BMPs and canonical Wnts are the representative developmental signals that enhance osteoblast differentiation and bone formation. Previously, we demonstrated that EGF inhibits BMP2-induced osteoblast differentiation through the induction of Smurf1 expression. However, the regulatory role of EGF in Wnt/β-catenin-induced osteoblast differentiation has not been elucidated. In this study, we investigated the effect of EGF on Wnt/β-catenin signaling-induced osteoblast differentiation using C2C12 cell line. EGF significantly suppressed the expression of osteoblast marker genes, which was induced by Wnt3a and GSK-3β inhibitor. EGF increased the expression levels of Smurf1 mRNA and protein. Smurf1 knockdown rescued Wnt/β-catenin-induced osteogenic marker gene expression in the presence of EGF. EGF treatment or Smurf1 overexpression did not affect the expression level of β-catenin mRNA but reduced β-catenin protein level and TOPFLASH activity. EGF and Smurf1 promoted β-catenin ubiquitination. Co-immunoprecipitation and GST pull-down assays showed that Smurf1 associates with β-catenin. These results suggest that EGF/Smurf1 inhibit Wnt/β-catenin-induced osteogenic differentiation and that Smurf1 downregulate Wnt/β-catenin signalling via enhancing proteasomal degradation of β-catenin.
17 May 2014 - 20 May 2014