Graduate Institute of Toxicology, College of Medicine, National Taiwan University, No, 1, Sec, 1, Ren-Ai Road, Taipei, 100, Taiwan.
Breast Cancer Res. 2011;13(6):R116. doi: 10.1186/bcr3059. Epub 2011 Nov 23.
Estrogen is involved in several physiological and pathological processes through estrogen receptor (ER)-mediated transcriptional gene regulation. miRNAs (miRs), which are noncoding RNA genes, may respond to estrogen and serve as posttranscriptional regulators in tumorigenic progression, especially in breast cancer; however, only limited information about this possibility is available. In the present study, we identified the estrogen-regulated miR-34b and investigated its functional role in breast cancer progression.
Estrogen-regulated miRNAs were identified by using a TaqMan low density array. Our in vivo Tet-On system orthotopic model revealed the tumor-suppressive ability of miR-34b. Luciferase reporter assays and chromatin immunoprecipitation assay demonstrated miR-34b were regulated by p53-ER interaction.
In this study, we identified one such estrogen downregulated miRNA, miR-34b, as an oncosuppressor that targets cyclin D1 and Jagged-1 (JAG1) in an ER+/wild-type p53 breast cancer cell line (MCF-7), as well as in ovarian and endometrial cells, but not in ER-negative or mutant p53 breast cancer cell lines (T47D, MBA-MB-361 and MDA-MB-435). There is a negative association between ERα and miR-34b expression levels in ER+ breast cancer patients. Tet-On induction of miR-34b can cause inhibition of tumor growth and cell proliferation. Also, the overexpression of miR-34b inhibited ER+ breast tumor growth in an orthotopic mammary fat pad xenograft mouse model. Further validation indicated that estrogen's inhibition of miR-34b expression was mediated by interactions between ERα and p53, not by DNA methylation regulation. The xenoestrogens diethylstilbestrol and zeranol also showed similar estrogenic effects by inhibiting miR-34b expression and by restoring the protein levels of the miR-34b targets cyclin D1 and JAG1 in MCF-7 cells.
These findings reveal that miR-34b is an oncosuppressor miRNA requiring both ER+ and wild-type p53 phenotypes in breast cancer cells. These results improve our ability to develop new therapeutic strategies to target the complex estrogenic pathway in human breast cancer progression through miRNA regulation.
雌激素通过雌激素受体（ER）介导的转录基因调控参与多种生理和病理过程。miRNA（miRs）是一种非编码 RNA 基因，可能会对雌激素做出反应，并在肿瘤发生进展中充当转录后调控因子，尤其是在乳腺癌中；然而，目前对于这种可能性的信息还很有限。在本研究中，我们鉴定了受雌激素调控的 miR-34b，并研究了其在乳腺癌进展中的功能作用。
采用 TaqMan 低密度阵列鉴定受雌激素调控的 miRNA。我们的体内 Tet-On 系统原位模型揭示了 miR-34b 的肿瘤抑制能力。荧光素酶报告基因检测和染色质免疫沉淀实验证实，miR-34b 受 p53-ER 相互作用的调控。
在这项研究中，我们鉴定了一种受雌激素下调的 miRNA，miR-34b，作为一种抑癌基因，在 ER+/野生型 p53 乳腺癌细胞系（MCF-7）以及卵巢和子宫内膜细胞中，miR-34b 靶向细胞周期蛋白 D1 和 Jagged-1（JAG1），但在 ER 阴性或突变型 p53 乳腺癌细胞系（T47D、MBA-MB-361 和 MDA-MB-435）中则不然。在 ER+乳腺癌患者中，ERα 和 miR-34b 的表达水平呈负相关。Tet-On 诱导 miR-34b 的表达可抑制肿瘤生长和细胞增殖。此外，过表达 miR-34b 可抑制 ER+乳腺癌在原位乳腺脂肪垫异种移植小鼠模型中的肿瘤生长。进一步验证表明，雌激素通过 ERα 和 p53 之间的相互作用抑制 miR-34b 的表达，而不是通过 DNA 甲基化调节。外源性雌激素二乙基stilbestrol 和 zeranol 也通过抑制 miR-34b 的表达并恢复 miR-34b 靶标 cyclin D1 和 JAG1 在 MCF-7 细胞中的蛋白水平，显示出类似的雌激素作用。
这些发现表明，miR-34b 是一种抑癌 miRNA，在乳腺癌细胞中需要 ER+和野生型 p53 表型。这些结果提高了我们通过 miRNA 调节开发针对人类乳腺癌进展中复杂雌激素途径的新治疗策略的能力。
