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Histological diagnosis of the primary tumors

Increased number of small adenomas by Kras mutation

Villous-type morphology of intestinal tumors by AKF combination

Immune cell infiltration into metastasized liver tumors

Colorectal cancer is driven by the accumulation of driver mutations, but the contributions of specific mutations to different steps in malignant progression are not fully understood. In this study, we generated mouse models harboring different combinations of key colorectal cancer driver mutations (Apc, Kras, Tgfbr2, Trp53, Fbxw7) in intestinal epithelial cells to comprehensively investigate their roles in the development of primary tumors and metastases. ApcΔ716 mutation caused intestinal adenomas and combination with Trp53R270H mutation or Tgfbr2 deletion induced submucosal invasion. The addition of KrasG12D mutation yielded epithelial–mesenchymal transition (EMT)-like morphology and lymph vessel intravasation of the invasive tumors. In contrast, combinations of ApcΔ716 with KrasG12D and Fbxw7 mutation were insufficient for submucosal invasion, but still induced EMT-like histology. Studies using tumor-derived organoids showed that KrasG12D was critical for liver metastasis following splenic transplantation, when this mutation was combined with either ApcΔ716 plus Trp53R270H or Tgfbr2 deletion, with the highest incidence of metastasis displayed by tumors with a ApcΔ716 KrasG12D Tgfbr2−/− genotype. RNA sequencing analysis of tumor organoids defined distinct gene expression profiles characteristic for the respective combinations of driver mutations, with upregulated genes in ApcΔ716 KrasG12D Tgfbr2−/− tumors found to be similarly upregulated in specimens of human metastatic colorectal cancer. Our results show how activation of Wnt and Kras with suppression of TGFβ signaling in intestinal epithelial cells is sufficient for colorectal cancer metastasis, with possible implications for the development of metastasis prevention strategies.Significance: These findings illuminate how key driver mutations in colon cancer cooperate to drive the development of metastatic disease, with potential implications for the development of suitable prevention strategies. Cancer Res; 78(5); 1334–46. ©2017 AACR.

Submucosal tumors of transplanted AK organoids

Gene list of AKT common differentially genes (DEGs)

Submucosal invasion with desmoplasia and Snail2 expression

Genomic PCR results for confirmation of organoid genotypes

Supplementary Figure S5. Representative photographs of the whole intestine of X-ray irradiated wild-type and Tgfbr2ÃŽ?IEC mice.

Supplementary Figure S3. Histology of intestines of Tgfbr2ÃŽ?IEC mice.

Supplementary Figure S1. Representative photographs of the whole intestine of ApcÃŽ?716 mice and ApcÃŽ?716 Tgfbr2ÃŽ?IEC mice.

Supplementary Figure S2. Expression levels of microenvironment factors in stroma and epithelial cells of ApcÃŽ?716 mice.

Legends for Supplementary Figures S1-S6.

Supplementary Figure S6. Gene expression of inflammatory factors in normal and IBD tissue samples.

Supplementary Figure S4. Histological changes of X-ray-irradiated wild-type and Tgfbr2ÃŽ?IEC mouse intestines.

Genetic alterations in the TGFβ signaling pathway in combination with oncogenic alterations lead to cancer development in the intestines. However, the mechanisms of TGFβ signaling suppression in malignant progression of intestinal tumors have not yet been fully understood. We have examined ApcΔ716 Tgfbr2ΔIEC compound mutant mice that carry mutations in Apc and Tgfbr2 genes in the intestinal epithelial cells. We found inflammatory microenvironment only in the invasive intestinal adenocarcinomas but not in noninvasive benign polyps of the same mice. We thus treated simple Tgfbr2ΔIEC mice with dextran sodium sulfate (DSS) that causes ulcerative colitis. Importantly, these Tgfbr2ΔIEC mice developed invasive colon cancer associated with chronic inflammation. We also found that TGFβ signaling is suppressed in human colitis–associated colon cancer cells. In the mouse invasive tumors, macrophages infiltrated and expressed MT1-MMP, causing MMP2 activation. These results suggest that inflammatory microenvironment contributes to submucosal invasion of TGFβ signaling–repressed epithelial cells through activation of MMP2. We further found that regeneration was impaired in Tgfbr2ΔIEC mice for intestinal mucosa damaged by DSS treatment or X-ray irradiation, resulting in the expansion of undifferentiated epithelial cell population. Moreover, organoids of intestinal epithelial cells cultured from irradiated Tgfbr2ΔIEC mice formed “long crypts” in Matrigel, suggesting acquisition of an invasive phenotype into the extracellular matrix. These results, taken together, indicate that a simple genetic alteration in the TGFβ signaling pathway in the inflamed and regenerating intestinal mucosa can cause invasive intestinal tumors. Such a mechanism may play a role in the colon carcinogenesis associated with inflammatory bowel disease in humans. Cancer Res; 75(4); 766–76. ©2015 AACR.