Overexpressed miR-9 promotes tumor metastasis via targeting E-cadherin in serous ovarian cancer

MicroRNAs (miRNAs) play critical roles in the development and progression in various cancers. Dysfunctional miR-9 expression remains ambiguous, and no consensus on the metastatic progression of ovarian cancer has been reached. In this study, results from the bioinformatics analysis show that the 3′-UTR of the E-cadherin mRNA was directly regulated by miR-9. Luciferase reporter assay results confirmed that miR-9 could directly target this 3′-UTR. miR-9 and E-cadherin expression in ovarian cancer tissue was quantified by qRT-PCR. Migration and invasion were detected by wound healing and Transwell system assay in SKOV3 and A2780. qRT-PCR and Western blot were performed to detect the epithelial‒mesenchymal transition-associated mRNA and proteins. Immunofluorescence technique was used to analyze the expression and subcellular localization of E-cadherin, N-cadherin, and vimentin. The results showed that miR-9 was frequently upregulated in metastatic serous ovarian cancer tissue compared with paired primary ones. Upregulation of miR-9 could downregulate the expression of E-cadherin but upregulate the expression of mesenchymal markers (N-cadherin and vimentin). Overexpression of miR-9 could promote the cell migration and invasion in ovarian cancer, and these processes could be effectively inhibited via miR-9 inhibitor. Thus, our study demonstrates that miR-9 may promote ovarian cancer metastasis via targeting E-cadherin and a novel potential therapeutic approach to control metastasis of ovarian cancer.