The role of membrane homoeostasis of neural stem cell and glioma stem cells in neural development and gliomagenesis

项目摘要 所有的干细胞都有自我更新的能力，即在不分化的情况下产生子代干细胞的能力。 转化成其他细胞类型干细胞从它们的小生境接收信号，指示它们自我更新， 它们通过细胞器间的级联通信过程来区分。大量证据 最近发现，胶质母细胞瘤，最常见和致命的脑肿瘤类型，有“根源”在一个 神经胶质瘤干细胞（GSC）具有取之不尽的自我更新能力。不像神经干 虽然GSC是神经干细胞（NSC）的一部分，但GSC也能够在它们遇到的次优环境中维持它们的干细胞性 在他们的壁龛外GSC，而不是NSC，如何能够在细胞外保持其干细胞性？ 利基仍然不清楚。为了确定影响GSC和小生境相互作用的潜在胶质瘤抑制因子，我们 发现RNA结合蛋白Quaking（QKI）是控制受体的内吞作用的关键调节因子， 运输、降解和信号脱敏。从机制上讲，QKI调节前mRNA的稳定性， 调节内溶酶体的脂质成分，特别是不饱和脂肪酸（UFA）的基因。作为 由于内溶酶体功能缺陷，我们发现QKI耗竭和乌法抑制 生物合成导致细胞质膜结合受体的富集，所述受体是维持细胞内蛋白质合成所必需的。 干性此外，由于多不饱和脂肪酸（PUFA）是铁凋亡的底物， 由于Qki损失导致的PUFA下调使GSC对铁凋亡（一种主要的肿瘤抑制）具有抗性 机制支持由QKI和乌法调节的胞内囊泡运输系统的重要性 在胶质母细胞瘤的生物合成中，我们发现较低水平的QKI，内溶酶体和硬脂酰辅酶A去饱和酶， (SCD乌法生物合成的关键酶）均与胶质母细胞瘤的预后不良显著相关 患者我们的长期目标是开发针对内溶酶体功能缺陷的治疗方法， 胶质母细胞瘤鉴于QKI是SCD基因的主要调节因子，并且抑制QKI和乌法生物合成 可以损害内溶酶体活性并促进胶质瘤的发生，我们假设QKI缺失/突变 通过下调乌法生物合成和恢复破坏NSC和GSC中的内溶酶体功能 多不饱和脂肪酸水平的降低可以使肿瘤细胞对铁凋亡敏感。为了验证这一假设，我们将（a）确定 在NSC和GSC中，在QKI调节的内溶酶体功能中，Scd 1/2介导的乌法生物合成，（B）阐明 QKI调节NSCs和GSC中Scd 1/2前mRNA稳定性的机制，以及（c）评估 PUFA水平的恢复在使肿瘤细胞对铁凋亡敏感中的作用。这些研究将 阐明胶质瘤抑制因子QKI如何调节胞内囊泡运输的分子机制 在神经干细胞和GSC通过脂质代谢，更重要的是，他们将有助于发展， 特异性靶向QKI/SCD缺失的胶质母细胞瘤的治疗策略。

PROJECT SUMMARY All stem cells have the capacity for self-renewal, an ability to create daughter stem cells without differentiating into other cell types. Stem cells receive the signals from their niches that instruct them to self-renew and prevent them from differentiating through a cascade of inter-organelle communication processes. Substantial evidence has recently revealed that glioblastoma, the most common and lethal type of brain tumor, has “roots” in a population of glioma stem cells (GSCs) that possess an inexhaustible ability to self-renew. Unlike neural stem cells (NSCs), GSCs are also able to sustain their stemness in the suboptimal environments they encounter outside their niches during invasion. How GSCs, but not NSCs, are able to maintain their stemness outside the niches remains unclear. To identify potential glioma suppressors that affect interaction of GSCs and niches, we discovered that RNA-binding protein Quaking (QKI) is a key regulator of endocytosis that controls receptor trafficking, degradation, and signaling desensitization. Mechanistically, QKI regulates pre-mRNA stability of genes that regulate lipid components of endolysosomes, particularly the unsaturated fatty acids (UFAs). As a consequence of defective endolysosomal function, we showed that depletion of QKI and inhibition of UFA biosynthesis led to the enrichment of cytoplasmic membrane-bound receptors that are required for maintaining stemness. In addition, since polyunsaturated fatty acids (PUFAs) are the substrates of ferroptosis, downregulation of PUFA due to Qki loss renders GSCs resistant to ferroptosis, a major tumor suppression mechanism. Supporting the importance of intracellular vesicle trafficking system regulated by QKI and UFA biosynthesis in glioblastoma, we found that lower levels of QKI, endolysosome and Stearoyl-CoA desaturase (SCD, the key enzyme for UFA biosynthesis) all correlate significantly with poorer prognosis in glioblastoma patients. Our long-term goal is to develop therapies that target the defective endolysosome function in glioblastoma. Given that QKI is a major regulator of SCD genes and inhibition of both QKI and UFA biosynthesis can impair the endolysosome activity and promote gliomagenesis, we hypothesize that QKI deletions/mutations disrupt endolysosomal function in NSCs and GSCs through downregulation of UFA biosynthesis and restoration of PUFA levels can sensitize tumor cells to ferroptosis. To test this hypothesis, we will (a) determine the role of Scd1/2-mediated UFA biosynthesis in QKI-regulated endolysosome functions in both NSCs and GSCs, (b) clarify the mechanism by which QKI regulates Scd1/2 pre-mRNA stability in both NSCs and GSCs, and (c) evaluate the effects of restoration of PUFA levels in sensitizing tumor cells to ferroptosis. Together, these studies will elucidate the molecular mechanisms of how the glioma suppressor QKI regulates intracellular vesicle trafficking in NSCs and GSCs through lipid metabolism, and more importantly, they will contribute to the development of therapeutic strategies that specifically target QKI/SCD-depleted glioblastoma.