BMP-2 modulates beta-catenin signaling through stimulation of Lrp5 expression and inhibition of beta-TrCP expression in osteoblasts.

Canonical BMP and Wnt signaling pathways play critical roles in regulation of osteoblast function and bone formation. Recent studies demonstrate that BMP-2 acts synergistically with beta-catenin to promote osteoblast differentiation. To determine the molecular mechanisms of the signaling cross-talk between canonical BMP and Wnt signaling pathways, we have used primary osteoblasts and osteoblast precursor cell lines 2T3 and MC3T3-E1 cells to investigate the effect of BMP-2 on beta-catenin signaling. We found that BMP-2 stimulates Lrp5 expression and inhibits the expression of beta-TrCP, the F-box E3 ligase responsible for beta-catenin degradation and subsequently increases beta-catenin protein levels in osteoblasts. In vitro deletion of the beta-catenin gene inhibits osteoblast proliferation and alters osteoblast differentiation and reduces the responsiveness of osteoblasts to the BMP-2 treatment. These findings suggest that BMP-2 may regulate osteoblast function in part through modulation of the beta-catenin signaling. (c) 2009 Wiley-Liss, Inc.