MicroRNA-939 Directly Targets HDGF to Inhibit the Aggressiveness of Prostate Cancer via Deactivation of the WNT/beta-Catenin Pathway

Purpose: MicroRNA-939 (miR-939) has crucial roles in several types of human cancer. However, the expression profile and precise functions of miR-939 in prostate cancer (PCa) are still unclear. This study aimed to determine miR-939 expression in PCa and explore its roles in PCa tumorigenesis. Methods: miR-939 expression was determined in PCa tissues and cell lines using reverse transcription-quantitative polymerase chain reaction. Cell Counting Kit-8, colony formation, and flow cytometric assays were used to determine the role of miR-939 in PCa cell proliferation and apoptosis in vitro, whereas a tumor xenograft model was generated to evaluate the effect of miR-939 on tumor growth in vivo. Transwell assays were performed to investigate whether miR-939 affects the migration and invasiveness of PCa cells. Results: miR-939 was found to be downregulated in PCa tissues and cell lines, and this downregulation was significantly correlated with tumor stage and lymphatic metastasis. Patients with PCa exhibiting low miR-939 expression had shorter overall survival than those exhibiting high miR-939 expression. Exogenous miR-939 expression suppressed PCa cell proliferation, colony formation, migration, and invasion in vitro; enhanced apoptosis in vitro; and decreased tumor growth in vivo. Investigation of the underlying molecular mechanisms revealed hepatoma-derived growth factor (HDGF) as a direct target gene of miR-939 in PCa. HDGF was found to be significantly upregulated in PCa tissues, and its expression was inversely correlated with miR-939 expression. HDGF silencing and miR-939 upregulation showed similar effects in PCa. Restored HDGF expression counteracted the tumor-suppressive activity of miR-939 overexpression in PCa cells. Furthermore, ectopic miR-939 expression inhibited the WNT/beta-catenin pathway activation in PCa both in vitro and in vivo by downregulating HDGF. Conclusion: miR-939 functions as a tumor suppressor during PCa tumorigenesis by directly targeting HDGF and deactivating the WNT/beta-catenin pathway, suggesting the miR-939/ HDGF/WNT/beta-catenin pathway as an effective target for PCa therapy.