Proteolytic processing of cyclin E in breast cancer

描述（由申请人提供）：在许多乳腺癌中，全长细胞周期蛋白E通过弹性蛋白酶介导的氨基末端2个特异性位点的蛋白水解切割进行后修饰，导致产生低分子量（LMW）亚型，其在细胞周期中的活性增加，并对细胞周期蛋白依赖性激酶抑制剂具有抗性。低分子量形式的细胞周期蛋白E是重要的，因为它们在乳腺癌患者中作为预后标志物的重要作用和它们在细胞周期途径中的参与。我们以前的研究表明，在25-35%的乳腺癌患者中观察到细胞周期蛋白E的低分子量形式的表达，并且这种表达与不良的临床结果非常密切相关。此外，我们已经报道了低分子量形式的细胞周期蛋白E功能性过度活跃，并且对p21和p27的抑制具有抗性。最近，我们开发了在乳腺中过表达低分子量形式的细胞周期蛋白E的转基因小鼠。这些小鼠产生具有转移潜力的肿瘤。所提出的研究的中心假设是，细胞周期蛋白E的LMW形式的过表达，而不是全长细胞周期蛋白E，与乳腺癌的进展和转移直接相关，使乳腺上皮细胞易于发生肿瘤。本提案中概述的研究将提供有关低分子量形式的细胞周期蛋白E介导其在乳腺肿瘤发生中的作用的机制的详细信息。具体而言，我们将：1）确定全长细胞周期蛋白E的致癌潜力和弹性蛋白酶切割在介导LMW细胞周期蛋白E诱导的乳腺肿瘤中的作用。2)确定细胞周期蛋白E全长和低分子量形式之间的生化差异。3)研究CDK 2在乳腺中由LMW细胞周期蛋白E过表达介导的乳腺肿瘤形成中的作用，最后4）确定肿瘤维持和复发对细胞周期蛋白E的需求。拟议的研究是创新的，因为它不仅研究了低分子量形式的细胞周期蛋白E是否使乳腺上皮细胞易于发生肿瘤，而且还研究了细胞周期蛋白E相关下游改变导致体内肿瘤形成的机制。总的来说，通过拟议的研究获得的信息可能对早期和晚期乳腺癌妇女具有巨大的临床意义。我们已经知道细胞周期蛋白E过度表达与患者预后不良相关;如果细胞周期蛋白E过度表达也使乳腺易于发生遗传不稳定性，从而导致肿瘤发生，则表明低分子量形式的细胞周期蛋白E在乳腺癌中的表达具有致病功能。

DESCRIPTION (provided by applicant): In many breast cancers, full length cyclin E is post-translationally modified through elastase mediated proteolytic cleavage of 2 specific sites in the amino terminus, resulting in the generation of low molecular weight (LMW) isoforms that have increased activity in cell cycle and resistance to cyclin-dependent kinase inhibitors. The LMW forms of cyclin E are important because of their significant role as prognostic markers in breast cancer patients and their involvement in cell cycle pathways. Our previous studies have shown that the expression of the LMW forms of cyclin E is observed in 25-35% of patients affected with breast cancer and such expression correlates very strongly with poor clinical outcome. Additionally, we have reported that the LMW forms of cyclin E are functionally hyperactive and resistant to inhibition by p21 and p27. Recently we developed transgenic mice overexpressing the LMW forms of cyclin E in the mammary gland. These mice develop tumors with metastatic potential. The central hypothesis of the proposed research, is that the overexpression of the LMW forms of cyclin E, and not the full-length cyclin E, are directly related to breast cancer progression and metastasis, predisposing the mammary epithelium to oncogenesis. The investigations outlined in this proposal will provide details regarding the mechanism through which the LMW forms of cyclin E mediate their effects in mammary gland tumorigenesis. Specifically, we will: 1) Determine the oncogenic potential of full length cyclin E and the role of elastase cleavage in mediating LMW cyclin E-induced mammary tumors. 2) Identify the biochemical differences between the full length and LMW forms of cyclin E. 3) Investigate the role of CDK2 in breast tumor formation mediated by LMW cyclin E overexpression in the mammary gland, and lastly 4) Determine the requirement of cyclin E for tumor maintenance and recurrence. The proposed research is innovative because it investigates not only whether the LMW forms of cyclin E predispose mammary epithelium to oncogenesis, but also the mechanism by which cyclin E-associated downstream alterations lead to tumor formation in vivo. Collectively, the information gained through the proposed studies could have tremendous clinical relevance for women with early stage and advanced breast cancer. We already know that cyclin E overexpression correlates with poor patient outcome; if cyclin E overexpression also predisposes the mammary gland to genetic instability leading to tumorigenesis it would suggest a causative function for the expression of the LMW forms of cyclin E in breast cancer.