BUB1 in Chromosomal Instability and Tumorigenesis

描述(申请人提供)：非整倍体，错误的染色体数目，是癌症的常见特征。然而，染色体不稳定的遗传缺陷和分子机制，以及非整倍体在癌症病因学中的作用仍然知之甚少。Bub1是一种有丝分裂检查点基因，编码一种多功能的丝氨酸/苏氨酸蛋白激酶，已成为一个重要的癌症相关基因，在小鼠中既有上调又有下调导致肿瘤。尽管在人类肿瘤中观察到双向异常表达，但高表达Bub1是各种类型肿瘤临床预后不良的生物标志物，这意味着这种变化可能与肿瘤的发生特别相关。这项应用的目标是确定Bub1过表达如何机械地驱动肿瘤转化，以及它与肿瘤侵袭性和转移的因果联系的程度，长期目标是开发Bub1或其下游效应物用于预防和治疗目的。作为实现这些目标的第一步，我们设计了两个新的Bub1小鼠模型，一个过度表达Bub1，另一个缺乏Bub1激酶活性。对这些模型的初步表征表明，Bub1作为Aurora B的主调节器具有一种新的功能，Aurora B是“附着错误纠正机制”的关键组件，它通过解决异常的微管-动粒附着来防止染色体错误分离。我们的中心假设是，Bub1激酶活性的增加通过Aurora B激酶的过度激活来推动肿瘤的发展和侵袭性。在有说服力的初步数据的指导下，这一假说将通过追求两个具体目标来检验：1)确定Bub1如何机械地激活Aurora B，以及该机制在多大程度上与肿瘤的发展有关；2)确定Bub1过表达在多大程度上推动肿瘤的侵袭性，并与其他CIN基因缺陷协同工作。在第一个目标中，我们将使用已经建立的和新设计的Bub1突变小鼠模型，结合Aurora B的小分子抑制剂来解析Bub1调控Aurora B的分子机制，并测试这一机制的解除是否对Bub1的S致癌特性至关重要。在第二个目标中，我们将使用Bub1转基因小鼠结合Errb2乳腺癌模型来测试Bub1过度表达是否不仅是预后不良的生物标志物，而且实际上推动了肿瘤的侵袭和转移。此外，我们将探索Bub1过度表达与其他预测不良临床结果的CIN基因协同作用的新概念。该项目预期的总体影响是，它将从根本上促进我们对一个突出的致癌CIN基因的正常和肿瘤功能的机械理解，并为预测不良预后的CIN基因改变可以推动肿瘤侵袭性和相互协同的新概念提供证据。除了在概念上推进有丝分裂和癌症生物学领域外，还可以利用从这些努力中获得的知识来设计癌症治疗和预防的新战略。

DESCRIPTION (provided by applicant): Aneuploidy, an incorrect chromosome number, is a common trait of cancer. However, the genetic defects and molecular mechanisms underlying chromosome instability, and the role of aneuploidy in the etiology of cancer remain poorly understood. Bub1, a mitotic checkpoint gene encoding a multi-functional serine/threonine protein kinase, has emerged as a prominent cancer-associated gene, with both up- and downregulation causing tumors in mice. Although aberrant expression in both directions has been observed in human tumors, the discovery that high Bub1 expression is a biomarker for poor clinical outcome for various tumor types implies that this alteration may be particularly relevant in tumorigenesis. The goal of this application is to determine how mechanistically Bub1 overexpression drives neoplastic transformation, and the extent to which it is causally linked to tumor aggressiveness and metastasis, with the long-term goal to exploit Bub1 or its downstream effectors for preventive and therapeutic purposes. As a first step toward these goals, we engineered two novel Bub1 mouse models, one overexpressing Bub1 and one lacking Bub1 kinase activity. Initial characterization of these models suggests a novel function of Bub1 as a master regulator of Aurora B, a key component of the "attachment error correction machinery" that prevents chromosome missegregation by resolving aberrant microtubule-kinetochore attachments. Our central hypothesis is that increased Bub1 kinase activity drives tumor development and aggressiveness through hyperactivation of Aurora B kinase. Guided by persuasive preliminary data, this hypothesis will be tested by pursuing two specific aims: 1) Determine how mechanistically Bub1 activates Aurora B and the extent to which this mechanism is implicated in tumor development; and 2) Determine the extent to which Bub1 overexpression drives tumor aggressiveness and cooperates with other CIN gene defects. In the first aim, we will use already established and newly designed Bub1 mutant mouse models in combination with small molecule inhibitors of Aurora B to resolve the molecular mechanism by which Bub1 regulates Aurora B, and test whether deregulation of this mechanism is critical for Bub1's oncogenic properties. In the second aim, we will use Bub1 transgenic mice in combination with the Errb2 breast cancer model to test whether Bub1 overexpression is not just a biomarker for poor prognosis but in fact drives tumor invasiveness and metastasis. In addition, we will explore the novel concept that Bub1 overexpression synergizes with other CIN genes that predict poor clinical outcome. The expected overall impact of this project is that it will fundamentally advance our mechanistic understanding of the normal and neoplastic functions of a prominent cancer-causing CIN gene, and provide proof for the novel concepts that CIN gene alterations that predict poor prognosis can drive tumor aggressiveness and synergize with one another. Knowledge from these efforts could be exploited to devise novel strategies for cancer treatment and prevention in addition to conceptually advancing the fields of mitosis and cancer biology.