Hemodynamic Activation of -Catenin and T-Cell-Specific Transcription Factor Signaling in Vascular Endothelium Regulates Fibronectin Expression

Objective—The goal of this study was to assess the activity of ␤-catenin/T-cell-specific transcription factor (TCF) signaling in atherosclerosis development and its regulation of fibronectin in vascular endothelium. Methods and Results—Histological staining identified preferential nuclear localization of ␤-catenin in the endothelium of atheroprone aorta before and during lesion development. Transgenic reporter studies revealed that increased levels of TCF transcriptional activity in endothelium correlated anatomically with ␤-catenin nuclear localization and fibronectin deposition. Exposure of endothelial cells to human-derived atheroprone shear stress induced nuclear localization of ␤-catenin, transcriptional activation of TCF, and expression of fibronectin. Activation of fibronectin expression required ␤-catenin, TCF, and the transcriptional coactivator CRBP-binding protein. Finally, we identified platelet endothelial cell adhesion molecule-1 as a critical regulator of constitutive ␤-catenin and glycogen synthase kinase-3␤ activities. Conclusion—These data reveal novel constitutive activation of the endothelial ␤-catenin/TCF signaling pathway in atherosclerosis and regulation of fibronectin through hemodynamic shear stress. B eta-catenin (␤-cat) is a highly conserved, multifunctional member of the armadillo family whose nuclear translo-cation and coactivation of the T-cell-specific transcription factor (TCF)/lymphoid enhancer-binding factor (LEF) family of transcription factors represents a critical step in a variety of cell processes, including development, epithelial-mesenchymal transition, angiogenesis, and differentiation. 1 Studies have identified a role for TCF/LEF activity in several pathological features of advanced atherosclerotic lesions, including vascular calcification 2– 4 and smooth muscle cell proliferation. 5 However, the involvement of this signaling pathway in the endothelium during early atheroscle-rosis development is poorly understood. Cytosolic ␤-cat is constitutively targeted for ubiquitination-mediated degradation via glycogen synthase kinase 3␤ (GSK-3␤)-dependent phosphorylation. On stimulation by various factors (including canonical Wnts and growth factors) GSK-3␤ activity is decreased, leading to nuclear accumulation of ␤-cat, followed by binding and activation of the TCF/LEF family of transcription factors. One target of TCF/LEF-dependent transcription is the extracellular matrix protein fibronectin. 6 TCF-dependent fibronectin expression has been identified to play important roles in several cell contexts, including fibroblast differentiation, 7 lung branching morphogenesis, 8 and epithelial-mesenchymal transition. 6 Fi-bronectin is also highly regulated in atherosclerotic tissue and is involved in atherosclerosis development through promotion of inflammation and endothelial permeability. 9 –12 However , the role of endothelial ␤-cat/TCF in this process remains unknown. One prominent feature of the atherosclerotic environment is hemodynamic shear stress, which regulates the phenotype of endothelial cells (EC) 13,14 and largely explains the regional bias of atherosclerosis development. 15,16 Specifically, low-magnitude, reversing shear stress, such as that which …