Cancer Cell Adaption 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，并且在多种肿瘤中观察到谷氨酰胺用于促进合成代谢过程的使用增加。然而，随着肿瘤的生长，谷氨酰胺催化剂的增加往往会耗尽局部供应，导致肿瘤细胞面临谷氨酰胺缺乏的时期。肿瘤细胞如何感知谷氨酰胺水平并在这些短暂的谷氨酰胺缺乏期存活尚不清楚，但这种存活是肿瘤持续存在所必需的。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的新治疗方法的潜力。我们最近发现，谷氨酰胺剥夺导致蛋白磷酸酶2A调节亚基B55α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B55α亚基组成的活性PP 2A复合物的形成。这种含B55α的PP 2A复合物是谷氨酰胺耗尽后肿瘤细胞存活所必需的。我们进一步发现，B55α的诱导激活p53，这是代谢应激的重要传感器。我们的初步数据表明，B55α激活p53通过一种机制，涉及EDD的去磷酸化，EDD是B55α的一种以前未鉴定的底物，是已知的p53负调节因子。此外，我们有初步的数据表明，IKK β，NF-κ B转录因子的主要调节因子，在谷氨酰胺缺乏时被磷酸化，并且是B55α诱导所必需的。因此，我们假设B55α被IKK β通路诱导去磷酸化EDD，从而导致p53激活和癌细胞在低谷氨酰胺条件下存活。因此，靶向谷氨酰胺代谢和IKK β B55α-EDD-p53存活途径可能是杀死肿瘤细胞的有效治疗方法。为了验证这一假设，我们提出了三个具体的目标：1）确定IKK β在B55α介导的p53激活和谷氨酰胺剥夺后细胞存活中的作用; 2）检查B55α是否通过去磷酸化EDD激活谷氨酰胺剥夺后的p53; 3）确定IKK β和谷氨酰胺代谢抑制对不同p53状态的肿瘤生长的联合作用。拟议研究的结果将确定IKK β B55α-p53通路在谷氨酰胺剥夺代谢适应性反应中的分子机制和功能影响。多种人类癌细胞系对谷氨酰胺饥饿敏感，并且目前正在研究损害细胞利用谷氨酰胺的能力的试剂作为新型癌症疗法。拟议的研究将提供对谷氨酰胺代谢被阻断时癌细胞所使用的生存途径的更深入了解，从而揭示靶向谷氨酰胺代谢和生存途径的新治疗方向，以有效杀死肿瘤细胞。

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 B55α, thereby triggering the formation of an active PP2A complex consisting of catalytic C and scaffolding A subunits and the specifically-induced B55α subunit. This B55α- containing PP2A complex is required for tumor cell survival upon glutamine depletion. We further found that induction of B55α activates p53, an important sensor of metabolic stress. Our preliminary data suggest that B55α activates p53 through a mechanism that involves dephosphorylation of EDD, a previously unidentified substrate of B55α that is a known negative regulator of p53. In addition, we have preliminary data indicating that IKKß, the master regulator of NF-kB transcription factors, is phosphorylated upon glutamine deprivation and required for B55α induction. We therefore hypothesize that B55α is induced by the IKKß pathway to dephosphorylate EDD, thereby leading to p53 activation and cancer cell survival under low glutamine conditions. Thus, targeting both glutamine metabolism and the IKKß B55α-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 IKKß in B55α-mediated activation of p53 and cell survival upon glutamine deprivation; 2) Examine if B55α activates p53 upon glutamine deprivation by dephosphorylating EDD; 3) Determine the combined effect of IKKß 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 IKKß B55α-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.