Burnett School of Biomedical Sciences, University of Central Florida, College of Medicine Orlando, FL.
Am J Cancer Res. 2013 Aug 14;3(4):356-73. eCollection 2013.
The properties of stem cells can be induced during the epithelial to mesenchymal transition (EMT). The responsible molecular mechanisms, however, remain largely undefined. Here we report the identification of the microRNA-146a (miR-146a) as a common target of Krüppel-like factor 8 (KLF8) and TGF-β, both of which are known EMT-inducers. Upon KLF8 overexpression or TGF-β treatment, a significant portion of the MCF-10A cells gained stem cell traits as demonstrated by an increased expression of CD44(high)/CD24low, activity of aldehyde dehydrogenase (ALDH), mammosphere formation and chemoresistance. Along with this change, the expression of miR-146a was highly upregulated in the cells. Importantly, we found that miR-146a was aberrantly co-overexpressed with KLF8 in a panel of invasive human breast cancer cell lines. Ectopic expression of KLF8 failed to induce the stem cell traits in the MCF-10A cells if the cells were pre-treated with miR-146a inhibitor, whereas overexpression of miR-146a in the MCF-10A cells alone was sufficient to induce the stem cell traits. Co-staining and luciferase reporter analyses indicated that miR-146a targets the 3'-UTR of the Notch signaling inhibitor NUMB for translational inhibition. Overexpression of KLF8 dramatically potentiated the tumorigenecity of MCF-10A cells expressing the H-Ras oncogene, which was accompanied by a loss of NUMB expression in the tumors. Taken together, this study identifies a novel role and mechanism for KLF8 in inducing pro-tumorigenic mammary stem cells via miR-146a potentially by activating Notch signaling. This mechanism could be exploited as a therapeutic target against drug resistance of breast cancer.
干细胞的特性可在上皮间质转化（EMT）过程中被诱导。然而，负责的分子机制在很大程度上仍未被定义。在这里，我们报告了 microRNA-146a（miR-146a）作为已知 EMT 诱导剂 Krüppel 样因子 8（KLF8）和 TGF-β的共同靶标的鉴定。在 KLF8 过表达或 TGF-β处理后，相当一部分 MCF-10A 细胞获得了干细胞特性，表现为 CD44（高）/CD24（低）表达增加、醛脱氢酶（ALDH）活性增加、形成乳腺球体和化疗耐药性。随着这种变化，细胞中 miR-146a 的表达高度上调。重要的是，我们发现 miR-146a 在一组侵袭性人乳腺癌细胞系中与 KLF8 异常共过表达。如果 MCF-10A 细胞先用 miR-146a 抑制剂预处理，则 KLF8 的异位表达不能诱导 MCF-10A 细胞中的干细胞特性，而单独过表达 miR-146a 就足以诱导干细胞特性。共染色和荧光素酶报告分析表明，miR-146a 靶向 Notch 信号通路抑制剂 NUMB 的 3'-UTR 以进行翻译抑制。KLF8 的过表达显著增强了表达 H-Ras 癌基因的 MCF-10A 细胞的致瘤性，伴随着肿瘤中 NUMB 表达的丧失。总之，这项研究确定了 KLF8 通过 miR-146a 诱导促肿瘤发生的乳腺干细胞的新作用和机制，可能通过激活 Notch 信号通路。该机制可作为针对乳腺癌耐药性的治疗靶点。
