Nuclear targeting of β-catenin and p120ctn during thrombin-induced endothelial barrier dysfunction

Abstract

Aims: Cytosolic and nuclear localization of β-catenin was observed in leaky vessels and in tumours. Several lines of evidence indicate that nuclear β-catenin facilitates angiogenesis. We hypothesized that nuclear β-catenin liberated from endothelial junctional complexes marks the transition from hyperpermeability to angiogenesis. The aim of this study was, therefore, to investigate the fate of β-catenin and the related catenin p120catenin (p120ctn), during disruption of the endothelial barrier function in human umbilical vein endothelial cells (ECs). Methods and results: The hyperpermeability-inducer thrombin caused a Rho kinase-dependent redistribution of β-catenin from the membrane to the cytosol as evidenced by the western blot analysis of membrane and cytosol fractions and by immunohistochemistry. Glycogen synthase kinase 3β, which phosphorylates cytosolic β-catenin and thereby facilitates its proteasomal degradation, was inhibited by thrombin. The analysis of nuclear extracts demonstrated a thrombin-induced nuclear accumulation of β-catenin as well as p120ctn. Thrombin stimulation activated β-catenin-mediated transcriptional activity as evidenced by reporter assays. Finally, real-time-PCR revealed increased mRNA levels of several β-catenin target genes. Conclusion: Thrombin induced a cytosolic stabilization of membrane-liberated β-catenin, which, together with p120ctn, subsequently translocated to the nucleus where it induces several β-catenin target genes. This supports the suggestion that membrane-liberated β-catenin and p120ctn contribute to angiogenic responses of ECs following episodes of vascular leakage. © The Author 2008.