TGF-beta1/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-beta1 mRNA expression in mouse
colon cancer MC-26 cells. A mouse monoclonal anti-TGF-beta1
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-beta1/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-beta1 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.