title: Tumor necrosis factor receptor-associated factor 6 (TRAF6) associates with huntingtin protein and promotes its atypical ubiquitination to enhance aggregate formation.
abstract: Huntington disease (HD) is a neurodegenerative disorder caused by an expansion of polyglutamines in the first exon of huntingtin (HTT), which confers aggregation-promoting properties to amino-terminal fragments of the protein (N-HTT). Mutant N-HTT aggregates are enriched for ubiquitin and contain ubiquitin E3 ligases, thus suggesting a role for ubiquitination in aggregate formation. Here, we report that tumor necrosis factor receptor-associated factor 6 (TRAF6) binds to WT and polyQ-expanded N-HTT in vitro as well as to endogenous full-length proteins in mouse and human brain in vivo. Endogenous TRAF6 is recruited to cellular inclusions formed by mutant N-HTT. Transient overexpression of TRAF6 promotes WT and mutant N-HTT atypical ubiquitination with Lys(6), Lys(27), and Lys(29) linkage formation. Both interaction and ubiquitination seem to be independent from polyQ length. In cultured cells, TRAF6 enhances mutant N-HTT aggregate formation, whereas it has no effect on WT N-HTT protein localization. Mutant N-HTT inclusions are enriched for ubiquitin staining only when TRAF6 and Lys(6), Lys(27), and Lys(29) ubiquitin mutants are expressed. Finally, we show that TRAF6 is up-regulated in post-mortem brains from HD patients where it is found in the insoluble fraction. These results suggest that TRAF6 atypical ubiquitination warrants investigation in HD pathogenesis.
authors: Sector of Neurobiology, International School for Advanced Studies (SISSA), via Bonomea 265, 34136 Trieste, Italy.
authors: Silvia
authors: S
authors: Zucchelli
authors: Federica
authors: F
authors: Marcuzzi
authors: Marta
authors: M
authors: Codrich
authors: Elena
authors: E
authors: Agostoni
authors: Sandra
authors: S
authors: Vilotti
authors: Marta
authors: M
authors: Biagioli
authors: Milena
authors: M
authors: Pinto
authors: Alisia
authors: A
authors: Carnemolla
authors: Claudio
authors: C
authors: Santoro
authors: Stefano
authors: S
authors: Gustincich
authors: Francesca
authors: F
authors: Persichetti
mesh_terms: D000818:Animals; D001921:Brain / Q000378:metabolism* / Q000473:pathology; D057809:HEK293 Cells; D006801:Humans; D000071058:Huntingtin Protein; D006816:Huntington Disease / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D002479:Inclusion Bodies / Q000235:genetics / Q000378:metabolism / Q000473:pathology; D051379:Mice; D009154:Mutation; D009419:Nerve Tissue Proteins / Q000235:genetics / Q000378:metabolism*; D009687:Nuclear Proteins / Q000235:genetics / Q000378:metabolism*; D010455:Peptides / Q000235:genetics / Q000378:metabolism*; D011485:Protein Binding; D021381:Protein Transport / Q000235:genetics; D048029:TNF Receptor-Associated Factor 6 / Q000235:genetics / Q000378:metabolism*; D054875:Ubiquitination
chemical_list: C086055:HTT protein, human; C506812:Htt protein, mouse; D000071058:Huntingtin Protein; D009419:Nerve Tissue Proteins; D009687:Nuclear Proteins; D010455:Peptides; D048029:TNF Receptor-Associated Factor 6; C097188:polyglutamine