Role of PTEN in Mitosis and Chromosome Stability

描述(申请人提供)：PTEN是人类癌症中最常见的突变基因之一，PTEN蛋白因其在保护染色体完整性方面的重要作用而被认为是“基因组的守护者”。对缺乏功能PTEN的细胞和组织的结构染色体异常和非整倍体的观察使PTEN与染色体稳定性之间的联系成为人们关注的焦点。在我们最近的研究中，我们发现缺乏PTEN的细胞表现出染色体错误分离和显著的多倍体，这表明PTEN在有丝分裂过程中控制基因组和核型的稳定性。在异常有丝分裂过程中获得的染色体不稳定性在肿瘤的发生和发展中起着重要作用。这个研究项目的长期目标是建立这样一个新的概念，即PTEN在控制有丝分裂染色体稳定性方面起着至关重要的作用，并且它在维持有丝分裂保真度方面的功能是抑制肿瘤的主要驱动力。为了支持这一目标，我们令人兴奋的新的初步数据显示，PTEN缺乏导致以多倍化表现的总体基因组变化，并赋予细胞对纺锤体扰动的抵抗力。值得注意的是，我们发现PTEN的蛋白磷酸酶活性是维持正常核型和细胞对纺锤体药物敏感性所必需的。此外，我们的数据显示，一个关键的有丝分裂激酶，Polo-like kinase1(Plk1)，是一个潜在的PTEN靶点。这些发现导致了我们的假设，即PTEN在有丝分裂过程中是确保忠实的染色体遗传所必需的，并且PTEN的蛋白磷酸酶功能对于抑制异常的有丝分裂激酶活性以维持正常核型至关重要。为了验证这一假设，我们提出了两个具体目标如下。在目标1中，我们将证明有丝分裂染色体不稳定是PTEN缺乏的普遍表型结果。我们将使用Pten条件基因敲除白血病动物模型和一组Cowden综合征来源的人类淋巴母细胞系来验证PTEN缺陷与核型改变之间的潜在原因关系。在目标2中，我们将定义PTEN和Plk1之间的抑制信号链，并阐明它们之间的平衡相互作用有助于核型保真度和肿瘤抑制的机制。利用细胞和分子生物学的方法，我们将确定PTEN是一种重要的有丝分裂磷酸酶，并证明Plk1是维持有丝分裂染色体稳定性的PTEN磷酸酶的蛋白质靶标。这些目标的成功完成将有助于深入了解PTEN缺陷触发有丝分裂缺陷和染色体不稳定，从而导致肿瘤发生的机制。该项目的新发现将为进一步的机制研究和未来治疗人类癌症的治疗策略的发展提供一个新的视角。

DESCRIPTION (provided by applicant): PTEN is one of the most frequently mutated genes in human cancer and the PTEN protein is considered to be a "guardian of the genome" because of its important role in protecting chromosomal integrity. Observation of structural chromosome aberrations and aneuploidy in cells and tissues lacking functional PTEN brings the link between PTEN and chromosome stability sharply into focus. In our recent studies, we found that cells lacking PTEN exhibit chromosome missegregation and prominent polyploidy, suggesting that PTEN functions during mitosis to control genomic and karyotypic stability. Chromosome instability acquired during aberrant mitosis plays a causative role in tumor development and progression. The long-term goal of this research project is to establish the novel concept that PTEN plays an essential part in controlling mitotic chromosome stability and that its function in maintaining mitotic fidelity is a major driving force in tumor suppression. In support of this aim, our exciting new preliminary data reveal that PTEN deficiency leads to gross genomic alterations manifested by polyploidization and confers cellular resistance to spindle perturbation. Significantly, we found that the protein phosphatase activity of PTEN is required for maintenance of a normal karyotype, and for cellular sensitivity to spindle drugs. In addition, our data have revealed that a key mitotic kinase, polo-like kinase 1 (Plk1), is a potential PTEN target. These findings lead to our hypothesis that PTEN is required for ensuring faithful chromosome inheritance during mitosis and that the protein phosphatase function of PTEN is critical for restraining aberrant mitotic kinase activity in order to maintain a normal karyotype. To test this hypothesis, we propose two specific aims as follows. In Aim 1, we will demonstrate mitotic chromosome instability is a prevailing phenotypic consequence of PTEN deficiency. We will use a Pten conditional knockout leukemia animal model and a panel of Cowden syndrome-derived human lymphoblastoid cell lines to validate the potential causative relationship between PTEN deficiency and karyotypic alterations. In Aim 2, we will define the inhibitory signaling link between PTEN and Plk1 and elucidate the mechanism by which their balanced interplay contributes to karyotypic fidelity and tumor suppression. Using cellular and molecular biology approaches, we will characterize PTEN as an essential mitotic phosphatase and demonstrate that Plk1 is a protein target of the PTEN phosphatase that maintains mitotic chromosome stability. Successful completion of these aims will provide insight into the mechanisms whereby PTEN deficiency triggers mitotic defects and chromosomal instability, and thus leads to tumorigenesis. New findings from this project will offer a new perspective for further mechanistic studies and future development of therapeutic strategies in treating human cancers.