Vascular Endothelial Growth Factor Augments Arginine Transport and Nitric Oxide Generation via a KDR Receptor Signaling Pathway

Background/aims: Vascular endothelial growth factor (VEGF) is an endothelium-specific peptide that stimulates angiogenesis via two receptor tyrosine kinases, Flt-1 and KDR. Endothelial nitric oxide synthase (eNOS) plays a major role in VEGF signaling. Delivery of arginine to membrane bound eNOS by the cationic amino acid transporter-1 (CAT-1) has been shown to modulate eNOS activity. The current studies were designed to test the hypothesis that VEGF enhances eNOS activity via modulation of arginine transport by CAT-1.

Methods: Using radio-labeled arginine, {[3H] L-arginine} uptake was determined in human umbilical vein endothelial cells (HUVEC) following incubation with VEGF with and without silencing the VEGF receptors Flt-1 or KDR. Subsequently, western blotting for CAT-1, PKCα, ERK 1/2, JNK, and their phosphorylated forms were performed. NO generation was measured by the Griess reaction.

Results: VEGF (50 and 100 ng/ml) significantly augmented endothelial arginine transport in a time dependent manner, an effect which was prevented by Sunitinib (2 µM), a multi targeted receptor tyrosine kinase inhibitor. The increase in arginine transport velocities by VEGF was not affected by silencing Flt-1 while silencing KDR abrogated VEGF effect. Furthermore, incubating cells with 50 and 100 ng of VEGF for 30 minutes significantly augmented CAT-1 abundance. The expression of PKC-α, JNK, and ERK1/2 and their phosphorylated forms were unchanged following incubation of HUVEC with VEGF. The concentration of NO2/NO3 following incubation with VEGF was significantly higher than from untreated cells. This increase was significantly attenuated by silencing KDR.

Conclusions: VEGF increases arginine transport via modulation of CAT-1 in endothelial cells. This effect is exclusively dependent on KDR rather than Flt-1.