Capn4 expression is modulated by microRNA-520b and exerts an oncogenic role in prostate cancer cells by promoting Wnt/β-catenin signaling

Accumulating evidence reports that Capn4 plays an important role in the development and progression of various malignant cancers. However, whether Capn4 is involved in prostate cancer remains unclear. Therefore, the aim of this study was to investigate the expression, biological function and regulatory mechanism of Capn4 in prostate cancer. Herein, we found that Capn4 was highly expressed in prostate cancer cell lines compared with normal prostate cells. Capn4 gene silencing markedly suppressed the growth, invasion and Wnt/β-catenin signaling of prostate cancer cells, whereas Capn4 overexpression showed an oncogenic effect. Moreover, silencing of β-catenin significantly blocked the oncogenic effect of Capn4 overexpression. Bioinformatics analysis predicted that Capn4 was a potential target gene of microRNA-520b (miR-520b), which has been reported as a tumor suppressive miRNA in various cancers. The dual-luciferase reporter assay confirmed that miR-520b directly bound to the 3'-untranslated region of Capn4. Real-time quantitative PCR and Western blot analysis showed that miR-520b negatively regulated Capn4 expression in prostate cancer cells in vitro. Furthermore, we found that miR-520b was significantly downregulated in prostate cancer cell lines and tissues. In addition, miR-520b expression was inversely correlated with Capn4 expression in prostate cancer clinical specimens. Overexpression of miR-520b mimicked the tumor suppressive effect of Capn4 siRNA, whereas inhibition of miR-520b had an oncogenic effect. Restoration of Capn4 significantly blocked the antitumor effect of miR-520b in prostate cancer cells. Overall, our findings demonstrate an oncogenic role of Capn4 in prostate cancer and show that its expression is epigenetically regulated by miR-520b. Our results reveal that suppression of Capn4 by miR-520b inhibits the growth and invasion of prostate cancer cells associated with downregulated Wnt/β-catenin signaling, indicating an important role of the miR-520b/Capn4/Wnt/β-catenin regulation axis in the molecular pathogenesis of prostate cancer. Our study suggests that miR-520b and Capn4 may represent potential and novel therapeutic targets for prostate cancer.