Actin dynamics tune the integrated stress response by regulating eukaryotic initiation factor 2α dephosphorylation.
Actin dynamics tune the integrated stress response by regulating eukaryotic initiation factor 2α dephosphorylation.
复制标题
肌动蛋白动力学通过调节真核起始因子2α去磷酸化来调节综合应力反应。
DOI：
10.7554/elife.04872
复制
发表时间：
2015-03-16
期刊：
影响因子：
7.7
通讯作者：
Marciniak SJ
中科院分区：
文献类型：
--
作者：
Chambers JE;Dalton LE;Clarke HJ;Malzer E;Dominicus CS;Patel V;Moorhead G;Ron D;Marciniak SJ
四种应激敏感激酶磷酸化真核生物翻译起始因子2 α（eIF 2 α）的α亚基，激活整合的应激反应（ISR）。在动物中，ISR被选择性eIF 2 α磷酸酶拮抗，该酶包含与PPP 1 R15型调节亚基复合的催化蛋白磷酸酶1（PP 1）亚基。无偏搜索PPP 1 R15-PP 1磷酸酶的其他保守成分，确定单体G-肌动蛋白。像PP 1，G-肌动蛋白与PPP 1 R15家族成员的功能核心和G-肌动蛋白耗尽，海洋毒素jasplakinaldehyde，不稳定的内源性PPP 1 R15 A-PP 1复合物。PPP 1 R15-PP 1-G-肌动蛋白三元复合物的丰度对肌动蛋白聚合状态的整体变化具有响应性，其eIF 2 α-定向磷酸酶活性也是如此，而PPP 1 R15富集位点的局部G-肌动蛋白缺失增强了eIF 2 α磷酸化和下游ISR。G-肌动蛋白作为PPP 1 R15全磷酸酶的稳定剂的作用提供了一种机制，用于整合调节肌动蛋白动力学的信号与触发ISR的应力。DOI：http://dx.doi.org/10.7554/eLife.04872.001对于一个细胞来说，要构建一个蛋白质，它必须首先复制基因中包含的指令。一个叫做核糖体的复杂分子机器然后读取这些指令并将其翻译成蛋白质。这个翻译过程涉及许多步骤。被称为真核生物翻译起始因子（或简称eIFs）的蛋白质协调该过程中的第一步，即所谓的“起始”。eIF还为细胞提供了控制蛋白质合成速度的方法。例如，当细胞受到饥饿或毒素的压力时，它会在eIF蛋白的一部分上添加一个磷酸基团，称为eIF 2 α。这种修饰使得这种eIF蛋白不太能够启动翻译，因此细胞在应激期间构建更少的蛋白质并保存更多的资源。一旦压力条件结束，eIF 2 α上的磷酸基团就会被一种叫做磷酸酶的酶去除。这种磷酸酶包含两个亚基：一个识别eIF 2 α，另一个去除磷酸基团。然而，试图在试管中仅使用这两个亚基重建这种磷酸酶活性的实验未能产生特异性靶向eIF 2 α磷酸基团的工作酶。这表明，在细胞中，这种酶含有一个额外的未知亚基。现在，钱伯斯、道尔顿等人（以及陈等人）报告了一个“缺失的”第三个亚基的身份，即一种称为球状肌动蛋白或G-肌动蛋白的蛋白质。钱伯斯、道尔顿等人改造了人类和果蝇细胞，在磷酸酶的两个已知亚基上添加了“分子手柄”。然后，这些手柄可以用来将这些蛋白质从细胞内的分子混合物中拉出来，并看看还有哪些其他蛋白质也沿着而来。这两个已知的亚基都“拉”着G-肌动蛋白沿着移动，这表明它可能是磷酸酶缺失的部分。进一步的实验证实，G-肌动蛋白与其他两个亚基一起工作，特异性地去除了使用有害化学物质应激的小鼠细胞中eIF 2 α的磷酸基团。单个的G-肌动蛋白可以结合在一起形成长长的细丝，而鼓励细胞分裂或移动的信号也会触发肌动蛋白细丝的形成。这通过剥夺磷酸酶的关键组分，即，游离G-肌动蛋白。因此，Chambers，道尔顿等人描述的新机制表明生长和运动信号也可能改变细胞对压力的敏感性。这些发现有望使应激细胞成为药物治疗疾病的靶点;但未来的工作需要澄清在什么情况下将这些信号整合到应激反应中对细胞有益。DOI：http://dx.doi.org/10.7554/eLife.04872.002网站
Four stress-sensing kinases phosphorylate the alpha subunit of eukaryotic translation initiation factor 2 (eIF2α) to activate the integrated stress response (ISR). In animals, the ISR is antagonised by selective eIF2α phosphatases comprising a catalytic protein phosphatase 1 (PP1) subunit in complex with a PPP1R15-type regulatory subunit. An unbiased search for additional conserved components of the PPP1R15-PP1 phosphatase identified monomeric G-actin. Like PP1, G-actin associated with the functional core of PPP1R15 family members and G-actin depletion, by the marine toxin jasplakinolide, destabilised the endogenous PPP1R15A-PP1 complex. The abundance of the ternary PPP1R15-PP1-G-actin complex was responsive to global changes in the polymeric status of actin, as was its eIF2α-directed phosphatase activity, while localised G-actin depletion at sites enriched for PPP1R15 enhanced eIF2α phosphorylation and the downstream ISR. G-actin's role as a stabilizer of the PPP1R15-containing holophosphatase provides a mechanism for integrating signals regulating actin dynamics with stresses that trigger the ISR. DOI: http://dx.doi.org/10.7554/eLife.04872.001 For a cell to build a protein, it must first copy the instructions contained within a gene. A complex molecular machine called a ribosome then reads these instructions and translates them into a protein. This translation process involves a number of steps. Proteins called eukaryotic translation initiation factors (or eIFs for short) coordinate the first step in the process, which is known as ‘initiation’. The eIFs also provide the cell with ways to control how quickly it makes proteins. For example, when a cell is stressed, either by starvation or toxins, it adds a phosphate group onto part of an eIF protein, called eIF2α. This modification makes this eIF protein less able to initiate translation, and so the cell builds fewer proteins and conserves more of its resources during times of stress. Once the stressful conditions are over, the phosphate group is removed from eIF2α by an enzyme called a phosphatase. This phosphatase contains two subunits: one that recognizes eIF2α and another that removes the phosphate group. However, experiments that attempted to recreate this phosphatase activity using just these two subunits in a test tube failed to generate a working enzyme that specifically targeted the phosphate group of eIF2α. This suggests that in cells this enzyme contains an additional unknown subunit. Now, Chambers, Dalton et al. (and Chen et al.) report the identity of a ‘missing’ third subunit as a protein known as globular-actin or G-actin. Chambers, Dalton et al. engineered human and fruit fly cells to add ‘molecular handles’ on the two known subunits of the phosphatase enzyme. These handles could then be used to essentially pull these proteins out of the mixture of molecules within a cell and see what other proteins came along too. Both of the known subunits ‘pulled’ G-actin along with them; this suggested that it could be the missing part of the phosphatase enzyme. Further experiments confirmed that G-actin works together with the other two subunits to specifically remove the phosphate group from eIF2α in mouse cells that had been stressed using a harmful chemical. Individual G-actin proteins can bind together to form long filaments, and signals that encourage a cell to divide or move also trigger the formation of actin filaments. This reduces the activity of the phosphatase enzyme by depriving it of a crucial component, i.e., free G-actin proteins. As such, the new mechanism described by Chambers, Dalton et al. suggests how growth and movement signals might also change a cell's sensitivity to stress. These findings may hopefully enable stressed cells to be targeted by drugs to treat disease; but future work is needed to clarify under what circumstances the integration of such signals into the stress response is beneficial to the cell. DOI: http://dx.doi.org/10.7554/eLife.04872.002