ZONULA OCCLUDENS TOXIN MODULATES TIGHT JUNCTIONS THROUGH PROTEIN-KINASE C-DEPENDENT ACTIN REORGANIZATION, IN-VITRO

The intracellular signaling involved in the mechanism of action of zonula occludens toxin (ZOT) was studied using several in vitro and ex vivo models, ZOT showed a selective effect among various cell lines tested, suggesting that it may interact with a specific receptor, whose surface expression on various cells differs. When tested in IEC6 cell monolayers, ZOT-containing supernatants induced a redistribution of the F-actin cytoskeleton, Similar results were obtained with rabbit heal mucosa, where the reorganization of F-actin paralleled the increase in tissue permeability, In endothelial cells, the cytoskeletal rearrangement involved a decrease of the soluble G-actin pool (-27%) and a reciprocal increase in the filamentous F-actin pool (+22%), This actin polymerization was time- and dose-dependent, and was reversible. Pretreatment with a specific protein kinase C inhibitor, CGP41251, completely abolished the ZOT effects on both tissue permeability and actin polymerization, In IEC6 cells ZOT induced a peak increment of the PKC-alpha isoform after 3 min incubation, Taken together, these results suggest that ZOT activates a complex intracellular cascade of events that regulate tight junction permeability, probably mimicking the effect of physiologic modulator(s) of epithelial barrier function.