FGF-1-induced platelet-derived growth factor-A chain gene expression in endothelial cells involves transcriptional activation by early growth response factor-1

Fibroblast growth factor-1 (FGF-1), a prototype member of the heparin-binding growth factor family, is a potent mitogen for vascular endothelial cells and a variety of other cell types. FGF-1 can induce the expression of the platelet-derived growth factor-A chain (PDGF-A) gene in endothelial cells; however, the underlying transcriptional mechanisms are not known. We used serial 5' deletion and transient transfection analysis of the human PDGF-A promoter to demonstrate that a 16-bp element, located 55 to 71 bp upstream of the transcriptional start site, is required for FGF-1-inducible promoter-dependent expression. This region contains nucleotide recognition elements for the early growth response gene product, early growth response factor-1 (Egr-1), and the related zinc-finger transcription factor, Spl. Reverse-transcription polymerase chain reaction revealed that FGF-1 induced Egr-1 mRNA expression within 30 minutes. Electrophontic mobility shift, supershift, and Western blot analysis demonstrated that Egr-1 protein accumulated in the nuclei of endothelial cells exposed to the growth factor, whereas levels of Spl did not change. Egr-1 bound to the FGF-I response element in the proximal PDGF-A promoter in a specific and time-dependent manner. These findings indicate that Egr-1 plays a key regulatory role in FGF-l-inducible endothelial PDGF-A expression and implicate this transcription factor in pathological settings in which these mitogens are both expressed.