Transcriptional regulation of the human bone sialoprotein gene by fibroblast growth factor 2

Fibroblast growth factor 2 (FGF2), a member of the FGF family, positively regulates bone formation and osteoblast differentiation. Bone sialoprotein (BSP) is highly expressed during early bone formation and may play a role in primary mineralization of bone. In the present study, FGF2 (10 ng/mL) was found to increase the levels of Runx2 and BSP mRNA at 3 and 12 h in human osteoblast-like Saos2 cells. Transient transfection assays were performed using chimeric constructs of the human BSP gene promoter ligated with a luciferase reporter gene. FGF2 (10 ng/mL, 12 h) induced the luciferase activities of the -84LUC and -927LUC constructs in Saos2 cells. The results of gel shift assays showed that FGF2 (10 ng/mL) increased the binding of nuclear protein to the FGF2 response element (FRE) and the activator protein 1 (AP1) binding site. Antibodies against Dlx5, Msx2, Runx2 and Smad1 blocked FRE-protein complex formation, and antibodies against CREB1, c-Jun and Fra2 interrupted AP1-protein complex formation. These results indicate that FGF2 increases BSP transcription by targeting the FRE and AP1 elements in the proximal promoter of the human BSP gene. Moreover, the transcription factors Dlx5, Msx2, Runx2, Smad1, CREB1, c-Jun and Fra2 could be key regulators of the effects of FGF2 on human BSP transcription.