Biological activity of substrate-bound basic fibroblast growth factor (FGF2): recruitment of FGF receptor-1 in endothelial cell adhesion contacts

Abstract

Substrate-bound FGF2 promotes endothelial cell adhesion by interacting with α_vβ₃ integrin. Here, endothelial GM7373 cells spread and organize focal adhesion plaques on immobilized FGF2, fibronectin (FN), and vitronectin (VN). α_vβ₃ integrin, paxillin, focal adhesion kinase, vinculin and pp60^src localize in cell-substratum contact sites on FGF2, FN or VN. However, only immobilized FGF2 induces a long-lasting activation of extracellular signal-regulated kinases_1/2 (ERK_1/2) and cell proliferation that was inhibited by the ERK_1/2 inhibitor PD 098059 and the tyrosine kinase (TK) inhibitor tyrphostin 23, pointing to the engagement of FGF receptor (FGFR) at the basal side of the cell. To assess this hypothesis, GM7373 cells were transfected with a dominant negative TK⁻-ΔFGFR1 mutant (GM7373-ΔFGFR1 cells) or with the full-length receptor (GM7373-FGFR1 cells). Both transfectants adhere and spread on FGF2 but GM7373-ΔFGFR1 cells do not proliferate. Also, parental and GM7373-FGFR1 cells, but not GM7373-ΔFGFR1 cells, undergo morphological changes and increased motility on FGF2-coated plastic. Finally, FGFR1, but not TK⁻-ΔFGFR1, localizes in cell adhesion contacts on immobilized FGF2. In conclusion, substrate-bound FGF2 induces endothelial cell proliferation, motility, and the recruitment of FGFR1 in cell-substratum contacts. This may contribute to the cross talk among intracellular signaling pathways activated by FGFR1 and α_vβ₃ integrin in endothelial cells.