BACKGROUND: Machado-Joseph Disease (MJD), a form of dominantly inherited ataxia belonging to the group of polyQ expansion neurodegenerative disorders, occurs when a threshold value for the number of glutamines in Ataxin-3 (Atx3) polyglutamine region is exceeded. As a result of its modular multidomain architecture, Atx3 is known to engage in multiple macromolecular interactions, which might be unbalanced when the polyQ tract is expanded, culminating in the aggregation and formation of intracellular inclusions, a unifying fingerprint of this group of neurodegenerative disorders. Since aggregation is specific to certain brain regions, localization-dependent posttranslational modifications that differentially affect Atx3 might also contribute for MJD. METHODS: We combined in vitro and cellular approaches to address SUMOylation in the brain-predominant Atx3 isoform and assessed the impact of this posttranslational modification on Atx3 self-assembly and interaction with its native partner, p97. RESULTS: We demonstrate that Atx3 is SUMOylated at K356 both in vitro and in cells, which contributes for decreased formation of amyloid fibrils and for increased affinity towards p97. CONCLUSIONS AND GENERAL SIGNIFICANCE: These findings highlight the role of SUMOylation as a regulator of Atx3 function, with implications on Atx3 protein interaction network and self-assembly, with potential impact for further understanding the molecular mechanisms underlying MJD pathogenesis.

This work was funded by the Fundação para a Ciência e a Tecnologia (FCT, Portugal) through grants PTDC/BIA-PRO/100059/2008 and PTDC/SAU-NMC/110602/2009 (EU-FEDER funding through COMPETEFCOMP-01-0124-FEDER-009031 and FCOMP-01-0124-FEDER-015860, respectively), and by QREN — Quadro de Referência Estratégica Nacional through Programa Operacional Regional do Norte ON. 2 (Neurodegenerative Disorders — NORTE-01-0124-FEDER-000001). C.M., S.F., I.A.A. and B.A. acknowledge the financial support from FCT through fellowships SFRH/BD/47160/2008, SFRH/BPD/77009/2011, Ciência 2008 Programme, and SFRH/BPD/70783/2010, respectively.