McKenzie Jenna, Johannes Ludger, Taguchi Tomohiko, Sheff David
Department of Pharmacology, Carver College of Medicine, University of Iowa, Iowa City, IA 52242-2600, USA.
FEBS J. 2009 Mar;276(6):1581-95. doi: 10.1111/j.1742-4658.2009.06890.x. Epub 2008 Feb 7.
Both Shiga holotoxin and the isolated B subunit, navigate a retrograde pathway from the plasma membrane to the endoplasmic reticulum (ER) of mammalian cells to deliver catalytic A subunits into the cytosol. This route passes through early/recycling endosomes and then through the Golgi. Although passage through the endosomes takes only 30 min, passage through the Golgi is much slower, taking hours. This suggests that Golgi passage is a key step in retrograde traffic. However, there is no empirical data demonstrating that Golgi passage is required for the toxins to enter the ER. In fact, an alternate pathway bypassing the Golgi is utilized by SV40 virus. Here we find that blocking Shiga toxin B access to the entire Golgi with AlF(4)(-) treatment, temperature block or subcellular surgery prevented Shiga toxin B from reaching the ER. This suggests that there is no direct endosome to ER route available for retrograde traffic. Curiously, when Shiga toxin B was trapped in endosomes, it entered the cytosol directly from the endosomal compartment. Our results suggest that trafficking through the Golgi apparatus is required for Shiga toxin B to reach the ER and that diversion into the Golgi may prevent toxin escape from endosomes into the cytosol.
志贺全毒素和分离出的B亚基都沿着一条从质膜到哺乳动物细胞内质网（ER）的逆行途径，将具有催化活性的A亚基递送至胞质溶胶。这条途径经过早期/再循环内体，然后穿过高尔基体。虽然通过内体只需30分钟，但通过高尔基体的速度要慢得多，需要数小时。这表明高尔基体通路是逆行运输中的关键步骤。然而，尚无实验数据表明毒素进入内质网需要经过高尔基体。事实上，SV40病毒利用了一条绕过高尔基体的替代途径。在此我们发现，用AlF(4)(-)处理、温度阻断或亚细胞手术阻止志贺毒素B进入整个高尔基体，可防止志贺毒素B到达内质网。这表明不存在可供逆行运输的直接从内体到内质网的途径。奇怪的是，当志贺毒素B被困在内体中时，它直接从内体区室进入胞质溶胶。我们的结果表明，志贺毒素B到达内质网需要通过高尔基体进行运输，而进入高尔基体可能会阻止毒素从内体逃逸到胞质溶胶中。
