Identification of NUB1 as a suppressor of mutant Huntingtin toxicity via enhanced protein clearance

Abstract

Huntington's disease is caused by expanded CAG repeats in HTT, conferring toxic gain of function on mutant HTT (mHTT) protein. Reducing mHTT amounts is postulated as a strategy for therapeutic intervention. We conducted genome-wide RNA interference screens for genes modifying mHTT abundance and identified 13 hits. We tested 10 in vivo in a Drosophila melanogaster Huntington's disease model, and 6 exhibited activity consistent with the in vitro screening results. Among these, negative regulator of ubiquitin-like protein 1 (NUB1) overexpression lowered mHTT in neuronal models and rescued mHTT-induced death. NUB1 reduces mHTT amounts by enhancing polyubiquitination and proteasomal degradation of mHTT protein. The process requires CUL3 and the ubiquitin-like protein NEDD8 necessary for CUL3 activation. As a potential approach to modulating NUB1 for treatment, interferon-β lowered mHTT and rescued neuronal toxicity through induction of NUB1. Thus, we have identified genes modifying endogenous mHTT using high-throughput screening and demonstrate NUB1 as an exemplar entry point for therapeutic intervention of Huntington's disease.

scyllo-Inositol Promotes Robust Mutant Huntingtin Protein Degradation

“…Recently, a genetic screen identified an endogenous protein, NUB1, as a regulator of mutant huntingtin protein abundance by promotion of degradation via the proteasomal pathway (18). Furthermore, this study demonstrated that targeting mutant huntingtin protein degradation is sufficient to inhibit in vitro toxicity and in vivo neurodegeneration.…”

“…Similarly, endogenous chaperones have been shown to inhibit polyQ-Htt aggregation also without affecting total polyQ-Htt protein levels (15)(16)(17). Recently, overexpression of the endogenous protein, negative regulator of ubiquitin-like protein 1 (NUB1), decreased mt-Htt protein accumulation and rescued toxicity via activation of proteasomal degradation of mt-Htt in both in vitro and in vivo models (18). These latter experiments suggest that compounds that promote reduction of mutant huntingtin protein and resultant toxicity via efficient protein degradation pathways may be sufficient for disease modification.…”

Hunting for the mutant without the MAP(K)

“…To date, several groups have performed unbiased RNA interference (RNAi) screens to identify candidate molecules whose modulation may alter the development and progression of HD, however, these screens have been primarily performed in models that rely on the exogenous overexpression of polyQ expanded mHTT [5][6][7][8][9]. Although these previous reports have successfully identified a diverse set of pharmacologically targetable molecules capable of reducing mHTT aggregation and its associated toxicity in cellular and animal models of HD, these target pathways may not directly apply to the endogenous expression of pathological mHTT, especially in the context of HDrelevant human cell types.…”

NUB1 suppression of Huntington toxicity: mechanistic insights

“…[19][20][21][22] As a result, identification of pathways that can lower mHTT levels is of great therapeutic as well as biological interest.…”

“…20 Here we will discuss the likely mechanism of NUB1-mediated clearance of mHTT and potential therapeutic strategies.…”