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first cysteine-rich (Cys-1) domain of Dickkopf-related protein 4 Dickkopf 4 (Dkk4) is a secreted protein which directly binds to LRP5/6 (low-density lipoprotein receptor related protein 5 and 6), and is an inhibitor of Wnt/beta-catenin signaling. Dkk4, which is upregulated by the activated Wnt pathway, contributes to tumor malignancy in variable tumors, promoting tumor cell invasion and progression. Aberrant accumulation of Dkk4 has been shown to promote tumor progression by forming the immune suppressive microenvironment in gastrointestinal stromal tumor, and thus Dkk4 may be used as a tumor biomarker for prognosis prediction and recurrence monitoring. Dkk4 belongs to the Dickkopf (Dkk) family that comprises a discrete class of secreted Wnt inhibitors. The Wnt gene family is a large class of secreted proteins that are expressed in a variety of tissues and organs, and are required for many developmental processes, including segmentation, endoderm development, limb polarity, neural crest differentiation, kidney morphogenesis, sex determination and brain development. Dkks 1-4 each possesses an N-terminal signal peptide and contains two conserved cysteine-rich domains (Cys-1 and Cys-2) separated by a linker region. Each domain possesses 10 conserved cysteine residues. The Cys-2 domain is closely similar to those in the colipase family; it has been suggested that the Cys-2 domain of Dkks may enable interaction with lipids in order to regulate Wnt function. This model corresponds to the Cys-1 domain of Dkk4. |
Jiyao W et al.(2023). "The conserved domain database in 2023.",