CKAP4 and head and neck squamous cell carcinoma: DKK3 was previously shown to bind to Cytoskeleton-Associated Protein 4 (CKAP4) on esophageal cancer cells (39), and DKK3 and CKAP4 were found to be required for the phosphorylation of the Akt serine/threonine kinase in HNSCC cell lines (40).