SMAD4 and malignant colon neoplasm: We used the colon cancer cell line Caco-2, which has lost one allele of smad4 while the other allele harbors the Asn351His Smad4 point mutation (smad4−/N315H).31 Caco-2 cells were transfected with the TGF-β–specific reporter CAGA12-luciferase (and pCS2-Renilla for normalization), incubated with or without LiCl, and treated for 8 h with different amounts of TGF-β1 ligand (Fig. 5).