H2O2-mediated permeability II: importance of tyrosine phosphatase and kinase activity

We previously reported that exposure of endothelial cells to H2O2results in a loss of cell-cell apposition and increased endothelial solute permeability. The purpose of this study was to determine how tyrosine phosphorylation and tyrosine phosphatases contribute to oxidant-mediated disorganization of endothelial cell junctions. We found that H2O2caused a rapid decrease in total cellular phosphatase activity that facilitates a compensatory increase in cellular phosphotyrosine residues. H2O2exposure also results in increased endothelial monolayer permeability, which was attenuated by pp60, an inhibitor of src kinase. Inhibition of protein tyrosine phosphatase activity by phenylarsine oxide (PAO) demonstrated a similar permeability profile compared with H2O2, suggesting that tyrosine phosphatase activity is important in maintaining a normal endothelial solute barrier. Immunofluorescence shows that H2O2exposure caused a loss of pan-reactive cadherin and β-catenin from cell junctions that was not blocked by the src kinase inhibitor PP1. H2O2also caused β-catenin to dissociate from the endothelial cytoskeleton, which was not prevented by PP1. Finally, we determined that PP1 did not prevent cadherin internalization. These data suggest that oxidants like H2O2produce biological effects through protein phosphotyrosine modifications by decreasing total cellular phosphatase activity combined with increased src kinase activity, resulting in increased endothelial solute permeability.