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. The mechanism of inhibition is poorly understood. We have investigated the mechanism of inhibition by examining the interaction of PF-4 and the fibroblast growth factor-2 (FGF-2)/fibroblast growth factor receptor (FGFR) system. PF-4 inhibited the binding of FGF-2 to high-affinity and low-affinity binding sites in murine microvascular endothelial cells (LEII cells) and proliferation. Maximum inhibition of binding to endothelial FGF receptors was observed at PF-4 concentrations between 5 and 10 microg/mL (half maximum inhibition at 0.6 micro/mL), and proliferation was completely inhibited at 2 microg/mL. At this concentration, PF-4 reduced internalization of 125I-FGF-2 by threefold and delayed degradation. To gain insight into the mechanism of inhibition, we have analyzed the interaction of PF-4 with FGF-2/FGFR by using mutant heparan sulfate-deficient Chinese hamster ovary (CHO) cells transfected with the FGFR-1 cDNA (CHOm-FGFR-1) and by examining the direct interaction with FGF-2. In the absence of heparin, PF-4 inhibited binding of 125I-FGF-2 to CHOm-FGFR-1 cells in a concentration-dependent manner, although 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. These results indicate that PF-4 interacts with FGF-2 by complex formation, inhibiting FGF-2 dimerization, binding to FGF receptors, and internalization. This mechanism most likely contributes to the antiangiogenic properties of PF-4.
Perollet
C
C
Growth Factor and Cell Differentiation Laboratory, University Bordeaux; Institut des Vaisseaux et du Sang, Paris, France.
Han
Z C
ZC
Savona
C
C
Caen
J P
JP
Bikfalvi
A
A
D000818:Animals; D016466:CHO Cells; D002455:Cell Division; D002478:Cells, Cultured; D006224:Cricetinae; D019281:Dimerization; D004705:Endocytosis / Q000187:drug effects; D004730:Endothelium, Vascular / Q000378:metabolism*; D016222:Fibroblast Growth Factor 2 / Q000378:metabolism*; D006497:Heparan Sulfate / Q000502:physiology; D051379:Mice; D010978:Platelet Factor 4 / Q000502:physiology*; D020794:Receptor Protein-Tyrosine Kinases; D051496:Receptor, Fibroblast Growth Factor, Type 1; D017468:Receptors, Fibroblast Growth Factor / Q000378:metabolism*
D016222:Fibroblast Growth Factor 2; D006497:Heparan Sulfate; D010978:Platelet Factor 4; D020794:Receptor Protein-Tyrosine Kinases; D051496:Receptor, Fibroblast Growth Factor, Type 1; D017468:Receptors, Fibroblast Growth Factor; C496349:Fgfr1 protein, mouse