Abstract
Mutations in superoxide dismutase 1 (SOD1) are a major cause of familial amyotrophic lateral sclerosis (ALS), whereby the mutant proteins misfold and aggregate to form intracellular inclusions. We report that both small ubiquitin-like modifier (SUMO) 1 and SUMO2/3 modify ALS-linked SOD1 mutant proteins at lysine 75 in a motoneuronal cell line, the cell type affected in ALS. In these cells, SUMO1 modification occurred on both lysine 75 and lysine 9 of SOD1, and modification of ALS-linked SOD1 mutant proteins by SUMO3, rather than by SUMO1, significantly increased the stability of the proteins and accelerated intracellular aggregate formation. These findings suggest the contribution of sumoylation, particularly by SUMO3, to the protein aggregation process underlying the pathogenesis of ALS.
Highlights
Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder that causes the selective loss of motor neurons leading to paralysis and death within 2–5 years
The FLAG-superoxide dismutase 1 (SOD1) proteins were immunoprecipitated with an anti-FLAG antibody, and the precipitates were subjected to western blotting using an anti-HA antibody to detect HA-SUMO1
Minor bands with a higher molecular mass were detected but were not derivatives of sumoylated SOD1 because the anti-FLAG antibody did not detect these bands in the antiFLAG (Fig. S1A and B, lane 5) or anti-HA (Fig. S1A and B, lane 8) antibody precipitates, suggesting that sumoylated proteins other than SOD1 were coimmunoprecipitated with FLAG-SOD1
Summary
Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disorder that causes the selective loss of motor neurons leading to paralysis and death within 2–5 years. Mutations in superoxide dismutase 1 (SOD1) are the second most common cause of familial ALS (FALS) after C9ORF72 [1,2]. SOD1 mutants have been widely used for in vitro and in vivo models to investigate the pathomechanisms of ALS [3,4]. Mice or rats overexpressing FALS-linked SOD1 mutants develop a human ALS-like phenotype that involves motor neuron degeneration. FALS-linked mutant SOD1 proteins misfold and aggregate into intracellular inclusions both in vitro and in vivo [5], and it is generally accepted that the propensity for aggregation is associated with the pathobiology of SOD1 mutants [4,5,6]. Elucidating the process of aggregate formation is important for understanding the pathomechanisms of ALS and other neurodegenerative disorders in which pathological intraneuronal inclusions develop
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