Fig. 5

TNF-α-induced canonical NF-κB signaling inhibited the activation of canonical TGF-β-SMAD signaling pathway. a A novel model of the cross-talk between NF-κB and TGF-β-SMAD signaling pathway mediated by SMAD7 in DESC differentiation. Under the stimulation of TNF-α, canonical NF-κB signaling pathway is activated and IKK complex is recruited to TNF-α receptor-associated proteins (TRAF), where it is activated and further brings about phosphorylation, ubiquitination, and proteasomal degradation of IκB. These events allow translocation of prototypical p65/p50 dimer into the nucleus, which induces the SMAD7 expression and in turn suppresses the phosphorylation of SMAD2/3 to inhibit the TGF-β-SMAD signaling pathway. b The expressions of canonical TGF-β-SMAD signaling components (p-SMAD2/3, SMAD2/3, SMAD4) were downregulated in TNFα-treated DESCs, while increased in BMS-345541-treated DESCs. In contrast, the SMAD7 expression was increased in TNFα-treated DESCs, while downregulated in BMS-345541-treated DESCs by Western blot analyses. GAPDH served as an internal control. c DESCs were preincubated with the recombinant TGF-β prior to stimulation with TNFα (10 ng/ml), and expressions of amelogenesis-related proteins and canonical TGF-β signaling components were detected by Western blot analysis. d Gray level analysis of the TGF-β-SMAD signaling components and SMAD7 in b. e Gray level analysis of proteins in c. All values were presented as the means ± SD of triplicate experiments. *P < 0.05, **P < 0.01, and ***P < 0.001