Antagonizes canonical Wnt signaling by inhibiting LRP5/6 interaction with Wnt and by forming a ternary complex with the transmembrane protein KREMEN that promotes internalization of LRP5/6 (PubMed:22000856). DKKs play an important role in vertebrate development, where they locally inhibit Wnt regulated processes such as antero-posterior axial patterning, limb development, somitogenesis and eye formation. In the adult, Dkks are implicated in bone formation and bone disease, cancer and Alzheimer disease (PubMed:17143291). Inhibits the pro-apoptotic function of KREMEN1 in a Wnt-independent manner, and has anti-apoptotic activity (By similarity). Interacts with LRP6 (PubMed:11448771, PubMed:17804805, PubMed:20093360, PubMed:22000856). Interacts (via the C-termianl Cys-rich domain) with LRP5 (via beta-propeller regions 3 and 4); the interaction, enhanced by MESD and or KREMEN, antagonizes Wnt-mediated signaling (PubMed:19746449). Forms a ternary complex with LRP6 and KREM1 (PubMed:27524201). Interacts with KREM1 (PubMed:17804805). Placenta. The C-terminal cysteine-rich domain mediates interaction with LRP5 and LRP6. Belongs to the dickkopf family.