(A) Impact of the I500V variant on basal and TGFβ1-activated SBE(4)-luc was assessed by luciferase assays, ***<0.001, **** < 0.0001, n = 9–12. (B) Impact of the I500V variant on basal and BMP4-activated Xvent2-luc was assessed by luciferase assays, * < 0.05, ** < 0.01, **** < 0.0001, n = 9–12. Luciferase activity was normalized to Renilla and analyzed by one-way ANOVA, presented as mean ± SD. (C) Dominant-negative response of the I500V variant on WT-SMAD4 action on SBE(4)-luc in basal and TGFβ1-treated cells. (D) Dominant-negative response of the I500V variant on WT-SMAD4 action on Xvent2-luc in basal and BMP4-treated cells, a: comparison between WT-SMAD4- and WT/I500V- or I500V-transfected cells in basal conditions, p < 0.0001; b: comparison between WT-SMAD4- and WT/I500V- or I500V-transfected cells in TGFβ1/BMP4-treated cells, p < 0.001–0.0001; c: comparison between WT/I500V- and I500V-transfected cells in basal and BMP4-treated cells, p < 0.001–0.01. Luciferase activity was normalized to vector transfected cells within each treatment group, analyzed by one-way ANOVA, presented as mean ± SD, n = 6.