Novel Regulation of Vascular Endothelial Growth Factor-A (VEGF-A) by Transforming Growth Factor β1

Abstract

Vascular endothelial growth factor (VEGF) is a vital angiogenic effector, regulating key angiogenic processes. Vascular development relies on numerous signaling pathways, of which those induced by transforming growth factor-β (TGFβ) are critical. The Wnt/β-catenin signaling pathway is emerging as necessary for vascular development. Although VEGF, TGFβ, and Wnt signal transductions are well studied individually, it has not been demonstrated previously that all three can interact or be dependent on each other. We show that regulation of VEGF by TGFβ1, in human pulmonary artery smooth muscle cells (PASMCs), depends on a direct interaction between TGFβ signaling proteins, Smads, and members of the Wnt/β-catenin signaling family. VEGF promoter reporter constructs identified a region of the VEGF promoter containing two T cell factor (TCF)-binding sites as necessary for TGFβ1-induced VEGF transcription. Mutation of TCF sites and expression of dominant negative TCF4 abolished TGFβ1-induced VEGF promoter activity. Studies in Smad2 and Smad3 knock-out mouse embryonic fibroblasts demonstrated that one or both are required for VEGF regulation by TGFβ1, with transfection of dominant negative Smad2 or Smad3 into PASMCs confirming this. Chromatin immunoprecipitation assays showed in cell interactions of Smad2 and Smad3 with TCF4 and β-catenin at the VEGF promoter, whereas co-immunoprecipitation showed a direct physical interaction between Smad2 and β-catenin in the nucleus of PASMCs. Finally, we demonstrate that TGFβ1 regulates TCF by modifying β-catenin phosphorylation via regulation of glycogen synthase kinase 3β. These results provide new insight into the molecular regulation of VEGF by two interacting pathways necessary for vascular development, maintenance, and disease.