How do ALS-associated mutations in superoxide dismutase 1 promote aggregation of the protein?

Department of Chemistry and Biochemistry, University of California-Los Angeles, Los Angeles, CA 90095, USA.
Trends in Biochemical Sciences (Impact Factor: 11.23). 03/2007; 32(2):78-85. DOI: 10.1016/j.tibs.2006.12.005
Source: PubMed


More than 100 different mutations in the gene encoding copper-zinc superoxide dismutase (SOD1) cause familial forms of amyotrophic lateral sclerosis (ALS)--a fatal neurodegenerative disease in which aggregation of the SOD1 protein is considered to be the primary mode of pathogenesis. Recent results show that these mutations have remarkably diverse and unexpected effects on the structure, activity and native state stability of SOD1. Intriguingly, many mutations seem to have no measurable effect on the biophysical and biochemical properties of SOD1, except for decreasing the net charge of the protein. Thus, it seems likely that different ALS-associated mutations promote SOD1 aggregation by fundamentally distinct mechanisms. Understanding this complexity has implications for drug development and treatment of the disease.

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    • "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]–[6]. The aggregation of disease-specific proteins is implicated in the pathogenesis of other neurodegenerative disorders, such as amyloid β in Alzheimer’s disease and α-synuclein in Parkinson’s disease. "
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    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.
    PLoS ONE 06/2014; 9(6):e101080. DOI:10.1371/journal.pone.0101080 · 3.23 Impact Factor
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    • "The aggregation of nascent SOD1 prior to metallation is also supported by the very high stability of most metallated SOD1 mutations, making them less likely to aggregate once they are metallated (Hayward et al., 2002; Rodriguez et al., 2002). In contrast, apo-SOD1 is significantly less stable and contains large, intrinsically disordered regions that make the protein much more prone to aggregation (Rodriguez et al., 2005; Shaw and Valentine, 2007; Lelie et al., 2011). "
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    ABSTRACT: Disruptions in metal ion homeostasis have been described in association with amyotrophic lateral sclerosis (ALS) for a number of years but the precise mechanism of involvement is poorly understood. Metal ions are especially important to familial ALS cases caused by mutations in the metalloenzyme copper-zinc superoxide dismutase (SOD1). To investigate the role of metals in aggregation of mutant SOD1, we have examined the localization of metal ions in a cell culture model of overexpression. Chinese hamster ovary cells (CHO-K1) were transfected to overexpress SOD1 fused to yellow fluorescent protein (YFP) to readily identify the transfected cells and the intracellular aggregates that develop in the cells expressing mutant or wild-type (WT) SOD1. The concentration and distribution of iron, copper, and zinc were determined for four SOD1 mutants (A4V, G37R, H80R, and D125H) as well as a WT SOD1 using X-ray fluorescence microscopy (XFM). Results demonstrated that the SOD1 aggregates were metal-deficient within the cells, which is consistent with recent in vitro studies. In addition, all SOD1 mutants showed significantly decreased copper content compared to the WT SOD1 cells, regardless of the mutant's ability to bind copper. These results suggest that SOD1 overexpression creates an unmet demand on the cell for copper. This is particularly true for the SOD1 mutants where copper delivery may also be impaired. Hence, the SOD1 mutants are less stable than WT SOD1 and if copper is limited, aggregate formation of the metal-deficient, mutant SOD1 protein occurs.
    Frontiers in Aging Neuroscience 06/2014; 6:110. DOI:10.3389/fnagi.2014.00110 · 4.00 Impact Factor
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    • "Mutated SOD1 has been implicated in ALS pathology via excitotoxicity, mitochondrial dysfunction, oxidative stress, axonopathy and endosomal trafficking (Al Chalabi et al., 2012). ER stress in the presence of mutated SOD1 may be a consequence of several factors, which all play an important role in ALS: 1) oligomerization of the SOD1 protein with itself or with other proteins, thus forming aggregates (Shaw and Valentine, 2007); 2) aggregation of mutant SOD1 with the ER luminal chaperone, Grp78 (Kikuchi et al., 2006); 3) mitochondrial dysfunction (Carri and Cozzolino, 2011) or 4) direct interaction between mutant SOD1 and derlin-1, which is an ER protein that is necessary for the translocation of misfolded proteins from the ER to the cytosol, resulting in inhibition of the ER-associated degradation pathway (Nishitoh et al., 2008). However , the exact mechanism remains unclear, despite nearly two decades of research on this subject, since 1993, a time at which mutated SOD1 was identified in ALS (Rosen et al., 1993). "
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    ABSTRACT: Background Recent studies have indicated that endoplasmic reticulum (ER) stress is involved in the pathogenesis of amyotrophic lateral sclerosis (ALS). ER stress occurs when the ER–mitochondria calcium cycle is disturbed and misfolded proteins accumulate in the ER. To cope with ER stress, cells activate the unfolded protein response (UPR). Accumulating evidence from non-neuronal cell models suggests that there is extensive cross-talk between the UPR and the NF-κB pathway. Methods Here we investigated the expression of NF-κB and the main UPR markers X-box binding protein 1 (XBP1), basic leucine-zipper transcription factor 6 (ATF6) and phosphorylated eukaryotic initiation factor-2α (p-eIF2) in mutated SOD1G93A cell models of ALS, as well as their modulation by lipopolysaccharide and ER-stressing (tunicamycin) stimuli. Results Expression of NF-κB was enhanced in the presence of SOD1G93A. Lipopolysaccharide did not induce NF-κB or the UPR in NSC34 cells and motor neurons in a mixed motor neuron-glia coculture system. The induction of the UPR by tunicamycin was accompanied by activation of NF-κB in NSC34 cells and motor neurons. Conclusion Our data linked two important pathogenic mechanisms of ALS, ER stress and NF-κB signalling, in motor neurons.
    Journal of neuroimmunology 05/2014; 270(1). DOI:10.1016/j.jneuroim.2014.03.005 · 2.47 Impact Factor
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