Driving Forces of TDP-43 Phase Transitions and their Physiological and Pathological Consequences in Cells
Aberrant liquid-to-solid phase transitions of RNA-binding proteins (RBPs) with prion-like low complexity domains (LCD) are thought to underlie the formation of pathological RBP aggregates in a number of neurodegenerative diseases, most notably amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). In most ALS and FTD cases, the aggregating RBP is TDP-43, a ubiquitously expressed nuclear protein involved in multiple steps of RNA processing. Mutations in TDP-43 cause familial ALS and are mostly clustered in the C-terminal LCD.
Aggregated TDP-43 is abnormally post-translationally modified in ALS and FTD patients, e.g. by phosphorylation and N-terminal truncation. How disease-linked LCD mutations and abnormal post-translational modifications (PTMs) affect LLPS or aberrant liquid-to-solid transitions of TDP-43 is so far not known. Moreover, it is unclear how altered phase separation behavior of TDP-43 affects its physiological functions, its intracellular trafficking and the dynamics of TDP-43-containing membrane-less organelles, e.g. stress granules (SG). This proposal aims at (1) deciphering how disease-linked changes in the protein sequence of TDP-43 affect its phase transition behavior and (2) elucidating the cellular consequences of such altered phase transition behavior.
Current State of Research
Currently, we are mainly focusing on understanding how disease-linked hyperphosphorylation of serine residues in the C-terminal LCD of TDP-43 affects the phase separation behavior of TDP-43 as well as the protein’s cellular localization, physiological function and partitioning into SG. To this end we have introduced phosphomimetic serine-to-aspartate mutations into the C-terminal LCD of TDP-43 or in vitro phosphorylated TDP-43 with Casein kinase 1 (CK1). Presently, we are studying the impact of LCD phosphorylation on the phase separation behavior, e.g. critical concentration and material properties of TDP-43 condensates. Further studies in cells will reveal the impact of TDP-43 phosphomimetic mutations on TDP-43’s physiological function in pre-mRNA splicing regulation, its nucleocytoplasmic shuttling, its recruitment into membrane-less organelles and its stability/degradation.
The Dormann lab is focused on the role of RNA-binding proteins in neurodegenerative diseases, especially amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). We are especially interested in two nuclear RNA-binding proteins (FUS and TDP-43), which are genetically linked to ALS and FTD and accumulate in aberrant cytoplasmic aggregates in the brains of ALS and FTD patients. Our previous work has established that neurodegeneration in ALS/FTD patients is driven by defects in 1) nucleocytoplasmic transport 2) phase separation and 3) post-translational modifications of disease-linked RNA-binding proteins. Using biochemical and cell biological approaches, we investigate how these three mechanisms are normally regulated and how they are disturbed in disease.
In particular working on the project:
Lara Silva (PhD Student)
Nuclear Import Receptors Directly Bind to Arginine-Rich Dipeptide Repeat Proteins and Suppress Their Pathological Interactions.
Hutten S, Usluer S, Bourgeois B, Simonetti F, Odeh HM, Fare CM, Czuppa M, Hruska-Plochan M, Hofweber M, Polymenidou M, Shorter J, Edbauer D, Madl T, Dormann D. Cell Rep. 2020 Dec 22;33(12):108538. doi: 10.1016/j.celrep.2020.108538. PMID: 33357437
Nonclassical nuclear localization signals mediate nuclear import of CIRBP.
Bourgeois B, Hutten S, Gottschalk B, Hofweber M, Richter G, Sternat J, Abou-Ajram C, Göbl C, Leitinger G, Graier WF, Dormann D, Madl T.
Proc Natl Acad Sci U S A. 2020 Apr 14;117(15):8503-8514. doi: 10.1073/pnas.1918944117. Epub 2020 Mar 31.
FG-nucleoporins caught in the act of liquid-liquid phase separation.
J Cell Biol. 2020 Jan 6;219(1). pii: e201910211. doi: 10.1083/jcb.201910211.
Liquid-Liquid Phase Separation in Disease.
Alberti S, Dormann D.
Annu Rev Genet. 2019 Dec 3;53:171-194. doi: 10.1146/annurev-genet-112618-043527. Epub 2019 Aug 20. Review.
Friend or foe-Post-translational modifications as regulators of phase separation and RNP granule dynamics.
Hofweber M, Dormann D.J Biol Chem. 2019 May 3;294(18):7137-7150. doi: 10.1074/jbc.TM118.001189. Epub 2018 Dec 26.PMID: 30587571