Downregulation of vascular endothelial growth factor receptors by tumor necrosis factor-α in cultured human vascular endothelial cells

Abstract

Vascular endothelial growth factor (VEGF) potently stimulates angiogenesis, whereas TNF-α has both pro- and antiangiogenic activity. By measuring thymidine uptake, we found that TNF-α blocked a 2.3-fold increase in DNA synthesis induced by VEGF in human endothelial cells. To explore the possibility that the two interact to regulate endothelial cell proliferation, we examined the effect of TNF-α on VEGF receptor expression. In venous and arterial endothelial cells, TNF-α potently reduced mRNA transcripts of the two VEGF receptors (KDR/flk-1 and flt-1) in a dose-and time-dependent fashion. TNF-α at 1 ng/ml induced maximal inhibition of mRNA expression, which fell by ~ 70% after 24 h. TNF-α treatment did not significantly affect the KDR/flk-1 half-life but did decrease its rate of transcription to 40% of control. The decrease in KDR/flk-1 mRNA depended partially on new protein synthesis and was abolished by phorbol ester pretreatment. TNF-α decreased the amount of 35S-labeled KDR/flk-1 immunoprecipitated by an antibody specific for KDR/flk-1 to 18% of control. We conclude that TNF-α downregulates expression of both VEGF receptors in human endothelial cells and that this effect is transcriptional (at least for KDR/flk-1). These data support the hypothesis that TNF-α exerts its antiangiogenic effect in part by modulating the VEGF-specific angiogenic pathway.