HEPARIN INHIBITS THE BINDING OF BASIC FIBROBLAST GROWTH-FACTOR TO CULTURED HUMAN AORTIC SMOOTH-MUSCLE CELLS

Basic fibroblast growth factor (bFGF) and its specific receptors have diverse roles on a variety of cell types, such as the induction of vas cular smooth-muscle cell proliferation which contributes to restenosis after coronary balloon angioplasty. bFGF is also known to interact wi th heparan sulphate proteoglycans present on the cell surface or in th e extracellular matrix. In this study, the binding of I-125-bFGF to hu man aortic smooth-muscle cells was investigated. I-125-bFGF binding to these cells was reversible and saturable. Scatchard analysis revealed the presence of two distinct binding sites: a high-affinity receptor (K-d = 38 +/- 7 pM; 1480 +/- 220 sites/cell) and a low-affinity non-sa turable binding site (K-d = 8.0 +/- 2.0 nM). Pretreatment of the cells with heparinase resulted in a large reduction of I-125-bFGF binding t o its low affinity receptors, suggesting that they are heparin-like mo lecules, The specificity of the low-and high-affinity binding sites fo r bFGF was determined with acidic FGF, platelet-derived growth factor- BE and epidermal growth factor, which did not compete for I-125-bFGF b inding. Expression of FGF receptor isoforms analysed by reverse transc riptase-PCR revealed the presence of only the type-1 receptor. Binding to low-affinity binding sites was antagonized by heparin, suramin, pr otamine sulphate and platelet factor 4. Unexpectedly, these molecules also reduced the binding of I-125-bFGF to its high-affinity sites. Con sistent with these results, heparin, suramin, protamine sulphate and p latelet factor 4 inhibited bFGF-induced proliferation of human aortic smooth-muscle cells. Heparin abrogated bFGF-induced release of tissue- type plasminogen activator by these cells. These observations suggest that the interaction of bFGF with human aortic smooth-muscle cells is different from that described for other cells. such as endothelial cel ls, in which heparin acts as a potentiating factor of the mitogenic ac tivity of bFGF.