The pathogenic mechanism of the Mycobacterium ulcerans virulence factor, mycolactone, depends on blockade of protein translocation into the ER.
The pathogenic mechanism of the Mycobacterium ulcerans virulence factor, mycolactone, depends on blockade of protein translocation into the ER.
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DOI：
10.1371/journal.ppat.1004061
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发表时间：
2014-04
期刊：
影响因子：
6.7
通讯作者：
Simmonds RE
中科院分区：
文献类型：
--
作者：
Hall BS;Hill K;McKenna M;Ogbechi J;High S;Willis AE;Simmonds RE
溃疡分枝杆菌感染的特征是组织坏死和由于分枝杆菌内酯引起的免疫抑制，分枝杆菌内酯是布鲁里溃疡病病理学的必要和充分的毒力因子。已知其许多作用涉及下调与重要细胞过程有关的特定蛋白质，如免疫反应和细胞粘附。我们先前已经证明，菌内酯完全阻断了LPS依赖性促炎介质的转录后产生。使用多核糖体分析，我们现在最终证明，菌内酯不能阻止TNF，IL-6和考克斯-2 mRNA在巨噬细胞中的翻译。相反，它抑制这些蛋白质的产生，沿着几乎所有其他通过ER转运的（诱导的和组成性的）蛋白质。这是由于蛋白质易位的阻断和随后的异常定位蛋白质的降解。有几条证据支持这种对菌内酯功能的变革性解释。首先，如果同时抑制26 S蛋白酶体的作用，则可以再次检测到细胞TNF和考克斯-2。第二，在细胞质中发现恢复的蛋白质，表明不能易位。第三，体外翻译试验表明，分枝菌内酯阻止TNF和其他蛋白质易位到ER中。这是特异性的，因为尾锚定蛋白插入ER不受影响，表明ER在结构上保持完整。第四，代谢标记揭示了从处理的细胞糖基化和分泌的蛋白质几乎完全损失，而胞质蛋白质不受影响。值得注意的是，糖基化和分泌蛋白质生产的严重缺乏在一系列不同的疾病相关细胞类型中是明显的。这些研究提供了一个新的机制，在体外和体内观察到的病理活动的分枝菌内酯。菌内酯依赖性抑制蛋白质易位进入ER不仅解释了先天性细胞因子的缺陷，而且还解释了驱动布鲁里溃疡病因的膜受体、粘附分子和T细胞因子的损失。布鲁里溃疡是由人类病原体溃疡分枝杆菌感染引起的进行性坏死性皮肤病变。由分枝杆菌产生的一种小化合物Mycolactone是疾病病理学的根本原因，但直到现在还没有统一的机制来解释为什么。我们一直在使用一个模型系统，以调查的原因，选择性损失的蛋白质，这是一个共同的特点，菌内酯曝光。具体来说，这涉及到确定它阻止免疫细胞产生炎症介质的点。在这项工作中，我们证明了菌内酯通过阻断蛋白质输出的第一步来抑制这些蛋白质的产生：转运到称为内质网（ER）的细胞隔室。而应输出的蛋白质则在细胞胞质溶胶中产生，在那里它们被识别为处于错误的位置并被迅速降解，导致必须通过ER的蛋白质的生产普遍停止，包括几乎所有分泌和表面蛋白质。这对基本细胞功能如生长、粘附和存活具有深远的影响。因此，我们已经确定了布鲁里溃疡关键特征的分子基础，这将改变我们对疾病进展的理解。
Infection with Mycobacterium ulcerans is characterised by tissue necrosis and immunosuppression due to mycolactone, the necessary and sufficient virulence factor for Buruli ulcer disease pathology. Many of its effects are known to involve down-regulation of specific proteins implicated in important cellular processes, such as immune responses and cell adhesion. We have previously shown mycolactone completely blocks the production of LPS-dependent proinflammatory mediators post-transcriptionally. Using polysome profiling we now demonstrate conclusively that mycolactone does not prevent translation of TNF, IL-6 and Cox-2 mRNAs in macrophages. Instead, it inhibits the production of these, along with nearly all other (induced and constitutive) proteins that transit through the ER. This is due to a blockade of protein translocation and subsequent degradation of aberrantly located protein. Several lines of evidence support this transformative explanation of mycolactone function. First, cellular TNF and Cox-2 can be once more detected if the action of the 26S proteasome is inhibited concurrently. Second, restored protein is found in the cytosol, indicating an inability to translocate. Third, in vitro translation assays show mycolactone prevents the translocation of TNF and other proteins into the ER. This is specific as the insertion of tail-anchored proteins into the ER is unaffected showing that the ER remains structurally intact. Fourth, metabolic labelling reveals a near-complete loss of glycosylated and secreted proteins from treated cells, whereas cytosolic proteins are unaffected. Notably, the profound lack of glycosylated and secreted protein production is apparent in a range of different disease-relevant cell types. These studies provide a new mechanism underlying mycolactone's observed pathological activities both in vitro and in vivo. Mycolactone-dependent inhibition of protein translocation into the ER not only explains the deficit of innate cytokines, but also the loss of membrane receptors, adhesion molecules and T-cell cytokines that drive the aetiology of Buruli ulcer. Buruli ulcer is a progressive necrotic skin lesion caused by infection with the human pathogen Mycobacterium ulcerans. Mycolactone, a small compound produced by the mycobacterium, is the root cause of the disease pathology, but until now there has been no unifying mechanism explaining why. We have been using a model system to investigate the reason for the selective loss of protein that is a common feature of mycolactone exposure. Specifically, this involves identifying the point at which it stops immune cells making inflammatory mediators. In this work, we demonstrate that mycolactone inhibits production of such proteins by blocking the first step of protein export: translocation into a cellular compartment called the endoplasmic reticulum (ER). Proteins due for export are instead made in the cell cytosol where they are recognised as being in the wrong place and are rapidly degraded, causing a general cessation of the production of proteins that have to travel through the ER, including almost all secreted and surface proteins. This has a profound effect on basic cell functions such as growth, adhesion and survival. Therefore, we have identified the molecular basis underlying the key features of Buruli ulcer, and this will transform our understanding of disease progression.
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DOI：
10.1038/nrm3226
发表时间：
2011-11-16
期刊：
Nature reviews. Molecular cell biology
影响因子：
--
作者：
通讯作者：
--
影响因子：
64.8
作者：
Besemer, J;Harant, H;Lindley, IJD
通讯作者：
Lindley, IJD
影响因子：
3.8
作者：
Hong, Hui;Coutanceau, Emmanuelle;Demangel, Caroline
通讯作者：
Demangel, Caroline
影响因子：
4.5
作者：
Johannes, G;Sarnow, P
通讯作者：
Sarnow, P
影响因子：
3.3
作者：
Luna, A;Matas, OB;Egea, G
通讯作者：
Egea, G