DOWN-REGULATION OF VASCULAR ENDOTHELIAL GROWTH-FACTOR RECEPTORS BY TUMOR-NECROSIS-FACTOR-ALPHA IN CULTURED HUMAN VASCULAR ENDOTHELIAL-CELLS

Vascular endothelial growth factor (VEGF) potently stimulates angiogen esis, whereas TNF-alpha has both pro- and antiangiogenic activity, By measuring thymidine uptake, we found that TNF-alpha 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 endothel ial cell proliferation, we examined the effect of TNF-alpha on VEGF re ceptor expression, In venous and arterial endothelial cells, TNF-alpha potently reduced mRNA transcripts of the two VEGF receptors (KDR/flk- 1 and flt-1) in a dose- and time-dependent fashion, TNF-alpha at 1 ng/ ml induced maximal inhibition of mRNA expression, which fell by simila r to 70% after 24 h. TNF-alpha 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 n ew protein synthesis and was abolished by phorbol ester pretreatment. TNF-alpha decreased the amount of S-35-labeled KDR/flk-1 immunoprecipi tated by an antibody specific for KDR/flk-1 to 18% of control. We conc lude that TNF-alpha downregulates expression of both VEGF receptors in human endothelial cells and that this effect is transcriptional (at l east for KDR/flk-1). These data support the hypothesis that TNF-alpha exerts its antiangiogenic effect in part by modulating the VEGF-specif ic angiogenic pathway.