title: Nuclear import impairment causes cytoplasmic trans-activation response DNA-binding protein accumulation and is associated with frontotemporal lobar degeneration.
abstract: Trans-activation response DNA-binding protein (TDP-43) accumulation is the major component of ubiquitinated protein inclusions found in patients with amyotrophic lateral sclerosis, and frontotemporal lobar degeneration with TDP-43 positive ubiquitinated inclusions, recently relabelled the 'TDP-43 proteinopathies'. TDP-43 is predominantly located in the nucleus, however, in disease it mislocalizes to the cytoplasm where it aggregates to form hallmark pathological inclusions. The identification of TDP-43 mutations in familial and sporadic amyotrophic lateral sclerosis cases confirms its pathogenic role; but it is wild-type TDP-43 that is deposited in the vast majority of TDP-43 proteinopathies, implicating other unknown factors for its mislocalization and aggregation. One such mechanism may be defective nuclear import of TDP-43 protein, as a disruption of its nuclear localization signal leads to mislocalization and aggregation of TDP-43 in the cytoplasm. In order to explore the factors that regulate the nuclear import of TDP-43, we used a small interfering RNA library to silence 82 proteins involved in nuclear transport and found that knockdowns of karyopherin-beta1 and cellular apoptosis susceptibility protein resulted in marked cytoplasmic accumulation of TDP-43. In glutathione S-transferase pull-down assays, TDP-43 bound to karyopherin-alphas, thereby confirming the classical nuclear import pathway for the import of TDP-43. Analysis of the expression of chosen nuclear import factors in post-mortem brain samples from patients with TDP-43 positive frontotemporal lobar degeneration, and spinal cord samples from patients with amyotrophic lateral sclerosis, revealed a considerable reduction in expression of cellular apoptosis susceptibility protein in frontotemporal lobar degeneration. We propose that cellular apoptosis susceptibility protein associated defective nuclear transport may play a mechanistic role in the pathogenesis of the TDP-43 positive frontotemporal lobar degeneration.
authors.affiliation: Medical Research Council (MRC) Centre for Neurodegeneration Research, King's College London, Institute of Psychiatry, London, SE5 8AF, UK.
authors.forename: Agnes L
authors.initials: AL
authors.lastname: Nishimura
authors.forename: Vera
authors.initials: V
authors.lastname: Zupunski
authors.forename: Claire
authors.initials: C
authors.lastname: Troakes
authors.forename: Claudia
authors.initials: C
authors.lastname: Kathe
authors.forename: Pietro
authors.initials: P
authors.lastname: Fratta
authors.forename: Michael
authors.initials: M
authors.lastname: Howell
authors.forename: Jean-Marc
authors.initials: JM
authors.lastname: Gallo
authors.forename: Tibor
authors.initials: T
authors.lastname: Hortobágyi
authors.forename: Christopher E
authors.initials: CE
authors.lastname: Shaw
authors.forename: Boris
authors.initials: B
authors.lastname: Rogelj
mesh_terms: D021581:Active Transport, Cell Nucleus / Q000502:physiology*; D000368:Aged; D000690:Amyotrophic Lateral Sclerosis / Q000378:metabolism; D000818:Animals; D001921:Brain / Q000378:metabolism; D002460:Cell Line; D045744:Cell Line, Tumor; D029563:Cellular Apoptosis Susceptibility Protein / Q000378:metabolism; D003593:Cytoplasm / Q000378:metabolism*; D004268:DNA-Binding Proteins / Q000378:metabolism*; D005260:Female; D057174:Frontotemporal Lobar Degeneration / Q000378:metabolism*; D005982:Glutathione Transferase / Q000378:metabolism; D006801:Humans; D008297:Male; D051379:Mice; D008875:Middle Aged; D015398:Signal Transduction / Q000235:genetics; D013116:Spinal Cord / Q000378:metabolism; D028901:alpha Karyopherins / Q000378:metabolism; D028961:beta Karyopherins / Q000378:metabolism
chemical_list: D029563:Cellular Apoptosis Susceptibility Protein; D004268:DNA-Binding Proteins; C424166:KPNB1 protein, human; D028901:alpha Karyopherins; D028961:beta Karyopherins; D005982:Glutathione Transferase