Cell Stress Induces Mislocalization of Transcription Factors with Mitochondrial Enrichment

Abstract

Previous evidence links the formation of extranuclear inclusions of transcription factors, such as ERK, Jun, TDP-43, and REST with oxidative, endoplasmic-reticulum, proteasomal, and osmotic stress. To further characterize its extranuclear location, we performed a high-content screening based on confocal microscopy and automatized image analyses of an epithelial cell culture treated with hydrogen peroxide, thapsigargin, epoxomicin, or sorbitol at different concentrations and times to recreate the stresses mentioned above. We also performed subcellular fractionation of the brain from transgenic mice overexpressing the Q331K mutated TARDBP, and we analyzed REST-regulated mRNAs. The results show that these nuclear proteins exhibit a mitochondrial location, together with significant nuclear/extranuclear ratio changes, in a protein and stress-specific manner. The presence of these proteins in enriched mitochondrial fractions in vivo confirmed the results of image analyses. TDP-43 aggregation was associated with alteration in mRNA levels of REST target genes involved in calcium homeostasis, apoptosis, and metabolism. In conclusion, cell stress increased mitochondrial translocation of nuclear proteins, increasing the chance of proteostasis alterations. Further, TDP-43 aggregation impacts REST target genes, disclosing an exciting interaction between these two transcription factors in neurodegenerative processes.

Unraveling the toxic effects mediated by the neurodegenerative disease–associated S375G mutation of TDP-43 and its S375E phosphomimetic variant

“…Many recent observations have linked the presence of mitochondrial problems in several neuronal populations in the presence of TDP-43 aggregation or toxic C-terminal fragment expression (88)(89)(90)(91)(92). Moreover, TDP-43 itself has been described to be present in mitochondrial fractions of transgenic mice overexpressing the Q331K disease-associated mutant (93) and interact with mitochondrial proteins to influence the dynamics of these organelles (94). Indeed, inhibition of TDP-43 mitochondrial localization has been shown to block its neuronal toxicity (95).…”