Loss of DRO1/CCDC80 in the tumor microenvironment promotes carcinogenesis.

Tumors are composed of the tumor cells and the surrounding microenvironment. Both are closely interwoven and interact by a complex and multifaceted cross-talk which plays an integral part in tumor initiation, growth, and progression. Dro1/Ccdc80 has been shown to be a potent suppressor of colorectal cancer and ubiquitous inactivation of Dro1/Ccdc80 strongly promoted colorectal carcinogenesis in Apc(Min/+) mice and in a chemically-induced colorectal cancer model. The aim of the present study was to investigate whether Dro1/Ccdc80's tumor suppressive function is tumor-cell-autonomous. Expression of Dro1/Ccdc80 in cancer cells had no effect on both colon tumor development in Apc(Min/+) mice and formation of xenograft tumors. In contrast, DRO1/CCDC80 loss in the microenvironment strongly increased tumor growth in xenograft models, inhibited cancer cell apoptosis, and promoted intestinal epithelial cell migration. Moreover, stromal Dro1/Ccdc80 inactivation facilitated formation of intestinal epithelial organoids. Expression analyses showed Dro1/Ccdc80 to be significantly down-regulated in murine gastric cancer associated fibroblasts, in Apc(Min/+) colon tumor primary stromal cells and in microdissected stroma from human colorectal cancer compared to normal, non-tumor stroma. Our results demonstrate epithelial derived DRO1/CCDC80 to be dispensable for intestinal tissue homeostasis and identify Dro1/Ccdc80 as tumor suppressor in the tumor microenvironment.