Molecular Mechanisms of Organelle-based Metabolic Signaling

摘要 细胞感知营养的分子机制在很大程度上仍不清楚，但它们的 阐明是我们理解正常和疾病状态下代谢调节的关键。在中心 是一种古老的蛋白激酶，被称为 雷帕霉素复合体1(MTORC1)。作为对营养等代谢输入的综合作用的反应， 生长因子、能量和氧气，mTORC1从细胞质转移到溶酶体表面， 在那里它会被激活。越来越多的证据表明，溶酶体上mTORC1的异常激活 可能是从癌症到2型糖尿病再到神经退化等疾病的驱动力。因此，一个很深的 对mTORC1如何被激活然后失活对营养的反应的机械理解可能指向 这些疾病的新治疗策略的途径。我的实验室为 了解mTORC1途径的组织，以及它的功能如何与许多活动相结合 溶酶体。特别是，我们已经确定了一条专门的信号通路，通过它，胆固醇是一种重要的 细胞膜的构建块，促进mTORC1募集到溶酶体并激活其 下游项目。我们发现了溶酶体和内质网之间的膜接触部位 网状结构是胆固醇激活mTORC1的关键节点，因此涉及细胞器间 沟通作为mTORC1监管的一个重要方面。此外，我们还发现，过量的mTORC1 由溶酶体中的胆固醇积累引起的信号会导致细胞功能障碍，可能是一种驱动力 神经退行性和代谢性疾病中的力量，Niemann-Pick C型(NPC)。 这些发现直接导致了关于细胞营养传感组织的深刻问题，这是 是目前米拉提案的核心。一个关键的挑战是阐明其机制和生理 脂质依赖的mTORC1调节的作用，特别是是否存在专门的胆固醇传感器在 溶酶体膜，以及它们如何将丰富的甾醇分子偶联到mTORC1的激活和 在细胞和生物体水平上的整体代谢调节。根据我们的发现，通过 MTORC1涉及溶酶体和内质网之间的物理通信，这是 建议是描述调解沟通和代谢物交换的机制 溶酶体和内质网，以及这一机制如何参与mTORC1以及另一主要 代谢激酶，蛋白激酶A。最后，mTORC1在鼻咽癌中的致病作用，以及 对mTORC1的抑制能恢复鼻咽癌细胞功能的几个参数，强烈支持mTORC1作为素数 神经退行性疾病的靶点。因此我们将确定溶酶体mTORC1是如何控制神经细胞的 动态平衡，以及失调的mTORC1信号如何导致神经元退化。加在一起，这些 研究将阐明健康和疾病状态下新陈代谢组织的基本原则。

ABSTRACT The molecular mechanisms through which cells sense nutrients remain largely unknown, but their elucidation is key to our understanding of metabolic regulation both in normal and disease states. At the center of nutrient sensing and growth regulation is an ancient protein kinase known as the mechanistic Target of Rapamycin Complex 1 (mTORC1). In response to the combined action of metabolic inputs such as nutrients, growth factors, energy and oxygen, mTORC1 translocates from the cytoplasm to the surface of lysosomes, where it becomes activated. Accumulating evidence indicates that aberrant mTORC1 activation at the lysosome could be a driving force in diseases ranging from cancer to type-2 diabetes to neurodegeneration. Thus, a deep mechanistic understanding of how mTORC1 is activated and then inactivated in response to nutrients could point the way to novel therapeutic strategies in these diseases. My lab has made important contributions to the understanding of mTORC1 pathway organization, and how its function is integrated with the many activities of the lysosome. In particular, we have identified a dedicated signaling pathway via which cholesterol, an important building block for cellular membranes, promotes mTORC1 recruitment to the lysosome and activation of its downstream programs. We have uncovered membrane contact sites between lysosomes and the endoplasmic reticulum as key nodes where mTORC1 activation by cholesterol occurs, thus implicating inter-organelle communication as an important aspect of mTORC1 regulation. Furthermore, we found that excess mTORC1 signaling, caused by cholesterol accumulation in the lysosome, drives cellular dysfunction and could be a driving force in a neurodegenerative and metabolic disease, Niemann-Pick type C (NPC). These discoveries directly lead to deep questions on the organization of cellular nutrient sensing, which are at the core of the current MIRA proposal. One key challenge is to elucidate the mechanisms and physiological roles of lipid-dependent mTORC1 regulation, specifically whether dedicated cholesterol sensors exist in the lysosomal membrane, and how they couple the abundance of sterol molecules to mTORC1 activation and to overall metabolic regulation at the cell and organism level. Based on our finding that cholesterol sensing by mTORC1 involves physical communication between the lysosome and the ER, another major goal of the proposal is to delineate the machinery that mediates communication and metabolite exchange between the lysosome and the ER, and how this machinery participates in regulation of mTORC1 as well as another major metabolic kinase, protein kinase A. Finally, the pathogenic role of dysregulated mTORC1 in NPC, and the ability of mTORC1 inhibition to restore several parameters of NPC cell function, strongly support mTORC1 as a prime target in neurodegenerative disease. We will thus determine how lysosomal mTORC1 controls neuronal cell homeostasis, and how dysregulated mTORC1 signaling contributes to neuronal degeneration. Together, these studies will shed light on fundamental principles of metabolic organization in health and disease states.