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 zon ula occludens toxin (ZOT) was studied using several in vitro and ex vi vo models, ZOT showed a selective effect among various cell lines test ed, suggesting that it may interact with a specific receptor, whose su rface expression on various cells differs. When tested in IEC6 cell mo nolayers, ZOT-containing supernatants induced a redistribution of the F-actin cytoskeleton, Similar results were obtained with rabbit heal m ucosa, where the reorganization of F-actin paralleled the increase in tissue permeability, In endothelial cells, the cytoskeletal rearrangem ent involved a decrease of the soluble G-actin pool (-27%) and a recip rocal increase in the filamentous F-actin pool (+22%), This actin poly merization was time- and dose-dependent, and was reversible. Pretreatm ent with a specific protein kinase C inhibitor, CGP41251, completely a bolished the ZOT effects on both tissue permeability and actin polymer ization, In IEC6 cells ZOT induced a peak increment of the PKC-alpha i soform after 3 min incubation, Taken together, these results suggest t hat ZOT activates a complex intracellular cascade of events that regul ate tight junction permeability, probably mimicking the effect of phys iologic modulator(s) of epithelial barrier function.