Rudolf Virchow Center for Integrative and Translational Bioimaging, University of Würzburg, 97080 Würzburg, Germany; Imaging Core Facility, Biocenter, University of Würzburg, 97074 Würzburg, Germany.
Department of Genetics, Stanford University School of Medicine, Stanford, CA 94305, USA.
Curr Biol. 2023 Feb 27;33(4):607-621.e7. doi: 10.1016/j.cub.2022.12.041. Epub 2023 Jan 17.
Phagocytic clearance is important to provide cells with metabolites and regulate immune responses, but little is known about how phagolysosomes finally resolve their phagocytic cargo of cell corpses, cell debris, and pathogens. While studying the phagocytic clearance of non-apoptotic polar bodies in C. elegans, we previously discovered that phagolysosomes tubulate into small vesicles to facilitate corpse clearance within 1.5 h. Here, we show that phagolysosome vesiculation depends on amino acid export by the solute transporter SLC-36.1 and the activation of TORC1. We demonstrate that downstream of TORC1, BLOC-1-related complex (BORC) is de-repressed by Ragulator through the BORC subunit BLOS-7. In addition, the BORC subunit SAM-4 is needed continuously to recruit the small GTPase ARL-8 to the phagolysosome for tubulation. We find that disrupting the regulated GTP-GDP cycle of ARL-8 reduces tubulation by kinesin-1, delays corpse clearance, and mislocalizes ARL-8 away from lysosomes. We also demonstrate that mammalian phagocytes use BORC to promote phagolysosomal degradation, confirming the conserved importance of TOR and BORC. Finally, we show that HOPS is required after tubulation for the rapid degradation of cargo in small phagolysosomal vesicles, suggesting that additional rounds of lysosome fusion occur. Thus, by observing single phagolysosomes over time, we identified the molecular pathway regulating phagolysosome vesiculation that promotes efficient resolution of phagocytosed cargos.
吞噬作用的清除对于为细胞提供代谢物和调节免疫反应很重要，但对于吞噬溶酶体如何最终清除细胞尸体、细胞碎片和病原体等吞噬物知之甚少。在研究秀丽隐杆线虫中非凋亡极体的吞噬清除过程中，我们之前发现吞噬溶酶体通过小管化形成小泡，在 1.5 小时内促进尸体清除。在这里，我们表明吞噬溶酶体泡囊化依赖于溶质转运蛋白 SLC-36.1 的氨基酸输出和 TORC1 的激活。我们证明，在 TORC1 下游，BLOC-1 相关复合物（BORC）通过 Ragulator 被 BORC 亚基 BLOS-7 去抑制。此外，BORC 亚基 SAM-4 持续需要招募小 GTP 酶 ARL-8 到吞噬溶酶体进行小管化。我们发现，破坏 ARL-8 的调节性 GTP-GDP 循环会减少肌球蛋白-1的小管化，延迟尸体清除，并使 ARL-8 错误定位远离溶酶体。我们还证明，哺乳动物吞噬细胞利用 BORC 促进吞噬溶酶体降解，证实了 TOR 和 BORC 的保守重要性。最后，我们表明，在小管化后，HOPS 对于小吞噬溶酶体泡中的货物的快速降解是必需的，这表明发生了额外轮次的溶酶体融合。因此，通过观察单个吞噬溶酶体随时间的变化，我们确定了调节吞噬溶酶体泡囊化的分子途径，该途径促进了吞噬物的有效清除。
