Suppression of Mir-708 Promotes DKK3 to Inhibit Wnt/β-Catenin Signaling Pathway in Adult B-ALL

Dickkopf-3 (DKK-3) is a Wnt signaling antagonist, and DKK3 inactivation is associated with poor prognosis in various solid tumors and hematologic malignancies. Epigenetic hypermethylation has been implicated in downregulation of DKK3, but other regulatory mechanisms remain to be investigated. In this study, we examined DKK3 expression and the role of microRNA in the regulation of DKK3 in adult B-ALL. Our results showed low levels of DKK3 expression in Nalm-6 and BALL-1 cell lines, and leukemia cells from adult B-ALL patients. DKK3 expression was remarkably lower in the initial diagnosis and relapse samples than in the matched samples during remission. In addition to hypermethylation, low levels of DKK3 were associated with high expression of miR-708. This finding was similar to that in childhood ALL. The miR-708 was predicted to bind to the 3'-UTR of DKK3. By using miR-708 mimics, we found that miR-708 targets DKK3 to promote B-ALL cell proliferation through cell cycle promotion and apoptosis inhibition. The treatment with 5-aza-2'-deoxycytidine significantly increased DKK3 and decreased p-GSK3β, cyclin D1 and nuclear and cytoplasmic β-catenin protein expression. A synergistic effect was seen when the miR-708 inhibitor and 5-aza were used simultaneously. Although miR-708 was reported to either promote or suppress tumorigenecity in some solid tumors, our findings indicate that suppression of miR-708 increases DKK3 expression to inhibit the Wnt/β- catenin signaling pathway in B-ALL.