Meehan Tracy L, Joudi Tony F, Timmons Allison K, Taylor Jeffrey D, Habib Corey S, Peterson Jeanne S, Emmanuel Shanan, Franc Nathalie C, McCall Kimberly
Department of Biology, Boston University, Boston, Massachusetts, United States of America.
The Scripps Research Institute, Department of Immunology and Microbial Science, La Jolla, California, United States of America.
PLoS One. 2016 Jun 27;11(6):e0158217. doi: 10.1371/journal.pone.0158217. eCollection 2016.
Billions of cells die in our bodies on a daily basis and are engulfed by phagocytes. Engulfment, or phagocytosis, can be broken down into five basic steps: attraction of the phagocyte, recognition of the dying cell, internalization, phagosome maturation, and acidification. In this study, we focus on the last two steps, which can collectively be considered corpse processing, in which the engulfed material is degraded. We use the Drosophila ovarian follicle cells as a model for engulfment of apoptotic cells by epithelial cells. We show that engulfed material is processed using the canonical corpse processing pathway involving the small GTPases Rab5 and Rab7. The phagocytic receptor Draper is present on the phagocytic cup and on nascent, phosphatidylinositol 3-phosphate (PI(3)P)- and Rab7-positive phagosomes, whereas integrins are maintained on the cell surface during engulfment. Due to the difference in subcellular localization, we investigated the role of Draper, integrins, and downstream signaling components in corpse processing. We found that some proteins were required for internalization only, while others had defects in corpse processing as well. This suggests that several of the core engulfment proteins are required for distinct steps of engulfment. We also performed double mutant analysis and found that combined loss of draper and αPS3 still resulted in a small number of engulfed vesicles. Therefore, we investigated another known engulfment receptor, Crq. We found that loss of all three receptors did not inhibit engulfment any further, suggesting that Crq does not play a role in engulfment by the follicle cells. A more complete understanding of how the engulfment and corpse processing machinery interact may enable better understanding and treatment of diseases associated with defects in engulfment by epithelial cells.
我们体内每天都有数十亿细胞死亡并被吞噬细胞吞噬。吞噬，即吞噬作用，可分为五个基本步骤：吞噬细胞的吸引、死亡细胞的识别、内化、吞噬体成熟和酸化。在本研究中，我们关注最后两个步骤，这两个步骤可统称为尸体处理，即被吞噬的物质被降解。我们使用果蝇卵巢滤泡细胞作为上皮细胞吞噬凋亡细胞的模型。我们发现，被吞噬的物质通过涉及小GTP酶Rab5和Rab7的经典尸体处理途径进行处理。吞噬受体Draper存在于吞噬杯以及新生的、磷脂酰肌醇3-磷酸（PI(3)P）和Rab7阳性的吞噬体上，而整合素在吞噬过程中维持在细胞表面。由于亚细胞定位的差异，我们研究了Draper、整合素和下游信号成分在尸体处理中的作用。我们发现一些蛋白质仅在内化过程中是必需的，而其他蛋白质在尸体处理中也存在缺陷。这表明一些核心吞噬蛋白在吞噬的不同步骤中是必需的。我们还进行了双突变分析，发现Draper和αPS3的联合缺失仍会导致少量被吞噬的囊泡。因此，我们研究了另一种已知的吞噬受体Crq。我们发现所有三种受体的缺失并没有进一步抑制吞噬作用，这表明Crq在滤泡细胞的吞噬过程中不起作用。对吞噬和尸体处理机制如何相互作用有更全面的了解，可能有助于更好地理解和治疗与上皮细胞吞噬缺陷相关的疾病。
