Role of SHOX2 in breast tumor progression and metastasis

描述（由申请人提供）：上皮癌细胞从原发肿瘤转移到远处器官，肿瘤细胞必须获得间充质特征并失去上皮特征，这种现象称为上皮-间充质转化（EMT）。多种因素可诱导EMT，包括肿瘤微环境中的细胞因子/生长因子、同源盒（HOX）超家族的转录因子和microRNAs （miRNAs）。在对乳腺癌细胞EMT重要的miRNA:mRNA对的系统评估中，我们发现miR-375在上皮样细胞中丰度很高，但在间质样细胞中丰度很低。在miR-375的推测靶点中，SHOX2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表达。为了研究miR-375:SHOX2对在乳腺癌细胞EMT中的作用，我们发现，在间质样乳腺癌细胞中，强制表达miR-375足以消除EMT特征，而过表达SHOX2可以在上皮样细胞中有效诱导EMT。我们发现了一个双负的miR-375/SHOX2反馈回路，其中miR-375通过直接靶向SHOX2的3'-UTR抑制内源性SHOX2表达，而SHOX2通过赖氨酸(K)特异性去甲基酶5B （KDM5B）的作用抑制miR-375的转录。此外，SHOX2还促进TGF -受体I （T - RI）转录，这一事件也能够促进EMT。基于这些发现，我们形成了我们的中心假设：miR-375/SHOX2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已得到公认，我们的目标是阐明miR-375/SHOX2反馈调控回路的基础以及SHOX2在EMT诱导中的双重作用的机制。此外，我们还打算通过针对shox2诱导EMT的关键事件开发一种治疗策略。本应用提出了三个具体目的：1)了解SHOX2如何抑制miR-375在乳腺癌细胞中的表达；2)明确SHOX2/miR-375调控乳腺癌细胞EMT的机制；3)确定SHOX2在乳腺肿瘤发生中的作用。这一应用的成功将对理解EMT和建立新的抗癌治疗模式产生重要的影响。

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.