PROXIMAL PROMOTER-BINDING PROTEIN CONTRIBUTES TO DEVELOPMENTAL, TISSUE-RESTRICTED EXPRESSION OF THE RAT OSTEOCALCIN GENE

Osteocalcin is a 6 kD tissue-specific calcium binding protein associat ed with the bone extracellular matrix. The osteocalcin gene is develop mentally expressed in postproliferative rat osteoblasts with regulatio n at least in part at the transcriptional level. Multiple, basal promo ter and enhancer elements which control transcriptional activity in re sponse to physiological mediators, including steroid hormones, have be en identified in the modularly organized osteocalcin gene promoter. Th e osteocalcin box (OC box) is a highly conserved basal regulatory elem ent residing between nucleotides -99 and -76 of the proximal promoter. We recently established by in vivo competition analysis that protein interactions at the CCAAT motif, which is the central core of the rat OC box, are required for support of basal transcription [Heinrichs et al. J Cell Biochem 53:240-250, 1993]. In this study, by the combined u tilization of electrophoretic mobility shift analysis, UV cross linkin g, and DNA affinity chromatography, we have identified a protein that binds to the rat OC box. Results are presented that support involvemen t of the OC box-binding protein in regulating selective expression of the osteocalcin gene during differentiation of the rat osteoblast phen otype and suggest that this protein is tissue restricted. (C) 1995 Wil ey-Liss, Inc.