Intestinal cancer progression by mutant p53 through the acquisition of invasiveness associated with complex glandular formation

Tumor suppressor TP53 is frequently mutated in colorectal cancer (CRC), and most mutations are missense type. Although gain-of-functions by mutant p53 have been demonstrated experimentally, the precise mechanism for malignant progression in in vivo tumors remains unsolved. We generated Apc(Δ716) Trp53(LSL•R270H) villin-CreER compound mice, in which mutant p53(R270H) was expressed in the intestinal epithelia upon tamoxifen treatment, and examined the intestinal tumor phenotypes and tumor-derived organoids. Mutant Trp53(R270H), but not Trp53-null mutation accelerated submucosal invasion with generation of desmoplastic microenvironment. The nuclear accumulation of p53 was evident in Apc(Δ716) Trp53(R270H/R270H) homozygous tumors like human CRC. Although p53 was distributed to the cytoplasm in Apc(Δ716) Trp53(+/R270H) heterozygous tumors, it accumulated in the nuclei at the invasion front, suggesting a regulation mechanism for p53 localization by the microenvironment. Importantly, mutant p53 induced drastic morphological changes in the tumor organoids to complex glandular structures, which was associated with the acquisition of invasiveness. Consistently, the branching scores of human CRC that carry TP53 mutations at codon 273 significantly increased in comparison with those of TP53 wild-type tumors. Moreover, allografted Apc(Δ716) Trp53(R270H/R270H) organoid tumors showed a malignant histology with an increased number of myofibroblasts in the stroma. These results indicate that nuclear-accumulated mutant p53(R270H) induces malignant progression of intestinal tumors through complex tumor gland formation and acquisition of invasiveness. Furthermore, RNA sequencing analyses revealed global gene upregulation by mutant p53(R270H), which was associated with the activation of inflammatory and innate immune pathways. Accordingly, it is possible that mutant p53(R270H) induces CRC progression, not only by a cell intrinsic mechanism, but also by the generation or activation of the microenvironment, which may synergistically contribute to the acceleration of submucosal invasion. Therefore, the present study indicates that nuclear-accumulated mutant p53(R270H) is a potential therapeutic target for the treatment of advanced CRCs.