MicroRNA Let-7c Contributes to Paclitaxel Resistance via Aurora-B in Endometrial Serous Carcinoma

The incidence of endometrial cancer has rapidly risen over recent years. Paclitaxel, a key drug for endometrial cancer treatment, inhibits microtubule depolymerization and induces apoptosis in cancer cells. Endometrial serous carcinoma (ESC) accounts for < 10% of all endometrial carcinomas, but its aggressive nature makes it responsible for close to 40% of cancer deaths. Thus, novel therapeutic targets are required for ESC. To identify microRNAs that promote paclitaxel resistance, we established two paclitaxel-resistant cell lines from USPC1 human ESC cells by exposing paclitaxel to parental cells for 12 weeks. Paclitaxel concentrations were increased every 2 weeks, and after 12 weeks of paclitaxel exposure, two replicate paclitaxel-resistant cell lines were established (USPC1-PTSR1 and USPC1-PTXR2). The microarray analysis was performed using USPC1 cells and USPC1-PTXR1 cells, and eight candidate microRNAs were thus selected as potential mediators of paclitaxel sensitivity. Among these candidate microRNAs, let-7c precursor treatment of paclitaxel-resistant USPC1-PTXR1 cells caused the greatest increase in paclitaxel-mediated cytotoxicity. Let-7c inhibition conversely decreased paclitaxel-induced apoptosis. It is known that let-7a microRNA, a member of the let-7 family, inhibits growth of endometrial carcinoma cells targeting Aurora-B that controls progression through each phase of mitosis. We thus studied whether let-7c mediates Aurora-B expression in ESC cells. The expression levels of Aurora-B mRNA and protein were higher in USPC-PTXR1 cells compared with USPC1 cells. Let-7c inhibition increased Aurora-B expression in USPC1 cells but decreased Aurora-B expression in USPC1-PTXR1 cells. These results indicate that let-7c mediates paclitaxel resistance via inhibition of Aurora-B expression in ESC cells.