Abstract:Several neurodegenerative disorders, including Huntington's disease, are caused by expansion of the polyglutamine (polyQ) tract over 40 glutamines in the disease-related protein.Fragments of these proteins containing the expanded polyQ tract are thought to initiate aggregation and represent the toxic species. Although it is not clear how these toxic fragments are generated, in vitro data suggest that proteasomes are unable to digest polyQ tracts. To examine whether the resulting polyQ peptides could initiate a… Show more
“…However, it remained unclear whether expanded polyQ stretches embedded in native polyQ protein sequences like mHtt-exon1 are also inefficiently degraded by proteasomes in living cells. In the case of remaining polyQ stretches as partial cleavage products of incomplete proteolysis, these fragments would accumulate within the cell and start to aggregate, as previously shown in living cells expressing pure expanded polyQ peptides without flanking sequences (23).…”
Section: Mhtt-exon1 Ismentioning
confidence: 60%
“…The Htt-exon1-25Q-GFP construct was kindly provided by R. Kopito (Stanford University). GFP-Ub, GFP-Ub-Q112, and Ub-Q112 were generated as described previously (23). Ub-G76V-GFP was a kindly provided by N. Dantuma (Karolinska Institute, Stockholm).…”
Section: Methodsmentioning
confidence: 99%
“…Furthermore, levels of soluble and aggregated mHtt increase upon pro-teasomal inhibition in cell culture and HD mouse brain material (16 -18). Because IBs recruit proteins, including ubiquitin (Ub), many types of chaperones, and whole proteasomes, this suggests that cells attempt to clear the aggregation-prone mHtt protein by the proteasomal pathway (17,18,23,24).…”
Section: Huntington Disease (Hd)mentioning
confidence: 99%
“…3D). To prove that this particular antibody is able to detect pure polyQ tracts independent of the flanking Htt sequences by Western blot analysis, we expressed the constructs GFP-Ub-Q112 and, as a control, GFP-Ub in Neuro-2a cells and analyzed the polyQ peptides generated after N-terminal GFP-Ub hydrolysis by cellular deubiquitinases (23). The specific polyQ antibody 3B5H10 is able to detect polyQ peptides with a size of ϳ30 kDa (arrow) and higher molecular species, which may represent polyQ oligomers (asterisks) (Fig.…”
Section: Volume 288 • Number 38 • September 20 2013mentioning
Background: Huntington disease is caused by an expanded polyglutamine repeat within the protein huntingtin. Results: Proteasomal degradation of mutant huntingtin fragments is devoid of polyglutamine peptides as partial cleavage products. Conclusion: Mammalian proteasomes are capable of entirely degrading expanded polyglutamine sequences. Significance: Accelerating the mutant huntingtin degradation by the proteasomal pathway obviates toxic species and represents a beneficial therapeutic strategy.
“…However, it remained unclear whether expanded polyQ stretches embedded in native polyQ protein sequences like mHtt-exon1 are also inefficiently degraded by proteasomes in living cells. In the case of remaining polyQ stretches as partial cleavage products of incomplete proteolysis, these fragments would accumulate within the cell and start to aggregate, as previously shown in living cells expressing pure expanded polyQ peptides without flanking sequences (23).…”
Section: Mhtt-exon1 Ismentioning
confidence: 60%
“…The Htt-exon1-25Q-GFP construct was kindly provided by R. Kopito (Stanford University). GFP-Ub, GFP-Ub-Q112, and Ub-Q112 were generated as described previously (23). Ub-G76V-GFP was a kindly provided by N. Dantuma (Karolinska Institute, Stockholm).…”
Section: Methodsmentioning
confidence: 99%
“…Furthermore, levels of soluble and aggregated mHtt increase upon pro-teasomal inhibition in cell culture and HD mouse brain material (16 -18). Because IBs recruit proteins, including ubiquitin (Ub), many types of chaperones, and whole proteasomes, this suggests that cells attempt to clear the aggregation-prone mHtt protein by the proteasomal pathway (17,18,23,24).…”
Section: Huntington Disease (Hd)mentioning
confidence: 99%
“…3D). To prove that this particular antibody is able to detect pure polyQ tracts independent of the flanking Htt sequences by Western blot analysis, we expressed the constructs GFP-Ub-Q112 and, as a control, GFP-Ub in Neuro-2a cells and analyzed the polyQ peptides generated after N-terminal GFP-Ub hydrolysis by cellular deubiquitinases (23). The specific polyQ antibody 3B5H10 is able to detect polyQ peptides with a size of ϳ30 kDa (arrow) and higher molecular species, which may represent polyQ oligomers (asterisks) (Fig.…”
Section: Volume 288 • Number 38 • September 20 2013mentioning
Background: Huntington disease is caused by an expanded polyglutamine repeat within the protein huntingtin. Results: Proteasomal degradation of mutant huntingtin fragments is devoid of polyglutamine peptides as partial cleavage products. Conclusion: Mammalian proteasomes are capable of entirely degrading expanded polyglutamine sequences. Significance: Accelerating the mutant huntingtin degradation by the proteasomal pathway obviates toxic species and represents a beneficial therapeutic strategy.
“…However, it remains unclear whether these nuclear structures are storage depots for misfolded proteins or are actively engaged in degrading misfolded proteins. Previous studies reported that N/Q-rich proteins cannot be degraded efficiently by the proteasome (74)(75)(76), unless proteasomal activity is increased (77). Therefore, we speculate that D. discoideum has evolved mechanisms to efficiently degrade and prevent the aggregation of prion-like proteins.…”
Many protein-misfolding diseases are caused by proteins carrying prion-like domains. These proteins show sequence similarity to yeast prion proteins, which can interconvert between an intrinsically disordered and an aggregated prion state. The natural presence of prions in yeast has provided important insight into disease mechanisms and cellular proteostasis. However, little is known about prions in other organisms, and it is not yet clear whether the findings in yeast can be generalized. Using bioinformatics tools, we show that Dictyostelium discoideum has the highest content of prion-like proteins of all organisms investigated to date, suggesting that its proteome has a high overall aggregation propensity. To study mechanisms regulating these proteins, we analyze the behavior of several well-characterized prion-like proteins, such as an expanded version of human huntingtin exon 1 (Q103) and the prion domain of the yeast prion protein Sup35 (NM), in D. discoideum. We find that these proteins remain soluble and are innocuous to D. discoideum, in contrast to other organisms, where they form cytotoxic cytosolic aggregates. However, when exposed to conditions that compromise molecular chaperones, these proteins aggregate and become cytotoxic. We show that the disaggregase Hsp101, a molecular chaperone of the Hsp100 family, dissolves heat-induced aggregates and promotes thermotolerance. Furthermore, prion-like proteins accumulate in the nucleus, where they are targeted by the ubiquitin-proteasome system. Our data suggest that D. discoideum has undergone specific adaptations that increase the proteostatic capacity of this organism and allow for an efficient regulation of its prion-like proteome. molecular chaperones | proteostasis | Dictyostelium discoideum | protein aggregation | prion
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