长链非编码RNA（lncRNA）的发现指出了肿瘤基因表达微观调控的新方向，而鉴定其结合蛋白是阐明其作用机制的关键。申请人曾建立分离RNA结合蛋白的亲和纯化技术并鉴定出介导mRNA出核功能的主要蛋白（PNAS, 2011; NAR, 2013）。预实验发现lncRNA MEG3在乳腺癌中低表达并抑制乳腺癌细胞系增殖，但介导MEG3 抑制肿瘤细胞增殖功能的结合蛋白及其调控乳腺癌发生发展的分子机制均不清楚。故将从分子水平鉴定MEG3结合蛋白并确定直接介导MEG3抑制肿瘤细胞增殖的关键蛋白；在细胞水平上检测MEG3结合蛋白对P53通路、PI3K通路以及血管生成基因表达的影响探讨其调控乳腺癌进程机制；然后验证MEG3结合蛋白稳转细胞株在裸鼠中诱发乳腺癌的能力，并在临床样本中检测MEG3及其结合蛋白的表达，分析与临床指标的相关性。本研究将阐明MEG3及其结合蛋白作用机制，为乳腺癌靶向治疗提供潜在靶点。

The presence of unexpected huge number of long non-coding RNA opens up a new research direction in the micro-regulation of gene expression in cancer, and it is crucial to identify lncRNA binding proteins in order to gain deep insight into the role of lncRNA and how it works. In previous work, we have developed an affinity purification method that can efficiently identify RNA binding proteins, and revealed key proteins for mRNA export (PNAS, 2011; NAR, 2013). Our preliminary data show that the expression of MEG3 is significantly decreased in breast cancer samples and re-expression of MEG3 in breast cancer cell line inhibits its growth, however，proteins bound to MEG3 that mediate its role in growth inhibition have not been identified yet, nor has the molecular mechanism on its regulation of occurrence and progression of breast cancer been elucidated. Thus we will first define proteins bound to MEG3 at the molecular level in this project, then screen for key factors directly underlying the role of MEG3 as growth suppressor. Secondly, we will explore the mechanism of MEG3 binding protein in the progression of breast cancer at the cellular level，by checking the expression of genes in P53 and PI3K pathway as well as in angiogenesis. Thirdly, we will examine breast cancer tumorigenesis in nude mice using stable cell line expressing MEG3 binding proteins. Finally, we will determine the expression of MEG3 and its binding proteins in clinical breast cancer samples and perform correlation analysis according to clinical indexes. The project aims to elucidate the mechanism on the regulation of occurrence and progression of breast cancer by MEG3 and its binding proteins, which may eventually lead to potential target in targeted cancer therapy.