Clearance of membrane aggregates in mutant ALS8

一个单一的氨基酸突变，脯氨酸残基在位置56取代丝氨酸（P56 S），在以前确定的基因命名为VAPB的原因迟发性，常染色体显性形式的肌萎缩侧索硬化症（ALS 8）。VAPB是一种锚定在内质网（ER）膜上的蛋白质，内质网是一种细胞膜网络，是分泌蛋白和膜蛋白的进入点。ER具有质量控制功能，以确保蛋白质在离开ER到达最终目的地之前正确折叠。VAPB-P56 S的表达破坏了这种质量控制特征，并减缓了蛋白质从ER的退出。这会造成蛋白质交通堵塞，最终导致ER聚集和应激。细胞具有一个称为未折叠蛋白反应或UPR的适应过程来抵消ER应激。UPR旨在通过（1）扩大ER的膜容量以适应增加的负荷;（2）促进未折叠蛋白质的降解;（3）暂时关闭新蛋白质合成以减少进入ER的蛋白质量来减少蛋白质负荷增加的影响。然而，如果这些对策不能缓解压力，导致细胞死亡的基因就会被激活，以消除受影响的细胞。我们已经发现，称为FFAT基序（酸性区中的两个苯丙氨酸）的短肽序列可以改变VAPB的活性。它挽救了由P56 S突变引起的缺陷，因此蛋白质现在可以有效地离开ER，从而缓解ER的压力。这项研究将确定ALS 8突变如何改变UPR，以及FFAT如何解决ER膜聚集体。它将探索这种方法是否可以应用于其他聚集倾向的神经退行性疾病，如亨廷顿病和帕金森病。

A single amino acid mutation, proline residue at position 56 substituted by serine (P56S), in a previously identified gene named VAPB causes late-onset, autosomal dominant form of Amyotrophic Lateral Sclerosis (ALS8). VAPB is a protein anchored to the membrane of the endoplasmic reticulum (ER), a cellular network of membranes that is the entry point for secretory and membrane proteins. The ER has a quality control feature to ensure that proteins are correctly folded before they can leave the ER en route to their final destinations. Expression of VAPB-P56S disrupts this quality control feature and slows down the exit of proteins from the ER. This creates a protein traffic jam that eventually causes aggregation and stress to the ER. Cells have an adaptive process known as the unfolded protein response or UPR to counteract ER stress. UPR is designed to reduce the effect of increased protein load by (1) expanding the membrane capacity of the ER to accommodate the increased load; (2) by promoting the degradation of unfolded proteins; and (3) by temporarily shutting down new protein synthesis to reduce the amount of proteins entering the ER. However, if these countermeasures fail to relieve the stress, genes leading to cell death are then activated to eliminate the affected cell. We have discovered that a short peptide sequence known as the FFAT motif (two phenylalanines in an acidic tract) can change the activity of VAPB. It rescued the defect caused by the P56S mutation, so that proteins can now effectively leave the ER thereby relieving stress to the ER. This study will determine how the ALS8 mutation changes the UPR, and how FFAT resolves the ER membrane aggregates. It will explore whether this approach can be applied to other aggregate-prone neurodegenerative diseases such as Huntington's and Parkinson's Diseases.