Human Molecular Genetics Advance Access originally published online on November 1, 2007
Human Molecular Genetics 2008 17(3):431-439; doi:10.1093/hmg/ddm320
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Lysine 63-linked ubiquitination promotes the formation and autophagic clearance of protein inclusions associated with neurodegenerative diseases
,1 Neurodegeneration Research Lab, National Neuroscience Institute, Singapore 2 Institute for Cell Engineering, Johns Hopkins University School of Medicine, Baltimore, MD, USA 3 Department of Neurology, Johns Hopkins University School of Medicine, Baltimore, MD, USA 4 Department of Neuroscience and Physiology, Johns Hopkins University School of Medicine, Baltimore, MD, USA 5 Department of Pathology, Johns Hopkins University School of Medicine, Baltimore, MD, USA 6 Department of Cell Biology, Harvard Medical School, Boston, MA, USA 7 Duke-NUS Graduate Medical School, National University of Singapore, Singapore 8 Department of Biological Sciences, National University of Singapore, Singapore
* To whom correspondence should be addressed at: Neurodegeneration Research Laboratory, National Neuroscience Institute, 11 Jalan Tan Tock Seng, 308433, Singapore. Tel: 6563577520; Fax: 6562569178; Email: kah_leong_lim{at}nni.com.sg
Received September 19, 2007; Accepted October 29, 2007
Although ubiquitin-enriched protein inclusions represent an almost invariant feature of neurodegenerative diseases, the mechanism underlying their biogenesis remains unclear. In particular, whether the topology of ubiquitin linkages influences the dynamics of inclusions is not well explored. Here, we report that lysine 48 (K48)- and lysine 63 (K63)-linked polyubiquitination, as well as monoubiquitin modification contribute to the biogenesis of inclusions. K63-linked polyubiquitin is the most consistent enhancer of inclusions formation. Under basal conditions, ectopic expression of K63 mutant ubiquitin in cultured cells promotes the accumulation of proteins and the formation of intracellular inclusions in the apparent absence of proteasome impairment. When co-expressed with disease-associated tau and SOD1 mutants, K63 ubiquitin mutant facilitates the formation of tau- and SOD-1–positive inclusions. Moreover, K63-linked ubiquitination was found to selectively facilitate the clearance of inclusions via autophagy. These data indicate that K63-linked ubiquitin chains may represent a common denominator underlying inclusions biogenesis, as well as a general cellular strategy for defining cargo destined for the autophagic system. Collectively, our results provide a novel mechanistic route that underlies the life cycle of an inclusion body. Harnessing this pathway may offer innovative approaches in the treatment of neurodegenerative disorders.
Present address: Department of Anatomy and Structural Biology, Marion Bessin Liver Research Center, Albert Einstein College of Medicine, Jack and Pearl Resnick Campus, 1300 Morris Park Avenue, Bronx, NY, USA.
J.M.M.T., E.S.P.W., T.M.D and K.L.L contributed equally to this work.