ObjectiveBladder cancer is a common malignant tumor of the urinary tract as well as one of the most common cancers worldwide. Therefore, the study of key molecular targets involved in bladder carcinogenesis and progression is crucial for the prognosis of bladder cancer. Our study aims to investigate the mechanism by which cytokeratin 17 induces epithelial-mesenchymal transition and promotes bladder cancer progression.MethodsIn this study, 78 bladder cancer tissue specimens were collected, the expression level of cytokeratin 17 (CK17) in bladder cancer and paracancerous tissues was detected by immunohistochemistry, and the relationship between the CK17 expression level and the prognosis of the patients was analyzed via follow-up visits. Western Blot was performed to detect the expression level of CK17 in common bladder cancer cell lines, and the CK17-silenced and overexpressed cell lines were constructed from the selected T24 cell line with high expression of CK17 and 5637 cell line with low expression of CK17. The effects of CK17 on the proliferation, migration and invasion abilities of bladder cancer cells were evaluated by flow cytometry, Cell Counting Kit-8 (CCK-8) assay, Trans-well assay, and scratch assay. The effect of CK17 on epithelial-mesenchymal transition (EMT) markers was further detected by Western Blot and immunofluorescence, and the phosphorylation levels of AKT Ser473 and Thr308 were detected by Western Blot.ResultsIn the clinical samples, CK17 expression was significantly up-regulated in cancer tissues compared with paracancerous tissues, and high levels of CK17 indicated shortened progression free survival and predicted a poorer clinical prognosis. By analyzing the relationship between CK17 and clinicopathological features, we found that the CK17 expression level was correlated with bladder cancer grade and TNM stage. Overexpression of CK17 promoted the proliferation, migration and invasion abilities of bladder cancer cells 5637, and silencing of CK17 inhibited the proliferation, migration and invasion abilities of bladder cancer cells T24. Further, we found that overexpression of CK17 in 5637 cells activated the AKT signaling pathway by increasing the phosphorylation level of AKT (Ser473), so as to up-regulate the expressions of the EMT mesenchymal markers vimentin, N-cadherin, and the transcription factors Slug and twist, while the opposite results were obtained by silencing CK17 in T24 cells.ConclusionWe found that high expression of CK17 promoted the proliferation, migration and invasion of bladder cancer cells and induced EMT through AKT-Ser473 phosphorylation. These findings suggest that CK17 is significantly associated with malignant progression and poor prognosis of bladder cancer patients, and it may become a new biological target for bladder cancer treatment.