title: Mutant huntingtin N-terminal fragments of specific size mediate aggregation and toxicity in neuronal cells.
abstract: Huntingtin proteolysis is implicated in Huntington disease pathogenesis, yet, the nature of huntingtin toxic fragments remains unclear. Huntingtin undergoes proteolysis by calpains and caspases within an N-terminal region between amino acids 460 and 600. We have focused on proteolytic steps producing shorter N-terminal fragments, which we term cp-1 and cp-2 (distinct from previously described cp-A/cp-B). We used HEK293 cells to express the first 511 residues of huntingtin and further define the cp-1 and cp-2 cleavage sites. Based on epitope mapping with huntingtin-specific antibodies, we found that cp-1 cleavage occurs between residues 81 and 129 of huntingtin. Affinity and size exclusion chromatography were used to further purify huntingtin cleavage products and enrich for the cp-1/cp-2 fragments. Using mass spectrometry, we found that the cp-2 fragment is generated by cleavage of huntingtin at position Arg(167). This site was confirmed by deletion analysis and specific detection with a custom-generated cp-2 site neo-epitope antibody. Furthermore, alterations of this cleavage site resulted in a decrease in toxicity and an increase in aggregation of huntingtin in neuronal cells. These data suggest that cleavage of huntingtin at residue Arg(167) may mediate mutant huntingtin toxicity in Huntington disease.
authors.affiliation: Division of Neurobiology, Department of Psychiatry, Mass Spectrometry and Proteomics Facility, Johns Hopkins University School of Medicine, Baltimore, Maryland 21287, USA. tratovi1@jhmi.edu
authors.forename: Tamara
authors.initials: T
authors.lastname: Ratovitski
authors.forename: Marjan
authors.initials: M
authors.lastname: Gucek
authors.forename: Haibing
authors.initials: H
authors.lastname: Jiang
authors.forename: Ekaterine
authors.initials: E
authors.lastname: Chighladze
authors.forename: Elaine
authors.initials: E
authors.lastname: Waldron
authors.forename: James
authors.initials: J
authors.lastname: D'Ambola
authors.forename: Zhipeng
authors.initials: Z
authors.lastname: Hou
authors.forename: Yideng
authors.initials: Y
authors.lastname: Liang
authors.forename: Michelle A
authors.initials: MA
authors.lastname: Poirier
authors.forename: Ricky R
authors.initials: RR
authors.lastname: Hirschhorn
authors.forename: Rona
authors.initials: R
authors.lastname: Graham
authors.forename: Michael R
authors.initials: MR
authors.lastname: Hayden
authors.forename: Robert N
authors.initials: RN
authors.lastname: Cole
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Ross
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D002460:Cell Line; D006801:Humans; D000071058:Huntingtin Protein; D006816:Huntington Disease / Q000378:metabolism / Q000473:pathology; D008969:Molecular Sequence Data; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism* / Q000633:toxicity*; D009474:Neurons / Q000166:cytology / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism* / Q000633:toxicity*; D010446:Peptide Fragments / Q000235:genetics / Q000378:metabolism* / Q000633:toxicity*
chemical_list: C086055:HTT protein, human; D000071058:Huntingtin Protein; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D010446:Peptide Fragments