The retromer complex and clathrin define an early endosomal retrograde exit site
The retromer complex and clathrin define an early endosomal retrograde exit site
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DOI：
10.1242/jcs.003020
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发表时间：
2007-06-15
影响因子：
4
通讯作者：
Johannes, Ludger
中科院分区：
文献类型：
--
作者：
Popoff, Vincent;Mardones, Gonzalo A.;Johannes, Ludger
先前的研究表明，网格蛋白、网格蛋白接头AP1和epsinR以及反转录复合物在从早期/循环核内体到反式高尔基网络（TGN）的逆行分选中起作用。然而，目前尚不清楚这些蛋白质机制是否在相同或平行的途径上起作用。我们在这里表明，网格蛋白和反转录亚基Vps26在含有志贺毒素b亚基的早期/循环内体的超微结构水平上共定位，这是一种经过充分研究的逆行运输货物。正如之前对网格蛋白的描述，我们发现干扰Vps26的表达可以抑制志贺毒素b亚基向TGN的逆行转运。在这些条件下，将志贺毒素b亚基从含转铁蛋白的早期/循环内体中取出的内体小管似乎是稳定的。这种情况与先前描述的低温孵育和网格蛋白耗尽条件不同，在这种条件下，志贺毒素b亚基标记被发现与转铁蛋白受体重叠。此外，我们发现志贺毒素b亚基和转铁蛋白受体在网格蛋白缺失的细胞中聚集在多泡核内体附近，这表明网格蛋白在液泡早期核内体上启动逆行分选，然后需要逆行酶来处理逆行小管。因此，我们的研究结果确定了反转录复合物在志贺毒素b亚基逆行转运中的作用，并强烈表明网格蛋白和反转录复合物在早期核内体的连续逆行分选步骤中起作用。
Previous studies have indicated a role for clathrin, the clathrin adaptors AP1 and epsinR, and the retromer complex in retrograde sorting from early/recycling endosomes to the trans Golgi network (TGN). However, it has remained unclear whether these protein machineries function on the same or parallel pathways. We show here that clathrin and the retromer subunit Vps26 colocalize at the ultrastructural level on early/recycling endosomes containing Shiga toxin B-subunit, a well-studied retrograde transport cargo. As previously described for clathrin, we find that interfering with Vps26 expression inhibits retrograde transport of the Shiga toxin B-subunit to the TGN. Under these conditions, endosomal tubules that take the Shiga toxin B-subunit out of transferrin-containing early/recycling endosomes appear to be stabilized. This situation differs from that previously described for low-temperature incubation and clathrin-depletion conditions under which Shiga toxin B-subunit labeling was found to overlap with that of the transferrin receptor. In addition, we find that the Shiga toxin B-subunit and the transferrin receptor accumulate close to multivesicular endosomes in clathrin-depleted cells, suggesting that clathrin initiates retrograde sorting on vacuolar early endosomes, and that retromer is then required to process retrograde tubules. Our findings thus establish a role for the retromer complex in retrograde transport of the B-subunit of Shiga toxin, and strongly suggest that clathrin and retromer function in consecutive retrograde sorting steps on early endosomes.