cycle arrest at G 0 /G 1 stage and decreased the protein level of cyclin E/cyclin-dependent kinases (cdk) 2 and/or cyclin D/ cdk4/cdk6. Conclusion: These results suggest the inhibitory effect of IF1 knockdown on BCa cell proliferation is via the suppression of cyclins and cdks related to G 1 /S transition and then induction of G 0 /G 1 arrest, and firstly indicate IF1 mediates the tumor cell cycle. We concluded that IF1 may be a novel therapeutic target for BCa. Abstract Objective: The role of

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... he ATPase inhibitory factor 1 (IF1) is inhibit the hydrolase activity of F 1 F o -ATPase when oxidative phosphorylation is impaired. It has been demonstrated that IF1 is overexpressed in various carcinomas and mediates tumor cell activities, but the detailed mechanisms of IF1-mediated tumor progression and the link between IF1 and cell cycle progression remain unclear. Herein, we aimed to investigate the potential role of IF1 in cell cycle progression of human bladder cancer (BCa). Methods: The expression of IF1 was analyzed by immunohistochemistry in tumor tissues. Western blot was used to detect protein expression in the cells. Cell proliferation was determined by MTT and colony formation assays. The cell cycle was analyzed using flow cytometry. Results: We firstly showed IF1 was overexpressed in BCa. Silencing of IF1 by small interfering RNA led to a significant decrease in cell proliferation and migration in T24 and UM-UC-3 cells. Importantly, IF1 knockdown caused cell