Identification of miR-181a target genes in Epithelial Ovarian Cancer

We have identified a single miRNA, miR-181a, that can modulate TGF-ß signaling to induce and maintain EMT, and effect further downstream events of tumour cell survival, altered response to chemotherapy, migration, invasion and dissemination in vivo. Our present study provides an understanding of how enhanced expression of miR-181a can confer malignant and invasive traits through the modulation of a canonical signaling pathway and a consequent maintenance of a mesenchymal state. Furthermore, inhibition of miR-181a led to a reversion of EMT and subsequent events through decreased TGF-ß signaling. Our data confirmed Smad7 as a functional target through which TGF-ß-mediated EMT occurs; re-expression of Smad7 lacking its 3'UTR was able to rescue miR-181a-mediated phenotypes, deeming Smad7 as a critical mediator of miR-181a-induced EMT. Other recent studies support the crucial role(s) that miRNAs play in mediating EMT and consequent aggressive disease traits. For example, the miR-106b-25 cluster has also been shown to target Smad7 and mediate TGF-ß-induced EMT downstream to Six1 in breast cancer34. miR-9 directly targets E-cadherin and inhibition of miR-9 had led to an inhibition of metastasis35. Conversely, the miR-200 and -205 family was shown to target transcriptional repressors of E-cadherin, ZEB1 and SIP1, and re-expression of these miRNAs led to a mesenchymal-to-epithelial transition and prevented TGF-ß -induced EMT36. Overall design: A2780 ovarian cancer cell lines stably expressing either pBABE (control vector), p181a#1( clone 1 expressing miR-181a) or p181a#2( clone 2 expressing miR-181a)