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Mutant torsinA in the heterozygous DYT1 state compromises HSV propagation in infected neurons and fibroblasts.

ABSTRACT: Most cases of early onset torsion dystonia (DYT1) are caused by a 3-base pair deletion in one allele of the TOR1A gene causing loss of a glutamate in torsinA, a luminal protein in the nuclear envelope. This dominantly inherited neurologic disease has reduced penetrance and no other medical manifestations. It has been challenging to understand the neuronal abnormalities as cells and mouse models which are heterozygous (Het) for the mutant allele are quite similar to wild-type (WT) controls. Here we found that patient fibroblasts and mouse neurons Het for this mutation showed significant differences from WT cells in several parameters revealed by infection with herpes simplex virus type 1 (HSV) which replicates in the nucleus and egresses out through the nuclear envelope. Using a red fluorescent protein capsid to monitor HSV infection, patient fibroblasts showed decreased viral plaque formation as compared to controls. Mouse Het neurons had a decrease in cytoplasmic, but not nuclear HSV fluorescence, and reduced numbers of capsids entering axons as compared to infected WT neurons. These findings point to altered dynamics of the nuclear envelope in cells with the patient genotype, which can provide assays to screen for therapeutic agents that can normalize these cells.

SUBMITTER: Gyorgy B

PROVIDER: S-EPMC5797141 | biostudies-literature | 2018 Feb

REPOSITORIES: biostudies-literature

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Mutant torsinA in the heterozygous DYT1 state compromises HSV propagation in infected neurons and fibroblasts.

György Bence B Cruz Lilian L Yellen David D Aufiero Massimo M Alland Isabel I Zhang Xuan X Ericsson Maria M Fraefel Cornel C Li Yu-Ching YC Takeda Shuko S Hyman Bradley T BT Breakefield Xandra O XO

Scientific reports 20180202 1

Most cases of early onset torsion dystonia (DYT1) are caused by a 3-base pair deletion in one allele of the TOR1A gene causing loss of a glutamate in torsinA, a luminal protein in the nuclear envelope. This dominantly inherited neurologic disease has reduced penetrance and no other medical manifestations. It has been challenging to understand the neuronal abnormalities as cells and mouse models which are heterozygous (Het) for the mutant allele are quite similar to wild-type (WT) controls. Here ...[more]

PMID: 29396398

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Project description:DYT1 is the most common inherited dystonia, a neurological syndrome that causes disabling involuntary muscle contractions. This autosomal dominant disease is caused by a glutamic acid deletion near the carboxy-terminus in the protein torsinA. Cell- and animal-based studies have shown how the DYT1 mutation causes mutant torsinA to redistribute from the endoplasmic reticulum to the nuclear envelope, acting through a dominant negative effect over the wild type protein. As a result, the wild type:mutant torsinA expression ratio would be important for disease pathogenesis, and events that influence it, such as a differential degradation process for each protein, might modulate DYT1 pathobiology. The DYT1 mutation also triggers the formation of abnormal intermolecular disulfide bonds in torsinA, although the significance of this finding is unclear. How the protein quality control machinery handles torsinA, and whether this process is affected by its abnormal oligomerization remain unknown. Here, we first explored how the disease-linked mutation influences the catabolic process of human torsinA, demonstrating that the differences in subcellular localization between both forms of torsinA lead to divergences in their degradation pathways and, whereas torsinA is normally recycled through autophagy, the proteasome is also required for the efficient clearance of the mutated form. Subsequently, we determined that the abnormal disulfide bond-dependent oligomerization of mutant torsinA is not a result of its redistribution to the nuclear envelope, but a direct consequence of the mutation. Finally, we established that the presence of disulfide links in mutant torsinA oligomers interfere with their degradation by the proteasome, thus relying on autophagy as the main pathway for clearance. In conclusion, the abnormal subcellular localization and oligomerization of DYT1-linked torsinA influences its catabolic process, opening the door to the modulation of the wild type:mutant torsinA ratio through pharmacological manipulation of protein degradation pathways.

Project description: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.

Dataset Information

Mutant torsinA in the heterozygous DYT1 state compromises HSV propagation in infected neurons and fibroblasts.

Publications

Mutant torsinA in the heterozygous DYT1 state compromises HSV propagation in infected neurons and fibroblasts.

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