaC results in general changes in cellular phosphoprotein c ontent, demonstrating this protein's ability to influence cellular pro tein kinase activities, These results contrast dramatically with those seen for recombinant IpaD, which does not bind to or induce detectabl e changes in the normal activities of cultured epithelial cells. In ad dition to influencing host cell activities, preincubation of epithelia l cells with purified IpaC enhances uptake of S. flexneri by host cell s, A similar result is seen when the cells are preincubated with a hig hly concentrated water extract of virulent S. flexneri 2a (strain 2457 T). Interestingly, soluble IpaC also appears to promote uptake of the noninvasive S. flexneri 2a strain BS103. Purified IpaD failed to enhan ce the uptake of virulent S. flexneri and did not facilitate uptake of BS103, Taken together, the data suggest that IpaC is a potential effe ctor of the host cell biological activities and may be responsible for entry of S. flexneri into target cells.