C10ORF99 (GPR15L) increases susceptibility to colitis and colitis-induced colorectal cancer via GPR15-independent mechanisms, while mediating GPR15-dependent T cell migration to the large intestine.

GPR15 is a homing receptor important for T cell migration to the large intestine, the primary site of inflammation in ulcerative colitis. Both GPR15 and its ligand, C10ORF99, represent potential therapeutic targets for the treatment of IBD; however, the roles of C10ORF99 in the large intestine are not fully elucidated. Here, we demonstrate that C10ORF99 is the non-redundant ligand of GPR15 mediating T cell migration to the large intestine. Furthermore, we demonstrate that C10ORF99 has GPR15-independent functions in the large intestine: C10ORF99 deficiency is protective in chemically induced colitis, and this appears to result from enhanced epithelial barrier regeneration. We found that C10ORF99 can inhibit intestinal epithelial proliferation in a cell-intrinsic manner. Additionally, due to this protection from colitis development in the absence of C10ORF99, C10ORF99 KO is also protected from colitis-associated colorectal cancer development. These data indicate that the deficiency of C10ORF99 can not only block pathogenic T cell migration to the large intestine, but can also promote epithelial barrier repair, potentially offering additional advantages for recovery from ulcerative colitis.