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Human J-Domain Protein DnaJB6 Protects Yeast from [PSI+] Prion Toxicity

ABSTRACT:

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DnaJB6 is a human cellular protein quality control factor that prevents diverse peptides from forming disease-associated amyloid, a highly ordered fibrous protein aggregate. DnaJB6 protects human cells, animals and yeast from toxicity caused by amyloids composed of Huntington’s-related polyglutamine, Parkinson’s-related α-synuclein, and ALS- associated TDP-43, and it cures yeast of endogenous prions (infectious amyloids). However, structurally different amyloids of one and the same prion protein, and prions composed of them, can be insensitive to anti-amyloid activity of DnaJB6. This limitation raises concerns about developing DnaJB6 as a therapeutic for amyloid diseases. Prions showing this insensitivity are highly toxic to yeast with reduced function of Sis1, a yeast protein related to DnaJB6. To begin assessing how DnaJB6 might act on amyloid in cells we tested if DnaJB6 could protect yeast from this toxicity. Although it does not eliminate the prion, it protects cells from prion toxicity, but differently than Sis1. Our work provides insight into how human DnaJB6 counteracts cellular toxicity caused by amyloid and establishes an in vivo genetic system useful for studying DnaJB6-amyloid interactions to decipher its mechanisms of action.

Abstract

Human J-domain protein (JDP) DnaJB6 has a broad and potent activity that prevents formation of amyloid by polypeptides such as polyglutamine, A-beta, and alpha-synuclein, related to Huntington’s, Alzheimer’s, and Parkinson’s diseases, respectively. In yeast, amyloid-based [PSI+] prions, which rely on the related JDP Sis1 for replication, have a latent toxicity that is exposed by reducing Sis1 function. Anti-amyloid activity of DnaJB6 is very effective against weak [PSI+] prions and the Sup35 amyloid that composes them, but ineffective against strong [PSI+] prions composed of structurally different amyloid of the same Sup35. This difference reveals limitations of DnaJB6 that have implications regarding its therapeutic use for amyloid disease. Here, we find that when Sis1 function is reduced, DnaJB6 represses toxicity of strong [PSI+] prions and inhibits their propagation. Both Sis1 and DnaJB6, which are regulators of protein chaperone Hsp70, counteract the toxicity by reducing excessive incorporation of the essential Sup35 into prion aggregates. However, while Sis1 apparently requires interaction with Hsp70 to detoxify [PSI+], DnaJB6 counteracts prion toxicity by a different, Hsp70-independent mechanism.

SUBMITTER: Dolder R

PROVIDER: S-EPMC9776390 | biostudies-literature | 2022 Dec

REPOSITORIES: biostudies-literature

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Project description:Interactions amongst different amyloid proteins have been proposed as a probable mechanism of aggregation and thus an important risk factor for the onset as well as progression of various neurodegenerative disorders including Alzheimer's, Parkinson's, Huntington's, and Amyotrophic Lateral Sclerosis. Evidences suggest that transthyretin (TTR), a plasma protein associated with transthyretin amyloidosis or familial polyneuropathy (FAP) interacts with heterologous amyloid proteins including amyloid beta and islet amyloid polypeptide. In addition, recent clinical studies have revealed the presence of systemic polyneuropathy associated with FAP mutations in patients with spinocerebral ataxia, amyotrophic lateral sclerosis, and new familial systematic prion disease. Hence, it is important to investigate the interactions amongst different amyloid proteins to gain better insight into the pathology of amyloid disorders. Yeast has been an excellent model system to study interaction/ cross-seeding between heterologous amyloid proteins, more because of presence of endogenous yeast prions. Here, we examined interactions of non-glutamine (non-Q)-rich transthyretin, with glutamine (Q)-rich yeast prion protein Sup35. We established aggregation of an engineered double (F87M/L110M) mutant M-TTR-GFP in yeast. This mutant is monomeric and readily formed aggregates compared to WT-TTR-GFP in yeast at acidic pH. Interestingly, aggregation of M-TTR-GFP was significantly enhanced in presence of [PSI+], an endogenous prion form of Sup35. Different variants of [PSI+] seeded M-TTR-GFP with different efficiencies and curing of [PSI+] (losing the prion form) in these strains reduced aggregation. Moreover, overexpression of prion domain of Sup35 fused to RFP (NM-RFP) also increased M-TTR-GFP aggregation. M-TTR-GFP and NM-RFP aggregates co-localized in perivacuolar and juxtranuclear region. Sup35 protein was even immunocaptured in M-TTR-GFP aggregates. However, M-TTR-GFP overexpression did not induce Sup35 aggregation. Thus, it appears to be a unidirectional interaction between these two amyloid proteins. However, no affect on M-TTR-GFP aggregation was observed due to another yeast prion, [PIN+]. Our findings thus show the molecular interaction of transthyretin with yeast prion and support that sequence similarity is not the prime requirement for heterologous amyloid interactions.

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Human J-Domain Protein DnaJB6 Protects Yeast from [PSI+] Prion Toxicity

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