microRNA-106a modulates cisplatin sensitivity by targeting PDCD4 in human ovarian cancer cells.

microRNAs (miRNAs/miRs) are a cluster of short non-protein coding RNAs that negatively regulate gene expression, which is involved in fundamental cellular processes, including the response of tumor cells to chemotherapeutic agents. The present study investigated the role of miR-106a in the development of drug resistance in ovarian cancer cells. The expression of miR-106a in the ovarian cancer OVCAR3 cell line and the cisplatin (CDDP)-resistant ovarian cancer OVCAR3/CIS cell line was detected using stem-loop quantitative (q)PCR. The OVCAR3 and OVCAR3/CIS cells were transfected with mimics or inhibitors of miR-106a or with negative control (NC) RNA using lipofectamine 2000. Luciferase reporter assays were used to determine whether PDCD4 was a direct target of miR-106a in the OVCAR3 cells. The expression levels of the PDCD4 proteins were assessed using qRT-PCR and western blotting, respectively. Drug sensitivity was analyzed using a 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide assay, while apoptosis was determined by fluorescence-activating cell sorting analysis. The expression levels of miR-106a were upregulated in the CDDP-resistant ovarian cancer OVCAR3/CIS cell line compared with the parental OVCAR3 cell line. However, the PDCD4 protein levels were decreased in the OVCAR3/CIS cells compared with the OVCAR3 cells. The luciferase reporter assays revealed that PDCD4 was a direct miR-106a target in the OVCAR3 cells. Transfection of the OVCAR3/CIS cells with inhibitors of miR-106a enhanced the sensitivity of the OVCAR3/CIS cells to CDDP and increased CDDP-induced apoptosis. The expression of the PDCD4 protein and the sensitivity to CDDP was decreased in the OVCAR3 cells that were transfected with the mimics of miR-106a. The knockdown of PDCD4 expression using PDCD4-specific siRNAs in the OVCAR3 cells demonstrated that PDCD4 is a key signaling molecule in OVCAR3 cell CDDP-induced resistance. miR-106a may be involved in the development of drug resistance and the regulation of PDCD4 expression, at least in part, by modulating CDDP-induced apoptosis in ovarian cancer cells.