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.