Neuroscience Graduate Group, Perelman School of Medicine, University of Pennsylvania, Philadelphia, PA, 19104, USA.
Department of Neuroscience, Mayo Clinic, Jacksonville, FL, 32224, USA.
Acta Neuropathol Commun. 2019 Apr 25;7(1):62. doi: 10.1186/s40478-019-0711-9.
The discovery of an expanded (GGGGCC)n repeat (termed G4C2) within the first intron of C9orf72 in familial ALS/FTD has led to a number of studies showing that the aberrant expression of G4C2 RNA can produce toxic dipeptides through repeat-associated non-AUG (RAN-) translation. To reveal canonical translation factors that impact this process, an unbiased loss-of-function screen was performed in a G4C2 fly model that maintained the upstream intronic sequence of the human gene and contained a GFP tag in the GR reading frame. 11 of 48 translation factors were identified that impact production of the GR-GFP protein. Further investigations into two of these, eIF4B and eIF4H, revealed that downregulation of these factors reduced toxicity caused by the expression of expanded G4C2 and reduced production of toxic GR dipeptides from G4C2 transcripts. In patient-derived cells and in post-mortem tissue from ALS/FTD patients, eIF4H was found to be downregulated in cases harboring the G4C2 mutation compared to patients lacking the mutation and healthy individuals. Overall, these data define eIF4B and eIF4H as disease modifiers whose activity is important for RAN-translation of the GR peptide from G4C2-transcripts.
在家族性肌萎缩侧索硬化症/额颞叶痴呆患者的 C9orf72 基因第一个内含子中发现了一个扩展的（GGGGCC）n 重复序列（称为 G4C2），这导致了许多研究表明，G4C2 RNA 的异常表达可以通过重复相关的非 AUG（RAN）翻译产生有毒的二肽。为了揭示影响这一过程的规范翻译因子，在一个维持人类基因上游内含子序列并在 GR 阅读框中含有 GFP 标签的 G4C2 果蝇模型中进行了无偏向的功能丧失筛选。在 48 个翻译因子中，有 11 个影响 GR-GFP 蛋白的产生。对其中两个因子（eIF4B 和 eIF4H）的进一步研究表明，这些因子的下调降低了扩展的 G4C2 表达引起的毒性，并减少了 G4C2 转录本中有毒 GR 二肽的产生。在患者来源的细胞和肌萎缩侧索硬化症/额颞叶痴呆患者的死后组织中，与缺乏突变的患者和健康个体相比，携带 G4C2 突变的病例中发现 eIF4H 下调。总的来说，这些数据将 eIF4B 和 eIF4H 定义为疾病修饰因子，其活性对于从 G4C2 转录本中 RAN 翻译 GR 肽很重要。
