Expanded Polyglutamine-containing N-terminal Huntingtin Fragments Are Entirely Degraded by Mammalian Proteasomes

• Published in: The Journal of biological chemistry Vol. 288; no. 38; pp. 27068 - 27084
• Main Authors: Juenemann, Katrin, Schipper-Krom, Sabine, Wiemhoefer, Anne, Kloss, Alexander, Sanz Sanz, Alicia, Reits, Eric A.J.
• Format: Journal Article
• Language: English
• Published: United States Elsevier Inc 20.09.2013; American Society for Biochemistry and Molecular Biology
• Subjects: Aggregation; Animals; Autophagy; Cell Line; Humans; Huntingtin Protein; Huntington Disease; Mice; Mice, Knockout; Molecular Bases of Disease; Nerve Tissue Proteins - genetics; Nerve Tissue Proteins - metabolism; Nuclear Proteins - genetics; Nuclear Proteins - metabolism; Peptides - genetics; Peptides - metabolism; Polyglutamine; Proteasome; Proteasome Endopeptidase Complex - genetics; Proteasome Endopeptidase Complex - metabolism; Proteolysis; Repetitive Sequences, Amino Acid; Aggregation; Huntington Disease; Polyglutamine; Autophagy; Proteasome
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M113.486076

Huntington disease is a neurodegenerative disorder caused by an expanded polyglutamine (polyQ) repeat within the protein huntingtin (Htt). N-terminal fragments of the mutant Htt (mHtt) proteins containing the polyQ repeat are aggregation-prone and form intracellular inclusion bodies. Improving the clearance of mHtt fragments by intracellular degradation pathways is relevant to obviate toxic mHtt species and subsequent neurodegeneration. Because the proteasomal degradation pathway has been the subject of controversy regarding the processing of expanded polyQ repeats, we examined whether the proteasome can efficiently degrade Htt-exon1 with an expanded polyQ stretch both in neuronal cells and in vitro. Upon targeting mHtt-exon1 to the proteasome, rapid and complete clearance of mHtt-exon1 was observed. Proteasomal degradation of mHtt-exon1 was devoid of polyQ peptides as partial cleavage products by incomplete proteolysis, indicating that mammalian proteasomes are capable of efficiently degrading expanded polyQ sequences without an inhibitory effect on the proteasomal activity. Background: Huntington disease is caused by an expanded polyglutamine repeat within the protein huntingtin. Results: Proteasomal degradation of mutant huntingtin fragments is devoid of polyglutamine peptides as partial cleavage products. Conclusion: Mammalian proteasomes are capable of entirely degrading expanded polyglutamine sequences. Significance: Accelerating the mutant huntingtin degradation by the proteasomal pathway obviates toxic species and represents a beneficial therapeutic strategy.