Abstract 10778: Balpha[[Unable to Display Character: ]]Regulatory Subunit Targets PP2A to Adherens Junctions and Regulate the Dephosphorylation of Beta-catenin in Endothelial Cells
Endothelial cells communicate through junctional structures such as adherent junctions (AJs), formed by transmembrane proteins. Phosphorylation and dephosphorylation of cytoskeletal and AJs proteins are essential in the regulation of endothelial cell (EC) barrier function. Phosphorylation of beta-catenin by casein kinase I and GSK3beta on Ser45 and subsequently on Ser33/37, Thr41, respectively, leads to its ubiquitination and proteosomal degradation. PKA and AKT phosphorylate beta-catenin on Ser552 and Ser675 residues resulting in the dissociation of beta-catenin from cell-cell contacts. However, the protein phosphatases involved in the dephosphorylation of AJs proteins are not characterized. Ser/Thr protein phosphatase 2A (PP2A) is involved in many physiological processes in the cell. We have shown the important role of PP2A in the maintenance of EC barrier function and cytoskeletal integrity. To better understand the functional role of PP2A in the regulation of EC cytoskeleton we employed different methods. Immunfluorescence staining revealed colocalization of the regulatory Balpha subunit and beta-catenin, the main component of AJs. Moreover, specific protein-protein interaction was detected between PP2A B and AJs proteins with pull down assay. Inhibition of PP2A activity with okadaic acid negatively affected the normal endothelial function, and caused the redistribution of VE-cadherin and beta-catenin from the cell junctions to the cytosol, and the hyperphosphorylation of beta-catenin. Furthermore, depletion of Balpha with specific siRNA affected the actin cytoskeleton organization in EC, and lead to the translocation of beta-catenin and VE-cadherin from the cell junctions to the cytoplasm parallel with the phosphorylation of[[Unable to Display Character: ]]beta-catenin on Ser552. The effect of Balpha depletion was further enhanced by thrombin treatment. Our results support the critical role of Balpha in the barrier protective function of PP2A and strongly suggest that Balpha subunit of PP2A has a functional role in the regulation of AJs proteins via the dephosphorylation of beta-catenin.
- © 2012 by American Heart Association, Inc.