Selective binding of VEGF(121) to one of the three vascular endothelial growth factor receptors of vascular endothelial cells

VEGF(121) and VEGF(165) are vascular endothelial growth factor splice variants that promote the proliferation of endothelial cells and angiogenesis. VEGF(165) contains the 44 additional amino acids encoded by exon 7 of the VEGF gene. These amino acids confer upon VEGF(165) a heparin binding capability which VEGF(121) lacks. I-125-VEGF(165) bound to three vascular endothelial growth factor (VEGF) receptors on endothelial cells, while I-125-VEGF(165) bound selectively only to the flk-1 VEGF receptor which corresponds to the larger of the three VEGF receptors. The binding of I-125-VEGF(121) to flk-1 was not affected by the removal of cell surface heparan sulfates or by heparin. Both VEGF(165) and VEGF(121) inhibited the binding of I-125-VEGF(121) to soluble extracellular domain of the flk-1 VEGF receptor in the absence of heparin. However, heparin potentiated the inhibitory effect of VEGF(165) by 23-fold. These results contrast with previous observations which have indicated that the binding of I-125-VEGF(165) to the flk-1 receptor is strongly dependent on heparin-like molecules. Further experiments showed that the receptor binding ability of VEGF(165) is susceptible to oxidative damage caused by oxidants such as H2O2 or chloramine-T. VEGF(121) was also damaged by oxidants but to a lesser extent. Heparin or cell surface heparan sulfates restored the flk-1 binding ability of damaged VEGF(165) but not the receptor binding ability of damaged VEGF(121). These observations suggest that alternative splicing can generate a diversity in growth factor signaling by determining receptor recognition patterns. They also indicate that the heparin binding ability of VEGF(165) may enable the restoration of damaged VEGF(165) function in processes such as inflammation or wound healing.