BUB1 in Chromosomal Instability and Tumorigenesis

描述（由申请人提供）：非整倍性，即不正确的染色体数目，是癌症的共同特征。然而，染色体不稳定性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是一种编码多功能丝氨酸/苏氨酸蛋白激酶的有丝分裂检查点基因，是一种重要的癌症相关基因，其上调和下调均可导致小鼠肿瘤。尽管在人类肿瘤中已经观察到这两个方向的异常表达，但发现高Bub1表达是各种肿瘤类型不良临床结果的生物标志物，这意味着这种改变可能与肿瘤发生特别相关。本应用的目的是确定Bub1过表达驱动肿瘤转化的机制，以及它与肿瘤侵袭性和转移的因果关系程度，长期目标是利用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，我们设计了两种新的Bub1小鼠模型，一种过表达Bub1，另一种缺乏Bub1激酶活性。这些模型的初步表征表明，Bub1的新功能是作为Aurora B的主调控因子，Aurora B是“附着错误纠正机制”的关键组成部分，通过解决微管-着丝点的异常附着来防止染色体错误分离。我们的中心假设是增加的Bub1激酶活性通过极光B激酶的过度激活来驱动肿瘤的发展和侵袭性。在有说服力的初步数据的指导下，这一假设将通过追求两个具体目标来验证：1)确定Bub1激活Aurora B的机制以及该机制在肿瘤发展中的作用程度；2)确定Bub1过表达对肿瘤侵袭性的驱动程度以及与其他CIN基因缺陷的配合程度。在第一个目标中，我们将使用已经建立和新设计的Bub1突变小鼠模型，结合Aurora B的小分子抑制剂来解决Bub1调节Aurora B的分子机制，并测试该机制的解除是否对Bub1的致癌特性至关重要。在第二个目标中，我们将使用Bub1转基因小鼠与Errb2乳腺癌模型结合来测试Bub1过表达是否不仅仅是不良预后的生物标志物，而是实际上驱动肿瘤侵袭和转移。此外，我们将探索Bub1过表达与其他CIN基因协同作用的新概念，这些基因可预测不良的临床结果。该项目的预期总体影响是，它将从根本上推进我们对一个突出的致癌CIN基因的正常和肿瘤功能的机制理解，并为预测不良预后的CIN基因改变可以驱动肿瘤侵袭性并相互协同的新概念提供证据。从这些努力中获得的知识可以用来设计新的癌症治疗和预防策略，除了在概念上推进有丝分裂和癌症生物学领域。

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. PUBLIC HEALTH RELEVANCE: Cancer cells are characterized by an abnormal number of chromosomes, but the genetic and molecular defects driving this condition and its precise role in the development of cancer remain poorly understood, which is a critical barrier to the development of novel cancer intervention strategies. Our goal is to fill this gap in knowledge through a series of innovative studies of Bub1, a prominent chromosomal instability gene that is overexpressed in various human cancer types and associated with poor clinical prognosis.