A Rab6 to Rab11 transition is required for dense-core granule and exosome biogenesis in Drosophila secondary cells.
A Rab6 to Rab11 transition is required for dense-core granule and exosome biogenesis in Drosophila secondary cells.
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DOI：
10.1371/journal.pgen.1010979
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发表时间：
2023-10
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影响因子：
4.5
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腺体和神经系统中的分泌细胞经常将用于调节分泌的蛋白质包装和储存在致密核心颗粒（DCG）中，当从细胞表面释放时，所述致密核心颗粒分散。尽管这种动态过程与糖尿病和人类神经退行性疾病等疾病相关，但由于缺乏良好的细胞模型来跟踪所涉及的纳米级事件，我们对机制的理解相对有限。在这里，我们采用果蝇雄性附腺的前列腺样次级细胞（SC）来剖析DCG生物发生的细胞生物学和遗传学。这些细胞含有异常增大的DCG，它们组装在也形成称为外泌体的分泌纳米囊泡的隔室中。我们证明了已知的保守的DCG生物合成的调节剂，包括小G蛋白Arf 1和外套复合物AP-1，在SC DCG中发挥关键作用。使用实时成像，我们发现，驱动DCG生物发生的聚集事件伴随着膜相关的小Rab GTPases的变化，这些GTPases是分泌和内体系统中膜和蛋白质运输的主要调节因子。事实上，从trans-Golgi Rab6到再循环内体蛋白Rab11的转变，需要保守的DCG调节因子如AP-1，对于DCG和外泌体生物发生是必不可少的。我们的数据使我们能够开发一个模型DCG生物合成，汇集了几个以前不同的观察有关这个过程，并强调了分泌和内体系统之间的通信在控制调节分泌的重要性。细胞通过释放信号分子来相互交流，这些信号分子与靶细胞上的受体结合并改变它们的行为。在释放之前，这些信号通常存储在称为致密核心颗粒（DCG）的浓缩结构中。DCG存在于许多动物物种中，它们的失调与几种主要疾病有关，如糖尿病和神经退行性疾病。然而，控制DCG形成和分泌的机制仅部分了解。在这里，我们研究这个过程中使用的分泌细胞，含有异常大的DCG果蝇。我们发现，已知的哺乳动物DCG形成的监管机构也控制DCG生产在这些苍蝇细胞，并确定新的组装步骤，通过以下过程中的活细胞。最重要的是，我们表明，细胞的分泌隔间和其回收内体隔间之间的相互作用是需要在几分钟内诱导蛋白质的凝聚成DCG。我们进一步发现，DCG形成的已知监管机构需要这种关键的相互作用发生。我们的工作提供了一个平台，未来的研究可以建立在此基础上，以揭示这种关键的分泌-内体相互作用的分子机制，并探索其在分泌疾病中的作用。
Secretory cells in glands and the nervous system frequently package and store proteins destined for regulated secretion in dense-core granules (DCGs), which disperse when released from the cell surface. Despite the relevance of this dynamic process to diseases such as diabetes and human neurodegenerative disorders, our mechanistic understanding is relatively limited, because of the lack of good cell models to follow the nanoscale events involved. Here, we employ the prostate-like secondary cells (SCs) of the Drosophila male accessory gland to dissect the cell biology and genetics of DCG biogenesis. These cells contain unusually enlarged DCGs, which are assembled in compartments that also form secreted nanovesicles called exosomes. We demonstrate that known conserved regulators of DCG biogenesis, including the small G-protein Arf1 and the coatomer complex AP-1, play key roles in making SC DCGs. Using real-time imaging, we find that the aggregation events driving DCG biogenesis are accompanied by a change in the membrane-associated small Rab GTPases which are major regulators of membrane and protein trafficking in the secretory and endosomal systems. Indeed, a transition from trans-Golgi Rab6 to recycling endosomal protein Rab11, which requires conserved DCG regulators like AP-1, is essential for DCG and exosome biogenesis. Our data allow us to develop a model for DCG biogenesis that brings together several previously disparate observations concerning this process and highlights the importance of communication between the secretory and endosomal systems in controlling regulated secretion. Cells communicate with each other by releasing signalling molecules that bind receptors on target cells and alter their behaviour. Before their release, these signals are typically stored in condensed structures called dense-core granules (DCGs). DCGs are found in many animal species and their dysregulation is linked to several major diseases, such as diabetes and neurodegenerative disorders. However, the mechanisms controlling DCG formation and secretion are only partly understood. Here we study this process in fruit flies using a secretory cell that contains unusually large DCGs. We show that known regulators of DCG formation in mammals also control DCG production in these fly cells and identify new assembly steps by following the process in living cells. Most importantly, we show that an interaction between the cell’s secretory compartments and its recycling endosomal compartments is required to induce within minutes the condensation of proteins into a DCG. We further find that known regulators of DCG formation are needed for this crucial interaction to take place. Our work provides a platform, which future studies can build upon, to uncover the molecular mechanisms that enable this critical secretory-endosomal interaction and probe its role in diseases of secretion.