The RNA-binding protein FUS is chaperoned and imported into the nucleus by a network of import receptors

Baade, Imke; Hutten, Saskia; Sternburg, Erin L.; Pörschke, Marius; Hofweber, Mario; Dormann, Dorothee; Kehlenbach, Ralph H.

doi:10.1016/j.jbc.2021.100659

Cited by 34 publications

(29 citation statements)

References 78 publications

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“…It is widely known that the karyopherin family have redundant functions and multiple transport receptors can bind the same cargo protein. For example, a recent study demonstrated that FUS can form stable complexes with additional import receptors, such as transportin-3, importin b, and importin 7, and these interactions reduced FUS stress granule recruitment in HeLa cells (Baade et al, 2021). Since they are in the same family as Kapb2, it is possible that these newly-identified transport receptors may be new targets to explore.…”

Section: Nuclear Import Receptorsmentioning

confidence: 99%

Liquid-Liquid Phase Separation of TDP-43 and FUS in Physiology and Pathology of Neurodegenerative Diseases

Carey

Guo

2022

Front. Mol. Biosci.

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Liquid-liquid phase separation of RNA-binding proteins mediates the formation of numerous membraneless organelles with essential cellular function. However, aberrant phase transition of these proteins leads to the formation of insoluble protein aggregates, which are pathological hallmarks of neurodegenerative diseases including ALS and FTD. TDP-43 and FUS are two such RNA-binding proteins that mislocalize and aggregate in patients of ALS and FTD. They have similar domain structures that provide multivalent interactions driving their phase separation in vitro and in the cellular environment. In this article, we review the factors that mediate and regulate phase separation of TDP-43 and FUS. We also review evidences that connect the phase separation property of TDP-43 and FUS to their functional roles in cells. Aberrant phase transition of TDP-43 and FUS leads to protein aggregation and disrupts their regular cell function. Therefore, restoration of functional protein phase of TDP-43 and FUS could be beneficial for neuronal cells. We discuss possible mechanisms for TDP-43 and FUS aberrant phase transition and aggregation while reviewing the methods that are currently being explored as potential therapeutic strategies to mitigate aberrant phase transition and aggregation of TDP-43 and FUS.

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Section: Nuclear Import Receptorsmentioning

confidence: 99%

Liquid-Liquid Phase Separation of TDP-43 and FUS in Physiology and Pathology of Neurodegenerative Diseases

Carey

Guo

2022

Front. Mol. Biosci.

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“…Thus, the subtle difference that G156E mutation causes in condensate formation might be augmented in the case of the full-length FUS protein (Ito et al, 2011). These differential effects of mutations in the IDR region, NLS, or RRM, as well as the interaction with other proteins such as importins/exportins (Baade et al, 2021), certainly warrant being investigated. It also remains to be determined whether different condensation states of FUS interact with a distinct subset of stress granule proteins or specific RNAs (e.g., with specific posttranscriptional modifications, tertiary structures) (Ries et al, 2019;Roden and Gladfelter, 2021).…”

Section: Discussionmentioning

confidence: 99%

Aberrant Phase Separation of FUS Leads to Lysosome Sequestering and Acidification

Trnka

Hoffmann

Wang

et al. 2021

Front. Cell Dev. Biol.

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Amyotrophic lateral sclerosis (ALS) is a progressive neurodegenerative disease that leads to the death of upper and lower motor neurons. While most cases of ALS are sporadic, some of the familial forms of the disease are caused by mutations in the gene encoding for the RNA-binding protein FUS. Under physiological conditions, FUS readily phase separates into liquid-like droplets in vivo and in vitro. ALS-associated mutations interfere with this process and often result in solid-like aggregates rather than fluid condensates. Yet, whether cells recognize and triage aberrant condensates remains poorly understood, posing a major barrier to the development of novel ALS treatments. Using a combination of ALS-associated FUS mutations, optogenetic manipulation of FUS condensation, chemically induced stress, and pH-sensitive reporters of organelle acidity, we systematically characterized the cause-effect relationship between the material state of FUS condensates and the sequestering of lysosomes. From our data, we can derive three conclusions. First, regardless of whether we use wild-type or mutant FUS, expression levels (i.e., high concentrations) play a dominant role in determining the fraction of cells having soluble or aggregated FUS. Second, chemically induced FUS aggregates recruit LAMP1-positive structures. Third, mature, acidic lysosomes accumulate only at FUS aggregates but not at liquid-condensates. Together, our data suggest that lysosome-degradation machinery actively distinguishes between fluid and solid condensates. Unraveling these aberrant interactions and testing strategies to manipulate the autophagosome-lysosome axis provides valuable clues for disease intervention.

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“…The P525L mutation, however, seems to reflect better the deletion of the NLS domain, which prevents the protein from binding mainly to TNPO-1 with consequent reduction of its import into the nucleus ( Dormann et al, 2010 , 2012 ; Baade et al, 2021 ).…”

Section: Discussionmentioning

confidence: 99%

“…Exon 15 encodes for the C-terminal region of the protein, containing the nuclear localization signal (NLS) domain, which is formed by an arginine-glycine-rich region (RGG3) followed by a proline-tyrosine (PY) consensus sequence ( Dormann et al, 2012 ; Hofweber et al, 2018 ). Several proteins (i.e., Transportin-1 (TNPO-1), Transportin-3, importin β, importin 7 and importin β/7 dimer) can chaperone and import FUS to the nucleus through the RGG (i.e., RGG1, RGG2, RGG3) and the PY motifs ( Baade et al, 2021 ).…”

Section: Introductionmentioning

confidence: 99%

A Deletion of the Nuclear Localization Signal Domain in the Fus Protein Induces Stable Post-stress Cytoplasmic Inclusions in SH-SY5Y Cells

2021

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Mutations in Fused-in-Sarcoma (FUS) gene involving the nuclear localization signal (NLS) domain lead to juvenile-onset Amyotrophic Lateral Sclerosis (ALS). The mutant protein mislocalizes to the cytoplasm, incorporating it into Stress Granules (SG). Whether SGs are the first step to the formation of stable FUS-containing aggregates is still unclear. In this work, we used acute and chronic stress paradigms to study the SG dynamics in a human SH-SY5Y neuroblastoma cell line carrying a deletion of the NLS domain of the FUS protein (homozygous: ΔNLS–/–; heterozygous: ΔNLS+/–). Wild-type (WT) cells served as controls. We evaluated the subcellular localization of the mutant protein through immunoblot and immunofluorescence, in basal conditions and after acute stress and chronic stress with sodium arsenite (NaAsO2). Cells were monitored for up to 24 h after rescue. FUS was expressed in both nucleus and cytoplasm in the ΔNLS+/– cells, whereas it was primarily cytoplasmic in the ΔNLS–/–. Acute NaAsO2 exposure induced SGs: at rescue,>90% of ΔNLS cells showed abundant FUS-containing if compared to less than 5% of the WT cells. The proportion of FUS-positive SGs remained 15–20% at 24 h in mutant cells. Cycloheximide did not abolish the long-lasting SGs in mutant cells. Chronic exposure to NaAsO2 did not induce significant SGs formation. A wealth of research has demonstrated that ALS-associated FUS mutations at the C-terminus facilitate the incorporation of the mutant protein into SGs. We have shown here that mutant FUS-containing SGs tend to fail to dissolve after stress, facilitating a liquid-to-solid phase transition. The FUS-containing inclusions seen in the dying motor neurons might therefore directly derive from SGs. This might represent an attractive target for future innovative therapies.

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The RNA-binding protein FUS is chaperoned and imported into the nucleus by a network of import receptors

Cited by 34 publications

References 78 publications

Liquid-Liquid Phase Separation of TDP-43 and FUS in Physiology and Pathology of Neurodegenerative Diseases

Liquid-Liquid Phase Separation of TDP-43 and FUS in Physiology and Pathology of Neurodegenerative Diseases

Aberrant Phase Separation of FUS Leads to Lysosome Sequestering and Acidification

A Deletion of the Nuclear Localization Signal Domain in the Fus Protein Induces Stable Post-stress Cytoplasmic Inclusions in SH-SY5Y Cells

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