Down-regulation of USP8 Inhibits Cholangiocarcinoma Cell Proliferation and Invasion.

Objective: Cholangiocarcinoma is the second most common primary hepatobiliary malignancy with high incidence and recurrence rate. Ubiquitin-specific protease 8 (USP8) is recently reported to be involved in tumor progression. Herein, we aimed to investigate the effects of USP8 on the growth and metastasis abilities of cholangiocarcinoma cells. Methods: The siRNA interference was used to knock down USP8 in cholangiocarcinoma cell lines QBC939 and RBE; Hucct-1 cells were transfected with pcDNA3.1-USP8 to up-regulate its expression. The effects of USP8 on cholangiocarcinoma were detected by cell function assays. We analyzed the expressions of USP8, Bcl2, Bax, cleaved caspase-3, cleaved caspase-9, Akt, p-Akt, Cyclin D1 and P70S6K by Western blot analysis. Results: We demonstrated that knockdown of USP8 significantly inhibited the proliferation, migration and invasion of QBC939 and RBE cells in vitro, while USP8 overexpression showed significant promoting effects on Hucct-1 cells. Moreover, silencing of USP8 also promoted apoptosis in cholangiocarcinoma cells by regulating the Bcl-2/Bax axis and Caspase cascade; up-regulation of USP8 decreased apoptosis in Hucct-1 cells. Importantly, knockdown of USP8 inhibited activation of the Akt signaling pathway by decreasing the phosphorylation level of Akt and up-regulated p53 expression, while USP8 overexpression increased activation of the Akt signaling pathway in Hucct-1 cells. Further, IGF-1 could reverse the inhibitory effects of USP8 knockdown on the Akt signaling pathway and the proliferation of QBC939 and RBE cells. Conclusion: Taken together, our findings suggest that USP8 exerts an oncogenic role in the progression of cholangiocarcinoma and may be a potential therapeutic target for cholangiocarcinoma treatment.