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.
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The authors wish to thank D. Curtis for discussions and suggestions during the project, X. Shi for performing the control screening on SMN level changes, C. Mazur for assistance with cloning and sample processing, P. Manos and C. Littlefield for assistance with the hESC and human iPSC experiments, and E. Kim for assistance with the fly experiments. I.A. was funded by a John J. Wasmuth postdoctoral fellowship from the Hereditary Disease Foundation. A.V. was funded by the Hereditary Disease Foundation. M.D. was funded by US National Institutes of Health grant NS074381.
The authors declare no competing financial interests.
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Lu, B., Al-Ramahi, I., Valencia, A. et al. Identification of NUB1 as a suppressor of mutant Huntingtin toxicity via enhanced protein clearance. Nat Neurosci 16, 562–570 (2013). https://doi.org/10.1038/nn.3367
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