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Abstract
Because of the association between aberrant nuclear structure and tumour grade, nuclear morphology is an indispensible criterion in the current pathological assessment of cancer. Components of the nuclear envelope environment have central roles in many aspects of cell function that affect tumour development and progression. As the roles of the nuclear envelope components, including nuclear pore complexes and nuclear lamina, are being deciphered in molecular detail there are opportunities to harness this knowledge for cancer therapeutics and biomarker development. In this Review, we summarize the progress that has been made in our understanding of the nuclear envelope and the implications of changes in this environment for cancer biology.
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Affiliation(s)
- Kin-Hoe Chow
- Department of Oncological Sciences, Huntsman Cancer Institute, University of Utah, Salt Lake City, Utah 84112, USA
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102
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103
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Wang L, Yang W, Ju W, Wang P, Zhao X, Jenkins EC, Brown WT, Zhong N. A proteomic study of Hutchinson-Gilford progeria syndrome: Application of 2D-chromotography in a premature aging disease. Biochem Biophys Res Commun 2011; 417:1119-26. [PMID: 22210539 DOI: 10.1016/j.bbrc.2011.12.056] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/29/2011] [Accepted: 12/14/2011] [Indexed: 11/17/2022]
Abstract
The Hutchinson-Gilford progeria syndrome (HGPS) is a rare genetic disease characterized by segmental premature aging. Applying a two-dimensional chromatographic proteomic approach, the 2D Protein Fractionation System (PF2D), we identified 30 differentially expressed proteins in cultured HGPS fibroblasts. We categorized them into five groups: methylation, calcium ion binding, cytoskeleton, duplication, and regulation of apoptosis. Among these 30 proteins, 23 were down-regulated, while seven were up-regulated in HGPS fibroblasts as compared to normal fibroblasts. Three differentially expressed cytoskeleton proteins, vimentin, actin, and tubulin, were validated via Western blotting and characterized by immunostaining that revealed densely thickened bundles and irregular structures. Furthermore in the HGPS cells, the cell cycle G1 phase was elongated and the concentration of free cytosolic calcium was increased, suggesting intracellular retention of calcium. The results that we obtained have implications for understanding the aging process.
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Affiliation(s)
- Li Wang
- Peking University Center of Medical Genetics, Beijing, China
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104
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Hampoelz B, Lecuit T. Nuclear mechanics in differentiation and development. Curr Opin Cell Biol 2011; 23:668-75. [PMID: 22079175 DOI: 10.1016/j.ceb.2011.10.001] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/13/2011] [Revised: 09/23/2011] [Accepted: 10/10/2011] [Indexed: 11/30/2022]
Abstract
The nucleus is by far one of the stiffest organelles within cells of higher eukaryotes. Its mechanical properties are determined by contributions from the nuclear lamina and chromatin. Together they allow a viscoelastic response of the nucleus to applied stresses, where the lamina is thought to behave as an elastic shell, while the nucleoplasm contributes as a largely viscous material. Nuclear mechanics changes during differentiation and development. Altered nuclear mechanics reflects but might also influence global re-arrangements in chromatin architecture, which take place when cells commit themselves into distinct lineages. Thus it is likely that the mechanical characteristics of nuclei significantly contribute to proper differentiation.
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Affiliation(s)
- Bernhard Hampoelz
- IBDML, UMR6216 CNRS-Université de la Méditerranée, Campus de Luminy, case 907, 13288 Marseille Cedex 09, France
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105
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Ahlenstiel CL, Lim HGW, Cooper DA, Ishida T, Kelleher AD, Suzuki K. Direct evidence of nuclear Argonaute distribution during transcriptional silencing links the actin cytoskeleton to nuclear RNAi machinery in human cells. Nucleic Acids Res 2011; 40:1579-95. [PMID: 22064859 PMCID: PMC3287199 DOI: 10.1093/nar/gkr891] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022] Open
Abstract
Mammalian RNAi machinery facilitating transcriptional gene silencing (TGS) is the RNA-induced transcriptional gene silencing-like (RITS-like) complex, comprising of Argonaute (Ago) and small interfering RNA (siRNA) components. We have previously demonstrated promoter-targeted siRNA induce TGS in human immunodeficiency virus type-1 (HIV-1) and simian immunodeficiency virus (SIV), which profoundly suppresses retrovirus replication via heterochromatin formation and histone methylation. Here, we examine subcellular co-localization of Ago proteins with promoter-targeted siRNAs during TGS of SIV and HIV-1 infection. Analysis of retrovirus-infected cells revealed Ago1 co-localized with siRNA in the nucleus, while Ago2 co-localized with siRNA in the inner nuclear envelope. Mismatched and scrambled siRNAs were observed in the cytoplasm, indicating sequence specificity. This is the first report directly visualizing nuclear compartment distribution of Ago-associated siRNA and further reveals a novel nuclear trafficking mechanism for RITS-like components involving the actin cytoskeleton. These results establish a model for elucidating mammalian TGS and suggest a fundamental mechanism underlying nuclear delivery of RITS-like components.
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106
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Simon DN, Wilson KL. The nucleoskeleton as a genome-associated dynamic 'network of networks'. Nat Rev Mol Cell Biol 2011; 12:695-708. [PMID: 21971041 DOI: 10.1038/nrm3207] [Citation(s) in RCA: 222] [Impact Index Per Article: 17.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/11/2022]
Abstract
In the cytosol, actin polymers, intermediate filaments and microtubules can anchor to cell surface adhesions and interlink to form intricate networks. This cytoskeleton is anchored to the nucleus through LINC (links the nucleoskeleton and cytoskeleton) complexes that span the nuclear envelope and in turn anchor to networks of filaments in the nucleus. The metazoan nucleoskeleton includes nuclear pore-linked filaments, A-type and B-type lamin intermediate filaments, nuclear mitotic apparatus (NuMA) networks, spectrins, titin, 'unconventional' polymers of actin and at least ten different myosin and kinesin motors. These elements constitute a poorly understood 'network of networks' that dynamically reorganizes during mitosis and is responsible for genome organization and integrity.
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Affiliation(s)
- Dan N Simon
- Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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107
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Blanco FJ, Bernabeu C. Alternative splicing factor or splicing factor-2 plays a key role in intron retention of the endoglin gene during endothelial senescence. Aging Cell 2011; 10:896-907. [PMID: 21668763 DOI: 10.1111/j.1474-9726.2011.00727.x] [Citation(s) in RCA: 43] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Alternative splicing involving intron retention plays a key role in the regulation of gene expression. We previously reported that the alternatively spliced short isoform of endoglin (S-endoglin) is induced during the aging or senescence of endothelial cells by a mechanism of intron retention. In this work, we demonstrate that the alternative splicing factor or splicing factor-2 (ASF/SF2) is involved in the synthesis of endoglin. Overexpression of ASF/SF2 in endothelial cells switched the balance between the two endoglin isoforms, favoring the synthesis of S-endoglin. Using a minigene reporter vector and RNA immunoprecipitation experiments, it was shown that ASF/SF2 interacts with the nucleotide sequence of the endoglin minigene, suggesting the direct involvement of ASF/SF2. Accordingly, the sequence recognized by ASF/SF2 in the endoglin gene was identified inside the retained intron near the consensus branch point. Finally, the ASF/SF2 subcellular localization during endothelial senescence showed a preferential scattered distribution throughout the cytoplasm, where it interferes with the activity of the minor spliceosome, leading to an increased expression of S-endoglin mRNA. In summary, we report for the first time the molecular mechanisms by which ASF/SF2 regulates the alternative splicing of endoglin in senescent endothelial cells, as well as the involvement of ASF/SF2 in the minor spliceosome.
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MESH Headings
- Alternative Splicing
- Antigens, CD/genetics
- Antigens, CD/metabolism
- Base Sequence
- Blotting, Western
- Cellular Senescence
- Conserved Sequence
- Cytoplasm/genetics
- Cytoplasm/metabolism
- Endoglin
- Genetic Vectors/genetics
- Genetic Vectors/metabolism
- HEK293 Cells
- Human Umbilical Vein Endothelial Cells
- Humans
- Immunoprecipitation/methods
- Introns
- Microscopy, Fluorescence
- Mutagenesis, Site-Directed
- Nuclear Proteins/genetics
- Nuclear Proteins/metabolism
- Protein Isoforms/genetics
- Protein Isoforms/metabolism
- RNA, Messenger/genetics
- RNA, Messenger/metabolism
- RNA, Small Interfering/genetics
- RNA, Small Interfering/metabolism
- RNA-Binding Proteins/genetics
- RNA-Binding Proteins/metabolism
- Receptors, Cell Surface/genetics
- Receptors, Cell Surface/metabolism
- Reverse Transcriptase Polymerase Chain Reaction
- Sequence Alignment
- Sequence Analysis, DNA
- Serine-Arginine Splicing Factors
- Spliceosomes/genetics
- Spliceosomes/metabolism
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Affiliation(s)
- Francisco J Blanco
- Centro de Investigaciones Biológicas, Consejo Superior de Investigaciones Científicas, and Centro de Investigación Biomédica en Red de Enfermedades Raras, c/Ramiro de Maeztu 9, Madrid, Spain.
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108
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Elizondo LI, Jafar-Nejad P, Clewing JM, Boerkoel CF. Gene clusters, molecular evolution and disease: a speculation. Curr Genomics 2011; 10:64-75. [PMID: 19721813 PMCID: PMC2699835 DOI: 10.2174/138920209787581271] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/21/2008] [Revised: 12/20/2008] [Accepted: 12/21/2008] [Indexed: 01/10/2023] Open
Abstract
Traditionally eukaryotic genes are considered independently expressed under the control of their promoters and cis-regulatory domains. However, recent studies in worms, flies, mice and humans have shown that genes co-habiting a chromatin domain or “genomic neighborhood” are frequently co-expressed. Often these co-expressed genes neither constitute part of an operon nor function within the same biological pathway. The mechanisms underlying the partitioning of the genome into transcriptional genomic neighborhoods are poorly defined. However, cross-species analyses find that the linkage among the co-expressed genes of these clusters is significantly conserved and that the expression patterns of genes within clusters have coevolved with the clusters. Such selection could be mediated by chromatin interactions with the nuclear matrix and long-range remodeling of chromatin structure. In the context of human disease, we propose that dysregulation of gene expression across genomic neighborhoods will cause highly pleiotropic diseases. Candidate genomic neighborhood diseases include the nuclear laminopathies, chromosomal translocations and genomic instability disorders, imprinting disorders of errant insulator function, syndromes from impaired cohesin complex assembly, as well as diseases of global covalent histone modifications and DNA methylation. The alteration of transcriptional genomic neighborhoods provides an exciting and novel model for studying epigenetic alterations as quantitative traits in complex common human diseases.
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109
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Affiliation(s)
- Kris Noel Dahl
- Department of Biomedical Engineering, Carnegie Mellon University, 5000 Forbes Avenue, Pittsburgh, PA 15213, USA.
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110
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Meyer AJ, Almendrala DK, Go MM, Krauss SW. Structural protein 4.1R is integrally involved in nuclear envelope protein localization, centrosome-nucleus association and transcriptional signaling. J Cell Sci 2011; 124:1433-44. [PMID: 21486941 DOI: 10.1242/jcs.077883] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/23/2023] Open
Abstract
The multifunctional structural protein 4.1R is required for assembly and maintenance of functional nuclei but its nuclear roles are unidentified. 4.1R localizes within nuclei, at the nuclear envelope, and in cytoplasm. Here we show that 4.1R, the nuclear envelope protein emerin and the intermediate filament protein lamin A/C co-immunoprecipitate, and that 4.1R-specific depletion in human cells by RNA interference produces nuclear dysmorphology and selective mislocalization of proteins from several nuclear subcompartments. Such 4.1R-deficiency causes emerin to partially redistribute into the cytoplasm, whereas lamin A/C is disorganized at nuclear rims and displaced from nucleoplasmic foci. The nuclear envelope protein MAN1, nuclear pore proteins Tpr and Nup62, and nucleoplasmic proteins NuMA and LAP2α also have aberrant distributions, but lamin B and LAP2β have normal localizations. 4.1R-deficient mouse embryonic fibroblasts show a similar phenotype. We determined the functional effects of 4.1R-deficiency that reflect disruption of the association of 4.1R with emerin and A-type lamin: increased nucleus-centrosome distances, increased β-catenin signaling, and relocalization of β-catenin from the plasma membrane to the nucleus. Furthermore, emerin- and lamin-A/C-null cells have decreased nuclear 4.1R. Our data provide evidence that 4.1R has important functional interactions with emerin and A-type lamin that impact upon nuclear architecture, centrosome-nuclear envelope association and the regulation of β-catenin transcriptional co-activator activity that is dependent on β-catenin nuclear export.
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Affiliation(s)
- Adam J Meyer
- Department of Genome Dynamics, University of California, Berkeley, CA 94720, USA
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111
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Nesprins LINC the nucleus and cytoskeleton. Curr Opin Cell Biol 2010; 23:47-54. [PMID: 21177090 DOI: 10.1016/j.ceb.2010.11.006] [Citation(s) in RCA: 112] [Impact Index Per Article: 8.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/13/2010] [Revised: 11/19/2010] [Accepted: 11/27/2010] [Indexed: 01/08/2023]
Abstract
Like other spectrin repeat proteins, nesprins co-ordinate and maintain cellular architecture by linking membranous organelles to the cytoskeleton. However nuclear envelope (NE) nesprins, uniquely hardwire the nuclear lamina to the cytoskeleton and molecular motors. Emerging evidence suggests that nesprins also form a continuous network linking the plasma membrane to the NE that potentially translates mechanical stimuli into nuclear reorganisation. Surprisingly, this network is also essential for cytoskeletal organisation and its disruption has dramatic effects on nuclear migration, centrosomal positioning, focal adhesion maturation and cell motility. Herein we review recent advances in our understanding of how nesprins couple to various filamentous systems within the cell and emphasise the importance of both KASH and KASH-less nesprin isoforms in these interactions.
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112
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Friedl P, Wolf K, Lammerding J. Nuclear mechanics during cell migration. Curr Opin Cell Biol 2010; 23:55-64. [PMID: 21109415 DOI: 10.1016/j.ceb.2010.10.015] [Citation(s) in RCA: 341] [Impact Index Per Article: 24.4] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/17/2010] [Revised: 10/21/2010] [Accepted: 10/30/2010] [Indexed: 12/30/2022]
Abstract
During cell migration, the movement of the nucleus must be coordinated with the cytoskeletal dynamics at the leading edge and trailing end, and, as a result, undergoes complex changes in position and shape, which in turn affects cell polarity, shape, and migration efficiency. We here describe the steps of nuclear positioning and deformation during cell polarization and migration, focusing on migration through three-dimensional matrices. We discuss molecular components that govern nuclear shape and stiffness, and review how nuclear dynamics are connected to and controlled by the actin, tubulin and intermediate cytoskeleton-based migration machinery and how this regulation is altered in pathological conditions. Understanding the regulation of nuclear biomechanics has important implications for cell migration during tissue regeneration, immune defence and cancer.
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Affiliation(s)
- Peter Friedl
- Department of Cell Biology, Nijmegen Center for Molecular Life Science, Radboud University Nijmegen Medical Centre, P.O. 9101, 6500 HB Nijmegen, The Netherlands.
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113
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Characterization of engineered actin binding proteins that control filament assembly and structure. PLoS One 2010; 5:e13960. [PMID: 21103060 PMCID: PMC2980482 DOI: 10.1371/journal.pone.0013960] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/28/2010] [Accepted: 10/26/2010] [Indexed: 01/11/2023] Open
Abstract
BACKGROUND Eukaryotic cells strictly regulate the structure and assembly of their actin filament networks in response to various stimuli. The actin binding proteins that control filament assembly are therefore attractive targets for those who wish to reorganize actin filaments and reengineer the cytoskeleton. Unfortunately, the naturally occurring actin binding proteins include only a limited set of pointed-end cappers, or proteins that will block polymerization from the slow-growing end of actin filaments. Of the few that are known, most are part of large multimeric complexes that are challenging to manipulate. METHODOLOGY/PRINCIPAL FINDINGS We describe here the use of phage display mutagenesis to generate of a new class of binding protein that can be targeted to the pointed-end of actin. These proteins, called synthetic antigen binders (sABs), are based on an antibody-like scaffold where sequence diversity is introduced into the binding loops using a novel "reduced genetic code" phage display library. We describe effective strategies to select and screen for sABs that ensure the generated sABs bind to the pointed-end surface of actin exclusively. CONCLUSIONS/SIGNIFICANCE From our set of pointed-end binders, we identify three sABs with particularly useful properties to systematically probe actin dynamics: one protein that caps the pointed end, a second that crosslinks actin filaments, and a third that severs actin filaments and promotes disassembly.
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114
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Castano E, Philimonenko VV, Kahle M, Fukalová J, Kalendová A, Yildirim S, Dzijak R, Dingová-Krásna H, Hozák P. Actin complexes in the cell nucleus: new stones in an old field. Histochem Cell Biol 2010; 133:607-26. [PMID: 20443021 DOI: 10.1007/s00418-010-0701-2] [Citation(s) in RCA: 49] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 04/12/2010] [Indexed: 01/13/2023]
Abstract
Actin is a well-known protein that has shown a myriad of activities in the cytoplasm. However, recent findings of actin involvement in nuclear processes are overwhelming. Actin complexes in the nucleus range from very dynamic chromatin-remodeling complexes to structural elements of the matrix with single partners known as actin-binding proteins (ABPs). This review summarizes the recent findings of actin-containing complexes in the nucleus. Particular attention is given to key processes like chromatin remodeling, transcription, DNA replication, nucleocytoplasmic transport and to actin roles in nuclear architecture. Understanding the mechanisms involving ABPs will definitely lead us to the principles of the regulation of gene expression performed via concerting nuclear and cytoplasmic processes.
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Affiliation(s)
- E Castano
- Department of Biology of the Cell Nucleus, Institute of Molecular Genetics of the ASCR, Prague, Czech Republic
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115
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Mekhail K, Moazed D. The nuclear envelope in genome organization, expression and stability. Nat Rev Mol Cell Biol 2010; 11:317-28. [PMID: 20414256 DOI: 10.1038/nrm2894] [Citation(s) in RCA: 223] [Impact Index Per Article: 15.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
Non-random positioning of chromosomal domains relative to each other and to nuclear landmarks is a common feature of eukaryotic genomes. In particular, the distribution of DNA loci relative to the nuclear periphery has been linked to both transcriptional activation and repression. Nuclear pores and other integral membrane protein complexes are key players in the dynamic organization of the genome in the nucleus, and recent advances in our understanding of the molecular networks that organize genomes at the nuclear periphery point to a further role for non-random locus positioning in DNA repair, recombination and stability.
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Affiliation(s)
- Karim Mekhail
- Department of Laboratory Medicine and Pathobiology, Faculty of Medicine, University of Toronto, 1 Kings College Circle, Toronto, Ontario, Canada.
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116
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Simon DN, Zastrow MS, Wilson KL. Direct actin binding to A- and B-type lamin tails and actin filament bundling by the lamin A tail. Nucleus 2010; 1:264-72. [PMID: 21327074 PMCID: PMC3027033 DOI: 10.4161/nucl.1.3.11799] [Citation(s) in RCA: 76] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/31/2009] [Revised: 03/08/2010] [Accepted: 03/11/2010] [Indexed: 04/13/2023] Open
Abstract
Nuclear intermediate filament networks formed by A- and B-type lamins are major components of the nucleoskeleton. Lamins have growing links to human physiology and disease including Emery-Dreifuss muscular dystrophy (EDMD), lipodystrophy, cardiomyopathy, neuropathy, cerebellar disorders and segmental accelerated 'aging' syndromes. How lamins interact with other nucleoskeletal components, and even the identities of these other components, are open questions. Previous studies suggested lamins might bind actin. We report that the recombinant C-terminal tail domain of human A- and B-type lamins binds directly to purified actin in high-speed pelleting assays. This interaction maps to a conserved Actin Binding site (AB-1) comprising lamin A residues 461-536 in the Ig-fold domain, which are 54% identical in lamin B1. Two EDMD-causing missense mutations (R527P and L530P) in lamin A that are predicted to disrupt the Ig-fold, each reduced F-actin binding by ∼66%, whereas the surface-exposed lipodystrophy-causing R482Q mutation had no significant effect. The lamin A tail was unique among lamins in having a second actin-binding site (AB-2). This second site was mapped to lamin A tail residues 564-608, based on actin-binding results for the lamin C tail and internal deletions in the lamin A tail that cause Hutchinson-Gilford Progeria Syndrome (Δ35, Δ50) or restrictive dermopathy (Δ90). Supporting the presence of two actin-binding sites, recombinant precursor (unmodified) and mature lamin A tails (not C or B1 tails) each bundled F-actin in vitro: furthermore F-actin bundling was reduced 25-40% by the R527P, L530P, Δ35 and Δ50 mutations, and was abolished by Δ90. Unexpectedly, the mature lamin A tail bound F-actin significantly more efficiently than did the prelamin A tail; this suggested unmodified residues 647-664, unique to prelamin A, might auto-inhibit binding to actin (and potentially other partners). These biochemical results suggest direct mechanisms by which lamins, particularly lamin A, might impact the concentration of free actin in the nucleus or pathways including transcription, nuclear export, chromatin remodeling, chromatin movement and nuclear assembly that require nuclear myosin 1c and polymerizable actin.
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Affiliation(s)
- Dan N Simon
- Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, MD, USA
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117
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Wheeler MA, Warley A, Roberts RG, Ehler E, Ellis JA. Identification of an emerin-beta-catenin complex in the heart important for intercalated disc architecture and beta-catenin localisation. Cell Mol Life Sci 2010; 67:781-96. [PMID: 19997769 PMCID: PMC11115513 DOI: 10.1007/s00018-009-0219-8] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/04/2009] [Revised: 10/29/2009] [Accepted: 11/16/2009] [Indexed: 10/20/2022]
Abstract
How mutations in the protein emerin lead to the cardiomyopathy associated with X-linked Emery-Dreifuss muscular dystrophy (X-EDMD) is unclear. We identified emerin at the adherens junction of the intercalated disc, where it co-localised with the catenin family of proteins. Emerin bound to wild type beta-catenin both in vivo and in vitro. Mutating the GSK3beta phosphorylation sites on beta-catenin abolished this binding. Wild type but not mutant forms of emerin associated with X-EDMD were able to reduce beta-catenin protein levels. Cardiomyocytes from emerin-null mice hearts exhibited erroneous beta-catenin distribution and intercalated disc architecture. Treatment of wild type cardiomyocytes with phenylephrine, which inactivates GSK3beta, redistributed emerin and beta-catenin. Emerin was identified as a direct target of GSK3beta activity since exogenous expression of GSK3beta reduced emerin levels at the nuclear envelope. We propose that perturbation to or total loss of the emerin-beta-catenin complex compromises both intercalated disc function and beta-catenin signalling in cardiomyocytes.
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Affiliation(s)
- Matthew A Wheeler
- The Randall Division of Cell and Molecular Biophysics, King's College London, New Hunts House, Guy's Campus, London, SE1 1UL, UK.
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118
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Abstract
A- and B-type lamins are the major intermediate filaments of the nucleus. Lamins engage in a plethora of stable and transient interactions, near the inner nuclear membrane and throughout the nucleus. Lamin-binding proteins serve an amazingly diverse range of functions. Numerous inner-membrane proteins help anchor lamin filaments to the nuclear envelope, serving as part of the nuclear "lamina" network that is essential for nuclear architecture and integrity. Certain lamin-binding proteins of the inner membrane bind partners in the outer membrane and mechanically link lamins to the cytoskeleton. Inside the nucleus, lamin-binding proteins appear to serve as the "adaptors" by which the lamina organizes chromatin, influences gene expression and epigenetic regulation, and modulates signaling pathways. Transient interactions of lamins with key components of the transcription and replication machinery may provide an additional level of regulation or support to these essential events.
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Affiliation(s)
- Katherine L Wilson
- Department of Cell Biology, Johns Hopkins University School of Medicine, Baltimore, Maryland 21205, USA
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119
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Andrés V, González JM. Role of A-type lamins in signaling, transcription, and chromatin organization. ACTA ACUST UNITED AC 2010; 187:945-57. [PMID: 20038676 PMCID: PMC2806284 DOI: 10.1083/jcb.200904124] [Citation(s) in RCA: 214] [Impact Index Per Article: 15.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/01/2023]
Abstract
A-type lamins (lamins A and C), encoded by the LMNA gene, are major protein constituents of the mammalian nuclear lamina, a complex structure that acts as a scaffold for protein complexes that regulate nuclear structure and functions. Interest in these proteins has increased in recent years with the discovery that LMNA mutations cause a variety of human diseases termed laminopathies, including progeroid syndromes and disorders that primarily affect striated muscle, adipose, bone, and neuronal tissues. In this review, we discuss recent research supporting the concept that lamin A/C and associated nuclear envelope proteins regulate gene expression in health and disease through interplay with signal transduction pathways, transcription factors, and chromatin-associated proteins.
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Affiliation(s)
- Vicente Andrés
- Department of Atherothrombosis and Cardiovascular Imaging, Fundación Centro Nacional de Investigaciones Cardiovasculares Carlos III, Madrid, Spain.
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120
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Haque F, Mazzeo D, Patel JT, Smallwood DT, Ellis JA, Shanahan CM, Shackleton S. Mammalian SUN protein interaction networks at the inner nuclear membrane and their role in laminopathy disease processes. J Biol Chem 2010; 285:3487-98. [PMID: 19933576 PMCID: PMC2823409 DOI: 10.1074/jbc.m109.071910] [Citation(s) in RCA: 216] [Impact Index Per Article: 15.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/01/2009] [Revised: 11/20/2009] [Indexed: 11/06/2022] Open
Abstract
The nuclear envelope (NE) LINC complex, in mammals comprised of SUN domain and nesprin proteins, provides a direct connection between the nuclear lamina and the cytoskeleton, which contributes to nuclear positioning and cellular rigidity. SUN1 and SUN2 interact with lamin A, but lamin A is only required for NE localization of SUN2, and it remains unclear how SUN1 is anchored. Here, we identify emerin and short nesprin-2 isoforms as novel nucleoplasmic binding partners of SUN1/2. These have overlapping binding sites distinct from the lamin A binding site. However, we demonstrate that tight association of SUN1 with the nuclear lamina depends upon a short motif within residues 209-228, a region that does not interact significantly with known SUN1 binding partners. Moreover, SUN1 localizes correctly in cells lacking emerin. Importantly then, the major determinant of SUN1 NE localization has yet to be identified. We further find that a subset of lamin A mutations, associated with laminopathies Emery-Dreifuss muscular dystrophy (EDMD) and Hutchinson-Gilford progeria syndrome (HGPS), disrupt lamin A interaction with SUN1 and SUN2. Despite this, NE localization of SUN1 and SUN2 is not impaired in cell lines from either class of patients. Intriguingly, SUN1 expression at the NE is instead enhanced in a significant proportion of HGPS but not EDMD cells and strongly correlates with pre-lamin A accumulation due to preferential interaction of SUN1 with pre-lamin A. We propose that these different perturbations in lamin A-SUN protein interactions may underlie the opposing effects of EDMD and HGPS mutations on nuclear and cellular mechanics.
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Affiliation(s)
- Farhana Haque
- From the Department of Biochemistry, University of Leicester, Leicester LE1 9HN
| | - Daniela Mazzeo
- From the Department of Biochemistry, University of Leicester, Leicester LE1 9HN
| | - Jennifer T. Patel
- From the Department of Biochemistry, University of Leicester, Leicester LE1 9HN
| | - Dawn T. Smallwood
- From the Department of Biochemistry, University of Leicester, Leicester LE1 9HN
| | - Juliet A. Ellis
- The Randall Division of Cell and Molecular Biophysics, Kings College, London SE1 1UL, and
| | - Catherine M. Shanahan
- the Cardiovascular Division, James Black Centre, Kings College London, 125 Coldharbour Lane, London SE5 9NU, United Kingdom
| | - Sue Shackleton
- From the Department of Biochemistry, University of Leicester, Leicester LE1 9HN
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121
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Zhong Z, Wilson KL, Dahl KN. Beyond lamins other structural components of the nucleoskeleton. Methods Cell Biol 2010; 98:97-119. [PMID: 20816232 DOI: 10.1016/s0091-679x(10)98005-9] [Citation(s) in RCA: 39] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023]
Abstract
The nucleus is bordered by a double bilayer nuclear envelope, communicates with the cytoplasm via embedded nuclear pore complexes, and is structurally supported by an underlying nucleoskeleton. The nucleoskeleton includes nuclear intermediate filaments formed by lamin proteins, which provide major structural and mechanical support to the nucleus. However, other structural proteins also contribute to the function of the nucleoskeleton and help connect it to the cytoskeleton. This chapter reviews nucleoskeletal components beyond lamins and summarizes specific methods and strategies useful for analyzing nuclear structural proteins including actin, spectrin, titin, linker of nucleoskeleton and cytoskeleton (LINC) complex proteins, and nuclear spindle matrix proteins. These components can localize to highly specific functional subdomains at the nuclear envelope or nuclear interior and can interact either stably or dynamically with a variety of partners. These components confer upon the nucleoskeleton a functional diversity and mechanical resilience that appears to rival the cytoskeleton. To facilitate the exploration of this understudied area of biology, we summarize methods useful for localizing, solubilizing, and immunoprecipitating nuclear structural proteins, and a state-of-the-art method to measure a newly-recognized mechanical property of nucleus.
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Affiliation(s)
- Zhixia Zhong
- Department of Chemical Engineering, Carnegie Mellon University, Pittsburgh, Pennsylvania 15213, USA
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122
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Tifft KE, Bradbury KA, Wilson KL. Tyrosine phosphorylation of nuclear-membrane protein emerin by Src, Abl and other kinases. J Cell Sci 2009; 122:3780-90. [PMID: 19789182 DOI: 10.1242/jcs.048397] [Citation(s) in RCA: 45] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/30/2023] Open
Abstract
X-linked recessive Emery-Dreifuss muscular dystrophy (EDMD) is caused by loss of emerin, a nuclear-membrane protein with roles in nuclear architecture, gene regulation and signaling. Phosphoproteomic studies have identified 13 sites of tyrosine phosphorylation in emerin. We validated one study, confirming that emerin is hyper-tyrosine-phosphorylated in Her2-overexpressing cells. We discovered that non-receptor tyrosine kinases Src and Abl each phosphorylate emerin and a related protein, LAP2beta, directly. Src phosphorylated emerin specifically at Y59, Y74 and Y95; the corresponding triple Y-to-F (;FFF') mutation reduced tyrosine phosphorylation by approximately 70% in vitro and in vivo. Substitutions that removed a single hydroxyl moiety either decreased (Y19F, Y34, Y161F) or increased (Y4F) emerin binding to BAF in cells. Y19F, Y34F, Y161F and the FFF mutant also reduced recombinant emerin binding to BAF from HeLa lysates, demonstrating the involvement of both LEM-domain and distal phosphorylatable tyrosines in binding BAF. We conclude that emerin function is regulated by multiple tyrosine kinases, including Her2, Src and Abl, two of which (Her2, Src) regulate striated muscle. These findings suggest roles for emerin as a downstream effector and ;signal integrator' for tyrosine kinase signaling pathway(s) at the nuclear envelope.
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Affiliation(s)
- Kathryn E Tifft
- Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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123
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Lai NS, Wang TF, Wang SL, Chen CY, Yen JY, Huang HL, Li C, Huang KY, Liu SQ, Lin TH, Huang HB. Phostensin caps to the pointed end of actin filaments and modulates actin dynamics. Biochem Biophys Res Commun 2009; 387:676-81. [PMID: 19622346 DOI: 10.1016/j.bbrc.2009.07.086] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/03/2009] [Accepted: 07/15/2009] [Indexed: 10/20/2022]
Abstract
Phostensin, a protein phosphatase 1 F-actin cytoskeleton targeting subunit encoded by KIAA1949, consists of 165 amino acids and is located between HLA-C and HLA-E gene clusters on human chromosome 6. In this current study, we characterized the biochemical functions of phostensin. Actin dynamics assays using gelsolin-actin seeds showed that phostensin decreases the elongation and depolymerization rates of actin filament pointed ends. The feature of phostensin that binds to the pointed ends of actin filaments was observed through fluorescent single filament binding assay. Taken together, our results suggested that phostensin is an actin filament pointed end-capping protein that is capable of modulating actin dynamics.
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Affiliation(s)
- Ning-Sheng Lai
- Department of Medicine, DaLin Tzu Chi Buddhist Hospital, Chia-Yi, Taiwan
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124
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Gieni RS, Hendzel MJ. Actin dynamics and functions in the interphase nucleus: moving toward an understanding of nuclear polymeric actin. Biochem Cell Biol 2009; 87:283-306. [PMID: 19234542 DOI: 10.1139/o08-133] [Citation(s) in RCA: 112] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022] Open
Abstract
Actin exists as a dynamic equilibrium of monomers and polymers within the nucleus of living cells. It is utilized by the cell for many aspects of gene regulation, including mRNA processing, chromatin remodelling, and global gene expression. Polymeric actin is now specifically linked to transcription by RNA polymerase I, II, and III. An active process, requiring both actin polymers and myosin, appears to drive RNA polymerase I transcription, and is also implicated in long-range chromatin movement. This type of mechanism brings activated genes from separate chromosomal territories together, and then participates in their compartmentalization near nuclear speckles. Nuclear speckle formation requires polymeric actin, and factors promoting polymerization, such as profilin and PIP2, are concentrated there. A review of the literature shows that a functional population of G-actin cycles between the cytoplasm and the nucleoplasm. Its nuclear concentration is dependent on the cytoplasmic G-actin pool, as well as on the activity of import and export mechanisms and the availability of interactions that sequester it within the nucleus. The N-WASP-Arp2/3 actin polymer-nucleating mechanism functions in the nucleus, and its mediators, including NCK, PIP2, and Rac1, can be found in the nucleoplasm, where they likely influence the kinetics of polymer formation. The actin polymer species produced are tightly regulated, and may take on conformations not easily recognized by phalloidin. Many of the factors that cleave F-actin in the cytoplasm are present at high levels in the nucleoplasm, and are also likely to affect actin dynamics there. The absolute and relative G-actin content in the nucleoplasm and the cytoplasm of a cell contains information about the homeostatic state of that cell. We propose that the cycling of G-actin between the nucleus and cytoplasm represents a signal transduction mechanism that can function through both extremes of global cellular G-actin content. MAL signalling within the serum response factor pathway, when G-actin levels are low, represents a well-studied example of actin functioning in signal transduction. The translocation of NCK into the nucleus, along with G-actin, during dissolution of the cytoskeleton in response to DNA damage represents another instance of a unique signalling mechanism operating when G-actin levels are high.
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Affiliation(s)
- Randall S Gieni
- Cross Cancer Institute and Department of Oncology, Faculty of Medicine, University of Alberta, Edmonton, ABT6G1Z2, Canada
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125
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Actin microfilaments guide the polarized transport of nuclear pore complexes and the cytoplasmic dispersal of Vasa mRNA during GVBD in the ascidian Halocynthia roretzi. Dev Biol 2009; 330:377-88. [PMID: 19362546 DOI: 10.1016/j.ydbio.2009.04.006] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/03/2008] [Revised: 03/30/2009] [Accepted: 04/03/2009] [Indexed: 12/16/2022]
Abstract
Meiosis reinitiation starts with the germinal vesicle breakdown (GVBD) within the gonad before spawning. Here, we have extended our previous observations and identified the formation of conspicuous actin bundles emanating from the germinal vesicle (GV) during its breakdown in the ascidian Halocynthia roretzi. Time-lapse video recordings and fluorescent labelling of microfilaments (MFs) indicate that these microfilamentous structures invariantly elongate towards the vegetal hemisphere at the estimated speed of 20 mum/min. Interestingly, the nuclear pore complex protein Nup153 accumulates at the vegetal tip of actin bundles. To determine if these structures play a role in the formation of the germ plasm, we have analyzed the localization pattern of Vasa transcript in maturing oocytes and early embryos. We found that Hr-Vasa mRNA, one of Type II postplasmic/PEM mRNAs, changes from a granular and perinuclear localization to an apparent uniform cytoplasmic distribution during oocyte maturation, and then concentrate in the centrosome-attracting body (CAB) by the eight-cell stage. In addition, treatments with Latrunculin B, but not with Nocodazole, blocked the redistribution of Nup153 and Hr-Vasa mRNA, suggesting that these mechanisms are both actin-dependant. We discuss the pleiotropic role played by MFs, and the relationship between nuclear pores, maternal Vasa mRNA and germ plasm in maturing ascidian oocytes.
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126
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KASH-domain proteins and the cytoskeletal landscapes of the nuclear envelope. Biochem Soc Trans 2009; 36:1368-72. [PMID: 19021557 DOI: 10.1042/bst0361368] [Citation(s) in RCA: 11] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Over the last few years, several novel proteins have been identified that facilitate the physical integration of the nucleus with the cytoplasmic compartment. The majority belong to the evolutionarily conserved KASH [klarsicht/ANC-1 (anchorage 1)/SYNE (synaptic nuclear envelope protein) homology]-domain family, which function primarily as exclusive outer nuclear membrane scaffolds that associate with the cytoskeleton, the centrosome and the motor protein apparatus. In the present paper, we propose a novel model, which may explain why these proteins also determine nuclear architecture. Moreover, we discuss further nuclear membrane-tethering devices, which indicate collectively the presence of specific molecular mechanisms that organize the cytoplasmic-nuclear membrane interface in mammalian cells.
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127
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Wang N, Tytell JD, Ingber DE. Mechanotransduction at a distance: mechanically coupling the extracellular matrix with the nucleus. Nat Rev Mol Cell Biol 2009; 10:75-82. [DOI: 10.1038/nrm2594] [Citation(s) in RCA: 1267] [Impact Index Per Article: 84.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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128
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Hofmann WA. Cell and molecular biology of nuclear actin. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2009; 273:219-63. [PMID: 19215906 DOI: 10.1016/s1937-6448(08)01806-6] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/22/2023]
Abstract
Actin is a highly conserved protein and one of the major components of the cytoplasm and the nucleus in eukaryotic cells. In the nucleus, actin is involved in a variety of nuclear processes that include transcription and transcription regulation, RNA processing and export, intranuclear movement, and structure maintenance. Recent advances in the field of nuclear actin have established that functions of actin in the nucleus are versatile, complex, and interconnected. It also has become increasingly evident that the cytoplasmic and nuclear pools of actin are functionally linked. However, while the biological significance of nuclear actin has become clear, we are only beginning to understand the mechanisms that lie behind the regulation of nuclear actin. This review provides an overview of our current understanding of the functions of actin in the nucleus.
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Affiliation(s)
- Wilma A Hofmann
- Department of Physiology and Biophysics, State University of New York, Buffalo, NY, USA
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129
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Dingová H, Fukalová J, Maninová M, Philimonenko VV, Hozák P. Ultrastructural localization of actin and actin-binding proteins in the nucleus. Histochem Cell Biol 2008; 131:425-34. [PMID: 19039601 DOI: 10.1007/s00418-008-0539-z] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Accepted: 10/31/2008] [Indexed: 12/11/2022]
Abstract
Nuclear actin plays an important role in such processes as chromatin remodeling, transcriptional regulation, RNA processing, and nuclear export. Recent research has demonstrated that actin in the nucleus probably exists in dynamic equilibrium between monomeric and polymeric forms, and some of the actin-binding proteins, known to regulate actin dynamics in cytoplasm, have been also shown to be present in the nucleus. In this paper, we present ultrastructural data on distribution of actin and various actin-binding proteins (alpha-actinin, filamin, p190RhoGAP, paxillin, spectrin, and tropomyosin) in nuclei of HeLa cells and resting human lymphocytes. Probing extracts of HeLa cells for the presence of actin-binding proteins also confirmed their presence in nuclei. We report for the first time the presence of tropomyosin and p190RhoGAP in the cell nucleus, and the spatial colocalization of actin with spectrin, paxillin, and alpha-actinin in the nucleolus.
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Affiliation(s)
- Hana Dingová
- Institute of Molecular Genetics, vvi, Academy of Sciences of the Czech Republic, Prague 4, Czech Republic
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130
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Rowat AC, Lammerding J, Herrmann H, Aebi U. Towards an integrated understanding of the structure and mechanics of the cell nucleus. Bioessays 2008; 30:226-36. [PMID: 18293361 DOI: 10.1002/bies.20720] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
Changes in the shape and structural organization of the cell nucleus occur during many fundamental processes including development, differentiation and aging. In many of these processes, the cell responds to physical forces by altering gene expression within the nucleus. How the nucleus itself senses and responds to such mechanical cues is not well understood. In addition to these external forces, epigenetic modifications of chromatin structure inside the nucleus could also alter its physical properties. To achieve a better understanding, we need to elucidate the relationship between nuclear structure and material properties. Recently, new approaches have been developed to systematically investigate nuclear mechanical properties. These experiments provide important new insights into the disease mechanism of a growing class of tissue-specific disorders termed 'nuclear envelopathies'. Here we review our current understanding of what determines the shape and mechanical properties of the cell nucleus.
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Affiliation(s)
- Amy C Rowat
- Department of Physics/School of Engineering and Applied Science, Harvard University, Cambridge, MA 02138, USA.
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131
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The nuclear envelope as an integrator of nuclear and cytoplasmic architecture. FEBS Lett 2008; 582:2023-32. [PMID: 18474238 DOI: 10.1016/j.febslet.2008.05.001] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/29/2008] [Revised: 05/02/2008] [Accepted: 05/05/2008] [Indexed: 12/11/2022]
Abstract
Initially perceived as little more than a container for the genome, our view of the nuclear envelope (NE) and its role in defining global nuclear architecture has evolved significantly in recent years. The recognition that certain human diseases arise from defects in NE components has provided new insight into its structural and regulatory functions. In particular, NE defects associated with striated muscle disease have been shown to cause structural perturbations not just of the nucleus itself but also of the cytoplasm. It is now becoming increasingly apparent that these two compartments display co-dependent mechanical properties. The identification of cytoskeletal binding complexes that localize to the NE now reveals a molecular framework that can seamlessly integrate nuclear and cytoplasmic architecture.
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132
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Vartiainen MK. Nuclear actin dynamics--from form to function. FEBS Lett 2008; 582:2033-40. [PMID: 18423404 DOI: 10.1016/j.febslet.2008.04.010] [Citation(s) in RCA: 66] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/16/2008] [Revised: 03/28/2008] [Accepted: 04/09/2008] [Indexed: 01/10/2023]
Abstract
Cell biological functions of actin have recently expanded from cytoplasm to nucleus, with actin implicated in such diverse processes as gene expression, transcription factor regulation and intranuclear motility. Actin in the nucleus seems to behave differently than in the cytoplasm, raising new questions regarding the molecular mechanisms by which actin functions in cells. In this review, I will discuss dynamic properties of nuclear actin that are related to its polymerization cycle and nucleocytoplasmic shuttling. By comparing the behaviour of nuclear and cytoplasmic actin and their regulators, I try to dissect the underlying differences of these equally important cellular actin pools.
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Affiliation(s)
- Maria K Vartiainen
- Research Program in Cellular Biotechnology, Institute of Biotechnology, University of Helsinki, Viikinkaari 9, 00014 Helsinki, Finland.
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133
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Louvet E, Percipalle P. Transcriptional control of gene expression by actin and myosin. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2008; 272:107-47. [PMID: 19121817 DOI: 10.1016/s1937-6448(08)01603-1] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/01/2022]
Abstract
Recent years have witnessed a new turn in the field of gene expression regulation. Actin and an ever-growing family of actin-associated proteins have been accepted as members of the nuclear crew, regulating eukaryotic gene transcription. In complex with heterogeneous nuclear ribonucleoproteins and certain myosin species, actin has been shown to be an important regulator in RNA polymerase II transcription. Furthermore, actin-based molecular motors are believed to facilitate RNA polymerase I transcription and possibly downstream events during rRNA biogenesis. Probably these findings represent the tip of the iceberg of a rapidly expanding area within the functional architecture of the cell nucleus. Further studies will contribute to clarify how actin mediates nuclear functions with a glance to cytoplasmic signalling. These discoveries have the potential to define novel regulatory networks required to control gene expression at multiple levels.
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Affiliation(s)
- Emilie Louvet
- Department of Cell and Molecular Biology, Medical Nobel Institute, Karolinska Institutet, S-171 77 Stockholm, Sweden
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134
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135
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Stewart CL, Roux KJ, Burke B. Blurring the Boundary: The Nuclear Envelope Extends Its Reach. Science 2007; 318:1408-12. [DOI: 10.1126/science.1142034] [Citation(s) in RCA: 208] [Impact Index Per Article: 12.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
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136
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Wheeler MA, Davies JD, Zhang Q, Emerson LJ, Hunt J, Shanahan CM, Ellis JA. Distinct functional domains in nesprin-1α and nesprin-2β bind directly to emerin and both interactions are disrupted in X-linked Emery–Dreifuss muscular dystrophy. Exp Cell Res 2007; 313:2845-57. [PMID: 17462627 DOI: 10.1016/j.yexcr.2007.03.025] [Citation(s) in RCA: 77] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/15/2007] [Revised: 03/14/2007] [Accepted: 03/18/2007] [Indexed: 11/20/2022]
Abstract
Emerin and specific isoforms of nesprin-1 and -2 are nuclear membrane proteins which are binding partners in multi-protein complexes spanning the nuclear envelope. We report here the characterisation of the residues both in emerin and in nesprin-1alpha and -2beta which are involved in their interaction and show that emerin requires nesprin-1 or -2 to retain it at the nuclear membrane. Using several protein-protein interaction methods, we show that residues 368 to 627 of nesprin-1alpha and residues 126 to 219 of nesprin-2beta, which show high homology to one another, both mediate binding to emerin residues 140-176. This region has previously been implicated in binding to F-actin, beta-catenin and lamin A/C suggesting that it is critical for emerin function. Confirmation that these protein domains interact in vivo was shown using GFP-dominant negative assays. Exogenous expression of either of these nesprin fragments in mouse myoblast C2C12 cells displaced endogenous emerin from the nuclear envelope and reduced the targeting of newly synthesised emerin. Furthermore, we are the first to report that emerin mutations which give rise to X-linked Emery-Dreifuss muscular dystrophy, disrupt binding to both nesprin-1alpha and -2beta isoforms, further indicating a role of nesprins in the pathology of Emery-Dreifuss muscular dystrophy.
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Affiliation(s)
- Matthew A Wheeler
- The Randall Division of Cell and Molecular Biophysics, King's College, New Hunts House, Guy's Campus, London, UK
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137
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Leach N, Bjerke SL, Christensen DK, Bouchard JM, Mou F, Park R, Baines J, Haraguchi T, Roller RJ. Emerin is hyperphosphorylated and redistributed in herpes simplex virus type 1-infected cells in a manner dependent on both UL34 and US3. J Virol 2007; 81:10792-803. [PMID: 17652388 PMCID: PMC2045475 DOI: 10.1128/jvi.00196-07] [Citation(s) in RCA: 97] [Impact Index Per Article: 5.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Cells infected with wild-type herpes simplex virus type 1 (HSV-1) show disruption of the organization of the nuclear lamina that underlies the nuclear envelope. This disruption is reflected in changes in the localization and phosphorylation of lamin proteins. Here, we show that HSV-1 infection causes relocalization of the LEM domain protein emerin. In cells infected with wild-type virus, emerin becomes more mobile in the nuclear membrane, and in cells infected with viruses that fail to express UL34 protein (pUL34) and US3 protein (pUS3), emerin no longer colocalizes with lamins, suggesting that infection causes a loss of connection between emerin and the lamina. Infection causes hyperphosphorylation of emerin in a manner dependent upon both pUL34 and pUS3. Some emerin hyperphosphorylation can be inhibited by the protein kinase Cdelta (PKCdelta) inhibitor rottlerin. Emerin and pUL34 interact physically, as shown by pull-down and coimmunoprecipitation assays. Emerin expression is not, however, necessary for infection, since virus growth is not impaired in cells derived from emerin-null transgenic mice. The results suggest a model in which pUS3 and PKCdelta that has been recruited by pUL34 hyperphosphorylate emerin, leading to disruption of its connections with lamin proteins and contributing to the disruption of the nuclear lamina. Changes in emerin localization, nuclear shape, and lamin organization characteristic of cells infected with wild-type HSV-1 also occur in cells infected with recombinant virus that does not make viral capsids, suggesting that these changes occur independently of capsid envelopment.
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Affiliation(s)
- Natalie Leach
- Department of Microbiology, The University of Iowa, 3-432 Bowen Science Building, Iowa City, IA 52242, USA
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138
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Holaska JM, Wilson KL. An emerin "proteome": purification of distinct emerin-containing complexes from HeLa cells suggests molecular basis for diverse roles including gene regulation, mRNA splicing, signaling, mechanosensing, and nuclear architecture. Biochemistry 2007; 46:8897-908. [PMID: 17620012 PMCID: PMC2635128 DOI: 10.1021/bi602636m] [Citation(s) in RCA: 140] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/16/2022]
Abstract
Using recombinant bead-conjugated emerin, we affinity-purified seven proteins from HeLa cell nuclear lysates that bind emerin either directly or indirectly. These proteins were identified by mass spectrometry as nuclear alphaII-spectrin, nonmuscle myosin heavy chain alpha, Lmo7 (a predicted transcription regulator; reported separately), nuclear myosin I, beta-actin (reported separately), calponin 3, and SIKE. We now report that emerin binds nuclear myosin I (NMI, a molecular motor) directly in vitro. Furthermore, bead-conjugated emerin bound nuclear alphaII-spectrin and NMI equally well with or without ATP (which stimulates motor activity), whereas ATP decreased actin binding by 65%. Thus alphaII-spectrin and NMI interact stably with emerin. To investigate the physiological relevance of these interactions, we used antibodies against emerin to affinity-purify emerin-associated protein complexes from HeLa cells and then further purified by ion-exchange chromatography to resolve by net charge and by size exclusion chromatography yielding six distinct emerin-containing fractions (0.5-1.6 MDa). Western blotting suggested that each complex had distinct components involved in nuclear architecture (e.g., NMI, alphaII-spectrin, lamins) or gene or chromatin regulation (BAF, transcription regulators, HDACs). Additional constituents were identified by mass spectrometry. One putative gene-regulatory complex (complex 32) included core components of the nuclear corepressor (NCoR) complex, which mediates gene regulation by thyroid hormone and other nuclear receptors. When expressed in HeLa cells, FLAG-tagged NCoR subunits Gps2, HDAC3, TBLR1, and NCoR each co-immunoprecipitated emerin, validating one putative complex. These findings support the hypothesis that emerin scaffolds a variety of functionally distinct multiprotein complexes at the nuclear envelope in vivo. Notably included are nuclear myosin I-containing complexes that might sense and regulate mechanical tension at the nuclear envelope.
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Affiliation(s)
| | - Katherine L. Wilson
- Address correspondence to Katherine L. Wilson, Department of Cell Biology, The Johns Hopkins School of Medicine, 725 N. Wolfe St, Baltimore, MD 21205. Phone: 410-955-1801. Fax: 410-955-4129.
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139
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Gieni RS, Hendzel MJ. Mechanotransduction from the ECM to the genome: Are the pieces now in place? J Cell Biochem 2007; 104:1964-87. [PMID: 17546585 DOI: 10.1002/jcb.21364] [Citation(s) in RCA: 119] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
A multitude of biochemical signaling processes have been characterized that affect gene expression and cellular activity. However, living cells often need to integrate biochemical signals with mechanical information from their microenvironment as they respond. In fact, the signals received by shape alone can dictate cell fate. This mechanotrasduction of information is powerful, eliciting proliferation, differentiation, or apoptosis in a manner dependent upon the extent of physical deformation. The cells internal "prestressed" structure and its "hardwired" interaction with the extra-cellular matrix (ECM) appear to confer this ability to filter biochemical signals and decide between divergent cell functions influenced by the nature of signals from the mechanical environment. In some instances mechanical signaling through the tissue microenvironment has been shown to be dominant over genomic defects, imparting a normal phenotype on cells that otherwise have transforming genetic lesions. This mechanical control of phenotype is postulated to have a central role in embryogenesis, tissue physiology as well as the pathology of a wide variety of diseases, including cancer. We will briefly review studies showing physical continuity between the external cellular microenvironment and the interior of the cell nucleus. Newly characterized structures, termed nuclear envelope lamina spanning complexes (NELSC), and their interactions will be described as part of a model for mechanical transduction of extracellular cues from the ECM to the genome.
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Affiliation(s)
- Randall S Gieni
- Cross Cancer Institute and Department of Oncology, Faculty of Medicine, University of Alberta, Edmonton, Alberta, Canada
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140
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Vlcek S, Foisner R. A-type lamin networks in light of laminopathic diseases. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2007; 1773:661-74. [PMID: 16934891 DOI: 10.1016/j.bbamcr.2006.07.002] [Citation(s) in RCA: 37] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/10/2006] [Revised: 07/10/2006] [Accepted: 07/12/2006] [Indexed: 11/22/2022]
Abstract
Lamins are major structural components of the lamina providing mechanical support for the nuclear envelope in vertebrates. A subgroup of lamins, the A-type lamins, are only expressed in differentiated cells and serve important functions both at the nuclear envelope and in the nucleoplasm in higher order chromatin organization and gene regulation. Mutations in A-type lamins cause a variety of diseases from muscular dystrophy and lipodystrophy to systemic diseases such as premature ageing syndromes. The molecular basis of these diseases is still unknown. Here we summarize known interactions of A-type lamins with components of the nuclear envelope and the nucleoplasm and discuss their potential involvement in the etiology and molecular mechanisms of the diseases. Lamin binding partners involve chromatin proteins potentially involved in higher order chromatin organization, transcriptional regulators controlling gene expression during cell cycle progression, differentiation and senescence, and several enzymes involved in a multitude of functions.
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Affiliation(s)
- Sylvia Vlcek
- Max. F. Perutz Laboratories, Department of Medical Biochemistry, Medical University of Vienna, Dr. Bohr-Gasse 9, A-1030 Vienna, Austria
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141
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Houben F, Ramaekers FCS, Snoeckx LHEH, Broers JLV. Role of nuclear lamina-cytoskeleton interactions in the maintenance of cellular strength. BIOCHIMICA ET BIOPHYSICA ACTA-MOLECULAR CELL RESEARCH 2007; 1773:675-86. [PMID: 17050008 DOI: 10.1016/j.bbamcr.2006.09.018] [Citation(s) in RCA: 96] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 04/21/2006] [Revised: 07/12/2006] [Accepted: 09/08/2006] [Indexed: 01/08/2023]
Abstract
The response of individual cells to cellular stress is vital for cellular functioning. A large network of physically interconnected cellular components, starting from the structural components of the cells' nucleus, via cytoskeleton filaments to adhesion molecules and the extracellular matrix, constitutes an integrated matrix that functions as a scaffold allowing the cell to cope with mechanical stress. Next to a role in mechanical properties, this network also has a mechanotransductional function in the response to mechanical stress. This signaling route does not only regulate a rapid reorganization of structural components such as actin filaments, but also stimulates for example gene activation via NFkappaB and other transcription factors. The importance of an intact mechano-signaling network is illustrated by the physiological consequences of several genetic defects of cellular network components e.g. actin, dystrophin, desmin and lamins. These give rise to an impaired response of the affected cells to mechanical stress and often result in dystrophy of the affected tissue. Recently, the importance of the cell nucleus in cellular strength has been established. Several new interconnecting proteins, such as the nesprins that link the nuclear lamina to the cytoskeleton, have been identified. Furthermore, the function of nuclear lamins in determining cellular strength and nuclear stability was illustrated in lamin-knock-out cells. Absence of the A-type lamins or mutations in these structural components of the nuclear lamina lead to an impaired cellular response to mechanical stress and disturbances in cytoskeletal organization. In addition, laminopathies show clinical phenotypes comparable to those seen for diseases resulting from genetic defects in cytoskeletal components, further indicating that lamins play a central role in maintaining the mechanical properties of the cell.
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Affiliation(s)
- F Houben
- Department of Molecular Cell Biology, Cardiovascular Research Institute Maastricht (CARIM) and Research Institute for Growth and Development (GROW), University of Maastricht, Maastricht, The Netherlands.
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142
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Morris JB, Hofemeister H, O'Hare P. Herpes simplex virus infection induces phosphorylation and delocalization of emerin, a key inner nuclear membrane protein. J Virol 2007; 81:4429-37. [PMID: 17301149 PMCID: PMC1900177 DOI: 10.1128/jvi.02354-06] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/27/2006] [Accepted: 02/02/2007] [Indexed: 02/07/2023] Open
Abstract
The inner nuclear membrane (INM) contains specialized membrane proteins that selectively interact with nuclear components including the lamina, chromatin, and DNA. Alterations in the organization of and interactions with INM and lamina components are likely to play important roles in herpesvirus replication and, in particular, exit from the nucleus. Emerin, a member of the LEM domain class of INM proteins, binds a number of nuclear components including lamins, the DNA-bridging protein BAF, and F-actin and is thought to be involved in maintaining nuclear integrity. Here we report that emerin is quantitatively modified during herpes simplex virus (HSV) infection. Modification begins early in infection, involves multiple steps, and is reversed by phosphatase treatment. Emerin phosphorylation during infection involves one or more cellular kinases but can also be influenced by the US3 viral kinase, a protein whose function is known to be involved in HSV nuclear egress. The results from biochemical extraction analyses and from immunofluorescence of the detergent-resistant population demonstrate that emerin association with the INM significantly reduced during infection. We propose that the induction of emerin phosphorylation in infected cells may be involved in nuclear egress and uncoupling interactions with targets such as the lamina, chromatin, or cytoskeletal components.
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Affiliation(s)
- James B Morris
- Marie Curie Research Institute, The Chart, Oxted, Surrey RH8 0TL, United Kingdom
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143
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Roux KJ, Burke B. Nuclear envelope defects in muscular dystrophy. Biochim Biophys Acta Mol Basis Dis 2007; 1772:118-27. [PMID: 16904876 DOI: 10.1016/j.bbadis.2006.06.001] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/16/2006] [Accepted: 06/03/2006] [Indexed: 11/29/2022]
Abstract
Muscular dystrophies are a heterogeneous group of disorders linked to defects in 20-30 different genes. Mutations in the genes encoding a pair of nuclear envelope proteins, emerin and lamin A/C, have been shown to cause the X-linked and autosomal forms respectively of Emery-Dreifuss muscular dystrophy. A third form of muscular dystrophy, limb girdle muscular dystrophy 1b, has also been linked to mutations in the lamin A/C gene. Given that these two genes are ubiquitously expressed, a major goal is to determine how they can be associated with tissue specific diseases. Recent results suggest that lamin A/C and emerin contribute to the maintenance of nuclear envelope structure and at the same time may modulate the expression patterns of certain mechanosensitive and stress induced genes. Both emerin and lamin A/C may play an important role in the response of cells to mechanical stress and in this way may help to maintain muscle cell integrity.
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Affiliation(s)
- Kyle J Roux
- Department of Anatomy and Cell Biology, The University of Florida College of Medicine, 1600 SW Archer Road, Gainesville, FL 32606, USA
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144
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Brachner A, Reipert S, Foisner R, Gotzmann J. LEM2 is a novel MAN1-related inner nuclear membrane protein associated with A-type lamins. J Cell Sci 2007; 118:5797-810. [PMID: 16339967 DOI: 10.1242/jcs.02701] [Citation(s) in RCA: 115] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023] Open
Abstract
The LEM (lamina-associated polypeptide-emerin-MAN1) domain is a motif shared by a group of lamin-interacting proteins in the inner nuclear membrane (INM) and in the nucleoplasm. The LEM domain mediates binding to a DNA-crosslinking protein, barrier-to-autointegration factor (BAF). We describe a novel, ubiquitously expressed LEM domain protein, LEM2, which is structurally related to MAN1. LEM2 contains an N-terminal LEM motif, two predicted transmembrane domains and a MAN1-Src1p C-terminal (MSC) domain highly homologous to MAN1, but lacks the MAN1-specific C-terminal RNA-recognition motif. Immunofluorescence microscopy of digitonin-treated cells and subcellular fractionation identified LEM2 as a lamina-associated protein residing in the INM. LEM2 binds to the lamin C tail in vitro. Targeting of LEM2 to the nuclear envelope requires A-type lamins and is mediated by the N-terminal and transmembrane domains. Highly overexpressed LEM2 accumulates in patches at the nuclear envelope and forms membrane bridges between nuclei of adjacent cells. LEM2 structures recruit A-type lamins, emerin, MAN1 and BAF, whereas lamin B and lamin B receptor are excluded. Our data identify LEM2 as a novel A-type-lamin-associated INM protein involved in nuclear structure organization.
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Affiliation(s)
- Andreas Brachner
- Department of Medical Biochemistry, Max F. Perutz Laboratories, Vienna Biocenter, Medical University of Vienna, Dr Bohrgasse 9/3, A-1030 Vienna, Austria
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145
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de Visser M. Myopathies with early contractures. HANDBOOK OF CLINICAL NEUROLOGY 2007; 86:35-59. [PMID: 18808994 DOI: 10.1016/s0072-9752(07)86002-7] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/26/2023]
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146
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Wagner N, Krohne G. LEM‐Domain Proteins: New Insights into Lamin‐Interacting Proteins. INTERNATIONAL REVIEW OF CYTOLOGY 2007; 261:1-46. [PMID: 17560279 DOI: 10.1016/s0074-7696(07)61001-8] [Citation(s) in RCA: 119] [Impact Index Per Article: 7.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
LEM-domain proteins present a growing family of nonrelated inner nuclear membrane and intranuclear proteins, including emerin, MAN1, LEM2, several alternatively spliced isoforms of LAP2, and various uncharacterized proteins in higher eukaryotes as well as the Drosophila-specific proteins otefin and Bocksbeutel. LEM-domain proteins are involved in diverse cellular processes including replication and cell cycle control, chromatin organization and nuclear assembly, the regulation of gene expression and signaling pathways, as well as retroviral infection. Genetic analyses in different model organisms reveal new insights into the various functions of LEM-domain proteins, lamins, and their involvement in laminopathic diseases. All these findings as well as previously proposed ideas and models have been summarized to broaden our view of this exciting protein family.
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Affiliation(s)
- Nicole Wagner
- Department of Developmental Biology, Wenner-Gren Institute, Stockholm University, S-10691 Stockholm, Sweden
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147
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Rowat AC, Lammerding J, Ipsen JH. Mechanical properties of the cell nucleus and the effect of emerin deficiency. Biophys J 2006; 91:4649-64. [PMID: 16997877 PMCID: PMC1779937 DOI: 10.1529/biophysj.106.086454] [Citation(s) in RCA: 163] [Impact Index Per Article: 9.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/03/2006] [Accepted: 09/05/2006] [Indexed: 11/18/2022] Open
Abstract
Nuclear structure and mechanics are gaining recognition as important factors that affect gene expression, development, and differentiation in normal function and disease, yet the physical mechanisms that govern nuclear mechanical stability remain unclear. Here we examined the physical properties of the cell nucleus by imaging fluorescently labeled components of the inner nucleus (chromatin and nucleoli) and the nuclear envelope (lamins and membranes) in nuclei deformed by micropipette aspiration (confocal imaged microdeformation). We investigated nuclei, both isolated and in intact, living cells, and found that nuclear volume significantly decreased by 60-70% during aspiration. While nuclear membranes exhibited blebbing and fluid characteristics during aspiration, the nuclear lamina exhibited behavior of a solid-elastic shell. Under large deformations of GFP-lamin A-labeled nuclei, we observed a decay of fluorescence intensity into the tip of the deformed tongue that we interpreted in terms of nonlinear, two-dimensional elasticity theory. Here we applied this method to study nuclear envelope stability in disease and found that mouse embryo fibroblasts lacking the inner nuclear membrane protein, emerin, had a significantly decreased ratio of the area expansion to shear moduli (K/mu) compared to wild-type cells (2.1 +/- 0.2 versus 5.1 +/- 1.3). These data suggest that altered nuclear envelope elasticity caused by loss of emerin could contribute to increased nuclear fragility in Emery-Dreifuss muscular dystrophy patients with mutations in the emerin gene. Based on our experimental results and theoretical considerations, we present a model describing how the nucleus is stabilized in the pipette. Such a model is essential for interpreting the results of any micropipette study of the nucleus and porous materials in general.
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Affiliation(s)
- A C Rowat
- MEMPHYS Centre for Biomembrane Physics, Department of Physics, University of Southern Denmark, Odense, Denmark.
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148
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Feierbach B, Piccinotti S, Bisher M, Denk W, Enquist LW. Alpha-herpesvirus infection induces the formation of nuclear actin filaments. PLoS Pathog 2006; 2:e85. [PMID: 16933992 PMCID: PMC1550268 DOI: 10.1371/journal.ppat.0020085] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/11/2006] [Accepted: 06/12/2006] [Indexed: 02/07/2023] Open
Abstract
Herpesviruses are large double-stranded DNA viruses that replicate in the nuclei of infected cells. Spatial control of viral replication and assembly in the host nucleus is achieved by the establishment of nuclear compartments that serve to concentrate viral and host factors. How these compartments are established and maintained remains poorly understood. Pseudorabies virus (PRV) is an alpha-herpesvirus often used to study herpesvirus invasion and spread in the nervous system. Here, we report that PRV and herpes simplex virus type 1 infection of neurons results in formation of actin filaments in the nucleus. Filamentous actin is not found in the nucleus of uninfected cells. Nuclear actin filaments appear physically associated with the viral capsids, as shown by serial block-face scanning electron micropscopy and confocal microscopy. Using a green fluorescent protein-tagged viral capsid protein (VP26), we show that nuclear actin filaments form prior to capsid assembly and are required for the efficient formation of viral capsid assembly sites. We find that actin polymerization dynamics (e.g., treadmilling) are not necessary for the formation of these sites. Green fluorescent protein-VP26 foci co-localize with the actin motor myosin V, suggesting that viral capsids travel along nuclear actin filaments using myosin-based directed transport. Viral transcription, but not viral DNA replication, is required for actin filament formation. The finding that infection, by either PRV or herpes simplex virus type 1, results in formation of nuclear actin filaments in neurons, and that PRV infection of an epithelial cell line results in a similar phenotype is evidence that F-actin plays a conserved role in herpesvirus assembly. Our results suggest a mechanism by which assembly domains are organized within infected cells and provide insight into how the viral infectious cycle and host actin cytoskeleton are integrated to promote the infection process. Regulation of subcellular organization and transport is essential for control of crucial biological processes. However, our knowledge often is hampered because these processes tend to be transient and difficult to study. Studies of how opportunistic microbes hijack cellular machinery have provided insights into various normal cell processes. For example, studies with intracellular microorganisms, such as Listeria monocytogenes, Shigella spp., Rickettsia spp., and vaccinia virus, have significantly increased our understanding of the dynamic nature of the actin cytoskeleton. However, much less is known about subcellular organization and transport of cargo in the nucleus. The authors have discovered that alpha-herpesvirus infection of neurons leads to the transient formation of actin filaments in the nucleus. These filaments do not fill the nucleus, but rather associate with newly formed viral capsids. The nuclear actin filaments were initially identified in peripheral nervous system tissue using a new imaging technology, serial section scanning electron microscopy pioneered by Winfried Denk (a co-author). Their results suggest that nuclear actin filaments form as part of a general stress response to infection, but then are co-opted, perhaps to direct capsid transport to sites of budding along the nuclear envelope. This work illuminates a less well understood part of the viral life cycle and sets the stage for future work investigating control of how cargo is organized and moved in the nucleus.
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Affiliation(s)
- Becket Feierbach
- Department of Molecular Biology, Princeton University, Princeton, New Jersey, USA.
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149
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Holaska JM, Wilson KL. Multiple roles for emerin: implications for Emery-Dreifuss muscular dystrophy. ACTA ACUST UNITED AC 2006; 288:676-80. [PMID: 16761279 PMCID: PMC2559942 DOI: 10.1002/ar.a.20334] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023]
Abstract
X-linked Emery-Dreifuss muscular dystrophy (X-EDMD) is inherited through mutations in EMD, which encodes a nuclear membrane protein named emerin. Emerin is expressed in most cells, but EDMD strikes specific tissues. This review summarizes growing evidence that emerin has roles in both tissue-specific gene regulation and the mechanical integrity of the nucleus and discusses how these roles might impact EDMD.
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Affiliation(s)
| | - Katherine L. Wilson
- Corresponding Author: Katherine L. Wilson, , Phone: 410-955-1801, Fax: 410-955-4129
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150
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Holaska JM, Rais-Bahrami S, Wilson KL. Lmo7 is an emerin-binding protein that regulates the transcription of emerin and many other muscle-relevant genes. Hum Mol Genet 2006; 15:3459-72. [PMID: 17067998 DOI: 10.1093/hmg/ddl423] [Citation(s) in RCA: 122] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
X-linked Emery-Dreifuss muscular dystrophy (X-EDMD) is inherited through mutations in emerin, a nuclear membrane protein. Emerin has proposed roles in nuclear architecture and gene regulation, but direct molecular links to disease were unknown. We report that Lim-domain only 7 (Lmo7) binds emerin directly with 125 nM affinity; the C-terminal half of human Lmo7 (hLmo7C) was sufficient to bind emerin in vitro. Lmo7 appeared relevant to EDMD because a deletion that removes Lmo7 (plus eight exons of a neighboring gene) in mice causes dystrophic muscles [Semenova, E., Wang, X., Jablonski, M.M., Levorse, J. and Tilghman, S.M. (2003) An engineered 800 kilobase deletion of Uchl3 and Lmo7 on mouse chromosome 14 causes defects in viability, postnatal growth and degeneration of muscle and retina. Hum. Mol. Genet., 12, 1301-1312]. Lmo7 localizes in the nucleus, cytoplasm and cell surface, particularly adhesion junctions [Ooshio, T., Irie, K., Morimoto, K., Fukuhara, A., Imai, T. and Takai, Y. (2004) Involvement of LMO7 in the association of two cell-cell adhesion molecules, nectin and E-cadherin, through afadin and alpha-actinin in epithelial cells. J. Biol. Chem., 279, 31365-31373]. Our data suggest endogenous Lmo7 is a nucleocytoplasmic shuttling protein, and might also localize at focal adhesions in HeLa cells. Two key results show that Lmo7 regulates emerin gene expression: rat Lmo7 isoforms directly activated a luciferase reporter gene in vivo, and emerin mRNA expression decreased 93% in Lmo7-downregulated HeLa cells. Thus, Lmo7 not only binds emerin protein but is also required for emerin gene transcription. Microarray analysis of Lmo7-downregulated HeLa cells identified over 4200 misregulated genes, including 46 genes important for muscle or heart. Misregulation of 11 genes, including four (CREBBP, NAP1L1, LAP2, RBL2) known to be misregulated in X-EDMD patients and emerin-null mice [Bakay, M., Wang, Z., Melcon, G., Schiltz, L., Xuan, J., Zhao, P., Sartorelli, V., Seo, J., Pegoraro, E., Angelini, C. et al. (2006) Nuclear envelope dystrophies show a transcriptional fingerprint suggesting disruption of Rb-MyoD pathways in muscle regeneration. Brain, 129, 996-1013; Melcon, G., Kozlov, S., Cutler, D.A., Sullivan, T., Hernandez, L., Zhao, P., Mitchell, S., Nader, G., Bakay, M., Rottman, J.N. et al. (2006) Loss of emerin at the nuclear envelope disrupts the Rb1/E2F and MyoD pathways during muscle regeneration. Hum. Mol. Genet., 15, 637-651] was confirmed by real-time PCR. Overexpression of wild-type emerin, but not emerin mutant P183H (which causes EDMD and selectively disrupts binding to Lmo7), decreased the expression of CREBBP, NAP1L1 and LAP2, suggesting Lmo7 activity is both EDMD-relevant and inhibited by direct binding to emerin. We conclude that Lmo7 positively regulates many EDMD-relevant genes (including emerin), and is feedback-regulated by binding to emerin.
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Affiliation(s)
- James M Holaska
- Department of Cell Biology, The Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA
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