Nucleocytoplasmic Proteomic Analysis Uncovers eRF1 and Nonsense-Mediated Decay as Modifiers of ALS/FTD C9orf72 Toxicity

• DOI: 10.1016/j.neuron.2020.01.020
• Publication Date: 2020-02-13T15:32:25Z
• Authors: Juan A. Ortega; Elizabeth L. Daley; Sukhleen Kour; Marisa Samani; Liana Tellez; Haley S. Smith; Elizabeth A. Hall; Y. Taylan Esengul; Yung-Hsu Tsai; Tania F. Gendron; Christopher J. Do...; Teepu Siddique; Jeffrey N. Savas; Udai B. Pandey; Evangelos Kiskinis
• Keywords: Neurons; C9orf72 Protein; Proteome; Nuclear Envelope; Amyotrophic Lateral Sclerosis; Induced Pluripotent Stem Cells; Peptide Chain Termination, Translational; Cell Fractionation; Nonsense Mediated mRNA Decay; 3. Good health; Drosophila melanogaster; HEK293 Cells; Tandem Mass Spectrometry; Frontotemporal Dementia; Protein Biosynthesis; Animals; Drosophila Proteins; Humans; RNA, Messenger; Peptide Termination Factors; Subcellular Fractions

SUMMARYThe most common genetic cause of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) is a hexanucleotide repeat expansion in C9orf72 (C9-HRE). While RNA and dipeptide repeats produced by the C9-HRE disrupt nucleocytoplasmic transport, the proteins that become redistributed remain unknown. Here, we utilized subcellular fractionation coupled with tandem mass spectrometry and identified 126 proteins, enriched for protein translation and RNA metabolism pathways, which collectively drive a shift towards a more cytosolic proteome in C9-HRE cells. Amongst these was eRF1, which regulates translation termination and nonsense-mediated decay (NMD). eRF1 accumulates within elaborate nuclear envelope invaginations in patient iPSC-neurons and postmortem tissue and mediates a protective shift from protein translation to NMD-dependent mRNA degradation. Overexpression of eRF1 and the NMD-driver UPF1 ameliorate C9-HRE toxicity in vivo. Our findings provide a resource for proteome-wide nucleocytoplasmic alterations across neurodegeneration-associated repeat expansion mutations and highlight eRF1 and NMD as therapeutic targets in C9orf72-associated ALS/FTD.