FGF-R1 phosphorylation, FGF-2 internalization, and PDGF-Rα role. (A) On HUVEC lysates, FGF-R1 phosphorylation was evaluated by immunoprecipitation and was found to be markedly inhibited by FGF-2/PDGF-BB treatment (10 minutes) compared with FGF-2 alone (^*P < .001 vs FGF-2). Apparently, PDGF-BB alone induces FGF-R1 phosphorylation, according to data previously reported,³⁶  although a statistical significance was not reached in our experiments (B) FGF-2 internalization was abolished by PDGF-BB (^*P < .05 vs FGF-2) and PDGF-Rα–neutralizing antibody restored FGF-2 internalization, whereas neutralizing PDGF-Rβ had no effect (^**P < .01 vs FGF-2/PDGF-BB). (C) PDGF-BB inhibitory effect on FGF-2 mitogenic activity (^*P < .05 vs FGF-2) was abolished by neutralizing PDGF-Rα (^**P < .05 vs FGF-2/PDGF-BB), whereas PDGF-Rβ neutralization was ineffective. Bars indicate quantification of 3 experiments; 1 representative experiment is reported for each panel.