Dystonia-associated mutations cause premature degradation of torsinA protein and cell-type-specific mislocalization to the nuclear envelope

Abstract

An in-frame 3 bp deletion in the torsinA gene resulting in the loss of a glutamate residue at position 302 or 303 (torsinA DeltaE) is the major cause for early-onset torsion dystonia (DYT1). In addition, an 18 bp deletion in the torsinA gene resulting in the loss of residues 323-328 (torsinA Delta323-8) has also been associated with dystonia. Here we report that torsinA DeltaE and torsinA Delta323-8 mutations cause neuronal cell-type-specific mislocalization of torsinA protein to the nuclear envelope without affecting torsinA oligomerization. Furthermore, both dystonia-associated mutations destabilize torsinA protein in dopaminergic cells. We find that wild-type torsinA protein is degraded primarily through the macroautophagy-lysosome pathway. In contrast, torsinA DeltaE and torsinA Delta323-8 mutant proteins are degraded by both the proteasome and macroautophagy-lysosome pathways. Our findings suggest that torsinA mutation-induced premature degradation may contribute to the pathogenesis of dystonia via a loss-of-function mechanism and underscore the importance of both the proteasome and macroautophagy in the clearance of dystonia-associated torsinA mutant proteins.

LULL1 Retargets TorsinA to the Nuclear Envelope Revealing an Activity That Is Impaired by theDYT1Dystonia Mutation

“…As expected, TorA-mGFP is distributed evenly throughout the ER ( Figure 1A, left). The dystoniacausative mutant, ⌬GAG-TorA, also localizes to the ER but is enriched in the contiguous NE as expected based on earlier studies (Figure 1A, middle;Goodchild and Dauer, 2004;Naismith et al, 2004;Giles et al, 2008). TorA's binding partner LULL1-myc is also found throughout the ER ( Figure 1A, right).…”

“…Furthermore, AAAϩ proteins typically function as higher order oligomers, typically either hexamers or dodecamers (Hanson and Whiteheart, 2005). However, previous analyses of TorA's oligomeric state had not identified any such large assemblies (Kustedjo et al, 2003), although TorA can selfassociate as judged by coimmunoprecipitation (Torres et al, 2004;Giles et al, 2008). To reconcile these two lines of data, we hypothesized that TorA oligomers might be disrupted by the detergents used to prepare previous samples for analysis.…”

“…The DYT1 ⌬GAG Mutation Impairs the Effects of TorA on the NE ⌬GAG-TorA has consistently been found to be more enriched in the NE than is wild-type TorA (Gonzalez-Alegre and Paulson, 2004;Goodchild and Dauer, 2004;Naismith et al, 2004;Giles et al, 2008), leading to the hypothesis that mislocalization to the NE might contribute to the development of dystonia (Goodchild and Dauer, 2004). At the same time, ⌬GAG-TorA is thought to be less functional and less stable than wild-type TorA such that loss of normal enzyme function could underlie the disease Giles et al, 2008;Gordon and Gonzalez-Alegre, 2008).…”

“…At the same time, ⌬GAG-TorA is thought to be less functional and less stable than wild-type TorA such that loss of normal enzyme function could underlie the disease Giles et al, 2008;Gordon and Gonzalez-Alegre, 2008). As shown in Figure 1 and Supplemental Figure S2, coexpressing LULL1 with ⌬GAG-TorA-mGFP caused it to enrich further in the NE, albeit without the distinctive polarity that characterized the shift of wild-type protein.…”

Mutation in TOR1AIP1 encoding LAP1B in a form of muscular dystrophy: A novel gene related to nuclear envelopathies

“…TorsinA is diffusely distributed throughout the endoplasmic reticulum and the nuclear envelope continuity but some cell types exhibit a preference for the nuclear envelope [24,25]. Luminal domain-like LAP1 (LULL1) encoded by TOR1AIP2 is located in the endoplasmic reticulum and shares homologous C-terminal regions with LAP1 allowing interaction with ER-located torsinA [11,24].…”