Physiological and pathophysiological characteristics of ataxin-3 isoforms

Weishäupl, Daniel; Schneider, Juliane; Pinheiro, Barbara Peixoto; Ruess, Corinna; Dold, Sandra Maria; Zweydorf, Felix von; Gloeckner, Christian Johannes; Schmidt, Jana; Rieß, Olaf; Schmidt, Thorsten

doi:10.1074/jbc.ra118.005801

Cited by 37 publications

(37 citation statements)

References 101 publications

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“…This increase suggests that more autophagic structures were formed in ATXN3‐depleted cells during the treatment. To validate this finding, we stained similarly treated wild‐type and ATXN3 knockout murine embryonic fibroblasts (Schmitt et al, ; Weishaupl et al, ) for endogenous LC3, which confirmed elevated levels of both basal and starvation‐induced LC3 puncta in ATXN3 knockout cells (Figure f, Figure A,B). No increase in LC3 foci was observed when ATXN3‐depleted cells were starved in the presence of the phosphatidylinositol‐3‐kinase (PI3K) inhibitor wortmannin, indicating that ATXN3 acts in the canonical autophagy–lysosome pathway downstream of PI3K (Figure e, Figure C).…”

Section: Resultsmentioning

confidence: 59%

The Machado–Joseph disease deubiquitylase ataxin‐3 interacts with LC3C/GABARAP and promotes autophagy

et al. 2019

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The pathology of spinocerebellar ataxia type 3, also known as Machado‐Joseph disease, is triggered by aggregation of toxic ataxin‐3 (ATXN3) variants containing expanded polyglutamine repeats. The physiological role of this deubiquitylase, however, remains largely unclear. Our recent work showed that ATX‐3, the nematode orthologue of ATXN3, together with the ubiquitin‐directed segregase CDC‐48, regulates longevity in Caenorhabditis elegans. Here, we demonstrate that the long‐lived cdc‐48.1; atx‐3 double mutant displays reduced viability under prolonged starvation conditions that can be attributed to the loss of catalytically active ATX‐3. Reducing the levels of the autophagy protein BEC‐1 sensitized worms to the effect of ATX‐3 deficiency, suggesting a role of ATX‐3 in autophagy. In support of this conclusion, the depletion of ATXN3 in human cells caused a reduction in autophagosomal degradation of proteins. Surprisingly, reduced degradation in ATXN3‐depleted cells coincided with an increase in the number of autophagosomes while levels of lipidated LC3 remained unaffected. We identified two conserved LIR domains in the catalytic Josephin domain of ATXN3 that directly interacted with the autophagy adaptors LC3C and GABARAP in vitro. While ATXN3 localized to early autophagosomes, it was not subject to lysosomal degradation, suggesting a transient regulatory interaction early in the autophagic pathway. We propose that the deubiquitylase ATX‐3/ATXN3 stimulates autophagic degradation by preventing superfluous initiation of autophagosomes, thereby promoting an efficient autophagic flux important to survive starvation.

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Section: Resultsmentioning

confidence: 59%

The Machado–Joseph disease deubiquitylase ataxin‐3 interacts with LC3C/GABARAP and promotes autophagy

et al. 2019

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“…In all of our assays in this study, as well as in prior work (Johnson et al., 2019), isoform 2 of ataxin‐3 is less stable than isoform 1. As a result of the differences at their C‐termini, the two isoforms may also have different interacting partners (Harris et al., 2010; Johnson et al., 2019; Weishäupl et al., 2019). The question arises why there might be an evolutionary need for the production of two isoforms with different partners and half‐lives in cells, especially for a protein that, according to knockout mouse lines, appears unnecessary in vivo (Reina, Nabet, Young, & Pittman, 2012; Reina, Zhong, & Pittman, 2010; Schmitt et al., 2007; Switonski et al., 2011)?…”

Section: Resultsmentioning

confidence: 99%

Degron capability of the hydrophobic C‐terminus of the polyglutamine disease protein, ataxin‐3

Blount

Johnson

Libohova

et al. 2020

J of Neuroscience Research

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Ataxin‐3 is a deubiquitinase and polyglutamine disease protein whose cellular properties and functions are not entirely understood. Mutations in ataxin‐3 cause spinocerebellar ataxia type 3 (SCA3), a neurodegenerative disorder that is a member of the polyglutamine family of diseases. Two major isoforms arise from alternative splicing of ATXN3 and are differently toxic in vivo as a result of faster proteasomal degradation of one isoform compared to the other. The isoforms vary only at their C‐termini, suggesting that the hydrophobic C‐terminus of the more quickly degraded form of ataxin‐3 (here referred to as isoform 2) functions as a degron—that is, a peptide sequence that expedites the degradation of its host protein. We explored this notion in this study and present evidence that: (a) the C‐terminus of ataxin‐3 isoform 2 signals its degradation in a proteasome‐dependent manner, (b) this effect from the C‐terminus of isoform 2 does not require the ubiquitination of ataxin‐3, and (c) the isolated C‐terminus of isoform 2 can enhance the degradation of an unrelated protein. According to our data, the C‐terminus of ataxin‐3 isoform 2 is a degron, increasing overall understanding of the cellular properties of the SCA3 protein.

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“…3A). The resulting truncated ATXN3 protein, when containing an expanded CAG-repeat, is thought to be more aggregation-prone than other known ATXN3 protein isoforms (52). Among non-CAG expansion carriers (N=118) in our main study cohort, 56.8% of people had a "TAA 1118 " allele (C>A; p.Y349*) ( Fig.…”

Section: A Single-nucleotide Polymorphism Frequently Associated With mentioning

confidence: 88%

Toward allele-specific targeting therapy and pharmacodynamic marker for spinocerebellar ataxia type 3

et al. 2020

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Spinocerebellar ataxia type 3 (SCA3), caused by a CAG repeat expansion in the ataxin-3 gene (ATXN3), is characterized by neuronal polyglutamine (polyQ) ATXN3 protein aggregates. Although there is no cure for SCA3, gene-silencing approaches to reduce toxic polyQ ATXN3 showed promise in preclinical models. However, a major limitation in translating putative treatments for this rare disease to the clinic is the lack of pharmacodynamic markers for use in clinical trials. Here, we developed an immunoassay that readily detects polyQ ATXN3 proteins in human biological fluids and discriminates patients with SCA3 from healthy controls and individuals with other ataxias. We show that polyQ ATXN3 serves as a marker of target engagement in human fibroblasts, which may bode well for its use in clinical trials. Last, we identified a single-nucleotide polymorphism that strongly associates with the expanded allele, thus providing an exciting drug target to abrogate detrimental events initiated by mutant ATXN3. Gene-silencing strategies for several repeat diseases are well under way, and our results are expected to improve clinical trial preparedness for SCA3 therapies.

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Physiological and pathophysiological characteristics of ataxin-3 isoforms

Cited by 37 publications

References 101 publications

The Machado–Joseph disease deubiquitylase ataxin‐3 interacts with LC3C/GABARAP and promotes autophagy

The Machado–Joseph disease deubiquitylase ataxin‐3 interacts with LC3C/GABARAP and promotes autophagy

Degron capability of the hydrophobic C‐terminus of the polyglutamine disease protein, ataxin‐3

Toward allele-specific targeting therapy and pharmacodynamic marker for spinocerebellar ataxia type 3

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