BMP-2-induced Osterix expression is mediated by Dlx5 but is independent of Runx2.

BMP-2 stimulates the expression of three osteogenic master transcription factors: Runx2, Dlx5, and Osterix (Osx). However, the hierarchical regulatory relationships among them are not yet clearly understood. Osx was commonly stimulated in osteogenic and non-osteogenic cells in response to BMP-signaling, as Dlx5 was in our previous report. A cycloheximide experiment indicated that Osx expression by BMP-2 requires new protein synthesis. Even if Osx has been suggested as a downstream target of Runx2, the results of this study indicated that Osx expression was still induced by BMP-2 treatment in Runx2 null cells, but not induced by Runx2 overexpression in myogenic C2C12 cells. Instead, Osx expression by BMP-2 was completely abrogated by the antisense blocking of Dlx5. Depending upon the coincident expression pattern of Osx and Dlx5, and the blocking of Osx expression by the antisense Dlx5, BMP-2-induced Osx expression is mainly mediated not by Runx2, but by Dlx5.