Functional Gene Expression Profiling in Yeast Implicates Translational Dysfunction in Mutant Huntingtin Toxicity

Abstract

Huntington disease (HD) is a neurodegenerative disorder caused by the expansion of a polyglutamine tract in the huntingtin (htt) protein. To uncover candidate therapeutic targets and networks involved in pathogenesis, we integrated gene expression profiling and functional genetic screening to identify genes critical for mutant htt toxicity in yeast. Using mRNA profiling, we have identified genes differentially expressed in wild-type yeast in response to mutant htt toxicity as well as in three toxicity suppressor strains: bna4Δ, mbf1Δ, and ume1Δ. BNA4 encodes the yeast homolog of kynurenine 3-monooxygenase, a promising drug target for HD. Intriguingly, despite playing diverse cellular roles, these three suppressors share common differentially expressed genes involved in stress response, translation elongation, and mitochondrial transport. We then systematically tested the ability of the differentially expressed genes to suppress mutant htt toxicity when overexpressed and have thereby identified 12 novel suppressors, including genes that play a role in stress response, Golgi to endosome transport, and rRNA processing. Integrating the mRNA profiling data and the genetic screening data, we have generated a robust network that shows enrichment in genes involved in rRNA processing and ribosome biogenesis. Strikingly, these observations implicate dysfunction of translation in the pathology of HD. Recent work has shown that regulation of translation is critical for life span extension in Drosophila and that manipulation of this process is protective in Parkinson disease models. In total, these observations suggest that pharmacological manipulation of translation may have therapeutic value in HD.

Huntingtin protein interactions altered by polyglutamine expansion as determined by quantitative proteomic analysis

“…RNA processing has been previously implicated in HD based on several expression profiling studies in cells, mouse, yeast and fly models of HD. [72][73][74][75][76] These studies demonstrate enrichment in ribosomal and RNA-processing proteins. In line with this, we showed that expanded Htt complexes were enriched in proteins related to RNA processing and regulation of translation and identified several novel Htt interactors within these pathways.…”

Proteomic Analysis of Wild-type and Mutant Huntingtin-associated Proteins in Mouse Brains Identifies Unique Interactions and Involvement in Protein Synthesis

“…4b, compare the upper and lower FLAG blots). Translation factors have a modifying effect on the aggregation and toxicity of N-terminal fragment-based models of mutant Htt toxicity in Caenorhabditis elegans and Saccharomyces cerevisiae (52,53). The differences in sedimentation profiles, mass spectrometry-identified protein associations, and the modifying effect that translation proteins have on mutant Htt toxicity in model systems suggest that mutant Htt may affect translation.…”

Changes in BiP availability reveal hypersensitivity to acute endoplasmic reticulum stress in cells expressing mutant huntingtin

“…Translation or transcription might be attenuated to decrease the flux of incoming nascent proteins to accommodate the lower rate of ERAD in these cells. In yeast, translational dysfunction has been observed coincident with mHtt ex1 expression (Tauber et al, 2011). For diseases such as HD, the inability of cells to cope with ER stress could represent an important modulator of the mutant protein toxicity.…”