title: Tissue transglutaminase selectively modifies proteins associated with truncated mutant huntingtin in intact cells.
abstract: The cause of Huntington's disease (HD) is a pathological expansion of the polyglutamine domain within the N-terminal region of huntingtin. Neuronal intranuclear inclusions and cytoplasmic aggregates composed of the mutant huntingtin within certain neuronal populations are a characteristic hallmark of HD. However, how the expanded polyglutamine repeats of mutant huntingtin cause HD is not known. Because in vitro expanded polyglutamine repeats are excellent glutaminyl-donor substrates of tissue transglutaminase (tTG), it has been hypothesized that tTG may contribute to the formation of these aggregates in HD. However, an association between huntingtin and tTG or modification of huntingtin by tTG has not been demonstrated in cells. To examine the interactions between tTG and huntingtin human neuroblastoma SH-SY5Y cells were stably transfected with full-length huntingtin containing 23 (FL-Q23) (wild type) or 82 (FL-Q82) (mutant) glutamine repeats or a truncated N-terminal huntingtin construct containing 23 (Q23) (wild type) or 62 (Q62) (mutant) glutamine repeats. Aggregates were rarely observed in the cells expressing full-length mutant huntingtin, and no specific colocalization of full-length huntingtin and tTG was observed. In contrast, in cells expressing truncated mutant huntingtin (Q62) there were numerous complexes of truncated mutant huntingtin and many of these complexes co-localized with tTG. However, the complexes were not insoluble structures. Further, truncated huntingtin coimmunoprecipitated with tTG, and this association increased when tTG was activated. Activation of tTG did not result in the modification of either truncated or full-length huntingtin, however proteins that were associated with truncated mutant huntingtin were selectively modified by tTG. This study is the first to demonstrate that tTG specifically interacts with a truncated form of huntingtin, and that activated tTG selectively modifies mutant huntingtin-associated proteins. These data suggest that proteolysis of full-length mutant huntingtin likely precedes its interaction with tTG and this process may facilitate the modification of huntingtin-associated proteins and thus contribute to the etiology of HD.
authors.affiliation: Department of Psychiatry and Behavioral Neurobiology, University of Alabama at Birmingham, Birmingham, Alabama 35294-0017, USA.
authors.forename: W
authors.initials: W
authors.lastname: Chun
authors.forename: M
authors.initials: M
authors.lastname: Lesort
authors.forename: J
authors.initials: J
authors.lastname: Tucholski
authors.forename: P W
authors.initials: PW
authors.lastname: Faber
authors.forename: M E
authors.initials: ME
authors.lastname: MacDonald
authors.forename: C A
authors.initials: CA
authors.lastname: Ross
authors.forename: G V
authors.initials: GV
authors.lastname: Johnson
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology; D002470:Cell Survival / Q000502:physiology; D015870:Gene Expression / Q000502:physiology; D006801:Humans; D000071058:Huntingtin Protein; D006816:Huntington Disease / Q000378:metabolism*; D007150:Immunohistochemistry; D016296:Mutagenesis / Q000502:physiology; D009419:Nerve Tissue Proteins / Q000032:analysis / Q000235:genetics* / Q000378:metabolism*; D009447:Neuroblastoma; D009474:Neurons / Q000737:chemistry / Q000166:cytology / Q000201:enzymology*; D009687:Nuclear Proteins / Q000032:analysis / Q000235:genetics* / Q000378:metabolism*; D010455:Peptides / Q000378:metabolism; D011073:Polyamines / Q000378:metabolism; D011233:Precipitin Tests; D014162:Transfection; D011503:Transglutaminases / Q000032:analysis / Q000378:metabolism*; D014212:Tretinoin / Q000494:pharmacology; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; C086055:HTT protein, human; D000071058:Huntingtin Protein; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D010455:Peptides; D011073:Polyamines; C097188:polyglutamine; D014212:Tretinoin; D011503:Transglutaminases