The nuclear envelope localization of DYT1 dystonia torsinA-ΔE requires the SUN1 LINC complex component

Abstract

BackgroundDYT1 dystonia is an autosomal dominant neurological condition caused by a mutation that removes a single glutamic acid residue (ΔE) from the torsinA (torA) AAA+ protein. TorA appears to possess a nuclear envelope (NE) localized activity that requires Lamina-Associated-Polypeptide 1 (LAP1), which is an inner nuclear membrane localized torA-binding partner. Although hypoactive, the DYT1 dystonia torA-ΔE isoform often concentrates in the NE, suggesting that torA-ΔE also interacts with an NE-localized binding partner.ResultsWe confirm that NE-localized torA-ΔE does not co-immunoprecipitate with LAP1, and find that torA-ΔE continues to concentrate in the NE of cells that lack LAP1. Instead, we find that variability in torA-ΔE localization correlates with the presence of the SUN-domain and Nesprin proteins that assemble into the LINC complex. We also find that siRNA depletion of SUN1, but not other LINC complex components, removes torA-ΔE from the NE. In contrast, the LAP1-dependent NE-accumulation of an ATP-locked torA mutant is unaffected by loss of LINC complex proteins. This SUN1 dependent torA-ΔE localization requires the torA membrane association domain, as well as a putative substrate-interaction residue, Y147, neither of which are required for torA interaction with LAP1. We also find that mutation of these motifs, or depletion of SUN1, decreases the amount of torA-WT that colocalizes with NE markers, indicating that each also underlies a normal NE-localized torA binding interaction.ConclusionsThese data suggest that the disease causing ΔE mutation promotes an association between torA and SUN1 that is distinct to the interaction between LAP1 and ATP-bound torA. This evidence for two NE-localized binding partners suggests that torA may act on multiple substrates and/or possesses regulatory co-factor partners. In addition, finding that the DYT1 mutation causes abnormal association with SUN1 implicates LINC complex dysfunction in DYT1 dystonia pathogenesis, and suggests a gain-of-function activity contributes to this dominantly inherited disease.

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

“…Although knockdown of LAP1 or LULL1 does not seem to affect expression or localization of torsinA, mice lacking LAP1 exhibit perinatal lethality and LAP1 deficiency causes nuclear membrane abnormalities similar to those observed in torsinA-null cells [13,27]. On the other hand, overexpression of LAP1 and LULL1 recruits torsinA to the nuclear envelope [11,28].…”

“…LAP1 is not the sole torsinA partner localized in the nuclear envelope. Other torsinA-binding partners, including components of the LINC complex SUN1, SUN2 and nesprins, have been described [27,31,32]. A possible consequence of LAP1B deficiency might be altered interaction of cytoskeletal components with the nuclear envelope via misbinding of torsinA to other partners in the absence of LAP1B.…”

Access of torsinA to the inner nuclear membrane is activity dependent and regulated in the endoplasmic reticulum

“…The fact that torsinA entering the INM after LULL1-driven complex dissociation tends to remain there rather than diffusing back to the ONM and peripheral ER might be the result of differences between LULL1 and LAP1 including the fact that LAP1 is a less potent activator of torsinA than LULL1 (Zhao et al, 2013) and is far less mobile than LULL1 (Zuleger et al, 2011;Vander Heyden et al, 2009). However, the picture underlying torsinA retention in the INM is complex and there is evidence that multiple factors, including additional INM-localized torsinA-binding partners, influence torsinA retention (Jungwirth et al, 2011).…”

“…Cells were fixed and stained as described previously (Jungwirth et al, 2011;Vander Heyden et al, 2009). For selective permeabilization, fixed cells were incubated in buffer containing 0.1% Triton X-100 or 0.001% digitonin for 10 min on ice.…”

Inherited Isolated Dystonia: Clinical Genetics and Gene Function

“…Nesprins are anchored to NE through binding to SUN protein family members, which themselves are localized to the inner nuclear membrane. TorsinA has been reported to interact with SUN1 [75] and Nesprin-3, which itself is mislocalized in murine torsinA null fibroblasts and DYT1 patient fibroblasts. Overexpression of torsinA in a neuronal cell line inhibits neurite outgrowth [76], an effect that may relate to its interactions with nesprin-3 [77].…”