RESUMO
Polyglutamine diseases are nine dominantly inherited neurodegenerative pathologies caused by the expansion of a polyglutamine domain in a protein responsible for the disease. This expansion leads to protein aggregation, inclusion formation and toxicity. Despite numerous studies focusing on the subject, whether soluble polyglutamine proteins are responsible for toxicity or not remains debated. To focus on this matter, we evaluated the level of soluble and insoluble truncated pathological Ataxin-3 in vivo in Drosophila, in presence or absence of two suppressors (i.e. Hsp70 and non-pathological Ataxin-3) and along aging. Suppressing truncated Ataxin-3-induced toxicity resulted in a lowered level of aggregated polyglutamine protein. Interestingly, aggregates accumulated as flies aged and reached a maximum level when cell death was detected. Our results were similar with two other pathological polyglutamine proteins, namely truncated Ataxin-7 and full-length Ataxin-3. Our data suggest that accumulation of insoluble aggregates beyond a critical threshold could be responsible for toxicity.
Assuntos
Ataxina-3/química , Ataxina-3/metabolismo , Ataxina-7/química , Ataxina-7/metabolismo , Agregação Patológica de Proteínas/metabolismo , Proteínas Repressoras/química , Proteínas Repressoras/metabolismo , Envelhecimento/genética , Envelhecimento/metabolismo , Envelhecimento/patologia , Animais , Animais Geneticamente Modificados , Ataxina-3/genética , Ataxina-7/genética , Modelos Animais de Doenças , Drosophila melanogaster/genética , Drosophila melanogaster/metabolismo , Feminino , Transtornos Heredodegenerativos do Sistema Nervoso/genética , Transtornos Heredodegenerativos do Sistema Nervoso/metabolismo , Transtornos Heredodegenerativos do Sistema Nervoso/patologia , Humanos , Masculino , Modelos Neurológicos , Proteínas Mutantes/química , Proteínas Mutantes/genética , Proteínas Mutantes/metabolismo , Peptídeos/química , Peptídeos/genética , Peptídeos/metabolismo , Agregados Proteicos , Agregação Patológica de Proteínas/genética , Proteínas Recombinantes/química , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo , Proteínas Repressoras/genética , SolubilidadeRESUMO
The genome of the human immunodeficiency virus type 1 (HIV-1) encodes the canonical retroviral proteins, as well as additional accessory proteins that enhance the expression of viral genes, the infectivity of the virus and the production of virions. The accessory Viral Protein U (Vpu), in particular, enhances viral particle production, while also promoting apoptosis of HIV-infected human T lymphocytes. Some Vpu effects rely on its interaction with the ubiquitin-proteasome protein degradation system, but the mechanisms responsible for its pro-apoptotic effects in vivo are complex and remain largely to be elucidated.We took advantage of the Drosophila model to study the effects of Vpu activity in vivo. Expression of Vpu in the developing Drosophila wing provoked tissue loss due to caspase-dependent apoptosis. Moreover, Vpu induced expression of the pro-apoptotic gene reaper, known to down-regulate Inhibitor of Apoptosis Proteins (IAPs) which are caspase-antagonizing E3 ubiquitin ligases. Indeed, Vpu also reduced accumulation of Drosophila IAP1 (DIAP1). Though our results demonstrate a physical interaction between Vpu and the proteasome-addressing SLIMB/ß-TrCP protein, as in mammals, both SLIMB/ßTrCP-dependent and -independent Vpu effects were observed in the Drosophila wing. Lastly, the pro-apoptotic effect of Vpu in this tissue was abrogated upon inactivation of the c-Jun N-terminal Kinase (JNK) pathway. Our results in the fly thus provide the first functional evidence linking Vpu pro-apoptotic effects to activation of the conserved JNK pathway.