Role of SHOX2 in breast tumor progression and metastasis

描述（由申请人提供）：上皮癌细胞从原发性肿瘤转移扩散到远处器官，需要肿瘤细胞获得间充质特征并失去上皮特征，这一现象称为上皮-间充质转化（EMT）。肿瘤微环境中的细胞因子/生长因子、同源异型盒（HOX）超家族转录因子和microRNA（miRNAs）等多种因素均可诱导EMT。在对乳腺癌细胞EMT重要的miRNA：mRNA对的系统评价中，我们发现miR-375在上皮样细胞中以高丰度存在，但在间充质样细胞中非常低。在miR-375的假定靶点中，SHOX 2在间充质样乳腺癌细胞中高水平表达，而在上皮样乳腺癌细胞中低水平表达。为了研究miR-375：SHOX 2对在乳腺癌细胞EMT中的作用，我们发现，加强miR-375表达足以消除间充质样乳腺癌细胞中的EMT特征，而SHOX 2过表达可以有效地诱导上皮样细胞中的EMT。我们发现了一个双负性miR-375/SHOX 2反馈环，其中miR-375通过直接靶向SHOX 2的3 '-UTR抑制内源性SHOX 2表达，而SHOX 2通过赖氨酸（K）特异性脱甲基酶5 B（KDM 5 B）的作用抑制miR-375转录。此外，SHOX 2还促进TGF β受体I（TRI）转录，这也是一种能够促进EMT的事件。基于这些发现，我们形成了我们的中心假设：miR-375/SHOX 2对动态参与乳腺癌细胞EMT。由于EMT在乳腺恶性肿瘤中的重要性，我们的目标是阐明miR-375/SHOX 2反馈调节环的基础和SHOX 2在EMT诱导中的双重作用的机制。此外，我们还打算通过靶向对SHOX 2诱导的EMT至关重要的事件来开发治疗策略。在本申请中提出了三个具体目标：1）理解SHOX 2如何抑制乳腺癌细胞中的miR-375表达; 2）定义乳腺癌细胞中的EMT的SHOX 2/miR-375调节的潜在机制;和3）确定SHOX 2在乳腺肿瘤发生中的作用。这一应用的成功将对理解EMT和为新型抗癌治疗方式奠定基础提供知识产生重要影响。

DESCRIPTION (provided by applicant): The metastatic spread of epithelial cancer cells from the primary tumor to distant organs necessitates tumor cells to gain mesenchymal characteristics and to lose epithelial features, a phenomenon known as the epithelial-mesenchymal transition (EMT). Various factors, including cytokines/growth factors in tumor microenvironment, transcription factors belonging to homeobox (HOX) super-family and microRNAs (miRNAs), can induce EMT. In a systematic evaluation of miRNA:mRNA pair important for breast cancer cell EMT, we found that miR-375 is present in high abundance in epithelial-like cells but very low in mesenchymal-like ones. Among miR-375's putative targets, SHOX2 is expressed at high level in mesenchymal-like breast cancer cells but lowly expressed in epithelial-like ones. To investigate the role of miR-375:SHOX2 pair in breast cancer cell EMT, we found that enforced miR-375 expression is sufficient to abrogate EMT traits in mesenchymal-like breast cancer cells while SHOX2 overexpression can potently induce EMT in epithelial-like cells. We discovered a double negative miR-375/SHOX2 feedback loop in which miR-375 suppresses endogenous SHOX2 expression by directly targeting SHOX2's 3'-UTR whereas SHOX2 represses miR-375 transcription through the action of Lysine (K)-Specific Demethylase 5B (KDM5B). In addition, SHOX2 also promotes TGF� receptor I (T�RI) transcription, an event also capable of promoting EMT. Based on these findings, we formed our central hypothesis: miR-375/SHOX2 pair is dynamically involved in breast cancer cell EMT. Because of the well-recognized importance of EMT in breast malignancies, our goal of this proposal is to elucidate the basis of miR-375/SHOX2 feedback regulatory loop and the mechanisms underlying the dual action of SHOX2 in EMT induction. Moreover, we also intend to develop a therapeutic strategy through targeting events critical for SHOX2-induced EMT. Three specific aims are proposed in this application: 1) Understand how SHOX2 suppresses miR-375 expression in breast cancer cells; 2) Define mechanisms underlying SHOX2/miR-375 regulation of EMT in breast cancer cells; and 3) Determine the role of SHOX2 in breast tumorigenesis. The success of this application will have important impact in providing knowledge on both understanding EMT and building foundation for novel anti-cancer therapeutic modality.