TUMOR-NECROSIS-FACTOR-ALPHA REGULATES EXPRESSION OF VASCULAR ENDOTHELIAL GROWTH-FACTOR RECEPTOR-2 AND OF ITS CORECEPTOR NEUROPILIN-1 IN HUMAN VASCULAR ENDOTHELIAL-CELLS

Tumor necrosis factor-alpha (TNF-alpha) modulates gene expression in e ndothelial cells and is angiogenic in vivo, TNF-alpha does not activat e in vitro migration and proliferation of endothelium, and its angioge nic activity is elicited by synthesis of direct angiogenic inducers or of proteases, Here, we show that TNF-alpha up-regulates in a dose- an d time-dependent manner the expression and the function of vascular en dothelial growth factor receptor-2 (VEGFR-2) as well as the expression of its coreceptor neuropilin-1 in human endothelium, As inferred by n uclear run-on assay and transient expression of VEGFR-2 promoter-based reporter gene construct, the cytokine increased the transcription of the VEGFR-2 gene. Mithramycin, an inhibitor of binding of nuclear tran scription factor Spl to the promoter consensus sequence, blocked activ ation of VEGFR-2, suggesting that the up-regulation of the receptor re quired Spl binding sites. TNF-alpha increased the cellular amounts of VEGFR-2 protein and tripled the high affinity I-125-VEGF-A(165) capaci ty without affecting the K-d of ligand-receptor interaction. As a cons equence, TNF-alpha enhanced the migration and the wound healing trigge red by VEGF-A(165). Since VEGFR-2 mediates angiogenic signals in endot helium, our data indicate that its up-regulation is another mechanism by which TNF-alpha is angiogenic and may provide insight into the mech anism of neovascularization as occurs in TNF-alpha-mediated pathologic al settings.