Protein Kinase D Up-regulates Transcription of in Endothelial Cells by Suppressing Nuclear Localization of the Transcription Factor AP2β

Vascular endothelial growth factor A (VEGF) signals primarily through its cognate receptor VEGF receptor-2 (VEGFR-2) to control vasculogenesis and angiogenesis, key physiological processes in cardiovascular disease and cancer. In human umbilical vein endothelial cells (HUVECs), knockdown of protein kinase D-1 (PKD1) or PKD2 down-regulates VEGFR-2 expression and inhibits VEGF-induced cell proliferation and migration. However, how PKD regulates VEGF signaling is unclear. Previous bioinformatics analyses have identified binding sites for the transcription factor activating enhancer-binding protein 2 (AP2) in the promoter. Using ChIP analyses, here we found that PKD knockdown in HUVECs increases binding of AP2β to the promoter. Luciferase reporter assays with serial deletions of AP2-binding sites within the promoter revealed that its transcriptional activity negatively correlates with the number of these sites. Next we demonstrated that AP2β up-regulation decreases VEGFR-2 expression and that loss of AP2β enhances VEGFR-2 expression in HUVECs. experiments confirmed increased VEGFR-2 immunostaining in the spinal cord of AP2β knockout mouse embryos. Mechanistically, we observed that PKD phosphorylates AP2β at Ser and Ser and suppresses its nuclear accumulation. Inhibition of PKD activity with a pan-PKD inhibitor increased AP2β nuclear localization, and overexpression of both WT and constitutively active PKD1 or PKD2 reduced AP2β nuclear localization through a Ser- and Ser-dependent mechanism. Furthermore, substitution of Ser in AP2β increased its binding to the promoter. Our findings uncover evidence of a molecular pathway that regulates expression, insights that may shed light on the etiology of diseases associated with aberrant VEGF/VEGFR signaling.