Elucidating the role of GATOR2 in nutrient sensing by mTORC1

项目摘要/摘要 雷帕霉素复合体1(MTORC1)激酶的机制靶点是细胞生长的关键调节因子和 结合有丝分裂原信号、能量应激和营养供应的增殖，以协调中枢合成代谢和 分解代谢细胞过程1-4。MTORC1信号异常与多种人类疾病有关 包括癌症、糖尿病和癫痫，以及正常的生理过程，如1，5-6岁。因此， MTORC1激活的分子基础具有重要的基础和病理生理学意义。 同时检测生长因子信号和营养物质，包括氨基酸亮氨酸和精氨酸， 是mTORC1激活1-4所必需的。这些氨基酸的可用性通过 异二聚体RAG GTP酶，它将mTORC1募集到溶酶体表面以供mTOR激酶激活 激活剂Rheb11-12。GATOR1复合体通过其作为缺口的功能抑制mTORC1的招募 GATOR2复合体与GATOR118相互作用并抑制GATOR118。在没有氨基酸的情况下，亮氨酸 传感器Sestrin2和精氨酸传感器CASTOR1结合并抑制GATOR2，从而抑制mTORC1 激活19-24。 尽管鉴定了氨基酸感测机械的这些组件及其各自 功能，GATOR2复合体抑制GATOR1并导致mTORC1激活的机制 仍然难以捉摸。作为整合亮氨酸和精氨酸可利用性的节点，GATOR2是 MTORC1上游的营养传感分支。我们的初步结果表明，GATOR2作为一种 E3泛素连接酶，这种活性对mTORC1感知氨基酸是必不可少的。对分子的解释 GATOR2的机制将为哺乳动物细胞如何感知和响应必要的营养提供关键的见解 也可能为治疗药物提供新的靶点，旨在改善放松调控的mTORC1信号转导。 为了表征GATOR2的分子功能，我们提出了以下目标： 1.鉴定GATOR2的E3泛素连接酶活性 2.GATOR2底物的鉴定 3.确定GATOR2泛素连接酶活性在体内如何调节mTORC1的激活

Project Summary/Abstract The mechanistic target of rapamycin complex 1 (mTORC1) kinase is a key regulator of cell growth and proliferation that integrates mitogen cues, energy stress, and nutrient availability to coordinate central anabolic and catabolic cellular processes1-4. Aberrant mTORC1 signaling has been implicated in a variety of human diseases including cancer, diabetes, and epilepsy as well as normal physiological processes such as aging1,5-6. Accordingly, the molecular basis for mTORC1 activation is of significant fundamental and pathophysiological interest. Coincident detection of growth factor signals and nutrients, including the amino acids leucine and arginine, is required for mTORC1 activation1-4. Availability of these amino acids is conveyed to mTORC1 via the heterodimeric Rag GTPases, which recruit mTORC1 to the lysosomal surface for activation by the mTOR kinase activator Rheb11-12. The GATOR1 complex inhibits mTORC1 recruitment through its function as a GAP toward RagA/B. The GATOR2 complex interacts with and inhibits GATOR118. In the absence of amino acids, the leucine sensor Sestrin2 and arginine sensor CASTOR1 bind to and inhibit GATOR2 thereby repressing mTORC1 activation19-24. Despite identification of these components of the amino acid sensing machinery and their respective functions, the mechanism by which the GATOR2 complex inhibits GATOR1 and leads to mTORC1 activation remains elusive. As the node that integrates the availability of leucine and arginine, GATOR2 is a key component of the nutrient sensing branch upstream of mTORC1. Our preliminary results suggest that GATOR2 functions as an E3 ubiquitin ligase and that this activity is essential for mTORC1 to sense amino acids. Elucidation of the molecular mechanism of GATOR2 will provide key insight into how mammalian cells sense and respond to essential nutrients and may also provide novel targets for therapeutic agents designed to ameliorate deregulated mTORC1 signaling. To characterize the molecular function of GATOR2, we propose the following aims: 1. Characterize the E3 ubiquitin ligase activity of GATOR2 2. Identify substrates of GATOR2 3. Determine how GATOR2 ubiquitin ligase activity regulates mTORC1 activation in vivo