SELECTIVE BINDING OF VEGF(121) TO ONE OF THE 3 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 angio genesis. VEGF(165) contains the 44 additional amino acids encoded by e xon 7 of the VEGF gene. These amino acids confer upon VEGF(165) a hepa rin binding capability which VEGF(121) lacks. I-125-VEGF(165) bound to three vascular endothelial growth factor (VEGF) receptors on endothel ial cells, while I-125-VEGF(165) bound selectively only to the flk-1 V EGF receptor which corresponds to the larger of the three VEGF recepto rs. The binding of I-125-VEGF(121) to flk-1 was not affected by the re moval of cell surface heparan sulfates or by heparin. Both VEGF(165) a nd VEGF(121) inhibited the binding of I-125-VEGF(121) to soluble extra cellular 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 ind icated that the binding of I-125-VEGF(165) to the flk-1 receptor is st rongly dependent on heparin-like molecules. Further experiments showed that the receptor binding ability of VEGF(165) is susceptible to oxid ative 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 damage d VEGF(165) but not the receptor binding ability of damaged VEGF(121). These observations suggest that alternative splicing can generate a d iversity in growth factor signaling by determining receptor recognitio n patterns. They also indicate that the heparin binding ability of VEG F(165) may enable the restoration of damaged VEGF(165) function in pro cesses such as inflammation or wound healing.