FIGURE 7.

TGFα activates β-catenin in chondrocytes through LRP6 phosphorylation. A, primary chondrocyte cultures were pretreated with IWR-endo for 30 min followed by TGFα treatment for 48 h and subjected to immunoblot for active β-catenin (active), total β-catenin (total), and β-actin as internal control (actin). B and C, primary chondrocyte cultures were pretreated with gefitinib (gef), U0126, SB203580 (SB) (B) or DKK1 (C) for 30 min followed by TGFα for 15 min and subjected to immunoblot for phosphorylated and total LRP6. con, control. D, DKK1 abrogates the TGFα-induced nuclear translocation of β-catenin in chondrocytes as demonstrated by immunofluorescence analysis using anti-β-catenin antibody. **, p < 0.01 versus control. E, qRT-PCR revealed that TGFα-induced Mmp9 and RANKL expression but not MMP13 expression was partially abolished by DKK1. *, p < 0.05 versus TGFα-treated control. F, qRT-PCR revealed that 48 h of TGFα (50 ng/ml) and BIO (0.5 μg/ml) treatment synergistically increased Mmp9 and RANKL expression. *, p < 0.05, **, p < 0.01, ***, p < 0.001 versus vehicle-treated control; &, p < 0.001 versus TGFα alone or BIO alone.