Translocated EspF protein from enteropathogenic Escherichia coli disrupts host intestinal barrier function

The mechanisms by which enteropathogenic Escherichia coli (EPEC), an import ant cause of diarrhea among infants in developing countries, induce symptom s are not defined. EPEC have a type III secretion system required for chara cteristic attaching and effacing changes that modify the cytoskeleton and a pical surface of host cells. Infection of polarized intestinal epithelial c ell monolayers by EPEC leads to a loss of transepithelial electrical resist ance, which also requires the type III secretion system. We demonstrate her e that EspF, a protein chat is secreted by EPEC via the type III secretion system, is not required for quantitatively and qualitatively typical attach ing and effacing lesion formation in intestinal epithelial cells. However, EspF is required in a dose-dependent fashion for the loss of transepithelia l electrical resistance, for increased monolayer permeability, and for redi stribution of the tight junction-associated protein occludin, Furthermore, the analysis of EPEC strains expressing EspF-adenylate cyclase fusion prote ins indicates that EspF is translocated via the type III secretion system t o the cytoplasm of host cells, a result: confirmed by immunofluorescence mi croscopy. These studies suggest a novel role for EspF as an effector pro re in that disrupts intestinal barrier function without involvement in attachi ng and effacing lesion formation.