Role of SHOX2 in breast tumor progression and metastasis

描述(申请人提供)：上皮性癌细胞从原发肿瘤向远处器官的转移需要肿瘤细胞获得间质特征而失去上皮特征，这一现象被称为上皮间充质转变(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microRNAs(MiRNAs)等多种因素均可诱导EMT。在对乳腺癌细胞EMT重要的miRNA：mRNA对的系统评估中，我们发现miR-375在上皮样细胞中含量很高，而在间充质样细胞中含量很低。在miR-375‘S可能的靶点中，SHOX2在间叶样乳腺癌细胞中高表达，在上皮样癌细胞中低表达。为了研究miR-375：SHOX2对在乳腺癌细胞EMT中的作用，我们发现，增强miR-375的表达足以消除间充质样乳腺癌细胞的EMT特征，而SHOX2的过表达可以有效地诱导上皮样细胞的EMT。我们发现了一个双负的miR-375/SHOX2反馈环，其中miR-375通过直接靶向SHOX2‘S 3’-UTR抑制内源性SHOX2的表达，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还促进转化生长因子�受体I(T�RI)的转录，这也是一个能够促进EMT的事件。基于这些发现，我们形成了我们的中心假设：MIR-375/SHOX2对动态参与了乳腺癌细胞的EMT。鉴于EMT在乳腺恶性肿瘤中的重要性，我们的目标是阐明miR-375/SHOX2反馈调控环的基础以及SHOX2在EMT诱导中的双重作用机制。此外，我们还打算通过靶向SHOX2诱导的EMT的关键事件来开发治疗策略。在这项应用中提出了三个特定的目标：1)了解SHOX2如何抑制乳腺癌细胞中miR-375的表达；2)确定SHOX2/miR-375调控乳腺癌细胞中EMT的潜在机制；以及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和为新的抗癌治疗方式奠定基础产生重要的影响。

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.