title: Transportin 1 colocalization with Fused in Sarcoma (FUS) inclusions is not characteristic for amyotrophic lateral sclerosis-FUS confirming disrupted nuclear import of mutant FUS and distinguishing it from frontotemporal lobar degeneration with FUS inclusions.
abstract: OBJECTIVE
  Transportin 1 (TNPO 1) is an abundant component of the Fused in Sarcoma (FUS)-immunopositive inclusions seen in a subgroup of frontotemporal lobar degeneration (FTLD-FUS). TNPO 1 has been shown to bind to the C-terminal nuclear localizing signal (NLS) of FUS and mediate its nuclear import. Amyotrophic lateral sclerosis (ALS)-linked C-terminal mutants disrupt TNPO 1 binding to the NLS and impair nuclear import in cell culture. If this held true for human ALS then we predicted that FUS inclusions in patients with C-terminal FUS mutations would not colocalize with TNPO 1.
  
  
  METHODS
  Expression of TNPO 1 and colocalization with FUS was studied in the frontal cortex of FTLD-FUS (n = 3) and brain and spinal cord of ALS-FUS (n = 3), ALS-C9orf72 (n = 3), sporadic ALS (n = 7) and controls (n = 7). Expression levels and detergent solubility of TNPO 1 was measured by Western blot.
  
  
  RESULTS
  Aggregates of TNPO 1 were abundant and colocalized with FUS inclusions in the cortex of all FTLD-FUS cases. In contrast, no TNPO 1-positive aggregates or FUS colocalization was evident in two-thirds, ALS-FUS cases and was rare in one ALS-FUS case. Nor were they present in C9orf72 or sporadic ALS. No increase in the levels of TNPO 1 was seen in Western blots of spinal cord tissues from all ALS cases compared with controls.
  
  
  CONCLUSIONS
  These findings confirm that C-terminal FUS mutations prevent TNPO 1 binding to the NLS, inhibiting nuclear import and promoting cytoplasmic aggregation. The presence of TNPO 1 in wild-type FUS aggregates in FTLD-FUS distinguishes the two pathologies and implicates different disease mechanisms.
authors.affiliation: KHP Centre for Neurodegeneration Research, Institute of Psychiatry Department of Clinical Neuropathology, King's College London, London, UK. claire.troakes@kcl.ac.uk
authors.forename: C
authors.initials: C
authors.lastname: Troakes
authors.forename: T
authors.initials: T
authors.lastname: Hortobágyi
authors.forename: C
authors.initials: C
authors.lastname: Vance
authors.forename: S
authors.initials: S
authors.lastname: Al-Sarraj
authors.forename: B
authors.initials: B
authors.lastname: Rogelj
authors.forename: C E
authors.initials: CE
authors.lastname: Shaw
mesh_terms: D000328:Adult; D000368:Aged; D000690:Amyotrophic Lateral Sclerosis / Q000175:diagnosis* / Q000378:metabolism / Q000473:pathology; D001921:Brain / Q000378:metabolism* / Q000473:pathology; D003937:Diagnosis, Differential; D005260:Female; D057174:Frontotemporal Lobar Degeneration / Q000175:diagnosis* / Q000378:metabolism / Q000473:pathology; D006801:Humans; D002479:Inclusion Bodies / Q000378:metabolism / Q000473:pathology; D008297:Male; D008875:Middle Aged; D009474:Neurons / Q000378:metabolism / Q000473:pathology; D034702:RNA-Binding Protein FUS / Q000378:metabolism*; D013116:Spinal Cord / Q000378:metabolism* / Q000473:pathology; D028961:beta Karyopherins / Q000378:metabolism*
chemical_list: D034702:RNA-Binding Protein FUS; C108121:TNPO1 protein, human; D028961:beta Karyopherins