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

Abstract

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.

Ubiquitin-binding site 1 of pathogenic ataxin-3 regulates its toxicity in Drosophila models of Spinocerebellar Ataxia Type 3

“…Atxn3(Q80) cDNA sequence was based on the human ATXN3 sequences used in previous publications (Winborn et al, 2008;Todi et al, 2009Todi et al, , 2010Harris et al, 2010;Nicastro et al, 2010;Blount et al, 2014Blount et al, , 2020Tsou et al, 2015b;Costa et al, 2016;Sutton et al, 2017;Ristic et al, 2018;Johnson et al, 2019Johnson et al, , 2020Johnson et al, , 2021Johnson et al, , 2022a. The mutagenesis of Atxn3(Q80)-UbS1 * , Atxn3(Q80)-C14 * -UbS1 * and Atxn3(Q80)-UbS1 * -UIM * were carried out by Genscript 1 .…”

“…All flies were heterozygous for driver and transgene(s). All transgenic Atxn3 lines used here were generated by us and were reported previously (Tsou et al, 2013(Tsou et al, , 2015bSutton et al, 2017;Johnson et al, 2019Johnson et al, , 2020Johnson et al, , 2022aBlount et al, 2020) or are being reported here for the first time, as noted in the results section and figure legends. All crosses were conducted at 25 • C in diurnal environments with 12 h light/dark cycles and on conventional cornmeal media.…”

“…Nestled between the VBM and the terminal UIM is the polyQ repeat whose anomalous expansion causes SCA3 (Johnson et al, 2022b). There is also an isoform of Atxn3 that does not contain a terminal, third UIM but instead comprises a degron that expedites the host protein's degradation (Harris et al, 2010;Johnson et al, 2019;Blount et al, 2020). In this study, we utilize the 3-UIM version of Atxn3 as it is the dominant isoform (Harris et al, 2010).…”

“…Over the past several years, our group has dissected the individual and combined effects of the various Atxn3 protein domains to understand their role in SCA3 and to explore their utility as therapeutic targets: The catalytic site, UbS2, the VBM, and the UIMs (Tsou et al, 2013(Tsou et al, , 2015bBlount et al, 2014Blount et al, , 2018Blount et al, , 2020Ristic et al, 2018;Johnson et al, 2019Johnson et al, , 2020Johnson et al, , 2021Johnson et al, , 2022a. The final domain in this series of studies, UbS1, is the focus of this report.…”

A survey of protein interactions and posttranslational modifications that influence the polyglutamine diseases

“…(This isoform was the originally cloned version of ATXN3 .) The alternative isoform is no less toxic than the predominant version in fly models of SCA3, but it is present at markedly lower protein levels because of enhanced proteasomal degradation due to its C-terminus serving as a degron sequence ( Johnson et al, 2019 ; Blount et al, 2020 ).…”