Smad4 and p53 synergize in suppressing autochthonous intestinal cancer

BACKGROUND: Smad4 and p53 mutations are the most common mutations in human colorectal cancers (CRCs). We evaluated whether and how they are synergistic in intestinal carcinogenesis using novel autochthonous mouse models. METHOD: To recapitulate human CRCs, we generated Villin‐Cre;Smad4(F) (/) (F) ;Trp53(F) (/) (F) mice. We then compared the intestinal phenotype of Villin‐Cre;Smad4(F) (/) (F) ;Trp53(F) (/) (F) mice (n = 40) with Villin‐Cre;Smad4(F) (/) (F) (n = 30) and Villin‐Cre;Trp53(F) (/) (F) mice (n = 45). RESULTS: Twenty‐week‐old Villin‐Cre;Smad4(F) (/) (F) ;Trp53(F) (/) (F) mice displayed spontaneous highly proliferative intestinal tumors, and 85% of mice developed adenocarcinomas. p21 was downregulated in the intestinal mucosa in Villin‐Cre;Smad4(F) (/) (F) ;Trp53(F) (/) (F) mice than in Villin‐Cre;Smad4(F) (/) (F) and Villin‐Cre;Trp53(F) (/) (F) mice. Villin‐Cre;Smad4(F) (/) (F) ;Trp53(F) (/) (F) mice displayed multistep intestinal tumorigenesis and Wnt activation. Long‐term CWP232291 (small‐molecule Wnt inhibitor) treatment of Villin‐Cre;Smad4(F) (/) (F) ;Trp53(F) (/) (F) mice suppressed intestinal tumorigenesis and progression. CWP232291 treatment downregulated cancer stem cell (CSC) tumor markers including CD133, Lgr‐5, and Sca‐1. CWP232291 treatment reduced the CSC frequency. Small‐molecule Wnt inhibitors reduced intestinal CSC populations and inhibited their growth, along with Bcl‐X(L) downregulation. Furthermore, BH3I‐1, a Bcl‐X(L) antagonist, increasingly inhibited intestinal CSCs than bulk tumor cells. CONCLUSION: Smad4 loss and p53 loss are synergistic in autochthonous intestinal carcinogenesis, by downregulating p21 and activating Wnt/β‐catenin pathway.