TRANSCRIPTIONAL ACTIVATION OF THE HUMAN OSTEOCALCIN GENE BY BASIC FIBROBLAST GROWTH-FACTOR

Basic fibroblast growth factor (bFGF) has been detected in bone cells and stimulates osteoblast proliferation; however, its role in the regu lation of bone metabolism remains speculative. We demonstrated that th e human osteocalcin promoter is activated by bFGF when transfected int o rat osteoblastic (ROS 17/2.8) cells. This effect is concentration de pendent, with a twofold induction at 10 ng/ml detected after 20 h. The bFGF response is independent of both the 1,25-dihydroxyvitamin D-3 [1 ,25-(OH)(2)D-3] and retinoic acid activation of the osteocalcin promot er. To identify the promoter sequences through which bFGF exerts its e ffect, we tested a series of promoter deletion constructs for their re sponse to bFGF. Deletion of the upstream region between -673 and -588 bp results in a significant loss of induction. Gel-shift analysis demo nstrates that proteins present in ROS 17/2.8 nuclear extracts bind spe cifically to these sequences. This region alone was unable to confer t he bFGF response on a minimal osteocalcin or an heterologous promoter. However, sequences between -678 and -476 bp, which also includes the vitamin D response element (VDRE), were able to confer bFGF inducibili ty on both a minimal osteocalcin and a heterologous promoter. These da ta suggest that induction of the human osteocalcin promoter by bFGF re quires the interaction of more than one sequence element.