Human RME-8 Is Involved in Membrane Trafficking through Early Endosomes
Human RME-8 Is Involved in Membrane Trafficking through Early Endosomes
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DOI：
10.1247/csf.07045
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发表时间：
2008-01-01
影响因子：
1.5
通讯作者：
Sekiguchi, Kiyotoshi
中科院分区：
文献类型：
--
作者：
Fujibayashi, Akemi;Taguchi, Tomohiko;Sekiguchi, Kiyotoshi
RME-8是一种含有DnaJ结构域的蛋白质，其首先在秀丽隐杆线虫中被鉴定为摄取卵黄蛋白所需。RME-8也已在其他物种中鉴定，包括苍蝇和哺乳动物，其RME-8突变体的表型表明该蛋白在内吞作用中的重要性。在本研究中，我们克隆了人RME-8（hRME-8），并表征其生化特性和功能的内吞途径。发现hRME-8是通过其N-末端区域与膜紧密结合的外周蛋白。它部分共定位与几个早期内体标记，但不与晚期内体标记，与免疫电镜观察一致。当用一组显性活性Rab蛋白转染细胞时，hRME-8被限制在由Rab 5aQ 79 L表达诱导的大空泡中，而不是Rab 7 Q67 L。C-末端截短的hRME-8突变体的表达导致大斑点和空泡的形成，并损害通过早期内体的内吞途径，即，转铁蛋白再循环和表皮生长因子降解。总之，这些结果表明，hRME主要参与膜运输通过早期内体，但不通过降解细胞器，如多泡体和晚期内体。
RME-8 is a DnaJ-domain-containing protein that was first identified in Caenorhabditis elegans as being required for uptake of yolk proteins. RME-8 has also been identified in other species, including flies and mammals, and the phenotypes of their RME-8 mutants suggest the importance of this protein in endocytosis. In the present study, we cloned human RME-8 (hRME-8) and characterized its biochemical properties and functions in endocytic pathways. hRME-8 was found to be a peripheral protein that was tightly associated with the membrane via its N-terminal region. It partially colocalized with several early endosomal markers, but not with late endosomal markers, consistent with observations by immunoelectron microscopy. When cells were transfected with a panel of dominant-active Rab proteins, hRME-8 was confined to large vacuoles induced by expression of Rab5aQ79L, but not by Rab7Q67L. Expression of C-terminally-truncated hRME-8 mutants led to the formation of large puncta and vacuoles, and compromised endocytic pathways through early endosomes, i.e., recycling of transferrin and degradation of epidermal growth factor. Taken together, these results indicate that hRME is primarily involved in membrane trafficking through early endosomes, but not through degradative organelles, such as multivesicular bodies and late endosomes.