SMAD3 and breast cancer: In breast cancer cells, TIF1γ (transcriptional intermediary factor 1) is an E3 ubiquitin‐protein ligase responsible for the ubiquitination‐mediated degradation of Smad3/Smad4 protein complex, and FoxM1 protein could directly interact with the Smad3 proteins in the nucleus to inhibit the TIF1γ‐mediated Smad4 protein degradation and maintain the sustained activation of the Smad3/Smad4 complex.16