Role of PTEN in Chromosome Segregation and its Importance for Tumor Suppression

描述（由申请人提供）：在大部分人类癌症中，PTEN肿瘤抑制基因突变、缺失或表达水平降低。PTEN是一种脂质和蛋白磷酸酶，其通过使磷脂酰肌醇-3，4，5-三磷酸（PIP 3）去磷酸化来负调节磷酸肌醇-3-激酶（PI 3 K）/AKT信号传导。不受约束的PI 3 K/AKT信号传导导致细胞增殖增加和细胞死亡减少，从而驱动肿瘤发生。尽管拮抗PI 3 K/AKT信号传导被认为是PTEN的主要生理作用及其作为肿瘤抑制剂的最相关性质，但PTEN可能具有额外的肿瘤抑制功能，例如作为结构染色体完整性的监护人。然而，对于正常和肿瘤抑制性PTEN功能的全部库以及在人类癌症中发现的PTEN突变影响这些功能中的每一个的程度，存在不完全的理解。这是一个关键的障碍，正在减缓改善大部分癌症患者治疗策略的进展。我们提供了初步的数据，指出一个新的生物功能的PTEN在有丝分裂中确保准确的染色体分离和维持染色体数目的稳定性。本申请的中心目标是破译PTEN如何机械地调节适当的染色体分离，并确定这种功能的丧失在多大程度上有助于恶性细胞转化，最终目标是利用这些知识用于预防和治疗目的。我们的中心假设是，PTEN，通过其PDZ相互作用域，调节适当的染色体分离有丝分裂，这种新的功能代表了一个关键的肿瘤保护功能的PTEN。我们将测试这个 通过追求两个具体目标的假设。在第一个目标中，我们将通过使用来自Pten+/-和其他突变小鼠品系的小鼠胚胎成纤维细胞（MEFs）结合一套全面的细胞生物学和生物化学方法来确定PTEN调节适当的染色体分离的机制。在第二个目标中，我们将建立Pten PDZ相互作用结构域在正常发育和肿瘤抑制中的作用，使用新产生的缺乏该结构域的“敲入”小鼠品系。我们将确定这种“敲入”等位基因的杂合和纯合小鼠的有丝分裂、发育和癌症表型，并将其与Pten+/-小鼠的表型进行比较。这一创新提案的预期总体影响是，它将从根本上推进我们对人类癌症中第二大最常突变的肿瘤抑制基因的正常和肿瘤功能的机械理解。这些知识将为开发新的治疗策略奠定基础，这些策略将改善PTEN改变的癌症患者的临床结果，此外还将在概念上推进有丝分裂和癌症生物学领域。

DESCRIPTION (provided by applicant): The PTEN tumor suppressor gene is mutated, deleted or expressed at reduced levels in a large proportion of human cancers. PTEN is a lipid and protein phosphatase that negatively regulates phosphoinositol-3-kinase (PI3K)/AKT signaling by dephosphorylating phosphatidylinositol-3, 4, 5-triphosphate (PIP3). Unrestrained PI3K/AKT signaling leads to increased cell proliferation and reduced cell death, thereby driving tumorigenesis. Although antagonizing PI3K/AKT signaling is considered the primary physiological role of PTEN and its most relevant property as a tumor suppressor, PTEN may have additional tumor suppressive functions, for instance as a guardian of structural chromosome integrity. However, there is an incomplete understanding of the full repertoire of the normal and tumor suppressive PTEN functions and the extent to which PTEN mutations found in human cancer affect each of these functions. This represents a critical barrier that is slowing down progress toward improving treatment strategies for a large segment of cancer patients. We provide preliminary data that point to a novel biological function of PTEN in ensuring accurate chromosome segregation in mitosis and maintaining chromosome number stability. The central objective of this application is to decipher how mechanistically PTEN regulates proper chromosome segregation, and to determine the extent to which loss of this function contributes to malignant cell transformation, with the ultimate goal to exploit this knowledge for preventive and therapeutic purposes. Our central hypothesis is that PTEN, through its PDZ-interaction domain, regulates proper chromosome segregation in mitosis and that this novel function represents a critical tumor protective function of PTEN. We will test this hypothesis by pursuing two specific aims. In the first aim, we will determine the mechanism by which PTEN regulates proper chromosome segregation by using mouse embryonic fibroblasts (MEFs) from Pten+/- and other mutant mouse strains in combination with a comprehensive set of cell biological and biochemical approaches. In the second aim, we will establish the role of the Pten PDZ- interaction domain in normal development and tumor suppression using a newly generated "knockin" mouse strain that lacks this domain. We will determine the mitotic, developmental and cancer phenotypes of mice that are heterozygous and homozygous for this "knockin" allele and compare these to those of Pten+/- mice. The expected overall impact of this innovative proposal is that it will fundamentally advance our mechanistic understanding of the normal and neoplastic functions of the second most frequently mutated tumor suppressor gene in human cancer. This knowledge will lay the foundation for development of new therapeutic strategies that will improve the clinical outcome of cancer patients with alterations in PTEN, in addition to conceptually advancing the fields of mitosis and cancer biology.