SMAD2 and breast cancer: Similar to their inhibitory activities in NMuMG and breast cancer cells, retroviral-mediated expression of CystC or Δ14CystC in NRK cells prevented their morphological transformation stimulated by TGF-β (Fig. 6b), as well as inhibiting Smad2/3-mediated reporter gene expression (Fig. 6c) and cell invasion induced by TGF-β (Fig. 6d).