Article

Molecular Determinants and Genetic Modifiers of Aggregation and Toxicity for the ALS Disease Protein FUS/TLS

University of California San Francisco/Howard Hughes Medical Institute, United States of America
PLoS Biology (Impact Factor: 11.77). 04/2011; 9(4):e1000614. DOI: 10.1371/journal.pbio.1000614
Source: PubMed

ABSTRACT TDP-43 and FUS are RNA-binding proteins that form cytoplasmic inclusions in some forms of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). Moreover, mutations in TDP-43 and FUS are linked to ALS and FTLD. However, it is unknown whether TDP-43 and FUS aggregate and cause toxicity by similar mechanisms. Here, we exploit a yeast model and purified FUS to elucidate mechanisms of FUS aggregation and toxicity. Like TDP-43, FUS must aggregate in the cytoplasm and bind RNA to confer toxicity in yeast. These cytoplasmic FUS aggregates partition to stress granule compartments just as they do in ALS patients. Importantly, in isolation, FUS spontaneously forms pore-like oligomers and filamentous structures reminiscent of FUS inclusions in ALS patients. FUS aggregation and toxicity requires a prion-like domain, but unlike TDP-43, additional determinants within a RGG domain are critical for FUS aggregation and toxicity. In further distinction to TDP-43, ALS-linked FUS mutations do not promote aggregation. Finally, genome-wide screens uncovered stress granule assembly and RNA metabolism genes that modify FUS toxicity but not TDP-43 toxicity. Our findings suggest that TDP-43 and FUS, though similar RNA-binding proteins, aggregate and confer disease phenotypes via distinct mechanisms. These differences will likely have important therapeutic implications.

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Available from: Zamia Diaz, Sep 03, 2015
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    • "About FUS/TLS, closely related to TDP-43, the work done by Sun and collaborators is remarkable showing that FUS/TLS is readily aggregated in vitro in yeast model expressing human FUS/TLS when a yeast prion-like domain together with other molecular determinants is added. However, this aggregation capacity is not enhanced at least in vitro by the disease-linked mutations (Sun et al., 2011). The close relation between FUS and TDP-43 needs to be further assessed, as both are implicated in stress granules together with other prion-like domain showing proteins, and aggregates have been shown able to recruit native FUS and TDP-43 proteins possibly due to their yeast prion-like Q/N rich segment seeding (Polymenidou and Cleveland, 2011; Fuentealba et al., 2010). "
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    • "This unexpected function is mediated by its unusual structural switch from a folded, ubiquitin-like domain upon binding to single stranded DNA and in low protein concentrations, to an unfolded and aggregation-prone structure when protein concentrations are increased (Qin et al., 2014). FUS is characterized by even higher aggregation propensity compared to SOD1 or TDP-43, as it was shown to spontaneously aggregate into fibrils in a cell-free system within minutes (Sun et al., 2011). Aggregates reconstituted in vitro from recombinant wild type or mutant SOD1 (Furukawa et al., 2013; Münch et al., 2011) and TDP-43 (Furukawa et al., 2011) triggered aggregation of endogenously expressed protein in cell culture (Fig. 2D). "
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    ABSTRACT: Propagation of pathological protein assemblies via a prion-like mechanism has been suggested to drive neurodegenerative diseases, such as Parkinson's and Alzheimer's. Recently, amyotrophic lateral sclerosis (ALS)-linked proteins, such as SOD1, TDP-43 and FUS were shown to follow self-perpetuating seeded aggregation, thereby adding ALS to the group of prion-like disorders. The cell-to-cell spread of these pathological protein assemblies and their pathogenic mechanism is poorly understood. However, as ALS is a non-cell autonomous disease and pathology in glial cells was shown to contribute to motor neuron damage, spreading mechanisms are likely to underlie disease progression via the interplay between affected neurons and their neighboring glial cells.
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    • "As well, we found that HSPB8 counteracts the formation of oligomeric species of truncated TDP-43 and greatly reduces the total amount of insoluble TDP- 43 species, even when the proteasome is inhibited (Crippa et al., 2010a, 2010b). Regarding the correlation between FUS and UPS, inclusions of ubiquitinated FUS have not been detected in different in vitro or in vivo models, and aggregation of FUS seems not due to UPS impairment (Sun et al., 2011; Vance et al., 2009), even if it has been recently reported that impairment of protein degradation pathways also greatly accelerates formation of FUS-positive aggregates (Watabe et al., 2014). ALS related misfolded proteins aggregate and impair UPS, but can also modify the autophagic degradative pathway. "
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