TorsinA in the nuclear envelope

Abstract

Early-onset torsion dystonia, a CNS-based movement disorder, is usually associated with a single amino acid deletion (⌬E302͞303) in the protein torsinA. TorsinA is an AAA؉ ATPase in the endoplasmic reticulum, but what it does is unknown. Here, we use torsinA mutants with defects in ATP hydrolysis (E171Q, ATP-bound) and ATP binding (K108A, ATP-free) to probe torsinA's normal cellular function. Surprisingly, ATP-bound torsinA is recruited to the nuclear envelope (NE) of transfected cells, where it alters connections between inner and outer nuclear membranes. In contrast, ATP-free torsinA is diffusely distributed throughout the endoplasmic reticulum and has no effect on the NE. Among AAA؉ ATPases, affinity for substrates is high in the ATP-bound and low in the ATP-free state, leading us to propose that component(s) of the NE may be substrates for torsinA. We also find that the disease-promoting ⌬E302͞303 mutant is in the NE, and that this relocalization, as well as the mutant's previously described ability to induce membranous inclusions, is eliminated by the K108A ATP-binding mutation. These results suggest that changes in interactions involving torsinA in the NE could be important for the pathogenesis of dystonia and point to torsinA and related proteins as a class of ATPases that may operate in the NE.

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

“…Green fluorescent protein (GFP) in previously described TorA-GFP plasmids (Naismith et al, 2004) was changed to monomeric GFP (mGFP) by sitedirected mutagenesis of L221K in GFP (Snapp et al, 2003b). TorA-TagRFP was made by transferring TorA mutants excised with XhoI and EcoRI from EGFP-N1 into a RFP-N1 vector containing TagRFP (Merzlyak et al, 2007).…”

“…Although typically found throughout the ER, several things point to a function for TorA in the NE. Reducing TorA activity by gene knockout in mice or expressing a dominant negative form of the enzyme in cultured cells (Naismith et al, 2004) selectively perturbs NE structure. The NE is the favored binding site for hydrolysis deficient "substrate trap" TorA mutants (Goodchild and Dauer, 2004;Naismith et al, 2004;Kock et al, 2006).…”

“…Reducing TorA activity by gene knockout in mice or expressing a dominant negative form of the enzyme in cultured cells (Naismith et al, 2004) selectively perturbs NE structure. The NE is the favored binding site for hydrolysis deficient "substrate trap" TorA mutants (Goodchild and Dauer, 2004;Naismith et al, 2004;Kock et al, 2006). Finally, the outer nuclear membrane protein nesprin-3 (Wilhelmsen et al, 2005) is abnormally distributed in fibroblasts from TorA knockout mice, and these cells move slower than controls in a polarized cell migration assay (Nery et al, 2008).…”

Commentary: Dopaminergic dysfunction in DYT1 dystonia

“…Within neurons, wild-type torsinA localizes to the endoplasmic reticulum (Liu et al, 2003;Naismith et al, 2004;Hewett et al, 2007), while mutant torsinA protein is found in the perinuclear space (Hewett et al, 2000;Gonzalez-Alegre and Paulson, 2004;Goodchild and Dauer, 2004). Perhaps relevant to the topic of dopaminergic dysfunction to DYT1 dystonia, associations of mutant torsinA with the vesicular monoamine transporter (VMAT2) and with alphasynuclein have been described (Sharma et al, 2001;Misbahuddin et al, 2005).…”

A Predictable Worm: Application of Caenorhabditis elegans for Mechanistic Investigation of Movement Disorders

“…The absence of the dystonia-associated glutamic acid (ΔE302) residue in torsinA results in the formation of aberrant membranous inclusions and redistribution of the protein to the nuclear envelope in neurons [57][58][59], thereby resulting in a net loss of native torsinA function at the ER. Other studies have implicated interactions between torsinA and cytoskeletal proteins termed nesprins that mediate connections between the nuclear envelope and cytoskeleton [60].…”