Dissecting Torsin/cofactor function at the nuclear envelope: a genetic study

• Published in: Molecular biology of the cell Vol. 27; no. 25; pp. 3964 - 3971
• Main Authors: Laudermilch, Ethan, Tsai, Pei-Ling, Graham, Morven, Turner, Elizabeth, Zhao, Chenguang, Schlieker, Christian
• Format: Journal Article
• Language: English
• Published: United States The American Society for Cell Biology 15.12.2016
• Subjects: Adenosine Triphosphatases - genetics; Adenosine Triphosphatases - metabolism; Brief Reports; HeLa Cells; Humans; Intercellular Signaling Peptides and Proteins - genetics; Intercellular Signaling Peptides and Proteins - metabolism; Membrane Proteins - metabolism; Minor Histocompatibility Antigens - genetics; Minor Histocompatibility Antigens - metabolism; Molecular Chaperones - genetics; Molecular Chaperones - metabolism; Nuclear Envelope - metabolism; Nuclear Envelope - physiology; Nuclear Pore - metabolism; Nuclear Pore Complex Proteins - metabolism
• ISSN: 1059-1524; 1939-4586; 1939-4586
• DOI: 10.1091/mbc.E16-07-0511

The human genome encodes four Torsin ATPases, the functions of which are poorly understood. In this study, we use CRISPR/Cas9 engineering to delete all four Torsin ATPases individually and in combination. Using nuclear envelope (NE) blebbing as a phenotypic measure, we establish a direct correlation between the number of inactivated Torsin alleles and the occurrence of omega-shaped herniations within the lumen of the NE. A similar, although not identical, redundancy is observed for LAP1 and LULL1, which serve as regulatory cofactors for a subset of Torsin ATPases. Unexpectedly, deletion of Tor2A in a TorA/B/3A-deficient background results in a stark increase of bleb formation, even though Tor2A does not respond to LAP1/LULL1 stimulation. The robustness of the observed phenotype in Torsin-deficient cells enables a structural analysis via electron microscopy tomography and a compositional analysis via immunogold labeling. Ubiquitin and nucleoporins were identified as distinctively localizing components of the omega-shaped bleb structure. These findings suggest a functional link between the Torsin/cofactor system and NE/nuclear pore complex biogenesis or homeostasis and establish a Torsin-deficient cell line as a valuable experimental platform with which to decipher Torsin function.