VEGF Stimulates RCAN1.4 Expression in Endothelial Cells via a Pathway Requiring Ca2+/Calcineurin and Protein Kinase C-δ.

Background: Vascular endothelial growth factor (VEGF) has previously been shown to upregulate the expression of the endogenous calcineurin inhibitor, regulator of calcineurin 1, variant 4 (RCAN1.4). The aim of this study was to determine the role and regulation of VEGF-mediated RCAN1.4 expression, using human dermal microvascular endothelial cells (HDMECs) as a model system. Methodology/Principal Findings: We show that VEGF is able to induce RCAN1.4 expression during cellular proliferation and differentiation, and that VEGF-mediated expression of RCAN1.4 was inhibited by the use of inhibitors to protein kinase C (PKC) and calcineurin. Further analysis revealed that siRNA silencing of PKC-delta expression partially inhibited VEGFstimulated RCAN1.4 expression. Knockdown of RCAN1.4 with siRNA resulted in a decrease in cellular migration and disrupted tubular morphogenesis when HDMECs were either stimulated with VEGF in a collagen gel or in an endothelial/fibroblast co-culture model of angiogenesis. Analysis of intracellular signalling revealed that siRNA mediated silencing of RCAN1.4 resulted in increased expression of specific nuclear factor of activated T-cells (NFAT) regulated genes. Conclusions/Significance: Our data suggests that RCAN1.4 expression is induced by VEGFR-2 activation in a Ca²⁺ and PKCdelta dependent manner and that RCAN1.4 acts to regulate calcineurin activity and gene expression facilitating endothelial cell migration and tubular morphogenesis. [ABSTRACT FROM AUTHOR]