Mechanisms of intestinal epithelial tight junction disruption by enteropathogenic Escherichia coli

Enteropathogenic Escherichia coli (EPEC), a diarrheic intestinal pathogen that attaches to the gastrointestinal mucosa, facilitate infection by interfering with host cell function. The EPEC-induced alterations in tight junction structure and function were characterized by analyzing cultured epithelial monolayers in the absence and presence of EPEC bacteria. Dramatic disruption of protein-protein interactions and tight junction ultrastructure were observed following infection and the mechanism of this disruption was further analyzed. Modulations in cytoskeletal contraction through the activation of myosin light chain kinase were determined to facilitate a portion of the tight junction changes. Tight junction modulating effects appeared to be partly due to expression of an EPEC gene, orf3. Furthermore, increased endocytosis of the TJ proteins accounted for the dramatic loss of functional barrier. These events correlated strongly with the expression of bacterial EspF. Loss of functional tight junctions also led to failure of cell polarity. The mislocalization of previously polarized ligands such as beta1-integrin allowed for increased attachment to the cell surface and facilitated pathogenesis. Characterization of tight junction changes and the causative mechanisms led to fine tuning of the pathogenesis model. The dramatic alterations in tight junctions likely contribute to variations in host cell biology and diarrheal disease.