DKK-1 is a 266-amino acid protein with an approximate molecular mass of 26-kDa, and it possesses six secondary structures, which are two alpha helices and four β-sheets. It has the colipase-like fold in C-terminal Cys domain, which likely allows it to serve as an interactive surface. DKK-1 expression appears to be preferential in some adult tissues including bone, placenta, prostate, spleen, and colon. DKK-1 has been shown to play an important role as a Wnt signaling pathway antagonist in several studies. DKK-1 is down-regulated in human colon tumours; hence, it may act as a tumour suppressor. High DKK-1 expression indicated favourable responses to chemotherapy in brain tumours whereas; over-expression of DKK-1 was found in human hepatoblastomas, Wilms’ tumours and multiple myelomas. Moreover, since overexpression of DKK-1 in osteoblasts causes osteopenia, it is also regarded as a negative regulator of normal bone homeostasis.