Inhibitory effect of genistein on mouse colon cancer MC-26 cells involved TGF-β1/Smad pathway

TGF-β1/signaling has been shown to be associated with proapoptotic and antimitotic activities in epithelial tissues. Genistein, a major component of soybean isoflavone, has multiple functions resulting in anticancer proliferation. We herein showed that genistein dose-dependently increased TGF-β1 mRNA expression in mouse colon cancer MC-26 cells. A mouse monoclonal anti-TGF-β1 neutralizing antibody partially, but not completely, blocked the growth inhibition by genistein. By using adenoviral vector, we demonstrated that Smad7 overexpression attenuated genistein-induced growth inhibition and apoptosis as determined by MTT and apoptosis ELISA. Smad7 overexpression also inhibited upregulation of p21 and caspase-3 activity by geinistein. To further confirm inhibitory effect of genistein in MC-26 cells require TGF-β1/Smad signaling, we employed Western blot and electrophoretic mobility shift assay to detect formation of Smad-DNA complexes and phosphorylation of Smad2 and Smad3, respectively. Data revealed that genistein induced an evident formation of Smad-DNA complexes and phosphorylation of Smad2 and Smad3, indicating increased TGF-β1 signaling. Taken together, these findings first provided insights into possible molecular mechanisms of growth inhibition by genistein that required Smad signaling, which could aid in its evaluation for colon tumor prevention.