The binding of TGF-b to its receptors induces phosphorylation of Smad2 and Smad3, their subsequent association to Smad4 and their nuclear translocation. In the nucleus, the Smad3/Smad4 and Smad2/Smad4 heterodimers act as transcription factors and induce specific target genes. TGF-b pathway has a tumor suppressor function characterized by its ability to inhibit cell growth. Many cancer cell lines h ...