The osteocalcin and collagen type I (alpha 1) promoters share common basal regulatory units

Sequential activation of osteoblast-specific genes occurs during cell development. Regulation of these genes is through the cooperation between basal, hormone-responsive, and growth factor-responsive transcriptional control elements. The active hormone, 1,25-dihydroxyvitamin D3 plays an important role in the regulation of osteocalcin and other osteoblast-expressed genes. As well as containing a vitamin D response element, the upstream region of the osteocalcin promoter also has potent basal activity in the osteoblast-like ROS17/2.8 cell line. The present study identifies a short DNA sequence that contributes to basal promoter activity. This osteocalcin cis-acting response element (OSCARE-1) has two basal regulatory elements: a G/C-rich element and an adjacent reverse CCAAT element. Homologous sequences have been characterized as negative and positive basal regulatory elements, respectively, in the promoter of the collagen type I (alpha 1) gene. In electrophoretic mobility-shift assays, this collagen regulatory unit and OSCARE-1 produce similar banding patterns and bind common ROS17/2.8 nuclear proteins. Mutations of the G/C element in the collagen promoter showed that it functions as an inhibitory element in NIH-3T3 cells. Introduction of the same mutations into the G/C element of the OSCARE-1 unit exposed a similar repressive activity in NIH-3T3 cells, which correlated with an altered electrophoretic mobility-shift assay banding pattern. We have shown a similarity between a basal regulatory unit in the distal osteocalcin promoter and a unit in the proximal collagen type I (alpha 1) promoter. The fact that similar units are present in other osteoblast-specific promoters suggests that OSCARE-1-like units may be a common regulator of osteoblast-expressed genes.