Phosphorylation of trans‐active response DNA‐binding protein‐of 43 kDa promotes its cytoplasmic aggregation and modulates its function in tau mRNA stability and exon 10 alternative splicing

Abstract

Trans‐active response DNA‐binding protein of 43 kDa (TDP‐43) promotes tau mRNA instability and tau exon 10 inclusion. Aggregation of phosphorylated TDP‐43 is associated with amyotrophic lateral sclerosis (ALS) and frontotemporal lobar degeneration. Casein kinase 1ε (CK1ε) phosphorylates TDP‐43 at multiple sites, enhances its cytoplasmic aggregation, and modulates its function in tau mRNA processing. To determine roles of TDP‐43 site‐specific phosphorylation in its localization, aggregation, and function in tau mRNA processing, TDP‐43 was mutated to alanine or aspartic acid at Ser379, Ser403/404, or Ser409/410 to block or mimic phosphorylation. Site‐specific phosphorylation of TDP‐43 and its mutants by CK1ε was studied in vitro and in cultured cells. Cytoplasmic and nuclear TDP‐43 and phospho‐TDP‐43 were analyzed by western blots. Aggregation of TDP‐43 was assessed by immunostaining and level of radioimmunoprecipitation assay buffer‐insoluble TDP‐43. Green florescent protein tailed with tau 3′‐untranslated region and mini‐tau gene pCI/SI9‐LI10 were used to study tau mRNA stability and alternative splicing of tau exon 10. We found that phospho‐blocking mutations of TDP‐43 at Ser379, Ser403/404, or Ser409/410 were not effectively phosphorylated by CK1ε. Compared with TDP‐43, higher level of phosphorylated TDP‐43 in the cytoplasm was observed. Phospho‐mimicking mutations at these sites enhanced cytoplasmic aggregation of TDP‐43. Green florescent protein expression was not inhibited by phospho‐blocking mutants of TDP‐43, but tau exon 10 inclusion was further enhanced by phospho‐blocking mutations at Ser379 and Ser403/404. Phosphorylation of TDP‐43 at Ser379, Ser403/404, or Ser409/410 primes its phosphorylation by CK1ε, promotes TDP‐43 cytoplasmic aggregation, and modulates its function in tau mRNA processing in site‐specific manner.

Contribution of RNA/DNA Binding Protein Dysfunction in Oligodendrocytes in the Pathogenesis of the Amyotrophic Lateral Sclerosis/Frontotemporal Lobar Degeneration Spectrum Diseases

“…In addition, indirect mechanisms could also tune Mbp transport. To this end, it is worth mentioning that FUS and TDP-43 regulate the alternative splicing and the stability of Mapt (Orozco et al, 2012;Gu et al, 2017a,b;Ishigaki et al, 2017;Wu et al, 2021), the gene coding for tau, a protein involved in the regulation of the microtubular network and necessary for Mbp mRNA transport as well as for the correct maturation and myelination process of oligodendrocytes (Seiberlich et al, 2015). Intriguingly, ubiquitous TDP-43 Q331K knock-in mice can be stratified into two populations on the basis of their behavioral impairment and affected mice display altered Mapt splicing pattern, whereas unaffected animals upregulate genes regulating myelination (White et al, 2018).…”

IκB kinase phosphorylates cytoplasmic TDP-43 and promotes its proteasome degradation

“…Phosphospecific TDP-43 antibodies against the C-terminal epitopes are standard diagnostic tools for ALS and FTLD ( Hasegawa et al, 2008 ). However, no certain conclusions have yet been drawn regarding the effect of TDP-43 protein phosphorylation on the pathogenesis of TDP-43 proteinopathy ( Liachko et al, 2010 ; Iguchi et al, 2012 ; Nonaka et al, 2016 ; Wu et al, 2021 ). Furthermore, studies on the phosphorylation of TDP-43 other than those of C-terminal remain scarce.…”

Parvalbumin interneurons dysfunction is potentially associated with FαMNs decrease and NRG1-ErbB4 signaling inhibition in spinal cord in amyotrophic lateral sclerosis

“…As one of motoneuron (MN) spectrum of diseases, amyotrophic lateral sclerosis (ALS) is mainly characterized by the progressive death of MNs and early denervation of the neuromuscular junction [ 1 – 3 ]. As reported, the incidence of ALS is about 2/10,000 worldwide, with the mean onset age of 55~60 [ 4 ].…”