VEGF₁₂₁, a Vascular Endothelial Growth Factor (VEGF) Isoform Lacking Heparin Binding Ability, Requires Cell-surface Heparan Sulfates for Efficient Binding to the VEGF Receptors of Human Melanoma Cells*

Four vascular endothelial growth factor (VEGF) splice variants containing 121, 165, 189, and 206 amino acids are produced from a single human gene as a result of alternative splicing. VEGF₁₂₁ is not a heparin-binding protein, while the other VEGF species possess heparin binding ability. YU-ZAZ6 human melanoma cells expressed the mRNA encoding the VEGF receptor flt-1, but not the mRNA encoding the VEGF receptor KDR/flk-1. Both VEGF₁₂₁ and VEGF₁₆₅ bound to the VEGF receptors of these cells. Unexpectedly, heparin inhibited the binding of VEGF₁₂₁ as well as the binding of VEGF₁₆₅ to the VEGF receptors of the melanoma cells. Digestion of the cells with heparinase also inhibited the binding of both VEGF variants. The VEGF₁₆₅ binding ability of heparinase-digested cells could be partially restored by the addition of exogenous heparin to the binding reaction. In contrast, the addition of heparin to heparinase-digested cells did not restore VEGF₁₂₁ binding. These results suggest that cell-surface heparan sulfates may regulate the binding ability of the VEGF receptors of the melanoma cells. They also indicate that heparin is not able to fully substitute for cell surface-associated heparan sulfates since VEGF₁₂₁ binding to the VEGF receptors of heparinase-treated cells is not restored by heparin. These data suggest that changes in the composition of cell-surface heparin-like molecules may differentially affect the interaction of various VEGF isoforms with VEGF receptors.