The Experts below are selected from a list of 5916 Experts worldwide ranked by ideXlab platform
Philippe Bouvet - One of the best experts on this subject based on the ideXlab platform.
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Nucleolin Interacts and Co-Localizes with Components of Pre-Catalytic Spliceosome Complexes
Sci, 2019Co-Authors: Iva Ugrinova, Karine Monier, Mounira Chalabi-dchar, Philippe BouvetAbstract:Nucleolin is an RNA binding protein that is involved in many post-transcriptional regulation steps of messenger RNAs in addition to its nucleolar role in ribosomal RNA transcription and assembly in pre-ribosomes. Acetylated Nucleolin was found to be associated with nuclear speckles and to co-localize with the splicing factor SC35. Previous nuclear pull down of Nucleolin identified several splicing components and factors involved in RNA polymerase II transcription associated with Nucleolin. In this report, we show that these splicing components are specifics of the pre-catalytic A and B spliceosomes, while proteins recruited in the Bact, C and P complexes are absent from the Nucleolin interacting proteins. Furthermore, we show that acetylated Nucleolin co-localized with P-SF3B1, a marker of co-transcriptional active spliceosomes. P-SF3B1 complexes can be pulled down with Nucleolin specific antibodies. Interestingly, the alternative splicing of Fibronectin at the IIICS and EDB sites was affected by Nucleolin depletion. These data are consistent with a model where Nucleolin could be a factor bridging RNA polymerase II transcription and assembly of pre-catalytic spliceosome similarly to its function in the co-transcriptional maturation of pre-rRNA.
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Integrated analysis of mRNA and miRNA expression in HeLa cells expressing low levels of Nucleolin
Scientific Reports, 2017Co-Authors: Sanjeev Kumar, Iva Ugrinova, Sadhan Das, Karine Monier, Fabien Mongelard, Xavier Gaume, Mounira Chalabi-dchar, Elizabhet Cruz Gomez, Cong Rong, Philippe BouvetAbstract:Nucleolin is an essential protein that plays important roles in the regulation of cell cycle and cell proliferation. Its expression is up regulated in many cancer cells but its molecular functions are not well characterized. Nucleolin is present in the nucleus where it regulates gene expression at the transcriptional and post-transcriptional levels. Using HeLa cells depleted in Nucleolin we performed an mRNA and miRNA transcriptomics analysis to identify biological pathways involving Nucleolin. Bioinformatic analysis strongly points to a role of Nucleolin in lipid metabolism, and in many signaling pathways. Down regulation of Nucleolin is associated with lower level of cholesterol while the amount of fatty acids is increased. This could be explained by the decreased and mis-localized expression of the transcription factor SREBP1 and the down-regulation of enzymes involved in the beta-oxidation and degradation of fatty acids. Functional classification of the miRNA-mRNA target genes revealed that deregulated miRNAs target genes involved in apoptosis, proliferation and signaling pathways. Several of these deregulated miRNAs have been shown to control lipid metabolism. This integrated transcriptomic analysis uncovers new unexpected roles for Nucleolin in metabolic regulation and signaling pathways paving the way to better understand the global function of Nucleolin within the cell.
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Expression of Nucleolin Affects Microtubule Dynamics.
PloS one, 2016Co-Authors: Xavier Gaume, Karine Monier, Hélène Delage, Fabien Mongelard, Christophe Place, Philippe BouvetAbstract:Nucleolin is present in diverse cellular compartments and is involved in a variety of cellular processes from nucleolar structure and function to intracellular trafficking, cell adhesion and migration. Recently, Nucleolin has been localized at the mature centriole where it is involved in microtubule nucleation and anchoring. Although this new function of Nucleolin linked to microtubule regulation has been identified, the global effects of Nucleolin on microtubule dynamics have not been addressed yet. In the present study, we analyzed the roles of Nucleolin protein levels on global microtubule dynamics by tracking the EB3 microtubule plus end binding protein in live cells. We have found that during microtubule growth phases, Nucleolin affects both the speed and life time of polymerization and by analyzing catastrophe events, we showed that Nucleolin reduces catastrophe frequency. This new property of Nucleolin was then confirmed in a cold induced microtubule depolymerization experiment in which we have found that cold resistant microtubules were totally destabilized in Nucleolin depleted cells. Altogether, our data demonstrate a new function of Nucleolin on microtubule stabilization, thus bringing novel insights into understanding the multifunctional properties of Nucleolin in healthy and cancer cells.
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interaction of Nucleolin with ribosomal rna genes and its role in rna polymerase i transcription
Nucleic Acids Research, 2012Co-Authors: Rong Cong, Iva Ugrinova, Sadhan Das, Fabien Mongelard, Sanjeev Kumar, Jiemin Wong, Philippe BouvetAbstract:Nucleolin is a multi-functional nucleolar protein that is required for ribosomal RNA gene (rRNA) transcription in vivo, but the mechanism by which Nucleolin modulates RNA polymerase I (RNAPI) transcription is not well understood. Nucleolin depletion results in an increase in the heterochromatin mark H3K9me2 and a decrease in H4K12Ac and H3K4me3 euchromatin histone marks in rRNA genes. ChIP-seq experiments identified an enrichment of Nucleolin in the ribosomal DNA (rDNA) coding and promoter region. Nucleolin is preferentially associated with unmethylated rRNA genes and its depletion leads to the accumulation of RNAPI at the beginning of the transcription unit and a decrease in UBF along the coding and promoter regions. Nucleolin is able to affect the binding of transcription termination factor-1 on the promoter-proximal terminator T0, thus inhibiting the recruitment of TIP5 and HDAC1 and the establishment of a repressive heterochromatin state. These results reveal the importance of Nucleolin for the maintenance of the euchromatin state and transcription elongation of rDNA.
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The Multiple Properties and Functions of Nucleolin
The Nucleolus, 2011Co-Authors: Rong Cong, Sadhan Das, Philippe BouvetAbstract:Nucleolin, one of the most abundant proteins of the nucleolus is a fascinating protein with multiple proposed functions within and outside the nucleoli. Since its discovery almost 40 years ago, it was proposed that Nucleolin is involved in ribosome biogenesis but until recently the molecular mechanisms of this involvement were not known. Thanks to the development of new research strategies, it is now clear that Nucleolin is an essential protein for RNA polymerase I transcription, ribosome assembly, cell cycle, and cell proliferation, but the mechanisms of these functions have just begun to be unraveled. In this review, we highlight the most recent data on Nucleolin’s properties and functions in the nucleolus and nucleoplasm.
Angela Pearson - One of the best experts on this subject based on the ideXlab platform.
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Involvement of the UL24 protein in herpes simplex virus 1-induced dispersal of B23 and in nuclear egress.
Virology, 2011Co-Authors: Maria H Lymberopoulos, Amélie Bourget, Nawel Ben Abdeljelil, Angela PearsonAbstract:UL24 of herpes simplex virus 1 (HSV-1) is widely conserved within the Herpesviridae family. Herein, we tested the hypothesis that UL24, which we have previously shown to induce the redistribution of Nucleolin, also affects the localization of the nucleolar protein B23. We found that HSV-1-induced dispersal of B23 was dependent on UL24. The conserved N-terminal portion of UL24 was sufficient to induce the redistribution of B23 in transient transfection assays. Mutational analysis revealed that the endonuclease motif of UL24 was important for B23 dispersal in both transfected and infected cells. Nucleolar protein relocalization during HSV-1 infection was also observed in non-immortalized cells. Analysis of infected cells by electron microscopy revealed a decrease in the ratio of cytoplasmic versus nuclear viral particles in cells infected with a UL24-deficient strain compared to KOS-infected cells. Our results suggest that UL24 promotes nuclear egress of nucleocapsids during HSV-1 infection, possibly though effects on nucleoli.
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Conserved residues in the UL24 protein of herpes simplex virus 1 are important for dispersal of the nucleolar protein Nucleolin.
Journal of Virology, 2010Co-Authors: Luc Bertrand, Gabriel André Leiva-torres, Huda Hyjazie, Angela PearsonAbstract:The UL24 family of proteins is widely conserved among herpesviruses. We demonstrated previously that UL24 of herpes simplex virus 1 (HSV-1) is important for the dispersal of Nucleolin from nucleolar foci throughout the nuclei of infected cells. Furthermore, the N-terminal portion of UL24 localizes to nuclei and can disperse Nucleolin in the absence of any other viral proteins. In this study, we tested the hypothesis that highly conserved residues in UL24 are important for the ability of the protein to modify the nuclear distribution of Nucleolin. We constructed a panel of substitution mutations in UL24 and tested their effects on Nucleolin staining patterns. We found that modified UL24 proteins exhibited a range of subcellular distributions. Mutations associated with a wild-type localization pattern for UL24 correlated with high levels of Nucleolin dispersal. Interestingly, mutations targeting two regions, namely, within the first homology domain and overlapping or near the previously identified PD-(D/E)XK endonuclease motif, caused the most altered UL24 localization pattern and the most drastic reduction in its ability to disperse Nucleolin. Viral mutants corresponding to the substitutions G121A and E99A/K101A both exhibited a syncytial plaque phenotype at 39 degrees C. vUL24-E99A/K101A replicated to lower titers than did vUL24-G121A or KOS. Furthermore, the E99A/K101A mutation caused the greatest impairment of HSV-1-induced dispersal of Nucleolin. Our results identified residues in UL24 that are critical for the ability of UL24 to alter nucleoli and further support the notion that the endonuclease motif is important for the function of UL24 during infection.
Bernard Krust - One of the best experts on this subject based on the ideXlab platform.
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Surface Expressed Nucleolin Is Constantly Induced in Tumor Cells to Mediate Calcium-Dependent Ligand Internalization
PloS one, 2010Co-Authors: Ara G. Hovanessian, Calaiselvy Soundaramourty, Diala El Khoury, Isabelle Nondier, Josette Svab, Bernard KrustAbstract:Background Nucleolin is one of the major proteins of the nucleolus, but it is also expressed on the cell surface where is serves as a binding protein for variety of ligands implicated in tumorigenesis and angiogenesis. Emerging evidence suggests that the cell-surface expressed Nucleolin is a strategic target for an effective and nontoxic cancer therapy. Methodology/Principal Findings By monitoring the expression of Nucleolin mRNA, and by measuring the level of Nucleolin protein recovered from the surface and nucleus of cells, here we show that the presence of Nucleolin at the cell surface is dependent on the constant induction of Nucleolin mRNA. Indeed, inhibitors of RNA transcription or translation block expression of surface Nucleolin while no apparent effect is observed on the level of Nucleolin in the nucleus. The estimated half-life of surface Nucleolin is less than one hour, whereas that of nuclear Nucleolin is more than 8 hours. Nucleolin mRNA induction is reduced markedly in normal fibroblasts that reach confluence, while it occurs continuously even in post-confluent epithelial tumor cells consistent with their capacity to proliferate without contact inhibition. Interestingly, cold and heat shock induce Nucleolin mRNA concomitantly to enhanced mRNA expression of the heat shock protein 70, thus suggesting that surface Nucleolin induction also occurs in response to an environmental insult. At the cell surface, one of the main functions of Nucleolin is to shuttle specific extracellular ligands by an active transport mechanism, which we show here to be calcium dependent. Conclusion/Significance Our results demonstrate that the expression of surface Nucleolin is an early metabolic event coupled with tumor cell proliferation and stress response. The fact that surface Nucleolin is constantly and abundantly expressed on the surface of tumor cells, makes them a preferential target for the inhibitory action of anticancer agents that target surface Nucleolin.
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The cell-surface-expressed Nucleolin is associated with the actin cytoskeleton.
Experimental cell research, 2000Co-Authors: Ara G. Hovanessian, Josette Svab, Francine Puvion-dutilleul, Sébastien Nisole, Emmanuelle Perret, Jau-shyong Deng, Bernard KrustAbstract:Abstract Nucleolin is a RNA- and protein-binding multifunctional protein. Mainly characterized as a nucleolar protein, Nucleolin is continuously expressed on the surface of different types of cells along with its intracellular pool within the nucleus and cytoplasm. By confocal and electron microscopy using specific antibodies against Nucleolin, we show that cytoplasmic Nucleolin is found in small vesicles that appear to translocate Nucleolin to the cell surface. Translocation of Nucleolin is markedly reduced at low temperature or in serum-free medium, whereas conventional inhibitors of intracellular glycoprotein transport have no effect. Thus, translocation of Nucleolin is the consequence of an active transport by a pathway which is independent of the endoplasmic reticulum–Golgi complex. The cell-surface-expressed Nucleolin becomes clustered at the external side of the plasma membrane when cross-linked by the Nucleolin-specific monoclonal antibody mAb D3. This clustering, occurring at 20°C and in a well-organized pattern, is dependent on the existence of an intact actin cytoskeleton. At 37°C, mAb D3 becomes internalized, thus illustrating that surface Nucleolin can mediate intracellular import of specific ligands. Our results point out that Nucleolin should also be considered a component of the cell surface where it could be functional as a cell surface receptor for various ligands reported before.
Anna Greco - One of the best experts on this subject based on the ideXlab platform.
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Nucleolin interacts with US11 protein of herpes simplex virus 1 and is involved in its trafficking.
Journal of Virology, 2012Co-Authors: Anna Greco, Aleth Callé, Alberto L Epstein, Karine Monier, Xavier Gaume, Loredana Arata, Eric Soler, Yohann Couté, Sabine Hacot, Jean-charles SanchezAbstract:Herpes simplex virus type 1 (HSV-1) infection induces profound nucleolar modifications at the functional and organizational levels, including nucleolar invasion by several viral proteins. One of these proteins is US11, which exhibits several different functions and displays both cytoplasmic localization and clear nucleolar localization very similar to that of the major multifunctional nucleolar protein Nucleolin. To determine whether US11 interacts with Nucleolin, we purified US11 protein partners by coimmunoprecipitations using a tagged protein, Flag-US11. From extracts of cells expressing Flag-US11 protein, we copurified a protein of about 100 kDa that was further identified as Nucleolin. In vitro studies have demonstrated that Nucleolin interacts with US11 and that the C-terminal domain of US11, which is required for US11 nucleolar accumulation, is sufficient for interaction with Nucleolin. This association was confirmed in HSV-1-infected cells. We found an increase in the nucleolar accumulation of US11 in Nucleolin-depleted cells, thereby revealing that Nucleolin could play a role in US11 nucleocytoplasmic trafficking through one-way directional transport out of the nucleolus. Since Nucleolin is required for HSV-1 nuclear egress, the interaction of US11 with Nucleolin may participate in the outcome of infection.
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Nucleolin is required for an efficient herpes simplex virus type 1 infection.
Journal of Virology, 2008Co-Authors: Aleth Callé, Iva Ugrinova, Alberto L Epstein, Philippe Bouvet, Jean-jacques Diaz, Anna GrecoAbstract:Productive infection by herpes simplex virus type 1 (HSV-1), which occurs in the host cell nucleus, is accompanied by dramatic modifications of the nuclear architecture, including profound alterations of nucleolar morphology. Here, we show that the three most abundant nucleolar proteins--Nucleolin, B23, and fibrillarin--are redistributed out of the nucleoli as a consequence of HSV-1 infection. We show that the amount of Nucleolin increases progressively during the course of infection. We demonstrate for the first time that a nucleolar protein, i.e., Nucleolin, colocalizes with ICP8 in the viral replication compartments, at the time when viral replication is effective, suggesting an involvement of Nucleolin in the HSV-1 DNA replication process. At later times of infection, a granular form of Nucleolin localizes to the cytoplasm, in structures that display the characteristic features of aggresomes, indicating that this form of Nucleolin is very probably destined for degradation. The delocalization of Nucleolin from the nucleoli requires the viral ICP4 protein or a factor(s) whose expression involves ICP4. Using small interfering RNA technology, we show that viral replication requires a high level of Nucleolin expression, demonstrating for the first time a direct role for a nucleolar protein in herpes simplex virus biology.
Ara G. Hovanessian - One of the best experts on this subject based on the ideXlab platform.
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Surface Expressed Nucleolin Is Constantly Induced in Tumor Cells to Mediate Calcium-Dependent Ligand Internalization
PloS one, 2010Co-Authors: Ara G. Hovanessian, Calaiselvy Soundaramourty, Diala El Khoury, Isabelle Nondier, Josette Svab, Bernard KrustAbstract:Background Nucleolin is one of the major proteins of the nucleolus, but it is also expressed on the cell surface where is serves as a binding protein for variety of ligands implicated in tumorigenesis and angiogenesis. Emerging evidence suggests that the cell-surface expressed Nucleolin is a strategic target for an effective and nontoxic cancer therapy. Methodology/Principal Findings By monitoring the expression of Nucleolin mRNA, and by measuring the level of Nucleolin protein recovered from the surface and nucleus of cells, here we show that the presence of Nucleolin at the cell surface is dependent on the constant induction of Nucleolin mRNA. Indeed, inhibitors of RNA transcription or translation block expression of surface Nucleolin while no apparent effect is observed on the level of Nucleolin in the nucleus. The estimated half-life of surface Nucleolin is less than one hour, whereas that of nuclear Nucleolin is more than 8 hours. Nucleolin mRNA induction is reduced markedly in normal fibroblasts that reach confluence, while it occurs continuously even in post-confluent epithelial tumor cells consistent with their capacity to proliferate without contact inhibition. Interestingly, cold and heat shock induce Nucleolin mRNA concomitantly to enhanced mRNA expression of the heat shock protein 70, thus suggesting that surface Nucleolin induction also occurs in response to an environmental insult. At the cell surface, one of the main functions of Nucleolin is to shuttle specific extracellular ligands by an active transport mechanism, which we show here to be calcium dependent. Conclusion/Significance Our results demonstrate that the expression of surface Nucleolin is an early metabolic event coupled with tumor cell proliferation and stress response. The fact that surface Nucleolin is constantly and abundantly expressed on the surface of tumor cells, makes them a preferential target for the inhibitory action of anticancer agents that target surface Nucleolin.
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The cell-surface-expressed Nucleolin is associated with the actin cytoskeleton.
Experimental cell research, 2000Co-Authors: Ara G. Hovanessian, Josette Svab, Francine Puvion-dutilleul, Sébastien Nisole, Emmanuelle Perret, Jau-shyong Deng, Bernard KrustAbstract:Abstract Nucleolin is a RNA- and protein-binding multifunctional protein. Mainly characterized as a nucleolar protein, Nucleolin is continuously expressed on the surface of different types of cells along with its intracellular pool within the nucleus and cytoplasm. By confocal and electron microscopy using specific antibodies against Nucleolin, we show that cytoplasmic Nucleolin is found in small vesicles that appear to translocate Nucleolin to the cell surface. Translocation of Nucleolin is markedly reduced at low temperature or in serum-free medium, whereas conventional inhibitors of intracellular glycoprotein transport have no effect. Thus, translocation of Nucleolin is the consequence of an active transport by a pathway which is independent of the endoplasmic reticulum–Golgi complex. The cell-surface-expressed Nucleolin becomes clustered at the external side of the plasma membrane when cross-linked by the Nucleolin-specific monoclonal antibody mAb D3. This clustering, occurring at 20°C and in a well-organized pattern, is dependent on the existence of an intact actin cytoskeleton. At 37°C, mAb D3 becomes internalized, thus illustrating that surface Nucleolin can mediate intracellular import of specific ligands. Our results point out that Nucleolin should also be considered a component of the cell surface where it could be functional as a cell surface receptor for various ligands reported before.
