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.

Early onset generalized dystonia (DYT1) is an autosomal dominant neurological disorder caused by deletion of a single glutamate residue (torsinA ⌬E) in the C-terminal region of the AAA ؉ (ATPases associated with a variety of cellular activities) protein torsinA. The pathogenic mechanism by which torsinA ⌬E mutation leads to dystonia remains unknown. Here we report the identification and characterization of a 628-amino acid novel protein, printor, that interacts with torsinA. Printor co-distributes with torsinA in multiple brain regions and colocalizes with torsinA in the endoplasmic reticulum. Interestingly, printor selectively binds to the ATP-free form but not to the ATP-bound form of torsinA, supporting a role for printor as a cofactor rather than a substrate of torsinA. The interaction of printor with torsinA is completely abolished by the dystoniaassociated torsinA ⌬E mutation. Our findings suggest that printor is a new component of the DYT1 pathogenic pathway and provide a potential molecular target for therapeutic intervention in dystonia.Early onset generalized torsion dystonia (DYT1) is the most common and severe form of hereditary dystonia, a movement disorder characterized by involuntary movements and sustained muscle spasms (1). This autosomal dominant disease has childhood onset and its dystonic symptoms are thought to result from neuronal dysfunction rather than neurodegeneration (2, 3). Most DYT1 cases are caused by deletion of a single glutamate residue at positions 302 or 303 (torsinA ⌬E) of the 332-amino acid protein torsinA (4). In addition, a different torsinA mutation that deletes amino acids Phe 323 -Tyr 328(torsinA ⌬323-328) was identified in a single family with dystonia (5), although the pathogenic significance of this torsinA mutation is unclear because these patients contain a concomitant mutation in another dystonia-related protein, ⑀-sarcoglycan (6). Recently, genetic association studies have implicated polymorphisms in the torsinA gene as a genetic risk factor in the development of adult-onset idiopathic dystonia (7,8).TorsinA contains an N-terminal endoplasmic reticulum (ER) 3 signal sequence and a 20-amino acid hydrophobic region followed by a conserved AAA ϩ (ATPases associated with a variety of cellular activities) domain (9, 10). Because members of the AAA ϩ family are known to facilitate conformational changes in target proteins (11,12), it has been proposed that torsinA may function as a molecular chaperone (13,14). TorsinA is widely expressed in brain and multiple other tissues (15) and is primarily associated with the ER and nuclear envelope (NE) compartments in cells (16 -20). TorsinA is believed to mainly reside in the lumen of the ER and NE (17-19) and has been shown to bind lamina-associated polypeptide 1 (LAP1) (21), lumenal domain-like LAP1 (LULL1) (21), and nesprins (22). In addition, recent evidence indicates that a significant pool of torsinA exhibits a topology in which the AAA ϩ domain faces the cytoplasm (20). In support of this topology, torsinA is found in the...

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