Stromal ISLR promotes intestinal regeneration and cancer by suppressing epithelial Hippo signaling via FAT1

The YAP signaling activation in epithelial cells is essential for intestinal regeneration and tumorigenesis. However, the molecular mechanism linking stromal signals to YAP-mediated intestinal regeneration and tumorigenesis is poorly defined. Here we report a stroma-epithelia YAP signaling axis essential for stromal cells to modulate epithelial cell growth during intestinal regeneration and tumorigenesis. Specifically, upon inflammation and in cancer, an oncogenic transcription factor ETS1 in stromal cells induces expression of a secreted protein ISLR that can directly binds to a transmembrane protocadherin FAT1 on the surface of epithelial cells. This binding suppressed the Hippo signaling by disrupting MST1-FAT1 association, resulting in YAP signaling activation. Deletion of Islr in stromal cells in mice markedly impaired intestinal regeneration, and suppressed tumorigenesis in the colon. Moreover, the expression of stromal cell-specific ISLR and ETS1 significantly increased in inflamed mucosa of human IBD patients and in human colorectal adenocarcinoma, accounting for the epithelial YAP hyperactivation. Collectively, our findings uncovered a molecular mechanism governing signals for communication between stroma and epithelium during tissue regeneration and tumorigenesis.