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Moraleva AA, Malysheva MA, Khajdukov SV, Zatsepina OV. A Higher Level of Expression of the Nucleolar Protein SURF6 in Human Normal Activated Lymphocytes and in Lymphocytes of Patients with Lymphoproliferative Disorders. DOKL BIOCHEM BIOPHYS 2020; 494:261-265. [PMID: 33119830 DOI: 10.1134/s1607672920050099] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2020] [Revised: 06/29/2020] [Accepted: 06/29/2020] [Indexed: 11/22/2022]
Abstract
Proliferation of mammalian cells is often accompanied by an increase in the content of the nucleolar proteins, which allows researchers to consider such proteins as potential activation markers. To test this assumption experimentally, we examined the expression pattern of the nucleolar rRNA processing factor SURF6 in normal (resting) peripheral blood lymphocytes, lymphocytes activated for proliferation in vitro, and in blood samples from patients with lymphoproliferative diseases. Using two methods (immunofluorescence and immunoblotting), we for the first time showed that the SURF6 protein is not detected in normal lymphocytes but can easily be visualized in lymphocytes after PHA activation and in lymphocytes of lymphocytic leukemia patients. The level of SURF6 expression in patients correlated with the aggressiveness of the disease development determined by the content of Ki-67-positive lymphocytes. These results allow the SURF6 nucleolar protein to be considered as a putative activation marker of lymphocytes in human blood disorders.
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Affiliation(s)
- A A Moraleva
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Science, Moscow, Russia
| | - M A Malysheva
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Science, Moscow, Russia
| | - S V Khajdukov
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Science, Moscow, Russia
| | - O V Zatsepina
- Shemyakin-Ovchinnikov Institute of Bioorganic Chemistry, Russian Academy of Science, Moscow, Russia.
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52
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Abstract
The nucleolus is the most prominent nuclear body and serves a fundamentally important biological role as a site of ribonucleoprotein particle assembly, primarily dedicated to ribosome biogenesis. Despite being one of the first intracellular structures visualized historically, the biophysical rules governing its assembly and function are only starting to become clear. Recent studies have provided increasing support for the concept that the nucleolus represents a multilayered biomolecular condensate, whose formation by liquid-liquid phase separation (LLPS) facilitates the initial steps of ribosome biogenesis and other functions. Here, we review these biophysical insights in the context of the molecular and cell biology of the nucleolus. We discuss how nucleolar function is linked to its organization as a multiphase condensate and how dysregulation of this organization could provide insights into still poorly understood aspects of nucleolus-associated diseases, including cancer, ribosomopathies and neurodegeneration as well as ageing. We suggest that the LLPS model provides the starting point for a unifying quantitative framework for the assembly, structural maintenance and function of the nucleolus, with implications for gene regulation and ribonucleoprotein particle assembly throughout the nucleus. The LLPS concept is also likely useful in designing new therapeutic strategies to target nucleolar dysfunction.
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53
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Liquid-Liquid Phase Separation in Crowded Environments. Int J Mol Sci 2020; 21:ijms21165908. [PMID: 32824618 PMCID: PMC7460619 DOI: 10.3390/ijms21165908] [Citation(s) in RCA: 129] [Impact Index Per Article: 32.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2020] [Accepted: 08/13/2020] [Indexed: 12/23/2022] Open
Abstract
Biomolecular condensates play a key role in organizing cellular fluids such as the cytoplasm and nucleoplasm. Most of these non-membranous organelles show liquid-like properties both in cells and when studied in vitro through liquid–liquid phase separation (LLPS) of purified proteins. In general, LLPS of proteins is known to be sensitive to variations in pH, temperature and ionic strength, but the role of crowding remains underappreciated. Several decades of research have shown that macromolecular crowding can have profound effects on protein interactions, folding and aggregation, and it must, by extension, also impact LLPS. However, the precise role of crowding in LLPS is far from trivial, as most condensate components have a disordered nature and exhibit multiple weak attractive interactions. Here, we discuss which factors determine the scope of LLPS in crowded environments, and we review the evidence for the impact of macromolecular crowding on phase boundaries, partitioning behavior and condensate properties. Based on a comparison of both in vivo and in vitro LLPS studies, we propose that phase separation in cells does not solely rely on attractive interactions, but shows important similarities to segregative phase separation.
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Li W, Hu J, Shi B, Palomba F, Digman MA, Gratton E, Jiang H. Biophysical properties of AKAP95 protein condensates regulate splicing and tumorigenesis. Nat Cell Biol 2020; 22:960-972. [PMID: 32719551 PMCID: PMC7425812 DOI: 10.1038/s41556-020-0550-8] [Citation(s) in RCA: 87] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/02/2019] [Accepted: 06/24/2020] [Indexed: 12/14/2022]
Abstract
It remains unknown if biophysical or material properties of biomolecular condensates regulate cancer. Here we show that AKAP95, a nuclear protein that regulates transcription and RNA splicing, plays an important role in tumorigenesis by supporting cancer cell growth and suppressing oncogene-induced senescence. AKAP95 forms phase-separated and liquid-like condensates in vitro and in nucleus. Mutations of key residues to different amino acids perturb AKAP95 condensation in opposite directions. Importantly, the activity of AKAP95 in splice regulation is abolished by disruption of condensation, significantly impaired by hardening of condensates, and regained by substituting its condensation-mediating region with other condensation-mediating regions from irrelevant proteins. Moreover, the abilities of AKAP95 in regulating gene expression and supporting tumorigenesis require AKAP95 to form condensates with proper liquidity and dynamicity. These results link phase separation to tumorigenesis and uncover an important role of appropriate biophysical properties of protein condensates in gene regulation and cancer.
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Affiliation(s)
- Wei Li
- Department of Biochemistry and Molecular Genetics, University of Virginia School of Medicine, Charlottesville, VA, USA
- Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham School of Medicine, Birmingham, AL, USA
| | - Jing Hu
- Department of Biochemistry and Molecular Genetics, University of Virginia School of Medicine, Charlottesville, VA, USA
- Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham School of Medicine, Birmingham, AL, USA
| | - Bi Shi
- Department of Biochemistry and Molecular Genetics, University of Virginia School of Medicine, Charlottesville, VA, USA
| | - Francesco Palomba
- Laboratory of Fluorescence Dynamics, The Henry Samueli School of Engineering, University of California, Irvine, CA, USA
| | - Michelle A Digman
- Laboratory of Fluorescence Dynamics, The Henry Samueli School of Engineering, University of California, Irvine, CA, USA
| | - Enrico Gratton
- Laboratory of Fluorescence Dynamics, The Henry Samueli School of Engineering, University of California, Irvine, CA, USA
| | - Hao Jiang
- Department of Biochemistry and Molecular Genetics, University of Virginia School of Medicine, Charlottesville, VA, USA.
- Department of Biochemistry and Molecular Genetics, University of Alabama at Birmingham School of Medicine, Birmingham, AL, USA.
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55
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Cela I, Di Matteo A, Federici L. Nucleophosmin in Its Interaction with Ligands. Int J Mol Sci 2020; 21:E4885. [PMID: 32664415 PMCID: PMC7402337 DOI: 10.3390/ijms21144885] [Citation(s) in RCA: 18] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/29/2020] [Revised: 07/07/2020] [Accepted: 07/08/2020] [Indexed: 12/13/2022] Open
Abstract
Nucleophosmin (NPM1) is a mainly nucleolar protein that shuttles between nucleoli, nucleoplasm and cytoplasm to fulfill its many functions. It is a chaperone of both nucleic acids and proteins and plays a role in cell cycle control, centrosome duplication, ribosome maturation and export, as well as the cellular response to a variety of stress stimuli. NPM1 is a hub protein in nucleoli where it contributes to nucleolar organization through heterotypic and homotypic interactions. Furthermore, several alterations, including overexpression, chromosomal translocations and mutations are present in solid and hematological cancers. Recently, novel germline mutations that cause dyskeratosis congenita have also been described. This review focuses on NPM1 interactions and inhibition. Indeed, the list of NPM1 binding partners is ever-growing and, in recent years, many studies contributed to clarifying the structural basis for NPM1 recognition of both nucleic acids and several proteins. Intriguingly, a number of natural and synthetic ligands that interfere with NPM1 interactions have also been reported. The possible role of NPM1 inhibitors in the treatment of multiple cancers and other pathologies is emerging as a new therapeutic strategy.
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Affiliation(s)
- Ilaria Cela
- Center for Advanced Studies and Technology (CAST), University of Chieti “G. d’Annunzio”, Via Polacchi, 66100 Chieti, Italy;
- Department of Medical, Oral and Biotechnological Sciences, University of Chieti “G. d’Annunzio”, Via dei Vestini 31, 66100 Chieti, Italy
| | - Adele Di Matteo
- Institute of Molecular Biology and Pathology (IBPM) of the CNR, c/o “Sapienza University of Rome, Piazzale Aldo Moro 5, 00185 Roma, Italy;
| | - Luca Federici
- Center for Advanced Studies and Technology (CAST), University of Chieti “G. d’Annunzio”, Via Polacchi, 66100 Chieti, Italy;
- Department of Medical, Oral and Biotechnological Sciences, University of Chieti “G. d’Annunzio”, Via dei Vestini 31, 66100 Chieti, Italy
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56
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Hiregange D, Naick H, Rao BJ. ATR signalling mediates the prosurvival function of phospho-NPM against PIDDosome mediated cell death. Cell Signal 2020; 71:109602. [DOI: 10.1016/j.cellsig.2020.109602] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2020] [Accepted: 03/14/2020] [Indexed: 12/14/2022]
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57
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Composition-dependent thermodynamics of intracellular phase separation. Nature 2020; 581:209-214. [PMID: 32405004 DOI: 10.1038/s41586-020-2256-2] [Citation(s) in RCA: 364] [Impact Index Per Article: 91.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/10/2019] [Accepted: 04/01/2020] [Indexed: 01/01/2023]
Abstract
Intracellular bodies such as nucleoli, Cajal bodies and various signalling assemblies represent membraneless organelles, or condensates, that form via liquid-liquid phase separation (LLPS)1,2. Biomolecular interactions-particularly homotypic interactions mediated by self-associating intrinsically disordered protein regions-are thought to underlie the thermodynamic driving forces for LLPS, forming condensates that can facilitate the assembly and processing of biochemically active complexes, such as ribosomal subunits within the nucleolus. Simplified model systems3-6 have led to the concept that a single fixed saturation concentration is a defining feature of endogenous LLPS7-9, and has been suggested as a mechanism for intracellular concentration buffering2,7,8,10. However, the assumption of a fixed saturation concentration remains largely untested within living cells, in which the richly multicomponent nature of condensates could complicate this simple picture. Here we show that heterotypic multicomponent interactions dominate endogenous LLPS, and give rise to nucleoli and other condensates that do not exhibit a fixed saturation concentration. As the concentration of individual components is varied, their partition coefficients change in a manner that can be used to determine the thermodynamic free energies that underlie LLPS. We find that heterotypic interactions among protein and RNA components stabilize various archetypal intracellular condensates-including the nucleolus, Cajal bodies, stress granules and P-bodies-implying that the composition of condensates is finely tuned by the thermodynamics of the underlying biomolecular interaction network. In the context of RNA-processing condensates such as the nucleolus, this manifests in the selective exclusion of fully assembled ribonucleoprotein complexes, providing a thermodynamic basis for vectorial ribosomal RNA flux out of the nucleolus. This methodology is conceptually straightforward and readily implemented, and can be broadly used to extract thermodynamic parameters from microscopy images. These approaches pave the way for a deeper understanding of the thermodynamics of multicomponent intracellular phase behaviour and its interplay with the nonequilibrium activity that is characteristic of endogenous condensates.
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58
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Rubio K, Castillo-Negrete R, Barreto G. Non-coding RNAs and nuclear architecture during epithelial-mesenchymal transition in lung cancer and idiopathic pulmonary fibrosis. Cell Signal 2020; 70:109593. [PMID: 32135188 DOI: 10.1016/j.cellsig.2020.109593] [Citation(s) in RCA: 11] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/30/2019] [Revised: 02/28/2020] [Accepted: 02/29/2020] [Indexed: 12/13/2022]
Abstract
Lung cancer (LC) is the leading cause of cancer-related deaths worldwide. On the other hand, idiopathic pulmonary fibrosis (IPF) is the most common interstitial lung disease showing a prevalence of 20 new cases per 100,000 persons per year. Despite differences in cellular origin and pathological phenotypes, LC and IPF are lung diseases that share common features, including hyperproliferation of specific cell types in the lung, involvement of epithelial-mesenchymal transition (EMT) and enhanced activity of signaling pathways, such as tissue growth factor (TGFB), epidermal growth factor (EGF), fibroblast growth factor (FGF), wingless secreted glycoprotein (WNT) signaling, among others. EMT is a process during which epithelial cells lose their cell polarity and cell-cell adhesion, and acquire migratory and invasive properties to become mesenchymal cells. EMT involves numerous morphological hallmarks of hyperproliferative diseases, like cell plasticity, resistance to apoptosis, dedifferentiation and proliferation, thereby playing a central role during organ fibrosis and cancer progression. EMT was considered as an "all-or-none" process. In contrast to these outdated dichotomist interpretations, recent reports suggest that EMT occurs gradually involving different epithelial cell intermediate states with mesenchyme-like characteristics. These cell intermediate states of EMT differ from each other in their cell plasticity, invasiveness and metastatic potential, which in turn are induced by signals from their microenvironment. EMT is regulated by several transcription factors (TFs), which are members of prominent families of master regulators of transcription. In addition, there is increasing evidence for the important contribution of noncoding RNAs (ncRNAs) to EMT. In our review we highlight articles dissecting the function of different ncRNAs subtypes and nuclear architecture in cell intermediate states of EMT, as well as their involvement in LC and IPF.
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Affiliation(s)
- Karla Rubio
- Brain and Lung Epigenetics (BLUE), Glycobiology, Cell Growth and Tissue Repair Research Unit (Gly-CRRET), Université Paris-Est Créteil (UPEC), 94010 Créteil, France; Lung Cancer Epigenetic, Max-Planck-Institute for Heart and Lung Research, Parkstraße 1, 61231 Bad Nauheim, Germany
| | - Rafael Castillo-Negrete
- Brain and Lung Epigenetics (BLUE), Glycobiology, Cell Growth and Tissue Repair Research Unit (Gly-CRRET), Université Paris-Est Créteil (UPEC), 94010 Créteil, France; Lung Cancer Epigenetic, Max-Planck-Institute for Heart and Lung Research, Parkstraße 1, 61231 Bad Nauheim, Germany
| | - Guillermo Barreto
- Brain and Lung Epigenetics (BLUE), Glycobiology, Cell Growth and Tissue Repair Research Unit (Gly-CRRET), Université Paris-Est Créteil (UPEC), 94010 Créteil, France; Lung Cancer Epigenetic, Max-Planck-Institute for Heart and Lung Research, Parkstraße 1, 61231 Bad Nauheim, Germany; Institute of Fundamental Medicine and Biology, Kazan (Volga Region) Federal University, 420008 Kazan, Russian Federation; Universities of Giessen and Marburg Lung Center (UGMLC), The German Center of Lung Research (Deutsches Zentrum für Lungenforschung, DZL), Germany.
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59
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Gibbs E, Perrone B, Hassan A, Kümmerle R, Kriwacki R. NPM1 exhibits structural and dynamic heterogeneity upon phase separation with the p14ARF tumor suppressor. JOURNAL OF MAGNETIC RESONANCE (SAN DIEGO, CALIF. : 1997) 2020; 310:106646. [PMID: 31751897 PMCID: PMC6934896 DOI: 10.1016/j.jmr.2019.106646] [Citation(s) in RCA: 20] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 08/16/2019] [Revised: 11/04/2019] [Accepted: 11/08/2019] [Indexed: 06/10/2023]
Abstract
Nucleophosmin (NPM1) is an abundant nucleolar protein that aids in the maturation of pre-ribosomal particles and participates in oncogenic stress responses through its interaction with the Alternative Reading Frame tumor suppressor (p14ARF). NPM1 mediates multiple mechanisms of phase separation which contribute to the liquid-like properties of nucleoli. However, the effects of phase separation on the structure and dynamics of NPM1 are poorly understood. Here we show that NPM1 undergoes phase separation with p14ARF in vitro, forming condensates that immobilize both proteins. We probed the structure and dynamics of NPM1 within the condensed phase using solid-state NMR spectroscopy. Our results demonstrate that within the condensed phase, the NPM1 oligomerization domain forms an immobile scaffold, while the central intrinsically disordered region and the C-terminal nucleic acid binding domain exhibit relative mobility.
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Affiliation(s)
- Eric Gibbs
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, United States
| | - Barbara Perrone
- Bruker Switzerland AG, Industriestrasse 26, CH-8117 Fällanden, Switzerland
| | - Alia Hassan
- Bruker Switzerland AG, Industriestrasse 26, CH-8117 Fällanden, Switzerland
| | - Rainer Kümmerle
- Bruker Switzerland AG, Industriestrasse 26, CH-8117 Fällanden, Switzerland
| | - Richard Kriwacki
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, United States; Department of Microbiology, Immunology and Biochemistry, University of Tennessee Health Sciences Center, Memphis, United States.
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60
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Sagar A, Xue B. Recent Advances in Machine Learning Based Prediction of RNA-protein Interactions. Protein Pept Lett 2019; 26:601-619. [PMID: 31215361 DOI: 10.2174/0929866526666190619103853] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2018] [Revised: 04/04/2019] [Accepted: 06/01/2019] [Indexed: 12/18/2022]
Abstract
The interactions between RNAs and proteins play critical roles in many biological processes. Therefore, characterizing these interactions becomes critical for mechanistic, biomedical, and clinical studies. Many experimental methods can be used to determine RNA-protein interactions in multiple aspects. However, due to the facts that RNA-protein interactions are tissuespecific and condition-specific, as well as these interactions are weak and frequently compete with each other, those experimental techniques can not be made full use of to discover the complete spectrum of RNA-protein interactions. To moderate these issues, continuous efforts have been devoted to developing high quality computational techniques to study the interactions between RNAs and proteins. Many important progresses have been achieved with the application of novel techniques and strategies, such as machine learning techniques. Especially, with the development and application of CLIP techniques, more and more experimental data on RNA-protein interaction under specific biological conditions are available. These CLIP data altogether provide a rich source for developing advanced machine learning predictors. In this review, recent progresses on computational predictors for RNA-protein interaction were summarized in the following aspects: dataset, prediction strategies, and input features. Possible future developments were also discussed at the end of the review.
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Affiliation(s)
- Amit Sagar
- Department of Cell Biology, Microbiology and Molecular Biology, School of Natural Sciences and Mathematics, College of Arts and Sciences, University of South Florida, Tampa, Florida 33620, United States
| | - Bin Xue
- Department of Cell Biology, Microbiology and Molecular Biology, School of Natural Sciences and Mathematics, College of Arts and Sciences, University of South Florida, Tampa, Florida 33620, United States
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61
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Choi JM, Dar F, Pappu RV. LASSI: A lattice model for simulating phase transitions of multivalent proteins. PLoS Comput Biol 2019; 15:e1007028. [PMID: 31634364 PMCID: PMC6822780 DOI: 10.1371/journal.pcbi.1007028] [Citation(s) in RCA: 206] [Impact Index Per Article: 41.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/12/2019] [Revised: 10/31/2019] [Accepted: 10/01/2019] [Indexed: 12/21/2022] Open
Abstract
Many biomolecular condensates form via spontaneous phase transitions that are driven by multivalent proteins. These molecules are biological instantiations of associative polymers that conform to a so-called stickers-and-spacers architecture. The stickers are protein-protein or protein-RNA interaction motifs and / or domains that can form reversible, non-covalent crosslinks with one another. Spacers are interspersed between stickers and their preferential interactions with solvent molecules determine the cooperativity of phase transitions. Here, we report the development of an open source computational engine known as LASSI (LAttice simulation engine for Sticker and Spacer Interactions) that enables the calculation of full phase diagrams for multicomponent systems comprising of coarse-grained representations of multivalent proteins. LASSI is designed to enable computationally efficient phenomenological modeling of spontaneous phase transitions of multicomponent mixtures comprising of multivalent proteins and RNA molecules. We demonstrate the application of LASSI using simulations of linear and branched multivalent proteins. We show that dense phases are best described as droplet-spanning networks that are characterized by reversible physical crosslinks among multivalent proteins. We connect recent observations regarding correlations between apparent stoichiometry and dwell times of condensates to being proxies for the internal structural organization, specifically the convolution of internal density and extent of networking, within condensates. Finally, we demonstrate that the concept of saturation concentration thresholds does not apply to multicomponent systems where obligate heterotypic interactions drive phase transitions. This emerges from the ellipsoidal structures of phase diagrams for multicomponent systems and it has direct implications for the regulation of biomolecular condensates in vivo.
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Affiliation(s)
- Jeong-Mo Choi
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, United States of America
- Center for Science & Engineering of Living Systems (CSELS), Washington University in St. Louis, St. Louis, MO, United States of America
| | - Furqan Dar
- Center for Science & Engineering of Living Systems (CSELS), Washington University in St. Louis, St. Louis, MO, United States of America
- Department of Physics, Washington University in St. Louis, St. Louis, MO, United States of America
| | - Rohit V. Pappu
- Department of Biomedical Engineering, Washington University in St. Louis, St. Louis, MO, United States of America
- Center for Science & Engineering of Living Systems (CSELS), Washington University in St. Louis, St. Louis, MO, United States of America
- * E-mail:
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62
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Controlling the material properties and rRNA processing function of the nucleolus using light. Proc Natl Acad Sci U S A 2019; 116:17330-17335. [PMID: 31399547 DOI: 10.1073/pnas.1903870116] [Citation(s) in RCA: 48] [Impact Index Per Article: 9.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
The nucleolus is a prominent nuclear condensate that plays a central role in ribosome biogenesis by facilitating the transcription and processing of nascent ribosomal RNA (rRNA). A number of studies have highlighted the active viscoelastic nature of the nucleolus, whose material properties and phase behavior are a consequence of underlying molecular interactions. However, the ways in which the material properties of the nucleolus impact its function in rRNA biogenesis are not understood. Here we utilize the Cry2olig optogenetic system to modulate the viscoelastic properties of the nucleolus. We show that above a threshold concentration of Cry2olig protein, the nucleolus can be gelled into a tightly linked, low mobility meshwork. Gelled nucleoli no longer coalesce and relax into spheres but nonetheless permit continued internal molecular mobility of small proteins. These changes in nucleolar material properties manifest in specific alterations in rRNA processing steps, including a buildup of larger rRNA precursors and a depletion of smaller rRNA precursors. We propose that the flux of processed rRNA may be actively tuned by the cell through modulating nucleolar material properties, which suggests the potential of materials-based approaches for therapeutic intervention in ribosomopathies.
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63
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64
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White MR, Mitrea DM, Zhang P, Stanley CB, Cassidy DE, Nourse A, Phillips AH, Tolbert M, Taylor JP, Kriwacki RW. C9orf72 Poly(PR) Dipeptide Repeats Disturb Biomolecular Phase Separation and Disrupt Nucleolar Function. Mol Cell 2019; 74:713-728.e6. [PMID: 30981631 DOI: 10.1016/j.molcel.2019.03.019] [Citation(s) in RCA: 109] [Impact Index Per Article: 21.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/27/2018] [Revised: 02/12/2019] [Accepted: 03/18/2019] [Indexed: 12/11/2022]
Abstract
Repeat expansion in the C9orf72 gene is the most common cause of the neurodegenerative disorder amyotrophic lateral sclerosis (C9-ALS) and is linked to the unconventional translation of five dipeptide-repeat polypeptides (DPRs). The two enriched in arginine, poly(GR) and poly(PR), infiltrate liquid-like nucleoli, co-localize with the nucleolar protein nucleophosmin (NPM1), and alter the phase separation behavior of NPM1 in vitro. Here, we show that poly(PR) DPRs bind tightly to a long acidic tract within the intrinsically disordered region of NPM1, altering its phase separation with nucleolar partners to the extreme of forming large, soluble complexes that cause droplet dissolution in vitro. In cells, poly(PR) DPRs disperse NPM1 from nucleoli and entrap rRNA in static condensates in a DPR-length-dependent manner. We propose that R-rich DPR toxicity involves disrupting the role of phase separation by NPM1 in organizing ribosomal proteins and RNAs within the nucleolus.
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Affiliation(s)
- Michael R White
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA
| | - Diana M Mitrea
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA
| | - Peipei Zhang
- Department of Cell and Molecular Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA
| | - Christopher B Stanley
- Large Scale Structures Group, Neutron Scattering Division, Oak Ridge National Laboratory, Oak Ridge, TN 37830, USA
| | - Devon E Cassidy
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA
| | - Amanda Nourse
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA; Molecular Interaction Analysis Shared Resource, St. Jude Children's Research Hospital, Memphis, TN 38105, USA
| | - Aaron H Phillips
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA
| | - Michele Tolbert
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA
| | - J Paul Taylor
- Department of Cell and Molecular Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA; Howard Hughes Medical Institute, Department of Cell and Molecular Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA
| | - Richard W Kriwacki
- Department of Structural Biology, St. Jude Children's Research Hospital, Memphis, TN 38105, USA; Department of Microbiology, Immunology, and Biochemistry, University of Tennessee Health Sciences Center, Memphis, TN 38105, USA.
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