Molecular Basis and Regulatory Mechanisms of Exosome Secretion

摘要 外泌体是由细胞分泌到细胞外环境的脂质包裹的小囊泡，并且最近被 被认为是一种新颖且高效的细胞间通讯手段。外泌体携带生物活性分子 例如信号蛋白和微小RNA，它们可以有效地影响受体细胞的行为和功能。 近年来的研究表明，外泌体参与了广泛的病理生理过程，如 器官形成、病毒繁殖、肿瘤转移和免疫抑制。尽管人们对 尽管外泌体在各个领域都有广泛的应用，但对外泌体的基本细胞生物学理解却严重缺乏。的 当内体的界膜内陷形成管腔内时，外泌体的生物发生开始 囊泡（ILV）。这些内体，称为多泡体（MVB），然后被运输到细胞周边 用于释放ILV--外泌体。MVB的生物发生主要由ESCRT介导 复合物，介导MVB转运到细胞外周的分子机制，以及它们随后的细胞毒性。 与质膜对接和融合以释放外泌体仍然难以捉摸。此外， 外泌体的生物发生和细胞内运输受信号分子调节在很大程度上是未知的。 我们研究的目的是确定介导细胞内运输的基本机制， 外泌体，并阐明致癌信号如何控制这些过程的肿瘤进展。一是 研究几类蛋白质，包括Rab家族的小GTP酶，八聚体外囊复合物， 微管马达蛋白，并了解它们如何在运输，对接和融合的音乐会 MVB到质膜。这些工作将为基本的细胞生物学理解奠定基础， 外泌体分泌其次，我们将识别和表征调节各种肿瘤的致癌信号通路， 外泌体运输的方面，从外泌体蛋白质货物选择到外泌体在血浆中的释放 膜的在功能水平上，我们将研究肿瘤细胞的内在信号通路，如丝裂原， 活化的蛋白激酶（MAPK）轴通过外泌体影响肿瘤微环境和免疫反应， 系统以促进肿瘤生长和免疫逃避。一种结合生物化学， 细胞生物学、肿瘤生物学和免疫生物学将被用来解决这些问题。我们的研究将 基础外泌体细胞生物学到癌症生物学。它不仅为分子生物学奠定了细胞生物学基础， 和机制的理解，而且还开辟了新的途径，治疗靶向外泌体， 癌

ABSTRACT Exosomes are lipid-encapsulated small vesicles secreted by cells to the extracellular milieu, and are recently recognized as a novel and highly effective means of cell-cell communication. Exosomes carry bioactive molecules such as signaling proteins and microRNAs that potently affect the behavior and function of their recipient cells. Studies in recent years have implicated the exosomes in a wide range of pathophysiological processes such as organogenesis, viral propagation, tumor metastasis and immune suppression. Despite the great interest in exosomes in various fields, the basic cell biological understanding of exosomes is disproportionally lacking. The biogenesis of exosomes starts when the limiting membrane of endosomes invaginates to form intraluminal vesicles (ILVs). These endosomes, called multivesicular bodies (MVBs), are then transported to the cell periphery for the release of the ILVs–the exosomes. While the biogenesis of MVBs is mostly mediated by the ESCRT complex, the molecular machinery that mediates the transport of MVBs to the cell periphery, and their subsequent docking and fusion with the plasma membrane for exosome release, remains elusive. In addition, how the biogenesis and intracellular trafficking of the exosomes are regulated by signaling molecules is largely unknown. The goal of our research is to identify the basic machinery that mediating the intracellular trafficking of the exosomes, and to elucidate how oncogenic signaling control these processes for tumor progression. First, we will study several classes of proteins including the Rab family of small GTPases, the octameric exocyst complex, and microtubule motor proteins, and understand how they function in concert in the transport, docking and fusion of MVBs to the plasma membrane. These work will lay the foundation for the basic cell biological understanding of exosome secretion. Second, we will identify and characterize oncogenic signaling pathways that regulate various aspects of exosome trafficking, from exosome protein cargo selection, to exosome release at the plasma membrane. At the functional level, we will study how tumor cell-intrinsic signaling pathways such as the Mitogen- Activated Protein Kinase (MAPK) axis, through the exosomes, influence tumor microenvironment and the immune system to promote tumor growth and immune evasion. A multidisciplinary approach that combines biochemistry, cell biology, tumor biology, and immunobiology will be taken to address these questions. Our study will bridge basic exosome cell biology to cancer biology. It will not only lay the cell biological foundation for the molecular and mechanistic understanding of exosomes, but also open new venues for therapeutic targeting of exosomes in cancer.