Phospholipase D-mTOR Survival Signals in Tumorigenesis

描述(申请人提供)：默认的凋亡程序已被改编为对抗癌症的第一道防线，几乎所有的癌细胞都有突变，激活“生存信号”以抑制细胞凋亡。生存信号的中心节点是mTOR(雷帕霉素的哺乳动物靶点)。MTOR在磷脂酰肌醇-3-激酶(PI3K)信号通路介导的信号作用下被激活。然而，最近很明显，mTOR也是激活磷脂酶D(PLD)的信号的靶点。PLD产生磷脂酸(PA)，这是一种脂质第二信使，以与雷帕霉素竞争的方式直接与mTOR相互作用-而PA是激活mTOR所必需的。重要的是，PLD活性在几种类型的人类癌症中升高。PLD活性在许多人类癌细胞中升高，是mTOR介导的信号所必需的，而mTOR介导的信号对生存和促进细胞周期进展至关重要。该提案的中心假设是：人类癌细胞中PLD活性的升高促进了通过G1晚期的“细胞生长检查点”，并抑制了默认的凋亡程序。我们建议，几乎所有的癌细胞都必须激活信号，才能通过这个检查点。具体地说，我们建议：1)确定PLD-mTOR信号如何通过建议的细胞生长检查点影响细胞周期进程；2)确定PLD产生的PA与其他信号输入协同调节mTORC1和mTORC2的机制；以及3)表征导致人类癌细胞系PLD活性升高的信号，并在体外和体内评估针对这些信号的药理学作用。我们提出，人类癌细胞中的PLD-mTOR信号通路代表了癌细胞广泛采用的促进细胞周期进展和抑制默认凋亡程序的策略。这里提出的研究将为合理靶向大量依赖于G1细胞周期进展和抑制凋亡的PLD活性的明显的癌症提供一个框架。与公共健康相关：这项拟议的研究将评估调节人类癌细胞中磷脂酶D(PLD)和mTOR的细胞内机制，以及这些信号对我们建议的细胞周期G1期的“细胞生长检查点”的影响，我们建议在几乎所有人类癌症中都必须克服这些影响。该项目建立在我们之前的发现基础上，即许多人类癌细胞中存在磷脂酶D(PLD)活性升高，这些细胞中PLD活性的抑制会导致细胞凋亡。以癌细胞中的PLD-mTOR信号为靶点，是重振默认细胞死亡程序的一种非常有前途的策略，而默认细胞死亡程序可以说是抗癌的第一道防线--因此是翻译研究的肥沃领域。

DESCRIPTION (provided by applicant): Default apoptotic programs have been adapted as a first line of defense against cancer, and virtually all cancer cells have mutations that activate "survival signals" in order to suppress apoptosis. A central node in survival signaling is mTOR (the mammalian target of rapamycin). mTOR is activated in response to signals mediated by the phosphatidylinositol-3-kinase (PI3K) signaling pathway. However, more recently it has become apparent that mTOR is also targeted by signals that activate phospholipase D (PLD). PLD generates phosphatidic acid (PA), a lipid second messenger that interacts directly with mTOR in a manner that is competitive with rapamycin - and PA is required for the activation of mTOR. Importantly, PLD activity is elevated in several types of human cancer. PLD activity is elevated in many human cancer cells and is required for mTOR-mediated signals that are critical for survival and promote cell cycle progression. The CENTRAL HYPOTHESIS of the proposal is - Elevated PLD activity in human cancer cells promotes passage through a late G1 "Cell Growth Checkpoint" and suppresses default apoptotic programs. We are proposing that virtually all cancer cells must activate signals that allow passage through this checkpoint. SPECIFICALLY, we propose: 1) To determine how PLD-mTOR signaling impacts on cell cycle progression through a proposed Cell Growth Checkpoint; 2) To determine the mechanism by which PLD-generated PA regulates mTORC1 and mTORC2 in concert with other signaling inputs; and 3) To characterize signals that lead to elevated PLD activity in human cancer cell lines and to evaluate targeting these signals pharmacologically both in vitro and in vivo. We are proposing that a PLD-mTOR signaling pathway in human cancer cells represents a widely employed strategy by cancer cells to promote cell cycle progression and suppress default apoptotic programs. The studies proposed here will provide a framework for the rational targeting of an apparent large number of cancers that depend upon elevated PLD activity for G1 cell cycle progression and suppression of apoptosis. PUBLIC HEALTH RELEVANCE: The proposed study will evaluate the intracellular mechanisms that regulate phospholipase D (PLD) and mTOR in human cancer cells and the impact of these signals on a proposed "Cell Growth Checkpoint" in the G1 phase of the cell cycle that we are proposing must be overcome in virtually all human cancers. The project builds on our previous findings that there is elevated phospholipase D (PLD) activity in many human cancer cells and that suppression of PLD activity in these cells results in apoptotic cell death. Targeting the PLD-mTOR signals in cancer cells represents a very promising strategy for resurrecting the default cell death programs that are arguably the first line of defense against cancer - and is therefore a fertile area for translational research.