Spatial sequestration and detoxification of Huntingtin by the ribosome quality control complex.

Junsheng Yang,Xiuling Cao,Thomas Nyström,Beidong Liu,Xinxin Hao

doi:10.7554/elife.11792

Abstract

Huntington disease (HD) is a neurological disorder caused by polyglutamine expansions in mutated Huntingtin (mHtt) proteins, rendering them prone to form inclusion bodies (IB). We report that in yeast, such IB formation is a factor-dependent process subjected to age-related decline. A genome-wide, high-content imaging approach, identified the E3 ubiquitin ligase, Ltn1 of the ribosome quality control complex (RQC) as a key factor required for IB formation, ubiquitination, and detoxification of model mHtt. The failure of ltn1∆ cells to manage mHtt was traced to another RQC component, Tae2, and inappropriate control of heat shock transcription factor, Hsf1, activity. Moreover, super-resolution microscopy revealed that mHtt toxicity in RQC-deficient cells was accompanied by multiple mHtt aggregates altering actin cytoskeletal structures and retarding endocytosis. The data demonstrates that spatial sequestration of mHtt into IBs is policed by the RQC-Hsf1 regulatory system and that such compartmentalization, rather than ubiquitination, is key to mHtt detoxification.

Highlights

The Huntington disease (HD) is predominantly inherited, with a single gene, HTT, encoding the Huntingtin protein, at its origin (MacDonald, 1993)
To identify trans-acting factors required for inclusion bodies (IBs) formation in an unbiased genome-wide manner, we used high content microscopy (HCM) and a galactoseregulated version of mHtt103QP, which we introduced into the ordered yeast deletion library (SGAV2) (Tong, 2001) of S. cerevisiae (Figure 1c)
HCM was used to identify mutants that formed multiple aggregates/oligomers rather than a big IB (Class 3 mutants; Figure 1e), which revealed that IB formation requires proteasome/chaperone and ubiquitination functions, Golgi-vesicle trafficking, mRNA transport/metabolism, and cell cycle control (Figure 1f&g, see Supplementary file 1 for a list of confirmed mutants)

Summary

Introduction

The Huntington disease (HD) is predominantly inherited, with a single gene, HTT, encoding the Huntingtin protein, at its origin (MacDonald, 1993). When the innate proline-rich region adjacent the poly (Q) stretch of exon-1 is removed, the protein, mHtt103Q, forms multiple small, highly cytotoxic aggregates/oligomers (Figure 1a) (Dehay and Bertolotti, 2006; Duennwald et al, 2006; Meriin et al, 2002). These aggregates are associated with the actin cytoskeleton (Song et al, 2014) and interfere with the cytosolic ubiquitin-proteasome-system (UPS) by sequestering the Hsp chaperone Sis (Park et al, 2013). Chaperones, peptides, and prion-like proteins that either prevent/modify oligomer production (Behrends et al, 2006; Dehay and Bertolotti, 2006; Krobitsch and Lindquist, 2000; Muchowski et al, 2000; Gokhale et al, 2005) or convert small aggregates/oligomers into IBs (Kayatekin et al, 2014; Wolfe et al, 2014) can suppress the toxicity of the proline-less exon-1, suggesting that small aggregates and oligomers are likely culprits in mHtt103Q-derived toxicity (Arrasate et al, 2004; Miller et al, 2011)

Methods

Results

Conclusion