Evidence that tyrosine phosphorylation may increase tight junction permeability

Tight junction permeability control is important in a variety of physiological and pathological processes. We have investigated the role of tyrosine phosphorylation in the regulation of tight junction permeability. MDCK epithelial cells and brain endothelial cells were grown on filters and tight junction permeability was determined by transcellular electrical resistance (TER). The tyrosine phosphatase inhibitor pervanadate caused a concentration- and time-dependent decrease in TER in both MDCK and brain endothelial cells. However, as expected, pervanadate resulted in the tyrosine phosphorylation of many proteins; hence interpretation of its effects are extremely difficult. Phenylarsine oxide, a more selective tyrosine phosphatase inhibitor, caused the tyrosine phosphorylation of relatively few proteins as analyzed by immunoblotting of whole cell lysates. This inhibitor, like pervanadate, also elicited a decrease in TER in the two cell types. In the MDCK cells, the action of phenylarsine oxide could be reversed by the subsequent addition of the reducing agent 2,3-dimercaptopropanol. Immunocytochemistry revealed that phenylarsine oxide rapidly stimulated the tyrosine phosphorylation of proteins associated with intercellular junctions. Because of the known influence of the adherens junction on tight junctions, we analyzed immunoprecipitates of the E-cadherin/catenin complex from MDCK cells treated with phenylarsine oxide. This revealed an increase in the tyrosine phosphorylation of beta-catenin, but not of alpha-catenin. However, the tight junction associated protein ZO-1 was also tyrosine phosphorylated after PAO treatment. These data indicate that tight junction permeability may be regulated via mechanisms involving tyrosine phosphorylation of adherens junction and tight junction proteins.