Study of osteoblast-specific expression of one mouse osteocalcin gene: characterization of the factor binding to OSE2

In an attempt to understand the mechanisms of osteoblast-specific expression, we analyzed the promoter of the mouse osteocalcin gene 2, an osteoblast-specific gene. In this promoter, using a combination of DNA transfection experiments and DNA binding assays, we have identified two osteoblast-specific cis-acting elements called OSE1 and OSE2. Inspection of OSE2 DNA sequence and site-specific mutagenesis allowed us to define a core sequence for OSE2. This core sequence is identical to the DNA binding site of the PEBP2 alpha transcription factors, the mouse homologues of the Drosophila Runt protein. Here we show that OSF2, the factor present in osteoblast nuclear extracts and binding to OSE2, is immunologically related to the PEBP2 alpha transcription factors. In DNA cotransfection experiment, a human homologue of PEBP2 alpha transcription factor increases the activity of a short osteocalcin promoter through its binding to OSE2. Thus, this study presents evidence that OSF2 is a member of the PEBP2 alpha family of transcription factors.