Curcumin suppresses TGF-β signaling by inhibition of TGIF degradation in scleroderma fibroblasts

► We demonstrated a potent inhibitory effect of curcumin on TGF-β signaling in scleroderma fibroblasts. ► Curcumin counteracted TGF-β-induced phosphorylation of Smad2 but not Smad3. ► Curcumin induced upregulation of TGF-β-induced factor (TGIF), which is required in curcumin-mediated TGF-β/Smad2 suppression. ► The upregulation of TGIF by curcumin might result from decreased ubiquitination of TGIF, which blocks its proteasome-mediated degradation.