Purpose To investigate the effect of alendronate on the expression of Id genes in osteoblast differentiation. Methods 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

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... 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/enhancerbinding protein beta (C/EBPb). Results Alendronate treatment significantly increased not only ALP activity but also the expression of ALP, Col 1, and OCN, Id-1 and Id-2. C/EBPb and alendronate cooperatively increased the promoter activity and expression of Id-1. Conclusions These results suggest that C/EBPb-mediated Id-1 transcriptional activation may regulate alendronateinduced osteoblast differentiation of C2C12 cells.