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Kenney SP, Meng XJ. Identification and fine mapping of nuclear and nucleolar localization signals within the human ribosomal protein S17. PLoS One 2015; 10:e0124396. [PMID: 25853866 PMCID: PMC4390217 DOI: 10.1371/journal.pone.0124396] [Citation(s) in RCA: 16] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/21/2014] [Accepted: 03/13/2015] [Indexed: 01/29/2023] Open
Abstract
Human ribosomal protein S17 (RPS17) is mutated in Diamond-Blackfan Anemia (DBA), a bone marrow disorder that fails to produce sufficient red blood cells leading to anemia. Recently, an RPS17 protein sequence was also found to be naturally inserted in the genome of hepatitis E virus (HEV) from patients chronically-infected by HEV. The role of RPS17 in HEV replication and pathogenesis remains unknown due to the lack of knowledge about how RPS17 functions at a molecular level. Understanding the biological function of RPS17 is critical for elucidating its role in virus infection and DBA disease processes. In this study we probed the subcellular distribution of normal and mutant RPS17 proteins in a human liver cell line (Huh7). RPS17 was primarily detected within the nucleus, and more specifically within the nucleoli. Using a transient expression system in which RPS17 or truncations were expressed as fusions with enhanced yellow fluorescent protein (eYFP), we were able to identify and map, for the first time, two separate nuclear localization signals (NLSs), one to the first 13 amino acids of the amino-terminus of RPS17 and the other within amino acids 30-60. Additionally, we mapped amino acid sequences required for nucleolar accumulation of RPS17 to amino acids 60-70. Amino acids 60-70 possess a di-RG motif that may be necessary for nucleolar retention of RPS17. The results from this study enhance our knowledge of RSP17 and will facilitate future mechanistic studies about the roles of RSP17 in hepatitis E and DBA disease processes.
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Affiliation(s)
- Scott P. Kenney
- Center for Molecular Medicine and Infectious Diseases, Department of Biomedical Sciences and Pathobiology, College of Veterinary Medicine, Virginia Polytechnic Institute and State University (Virginia Tech), Blacksburg, Virginia, United States of America
| | - Xiang-Jin Meng
- Center for Molecular Medicine and Infectious Diseases, Department of Biomedical Sciences and Pathobiology, College of Veterinary Medicine, Virginia Polytechnic Institute and State University (Virginia Tech), Blacksburg, Virginia, United States of America
- * E-mail:
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Savelyeva AV, Semenov DV, Stepanov GA, Baryakin DN, Kuligina EV, Rabinov IV, Koval OA, Richter VA. [The influence of recombinant nucleophosmin 1 on artificial RNA internalization into human adenocarcinoma MCF-7 cells]. RUSSIAN JOURNAL OF BIOORGANIC CHEMISTRY 2014; 40:55-63. [PMID: 25898723 DOI: 10.1134/s1068162014010099] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
In this study we obtained and characterized the recombinant analogue of multifunctional nucleolar phosphoprotein nucleophosmin 1 (NPM1) involved in crucial cellular processes such as transcription, reparation and mitosis. The influence ofnucleophosmin 1 on extrcellular RNAs accumulation in human adenocarcinoma cells MCF-7 was analyzed. It was found that incubation of AluY RNA (n > 300 nt), U24 snoRNA analogues (n ~ 80 nt) with Npm1-His6 resulted in RNA-protein non-covalent complexes formation, but not in case of the short oligoribonucleotide (n = 22 nt). It was shown that interaction of AluY RNA analogue with Npm1-His6 significantly increases transfection efficacy of the RNA into MCF-7 human cells. Altogether, these data allow us to conclude, that nucleophosmin 1 not only binds RNA with complex secondary structure, but also promotes uptake and internalization of such RNA by human cells.
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3
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Xia X, Liu S, Xiao Z, Zhu F, Song NY, Zhou M, Liu B, Shen J, Nagashima K, Veenstra TD, Burkett S, Datla M, Willette-Brown J, Shen H, Hu Y. An IKKα-nucleophosmin axis utilizes inflammatory signaling to promote genome integrity. Cell Rep 2013; 5:1243-55. [PMID: 24290756 PMCID: PMC4159076 DOI: 10.1016/j.celrep.2013.10.046] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/14/2013] [Revised: 08/19/2013] [Accepted: 10/29/2013] [Indexed: 01/04/2023] Open
Abstract
The inflammatory microenvironment promotes skin tumorigenesis. However, the mechanisms by which cells protect themselves from inflammatory signals are unknown. Downregulation of IKKα promotes skin tumor progression from papillomas to squamous cell carcinomas, which is frequently accompanied by genomic instability, including aneuploid chromosomes and extra centrosomes. In this study, we found that IKKα promoted oligomerization of nucleophosmin (NPM), a negative centrosome duplication regulator, which further enhanced NPM and centrosome association, inhibited centrosome amplification, and maintained genome integrity. Levels of NPM hexamers and IKKα were conversely associated with skin tumor progression. Importantly, proinflammatory cytokine-induced IKKα activation promoted the formation of NPM oligomers and reduced centrosome numbers in mouse and human cells, whereas kinase-dead IKKα blocked this connection. Therefore, our findings suggest a mechanism in which an IKKα-NPM axis may use inflammatory signals to suppress centrosome amplification, promote genomic integrity, and prevent tumor progression.
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Affiliation(s)
- Xiaojun Xia
- Department of Nanomedicine, Houston Methodist Hospital Research Institute, Houston, TX 77030, USA
| | - Shuang Liu
- Cancer and Inflammation Program, Center for Cancer Research, National Cancer Institute, Frederick, MD 21701, USA
| | - Zuoxiang Xiao
- Cancer and Inflammation Program, Center for Cancer Research, National Cancer Institute, Frederick, MD 21701, USA
| | - Feng Zhu
- Cancer and Inflammation Program, Center for Cancer Research, National Cancer Institute, Frederick, MD 21701, USA
| | - Na-Young Song
- Cancer and Inflammation Program, Center for Cancer Research, National Cancer Institute, Frederick, MD 21701, USA
| | - Ming Zhou
- Laboratory of Proteomics and Analytical Technologies, SAIC-Frederick, Frederick National Laboratory for Cancer Research, Frederick, MD 21701, USA
| | - Bigang Liu
- Department of Molecular Carcinogenesis, The University of Texas M. D. Anderson Cancer Center, Unit 389, Smithville, TX 78957, USA
| | - Jianjun Shen
- Department of Molecular Carcinogenesis, The University of Texas M. D. Anderson Cancer Center, Unit 389, Smithville, TX 78957, USA
| | - Kunio Nagashima
- Advanced Technology Program, Electron Microscopy Laboratory, SAIC-Frederick, Frederick National Laboratory for Cancer Research, Frederick, MD 21701, USA
| | - Timothy D Veenstra
- Laboratory of Proteomics and Analytical Technologies, SAIC-Frederick, Frederick National Laboratory for Cancer Research, Frederick, MD 21701, USA
| | - Sandra Burkett
- Mouse Cancer Genetics Program, Center for Cancer Research, National Cancer Institute, Frederick, MD 21701, USA
| | - Mahesh Datla
- Cancer and Inflammation Program, Center for Cancer Research, National Cancer Institute, Frederick, MD 21701, USA
| | - Jami Willette-Brown
- Cancer and Inflammation Program, Center for Cancer Research, National Cancer Institute, Frederick, MD 21701, USA
| | - Haifa Shen
- Department of Nanomedicine, Houston Methodist Hospital Research Institute, Houston, TX 77030, USA
| | - Yinling Hu
- Cancer and Inflammation Program, Center for Cancer Research, National Cancer Institute, Frederick, MD 21701, USA.
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4
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Hernandez-Verdun D. Assembly and disassembly of the nucleolus during the cell cycle. Nucleus 2012; 2:189-94. [PMID: 21818412 DOI: 10.4161/nucl.2.3.16246] [Citation(s) in RCA: 204] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/15/2011] [Revised: 04/28/2011] [Accepted: 05/02/2011] [Indexed: 01/01/2023] Open
Abstract
The nucleolus is a large nuclear domain in which transcription, maturation and assembly of ribosomes take place. In higher eukaryotes, nucleolar organization in three sub-domains reflects the compartmentation of the machineries related to active or inactive transcription of the ribosomal DNA, ribosomal RNA processing and assembly with ribosomal proteins of the two (40S and 60S) ribosomal subunits. The assembly of the nucleoli during telophase/early G(1) depends on pre-existing machineries inactivated during prophase (the transcription machinery and RNP processing complexes) and on partially processed 45S rRNAs inherited throughout mitosis. In telophase, the 45S rRNAs nucleate the prenucleolar bodies and order the dynamics of nucleolar assembly. The assembly/disassembly processes of the nucleolus depend on the equilibrium between phosphorylation/dephosphorylation of the transcription machinery and on the RNP processing complexes under the control of the CDK1-cyclin B kinase and PP1 phosphatases. The dynamics of assembly/disassembly of the nucleolus is time and space regulated.
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5
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Mislocalization or low expression of mutated Shwachman–Bodian–Diamond syndrome protein. Int J Hematol 2011; 94:54-62. [DOI: 10.1007/s12185-011-0880-1] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/20/2010] [Revised: 05/17/2011] [Accepted: 05/19/2011] [Indexed: 11/27/2022]
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NPM1/B23: A Multifunctional Chaperone in Ribosome Biogenesis and Chromatin Remodeling. Biochem Res Int 2010; 2011:195209. [PMID: 21152184 PMCID: PMC2989734 DOI: 10.1155/2011/195209] [Citation(s) in RCA: 226] [Impact Index Per Article: 16.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/30/2010] [Accepted: 08/29/2010] [Indexed: 12/21/2022] Open
Abstract
At a first glance, ribosome biogenesis and chromatin remodeling are quite different processes, but they share a common problem involving interactions between charged nucleic acids and small basic proteins that may result in unwanted intracellular aggregations. The multifunctional nuclear acidic chaperone NPM1 (B23/nucleophosmin) is active in several stages of ribosome biogenesis, chromatin remodeling, and mitosis as well as in DNA repair, replication and transcription. In addition, NPM1 plays an important role in the Myc-ARF-p53 pathway as well as in SUMO regulation. However, the relative importance of NPM1 in these processes remains unclear. Provided herein is an update on the expanding list of the diverse activities and interacting partners of NPM1. Mechanisms of NPM1 nuclear export functions of NPM1 in the nucleolus and at the mitotic spindle are discussed in relation to tumor development. It is argued that the suggested function of NPM1 as a histone chaperone could explain several, but not all, of the effects observed in cells following changes in NPM1 expression. A future challenge is to understand how NPM1 is activated, recruited, and controlled to carry out its functions.
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7
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Posttranscriptional regulation of chicken ccn2 gene expression by nucleophosmin/B23 during chondrocyte differentiation. Mol Cell Biol 2008; 28:6134-47. [PMID: 18678650 DOI: 10.1128/mcb.00495-08] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
CCN2/CTGF is a multifunctional factor that plays a crucial role in the growth and differentiation of chondrocytes. The chicken ccn2 gene is regulated not only at the transcriptional level but also by the interaction between a posttranscriptional element in the 3' untranslated region (3'-UTR) and a cofactor. In the present study, we identified a nucleophosmin (NPM) (also called B23) as this cofactor. Binding of NPM to the element was confirmed, and subsequent analysis revealed a significant correlation between the decrease in cytosolic NPM and the increased stability of the ccn2 mRNA during chondrocyte differentiation in vivo. Furthermore, recombinant chicken NPM enhanced the degradation of chimeric RNAs containing the posttranscriptional cis elements in a chicken embryonic fibroblast extract in vitro. It is noteworthy that the RNA destabilization effect by NPM was far more prominent in the cytosolic extract of chondrocytes than in that of fibroblasts, representing a chondrocyte-specific action of NPM. Stimulation by growth factors to promote differentiation changed the subcellular distribution of NPM in chondrocytes, which followed the expected patterns from the resultant change in the ccn2 mRNA stability. Therefore, the present study reveals a novel aspect of NPM as a key player in the posttranscriptional regulation of ccn2 mRNA during the differentiation of chondrocytes.
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8
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Okada M, Jang SW, Ye K. Ebp1 association with nucleophosmin/B23 is essential for regulating cell proliferation and suppressing apoptosis. J Biol Chem 2007; 282:36744-54. [PMID: 17951246 DOI: 10.1074/jbc.m706169200] [Citation(s) in RCA: 48] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Ebp1 and NPM/B23 are essential for cell proliferation and survival. Ebp1 possesses p42 and p48 isoforms. Whereas p42 exclusively resides in the cytoplasm, p48 localizes in both the cytoplasm and the nucleolus. Here, we show that Ebp1 forms a complex with B23, and this complex plays a critical role in cell proliferation and survival. p42 specifically associates with B23 upon epidermal growth factor stimulation, while p48 constantly binds B23. Moreover, Ser360 phosphorylation in p42, but not p48, is critical for the interaction. p48 constitutively binds B23 in the nucleolus, for which B23 Lys263 sumoylation is indispensable. By contrast, p42 selectively binds unsumoylated B23 mutants. Interestingly, B23 K263R, an unsumoylated mutant, triggers p42 nuclear translocation and interacts with it in the nucleus even in the absence of epidermal growth factor. In contrast, the nucleolar residency of p48 is abolished in B23 K263R cells. During the cell cycle, p42 selectively colocalizes with B23 in the mitotic cells, correlating with its phosphorylation status in mitosis. Knocking down of B23 or Ebp1 substantially decreases ribosome biogenesis and cell survival. Thus, B23 distinctively binds Ebp1 isoforms and regulates cell proliferation and survival through p42 and p48, respectively.
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Affiliation(s)
- Masashi Okada
- Department of Pathology and Laboratory Medicine, Emory University School of Medicine, Atlanta, Georgia 30322, USA
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Maki N, Takechi K, Sano S, Tarui H, Sasai Y, Agata K. Rapid accumulation of nucleostemin in nucleolus during newt regeneration. Dev Dyn 2007; 236:941-50. [PMID: 17133523 DOI: 10.1002/dvdy.21027] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
In newt regeneration, differentiated cells can revert to stem cell-like cells in which the proliferative ability and multipotentiality are restored after dedifferentiation. However, the molecular events that occur during the dedifferentiation still remain obscure. Nucleostemin has been identified in mammals as a nucleolar protein specific to stem cells and cancer cells. In this study, a newt nucleostemin homologue was cloned and its regulation was analyzed. During lens regeneration, the expression of nucleostemin was activated and nucleostemin rapidly accumulated in the nucleoli of dedifferentiating pigmented epithelial cells 2 days before cell cycle reentry. During limb regeneration, nucleostemin also accumulated in the nucleoli of degenerating multinucleate muscle fibers before blastema formation. These findings suggest that nucleostemin plays a role in the dedifferentiation of newt cells and can provide crucial clues for addressing the molecular events at early steps of cellular dedifferentiation in newts.
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Affiliation(s)
- Nobuyasu Maki
- Center for Developmental Biology, RIKEN Kobe, Chuo-ku, Kobe, Japan.
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10
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Abstract
Nucleophosmin (NPM) is a nucleolar phosphoprotein that shuttles between the nucleus and cytoplasm during the cell cycle. NPM has several interacting partners and diverse cellular functions, including the processing of ribosomal RNA, centrosome duplication and the control of cellular processes to ensure genomic stability. Subcellular localization of NPM appears to be strongly correlated with NPM functions and cell proliferation. NPM is phosphorylated mainly at its central acidic domain by several upstream kinases, and its phosphorylation appears to be involved in regulating its functions in ribosome biogenesis and centrosome duplication. Recent studies suggest that NPM may act as a licensing factor to maintain proper centrosome duplication and that the Ran/CRM1 nucleocytoplasmic complex regulates local trafficking of NPM to centrosomes by interacting through its nuclear export sequence motif. Here, we provide a brief overview of NPM functions and its roles in human carcinogenesis, and discuss our recent findings related to the potential mechanisms underlying its regulation of centrosome duplication.
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Affiliation(s)
- Mi Jung Lim
- Laboratory of Human Carcinogenesis, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
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11
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Tillemans V, Leponce I, Rausin G, Dispa L, Motte P. Insights into nuclear organization in plants as revealed by the dynamic distribution of Arabidopsis SR splicing factors. THE PLANT CELL 2006; 18:3218-34. [PMID: 17114353 PMCID: PMC1693954 DOI: 10.1105/tpc.106.044529] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
Serine/arginine-rich (SR) proteins are splicing regulators that share a modular structure consisting of one or two N-terminal RNA recognition motif domains and a C-terminal RS-rich domain. We investigated the dynamic localization of the Arabidopsis thaliana SR protein RSZp22, which, as we showed previously, distributes in predominant speckle-like structures and in the nucleolus. To determine the role of RSZp22 diverse domains in its nucleolar distribution, we investigated the subnuclear localization of domain-deleted mutant proteins. Our results suggest that the nucleolar localization of RSZp22 does not depend on a single targeting signal but likely involves different domains/motifs. Photobleaching experiments demonstrated the unrestricted dynamics of RSZp22 between nuclear compartments. Selective inhibitor experiments of ongoing cellular phosphorylation influenced the rates of exchange of RSZp22 between the different nuclear territories, indicating that SR protein mobility is dependent on the phosphorylation state of the cell. Furthermore, based on a leptomycin B- and fluorescence loss in photobleaching-based sensitive assay, we suggest that RSZp22 is a nucleocytoplasmic shuttling protein. Finally, with electron microscopy, we confirmed that RSp31, a plant-specific SR protein, is dynamically distributed in nucleolar cap-like structures upon phosphorylation inhibition. Our findings emphasize the high mobility of Arabidopsis SR splicing factors and provide insights into the dynamic relationships between the different nuclear compartments.
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Affiliation(s)
- Vinciane Tillemans
- Laboratory of Plant Cell and Molecular Biology, Department of Life Sciences, Institute of Botany, University of Liège, B-4000 Liège, Belgium
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12
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Negi SS, Olson MOJ. Effects of interphase and mitotic phosphorylation on the mobility and location of nucleolar protein B23. J Cell Sci 2006; 119:3676-85. [PMID: 16912078 DOI: 10.1242/jcs.03090] [Citation(s) in RCA: 82] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
B23 (or nucleophosmin, NPM) is a multifunctional protein involved in ribosome biogenesis, control of centrosome duplication and in sensing cellular stress. It is phosphorylated during interphase by casein kinase 2 (CK2) and during mitosis by cyclin-dependent kinase (CDK). In this study we have addressed the role of these phosphorylation events in the dynamics and location of protein B23. Mutation of the CK2 phosphorylation site to alanine results in slower recovery of the mutant compared with the wild-type protein as measured by fluorescence recovery after photobleaching (FRAP). Immunofluorescence studies using an antibody against phosphorylated Thr199 revealed that B23 is phosphorylated at this CDK1 site at the start of mitosis and is dephosphorylated during anaphase. The CDK1-type phosphorylation sites are in the nucleic acid binding region of B23 and may contribute to its dissociation from the nucleolus during mitosis. A Thr to Glu mutant of the CDK1-type sites as well as other members of the nucleoplasmin family that lack the C-terminal nucleic-acid-binding region showed a greater mobility and/or faster recovery than wild-type B23.1, the longer variant. These results provide evidence that phosphorylation at these sites reduces the affinity of B23 for nucleolar components and might be a factor in regulating its location during the cell cycle.
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Affiliation(s)
- Sandeep S Negi
- Department of Biochemistry, University of Mississippi Medical Center, Jackson, MS 39216, USA
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Mariano AR, Colombo E, Luzi L, Martinelli P, Volorio S, Bernard L, Meani N, Bergomas R, Alcalay M, Pelicci PG. Cytoplasmic localization of NPM in myeloid leukemias is dictated by gain-of-function mutations that create a functional nuclear export signal. Oncogene 2006; 25:4376-80. [PMID: 16501600 DOI: 10.1038/sj.onc.1209453] [Citation(s) in RCA: 58] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
Nucleophosmin (NPM) is a nucleus-cytoplasmic shuttling protein that is implicated in centrosome duplication, cell cycle progression and stress response. At the steady state, NPM localizes mainly in the nucleolus, where it forms a complex with different cellular proteins. One-third of acute myeloid leukemias (AML) are characterized by aberrant cytoplasmic localization of NPM, due to mutations within its last coding exon (exon 12) that cause a frameshift and the formation of novel C-termini. We report here our investigations on the molecular basis for the aberrant localization of mutated NPM. Alignment of the C-terminus of the various NPM mutants revealed the obligatory presence of four amino-acid residues that match a CRM1-dependent nuclear export signal (NES). Single alanine-substitutions at these sites provoked nuclear re-localization, while fusion of the mutated C-terminus to a heterologous nuclear protein induced CRM1-dependent cytoplasmic localization. Molecular characterization of one exceptional AML carrying cytoplasmic NPM and germ line exon 12 revealed a somatic mutation in the splicing donor site of exon 9 that caused the formation of a functional NES. It appears, therefore, that AMLs are frequently characterized by gain-of-function mutations of NPM that create functional NES, suggesting that alterations of nuclear export might represent a general mechanism of leukemogenesis and a novel target for therapeutic intervention.
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Affiliation(s)
- A R Mariano
- Department of Experimental Oncology, European Institute of Oncology, Milan, Italy
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Cleary J, Sitwala KV, Khodadoust MS, Kwok RPS, Mor-Vaknin N, Cebrat M, Cole PA, Markovitz DM. p300/CBP-associated factor drives DEK into interchromatin granule clusters. J Biol Chem 2005; 280:31760-7. [PMID: 15987677 DOI: 10.1074/jbc.m500884200] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
DEK is a mammalian protein that has been implicated in the pathogenesis of autoimmune diseases and cancer, including acute myeloid leukemia, melanoma, glioblastoma, hepatocellular carcinoma, and bladder cancer. In addition, DEK appears to participate in multiple cellular processes, including transcriptional repression, mRNA processing, and chromatin remodeling. Sub-nuclear distribution of this protein, with the attendant functional ramifications, has remained a controversial topic. Here we report that DEK undergoes acetylation in vivo at lysine residues within the first 70 N-terminal amino acids. Acetylation of DEK decreases its affinity for DNA elements within the promoter, which is consistent with the involvement of DEK in transcriptional repression. Furthermore, deacetylase inhibition results in accumulation of DEK within interchromatin granule clusters (IGCs), sub-nuclear structures that contain RNA processing factors. Overexpression of P/CAF acetylase drives DEK into IGCs, and addition of a newly developed, synthetic, cell-permeable P/CAF inhibitor blocks this movement. To our knowledge, this is the first reported example of acetylation playing a direct role in relocation of a protein to IGCs, and this may explain how DEK can function in multiple pathways that take place in distinct sub-nuclear compartments. These findings also suggest that DEK-associated malignancies and autoimmune diseases might be amenable to treatment with agents that alter acetylation.
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Affiliation(s)
- Joanne Cleary
- Department of Internal Medicine, Division of Infectious Diseases, University of Michigan, Ann Arbor, Michigan 48109-0640, USA
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15
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Lipsius E, Walter K, Leicher T, Phlippen W, Bisotti MA, Kruppa J. Evolutionary conservation of nuclear and nucleolar targeting sequences in yeast ribosomal protein S6A. Biochem Biophys Res Commun 2005; 333:1353-60. [PMID: 15979583 DOI: 10.1016/j.bbrc.2005.06.043] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/30/2005] [Accepted: 06/07/2005] [Indexed: 11/25/2022]
Abstract
Over 1 billion years ago, the animal kingdom diverged from the fungi. Nevertheless, a high sequence homology of 62% exists between human ribosomal protein S6 and S6A of Saccharomyces cerevisiae. To investigate whether this similarity in primary structure is mirrored in corresponding functional protein domains, the nuclear and nucleolar targeting signals were delineated in yeast S6A and compared to the known human S6 signals. The complete sequence of S6A and cDNA fragments was fused to the 5'-end of the LacZ gene, the constructs were transiently expressed in COS cells, and the subcellular localization of the fusion proteins was detected by indirect immunofluorescence. One bipartite and two monopartite nuclear localization signals as well as two nucleolar binding domains were identified in yeast S6A, which are located at homologous regions in human S6 protein. Remarkably, the number, nature, and position of these targeting signals have been conserved, albeit their amino acid sequences have presumably undergone a process of co-evolution with their corresponding rRNAs.
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Affiliation(s)
- Edgar Lipsius
- Zentrum für Experimentelle Medizin, Institut für Molekulare Zellbiologie, Universität Hamburg, Hamburg, Germany
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16
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Namboodiri VMH, Akey IV, Schmidt-Zachmann MS, Head JF, Akey CW. The structure and function of Xenopus NO38-core, a histone chaperone in the nucleolus. Structure 2005; 12:2149-60. [PMID: 15576029 DOI: 10.1016/j.str.2004.09.017] [Citation(s) in RCA: 91] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/24/2004] [Revised: 09/12/2004] [Accepted: 09/16/2004] [Indexed: 11/17/2022]
Abstract
Xenopus NO38 is an abundant nucleolar chaperone and a member of the nucleoplasmin (Np) family. Here, we report high-resolution crystal structures of the N-terminal domain of NO38, as a pentamer and a decamer. As expected, NO38 shares the Np family fold. In addition, NO38- and Np-core pentamers each use highly conserved residues and numerous waters to form their respective decamers. Further studies show that NO38 and Np each bind equal amounts of the four core histones. However, NO38 prefers the (H3-H4)(2) tetramer, while Np probably prefers H2A-H2B dimers. We also show that NO38 and Np will each bind noncognate histones when the preferred partner is absent. We suggest that these chaperones must form decamers in order to bind histones and differentiate between histone tetramers and dimers. When taken together, these data imply that NO38 may function as a histone chaperone in the nucleolus.
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Affiliation(s)
- V M Haridasan Namboodiri
- Department of Physiology and Biophysics, Boston University School of Medicine, 700 Albany Street, Boston, MA 02118, USA
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17
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Aranburu A, Bennett M, Leanderson T. The kappa promoter penta-decamer binding protein CBF-A interacts specifically with nucleophosmin in the nucleus only. Mol Immunol 2005; 43:690-701. [PMID: 16360014 DOI: 10.1016/j.molimm.2005.03.016] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/11/2005] [Indexed: 02/05/2023]
Abstract
CArG box-binding factor-A (CBF-A) interacts with the penta-decamer (pd) element that is a conserved sequence element within mouse Vkappa promoters. The pd element acts in synergy with the octamer element to stimulate kappa transcription, especially in later stages of B cell development. To get further insight in the mechanism for CBF-A action we have characterised its protein-protein interactions. We show here that CBF-A interacts specifically with nucleophosmin (NPM). This interaction occurs via the homo-oligomerisation domain of NPM and the N-terminus of CBF-A and was exclusive for the nuclear compartment while the two proteins failed to interact in the cytosol. In contrast, CBF-A formed homocomplexes in this compartment. CBF-A was also shown to localise to the nucleoli, most likely dependent on a functional interaction with NPM. Lastly, the sequence fine specificity of CBF-A complexes in the nucleus and cytoplasm were found to differ and nuclear protein-DNA complexes were shown to contain NPM. Thus, CBF-A participates in several protein-protein interactions that may modulate its subcellular localisation and target gene specificity.
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Affiliation(s)
- Alaitz Aranburu
- Inflammation and Immunology Unit, BMC I:13, Department of Experimental Medical Science, Lund University, 221 84 Lund, Sweden
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18
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Eilbracht J, Reichenzeller M, Hergt M, Schnölzer M, Heid H, Stöhr M, Franke WW, Schmidt-Zachmann MS. NO66, a highly conserved dual location protein in the nucleolus and in a special type of synchronously replicating chromatin. Mol Biol Cell 2004; 15:1816-32. [PMID: 14742713 PMCID: PMC379278 DOI: 10.1091/mbc.e03-08-0623] [Citation(s) in RCA: 46] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/31/2022] Open
Abstract
It has recently become clear that the nucleolus, the most prominent nuclear subcompartment, harbors diverse functions beyond its classic role in ribosome biogenesis. To gain insight into nucleolar functions, we have purified amplified nucleoli from Xenopus laevis oocytes using a novel approach involving fluorescence-activated cell sorting techniques. The resulting protein fraction was analyzed by mass spectrometry and used for the generation of monoclonal antibodies directed against nucleolar components. Here, we report the identification and molecular characterization of a novel, ubiquitous protein, which in most cell types appears to be a constitutive nucleolar component. Immunolocalization studies have revealed that this protein, termed NO66, is highly conserved during evolution and shows in most cells analyzed a dual localization pattern, i.e., a strong enrichment in the granular part of nucleoli and in distinct nucleoplasmic entities. Colocalizations with proteins Ki-67, HP1alpha, and PCNA, respectively, have further shown that the staining pattern of NO66 overlaps with certain clusters of late replicating chromatin. Biochemical experiments have revealed that protein NO66 cofractionates with large preribosomal particles but is absent from cytoplasmic ribosomes. We propose that in addition to its role in ribosome biogenesis protein NO66 has functions in the replication or remodeling of certain heterochromatic regions.
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MESH Headings
- Amino Acid Sequence
- Animals
- Blotting, Northern
- Cell Line, Transformed
- Cell Line, Tumor
- Cell Nucleolus/metabolism
- Cell Nucleus/metabolism
- Cell Separation
- Cells, Cultured
- Centrifugation, Density Gradient
- Chromatin/chemistry
- Chromatin/metabolism
- Chromatography, Gel
- Chromobox Protein Homolog 5
- Chromosomal Proteins, Non-Histone/biosynthesis
- Chromosomal Proteins, Non-Histone/metabolism
- Chromosomal Proteins, Non-Histone/physiology
- Conserved Sequence
- Cytoplasm/metabolism
- DNA, Complementary/metabolism
- Dioxygenases
- Flow Cytometry
- HeLa Cells
- Heterochromatin/chemistry
- Histone Demethylases
- Humans
- Ki-67 Antigen/biosynthesis
- Microscopy, Electron
- Microscopy, Fluorescence
- Molecular Sequence Data
- Peptides/chemistry
- Precipitin Tests
- Proliferating Cell Nuclear Antigen/biosynthesis
- Protein Biosynthesis
- RNA/metabolism
- Ribosomes/metabolism
- Sequence Homology, Amino Acid
- Sucrose/pharmacology
- Time Factors
- Transcription, Genetic
- Xenopus Proteins/biosynthesis
- Xenopus Proteins/physiology
- Xenopus laevis/metabolism
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Affiliation(s)
- Jens Eilbracht
- Division of Cell Biology, German Cancer Research Center, D-69120 Heidelberg, Germany
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19
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Jensen BC, Wang Q, Kifer CT, Parsons M. The NOG1 GTP-binding protein is required for biogenesis of the 60 S ribosomal subunit. J Biol Chem 2003; 278:32204-11. [PMID: 12788953 DOI: 10.1074/jbc.m304198200] [Citation(s) in RCA: 74] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
NOG1 is a nucleolar GTP-binding protein present in eukaryotes ranging from trypanosomes to humans. In this report we demonstrate that NOG1 is functionally linked to ribosome biogenesis. In sucrose density gradients Trypanosoma brucei NOG1 co-sediments with 60 S ribosomal subunits but not with monosomes. 60 S precursor RNAs are co-precipitated with NOG1. Together with the nucleolar localization of NOG1, these data indicate that NOG1 is associated with a precursor particle to the 60 S subunit. Disruption of NOG1 function through RNA interference led to a dramatic decrease in the levels of free 60 S particles and the appearance of an atypical rRNA intermediate in which ITS2 was not cleaved. Overexpression of mutant nog1 with a defect in its GTP binding motif on a wild type background caused a modest defect in 60 S biogenesis and a relative decrease in processing of the large subunit rRNAs. In contrast to the mutant protein, neither the N-terminal half of NOG1, which contains the GTP binding motifs, nor the C-terminal half of NOG1 associated with pre-ribosomal particles, although both localized to the nucleolus.
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Affiliation(s)
- Bryan C Jensen
- Seattle Biomedical Research Institute, and Department of Pathobiology, School of Community Medicine and Public Health, University of Washington, Seattle, Washington, USA
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20
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Da Costa L, Tchernia G, Gascard P, Lo A, Meerpohl J, Niemeyer C, Chasis JA, Fixler J, Mohandas N. Nucleolar localization of RPS19 protein in normal cells and mislocalization due to mutations in the nucleolar localization signals in 2 Diamond-Blackfan anemia patients: potential insights into pathophysiology. Blood 2003; 101:5039-45. [PMID: 12586610 DOI: 10.1182/blood-2002-12-3878] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Ribosomal protein S19 (RPS19) is frequently mutated in Diamond-Blackfan anemia (DBA), a rare congenital hypoplastic anemia. Recent studies have shown that RPS19 expression decreases during terminal erythroid differentiation. Currently no information is available on the subcellular localization of normal RPS19 and the potential effects of various RPS19 mutations on cellular localization. In the present study, using wild-type and mutant RPS19 cDNA, we explored the subcellular distribution of normal and mutant proteins in a fibroblast cell line (Cos-7 cells). RPS19 was detected primarily in the nucleus, and more specifically in the nucleoli, where RPS19 colocalized with the nucleolar protein nucleolin. Using various N-terminal and C-terminal deletion constructs, we identified 2 nucleolar localization signals (NoSs) in RPS19: the first comprising amino acids Met1 to Arg16 in the NH2-terminus and the second comprising Gly120 to Asn142 in the COOH-terminus. Importantly, 2 mutations identified in DBA patients, Val15Phe and Gly127Gln, each of which localized to 1 of the 2 NoS, failed to localize RPS19 to the nucleolus. In addition to their mislocalization, there was a dramatic decrease in the expression of the 2 mutant proteins compared to the wild type. This decrease in protein expression was specific for the mutant RPS19, since expression of other proteins was normal. The present findings enable us to document the nucleolar localization signals in RPS19 and help define the phenotypic consequences of some mutations in RPS19 in DBA.
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Affiliation(s)
- Lydie Da Costa
- Laboratoire d'Hématologie, Hôpital de Bicêtre, Le Kremlin Bicêtre, France.
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21
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Okuwaki M, Tsujimoto M, Nagata K. The RNA binding activity of a ribosome biogenesis factor, nucleophosmin/B23, is modulated by phosphorylation with a cell cycle-dependent kinase and by association with its subtype. Mol Biol Cell 2002; 13:2016-30. [PMID: 12058066 PMCID: PMC117621 DOI: 10.1091/mbc.02-03-0036] [Citation(s) in RCA: 131] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Nucleophosmin/B23 is a nucleolar phosphoprotein. It has been shown that B23 binds to nucleic acids, digests RNA, and is localized in nucleolar granular components from which preribosomal particles are transported to cytoplasm. The intracellular localization of B23 is significantly changed during the cell cycle. Here, we have examined the cellular localization of B23 proteins and the effect of mitotic phosphorylation of B23.1 on its RNA binding activity. Two splicing variants of B23 proteins, termed B23.1 and B23.2, were complexed both in vivo and in vitro. The RNA binding activity of B23.1 was impaired by hetero-oligomer formation with B23.2. Both subtypes of B23 proteins were phosphorylated during mitosis by cyclin B/cdc2. The RNA binding activity of B23.1 was repressed through cyclin B/cdc2-mediated phosphorylation at specific sites in B23. Thus, the RNA binding activity of B23.1 is stringently modulated by its phosphorylation and subtype association. Interphase B23.1 was mainly localized in nucleoli, whereas B23.2 and mitotic B23.1, those of which were incapable of binding to RNA, were dispersed throughout the nucleoplasm and cytoplasm, respectively. These results suggest that nucleolar localization of B23.1 is mediated by its ability to associate with RNA.
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Affiliation(s)
- Mitsuru Okuwaki
- Department of Infection Biology, Institute of Basic Medical Sciences, University of Tsukuba, 1-1-1 Tennohdai, Tsukuba 305-8575, Japan
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22
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Abstract
In the January 8 issue of Current Biology, two papers from the Lamond and Mann laboratories describe the largest proteomics analysis to date of a cellular compartment, the nucleolus. As a byproduct of this tour de force, a novel nuclear compartment, the paraspeckles, was identified.
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Affiliation(s)
- Miroslav Dundr
- National Cancer Institute, National Institutes of Health, Bethesda, MD 20892, USA
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23
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Olson MOJ, Hingorani K, Szebeni A. Conventional and nonconventional roles of the nucleolus. INTERNATIONAL REVIEW OF CYTOLOGY 2002; 219:199-266. [PMID: 12211630 PMCID: PMC7133188 DOI: 10.1016/s0074-7696(02)19014-0] [Citation(s) in RCA: 144] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
As the most prominent of subnuclear structures, the nucleolus has a well-established role in ribosomal subunit assembly. Additional nucleolar functions, not related to ribosome biogenesis, have been discovered within the last decade. Built around multiple copies of the genes for preribosomal RNA (rDNA), nucleolar structure is largely dependent on the process of ribosome assembly. The nucleolus is disassembled during mitosis at which time preribosomal RNA transcription and processing are suppressed; it is reassembled at the end of mitosis in part from components preserved from the previous cell cycle. Expression of preribosomal RNA (pre-rRNA) is regulated by the silencing of individual rDNA genes via alterations in chromatin structure or by controlling RNA polymerase I initiation complex formation. Preribosomal RNA processing and posttranscriptional modifications are guided by a multitude of small nucleolar RNAs. Nearly completed ribosomal subunits are exported to the cytoplasm by an established nuclear export system with the aid of specialized adapter molecules. Some preribosomal and nucleolar components are transiently localized in Cajal bodies, presumably for modification or assembly. The nonconventional functions of nucleolus include roles in viral infections, nuclear export, sequestration of regulatory molecules, modification of small RNAs, RNP assembly, and control of aging, although some of these functions are not well established. Additional progress in defining the mechanisms of each step in ribosome biogenesis as well as clarification of the precise role of the nucleolus in nonconventional activities is expected in the next decade.
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Affiliation(s)
- Mark O J Olson
- Department of Biochemistry, University of Mississippi Medical Center, Jackson 39216, USA
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24
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Neumann M, Afonina E, Ceccherini-Silberstein F, Schlicht S, Erfle V, Pavlakis GN, Brack-Werner R. Nucleocytoplasmic transport in human astrocytes: decreased nuclear uptake of the HIV Rev shuttle protein. J Cell Sci 2001; 114:1717-29. [PMID: 11309202 DOI: 10.1242/jcs.114.9.1717] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022] Open
Abstract
Astrocytes are cellular targets for the human immunodeficiency virus (HIV) that limit virus production, owing, at least in part, to the diminished functionality of the viral post-transcriptional stimulatory factor Rev. To understand the trafficking process in astrocytes, we compared nucleocytoplasmic transport of Rev and various proteins with well-characterized nucleocytoplasmic transport features in human astrocytes and control cells (HeLa). Localization and trafficking characteristics of several cellular and viral proteins, as well as nuclear trafficking of classical peptide signals upon microinjection were similar in both cell types, indicating maintenance of general features of nucleocytoplasmic transport in astrocytes. Quantification of fluorescence in living cells expressing Rev fused to green fluorescent protein (GFP) indicated a strong shift in intracellular distribution of Rev in astrocytes, with 50–70% of Rev in the cytoplasm, whereas the cytoplasmic proportion of Rev in HeLa cells is around 10%. The dynamics of nucleocytoplasmic trafficking of Rev were compared in astrocytes and Rev-permissive cells by monitoring migration of Rev-GFP in cell fusions using highly sensitive time-lapse imaging. Nuclear uptake of Rev was dramatically retarded in homo-polykaryons of astrocytes compared with control cells. Diminished nuclear uptake of Rev was also observed in hetero-polykaryons of Rev-permissive cells and astrocytes. These results indicate that astrocytes contain a cytoplasmic activity that interferes with nuclear uptake of Rev. Our studies suggest a model in which Rev is prevented from functioning efficiently in astrocytes by specific alterations of its nucleocytoplasmic trafficking properties. http://www.biologists.com/JCS/movies/jcs1709.html
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Affiliation(s)
- M Neumann
- Institute of Molecular Virology, GSF National Research Center for Environment and Health, D-85764 Neuherberg, Germany
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25
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Eilbracht J, Schmidt-Zachmann MS. Identification of a sequence element directing a protein to nuclear speckles. Proc Natl Acad Sci U S A 2001; 98:3849-54. [PMID: 11274404 PMCID: PMC31141 DOI: 10.1073/pnas.071042298] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/06/2000] [Accepted: 01/25/2001] [Indexed: 11/18/2022] Open
Abstract
SF3b(155) is an essential spliceosomal protein, highly conserved during evolution. It has been identified as a subunit of splicing factor SF3b, which, together with a second multimeric complex termed SF3a, interacts specifically with the 12S U2 snRNP and converts it into the active 17S form. The protein displays a characteristic intranuclear localization. It is diffusely distributed in the nucleoplasm but highly concentrated in defined intranuclear structures termed "speckles," a subnuclear compartment enriched in small ribonucleoprotein particles and various splicing factors. The primary sequence of SF3b(155) suggests a multidomain structure, different from those of other nuclear speckles components. To identify which part of SF3b(155) determines its specific intranuclear localization, we have constructed expression vectors encoding a series of epitope-tagged SF3b(155) deletion mutants as well as chimeric combinations of SF3b(155) sequences with the soluble cytoplasmic protein pyruvate kinase. Following transfection of cultured mammalian cells, we have identified (i) a functional nuclear localization signal of the monopartite type (KRKRR, amino acids 196--200) and (ii) a molecular segment with multiple threonine-proline repeats (amino acids 208--513), which is essential and sufficient to confer a specific accumulation in nuclear speckles. This latter sequence element, in particular amino acids 208--440, is required for correct subcellular localization of SF3b(155) and is also sufficient to target a reporter protein to nuclear speckles. Moreover, this "speckle-targeting sequence" transfers the capacity for interaction with other U2 snRNP components.
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Affiliation(s)
- J Eilbracht
- Division of Cell Biology, German Cancer Research Center, Im Neuenheimer Feld 280, D-69120 Heidelberg, Germany
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26
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Hingorani K, Szebeni A, Olson MO. Mapping the functional domains of nucleolar protein B23. J Biol Chem 2000; 275:24451-7. [PMID: 10829026 DOI: 10.1074/jbc.m003278200] [Citation(s) in RCA: 203] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Protein B23 is a multifunctional nucleolar protein whose cellular location and characteristics strongly suggest that it is a ribosome assembly factor. The protein has nucleic acid binding, ribonuclease, and molecular chaperone activities. To determine the contributions of unique polypeptide segments enriched in certain classes of amino acid residues to the respective activities, several constructs that produced N- and C-terminal deletion mutant proteins were prepared. The C-terminal quarter of the protein was shown to be necessary and sufficient for nucleic acid binding. Basic and aromatic segments at the N- and C-terminal ends, respectively, of the nucleic acid binding region were required for activity. The molecular chaperone activity was contained in the N-terminal half of the molecule, with important contributions from both nonpolar and acidic regions. The chaperone activity also correlated with the ability of the protein to form oligomers. The central portion of the molecule was required for ribonuclease activity and possibly contains the catalytic site; this region overlapped with the chaperone-containing segment of the molecule. The C-terminal, nucleic acid-binding region enhanced the ribonuclease activity but was not essential for it. These data suggest that the three activities reside in mainly separate but partially overlapping segments of the polypeptide chain.
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Affiliation(s)
- K Hingorani
- Department of Biochemistry, University of Mississippi Medical Center, Jackson, Mississippi 39216, USA
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27
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Warner AK, Sloboda RD. C-terminal domain of the mitotic apparatus protein p62 targets the protein to the nucleolus during interphase. CELL MOTILITY AND THE CYTOSKELETON 2000; 44:68-80. [PMID: 10470020 DOI: 10.1002/(sici)1097-0169(199909)44:1<68::aid-cm6>3.0.co;2-l] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Mitotic apparatuses from sea urchin embryos contain a protein (p62), previously shown to be required for mitotic progression. This protein localizes to the mitotic apparatus during cell division in urchin embryos and mammalian tissue culture cells. We show here by immunofluorescence that p62 is localized to the nucleus of mammalian cells during interphase and is highly concentrated in nucleoli. In addition, a fusion protein composed of full-length p62 and green fluorescent protein also localizes to nucleoli when expressed in COS-7 cells in culture. Analysis of the primary sequence of p62 reveals three distinct domains of the protein based on amino acid charge distribution: the acidic N-terminal domain, the basic C-terminal domain, and the central, M-domain, which contains alternating subdomains of clusters of acidic and basic residues. To identify the domain important for nucleolar localization during interphase, specific domains of p62 alone, or in combination with each other or with beta-galactosidase were fused to green fluorescent protein. Following confirmation of the fusion constructs by sequence analysis, the constructs were expressed in mammalian cells, expression was confirmed by immunoblotting, and the fusion proteins were localized via fluorescence microscopy. The data demonstrate that the C-terminal domain of p62 is both necessary and sufficient for the nuclear localization and nucleolar binding of p62 that is observed during interphase.
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Affiliation(s)
- A K Warner
- Department of Biological Sciences, 6044 Gilman Laboratory, Dartmouth College, Hanover, New Hampshire 03755, USA
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28
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Nakajima H, Matoba K, Matsumoto Y, Hongo T, Kiritaka K, Sugino H, Nagamatsu Y, Hamaguchi Y, Ikegami S. Molecular characterization of a novel nucleolar protein in starfish oocytes which is phosphorylated before and during oocyte maturation. EUROPEAN JOURNAL OF BIOCHEMISTRY 2000; 267:295-304. [PMID: 10632699 DOI: 10.1046/j.1432-1327.2000.00931.x] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
In response to 1-methyladenine, a maturation-inducing substance, starfish oocytes undergo reinitiation of meiosis with germinal vesicle breakdown through activation of p34cdc2-cyclin B, which results in the dispersal of the nucleolus. Little information has been elucidated thus far on nucleolar proteins that are phosphorylated by p34cdc2-cyclin B during meiotic maturation. Here, we describe a novel nucleolar protein of the starfish Asterina pectinifera oocyte, which is designated ANO39 and which is phosphorylated during meiotic maturation. A full-length ANO39 cDNA of 2106 base pairs encodes a polypeptide of 346 amino acids having a calculated Mr of 39 005. The amount of ANO39 is kept nearly constant during oocyte maturation and embryogenesis up to the midgastrula stage. The transcript encoding ANO39 was present in growing oocytes but not in full-grown ones, as evidenced by Northern blot hybridization. Ser145 is specifically phosphorylated when ANO39 is incubated in vitro with purified starfish p34cdc2-cyclin B. This phosphorylation site corresponds to that is phosphorylated during meiotic maturation in vivo. Immunoblot analysis using phosphoserine145-specific antibody as a probe revealed that some populations of ANO39 of the immature oocytes at the G2 stage have been already phosphorylated on Ser145 and Ser145 is maximally phosphorylated during meiotic maturation.
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Affiliation(s)
- H Nakajima
- Department of Applied Biochemistry, Faculty of Applied Biological Sciences, Hiroshima University, Japan
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29
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Claussen M, Rudt F, Pieler T. Functional modules in ribosomal protein L5 for ribonucleoprotein complex formation and nucleocytoplasmic transport. J Biol Chem 1999; 274:33951-8. [PMID: 10567357 DOI: 10.1074/jbc.274.48.33951] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
Ribosomal protein L5 forms a small, extraribosomal complex with 5 S ribosomal RNA, referred to as the 5 S ribonucleoprotein complex, which shuttles between nucleus and cytoplasm in Xenopus oocytes. Mapping elements in L5 that mediate nuclear protein import defines three separate such activities (L5-nuclear localization sequence (NLS)-1, -2, and -3), which are functional in both oocytes and somatic cells. RNA binding activity involves N-terminal as well as C-terminal elements of L5. In contrast to the full-length protein, none of the individual NLSs carrying L5 fragments are able to allow for the predominating accumulation in the nucleoli that is observed with the full-length protein. The separate L5-NLSs differ in respect to two activities. Firstly, only L5-NLS-1 and -3, not L5-NLS-2, are capable of promoting the nuclear transfer of a heterologous, covalently attached ribonucleoprotein complex. Secondly, only L5-NLS-1 is able to bind strongly to a variety of different import receptors; those that recognize L5-NLS-2 and -3 have yet to be identified.
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Affiliation(s)
- M Claussen
- Institut für Biochemie und Molekulare Zellbiologie, Georg-August-Universität, Humboldtallee 23, D-37073 Göttingen, Germany
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30
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Jarrous N, Wolenski JS, Wesolowski D, Lee C, Altman S. Localization in the nucleolus and coiled bodies of protein subunits of the ribonucleoprotein ribonuclease P. J Cell Biol 1999; 146:559-72. [PMID: 10444065 PMCID: PMC2150555 DOI: 10.1083/jcb.146.3.559] [Citation(s) in RCA: 76] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023] Open
Abstract
The precise location of the tRNA processing ribonucleoprotein ribonuclease P (RNase P) and the mechanism of its intranuclear distribution have not been completely delineated. We show that three protein subunits of human RNase P (Rpp), Rpp14, Rpp29 and Rpp38, are found in the nucleolus and that each can localize a reporter protein to nucleoli of cells in tissue culture. In contrast to Rpp38, which is uniformly distributed in nucleoli, Rpp14 and Rpp29 are confined to the dense fibrillar component. Rpp29 and Rpp38 possess functional, yet distinct domains required for subnucleolar localization. The subunit Rpp14 lacks such a domain and appears to be dependent on a piggyback process to reach the nucleolus. Biochemical analysis suggests that catalytically active RNase P exists in the nucleolus. We also provide evidence that Rpp29 and Rpp38 reside in coiled bodies, organelles that are implicated in the biogenesis of several other small nuclear ribonucleoproteins required for processing of precursor mRNA. Because some protein subunits of RNase P are shared by the ribosomal RNA processing ribonucleoprotein RNase MRP, these two evolutionary related holoenzymes may share common intranuclear localization and assembly pathways to coordinate the processing of tRNA and rRNA precursors.
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Affiliation(s)
- Nayef Jarrous
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520
| | - Joseph S. Wolenski
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520
| | - Donna Wesolowski
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520
| | - Christopher Lee
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520
| | - Sidney Altman
- Department of Molecular, Cellular and Developmental Biology, Yale University, New Haven, Connecticut 06520
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31
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Arese M, Chen Y, Florkiewicz RZ, Gualandris A, Shen B, Rifkin DB. Nuclear activities of basic fibroblast growth factor: potentiation of low-serum growth mediated by natural or chimeric nuclear localization signals. Mol Biol Cell 1999; 10:1429-44. [PMID: 10233154 PMCID: PMC25296 DOI: 10.1091/mbc.10.5.1429] [Citation(s) in RCA: 94] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Human basic fibroblast growth factor (FGF-2) occurs in four isoforms: a low molecular weight (LMW FGF-2, 18 kDa) and three high molecular weight (HMW FGF-2, 22, 22.5, and 24 kDa) forms. LMW FGF-2 is primarily cytoplasmic and functions in an autocrine manner, whereas HMW FGF-2s are nuclear and exert activities through an intracrine, perhaps nuclear, pathway. Selective overexpression of HMW FGF-2 forms in fibroblasts promotes growth in low serum, whereas overexpression of LMW FGF-2 does not. The HMW FGF-2 forms have two functional domains: an amino-terminal extension and a common 18-kDa amino acid sequence. To investigate the role of these regions in the intracrine signaling of HMW FGF-2, we produced stable transfectants of NIH 3T3 fibroblasts overexpressing either individual HMW FGF-2 forms or artificially nuclear-targeted LMW FGF-2. All of these forms of FGF-2 localize to the nucleus/nucleolus and induce growth in low serum. The nuclear forms of FGF-2 trigger a mitogenic stimulus under serum starvation conditions and do not specifically protect the cells from apoptosis. These data indicate the existence of a specific role for nuclear FGF-2 and suggest that LMW FGF-2 represents the biological messenger in both the autocrine/paracrine and intracrine FGF-2 pathways.
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Affiliation(s)
- M Arese
- Department of Cell Biology, New York University Medical Center, New York, New York 10016, USA.
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32
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Das A, Park JH, Hagen CB, Parsons M. Distinct domains of a nucleolar protein mediate protein kinase binding, interaction with nucleic acids and nucleolar localization. J Cell Sci 1998; 111 ( Pt 17):2615-23. [PMID: 9701560 DOI: 10.1242/jcs.111.17.2615] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
Nopp44/46 is a phosphoprotein of the protozoan parasite Trypanosoma brucei that is localized to the nucleolus. Based on the primary sequence, Nopp44/46 appears to be a protein composed of distinct domains. This communication describes the relationship of these domains to the known functional interactions of the molecule and suggests that the amino-terminal region defines a novel homology region that functions in nucleolar targeting. We have previously shown that Nopp44/46 is capable of interacting with nucleic acids and associating with a protein kinase. Using in vitro transcription and translation, we now demonstrate that the nucleic acid binding function maps to the carboxy-terminal domain of the molecule, a region rich in arginine-glycine-glycine motifs. Our experiments reveal that a central region containing a high proportion of acidic residues is required for association with the protein kinase. Analysis of transfectants expressing epitope-tagged Nopp44/46 deletion constructs showed that the amino-terminal 96 amino acids allowed nuclear and nucleolar accumulation of the protein. This region of the molecule shows homology to several recently described nucleolar proteins. Deletion of a 27-amino-acid region within this domain abrogated nucleolar, but not nuclear, localization. These studies show that Nopp44/46 is composed of distinct modules, each of which plays a different role in molecular interactions. We suggest that this protein could facilitate interactions between sets of nucleolar molecules.
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Affiliation(s)
- A Das
- Seattle Biomedical Research Institute, Seattle, WA 98109, USA
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33
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North MT, Allison LA. Nucleolar targeting of 5S RNA in Xenopus laevis oocytes: somatic-type nucleotide substitutions enhance nucleolar localization. J Cell Biochem 1998; 69:490-505. [PMID: 9620175 DOI: 10.1002/(sici)1097-4644(19980615)69:4<490::aid-jcb10>3.0.co;2-d] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/08/2022]
Abstract
In Xenopus laevis oocytes, 5S RNA is stored in the cytoplasm until vitellogenesis, at which time it is imported into the nucleus and targeted to nucleoli for ribosome assembly. This article shows that throughout oogenesis there is a pool of nuclear 5S RNA which is not nucleolar-associated. This distribution reflects that of oocyte-type 5S RNA, which is the major 5S RNA species in oocytes; only small amounts of somatic-type, which differs by six nucleotides, are synthesized. Indeed, 32P-labeled oocyte-type 5S RNA showed a degree of nucleolar localization similar to endogenous 5S RNA (33%) after microinjection. In contrast, 32P-labeled somatic-type 5S RNA showed significantly enhanced localization, whereby 70% of nuclear RNA was associated with nucleoli. A chimeric RNA molecule containing only one somatic-specific nucleotide substitution also showed enhanced localization, in addition to other somatic-specific phenotypes, including enhanced nuclear import and ribosome incorporation. The distribution of 35S-labeled ribosomal protein L5 was similar to that of oocyte-type 5S RNA, even when preassembled with somatic-type 5S RNA. The distribution of a series of 5S RNA mutants was also analyzed. These mutants showed various degrees of localization, suggesting that the efficiency of nucleolar targeting can be influenced by many discrete regions of the 5S RNA molecule.
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Affiliation(s)
- M T North
- Department of Zoology, University of Canterbury, Christchurch, New Zealand
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Schmidt-Zachmann MS, Knecht S, Krämer A. Molecular characterization of a novel, widespread nuclear protein that colocalizes with spliceosome components. Mol Biol Cell 1998; 9:143-60. [PMID: 9436997 PMCID: PMC25229 DOI: 10.1091/mbc.9.1.143] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
We report the identification and molecular characterization of a novel type of constitutive nuclear protein that is present in diverse vertebrate species, from Xenopus laevis to human. The cDNA-deduced amino acid sequence of the Xenopus protein defines a polypeptide of a calculated mass of 146.2 kDa and a isoelectric point of 6.8, with a conspicuous domain enriched in the dipeptide TP (threonine-proline) near its amino terminus. Immunolocalization studies in cultured cells and tissues sections of different origin revealed an exclusive nuclear localization of the protein. The protein is diffusely distributed in the nucleoplasm but concentrated in nuclear speckles, which represent a subnuclear compartment enriched in small nuclear ribonucleoprotein particles and other splicing factors, as confirmed by colocalization with certain splicing factors and Sm proteins. During mitosis, when transcription and splicing are downregulated, the protein is released from the nuclear speckles and transiently dispersed throughout the cytoplasm. Biochemical experiments have shown that the protein is recovered in a approximately 12S complex, and gel filtration studies confirm that the protein is part of a large particle. Immunoprecipitation and Western blot analysis of chromatographic fractions enriched in human U2 small nuclear ribonucleoprotein particles of distinct sizes (12S, 15S, and 17S), reflecting their variable association with splicing factors SF3a and SF3b, strongly suggests that the 146-kDa protein reported here is a constituent of the SF3b complex.
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Ursic D, Himmel KL, Gurley KA, Webb F, Culbertson MR. The yeast SEN1 gene is required for the processing of diverse RNA classes. Nucleic Acids Res 1997; 25:4778-85. [PMID: 9365256 PMCID: PMC147120 DOI: 10.1093/nar/25.23.4778] [Citation(s) in RCA: 93] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
A single base change in the helicase superfamily 1 domain of the yeast Saccharomyces cerevisiae SEN1 gene results in a heat-sensitive mutation that alters the cellular abundance of many RNA species. We compared the relative amounts of RNAs between cells that are wild-type and mutant after temperature-shift. In the mutant several RNAs were found to either decrease or increase in abundance. The affected RNAs include tRNAs, rRNAs and small nuclear and nucleolar RNAs. Many of the affected RNAs have been positively identified and include end-matured precursor tRNAs and the small nuclear and nucleolar RNAs U5 and snR40 and snR45. Several small nucleolar RNAs co-immunoprecipitate with Sen1 but differentially associate with the wild-type and mutant protein. Its inactivation also impairs precursor rRNA maturation, resulting in increased accumulation of 35S and 6S precursor rRNAs and reduced levels of 20S, 23S and 27S rRNA processing intermediates. Thus, Sen1 is required for the biosynthesis of various functionally distinct classes of nuclear RNAs. We propose that Sen1 is an RNA helicase acting on a wide range of RNA classes. Its effects on the targeted RNAs in turn enable ribonuclease activity.
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Affiliation(s)
- D Ursic
- Laboratories of Molecular Biology and Genetics, 1525 Linden Drive, University of Wisconsin, Madison, WI 53706, USA.
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Zirwes RF, Schmidt-Zachmann MS, Franke WW. Identification of a small, very acidic constitutive nucleolar protein (NO29) as a member of the nucleoplasmin family. Proc Natl Acad Sci U S A 1997; 94:11387-92. [PMID: 9326619 PMCID: PMC23475 DOI: 10.1073/pnas.94.21.11387] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
We report the discovery and molecular characterization of a small and very acidic nucleolar protein of an SDS/PAGE mobility corresponding to Mr 29,000 (NO29). The cDNA-deduced sequence of the Xenopus laevis protein defines a polypeptide of a calculated molecular mass of 20,121 and a pI of 3.75, with an extended acidic region near its C terminus, and is related to the major nucleolar protein, NO38, and the histone-binding protein, nucleoplasmin. This member of the nucleoplasmin family of proteins was immunolocalized to nucleoli in Xenopus oocytes and diverse somatic cells. Protein NO29 is associated with nuclear particles from Xenopus oocytes, partly complexed with protein NO38, and occurs in preribosomes but not in mature ribosomes. The location and the enormously high content of negatively charged amino acids lead to the hypothesis that NO29 might be involved in the nuclear and nucleolar accumulation of ribosomal proteins and the coordinated assembly of pre-ribosomal particles.
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Affiliation(s)
- R F Zirwes
- Division of Cell Biology, German Cancer Research Center, D-69120 Heidelberg, Germany
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Paffenholz R, Franke WW. Identification and localization of a neurally expressed member of the plakoglobin/armadillo multigene family. Differentiation 1997; 61:293-304. [PMID: 9342840 DOI: 10.1046/j.1432-0436.1997.6150293.x] [Citation(s) in RCA: 93] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
The plakoglobin/armadillo multigene family comprises many proteins widely differing in sizes and functions which have in common a variable number of tandemly repeated arm sequences of about 42 amino acids (aa). In a search for proteins with sequence homology to the desmosomal-plaque-associated arm-repeat-containing protein, plakophilin 1, we have identified a novel plakoglobin/armadillo protein. This new member of the multigene family is predominantly, if not exclusively, expressed in neural and neuroendocrine tissues, hence the name neural plakophilin-related arm-repeat protein (NPRAP). The murine cDNA codes for a protein of 1247 aa, with a predicted molecular weight of 135 kDa and a pI of 7.57. The orthologous human protein differs only in a few aa, indicative of the evolutionary stability of NPRAP. In human and murine cDNAs, we have found different transcripts of the NPRAP gene, suggesting that in each species the protein exists in at least two isoforms. The NPRA protein contains three different regions: a 528-aa amino-terminal "head" domain, including a potential coiled-coil-forming alpha-helix segment, a central domain with 10 imperfect arm-repeat units, and a 212-aa carboxy-terminal "tail" domain. By aa sequence, NPRAP is highly homologous to three proteins: p120cas, p0071 and ARVCP, which represent a distinct subgroup within the plakoglobin/armadillo family. By in situ hybridization and immunofluorescence microscopy using NPRAP-specific antibodies, we have demonstrated NPRAP and its mRNA in the perikarya of various kinds of CNS neurons in embryonic and adult mice, but minimal amounts have also been detected by immunoblot analysis in some other tissues containing neural or neuroendocrine elements. We have not seen significant enrichment of NPRAP at cell junctions or in nuclei. Possible NPRAP functions are discussed and the correlation of NPRAP synthesis with neuronal differentiation processes is emphasized.
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Affiliation(s)
- R Paffenholz
- Division of Cell Biology, German Cancer Research Center, Heidelberg, Germany
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