SHORT-TERM INHIBITORY EFFECT BY HEPARIN ON THE INTERACTION OF BASIC FIBROBLAST GROWTH-FACTOR WITH ITS RECEPTOR

Fibroblast growth factor (FGF), a member of heparin-binding growth factor, is a family of nine structurally related polypeptides showing multiple biological activities: angiogenesis, wound healing and development. FGF is known to exert its biological effects by interacting with both low-affinity receptor, heparan sulfate proteoglycan which is often substituted by heparin, and high-affinity receptor, receptor tyrosine kinase. Formation of ternary complex, heparin, FGF, and the high-affinity receptor seems to be essential for the subsequent intracellular events. Therefore to interrupt an interaction between these components is a good strategy for development of a new drug. Basic FGF (bFGF) is well known for its potent angiogenic effects. To examine a feasibility of heparin as a modulator of angiogenesis, the effect of heparin on the binding of bFGF to FGF receptor (FGFR) in the human endothelial cells was evaluated. As a preliminary step, we determined the subtype of FGFRs expressed in the endothelial cells from bovine glomerulus and aorta, respectively. To date, four different FGFRs have been cloned and analyzed. In the endothelial cells FGFR-1 was found to be expressed predominantly. In human endothelial cells and NIH 3T3 cells heparin inhibited the binding of bFGF to low-affinity receptors as well as to high-affinity receptors in a dose-dependent manner. Tyrosine phosphorylation of She and other cellular proteins by bFGF were accordingly reduced in the presence of heparin (20 mu g/ml). In addition, c-fos induction was blocked by the same concentration of heparin. Collectively, these data indicate that high concentration of heparin is inhibitory to the action of bFGF during a short period of time in vitro.