Proteomics Analysis of Tangeretin-Induced Apoptosis through Mitochondrial Dysfunction in Bladder Cancer Cells

Tangeretin is one of the most abundant compounds in citrus peel, and studies have shown that it possesses anti-oxidant and anti-cancer properties. However, no study has been conducted on bladder cancer cells. Bladder cancer has the second highest mortality rate among urological cancers and is the fifth most common malignancy in the world. Currently, combination chemotherapy is the most common approach by which to treat patients with bladder cancer, and thus identifying more effective chemotherapeutic agents that can be safely administered to patients is a very important research issue. Therefore, this study investigated whether tangeretin can induce apoptosis and identified the signaling pathways of tangeretin-induced apoptosis in human bladder cancer cells using two-dimensional gel electrophoresis (2DGE). The results of the study demonstrated that 60 μM tangeretin reduced the cell survival of a BFTC-905 bladder carcinoma cell line by 42%, and induced early and late apoptosis in the cells. In this study 2DGE proteomics technology identified 41 proteins that were differentially-expressed in tangeretin-treated cells, and subsequently LC⁻MS/MS analysis was performed to identify the proteins. Based on the functions of the differentially-expressed proteins, the results suggested that tangeretin caused mitochondrial dysfunction and further induced apoptosis in bladder cancer cells. Moreover, western blotting analysis demonstrated that tangeretin treatment disturbed calcium homeostasis in the mitochondria, triggered cytochrome C release, and activated caspase-3 and caspase-9, which led to apoptosis. In conclusion, our results showed that tangeretin-induced apoptosis in human bladder cancer cells is mediated by mitochondrial inactivation, suggesting that tangeretin has the potential to be developed as a new drug for the treatment of bladder cancer.