Ubiquitin ligase Nedd4 regulates the abundance and toxicity of mutant huntingtin
Hyunkyung Jeong, Yiyang Qin, Fangke Xu, Katarina Trajkovic, Myung Jong Kim, Nicolas Marotta, Kana Hamada, Ravi Allada, Su Yang, Dimitri Krainc
Hyunkyung Jeong, Yiyang Qin, Fangke Xu, Katarina Trajkovic, Myung Jong Kim, Nicolas Marotta, Kana Hamada, Ravi Allada, Su Yang, Dimitri Krainc
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Research Article Cell biology Neuroscience

Ubiquitin ligase Nedd4 regulates the abundance and toxicity of mutant huntingtin

Abstract

Huntington’s disease (HD) is a neurodegenerative disorder caused by the expansion of CAG repeats in the gene encoding huntingtin. Since accumulation of mutant huntingtin (mHtt) leads to dysfunction of numerous cellular pathways and toxicity, reducing levels of the mutant protein represents a key therapeutic objective in HD. We found that ubiquitination of mHtt by E3 ubiquitin ligase Nedd4 promotes clearance of the mutant protein. Knockdown of Nedd4 increased toxicity of mHtt in mouse primary neurons and in a fly model of HD, suggesting the protective role of Nedd4. Importantly, levels of Nedd4 were decreased in mHtt-expressing neurons through impaired mTORC1 activity, suggesting a feedback loop of mHtt accumulation and Nedd4 reduction that leads to accumulation and, ultimately, toxicity of mHtt. These findings suggest that restoring Nedd4 activity may offer a novel therapeutic opportunity for HD.

Authors

Hyunkyung Jeong, Yiyang Qin, Fangke Xu, Katarina Trajkovic, Myung Jong Kim, Nicolas Marotta, Kana Hamada, Ravi Allada, Su Yang, Dimitri Krainc

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Figure 1

Nedd4 is an E3 ubiquitin ligase for Htt.

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Nedd4 is an E3 ubiquitin ligase for Htt. (A) Interaction between Nedd4 a...
(A) Interaction between Nedd4 and Htt Exon1-GFP. 293FT cells were transfected with Nedd4 together with GFP, Htt Exon1-25Q-GFP, or Htt Exon1-46Q-GFP. Cells were harvested 48 hours after transfection, and co-IP was performed followed by Western blot analysis. (B) Interaction of Nedd4 with Htt480-68Q. N2a cells were transfected with Nedd4 and Htt480-68Q and collected 26 hours after transfection. Co-IP was performed followed by Western blot analysis. T7 antibody was used to detect T7-tagged Nedd4. (C) Immunoblot analysis of Nedd4 expression in mouse brain regions: cortex (Ctx), cerebellum (Cer), striatum (Str), and hippocampus (Hip). Nedd4 was detected using an anti-Nedd4 antibody (Proteintech, 21698-1-AP), and Gapdh served as a loading control. (D) Quantification of relative Nedd4 expression normalized to Gapdh (n = 7; one-way ANOVA with Tukey’s post hoc test; Cer vs. Str, P = 0.0461). (E) Endogenous interaction between Htt and Nedd4 in mouse cortex. Co-IP was performed using cortical lysates, with Htt immunoprecipitated using an Htt antibody (EPR5526). Nedd4 was detected in the pulldown. IgG served as a negative control. (F) Nedd4 promotes Htt ubiquitination in a ligase activity–dependent manner. N2a cells were transfected with Htt571-72Q and HA-ubiquitin together with vector control, Nedd4, or catalytically inactive Nedd4-CS. Cells were harvested 50 hours after transfection, and denaturing IP was followed by Western blotting. n = 3; one-way ANOVA with Tukey’s multiple-comparison test (*P < 0.01; **P < 0.001; NS, not significant). (G) Htt undergoes monoubiquitination at multiple lysine residues. N2a cells were transfected with GFP-Htt480-68Q and either WT HA-ubiquitin or lysine-free HA-K0 ubiquitin. Denaturing IP and Western blot analysis were performed 25 hours after transfection. N4, Nedd4; Ub, ubiquitin; vec, vector; CS, Nedd4 CS; Pon S, Ponceau S.