PLATELET-FACTOR-4 MODULATES FIBROBLAST GROWTH-FACTOR-2 (FGF-2) ACTIVITY AND INHIBITS FGF-2 DIMERIZATION

Platelet factor 4 (PF-4) inhibits angiogenesis in vitro and in vivo. T he mechanism of inhibition is poorly understood. We have investigated the mechanism of inhibition by examining the interaction of PF-4 and t he fibroblast growth factor-2 (FGF-P)/fibroblast growth factor recepto r (FGFR) system. PF-4 inhibited the binding of FGF-2 to high affinity and low-affinity binding sites in murine microvascular endothelial cel ls (LEII cells) and proliferation, Maximum inhibition of binding to en dothelial FGF receptors was observed at PF-4 concentrations between 5 and 10 mu g/mL (half maximum inhibition at 0.6 mu g/mL), and prolifera tion was completely inhibited at 2 mu g/mL. At this concentration, PF- 4 reduced internalization of I-125-FGF-2 by threefold and delayed degr adation, To gain insight into the mechanism of inhibition, we have ana lyzed the interaction of PF-4 with FGF-2/FGFR by using mutant heparan sulfate-deficient Chinese hamster ovary (CHO) cells transfected with t he FGFR-1 cDNA (CHOm-FGFR-1) and by examining the direct interaction w ith FGF-2. In the absence of heparin, PF-4 inhibited binding of (125)1 -FGF-2 to CHOm-FGFR-1 cells in a concentration-dependent manner, altho ugh not completely. In the presence of heparin, PF-4 abolished totally the stimulatory effect of heparin, Furthermore, PF-4 complexed to FGF -2 and inhibited endogenous or heparin-induced FGF-2 dimerization. The se results indicate that PF-4 interacts with FGF-2 by complex formatio n, inhibiting FGF-2 dimerization, binding to FGF receptors, and intern alization, This mechanism most likely contributes to the antiangiogeni c properties of PF-4, (C) 1998 by The American Society of Hematology.