Summary

TGF-β1 is known to be both anti-inflammatory and profibrotic. Cross-talk between TGF-β/Smad and Wnt/β-catenin pathways in epithelial-mesenchymal transition (EMT) suggests a specific role for β-catenin in profibrotic effects of TGF-β1. However, no such mechanistic role has been demonstrated for β-catenin in the anti-inflammatory effects of TGF-β1. We explored the role of β-catenin in TGF-β1's profibrotic and anti-inflammatory effects by using a cytosolic but not membrane β-catenin knockdown chimera (F-TrCP-Ecad) and the β-catenin inhibitor ICG-001. TGF-β1 induced nuclear Smad3/β-catenin complex but not β-catenin/LEF-1 complex or TopFlash activity during EMT of C1.1 cells. F-TrCP-Ecad selectively degraded TGF-β1-induced cytoplasmic β-catenin and blocked EMT of C1.1 (renal tubular epithelial) cells. Both F-TrCP-Ecad and ICG-001 blocked TGF-β1-induced Smad3/β-catenin and Smad reporter activity in C1.1 cells, suggesting that TGF-β1-induced EMT depends on β-catenin binding to Smad3 but not LEF-1 downstream of Smad3 through canonical Wnt. In contrast, in J774 macrophages, the β-catenin level was low and was not changed by IFN-γ or LPS with or without TGF-β1. TGF-β1 inhibition of LPS-induced TNF-α and IFN-γ-stimulated iNOS expression was not affected by F-TrCP-Ecad, ICG-001 or by over expression of wild-type β-catenin in J774 cells. Inhibition of β-catenin by either F-TrCP-Ecad or ICG-001 abolished LiCl induced TopFlash but not TGF-β1-induced Smad reporter activity in J774 cells. These results demonstrate for the first time that β-catenin is required as a co-factor of Smad in TGF-β1-induced EMT of C1.1 epithelial cells, but not in TGF-β1 inhibition of macrophage activation. Targeting β-catenin may dissociate TGF-β1 profibrotic and anti-inflammatory effects.