To further explore the inhibitory effect of TGF-β on CCBE1 expression in CRC, a TGF-β-responsive CRC cell line (SW837) 34 and four CRC cell lines with defective TGF-β signaling (HCT116, TGFBR2 mutant; HT29, SMAD4 mutant; SW480, SMAD4 deficient; and LoVo, SMAD2 mutant) were used to investigate the effect of TGF-β on CCBE1 gene transcription in CRC cells. Here, SMAD4 is linked to colorectal carcinoma.