Proeolytic Processing of Cyclin E in Breast Cancer

描述（由申请人提供）：三阴性乳腺癌（TNBC）是侵袭性乳腺癌的一个高度侵袭性亚群，约占所有病例的15%，由缺乏雌激素受体、孕激素受体和HER2定义。TNBC患者治疗的改善可能来自于识别对TNBC发展和维持至关重要的癌基因。最重要的是，新的治疗方法不仅要治疗肿瘤细胞的增殖群，还要治疗播散性肿瘤起始细胞的潜伏群，这些细胞被认为是导致复发和转移的原因。我们过去的工作已经确定了细胞周期调节蛋白在乳腺肿瘤的发生和增殖中的重要作用，重点是低分子量形式的细胞周期蛋白E （LMW-E）。我们实验室最近的工作表明，LMW-E形式在70%的tnbc中过度表达，并与这些患者的预后不良相关。我们发现了LMW-E在肿瘤起始和不受调控的增殖之外发挥作用的新途径，证明了LMW-E在肿瘤进展中起作用。具体来说，我们已经确定了LMW-E在上皮-间质转化（EMT）的启动、转基因小鼠转移的产生以及肿瘤启动细胞群的富集中的作用。下一个挑战是在这些过程中对LMW-E的机制进行理解，并确定治疗性降低LMW-E活性以阻断肿瘤进展的可行性。然而，我们不知道EL cyclin E上游通路的解除管制是否是起始事件。周期蛋白E上游的关键蛋白之一是弹性蛋白酶，它裂解EL周期蛋白E生成LMW-E。一个悬而未决的问题是，肿瘤细胞中弹性蛋白酶的解除是否足以产生LMW-E，从而产生转化表型。该研究的中心假设是，弹性蛋白酶将EL细胞周期蛋白E水解为lmn -E，通过改变细胞周期蛋白E的相互作用伙伴和底物，以及异常激活导致EMT和具有肿瘤启动电位的细胞诱导的信号通路，使乳腺上皮易发生肿瘤。目的1：在可诱导的转基因小鼠模型中确定LMW-E的时间和表达对肿瘤维持和复发的要求，并与TNBC患者相关。目的2：探讨弹性蛋白酶水解全长周期蛋白E到LMW-E的过程在乳腺肿瘤发生中的作用。目的3：通过鉴定和表征细胞质低分子量e的新型结合蛋白和底物，研究低分子量e介导的致癌机制。这些研究的成功完成将对低分子量e表达在肿瘤发生中的影响形成机制观点，并将我们的发现转化为临床。此外，我们的小鼠模型系统将为我们提供一个独特的系统，在临床前体内环境中检测针对TNBC的新疗法的有效性。

DESCRIPTION (provided by applicant): Triple negative breast cancer (TNBC) is a highly aggressive subset of invasive breast cancer, accounting for approximately 15% of all cases and defined by lack of estrogen receptor, progesterone receptor, and HER2. Improvements in the treatment of TNBC patients will likely come from identifying the oncogenes critical to the development and maintenance of TNBC. Most importantly, new therapies must treat not only the proliferative population of tumor cells, but also latent populations of disseminated tumor initiating cells, which are hypothesized to be responsible for recurrence and metastasis. Our past work has established important roles for cell cycle regulatory proteins in the initiation and proliferation of tumors in the mammary gland, with an emphasis on the low molecular weight forms of cyclin E (LMW-E). Recent work in our laboratory has demonstrated that LMW-E forms are overexpressed in 70% of TNBCs and correlates with poor prognosis in these patients. We identified novel ways in which LMW-E functions beyond tumor initiation and deregulated proliferation, demonstrating that LMW-E has a role tumor progression. Specifically, we have identified roles for LMW-E in the initiation of the epithelial-mesenchymal transition (EMT), generation of metastases in transgenic mice, and enrichment of a tumor initiating population of cells. The next challenge is to develop a mechanistic understanding of LMW-E in these processes and determine the feasibility of therapeutic attenuation of LMW-E activity in blocking tumor progression. However, we do not know if deregulation of pathways upstream of EL cyclin E is the initiating event. One of the key proteins that is upstream of cyclin E is elastase, which cleaves EL cyclin E to generate LMW-E. An unanswered question is if the deregulation of elastase in tumor cells is sufficient to generate LMW-E giving rise to the transformed phenotype. The central hypothesis of the proposed research is that proteolytic processing of EL cyclin E to LMW-E by elastase predisposes mammary epithelium to oncogenesis by altering cyclin E interacting partners and substrates and aberrantly activating signaling pathways that lead to induction of the EMT and cells with tumor initiating potentials. The following aims are designed to test each aspect of this hypothesis: Aim 1: Determine the requirement of LMW-E timing and expression for tumor maintenance and recurrence in an inducible transgenic mouse model and correlate with TNBC patients. Aim 2: Investigate the role of proteolytic processing of full length cyclin E to LMW-E by elastase in mammary tumorigenesis. Aim 3: Examine the mechanism of LMW-E mediated oncogenecity through identification and characterization of novel binding proteins and substrates for cytoplasmic LMW-E The successful completion of these studies will develop a mechanistic view of consequences of LMW-E expression in tumorigenesis and translate our findings to clinic. Additionally, our mouse model system will provide us with a unique system to examine the effectiveness of novel therapeutics targeted to TNBC in a preclinical in vivo setting.