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Changes in Proteasome Structure and Function Caused by HAMLET in Tumor Cells

BACKGROUND: Proteasomes control the level of endogenous unfolded proteins by degrading them in the proteolytic core. Insufficient degradation due to altered protein structure or proteasome inhibition may trigger cell death. This study examined the proteasome response to HAMLET, a partially unfolded...

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Autores principales: Gustafsson, Lotta, Aits, Sonja, Önnerfjord, Patrik, Trulsson, Maria, Storm, Petter, Svanborg, Catharina
Formato: Texto
Lenguaje:English
Publicado: Public Library of Science 2009
Materias:
Acceso en línea:https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2664966/
https://www.ncbi.nlm.nih.gov/pubmed/19365565
http://dx.doi.org/10.1371/journal.pone.0005229
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author Gustafsson, Lotta
Aits, Sonja
Önnerfjord, Patrik
Trulsson, Maria
Storm, Petter
Svanborg, Catharina
author_facet Gustafsson, Lotta
Aits, Sonja
Önnerfjord, Patrik
Trulsson, Maria
Storm, Petter
Svanborg, Catharina
author_sort Gustafsson, Lotta
collection PubMed
description BACKGROUND: Proteasomes control the level of endogenous unfolded proteins by degrading them in the proteolytic core. Insufficient degradation due to altered protein structure or proteasome inhibition may trigger cell death. This study examined the proteasome response to HAMLET, a partially unfolded protein-lipid complex, which is internalized by tumor cells and triggers cell death. METHODOLOGY/PRINCIPAL FINDINGS: HAMLET bound directly to isolated 20S proteasomes in vitro and in tumor cells significant co-localization of HAMLET and 20S proteasomes was detected by confocal microscopy. This interaction was confirmed by co-immunoprecipitation from extracts of HAMLET-treated tumor cells. HAMLET resisted in vitro degradation by proteasomal enzymes and degradation by intact 20S proteasomes was slow compared to fatty acid-free, partially unfolded α-lactalbumin. After a brief activation, HAMLET inhibited proteasome activity in vitro and in parallel a change in proteasome structure occurred, with modifications of catalytic (β1 and β5) and structural subunits (α2, α3, α6 and β3). Proteasome inhibition was confirmed in extracts from HAMLET-treated cells and there were indications of proteasome fragmentation in HAMLET-treated cells. CONCLUSIONS/SIGNIFICANCE: The results suggest that internalized HAMLET is targeted to 20S proteasomes, that the complex resists degradation, inhibits proteasome activity and perturbs proteasome structure. We speculate that perturbations of proteasome structure might contribute to the cytotoxic effects of unfolded protein complexes that invade host cells.
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spelling pubmed-26649662009-04-14 Changes in Proteasome Structure and Function Caused by HAMLET in Tumor Cells Gustafsson, Lotta Aits, Sonja Önnerfjord, Patrik Trulsson, Maria Storm, Petter Svanborg, Catharina PLoS One Research Article BACKGROUND: Proteasomes control the level of endogenous unfolded proteins by degrading them in the proteolytic core. Insufficient degradation due to altered protein structure or proteasome inhibition may trigger cell death. This study examined the proteasome response to HAMLET, a partially unfolded protein-lipid complex, which is internalized by tumor cells and triggers cell death. METHODOLOGY/PRINCIPAL FINDINGS: HAMLET bound directly to isolated 20S proteasomes in vitro and in tumor cells significant co-localization of HAMLET and 20S proteasomes was detected by confocal microscopy. This interaction was confirmed by co-immunoprecipitation from extracts of HAMLET-treated tumor cells. HAMLET resisted in vitro degradation by proteasomal enzymes and degradation by intact 20S proteasomes was slow compared to fatty acid-free, partially unfolded α-lactalbumin. After a brief activation, HAMLET inhibited proteasome activity in vitro and in parallel a change in proteasome structure occurred, with modifications of catalytic (β1 and β5) and structural subunits (α2, α3, α6 and β3). Proteasome inhibition was confirmed in extracts from HAMLET-treated cells and there were indications of proteasome fragmentation in HAMLET-treated cells. CONCLUSIONS/SIGNIFICANCE: The results suggest that internalized HAMLET is targeted to 20S proteasomes, that the complex resists degradation, inhibits proteasome activity and perturbs proteasome structure. We speculate that perturbations of proteasome structure might contribute to the cytotoxic effects of unfolded protein complexes that invade host cells. Public Library of Science 2009-04-14 /pmc/articles/PMC2664966/ /pubmed/19365565 http://dx.doi.org/10.1371/journal.pone.0005229 Text en Gustafsson et al. http://creativecommons.org/licenses/by/4.0/ This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are properly credited.
spellingShingle Research Article
Gustafsson, Lotta
Aits, Sonja
Önnerfjord, Patrik
Trulsson, Maria
Storm, Petter
Svanborg, Catharina
Changes in Proteasome Structure and Function Caused by HAMLET in Tumor Cells
title Changes in Proteasome Structure and Function Caused by HAMLET in Tumor Cells
title_full Changes in Proteasome Structure and Function Caused by HAMLET in Tumor Cells
title_fullStr Changes in Proteasome Structure and Function Caused by HAMLET in Tumor Cells
title_full_unstemmed Changes in Proteasome Structure and Function Caused by HAMLET in Tumor Cells
title_short Changes in Proteasome Structure and Function Caused by HAMLET in Tumor Cells
title_sort changes in proteasome structure and function caused by hamlet in tumor cells
topic Research Article
url https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2664966/
https://www.ncbi.nlm.nih.gov/pubmed/19365565
http://dx.doi.org/10.1371/journal.pone.0005229
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