SMAD2 and neoplasm: In addition, TGF-β expression was also significantly inhibited in CT26 and LL/2 tumor cells treated with toxicarioside A. Western blot analysis indicated that Smad1 and phosphorylated Smad1 but not Smad2/3 and phosphorylated Smad2/3 were attenuated in HUVECs treated with toxicarioside A. Smad1 and Smad2/3 signaling remained unchanged in CT26 and LL/2 tumor cells treated with toxicarioside A. Endoglin knockout by small interfering RNA against endoglin induced alternations in Smad1 and Smad2/3 signaling in HUVECs.