Up-regulation of inhibitors of DNA binding/differentiation gene during alendronate-induced osteoblast differentiation

To investigate the effect of alendronate on the expression of Id genes in osteoblast differentiation. C2C12 cells were treated with alendronate for various concentrations and time periods. For evaluation of alendronate-induced osteoblast differentiation in C2C12 cells, alkaline phosphatase (ALP) activity was measured. The expression of osteoblast differentiation markers such as ALP, type-1 collagen (Col 1), and osteocalcin (OCN), and the expression of Id-1 and Id-2 were measured by RT-PCR. In order to understand the mechanism underlying the regulation of Id genes, the promoter region of the Id-1 gene was identified. Database analysis of the promoter region for Id-1 using known consensus sequences identified several putative response elements, including CCAAT/enhancer-binding protein beta (C/EBP beta). Alendronate treatment significantly increased not only ALP activity but also the expression of ALP, Col 1, and OCN, Id-1 and Id-2. C/EBP beta and alendronate cooperatively increased the promoter activity and expression of Id-1. These results suggest that C/EBP beta-mediated Id-1 transcriptional activation may regulate alendronate-induced osteoblast differentiation of C2C12 cells.