Rab5-associated Vacuoles play a unique role in phagocytosis of the enteric protozoan parasite Entamoeba histolytica
Rab5-associated Vacuoles play a unique role in phagocytosis of the enteric protozoan parasite Entamoeba histolytica
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DOI：
10.1074/jbc.m403987200
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发表时间：
2004-11-19
影响因子：
4.8
通讯作者：
Nozaki, T
中科院分区：
文献类型：
--
作者：
Saito-Nakano, Y;Yasuda, T;Nozaki, T
在哺乳动物中，Rab5和Rab7在吞噬体成熟过程中起着特定的协调作用。在这里，我们报道了肠道原虫溶组织内阿米巴寄生虫EhRab5和EhRab7A中的Rab5和Rab7参与的步骤与已知的哺乳动物不同。EhRab5和EhRab7A在稳态状态下定位于独立的小泡状结构。在5-10分钟的潜伏期内，红细胞诱导阿米巴原虫形成与EhRab5和EhRab7A相关的大液泡（“食前体液泡（PPV）”）。PPV在生理上是新生的，与吞噬体不同。PPV通过与含有消化水解酶、半胱氨酸蛋白酶和膜渗透肽阿米巴波的溶酶体融合而逐渐酸化和成熟。EhRab5与PPV分离后，5 ~ 10 min后，EhRab7A-PPV与吞噬体融合，最终EhRab7A与吞噬体分离。免疫电镜和光镜显示，PPV中含有含有液相标记物和变形虫的小泡样结构，这些结构在PPV中分布不均匀，提示其机制类似于PPV产生时的多泡体形成。与其他生物体的Rab5不同，EhRab5只参与吞噬作用，而不参与内吞作用。野生型EhRab5的过表达增强了吞噬作用和阿米巴虫向吞噬体的转运。相反，表达EhRab5Q67L GTP形式突变体会破坏PPV的形成和吞噬作用。总之，我们提出阿米巴Rab5在形成独特液泡中起重要作用，这对于红细胞的吞噬和溶酶体水解酶的包装至关重要，在靶向吞噬体之前。
In mammals, Rab5 and Rab7 play a specific and coordinated role in a sequential process during phagosome maturation. Here, we report that Rab5 and Rab7 in the enteric protozoan parasite Entamoeba histolytica, EhRab5 and EhRab7A, are involved in steps that are distinct from those known for mammals. EhRab5 and EhRab7A were localized to independent small vesicular structures at steady state. Priming with red blood cells induced the formation of large vacuoles associated with both EhRab5 and EhRab7A ("prephagosomal vacuoles (PPV)") in the amoeba within an incubation period of 5-10 min. PPV emerged de novo physically and distinct from phagosomes. PPV were gradually acidified and matured by fusion with lysosomes containing a digestive hydrolase, cysteine proteinase, and a membrane-permeabilizing peptide amoebapore. After EhRab5 dissociated from PPV, 5-10 min later, the EhRab7A-PPV fused with phagosomes, and EhRab7A finally dissociated from the phagosomes. Immunoelectron and light micrographs showed that PPV contained small vesicle-like structures containing fluid-phase markers and amoebapores, which were not evenly distributed within PPV, suggesting that the mechanism was similar to multivesicular body formation in PPV generation. In contrast to Rab5 from other organisms, EhRab5 was involved exclusively in phagocytosis, but not in endocytosis. Overexpression of wild-type EhRab5 enhanced phagocytosis and the transport of amoebapore to phagosomes. Conversely, expression of an EhRab5Q67L GTP form mutant impaired the formation of PPV and phagocytosis. Altogether, we propose that the amoebic Rab5 plays an important role in the formation of unique vacuoles, which is essential for engulfment of erythrocytes and important for packaging of lysosomal hydrolases, prior to the targeting to phagosomes.