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+1is a substrate for proteasomal degradation, however it can also inhibit the proteasome. Here, we show that UBB+1properties shift from substrate to inhibitor in a dose-dependent manner in cell culture using an inducible UBB+1expression system. At low expression levels, UBB+1was 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+1accumulation and concomitant proteasome inhibition was only induced at high expression levels. Our findings show that by varying UBB+1expression 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.

Additional Metadata
Keywords Alzheimer's disease, Neurodegeneration, Protein aggreration, Protein degradation, Ubiquitin, Ubiquitin-proteasome system
Persistent URL dx.doi.org/10.1242/jcs.03438, hdl.handle.net/1765/35443
Citation
van Tijn, P., Vrij, F.M.S., Schuurman, K.G., Dantuma, N.P., Fischer, D.F., van Leeuwen, F.W., & Hol, E.M.. (2007). Dose-dependent inhibition of proteasome activity by a mutant ubiquitin associated with neurodegenerative disease. Journal of Cell Science, 120(9), 1615–1623. doi:10.1242/jcs.03438