Function and Regulation Mechanisms of Polo-like Kinase 3 in Pancreatic Cancer

描述(申请人提供)：胰腺癌是癌症研究中最大的挑战之一。胰腺癌是美国成人癌症死亡的第四大原因。5年生存率保持在1-3%，确诊后中位生存期不到6个月。胰腺癌的特点是局部晚期或转移性疾病，对目前的治疗方法缺乏反应。根据在这种疾病中检测到的最频繁的突变，胰腺癌的基因图谱正在形成。Polo-like kinase3(Plk3)是四种哺乳动物Polo样蛋白之一，在近70%的人胰腺癌组织和大多数胰腺癌细胞系中的表达显著降低。此外，Plk3定位于染色体1p32，该基因被认为含有癌症易感基因。最近，Plk3基因敲除小鼠被产生，这些小鼠在高龄时出现了各种器官的肿瘤。Plk3是一种多功能蛋白，在调节细胞凋亡和对DNA损伤的反应中发挥重要作用。在细胞培养中，Plk3的表达诱导胰腺癌细胞的凋亡，并通过脂质体介导的基因转移抑制胰腺癌细胞的生长。这些发现表明Plk3作为一种肿瘤抑制因子，在胰腺癌细胞的凋亡中起着重要的作用。然而，Plk3被调控的潜在分子机制仍然不清楚。我们研究的长期目标是为胰腺癌患者开发更有效的治疗方法。根据我们的初步结果，我们假设Plk3的表达缺失在胰腺癌的发生发展中起着重要的作用，Plk3的激活是一种必要的调节，通过诱导磷酸化和/或与接头分子的相互作用来整合控制基因组不稳定性的信号。为了验证我们的假设，我们提出了三个具体的目标：(1)证实Plk3在胰腺癌发生发展中的作用；(2)确定Plk3在胰腺癌中的沉默表达以及Plk3在控制细胞分裂和DNA损伤检查点中的作用；(3)确定Plk3激活的调控机制。我们的研究结果将为深入了解Plk3的调控机制以及Plk3作为肿瘤抑制因子在胰腺癌中的重要作用提供依据。重要的是，这项研究可能会发现新的分子靶点，可能导致更有效的胰腺癌治疗。 公共卫生相关性：本项目旨在阐明Plk3在胰腺肿瘤发生发展中的肿瘤抑制功能，并确定Plk3沉默和调控的新机制。我们推测Plk3的下调在胰腺癌的发生发展中起重要作用，而PI3K通过蛋白水解性切割激活Plk3是受PI3K调控的。我们将使用Plk3基因敲除小鼠模型和Plk3基因敲除细胞系结合生化和细胞生物学方法，通过三个特定的目标来验证我们的假设，以填补我们对Plk3调控的新分子机制和Plk3在胰腺肿瘤发生中的作用的了解的空白。

DESCRIPTION (provided by applicant): Pancreatic cancer poses one of the greatest challenges in cancer research. Pancreatic adenocarcinoma is the fourth-leading cause of adult cancer mortality in the United States. The five-year survival rate remains at 1-3%, and the median survival duration after diagnosis is less than six months. Pancreatic cancer is characterized by locally advanced or metastatic disease and lack of response to current therapies. Based on the most frequently detected mutations in this disease, a genetic profile for pancreatic cancer is emerging. The expression of polo-like kinase 3 (Plk3), one of the four mammalian polo-like kinases, is significantly decreased in nearly 70% of human pancreatic cancer tissues and in most pancreatic cancer cell lines. Furthermore, Plk3 localizes to chromosome 1p32, a locus thought to contain cancer susceptibility genes. Recently, Plk3-knockout mice were generated and these mice developed tumors in various organs at advanced age. Plk3 is a multi-functional protein that plays critical roles in the regulation of apoptosis and responses to DNA damage. Expression of Plk3 induced apoptosis in pancreatic cancer cells in cell culture and inhibited pancreatic tumor growth by liposome- mediated gene transfer in a xenograft mouse model. These findings demonstrate that Plk3 functions as a tumor suppressor and plays an essential role in pancreatic cancer cell apoptosis. However, the underlying molecular mechanism through which Plk3 is regulated remains elusive. The long-term goal of our research is to develop more effective therapies for patients with pancreatic cancer. On the basis of our preliminary results, we hypothesize that loss of Plk3 expression plays an essential role in the development of pancreatic cancer and that Plk3 activation is an essential regulation that integrates signals that control genomic instability through inducible phosphorylation and/or interaction with adaptor molecules. To test our hypotheses, three specific aims were proposed: (1) demonstrate the role of Plk3 in the development of pancreatic cancer; (2) determine the expression of Plk3 is silenced in pancreatic cancer and role of Plk3 in the control of cell division and DNA damage checkpoints; (3) identify the mechanisms by which activation of Plk3 is regulated. The findings from our proposed study will provide insight into the mechanisms of Plk3 regulation and the essential role of Plk3 as a tumor suppressor in pancreatic cancer. Importantly, this study may discover novel molecular targets that could lead to more effective treatments for pancreatic cancer. PUBLIC HEALTH RELEVANCE: This project is aimed at elucidating the tumor suppressor function of Plk3 in pancreatic tumor development and determining the novel mechanism by which Plk3 is silenced and regulated. We hypothesize that down regulation of Plk3 plays an essential role in development of pancreatic cancer and activation of Plk3 by proteolytic cleavage is regulated by PI3K. We will test our hypothesis by three specific aims using a combination of Plk3 knockout mouse models and Plk3 knockdown cell lines with biochemical and cell biological approaches, to fill in the gaps in our understanding of the novel molecular mechanisms of Plk3 regulation and role of Plk3 in tumorigenesis of pancreas.