Interaction of vasculotropin/vascular endothelial cell growth factor with human umbilical vein endothelial cells: Binding, internalization, degradation, and biological effects

Vasculotropin/vascular endothelial cell growth factor (VAS/VEGF) is a newly purified growth factor with a unique specificity for vascular endothelial cells. We have investigated the interactions of VAS/VEGF with human umbilical vein endothelial cells (HUVE cells). 125I‐VAS/VEGF was bound to HUVE cells in a saturable manner with a half‐maximum binding at 2.8 ng/ml. Scatchard analysis did show two classes of high‐affinity binding sites. The first class displayed a dissociation constant of 9 pM with 500 sites/cell. The dissociation constant and the number of binding sites of the second binding class were variable for different HUVE cell cultures (KD = 179 ± 101 pM, 5,850 ± 2,950 sites/cell). Half‐maximal inhibition of 125I‐VAS/VEGF occurred with a threefold excess of unlabeled ligand. Basic fibroblast growth factor (bFGF) and heparin did not compete with 125I‐VAS/VEGF binding. In contrast, suramin and protamin sulfate completely displaced 125I‐VAS/VEGF binding from HUVE cells. VAS/VEGF was shown to be internalized in HUVE cells. Maximum internalization (55% of total cell‐associated radioactivity) was observed after 30 min. 125I‐VAS/VEGF was completely degraded 2–3 hr after binding. At 3 hr, the trichloroacetic acid (TCA)‐soluble radioactivity accumulated in the medium was 60% of the total radioactivity released by HUVE cells. No degradation fragment of 125I‐VAS/VEGF was observed. Chloroquine completely inhibited degradation. VAS/VEGF was able to induce angiogenesis in vitro in HUVE cells. However, it did not significantly modulate urokinase‐type plasminogen activator (u‐PA), tissue‐type plasminogen activator (t‐PA), plasminogen activator inhibitor (PAI‐1), and tissue factor (TF). Prostacyclin production was only stimulated at very high VAS/VEGF concentrations. Taken together, these results indicate that VAS/VEGF might be a potent inducer of neovascularization resulting from a direct interaction with endothelial cells. The angiogenic activity seems to be independent of the plasminogen activator or inhibitor system.