Ming Sun, Zhaofu Chen, Shutao Tan, Caigang Liu, Wenyan Zhao

FSIP1 plays a vital role in tumorigenesis and cancer progression. In bladder cancer, FSIP1 overexpression was associated with poor prognosis of bladder urothelial carcinoma. In this study, we investigated whether FSIP1 is essential in the progression of bladder cancer and the mechanism by which it mediates this effect. FSIP1 expression was knocked down in bladder cancer cells using lentiviral-mediated short hairpin RNA (shRNA). FSIP1 expression was detected using Western blotting, immunohistochemistry (IHC), and quantitative reverse transcriptase-polymerase chain reaction (qRT-PCR). The effects of FSIP1 knockdown on tumor cells were assessed using colony formation, 3-(4,5-Dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT), and flow cytometry (FCM) apoptosis assays in vitro and BALB/c nude mouse xenograft model in vivo. The findings suggested that FSIP1 protein was highly expressed in bladder cancer cell lines. Knockdown of FSIP1 resulted in reduced tumor cell viability, cell cycle arrest at G0/G1 phase and apoptosis of bladder cancer cell lines (P<0.05). Moreover, knockdown of FSIP1 expression suppressed the tumor formation and growth of bladder cancer xenografts (P<0.05). At the gene level, knockdown of FSIP1 expression downregulated the activity of the PI3K/AKT signaling pathway. This study demonstrated that knockdown of FSIP1 suppressed bladder cancer cell malignant behaviors in vitro and in vivo through the inhibition of the PI3K/AKT signaling pathway, suggesting that targeting FSIP1 could be further evaluated as a potential therapeutic strategy in bladder cancer.