Proteolytic processing of cyclin E in breast cancer

描述(申请人提供)：在许多乳腺癌中，全长细胞周期蛋白E是通过弹性酶介导的氨基末端2个特定位点的蛋白水解性切割而被翻译后修饰的，导致产生低分子量(LMW)亚型，这些亚型在细胞周期中具有更高的活性，并对细胞周期蛋白依赖的激酶抑制剂产生抗药性。低分子形式的细胞周期蛋白E之所以重要，是因为它们作为乳腺癌患者的预后标记物具有重要作用，并且参与了细胞周期通路。我们以前的研究表明，在25-35%的乳腺癌患者中可以观察到低分子形式的细胞周期蛋白E的表达，这种表达与不良的临床预后密切相关。此外，我们已经报道了低分子形式的细胞周期蛋白E在功能上高度活跃，并能抵抗p21和p27的抑制。最近，我们开发了在乳腺中高表达低分子形式的细胞周期蛋白E的转基因小鼠。这些小鼠会发展成具有转移潜能的肿瘤。这项研究的中心假设是，低分子形式的细胞周期蛋白E的过度表达，而不是全长细胞周期蛋白E的过度表达，与乳腺癌的进展和转移直接相关，从而使乳腺上皮易于发生肿瘤。这项提案中概述的研究将提供有关低分子形式的细胞周期蛋白E在乳腺肿瘤发生中的作用机制的详细信息。具体地说，我们将：1)确定全长细胞周期蛋白E的致癌潜力以及弹性酶裂解在介导低分子量细胞周期蛋白E诱导的乳腺肿瘤中的作用。2)确定细胞周期蛋白E的全长和低分子形式之间的生化差异；3)研究CDK2在低分子细胞周期蛋白E在乳腺过表达所介导的乳腺肿瘤形成中的作用；4)确定细胞周期蛋白E对肿瘤维持和复发的需求。这项拟议的研究具有创新性，因为它不仅研究了周期蛋白E的低分子形式是否使乳腺上皮易于发生肿瘤，而且还研究了与周期蛋白E相关的下游改变导致体内肿瘤形成的机制。总而言之，通过拟议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的过度表达与不良的患者预后相关；如果细胞周期蛋白E的过度表达也使乳腺易于发生遗传不稳定，从而导致肿瘤的发生，这可能是乳腺癌中低分子形式细胞周期蛋白E表达的原因之一。

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.