Therapeutic Potential of Dickkopf-1 in Wild-Type BRAF Papillary Thyroid Cancer via Regulation of β-Catenin/E-cadherin Signaling

Background: Aberrant activation of the Wnt/beta-catenin pathway is a common pathogenesis of various human cancers. We investigated the role of the Wnt inhibitor, Dkk-1, in papillary thyroid cancer (PTC). Methods: Immunohistochemical beta-catenin staining was performed in tissue microarray containing 148 PTCs and five normal thyroid tissues. In vivo effects of Dkk-1 were explored using ectopic tumors with BHP10-3SC cells. Results: In 27 PTC patients, 60% of patients showed beta-catenin up-regulation and Dkk-1 down-regulation in tumor vs normal tissues. Tissue microarray analysis showed that 14 of 148 PTC samples exhibited cytoplasmic-dominant beta-catenin expression compared to membranous-dominant expression in normal tissues. Aberrant beta-catenin expression was significantly correlated with higher rates of the loss of membranous E-cadherin expression and poor disease-free survival than that in the normal membranous expression group over a median follow-up period of 14 years. Implantation of Dkk-1-overexpressing BHP10-3SC cells revealed delayed tumor growth, resulting from the rescue of membranous beta-catenin and E-cadherin expressions. Furthermore, tissue microarray analysis demonstrated that BRAF(WT) patients had higher rates of aberrant expressions of beta-catenin and E-cadherin than BRAF(V600E) patients. Indeed, the inhibitory effects of Dkk-1 on cell survival were more sensitive in BRAF(WT) (BHP10-3SC and TPC-1) than in BRAF(V600E) (SNU-790 and BCPAP) cells. Overexpression of BRAF(V600E) in normal thyroid epithelial (H tori) cells also reduced the effects of Dkk-1 on cell survival. Conclusion: A subset of PTC patients showed aberrant expression of beta-catenin/E-cadherin signaling and poor disease-free survival. Dkk-1 might have a therapeutic role, particularly in BRAF(WT) patients.