Identification of an RNA Polymerase III Regulator Linked to Disease-Associated Protein Aggregation

Abstract

SummaryProtein aggregation is associated with age-related neurodegenerative disorders, such as Alzheimer’s and polyglutamine diseases. As a causal relationship between protein aggregation and neurodegeneration remains elusive, understanding the cellular mechanisms regulating protein aggregation will help develop future treatments. To identify such mechanisms, we conducted a forward genetic screen in a C. elegans model of polyglutamine aggregation and identified the protein MOAG-2/LIR-3 as a driver of protein aggregation. In the absence of polyglutamine, MOAG-2/LIR-3 regulates the RNA polymerase III-associated transcription of small non-coding RNAs. This regulation is lost in the presence of polyglutamine, which mislocalizes MOAG-2/LIR-3 from the nucleus to the cytosol. We then show biochemically that MOAG-2/LIR-3 can also catalyze the aggregation of polyglutamine-expanded huntingtin. These results suggest that polyglutamine can induce an aggregation-promoting activity of MOAG-2/LIR-3 in the cytosol. The concept that certain aggregation-prone proteins can convert other endogenous proteins into drivers of aggregation and toxicity adds to the understanding of how cellular homeostasis can be deteriorated in protein misfolding diseases.

Filter Retardation Assay for Detecting and Quantifying Polyglutamine Aggregates Using Caenorhabditis elegans Lysates

“…In Sin et al (2017), a forward genetic screen was performed on worms that express 40 glutamine (Q) repeats fused to YFP (here referred as Q40 worms) to search for mutants with reduced number of polyglutamine aggregates (Sin et al, 2017) (Figure 3A). The study identified a regulator of RNA polymerase III transcription– moag-2/lir-3 –as an aggregation-promoting factor.…”

“…Immunoblots were quantified by densitometry using ImageJ. An example of data analysis can be found in Figure 1F and S1E of Sin et al (2017). To quantify the relative amount of SDS-insoluble protein, a ratio (fold change) was calculated by dividing the values of Q40; moag-2/lir-3 mutants (undiluted sample of the point-mutation allele pk2183 and deletion allele tm813 shown on Figure 3B, top) by their corresponding wild-types ( wt , previously normalized to α-tubulin as a loading control).…”

“…A. Representative image of a Q40 worm (strain AM141) and a Q40; moag-2/lir-3 (pk2183) worm (Sin et al, 2017). Scale bar = 75 μm.…”

Meeting Report – proteostasis in Ericeira

“…Ellen Nollen's (University of Groningen, The Netherlands) talk focused on genes that act as modifiers of aggregation, whose inactivation reduces aggregation and toxicity of polyQ (Glutamine) proteins without regulating their expression levels. Examples of such aggregation-modifying proteins include MOAG-2/LIR-3, a nuclear protein that is hijacked to the cytosol to promote aggregate formation (Sin et al, 2017), and MOAG-4/SERF2, which catalyses aggregation through direct and transient interaction with disease proteins, thus affecting the structure of the aggregate (Yoshimura et al, 2017).…”

Genetic exploration of a nuclear receptor transcriptional regulatory complex

“…lir-1 and lin-26 reside in an operon and together regulate differentiation 424 of non-neuronal ectodermal cells and the somatic gonadal epithelium(Boer et al 1998; 425 Dufourcq et al 1999;Bosher et al 1999). In contrast, lir-3 is a modifier of polyglutamine 426 aggregation in particular neurons and muscle cells(Sin et al 2017). Thus, LIR proteins 427 share similar zinc-fingers at their C-termini, but the roles of those domains are unknown, 428 and the proteins themselves appear to be functionally distinct.429 430 It is well established in other metazoans that co-regulators carrying LxxLL motifs, or "NR 431 boxes", activate or repress transcription (Heery et al 1997; Nolte et al 1998; Savkur and 432 Burris 2004; Loinder and Söderström 2004; Plevin et al 2005) by associating with the AF-433 2 domain near NR C-termini.…”