Cancer cell adaptation to glutamine deprivation

描述（由申请人提供）：谷氨酰胺是支持癌细胞存活和增殖的必需营养素，谷氨酰胺的增加使用促进了多种肿瘤的合成代谢过程。然而，随着肿瘤的生长，谷氨酰胺分解代谢的增加往往会耗尽局部供应，导致肿瘤细胞面临谷氨酰胺剥夺期。肿瘤细胞如何感知谷氨酰胺水平并在短暂的谷氨酰胺缺乏期存活尚不清楚，但这种存活对于肿瘤的持续存在是必要的。我们的目标是确定在低谷氨酰胺条件下调节细胞存活的分子途径，并评估同时阻断谷氨酰胺代谢和适应性生存反应作为癌症治疗新方法的潜力。我们最近的研究表明，谷氨酰胺剥夺导致蛋白磷酸酶2A调节亚基B55a的诱导，从而触发由催化C和支架A亚基以及特异性诱导的B55a亚基组成的活性PP2A复合物的形成。这种含有B55a的PP2A复合体是谷氨酰胺耗竭后肿瘤细胞存活所必需的。我们进一步发现，B55a的诱导激活了p53，这是代谢应激的重要传感器。我们的初步数据表明，B55a通过一种机制激活p53，该机制涉及EDD的去磷酸化，EDD是B55a的一种底物，已知是p53的负调节因子。此外，我们有初步数据表明，IKK？NF-kB转录因子的主调控因子，在谷氨酰胺剥夺时被磷酸化，并且是B55a诱导所必需的。因此，我们假设B55a是由IKK？途径去磷酸化EDD，从而导致p53激活和低谷氨酰胺条件下的癌细胞存活。因此，针对谷氨酰胺代谢和IKK？B55a-EDD-p53存活通路可能是杀死肿瘤细胞的有效治疗途径。为了验证这一假设，我们提出了三个具体目标：1)确定IKK？谷氨酰胺剥夺后b55a介导的p53活化与细胞存活的关系；2)检验B55a是否通过去磷酸化EDD激活谷氨酰胺剥夺后的p53；3)确定IKK的综合效果？谷氨酰胺代谢对不同p53状态肿瘤生长的抑制作用。拟议研究的结果将确定IKK？谷氨酰胺剥夺代谢适应性反应中的B55a- p53通路。各种各样的人类癌细胞系对谷氨酰胺饥饿很敏感，目前正在研究损害细胞使用谷氨酰胺能力的试剂作为新的癌症治疗方法。本研究将进一步了解谷氨酰胺代谢被阻断时癌细胞的生存途径，从而揭示针对谷氨酰胺代谢和生存途径的新的治疗方向，从而有效地杀死肿瘤细胞。

DESCRIPTION (provided by applicant): Glutamine is an essential nutrient to support the survival and proliferation of cancer cells, and increased use of glutamine to fuel anabolic processes has been observed in a wide variety of tumors. However, as tumors grow, increased glutamine catabolism often depletes the local supply, leading tumor cells to face periods of glutamine deprivation. How tumor cells sense glutamine levels and survive these temporary periods of glutamine deprivation is unclear, but such survival is necessary for tumors to persist. Our goal is to define the molecular pathways that regulate cell survival under low glutamine conditions and evaluate the potential of simultaneously blocking both glutamine metabolism and the adaptive survival response as a novel therapeutic approach for cancer treatment. We have recently shown that glutamine deprivation leads to induction of the protein phosphatase 2A regulatory subunit B55a, thereby triggering the formation of an active PP2A complex consisting of catalytic C and scaffolding A subunits and the specifically-induced B55a subunit. This B55a- containing PP2A complex is required for tumor cell survival upon glutamine depletion. We further found that induction of B55a activates p53, an important sensor of metabolic stress. Our preliminary data suggest that B55a activates p53 through a mechanism that involves dephosphorylation of EDD, a previously unidentified substrate of B55a that is a known negative regulator of p53. In addition, we have preliminary data indicating that IKK?, the master regulator of NF-kB transcription factors, is phosphorylated upon glutamine deprivation and required for B55a induction. We therefore hypothesize that B55a is induced by the IKK? pathway to dephosphorylate EDD, thereby leading to p53 activation and cancer cell survival under low glutamine conditions. Thus, targeting both glutamine metabolism and the IKK? B55a-EDD-p53 survival pathway could be an effective therapeutic approach to kill tumor cells. To test this hypothesis, we propose three specific aims: 1) Determine the role of IKK? in B55a-mediated activation of p53 and cell survival upon glutamine deprivation; 2) Examine if B55a activates p53 upon glutamine deprivation by dephosphorylating EDD; 3) Determine the combined effect of IKK? and glutamine metabolism inhibition on growth of tumors with different p53 status. The results of the proposed studies will define the molecular mechanisms and functional impact of the IKK? B55a- p53 pathway in the metabolic adaptive response to glutamine deprivation. A wide variety of human cancer cell lines are sensitive to glutamine starvation, and reagents that impair cells' ability to use glutamine are currently being studied as novel cancer therapies. The proposed studies will provide deeper understanding of the survival pathway used by cancer cells when glutamine metabolism is blocked, and thus will reveal novel therapeutic directions for targeting both glutamine metabolism and the survival pathway in order to efficiently kill tumor cells.