Shi Zhendong, Li Yang, Qian Xiaomin, Hu Yunhui, Liu Jingjing, Zhang Sheng, Zhang Jin
3rd Department of Breast Cancer, China Tianjin Breast Cancer Prevention, Treatment and Research center, Tianjin Medical University Cancer Institute and Hospital.
Key laboratory of breast cancer prevention and therapy of ministry of education.
J Cancer. 2017 Sep 2;8(15):3037-3048. doi: 10.7150/jca.19315. eCollection 2017.
The anti-tumor efficacy of miR-340 has been recently characterized in cancers. However, the underlying mechanisms of miR-340 inhibited cell growth and invasion in triple-negative breast cancer (TNBC) have not been well elucidated. In this study, we found that miR-340 expression was negatively correlated with EZH2 (Enhancer of zeste homolog 2) expression in TNBC tissues and cell lines. Subsequent luciferase reporter assay confirmed that EZH2 was a novel molecule target of miR-340. Upregulated miR-340 levels by mimics transfection significantly inhibited the MDA-MB-231 and MDA-MB-468 breast cancer cells proliferation, invasion and migration, and induced more cell apoptosis. Meanwhile, miR-340 inhibited the tumor growth in an orthotopic MDA-MB-231 breast cancer mouse model. Furthermore, we found the reduced EZH2 expression by miR-340 mimics transfection decreased the DNMT1, H3K27me3, β-catenin and P-STAT3 expressions, which ultimately resulted in miR-21 activity blockage and miR-200a/b expression upregulation. The results of rescue experiments further confirmed that miR-340 inhibited triple-negative breast cancer progression through targeting EZH2. Taken together, our results identified miR-340 as a tumor suppressor in TNBC, moreover, an EZH2 medicated regulatory loop was established. Post-transcriptional suppression of EZH2 expression not only blocked STAT3 mediated miR-21 trans-activation, but also reversed the miR-200a/b silencing via reducing DNMT1 and H3K27me3 expressions. MiR-21 inhibition and miR-200a/b expression triggered by miR-340 ultimately cooperated in the TNBC progression.
最近已明确了miR - 340在癌症中的抗肿瘤功效。然而，miR - 340抑制三阴性乳腺癌（TNBC）细胞生长和侵袭的潜在机制尚未完全阐明。在本研究中，我们发现TNBC组织和细胞系中miR - 340的表达与EZH2（zeste同源物2增强子）的表达呈负相关。随后的荧光素酶报告基因检测证实EZH2是miR - 340的一个新分子靶点。通过转染模拟物上调miR - 340水平可显著抑制MDA - MB - 231和MDA - MB - 468乳腺癌细胞的增殖、侵袭和迁移，并诱导更多细胞凋亡。同时，miR - 340在原位MDA - MB - 231乳腺癌小鼠模型中抑制肿瘤生长。此外，我们发现转染miR - 340模拟物后EZH2表达降低，从而降低了DNMT1、H3K27me3、β - 连环蛋白和P - STAT3的表达，最终导致miR - 21活性受阻和miR - 200a/b表达上调。拯救实验结果进一步证实miR - 340通过靶向EZH2抑制三阴性乳腺癌进展。综上所述，我们的结果确定miR - 340是TNBC中的一种肿瘤抑制因子，此外，还建立了一个EZH2介导的调控环路。EZH2表达的转录后抑制不仅阻断了STAT3介导的miR - 21反式激活，还通过降低DNMT1和H3K27me3的表达逆转了miR - 200a/b的沉默。miR - 340引发的miR - 21抑制和miR - 200a/b表达最终在TNBC进展中协同作用。
