THE SECRETED IPA COMPLEX OF SHIGELLA-FLEXNERI PROMOTES ENTRY INTO MAMMALIAN-CELLS

The bacterial pathogen Shigella flexneri causes bacillary dysentery in humans by invading colonocytes. Upon contact with epithelial cells, S . flexneri elicits localized plasma membrane projections sustained by long actin filaments which engulf the microorganism. The products nece ssary for Shigella entry include three secretory proteins: IpaB, IpaC, and IpaD. Extracellular IpaB and IpaC associate in a soluble complex, the Ipa complex. We have immunopurified this Ipa complex on latex bea ds and found that they were efficiently internalized into HeLa cells. Like S. flexneri entry, uptake of the beads bearing the Ipa complex wa s associated with membrane projections and polymerization of actin at the site of cell-bead interaction and was dependent on small Rho GTPas es. These results indicate that a secreted factor can promote S. flexn eri entry into epithelial cells.