TP53 and colorectal carcinoma: We then investigated the involvement of p21Waf1/Cip1 (p21), the downstream p53 target gene that mediates p53-induced cell cycle arrest, in the 5-FU-induced activation of the WNT/β-catenin signaling pathway using HCT116 p21 wild-type (p21+/+) and null (p21−/−) isogenic human CRC cell lines.