Truncation of the TAR DNA-binding protein 43 is not a prerequisite for cytoplasmic relocalization, and is suppressed by caspase inhibition and by introduction of the A90V sequence variant

PLoS One. 2017 May 16;12(5):e0177181. doi: 10.1371/journal.pone.0177181. eCollection 2017.

Abstract

The RNA-binding and -processing protein TAR DNA-binding protein 43 (TDP-43) is heavily linked to the underlying causes and pathology of neurodegenerative diseases such as amyotrophic lateral sclerosis and frontotemporal lobar degeneration. In these diseases, TDP-43 is mislocalized, hyperphosphorylated, ubiquitinated, aggregated and cleaved. The importance of TDP-43 cleavage in the disease pathogenesis is still poorly understood. Here we detail the use of D-sorbitol as an exogenous stressor that causes TDP-43 cleavage in HeLa cells, resulting in a 35 kDa truncated product that accumulates in the cytoplasm within one hour of treatment. We confirm that the formation of this 35 kDa cleavage product is mediated by the activation of caspases. Inhibition of caspases blocks the cleavage of TDP-43, but does not prevent the accumulation of full-length protein in the cytoplasm. Using D-sorbitol as a stressor and caspase activator, we also demonstrate that the A90V variant of TDP-43, which lies adjacent to the caspase cleavage site within the nuclear localization sequence of TDP-43, confers partial resistance against caspase-mediated generation of the 35 kDa cleavage product.

MeSH terms

  • Amino Acid Substitution
  • Caspases / metabolism
  • Codon*
  • Cytoplasm / metabolism
  • DNA-Binding Proteins / chemistry
  • DNA-Binding Proteins / genetics*
  • DNA-Binding Proteins / metabolism*
  • Genetic Variation*
  • HeLa Cells
  • Humans
  • Mutation
  • Osmotic Pressure
  • Oxidative Stress
  • Protein Binding
  • Protein Interaction Domains and Motifs
  • Protein Transport / drug effects
  • Proteolysis
  • Sorbitol / pharmacology

Substances

  • Codon
  • DNA-Binding Proteins
  • TDP-43 protein, human
  • Sorbitol
  • Caspases

Grant support

This work was supported by funding from AstraZeneca, National Institutes of Health (NIH)–National Institute of Neurological Disorders and Stroke Grants NS051195, NS056359, NS081735, R21NS080064 and NS087662 (SJM) and NIH–National Institute of Mental Health Grants MH097446, MH106954 and DOD, AR140209 (SJM). AstraZeneca provided support in the form of salaries [NJB, LD]. The specific roles of authors NJB and LD are articulated in the ‘author contributions’ section.