Disease-associated mutations of TDP-43 promote turnover of the protein through the proteasomal pathway.
TAR DNA-binding protein (TDP-43) is a major component of most ubiquitin-positive neuronal and glial inclusions of amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration (FTLD). A number of missense mutations in the TARDBP gene have been identified in patients with familial and sporadic ALS, as well as familial FTLD with ALS. In the diseased states, TDP-43 proteins exhibit characteristic alterations, including truncation, abnormal phosphorylation, and altered subcellular distribution. However, the mechanisms by which TDP-43 mutations induce neurodegeneration remain unclear at present. In the current study, we analyzed protein turnover and subcellular distribution of wild-type TDP-43 and two disease-associated mutants (G298S and A382T) in human neuroblastoma SH-SY5Y cells stably expressing TDP-43 with a C-terminal tag. Cycloheximide chase experiments revealed more rapid turnover of TDP-43 mutant proteins than their wild-type counterpart. The decrease in the TDP-43 level after cycloheximide treatment was partially recovered upon co-treatment with the proteasome inhibitor, epoxomicin, but not the lysosomotropic agent, chloroquine, suggesting involvement of the proteasomal pathway in TDP-43 degradation. Analysis of the subcellular distribution of TDP-43 revealed predominant localization in the nuclear fraction, whereas the relative level in the cytoplasm remained unaltered in cells expressing either mutant protein, compared with wild-type protein. Our results suggest that higher turnover of disease-associated mutant TDP-43 proteins through the ubiquitin proteasome system is pathogenetically relevant and highlight the significance of proteolysis in the pathogenetic mechanism of TDP-43 proteinopathy.
Department of Demyelinating Disease and Aging, National Institute of Neuroscience, NCNP, 4-1-1 Ogawahigashi, Kodaira, Tokyo, 187-8502, Japan, araki@ncnp.go.jp.
Wataru
W
Araki
Seiji
S
Minegishi
Kazumi
K
Motoki
Hideaki
H
Kume
Hirohiko
H
Hohjoh
Yumiko M
YM
Araki
Akira
A
Tamaoka
D000690:Amyotrophic Lateral Sclerosis / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D001921:Brain / Q000378:metabolism / Q000473:pathology; D045744:Cell Line, Tumor; D004268:DNA-Binding Proteins / Q000235:genetics / Q000378:metabolism*; D057174:Frontotemporal Lobar Degeneration / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D006801:Humans; D002479:Inclusion Bodies / Q000378:metabolism; D009154:Mutation; D010766:Phosphorylation; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*
D004268:DNA-Binding Proteins; D046988:Proteasome Endopeptidase Complex