Vascular Endothelial Growth Factor Up-regulates Nitric Oxide Synthase Expression in Endothelial Cells

Objective: Vascular endothelial growth factor (VEGF), secreted by vascular cells and a variety of tumour cells, is a potent angiogenic factor. Since nitric oxide (NO) seems to play a key role in the VEGF-induced proliferation of endothelial cells, the aim of the present study was to determine whether VEGF stimulates endothelial NO synthase (eNOS) expression and hence results in a maintained increase in NO formation.

Methods: Experiments were performed using cultured human umbilical vein endothelial cells (HUVEC) and isolated rat aortic rings. eNOS expression was assessed by Western blotting and RT-PCR analysis.

Results: Exposure of either confluent HUVEC or rat aortic rings to VEGF165 significantly increased eNOS mRNA and protein levels. This stimulatory effect of VEGF165 on eNOS expression was associated with an elevation in the basal production of cGMP in HUVEC, and with a leftward shift of the concentration-relaxation curve to acetylcholine in aortic rings. The VEGF-induced increase in eNOS mRNA levels was abolished by tyrosine kinase inhibitors suggesting involvement of a tyrosine kinase-dependent pathway. Since eNOS mRNA levels remained elevated in VEGF-treated cells in the presence of actinomycin D. it is likely that the VEGF-induced up-regulation of eNOS expression may be a consequence of a post-transcriptional effect on eNOS mRNA stability.

Conclusion: The results demonstrate that VEGF enhances the expression of eNOS in native and cultured endothelial cells, an effect which may be important in the process of VEGF-induced angiogenesis.