Sequestration of PRMT1 and Nd1-L mRNA into ALS-linked FUS mutant R521C-positive aggregates contributes to neurite degeneration upon oxidative stress

Mi-Hee Jun,Hyun-Hee Ryu,Yong-Seok Lee,Chae-Seok Lim,Yong-Woo Jun,Tongtong Liu,Deok-Jin Jang,Yan Li,Jin-A Lee,Bong-Kiun Kaang

doi:10.1038/srep40474

Abstract

Mutations in fused in sarcoma (FUS), a DNA/RNA binding protein, are associated with familial amyotrophic lateral sclerosis (ALS). However, little is known about how ALS-causing mutations alter protein-protein and protein-RNA complexes and contribute to neurodegeneration. In this study, we identified protein arginine methyltransferase 1 (PRMT1) as a protein that more avidly associates with ALS-linked FUS-R521C than with FUS-WT (wild type) or FUS-P525L using co-immunoprecipitation and LC-MS analysis. Abnormal association between FUS-R521C and PRMT1 requires RNA, but not methyltransferase activity. PRMT1 was sequestered into cytosolic FUS-R521C-positive stress granule aggregates. Overexpression of PRMT1 rescued neurite degeneration caused by FUS-R521C upon oxidative stress, while loss of PRMT1 further accumulated FUS-positive aggregates and enhanced neurite degeneration. Furthermore, the mRNA of Nd1-L, an actin-stabilizing protein, was sequestered into the FUS-R521C/PRMT1 complex. Nd1-L overexpression rescued neurite shortening caused by FUS-R521C upon oxidative stress, while loss of Nd1-L further exacerbated neurite shortening. Altogether, these data suggest that the abnormal stable complex of FUS-R521C/PRMT1/Nd1-L mRNA could contribute to neurodegeneration upon oxidative stress. Overall, our study provides a novel pathogenic mechanism of the FUS mutation associated with abnormal protein-RNA complexes upon oxidative stress in ALS and provides insight into possible therapeutic targets for this pathology.

Highlights

Amyotrophic lateral sclerosis (ALS) is the most common motor neuron disease affecting upper and lower motor neurons in the brain and spinal cord[1]
To identify the proteins abnormally associated with amyotrophic lateral sclerosis (ALS)-causing fused in sarcoma (FUS) mutants, FLAG-FUS-R521C, FLAG-FUS-P525L, or FLAG-FUS-WT was expressed in HEK293T cells[20]
liquid chromatography-mass spectrometry (LC-MS) analysis revealed that the most abundant peptides in tryptic digests of the corresponding band were derived from the human protein arginine N-methyltransferase 1 (PRMT1), the predominant type-I PRMT in mammalian cells which is involved in gene transcription, DNA repair, signal transduction, and protein translocation[21] (Supplementary Fig. 1)

Summary

Introduction

Amyotrophic lateral sclerosis (ALS) is the most common motor neuron disease affecting upper and lower motor neurons in the brain and spinal cord[1]. Stress granule (SG) marker proteins are localized to large cytoplasmic FUS-positive inclusions in neurons and glial cells of diseased brain tissue, suggesting a pathogenic role of dysregulated SGs in neurodegeneration. Accumulating evidence shows that ALS-linked FUS mutants affect the dynamics of SGs, leading to abnormal cytoplasmic inclusions in primary neurons and in induced pluripotent stem cell-derived neurons, thereby indicating that they play a role in disease progression[14,15]. Arginine methylation by protein arginine N-methyltransferase 1 (PRMT1) has been reported to regulate cellular localization of FUS, stress granule formation, and cellular toxicity of ALS-linked FUS mutants, indicating that post-translational modifications of FUS by PRMT1 affect its cellular function[16,17,18,19].

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Results

Conclusion