ZNRF3 (zinc/RING finger protein 3), also known as RNF203, is a predicted 101kDa type I transmembrane protein and a member of the ZNRF3 family of ubiquitin ligases. This protein is specifically expressed in stem cells located at the base of colon crypts, where it restricts the proliferative effects of Wnts proteins. ZNRF3 is also found in normal gastric tissues; however, its expression is downregulated in gastric adenocarcinomas.