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

描述（由申请人提供）：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率的第四大原因。5年生存率保持在1- 3%，诊断后的中位生存时间不到6个月。胰腺癌的特征是局部晚期或转移性疾病，对目前的治疗缺乏反应。基于这种疾病中最常检测到的突变，胰腺癌的遗传特征正在出现。Polo样激酶3（Polo-like kinase 3，Plk 3）是四种哺乳动物Polo样激酶之一，在近70%的人胰腺癌组织和大多数胰腺癌细胞系中表达显著降低。此外，Plk 3定位于染色体1 p32，这是一个被认为含有癌症易感基因的位点。最近，Plk 3基因敲除小鼠被产生，这些小鼠在高龄时在各种器官中发生肿瘤。Plk 3是一种多功能蛋白，在细胞凋亡和DNA损伤反应的调节中起着关键作用。Plk 3的表达在细胞培养中诱导胰腺癌细胞凋亡，并在异种移植小鼠模型中通过脂质体介导的基因转移抑制胰腺肿瘤生长。这些发现表明Plk 3作为肿瘤抑制因子发挥功能，并在胰腺癌细胞凋亡中起重要作用。然而，Plk 3通过其调节的潜在分子机制仍然难以捉摸。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。基于我们的初步结果，我们假设Plk 3表达的丧失在胰腺癌的发展中起着重要作用，并且Plk 3激活是整合通过诱导磷酸化和/或与接头分子相互作用控制基因组不稳定性的信号的重要调节。为了验证我们的假设，提出了三个具体目标：（1）证明Plk 3在胰腺癌发生中的作用;（2）确定Plk 3在胰腺癌中的表达沉默以及Plk 3在控制细胞分裂和DNA损伤检查点中的作用;（3）确定Plk 3激活的调节机制。从我们提出的研究结果将提供深入了解Plk 3的调节机制和Plk 3作为胰腺癌中的肿瘤抑制因子的重要作用。重要的是，这项研究可能会发现新的分子靶点，从而可能导致更有效的胰腺癌治疗。 公共卫生相关性：该项目旨在阐明Plk 3在胰腺肿瘤发展中的肿瘤抑制功能，并确定Plk 3沉默和调节的新机制。我们推测Plk 3的下调在胰腺癌的发展中起着重要作用，并且Plk 3通过蛋白水解裂解的激活受PI 3 K的调节。我们将通过三个特定的目标来测试我们的假设，使用Plk 3敲除小鼠模型和Plk 3敲除细胞系与生物化学和细胞生物学方法的组合，以填补我们对Plk 3调控的新分子机制的理解中的空白，以及Plk 3在胰腺肿瘤发生中的作用。

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.