title: Dose-dependent inhibition of proteasome activity by a mutant ubiquitin associated with neurodegenerative disease.
abstract: The ubiquitin-proteasome system is the main regulated intracellular proteolytic pathway. Increasing evidence implicates impairment of this system in the pathogenesis of diseases with ubiquitin-positive pathology. A mutant ubiquitin, UBB(+1), accumulates in the pathological hallmarks of tauopathies, including Alzheimer's disease, polyglutamine diseases, liver disease and muscle disease and serves as an endogenous reporter for proteasomal dysfunction in these diseases. UBB(+1) is a substrate for proteasomal degradation, however it can also inhibit the proteasome. Here, we show that UBB(+1) properties shift from substrate to inhibitor in a dose-dependent manner in cell culture using an inducible UBB(+1) expression system. At low expression levels, UBB(+1) was efficiently degraded by the proteasome. At high levels, the proteasome failed to degrade UBB(+1), causing its accumulation, which subsequently induced a reversible functional impairment of the ubiquitin-proteasome system. Also in brain slice cultures, UBB(+1) accumulation and concomitant proteasome inhibition was only induced at high expression levels. Our findings show that by varying UBB(+1) expression levels, the dual proteasome substrate and inhibitory properties can be optimally used to serve as a research tool to study the ubiquitin-proteasome system and to further elucidate the role of aberrations of this pathway in disease.
authors.affiliation: Netherlands Institute for Neuroscience, Meibergdreef 47, 1105 BA Amsterdam, The Netherlands.
authors.forename: Paula
authors.initials: P
authors.lastname: van Tijn
authors.forename: Femke M S
authors.initials: FM
authors.lastname: de Vrij
authors.forename: Karianne G
authors.initials: KG
authors.lastname: Schuurman
authors.forename: Nico P
authors.initials: NP
authors.lastname: Dantuma
authors.forename: David F
authors.initials: DF
authors.lastname: Fischer
authors.forename: Fred W
authors.initials: FW
authors.lastname: van Leeuwen
authors.forename: Elly M
authors.initials: EM
authors.lastname: Hol
mesh_terms: D000818:Animals; D015153:Blotting, Western; D002540:Cerebral Cortex / Q000187:drug effects / Q000378:metabolism; D015853:Cysteine Proteinase Inhibitors / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004317:Doxorubicin / Q000494:pharmacology; D005434:Flow Cytometry; D016368:Frameshift Mutation; D015870:Gene Expression / Q000187:drug effects; D049452:Green Fluorescent Proteins / Q000235:genetics / Q000378:metabolism; D006367:HeLa Cells; D006801:Humans; D007976:Leupeptins / Q000494:pharmacology; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D008954:Models, Biological; D019636:Neurodegenerative Diseases / Q000235:genetics / Q000378:metabolism*; D009842:Oligopeptides / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D061988:Proteasome Inhibitors; D046509:Tissue Culture Techniques; D014162:Transfection; D025801:Ubiquitin / Q000235:genetics / Q000378:metabolism*
chemical_list: D015853:Cysteine Proteinase Inhibitors; D007976:Leupeptins; D009842:Oligopeptides; D061988:Proteasome Inhibitors; C479419:UBB protein, human; D025801:Ubiquitin; D049452:Green Fluorescent Proteins; D004317:Doxorubicin; D046988:Proteasome Endopeptidase Complex; C072553:benzyloxycarbonylleucyl-leucyl-leucine aldehyde; C078846:epoxomicin