Regulation of nutrient access by growth factors and mTOR

描述（由申请人提供）： 哺乳动物细胞的生长和存活受到来自其他细胞的外部信号的可用性的限制。 这种对生长因子的需求导致组织稳态所需的合作、相互依赖的细胞生长。 我的假设是，与单细胞生物不同，哺乳动物细胞缺乏自主能力，无法摄取足够的细胞内营养物质来支持细胞生长和存活，或执行细胞类型特异性功能。 相反，由生长因子介导的信号可以调节细胞获得所需细胞外营养物的能力，并以这种方式控制细胞生长和存活。 相反，肿瘤细胞已经获得了赋予生长因子独立性的突变。 像酵母等单细胞生物一样，转化细胞的生长只受营养物质的限制。 肿瘤转化的一种常见机制是在缺乏配体的情况下激活生长因子信号传导途径。 磷脂酰肌醇3激酶（PI3K）被多种生长因子受体激活，并且该信号转导途径的激活是大部分人类癌症的原因。 Akt原癌基因位于PI3K的下游。 与生长因子驱动营养摄取的模型一致，Akt激酶活性刺激营养摄取和代谢，并且这种作用对其抗凋亡活性至关重要。 由于Akt依赖性的营养摄取增加需要mTOR蛋白激酶的活性，因此mTOR也可能在通过PI3K信号转导途径调节细胞获取细胞外营养物中发挥重要作用。 为了支持这一观点，最近对PTEN缺失肿瘤的研究表明，mTOR抑制剂雷帕霉素对转化细胞具有有效的抗增殖作用。 此外，我的初步实验表明，Akt独立的作用mTOR在增加营养摄取和致癌转化。 尽管雷帕霉素作为抗肿瘤药物的临床试验正在进行中，但mTOR在细胞生长中的作用以及调节mTOR活性的机制尚不完全清楚。 使用生长因子撤除的体外模型，我将尝试：1）确定营养转运蛋白从细胞表面的损失是否在生长因子撤除诱导的死亡中起直接作用，并澄清mTOR是否调节这一过程，2）定义mTOR在细胞存活中的作用，3）研究mTOR和哺乳动物细胞中PP2A磷酸酶之间的相互作用。

DESCRIPTION (provided by applicant): The growth and survival of mammalian cells is limited by the availability of extrinsic signals from other cells. This requirement for growth factors results in the cooperative, interdependent cellular growth required for tissue homeostasis. My hypothesis is that, unlike unicellular organisms, mammalian cells lack the autonomous ability to take up sufficient intracellular nutrients to support cellular growth and survival or to perform cell-type specific functions. Rather, signals mediated by growth factors may regulate the ability of cells to obtain required extracellular nutrients and in this way control cell growth and survival. Neoplastic cells, in contrast, have acquired mutations that confer growth factor-independence. Like unicellular organisms such as yeast, the growth of transformed cells is restrained only by the availability of nutrients. One common mechanism of neoplastic transformation is the activation of growth factor signaling pathways in the absence of ligand. Phosphatidylinositol 3 kinase (PI3K) is activated by multiple growth factor receptors and the activation of this signal transduction pathway is responsible for a large fraction of human cancers. The Akt proto-oncogene lies downstream of PI3K. Consistent with the model that growth factors drive nutrient uptake, Akt kinase activity stimulates nutrient uptake and metabolism, and this effect is critical for its anti-apoptotic activity. As Akt-dependent increases in nutrient uptake require the activity of the mTOR protein kinase, mTOR is also likely to play an important role in the regulation of cellular access to extracellular nutrients by the PI3K signal transduction pathway. In support of this idea, recent studies in PTEN-deleted tumors have shown that the mTOR inhibitor, rapamycin, has potent anti-proliferative effects on transformed cells. Furthermore, my preliminary experiments suggest an Akt-independent role for mTOR in increasing nutrient uptake and in oncogenic transformation. Despite ongoing clinical trials of rapamycin as an anti-neoplastic agent, the role of mTOR in cellular growth and the mechanisms by which mTOR activity is regulated are incompletely understood. Using in vitro models for growth factor withdrawal, I will attempt to: 1) determine whether the loss of nutrient transporters from the cell surface plays a direct role in growth factor withdrawal-induced death and clarify whether mTOR regulates this process, 2) define the role of mTOR in cell survival, and 3) investigate the interaction between mTOR and the PP2A phosphatase in mammalian cells.