Basic fibroblast growth factor stimulates collagenase-3 promoter activity in osteoblasts through an activator protein-1-binding site.

Basic fibroblast growth factor (bFGF) stimulates collagenase-3 synthesis in fetal rat osteoblast-enriched (Ob) cells. In this study we examined the mechanism of collagenase-3 regulation in Ob cells. bFGF at 0.6 nM or more increased the transcriptional rate of collagenase-3 by 3- to 7-fold. bFGF at 0.6 nM increased the activity of collagenase-3 promoter-luciferase reporter deletion constructs from -721 to -53 nucleotides transiently transfected into Ob cells by 3- to 5-fold. The minimal bFGF response was retained within the -53 to +28 sequence. Mutational analysis revealed that the bFGF effect was mediated through an activator protein-1 (AP-1)-binding site located at -48 to -42 nucleotides in the promoter. bFGF stimulated the binding of nuclear factors to the collagenase AP-1 site by 3- to 4-fold, as determined by electrophoretic mobility shift assays. Supershift analysis of nuclear extracts revealed that bFGF stimulates the occupancy of AP-1 site by c-Jun, JunB, JunD, c-Fos, FosB, and Fra2. In conclusion, bFGF increases collagenase-3 gene transcription, an effect mediated through an AP-1 site, due to the induction or activation of Jun and Fos family transcription factors. The stimulation of collagenase-3 synthesis by bFGF may be critical in mediating the actions of this growth factor in bone remodeling.