Combined ceRNA and epigenetic silencing of miR-193a lead to bistable switching of c-KIT in ovarian cancer

• Main Authors: CHENG, HSUEH-CHE, 鄭學澤
• Other Authors: CHAN, MICHAEL WING-YAN
• Format: Others
• Language: en_US
• Published: 2018
• Online Access: http://ndltd.ncl.edu.tw/handle/948u87

博士 === 國立中正大學 === 生命科學系分子生物研究所 === 107 === Ovarian cancer is one of the most lethal cancers in the female reproductive system. Previous study suggested that long term treatment of estrogen such as hormonal replacement therapy (HRT) may increase the risk of ovarian cancer. However the role of estrogen in ovarian carcinogenesis is still controversial. To decipher this complicated process, we generated a mathematical model and found that estrogen-mediated up-regulation of E2F6 could upregulate the ovarian cancer stem/initiating marker, c-KIT by two means one through epigenetic silencing of their co-targeted miR-193a by binding of E2F6 which subsequently recruit EZH2 to miR-193a promoter; and second, by competing endogenous (ceRNA) mechanism. To confirm this model, treatment of E2 or environmental hormone, BPA resulted in upregulation of both E2F6 and c-KIT but down-regulation of miR-193a in immortalized ovarian surface epithelial cells. Further bisulfite pyrosequencing, ChIP-qPCR and epigenetic treatment found that miR-193a was epigenetically silenced by DNA methylation and H3K27me3 in CP70 but not HeyC2 ovarian cancer cells. Overexpression of miR-193a inhibited tumor growth in vitro and in vivo. Depletion of EZH2 or E2F6 in CP70 restored miR-193a expression and decreased the number of “ovo” spheroid by reversing the repressive chromatin status of miR-193a promoter. To further explore the biological significance of this E2F6 ceRNA network, integrative RNA-Seq and computational analysis found that PBX1, a miR-193a target and transcriptional activator of the immunosuppressive cytokine IL-10, was down-regulated in E2F6 and EZH2 knockdown CP70 cells. Finally, clinical studies demonstrated that patients with higher promoter methylation of miR-193a were associated with poor survival. Taken together, our results showed that estrogen-mediated E2F6 ceRNA network can regulate cancer stemness and anti-tumor immunity of DC through epigenetic silencing of miR-193a. Anti-estrogen therapy together with the EZH2 inhibitor may be a novel strategy against this deadly cancer. Keyword: ovarian cancer, competing endogenous RNA, cancer stem cell, epigenetics