Molecular Basis and Regulatory Mechanisms of Exosome Secretion

摘要 Exosome是由细胞分泌到细胞外环境的脂质包裹的小囊泡，最近 被认为是一种新颖而高效的细胞间通讯方式。胞外体携带生物活性分子 例如，信号蛋白和microRNAs可以有效地影响其受体细胞的行为和功能。 近年来的研究表明，外切体与广泛的病理生理过程有关，例如 器官发生、病毒繁殖、肿瘤转移和免疫抑制。尽管人们对……非常感兴趣 外切体在各个领域中，对外切体的基本细胞生物学了解极不相称。这个 外体的生物发生始于内体的限制膜内陷形成管腔内 水泡(ILV)。这些内小体被称为多泡小体(MVB)，然后被运输到细胞外围 释放ILV--外体。而MVB的生物发生主要由ESCRT介导 复合体，介导MVB向细胞外围运输的分子机制，以及它们随后的 与质膜的对接和融合以释放外切体，仍然难以捉摸。此外，如何 外切体的生物发生和细胞内运输受到信号分子的调控，目前还不清楚。 我们研究的目标是确定调节细胞内转运的基本机制 并阐明致癌信号如何控制肿瘤进展的这些过程。首先，我们将 研究几类蛋白质，包括Rab家族的小GTP酶，八聚体外囊复合体，以及 微管马达蛋白，并了解它们如何在运输、对接和融合 MVBS到质膜上。这些工作将为基本的细胞生物学理解奠定基础。 外体分泌物。第二，我们将识别和表征调控各种不同基因的致癌信号通路 外切体运输的方方面面，从外切体蛋白货物选择到外切体在血浆中的释放 薄膜。在功能水平上，我们将研究肿瘤细胞内在信号通路，如有丝分裂原- 活化蛋白激酶(MAPK)轴通过外切体影响肿瘤微环境和免疫功能 促进肿瘤生长和免疫逃避的系统。一种结合了生物化学、 将采用细胞生物学、肿瘤生物学和免疫生物学来解决这些问题。我们的研究将架起桥梁 从基础外体细胞生物学到癌症生物学。它不仅将为分子的细胞生物学基础 和对外切体的机械理解，而且也为外切体的治疗靶向开辟了新的场所 癌症。

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.