Cancer Cell Adaption to Glutamine Deprivation

描述(由申请人提供)：谷氨酰胺是支持癌细胞生存和增殖的基本营养物质，在各种肿瘤中观察到越来越多的谷氨酰胺用于促进合成代谢过程。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当地的供应，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谷氨酰胺剥夺的短暂时期存活尚不清楚，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通路，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一种新方法的可能性。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，从而触发活性PP2A复合体的形成，该复合体由催化C和支架A亚基以及特定诱导的B55α亚基组成。这种含有B55α的PP2A复合体是肿瘤细胞在谷氨酰胺耗尽时生存所必需的。我们进一步发现，B55α的诱导激活了P53，P53是代谢应激的重要传感器。我们的初步数据表明，B55α通过一种涉及EDD去磷酸化的机制激活P53，EDD是B55α的一种先前未知的底物，是P53的已知负调控因子。此外，我们有初步数据表明，核因子-kB转录因子的主要调控因子ikk？在谷氨酰胺剥夺后被磷酸化，是B55α诱导所必需的。因此，我们假设B55α是由ikkç途径诱导的，以去磷酸化EDD，从而导致P53激活和低谷氨酰胺条件下癌细胞的存活。因此，同时针对谷氨酰胺代谢和ikk？B55α-edd-p53生存通路可能是一种有效的杀伤肿瘤细胞的治疗方法。为了验证这一假设，我们提出了三个特定的目标：1)确定IKK？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)检测B55α是否通过去磷酸化EDD在谷氨酰胺剥夺时激活P53；3)确定IKK？和谷氨酰胺代谢抑制对不同P53状态的肿瘤生长的联合影响。这些研究的结果将确定IKK？B55α-P53通路在谷氨酰胺剥夺的代谢适应性反应中的分子机制和功能影响。许多人类癌细胞对谷氨酰胺饥饿敏感，而削弱细胞利用谷氨酰胺能力的试剂目前正在作为新的癌症治疗方法进行研究。这些研究将使人们对谷氨酰胺代谢受阻时癌细胞的生存途径有更深入的了解，从而为同时针对谷氨酰胺代谢和生存途径以有效杀伤肿瘤细胞提供新的治疗方向。

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.