Unexpected role for AMPK and mTORC1 in cellular adaptation to nutrient stress

项目摘要 以保守的蛋白激酶AMPK(AMP激活的蛋白激酶)为中心的信号网络 和mTOR(雷帕霉素的机械靶点)使细胞能够对动态变化做出适当的感知和反应 各种系统性和局部性线索的波动。能量应激激活AMPK促进分解代谢和 抑制合成代谢途径，以平衡能源供需。AMPK还能促进血糖和血脂 动态平衡。事实上，激活AMPK的药物二甲双胍(又名格卢西汀)代表了最广泛的 二型糖尿病的处方治疗。奇怪的是，AMPK自相矛盾地发挥着肿瘤抑制或 肿瘤促进剂取决于细胞环境。营养素(即氨基酸)和生长因子(即IGF/胰岛素) 协同激活mTOR复合体1(MTORC1)，它驱动合成细胞代谢(即蛋白质和脂肪 合成)并抑制自噬。生理上，异常的mTORC1信号有助于不同 包括癌症和II型糖尿病在内的疾病以及mTOR抑制剂是FDA批准用于肾癌的药物， 结节性硬化症(TSC)和血管成形术后支架再狭窄。尽管生理上和 AMPK和mTORC1的治疗重要性，我们在分子水平上对它们的理解存在重大差距 细胞信令网络。在先前的工作中，我们发现mTOR(位于S1261上)的磷酸化促进mTORC1 信号和细胞生长/大小。出乎意料的是，一个Kinome屏幕确定AMPK是一个mTOR S1261激酶。 发现AMPK使mTORC1激活位点上的mTOR磷酸化呈现一个明显的悖论， 然而，AMPK经典地抑制mTORC1，以响应严重的能量压力。我们的初步结果 调和这一自相矛盾的发现，并揭示我们对AMPK及其与 MTORC1.我们发现，在诱导营养胁迫，特别是氨基酸饥饿之后，氨基酸提供了 通过重新摄食或自噬激活AMPK，增加mTOR S1261的磷酸化，从而重新激活 并以AMPK依赖的方式促进细胞存活。此外，mTOR S1261 磷酸化需要Rheb，这是一种受TSC负调控的上游mTORC1激活剂。在本建议书中 我们研究了AMPK和mTORC1在细胞对营养胁迫的适应中出乎意料的作用。我们 假设AMPK-mTORC1轴在长时间内维持新陈代谢的生存水平 当压力消退时，营养压力或促进新陈代谢恢复。这项研究使用了培养的 细胞和缺乏mTOR S1261磷酸化的CRISPR工程小鼠模型将提供概念性的 进展，因为它将改变我们对AMPK在代谢控制方面的看法，以及它与mTORC1的关系。 阐明AMPK对mTORC1的矛盾激活将促进我们对mTOR和AMPK的理解 健康和疾病，并可能确定治疗癌症等相关疾病的新治疗策略 和代谢性疾病。

Project Summary Signaling networks centered on the conserved protein kinases AMPK (AMP-activated protein kinase) and mTOR (mechanistic target of rapamycin) enable cells to sense and respond appropriately to dynamic fluctuations in a variety of systemic and local cues. Energetic stress activates AMPK to promote catabolic and suppress anabolic pathways to balance energy supply and demand. AMPK also promotes glucose and lipid homeostasis. In fact, the AMPK-activating drug metformin (aka, GlucoPhage) represents the most widely prescribed treatment for type II diabetes. Curiously, AMPK paradoxically functions as a tumor suppressor or tumor promoter depending on cellular context. Nutrients (i.e. amino acids) and growth factors (i.e. IGF/insulin) cooperate to activate mTOR complex 1 (mTORC1), which drives anabolic cell metabolism (i.e. protein and lipid synthesis) and suppresses autophagy. Physiologically, aberrant mTORC1 signaling contributes to diverse disorders including cancer and type II diabetes, and mTOR inhibitors are FDA-approved for renal cell carcinoma, tuberous sclerosis complex (TSC), and stent restenosis following angioplasty. Despite the physiologic and therapeutic importance of AMPK and mTORC1, major gaps exist in our molecular-level understanding of these cell signaling networks. In prior work we showed that phosphorylation of mTOR (on S1261) promotes mTORC1 signaling and cell growth/size. Unexpectedly, a kinome screen identified AMPK as an mTOR S1261 kinase. Finding that AMPK phosphorylates mTOR on an mTORC1-activating site presented an apparent paradox, however, as AMPK canonically inhibits mTORC1 in response to severe energetic stress. Our preliminary results reconcile this paradoxical finding and expose a major gap in our understanding of AMPK and its relationship with mTORC1. We find that after induction of nutrient stress, specifically amino acid starvation, amino acids provided either by re-feeding or autophagy activate AMPK and increase mTOR S1261 phosphorylation, which re-activates mTORC1 signaling and promotes cell survival in an AMPK dependent manner. Moreover, mTOR S1261 phosphorylation requires Rheb, an upstream mTORC1 activator under negative control by TSC. In this proposal we investigate an unexpected role for AMPK and mTORC1 in cellular adaptation to nutrient stress. We hypothesize that the AMPK-mTORC1 axis functions to maintain a survival level of metabolism during prolonged nutrient stress or facilitates metabolic recovery when the stress subsides. This research, which employs cultured cells and a CRISPR-engineered mouse model lacking mTOR S1261 phosphorylation, will provide conceptual advance as it will shift how we think about AMPK in metabolic control and its relationship with mTORC1. Elucidating paradoxical activation of mTORC1 by AMPK will advance our understanding of mTOR and AMPK in health and disease and may identify new therapeutic strategies for treatment of linked disorders, such as cancer and metabolic diseases.