Inefficient degradation of truncated polyglutamine proteins by the proteasome.
Accumulation of mutant proteins into misfolded species and aggregates is characteristic for diverse neurodegenerative diseases including the polyglutamine diseases. While several studies have suggested that polyglutamine protein aggregates impair the ubiquitin-proteasome system, the molecular mechanisms underlying the interaction between polyglutamine proteins and the proteasome have remained elusive. In this study, we use fluorescence live-cell imaging to demonstrate that the proteasome is sequestered irreversibly within aggregates of overexpressed N-terminal mutant Huntingtin fragment or simple polyglutamine expansion proteins. Moreover, by direct targeting of polyglutamine proteins for proteasomal degradation, we observe incomplete degradation of these substrates both in vitro and in vivo. Thus, our data reveal that intrinsic properties of the polyglutamine proteins prevent their efficient degradation and clearance. Additionally, fluorescence resonance energy transfer is detected between the proteasome and aggregated polyglutamine proteins indicative of a close and stable interaction. We propose that polyglutamine-containing proteins are kinetically trapped within proteasomes, which could explain their deleterious effects on cellular function over time.
Holmberg
Carina I
CI
Department of Biochemistry, Molecular Biology and Cell Biology, Rice Institute for Biomedical Research, Robert H Lurie Comprehensive Cancer Center, Northwestern University, Evanston, IL 60208, USA.
Staniszewski
Kristine E
KE
Mensah
Kwame N
KN
Matouschek
Andreas
A
Morimoto
Richard I
RI
D002460:Cell Line; D003546:Cysteine Endopeptidases / Q000235:genetics / Q000378:metabolism; D036681:Fluorescence Recovery After Photobleaching; D031541:Fluorescence Resonance Energy Transfer; D006801:Humans; D000071058:Huntingtin Protein; D008164:Luminescent Proteins / Q000235:genetics / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D019636:Neurodegenerative Diseases / Q000378:metabolism; D009687:Nuclear Proteins / Q000737:chemistry / Q000235:genetics / Q000378:metabolism; D010455:Peptides / Q000737:chemistry* / Q000378:metabolism*; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D017510:Protein Folding; D011993:Recombinant Fusion Proteins / Q000235:genetics / Q000378:metabolism; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism
C086055:HTT protein, human; D000071058:Huntingtin Protein; D008164:Luminescent Proteins; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D010455:Peptides; D011993:Recombinant Fusion Proteins; D025801:Ubiquitin; C071313:LMP-2 protein; C097188:polyglutamine; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex