Myoblasts are believed to be attracted by sites of bone repair following a gradient of bone morphogenetic protein-2 (BMP-2). However, it is not known which types of surface proteins are induced by higher BMP-2 concentrations or even immobilized BMP-2, usually found at the fracture site.

To address this question murine MC3T3-E1 cells were treated with ascending concentrations of BMP-2 (6, 60, and 600 ng/ml) for 24 or 72 h and the expression of relevant surface proteins were studied by RT- or real time PCR. While N-, OB-, and E-cadherin as well as integrin a2, and a5 showed no or minor changes, there was a pronounced up-regulation of integrin a9 mRNA and protein. BMP-2 dose-dependently evoked an up to 30fold increase in a9 mRNA and an 13fold increase in a9 protein. Although a9 forms functional heterodimers only with the common b1 subunit, the latter protein was not increased. Depots of immobilized BMP-2, which deliver BMP-2 both as a free and bound protein, similarly changed the pattern of integrins. The role of BMP-2 induced over-expression of integrin a9 is not yet known. However, since integrin a9 binds e.g. to VCAM-1 or VEGF-C which are expressed by blood vessels it may be particularly involved in tissue organization or wound-healing.