Disease-associated mutations of TDP-43 promote turnover of the protein through the proteasomal pathway.

Abstract

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.

• Authors: Wataru Araki, Seiji Minegishi, Kazumi Motoki, Hideaki Kume, Hirohiko Hohjoh, Yumiko M Araki, Akira Tamaoka
• Journal: Molecular neurobiology (Mol Neurobiol) Vol. 50 Issue 3 Pg. 1049-58 (Dec 2014) ISSN: 1559-1182 [Electronic] United States
• PMID: 24477737 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)

Chemical References

• DNA-Binding Proteins
• Proteasome Endopeptidase Complex

Topics

• Amyotrophic Lateral Sclerosis (genetics, metabolism, pathology)
• Brain (metabolism, pathology)
• Cell Line, Tumor
• DNA-Binding Proteins (genetics, metabolism)
• Frontotemporal Lobar Degeneration (genetics, metabolism, pathology)
• Humans
• Inclusion Bodies (metabolism)
• Mutation
• Phosphorylation
• Proteasome Endopeptidase Complex (metabolism)