IL-17RA signaling provides dual tumor-suppressor function during late-stage colorectal carcinogenesis

Expression of interleukin (IL)-17 family cytokines is associated with tumor-promoting inflammation. We found that low expression of IL17RA associated with worse prognosis in late-stage colorectal cancer (CRC) patients. Deletion of Il17ra in intestinal epithelial cells (IECs) in a murine model of CRC enhanced epithelial-to-mesenchymal transition (EMT) via increased expression of the epidermal growth factor receptor and subsequent activation of the kinase Src. Yet, these mice were protected from metastatic disease; Il17ra deletion impaired intestinal barrier function and enhanced systemic fungal invasion and associated immunity. However, in macrophages, IL-17RA was required for spleen tyrosine kinase (Syk) activation upon fungal-induced dectin-1 engagement, and Il17ra ablation impaired IL-18 release and protective CD8⁺ T cell-mediated anti-tumor immunity. Combining recombinant IL-17 and heat-killed Candida albicans rendered colorectal tumors sensitive to α-PD-1 treatment in a model of microsatellite stable (MSS) CRC. Thus, IL-17RA engages two distinct tumor-suppressive mechanisms in CRC, linking EMT and fungal-induced anti-tumor immunity during tumor progression.