Zoledronic Acid Suppresses Epithelial-to-Mesenchymal Transition and Invasion via Degradation of Ubiquitinated NEDD9 in PC-3 Prostate Cancer Cells

Abstract

Objective: Zoledronic acid (ZA) is highly effective in the treatment of castration-resistant prostate cancer (CRPC) patients with bone metastases. It is one of bone modifying agents (BMAs) that has been shown to exert not only inhibiting the activation of osteoclasts but also preventing the tumor cell growth, invasion and migration in some cancers. Neural precursor cell-expressed developmentally downregulated protein 9 (NEDD9) is a key regulator of tumor aggressiveness including invasion, epithelial-to-mesenchymal transition (EMT), dedifferentiation and resistance to chemo-drugs. However, research into a biological mechanism in the inhibitory effects of ZA on prostate cancer (PCa) metastasis is still limited. In this study, we examined its effects on tumor cell invasion and EMT via the ubiquitin-proteasomal system for NEDD9 in PC-3 cells.Methods: We assessed the expression of NEDD9 and its down-stream molecules associated with EMT in PC-3 cells exposure to ZA under the condition with/without TGF-β. By a boyden chamber assay, the suppressive effect of ZA on PC-3 cell invasion triggered by TGF-β was measured. We measured the expression levels of NEDD9 in PC-3 cells exposure to a proteasome inhibitor, MG132. In addition, we detected the effect of ZA on ubiquitinated NEDD9 using an immunoprecipitation method.Results: ZA markedly inhibited the expression of NEDD9 and its down-stream EMT molecules. Both the invasion and expression of EMT markers of PC-3 cells triggered by TGF-β were significantly suppressed by the exposure to ZA. The exposure to MG132 inhibited the degradation of NEDD9 in PC-3 cells. The further add-on of ZA enhanced the polyubiquitination of NEDD9 in PC-3 cells.Conclusion: The results from a current study indicate that ZA inhibited the invasion and expression of NEDD9 and its EMT markers, along with the enhanced degradation of ubiquitinated NEDD9 in PC-3 cells.