Bovine basic fibroblast growth factor: identification and binding of its receptor on PC12 cells

Basic fibroblast growth factor (FGF) was purified to homogeneity from bovine pituitary glands on the basis of its ability to stimulate Swiss 3T3 cell proliferation. The binding characteristics of biologically active 125[I]-FGF to PC12 cells have been studied. Binding of 125[I]-FGF was found to be specific, as the bound 125[I]-FGF was displaced by native FGF but not by epidermal growth factor (EGF) or nerve growth factor (NGF). Binding was saturable both as a function of time and of the concentration of 125[I]-FGF. Scatchard analysis of the binding data revealed the presence of 1.05.10(5) binding sites/cell with an apparent KD of 258 pM. When 125[I]-FGF binding was studied in PC12 cell membranes, it was found that the membraneous binding site displayed a lower KD of 28 pM. 125[I]-FGF was covalently cross-linked to its cell surface receptor on intact PC12 cells using the homobifunctional agent disuccinimidyl suberate. The covalently cross-linked 125[I]-FGF identified a single detergent soluble FGF binding site with an apparent molecular weight of 145,000 by SDS-PAGE analysis. Unlabeled FGF was found to compete with 125[I]-FGF for binding to the same receptor site. No labelling was observed in the absence of the cross-linker or when heat inactivated 125[I]-FGF was used. In conclusion, the present studies demonstrate for the first time the presence of FGF receptor on PC12 cells.