p63-Dependent Dickkopf3 Expression Promotes Esophageal Cancer Cell Proliferation via CKAP4

Dickkopf3 (DKK3) is a secretory protein that belongs to the DKK family, but exhibits structural divergence from other family members, and its corresponding receptors remain to be identified. Although DKK3 has been shown to have oncogenic functions in certain cancer types, the underlying mechanism by which DKK3 promotes tumorigenesis remains to be clarified. We show here that DKK3 stimulates esophageal cancer cell proliferation via cytoskeleton-associated protein 4 (CKAP4), which acts as a receptor for DKK3. DKK3 was expressed in approximately 50% of tumor lesions of esophageal squamous cell carcinoma(ESCC) cases; simultaneous expression of DKK3 and CKAP4 was associated with poor prognosis. Anti-CKAP4 antibody inhibited both binding of DKK3 to CKAP4 and xenograft tumor formation induced by ESCC cells. p63, a p53-related transcriptional factor frequently amplified in ESCC, bound to the upstream region of the DKK3 gene. Knockdown of p63 decreased DKK3 expression in ESCC cells, and reexpression of DKK3 partially rescued cell proliferation in p63-depleted ESCC cells. Expression of Delta Np63 alpha and DKK3 increased the size of tumor-like esophageal organoids, and anti-CKAP4 antibody inhibited growth of esophageal organoids. Taken together, these results suggest that the DKK3-CKAP4 axis might serve as a novel molecular target for ESCC. Significance: In esophageal cancer, findings identify DKK3 as a poor prognostic indicator and demonstrate CKAP4 inhibition as an effective therapeutic strategy. (C) 2018 AACR.