Dkk-3, also known as REIC, is a member of the Dickkopf family of secreted Wnt antagonists. Dkk-3 is expressed most strongly in adult heart, brain, and spinal cord as well as during early embryonic development. Dkk-3 is downregulated in many tumors which often is correlated with faster tumor progression and shorter survival. The prototype Dickkopf member, Dkk-1, antagonizes Wnt family signaling by binding to Wnt receptors LRP5 and LRP6 (low-density lipoprotein receptor-related proteins) and promoting their internalization. In contrast, Dkk-3 may either promote or inhibit Wnt signaling.