1. Unraveling Cellular Phenotypes of Novel TorsinA/TOR1A Mutations

Unraveling Cellular Phenotypes of Novel TorsinA/TOR1A Mutations

Franca Vulinović 1 Katja Lohmann, PhD 1 Aleksandar Rakovic, PhD 1 Philipp Capetian, MD 1 Daniel Alvarez-Fischer, MD 1 Alexander Schmidt, PhD 1 Anne Weißbach, MD 1 Alev Erogullari 1 Frank J. Kaiser, PhD 1 Karin Wiegers 1 Prof. Andreas Ferbert, MD 2 Prof. Arndt Rolfs, MD 3 Prof. Christine Klein, MD 1 Philip Seibler, PhD 1
1 University of Luebeck 2 Klinikum Kassel 3 University of Rostock
June 13, 2014

Human Mutation DOI: 10.1002/humu.22604

Abstract: A three-nucleotide (GAG) deletion (E) in TorsinA (TOR1A) has been identified as the most common cause of dominantly inherited early-onset torsion dystonia (DYT1). TOR1A encodes a chaperone-like AAA+-protein localized in the  endoplasmic reticulum. Currently, only three additional, likely mutations have been reported in single dystonia patients. Here, we report two new, putative TOR1A mutations (p.A14_P15del and p.E121K) that we examined functionally in comparison with wildtype (WT) protein and two known mutations (E and p.R288Q). While inclusion formation is a characteristic feature for E TOR1A, elevated levels of aggregates for other mutations were not observed when compared with WT TOR1A. WT and mutant TOR1A showed preferred  degradation through the autophagy-lysosome pathway, which is most pronounced for p.A14_P15del, p.R288Q, and E TOR1A. Notably, blocking of the autophagy pathway with bafilomycin resulted in a significant increase in inclusion formation in p.E121K TOR1A. In addition, all variants had an influence on protein stability. Although the p.A14_P15del mutation affects the proposed oligomerization domain of TOR1A, this mutation did not disturb the ability to dimerize. Our findings demonstrate functional changes for all four mutations on different levels. Thus, both diagnostic and research genetic screening of  dystonia patients should not be limited to testing for the E mutation.