Background: Bone morphogenetic protein‐2 (BMP‐2) stimulates osteoblast differentiation, but inhibits myogenic differentiation in C2C12 myoblasts. BMP‐2 induces transcription of Id1, an inhibitor for myogenesis, within 1 h in the cells. To examine the molecular mechanism of the action of BMP‐2, we analysed a BMP‐2‐responsive element (BRE) in the 5′ flanking region of the human Id1 gene.

Results: A GC‐rich region between −985 bp and −957 bp of the human Id1 gene was identified as a BRE. The BRE containing promoter activity was stimulated by BMP‐2 or by constitutively active BMP receptors (BMPR‐IA and BMPR‐IB). The stimulation was blocked by co‐transfecting with dominant negative BMPR‐IA or Smad7. A unique DNA–protein complex was induced in response to BMP‐2 on the BRE. The complex induced by BMP‐2 contained Smad1 and Smad4, possibly as a complex of both Smads. BMP‐2 failed to stimulate the expression of Id1 mRNA in Smad4‐deficient cells. Over‐expression of Smad4, but not Smad1, stimulated the Id1 reporter activity and the expression of endogenous Id1 mRNA in Smad4‐deficient cells.

Conclusion: Signalling of BMP‐2 to stimulate the expression of Id1 would be transduced by BMPR‐IA and mediated by Smad1 and Smad4, both of which form a complex on the 29 bp GC‐rich element.