Abstract: Objective To investigate the effect of miR-142-5p on epithelial-mesenchymal transition (EMT) and chemosensitivity of gemcitabine (GEM) in human cholangiocarcinoma cell line QBC939 by targeting myeloid cell leukemin-1 ( MCL-1 ). Methods Human cholangiocarcinoma cell line QBC939 and human normal bile duct epithelial cell line HIBEC were cultured in vitro and then randomly divided into control group, miR-142-5p negative control (NC) group and miR-142- 5p mimics group. The mRNA expression levels of miR-142-5p and MCL-1 in QBC939 cells and HIBEC cells were detected by real-time quantitative PCR (RT-qPCR); the migration and invasion of QBC939 cells were determined by wound healing assay and transwell assay; Western blotting was used to detect the expression level of E-cadherin, N-cadherin and Vimentin in QBC939 cells; dualluciferase assay was used to verify the relationship between miR-142-5p and MCL-1; QBC939 cells transfected with miR-142-5p were treated with GEM at a concentration of 0. 625 μg / mL. The viability and apoptosis of QBC939 cells were measured by MTT assay and Annexin V-FITC / PI kit respectively. Results The expression level of miR-142-5p was lower and the expression level of MCL-1 was higher in cholangiocarcinoma QBC939 cells than in human normal bile duct HIBEC cells. According to the prediction of TargetScan Human Database, there was a binding site for miR-142-5p on the 3′UTR region of MCL-1 mRNA. Compared with MCL-1-3′UTR-WT + miR-142-5p NC group, the luciferase activity of MCL-1-3′UTR-WT + miR-142-5p mimics group was significantly decreased (P< 0. 05). The expression level of miR-142-5p and E-cadherin were significantly increased (P< 0. 05), the expression level of MCL-1, N-cadherin and vimentin were significantly decreased (P< 0. 05), and the number of migratory and invasive cells were profoundly reduced in miR-142-5p mimics group compared with control group and miR-142-5p NC group (P < 0. 05 for all). The survival rate of QBC939 cells in miR-142-5p mimics + GEM group was significantly lower and the apoptosis rate was higher than that in miR-142-5p NC + GEM group (P < 0. 05). Conclusion Overexpression of miR-142-5p can inhibit the EMT of and increase the chemosensitivity of GEM to cholangiocarcinoma cells by targeting MCL-1.

Key words: miR-142-5p, myeloid cell leukemin-1, cholangiocarcinoma cells, epithelial-mesenchymal transition