- Participation of Smad2, Smad3, and Smad4 in transforming growth factor beta (TGF-beta)-induced activation of Smad7. THE TGF-beta response element of the promoter requires functional Smad binding element and E-box sequences for transcriptional regulation. Stopa, M., Anhuf, D., Terstegen, L., Gatsios, P., Gressner, A.M., Dooley, S. J. Biol. Chem. (2000)