Abstract
The nuclear RNA-binding protein TDP-43 forms abnormal cytoplasmic aggregates in the brains of amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD) patients and several molecular mechanisms promoting TDP-43 cytoplasmic mislocalization and aggregation have been proposed, including defects in nucleocytoplasmic transport, stress granules (SG) disassembly and post-translational modifications (PTM). SUMOylation is a PTM which regulates a variety of cellular processes and, similarly to ubiquitination, targets lysine residues. To investigate the possible regulatory effects of SUMOylation on TDP-43 activity and trafficking, we first assessed that TDP-43 is SUMO-conjugated in the nuclear compartment both covalently and non-covalently in the RRM1 domain at the predicted lysine 136 and SUMO-interacting motif (SIM, 106–110 residues), respectively. By using the SUMO-mutant TDP-43 K136R protein, we demonstrated that SUMOylation modifies TDP-43 splicing activity, specifically exon skipping, and influences its sub-cellular localization and recruitment to SG after oxidative stress. When promoting deSUMOylation by SENP1 enzyme over-expression or by treatment with the cell-permeable SENP1 peptide TS-1, the cytoplasmic localization of TDP-43 increased, depending on its SUMOylation. Moreover, deSUMOylation by TS-1 peptide favoured the formation of small cytoplasmic aggregates of the C-terminal TDP-43 fragment p35, still containing the SUMO lysine target 136, but had no effect on the already formed p25 aggregates. Our data suggest that TDP-43 can be post-translationally modified by SUMOylation which may regulate its splicing function and trafficking, indicating a novel and druggable mechanism to explore as its dysregulation may lead to TDP-43 pathological aggregation in ALS and FTD.
Highlights
TDP-43 is an ubiquitous RNA-binding protein (RBP) localized in the nucleus where it mainly regulates splicing but, by shuttling between the nucleus and the cytoplasm, it controls RNA metabolism at different levels, including miRNA biogenesis, mRNA transport, stability and translation [1]
The two predicted SUMO binding sites are both located within the TDP-43 RRM1 domain, which is highly conserved along phylogenesis (Supplementary Fig. 1a) and has an important function for target RNA recognition and binding
TDP-43 was reported to be modified by SUMO-1 in murine tissues and human experimental TDP-43 cell models [23, 24] and preliminary data already indicated that cytotoxic stress in HeLa cells was able to up-regulate protein SUMOylation, including that of TDP-43 [21]
Summary
TDP-43 is an ubiquitous RNA-binding protein (RBP) localized in the nucleus where it mainly regulates splicing but, by shuttling between the nucleus and the cytoplasm, it controls RNA metabolism at different levels, including miRNA biogenesis, mRNA transport, stability and translation [1]. Extended author information available on the last page of the article are found in the cytoplasm of both neuronal and glial cells [2,3,4]. In these pathological aggregates, TDP-43 is posttranslationally modified by C-terminal cleavage, ubiquitination, phosphorylation and acetylation [5]. The occurring post-translational modifications (PTM) primarily seem to reduce TDP-43 solubility and to induce its aggregation [5], but acetylation was shown to decrease its RNA-binding and splicing activities [6]. How and whether all these PTM are interconnected in regulating TDP-43 function and in promoting its pathological aggregation is still unknown
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
