RESUMO
Huntington's disease is a neurodegenerative disorder associated with the expansion of the polyglutamine tract in the exon-1 domain of the huntingtin protein (htte1). Above a threshold of 37 glutamine residues, htte1 starts to aggregate in a nucleation-dependent manner. A 17-residue N-terminal fragment of htte1 (N17) has been suggested to play a crucial role in modulating the aggregation propensity and toxicity of htte1. Here we identify N17 as a potential target for novel therapeutic intervention using the molecular tweezer CLR01. A combination of biochemical experiments and computer simulations shows that binding of CLR01 induces structural rearrangements within the htte1 monomer and inhibits htte1 aggregation, underpinning the key role of N17 in modulating htte1 toxicity.
Assuntos
Hidrocarbonetos Aromáticos com Pontes/farmacologia , Proteína Huntingtina/antagonistas & inibidores , Organofosfatos/farmacologia , Hidrocarbonetos Aromáticos com Pontes/química , Éxons , Humanos , Interações Hidrofóbicas e Hidrofílicas , Simulação de Dinâmica Molecular , Estrutura Molecular , Organofosfatos/química , Agregados Proteicos/efeitos dos fármacosRESUMO
Protein 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.
Assuntos
Proteínas de Caenorhabditis elegans/metabolismo , Caenorhabditis elegans/enzimologia , Doenças Neurodegenerativas/enzimologia , Peptídeos/metabolismo , Agregados Proteicos , Agregação Patológica de Proteínas , RNA Polimerase III/metabolismo , Fatores de Transcrição/metabolismo , Transporte Ativo do Núcleo Celular , Animais , Animais Geneticamente Modificados , Sítios de Ligação , Caenorhabditis elegans/genética , Proteínas de Caenorhabditis elegans/genética , Núcleo Celular/enzimologia , Citosol/enzimologia , Modelos Animais de Doenças , Doenças Neurodegenerativas/genética , Doenças Neurodegenerativas/patologia , Regiões Promotoras Genéticas , Ligação Proteica , Interferência de RNA , RNA Polimerase III/genética , Pequeno RNA não Traduzido/genética , Pequeno RNA não Traduzido/metabolismo , Fatores de Transcrição/genética , Transcrição GênicaRESUMO
Spinocerebellar ataxia type 7 (SCA7) is one of nine neurodegenerative disorders caused by expanded polyglutamine domains. These so-called polyglutamine (polyQ) diseases are all characterized by aggregation. Reducing the level of aggregating polyQ proteins via pharmacological activation of autophagy has been suggested as a therapeutic approach. However, recently, evidence implicating autophagic dysfunction in these disorders has also been reported. In this study, we show that the SCA7 polyglutamine protein ataxin-7 (ATXN7) reduces the autophagic activity via a previously unreported mechanism involving p53-mediated disruption of two key proteins involved in autophagy initiation. We show that in mutant ATXN7 cells, an increased p53-FIP200 interaction and co-aggregation of p53-FIP200 into ATXN7 aggregates result in decreased soluble FIP200 levels and subsequent destabilization of ULK1. Together, this leads to a decreased capacity for autophagy induction via the ULK1-FIP200-Atg13-Atg101 complex. We also show that treatment with a p53 inhibitor, or a blocker of ATXN7 aggregation, can restore the soluble levels of FIP200 and ULK1, as well as increase the autophagic activity and reduce ATXN7 toxicity. Understanding the mechanism behind polyQ-mediated inhibition of autophagy is of importance if therapeutic approaches based on autophagy stimulation should be developed for these disorders.
