The domain is duplicated in most members of this family. APCDD is directly regulated by the beta-catenin/Tcf complex, and its elevated expression promotes proliferation of colonic epithelial cells in vitro and in vivo [1]. APCDD1 has an N-terminal signal-peptide and a C-terminal transmembrane region. The domain is rich in cysteines, there being up to 12 such residues, a structural motif important for interaction between Wnt ligands and their receptors. APCDD1 is expressed in a broad repertoire of cell types, indicating that it may regulate a diverse range of biological processes controlled by Wnt signalling [2].

1: Isolation of a novel human gene, APCDD1, as a direct target of the beta-Catenin/T-cell factor 4 complex with probable involvement in colorectal carcinogenesis. Takahashi M, Fujita M, Furukawa Y, Hamamoto R, Shimokawa T, Miwa N, Ogawa M, Nakamura Y; Cancer Res. 2002;62:5651-5656. PMID:12384519

2: APCDD1 is a novel Wnt inhibitor mutated in hereditary hypotrichosis simplex. Shimomura Y, Agalliu D, Vonica A, Luria V, Wajid M, Baumer A, Belli S, Petukhova L, Schinzel A, Brivanlou AH, Barres BA, Christiano AM; Nature. 2010;464:1043-1047. PMID:20393562