Endocytosis： Is There Really a Recycling from Late Endosomes？

作     者：David G. Robinson 

作者机构：Centre for Organismal Studies University Heidelberg 69120 Heidelberg Germany 

出 版 物：《Molecular Plant》 (分子植物（英文版）)

年 卷 期：2015年第8卷第10期

页      面：1554-1556页

核心收录：

学科分类：0710[理学-生物学] 083002[工学-环境工程] 071010[理学-生物化学与分子生物学] 0830[工学-环境科学与工程（可授工学、理学、农学学位）] 07[理学] 08[工学] 

主　　题：soundness scenario consider 

摘      要：Dear Editor, Over the last 15 years endocytosis has moved from being a process of only minor importance to plant physiologists to being one of the most exciting research areas in plant cell biology. These days, nobody doubts the operation of clathrin-mediated endocytosis as a mechanism for the internalization of a range of physiologically important transmembrane protein complexes at the plasma membrane （PM） of plant cells. These include both receptors and transporters. As in animal cells, most of these proteins are constitutively recycled back to the PM from an early endosome （EE）. However, some are destined for degradation and proceed further downstream in the endocytic pathway to late endosomes （LE）, where they are internalized into the intraluminal vesicles of the LE. Fusion of the LE with the lysosome/vacuole releases the vesicles leading to their degradation. The signal that marks PM proteins for degradation has been known in mammalian and yeast cells for quite some time and is polyubiquitination （Mukhopadhyay and Riezman, 2007）. In their Spotlight article, Zelazny and Vert （2015） highlight recent publications from the plant field that also demonstrate a key role for multiple monoubiquitination in the endocytosis of the metal transporters IRT1 （Barberon et al., 2011）, BOR1 （Kasai et al., 2011）, as well as lysine63-1inked polyubiquitination in vacuolar sorting of the auxin transporter PIN2 （Leitner et al., 2012）. They also draw attention to the discovery of a ubiquitin-binding protein （FREE1 ; also termed FYVE1 by Barberon et al., 2014） which locates to the LE in plant cells and is part of the ESCRT-I （endosomal sorting complex for transport） complex （Gao et al., 2014）. This complex sequesters ubiquitinated membrane cargo proteins and internalizes them. Finally, Zelazny and Vert draw attention to the work of Ivanov et al. （2014） in showing an increase in IRT1 degradation and iron deficiency in SNX1 mutants. So far so good, but Zelazny and Vert go on to conclude that a portion of the internalized IRT1 molecules that reach the LE are recycled back to the EE, a process that they consider to be mediated by sorting nexin 1 （SNX1）, a retromer protein. I question the soundness of this scenario.