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The Physiological Roles of the Exon Junction Complex in Development and Diseases. Cells 2022; 11:cells11071192. [PMID: 35406756 PMCID: PMC8997533 DOI: 10.3390/cells11071192] [Citation(s) in RCA: 8] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/28/2022] [Revised: 03/19/2022] [Accepted: 03/24/2022] [Indexed: 01/12/2023] Open
Abstract
The exon junction complex (EJC) becomes an increasingly important regulator of early gene expression in the central nervous system (CNS) and other tissues. The EJC is comprised of three core proteins: RNA-binding motif 8A (RBM8A), Mago homolog (MAGOH), eukaryotic initiation factor 4A3 (EIF4A3), and a peripheral EJC factor, metastatic lymph node 51 (MLN51), together with various auxiliary factors. The EJC is assembled specifically at exon-exon junctions on mRNAs, hence the name of the complex. The EJC regulates multiple levels of gene expression, from splicing to translation and mRNA degradation. The functional roles of the EJC have been established as crucial to the normal progress of embryonic and neurological development, with wide ranging implications on molecular, cellular, and organism level function. Dysfunction of the EJC has been implicated in multiple developmental and neurological diseases. In this review, we discuss recent progress on the EJC’s physiological roles.
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Ye J, She X, Liu Z, He Z, Gao X, Lu L, Liang R, Lin Y. Eukaryotic Initiation Factor 4A-3: A Review of Its Physiological Role and Involvement in Oncogenesis. Front Oncol 2021; 11:712045. [PMID: 34458150 PMCID: PMC8386015 DOI: 10.3389/fonc.2021.712045] [Citation(s) in RCA: 19] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/19/2021] [Accepted: 07/27/2021] [Indexed: 12/30/2022] Open
Abstract
EIF4A3, a member of the DEAD-box protein family, is a nuclear matrix protein and a core component of the exon junction complex (EJC). Under physiological conditions, EIF4A3 participates in post-transcriptional gene regulation by promoting EJC control of precursor mRNA splicing, thus influencing nonsense-mediated mRNA decay. In addition, EIF4A3 maintains the expression of significant selenoproteins, including phospholipid hydroperoxide glutathione peroxidase and thioredoxin reductase 1. Several recent studies have shown that EIF4A3 promotes tumor growth in multiple human cancers such as glioblastoma, hepatocellular carcinoma, pancreatic cancer, and ovarian cancer. Molecular biology studies also showed that EIF4A3 is recruited by long non-coding RNAs to regulate the expression of certain proteins in tumors. However, its tumor-related functions and underlying mechanisms are not well understood. Here, we review the physiological role of EIF4A3 and the potential association between EIF4A3 overexpression and tumorigenesis. We also evaluate the protein's potential utility as a diagnosis biomarker, therapeutic target, and prognosis indicator, hoping to provide new ideas for future research.
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Affiliation(s)
- Jiazhou Ye
- Guangxi Medical University Cancer Hospital, Nanning, China
| | | | - Ziyu Liu
- Guangxi Medical University, Nanning, China
| | - Ziqin He
- Guangxi Medical University, Nanning, China
| | - Xing Gao
- Guangxi Medical University Cancer Hospital, Nanning, China
| | - Lu Lu
- Guangxi Medical University Cancer Hospital, Nanning, China
| | - Rong Liang
- Guangxi Medical University Cancer Hospital, Nanning, China
| | - Yan Lin
- Guangxi Medical University Cancer Hospital, Nanning, China
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Wang G, Sun D, Li W, Xin Y. CircRNA_100290 promotes GC cell proliferation and invasion via the miR-29b-3p/ITGA11 axis and is regulated by EIF4A3. Cancer Cell Int 2021; 21:324. [PMID: 34182990 PMCID: PMC8240270 DOI: 10.1186/s12935-021-01964-2] [Citation(s) in RCA: 22] [Impact Index Per Article: 7.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/07/2021] [Accepted: 05/04/2021] [Indexed: 12/29/2022] Open
Abstract
Background Circular RNAs (circRNAs) have been reported to be important regulators of the development and progression of various carcinomas. However, the role of circRNA_100290 in gastric cancer (GC) is still unclear. This study aimed to investigate the role of circRNA_100290 in GC invasion and metastasis and the possible underlying mechanism. Methods The expression of circRNA_100290 in GC cells and tissues was examined using quantitative real-time polymerase chain reaction (qRT-PCR). The role of circRNA_100290 in cell proliferation, migration, and invasion was evaluated in the AGS and HGC-27 cell lines in vitro. Bioinformatics tools, dual-luciferase reporter assays, Western blot assays and qRT-PCR were used to explore the pathways downstream of circRNA_100290. The mechanism underlying the regulation of circRNA_100290 expression was explored using RNA immunoprecipitation, qRT-PCR, and Western blot assays. Results The expression of circRNA_100290 was significantly upregulated in GC cells and 102 GC tissues, and high circRNA_100290 expression in GC was closely related to Borrmann’s type, lymph node metastasis and tumour-node-metastasis stage. In vitro, knockdown of circRNA_100290 in AGS and HGC-27 cells significantly inhibited cell proliferation, migration, and invasion. Mechanistically, a dual-luciferase reporter assay confirmed the direct interaction between circRNA_100290 and miR-29b-3p, which targets ITGA11, an oncogene that is closely related to epithelial–mesenchymal transition (EMT). In addition, EIF4A3, an RNA-binding protein (RBP), could inhibit the formation of circRNA_100290 by binding to the flanking sites of circRNA_100290. Low EIF4A3 expression in GC was related to a poor prognosis. Conclusions Elevated circRNA_100290 expression in GC promotes cell proliferation, invasion and EMT via the miR-29b-3p/ITGA11 axis and might be regulated by EIF4A3. CircRNA_100290 might be a promising biomarker and target for GC therapy. Graphical abstract ![]()
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Affiliation(s)
- Gang Wang
- Laboratory of Gastrointestinal Onco-Pathology, Cancer Institute, The First Affiliated Hospital of China Medical University, 155 Nanjing North Street, Heping District, Shenyang, Liaoning Province, China.,Department of Oncology, The First Affiliated Hospital of Shandong First Medical University & Shandong Provincial Qianfoshan Hospital, Shandong Key Laboratory of Rheumatic Disease and Translational Medicine, Shandong Lung Cancer Institute, 16766 Jingshi Road, Lixia District, Jinan, Shandong Province, China
| | - Dan Sun
- Laboratory of Gastrointestinal Onco-Pathology, Cancer Institute, The First Affiliated Hospital of China Medical University, 155 Nanjing North Street, Heping District, Shenyang, Liaoning Province, China
| | - Wenhui Li
- Laboratory of Gastrointestinal Onco-Pathology, Cancer Institute, The First Affiliated Hospital of China Medical University, 155 Nanjing North Street, Heping District, Shenyang, Liaoning Province, China
| | - Yan Xin
- Laboratory of Gastrointestinal Onco-Pathology, Cancer Institute, The First Affiliated Hospital of China Medical University, 155 Nanjing North Street, Heping District, Shenyang, Liaoning Province, China.
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Telomere Transcripts Target Telomerase in Human Cancer Cells. Genes (Basel) 2016; 7:genes7080046. [PMID: 27537914 PMCID: PMC4999834 DOI: 10.3390/genes7080046] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2016] [Revised: 07/24/2016] [Accepted: 07/29/2016] [Indexed: 12/14/2022] Open
Abstract
Long non-coding transcripts from telomeres, called telomeric repeat-containing RNA (TERRA), were identified as blocking telomerase activity (TA), a telomere maintenance mechanism (TMM), in tumors. We expressed recombinant TERRA transcripts in tumor cell lines with TA and with alternative lengthening of telomeres (ALT) to study effects on TMM and cell growth. Adeno- and lentivirus constructs (AV and LV) were established for transient and stable expression of approximately 130 units of telomere hexanucleotide repeats under control of cytomegalovirus (CMV) and human RNase P RNA H1 (hH1) promoters with and without polyadenylation, respectively. Six human tumor cell lines either using telomerase or ALT were infected and analyzed for TA levels. Pre-infection cells using telomerase had 1%-3% of the TERRA expression levels of ALT cells. AV and LV expression of recombinant TERRA in telomerase positive cells showed a 1.3-2.6 fold increase in TERRA levels, and a decrease in TA of 25%-58%. Dominant-negative or small hairpin RNA (shRNA) viral expression against human telomerase reverse transcriptase (hTERT) results in senescence, not induced by TERRA expression. Population doubling time, cell viability and TL (telomere length) were not impacted by ectopic TERRA expression. Clonal growth was reduced by TERRA expression in TA but not ALT cell lines. ALT cells were not affected by treatments applied. Established cell models and tools may be used to better understand the role of TERRA in the cell, especially for targeting telomerase.
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Huang CK, Sie YS, Chen YF, Huang TS, Lu CA. Two highly similar DEAD box proteins, OsRH2 and OsRH34, homologous to eukaryotic initiation factor 4AIII, play roles of the exon junction complex in regulating growth and development in rice. BMC PLANT BIOLOGY 2016; 16:84. [PMID: 27071313 PMCID: PMC4830029 DOI: 10.1186/s12870-016-0769-5] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/30/2015] [Accepted: 04/06/2016] [Indexed: 05/10/2023]
Abstract
BACKGROUND The exon junction complex (EJC), which contains four core components, eukaryotic initiation factor 4AIII (eIF4AIII), MAGO/NASHI (MAGO), Y14/Tsunagi/RNA-binding protein 8A, and Barentsz/Metastatic lymph node 51, is formed in both nucleus and cytoplasm, and plays important roles in gene expression. Genes encoding core EJC components have been found in plants, including rice. Currently, the functional characterizations of MAGO and Y14 homologs have been demonstrated in rice. However, it is still unknown whether eIF4AIII is essential for the functional EJC in rice. RESULTS This study investigated two DEAD box RNA helicases, OsRH2 and OsRH34, which are homologous to eIF4AIII, in rice. Amino acid sequence analysis indicated that OsRH2 and OsRH34 had 99 % identity and 100 % similarity, and their gene expression patterns were similar in various rice tissues, but the level of OsRH2 mRNA was about 58-fold higher than that of OsRH34 mRNA in seedlings. From bimolecular fluorescence complementation results, OsRH2 and OsRH34 interacted physically with OsMAGO1 and OsY14b, respectively, which indicated that both of OsRH2 and OsRH34 were core components of the EJC in rice. To study the biological roles of OsRH2 and OsRH34 in rice, transgenic rice plants were generated by RNA interference. The phenotypes of three independent OsRH2 and OsRH34 double-knockdown transgenic lines included dwarfism, a short internode distance, reproductive delay, defective embryonic development, and a low seed setting rate. These phenotypes resembled those of mutants with gibberellin-related developmental defects. In addition, the OsRH2 and OsRH34 double-knockdown transgenic lines exhibited the accumulation of unspliced rice UNDEVELOPED TAPETUM 1 mRNA. CONCLUSIONS Rice contains two eIF4AIII paralogous genes, OsRH2 and OsRH34. The abundance of OsRH2 mRNA was about 58-fold higher than that of OsRH34 mRNA in seedlings, suggesting that the OsRH2 is major eIF4AIII in rice. Both OsRH2 and OsRH34 are core components of the EJC, and participate in regulating of plant height, pollen, and seed development in rice.
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Affiliation(s)
- Chun-Kai Huang
- Department of Life Sciences, National Central University, Jhongli District, Taoyuan City 32001 Taiwan (ROC)
| | - Yi-Syuan Sie
- Department of Life Sciences, National Central University, Jhongli District, Taoyuan City 32001 Taiwan (ROC)
| | - Yu-Fu Chen
- Department of Life Sciences, National Central University, Jhongli District, Taoyuan City 32001 Taiwan (ROC)
| | - Tian-Sheng Huang
- Department of Life Sciences, National Central University, Jhongli District, Taoyuan City 32001 Taiwan (ROC)
| | - Chung-An Lu
- Department of Life Sciences, National Central University, Jhongli District, Taoyuan City 32001 Taiwan (ROC)
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Martineau Y, Azar R, Bousquet C, Pyronnet S. Anti-oncogenic potential of the eIF4E-binding proteins. Oncogene 2012; 32:671-7. [DOI: 10.1038/onc.2012.116] [Citation(s) in RCA: 76] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022]
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Albrethsen J, Knol JC, Jimenez CR. Unravelling the nuclear matrix proteome. J Proteomics 2008; 72:71-81. [PMID: 18957335 DOI: 10.1016/j.jprot.2008.09.005] [Citation(s) in RCA: 50] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/16/2008] [Revised: 09/29/2008] [Accepted: 09/30/2008] [Indexed: 12/28/2022]
Abstract
The nuclear matrix (NM) model posits the presence of a protein/RNA scaffold that spans the mammalian nucleus. The NM proteins are involved in basic nuclear function and are a promising source of protein biomarkers for cancer. Importantly, the NM proteome is operationally defined as the proteins from cells and tissue that are extracted following a specific biochemical protocol; in brief, the soluble proteins and lipids, cytoskeleton, and chromatin elements are removed in a sequential fashion, leaving behind the proteins that compose the NM. So far, the NM has not been sufficiently verified as a biological entity and only preliminary at the molecular level. Here, we argue for a combined effort of proteomics, immunodetection and microscopy to unravel the composition and structure of the NM.
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Affiliation(s)
- Jakob Albrethsen
- OncoProteomics Laboratory, CCA 1-60, Department Medical Oncology, VUmc-Cancer Center Amsterdam, De Boelelaan 1117, 1081 HV Amsterdam, The Netherlands
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Feng J, Lawson MA, Melamed P. A proteomic comparison of immature and mature mouse gonadotrophs reveals novel differentially expressed nuclear proteins that regulate gonadotropin gene transcription and RNA splicing. Biol Reprod 2008; 79:546-61. [PMID: 18480465 DOI: 10.1095/biolreprod.108.068106] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022] Open
Abstract
The alphaT3-1 and LbetaT2 gonadotroph cell lines contain all the known factors required for expression of gonadotropin genes, yet only the LbetaT2 cells express the beta subunits. We hypothesized that comparison of their nuclear proteomes would reveal novel proteins and/or modifications that regulate expression of these genes. We identified nine proteins with different expression profiles in the two cell lines, of which several were chosen for further functional studies. Of those found at higher levels in alphaT3-1 nuclei, 1110005A23RIK was found associated with the Fshb gene promoter and repressed its expression. Transgelin 3 overexpression reduced transcript levels of Fshb, and its knockdown elevated Lhb and Cga transcript levels, indicating an ongoing repressive effect on these more highly expressed genes, possibly through altering levels of phosphorylated mitogen-activated protein kinase. Heterogeneous nuclear ribonucleoprotein A2/B1 repressed splicing of the Fshb primary transcript, which it binds in the first intron. Proteins at higher levels in LbetaT2 nuclei included prohibitin, the overexpression of which reduced promoter activity of all three gonadotropin subunits, and appeared to mediate the differential effect of GnRH on proliferation of the two cell lines; its knockdown also altered cell morphology. Two other splicing factors were also found at higher levels in LbetaT2 nuclei: the knockdown of PRPF19 or EIF4A3 decreased splicing of Lhb, or of both beta subunit transcripts, respectively. The levels of Eif4a3 mRNA were increased by activin, and both factors increased Fshb splicing. This study has revealed a number of novel factors that alter gonadotropin expression and gonadotroph function, and likely mediate or moderate effects of the regulatory hormones.
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Affiliation(s)
- Jiajun Feng
- Department of Biological Sciences, National University of Singapore, Singapore
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Dhalia R, Marinsek N, Reis CRS, Katz R, Muniz JRC, Standart N, Carrington M, de Melo Neto OP. The two eIF4A helicases in Trypanosoma brucei are functionally distinct. Nucleic Acids Res 2006; 34:2495-507. [PMID: 16687655 PMCID: PMC1459412 DOI: 10.1093/nar/gkl290] [Citation(s) in RCA: 53] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/01/2006] [Revised: 03/04/2006] [Accepted: 04/06/2006] [Indexed: 11/13/2022] Open
Abstract
Protozoan parasites belonging to the family Trypanosomatidae are characterized by an unusual pathway for the production of mRNAs via polycistronic transcription and trans-splicing of a 5' capped mini-exon which is linked to the 3' cleavage and polyadenylation of the upstream transcript. However, little is known of the mechanism of protein synthesis in these organisms, despite their importance as agents of a number of human diseases. Here we have investigated the role of two Trypanosoma brucei homologues of the translation initiation factor eIF4A (in the light of subsequent experiments these were named as TbEIF4AI and TbEIF4AIII). eIF4A, a DEAD-box RNA helicase, is a subunit of the translation initiation complex eIF4F which binds to the cap structure of eukaryotic mRNA and recruits the small ribosomal subunit. TbEIF4AI is a very abundant predominantly cytoplasmic protein (over 1 x 10(5) molecules/cell) and depletion to approximately 10% of normal levels through RNA interference dramatically reduces protein synthesis one cell cycle following double-stranded RNA induction and stops cell proliferation. In contrast, TbEIF4AIII is a nuclear, moderately expressed protein (approximately 1-2 x 10(4) molecules/cell), and its depletion stops cellular proliferation after approximately four cell cycles. Ectopic expression of a dominant negative mutant of TbEIF4AI, but not of TbEIF4AIII, induced a slow growth phenotype in transfected cells. Overall, our results suggest that only TbEIF4AI is involved in protein synthesis while the properties and sequence of TbEIF4AIII indicate that it may be the orthologue of eIF4AIII, a component of the exon junction complex in mammalian cells.
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Affiliation(s)
- Rafael Dhalia
- Centro de Pesquisas Aggeu Magalhães, Fundação Oswaldo CruzAvenue Moraes Rego s/n, Campus UFPE, Recife PE 50670-420, Brazil
- Department of Biochemistry, University of Cambridge80 Tennis Court Road, Cambridge CB2 1GA, UK
- Instituto de Física de São Carlos, Universidade de São PauloCaixa Postal 369, São Carlos SP 13560-970, Brazil
| | - Nina Marinsek
- Department of Biochemistry, University of Cambridge80 Tennis Court Road, Cambridge CB2 1GA, UK
| | - Christian R. S. Reis
- Centro de Pesquisas Aggeu Magalhães, Fundação Oswaldo CruzAvenue Moraes Rego s/n, Campus UFPE, Recife PE 50670-420, Brazil
- Department of Biochemistry, University of Cambridge80 Tennis Court Road, Cambridge CB2 1GA, UK
- Instituto de Física de São Carlos, Universidade de São PauloCaixa Postal 369, São Carlos SP 13560-970, Brazil
| | - Rodolfo Katz
- Centro de Pesquisas Aggeu Magalhães, Fundação Oswaldo CruzAvenue Moraes Rego s/n, Campus UFPE, Recife PE 50670-420, Brazil
- Department of Biochemistry, University of Cambridge80 Tennis Court Road, Cambridge CB2 1GA, UK
- Instituto de Física de São Carlos, Universidade de São PauloCaixa Postal 369, São Carlos SP 13560-970, Brazil
| | - João R. C. Muniz
- Instituto de Física de São Carlos, Universidade de São PauloCaixa Postal 369, São Carlos SP 13560-970, Brazil
| | - Nancy Standart
- Department of Biochemistry, University of Cambridge80 Tennis Court Road, Cambridge CB2 1GA, UK
| | - Mark Carrington
- Department of Biochemistry, University of Cambridge80 Tennis Court Road, Cambridge CB2 1GA, UK
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Shibuya T, Tange TØ, Stroupe ME, Moore MJ. Mutational analysis of human eIF4AIII identifies regions necessary for exon junction complex formation and nonsense-mediated mRNA decay. RNA (NEW YORK, N.Y.) 2006; 12:360-74. [PMID: 16495234 PMCID: PMC1383576 DOI: 10.1261/rna.2190706] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/06/2023]
Abstract
The exon junction complex (EJC) is deposited on mRNAs by the process of pre-mRNA splicing and is a key effector of downstream mRNA metabolism. We previously demonstrated that human eIF4AIII, which is essential for nonsense-mediated mRNA decay (NMD), constitutes at least part of the RNA-binding platform anchoring other EJC components to the spliced mRNA. To determine the regions of eIF4AIII that are functionally important for EJC formation, for binding to other EJC components, and for NMD, we now report results of an extensive mutational analysis of human eIF4AIII. Using GFP-, GST- or Flag-fusions of eIF4AIII versions containing site-specific mutations or truncations, we analyzed subcellular localizations, protein-protein interactions, and EJC formation in vivo and in vitro. We also tested whether mutant proteins could rescue NMD inhibition resulting from RNAi depletion of endogenous eIF4AIII. Motifs Ia and VI, which are conserved among the eIF4A family of RNA helicases (DEAD-box proteins), are crucial for EJC formation and NMD, as is one eIF4AIII-specific region. An additional eIF4AIII-specific motif forms part of the binding site for MLN51, another EJC core component. Mutations in the canonical Walker A and B motifs that eliminate RNA-dependent ATP hydrolysis by eIF4AIII in vitro are of no detectable consequence for EJC formation and NMD activation. Implications of these findings are discussed in the context of other recent results and a new structural model for human eIF4AIII based on the known crystal structure of Saccharomyces cerevisiae eIF4AI.
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Affiliation(s)
- Toshiharu Shibuya
- Howard Hughes Medical Institute, Department of Biochemistry, MS009, Brandeis University, 415 South Street, Waltham, MA 02454, USA
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Xia Q, Kong XT, Zhang GA, Hou XJ, Qiang H, Zhong RQ. Proteomics-based identification of DEAD-box protein 48 as a novel autoantigen, a prospective serum marker for pancreatic cancer. Biochem Biophys Res Commun 2005; 330:526-32. [PMID: 15796914 DOI: 10.1016/j.bbrc.2005.02.181] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/18/2005] [Indexed: 12/13/2022]
Abstract
Patients with cancer frequently develop autoantibodies, and the identification of panels of tumor autoantigens may have utility in early cancer diagnosis and immunotherapy. This study aims to exploit the autoantibody repertoire in pancreatic cancer and identify the possible serum marker for pancreatic cancer. Sera from 55 newly diagnosed patients with pancreatic cancer and 52 healthy controls were analyzed for antibody-based reactivity against Hep-2, a human larynx epithelioma cancer cell line, with one-dimensional immunoblot assay. From this analysis, we observed a prominent band with a molecular weight of 47 kDa in 63.64% (35/55) patients, while in only 1.9% normal group (1/52). Using immunoblot analysis after two-dimensional electrophoresis combined with liquid chromatography-electrospray ionization tandem mass spectrometry, this target antigen was identified as DEAD-box protein 48 (DDX48). BLAST analysis showed that it was highly similar to eukaryotic initiation factor 4A and might play a role in pre-mRNA processing. An enzyme-linked immunosorbent assay was performed using recombinant, purified DDX48 as an antigen to detect anti-DDX48 autoantibodies in sera. Reactivity was observed in 20 of 60 (33.33%) pancreatic cancer patients, 3 of 30 (10.00%) colorectal cancer patients, 2 of 30 (6.67%) gastric cancer patients, 2 of 30 (6.67%) hepatocellular cancer patients, while none of the 20 chronic pancreatitis patients, 30 lung cancer patients, and 60 normal individuals. Together, these results demonstrate that the detection of autoantibodies to DDX48 may have clinical utility for the improved diagnosis of pancreatic cancer.
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Affiliation(s)
- Qing Xia
- Department of Molecular Immunology, Institute of Basic Medical Science, TaiPing Road 27, Beijing 100850, PR China
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12
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Simmons HM, Ruis BL, Kapoor M, Hudacek AW, Conklin KF. Identification of NOM1, a nucleolar, eIF4A binding protein encoded within the chromosome 7q36 breakpoint region targeted in cases of pediatric acute myeloid leukemia. Gene 2005; 347:137-45. [PMID: 15715967 DOI: 10.1016/j.gene.2004.12.027] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/07/2004] [Revised: 12/02/2004] [Accepted: 12/15/2004] [Indexed: 11/19/2022]
Abstract
Proteins that contain the recently described MIF4G and/or MA3 domains function in translation, cell growth, proliferation, transformation, and apoptosis. Examples of MIF4G/MA3 containing proteins and their functions include eIF4G, which serves as a scaffold for assembly of factors required for translation initiation, programmed cell death protein 4 (Pdcd4) that inhibits translation and functions as a tumor suppressor, and NMD2, which is essential for nonsense-mediated mRNA decay. MIF4G and MA3 domains serve as binding sites for one or more isoforms of the eIF4A family of ATP-dependent DEAD-box RNA helicases that are required for translation and for nonsense-mediated decay. In this report, we describe the characterization of a novel MIF4G/MA3 family member called NOM1 (nucleolar protein with MIF4G domain 1) that was identified at the chromosome 7q36 breakpoint involved in 7;12 translocations associated with certain acute leukemias of childhood. NOM1, which includes a previously described EST called c7orf3, encodes a ubiquitously expressed transcript composed of 11 exons and an approximately 3 kb 3' UTR that contains several Alu repeats. The predicted NOM1 protein contains one MIF4G domain and one MA3 domain and, consistent with data obtained with other MIF4G/MA3 proteins, interacts with members of the eIF4A family of helicases. Database searches reveal that NOM1 homologs exist in several organisms and that at least two of these are essential genes. Finally, like its Saccharomyces cerevisiae homolog Sgd1p, NOM1 localizes predominantly to the nucleolus. These data demonstrate that NOM1 is a new member of the MIF4G/MA3 family of proteins and suggest that it may provide an essential function in metazoans.
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MESH Headings
- Alu Elements/genetics
- Alu Elements/physiology
- Apoptosis/genetics
- Apoptosis/physiology
- Cell Nucleus/metabolism
- Cell Proliferation
- Cell Transformation, Neoplastic/genetics
- Cell Transformation, Neoplastic/metabolism
- Chromosome Breakage/genetics
- Chromosomes, Human, Pair 7/genetics
- Codon, Nonsense/genetics
- Codon, Nonsense/metabolism
- Eukaryotic Initiation Factor-4A/genetics
- Eukaryotic Initiation Factor-4A/metabolism
- Exons/genetics
- Exons/physiology
- Gene Expression Regulation, Leukemic/genetics
- Gene Expression Regulation, Leukemic/physiology
- Humans
- Leukemia, Myeloid, Acute/genetics
- Leukemia, Myeloid, Acute/metabolism
- Nuclear Proteins/genetics
- Nuclear Proteins/metabolism
- Protein Binding/genetics
- Protein Binding/physiology
- RNA Stability/genetics
- RNA Stability/physiology
- RNA-Binding Proteins/genetics
- RNA-Binding Proteins/metabolism
- Transcription, Genetic/genetics
- Transcription, Genetic/physiology
- Translocation, Genetic/genetics
- Translocation, Genetic/physiology
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Affiliation(s)
- Heidi M Simmons
- Department of Biochemistry, Molecular Biology and Biophysics, University of Minnesota, Minneapolis, MN 55455, USA
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Abdelhaleem M. Do human RNA helicases have a role in cancer? Biochim Biophys Acta Rev Cancer 2004; 1704:37-46. [PMID: 15238243 DOI: 10.1016/j.bbcan.2004.05.001] [Citation(s) in RCA: 42] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/26/2004] [Accepted: 05/06/2004] [Indexed: 11/24/2022]
Abstract
Human RNA helicases (HRH) represent a large family of enzymes that play important roles in RNA processing. The biochemical characteristics and biological functions of the majority of HRH are still to be determined. However, there are examples of dysregulation of HRH expression in various types of cancer. In addition, some HRH have been shown to be involved in the regulation of, or the molecular interaction with, molecules implicated in cancer. Other helicases take part in fusion transcripts resulting from cancer-associated chromosomal translocation. These findings raise the question of whether HRH can contribute to cancer development/progression. In this review, I summarize the cancer-related features of HRH.
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Affiliation(s)
- Mohamed Abdelhaleem
- Division of Haematopathology, Department of Paediatric Laboratory Medicine, Hospital for Sick Children, University of Toronto, Room 3691 Atrium, 555 University Avenue, Toronto, ON M5G 1X8, Canada.
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Saitoh N, Spahr CS, Patterson SD, Bubulya P, Neuwald AF, Spector DL. Proteomic analysis of interchromatin granule clusters. Mol Biol Cell 2004; 15:3876-90. [PMID: 15169873 PMCID: PMC491843 DOI: 10.1091/mbc.e04-03-0253] [Citation(s) in RCA: 220] [Impact Index Per Article: 11.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
A variety of proteins involved in gene expression have been localized within mammalian cell nuclei in a speckled distribution that predominantly corresponds to interchromatin granule clusters (IGCs). We have applied a mass spectrometry strategy to identify the protein composition of this nuclear organelle purified from mouse liver nuclei. Using this approach, we have identified 146 proteins, many of which had already been shown to be localized to IGCs, or their functions are common to other already identified IGC proteins. In addition, we identified 32 proteins for which only sequence information is available and thus these represent novel IGC protein candidates. We find that 54% of the identified IGC proteins have known functions in pre-mRNA splicing. In combination with proteins involved in other steps of pre-mRNA processing, 81% of the identified IGC proteins are associated with RNA metabolism. In addition, proteins involved in transcription, as well as several other cellular functions, have been identified in the IGC fraction. However, the predominance of pre-mRNA processing factors supports the proposed role of IGCs as assembly, modification, and/or storage sites for proteins involved in pre-mRNA processing.
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Affiliation(s)
- Noriko Saitoh
- Cold Spring Harbor Laboratory, Cold Spring Harbor, New York 11724, USA
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15
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Ferraiuolo MA, Lee CS, Ler LW, Hsu JL, Costa-Mattioli M, Luo MJ, Reed R, Sonenberg N. A nuclear translation-like factor eIF4AIII is recruited to the mRNA during splicing and functions in nonsense-mediated decay. Proc Natl Acad Sci U S A 2004; 101:4118-23. [PMID: 15024115 PMCID: PMC384704 DOI: 10.1073/pnas.0400933101] [Citation(s) in RCA: 147] [Impact Index Per Article: 7.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/19/2004] [Indexed: 11/18/2022] Open
Abstract
In eukaryotes, a surveillance mechanism known as nonsense-mediated decay (NMD) degrades the mRNA when a premature-termination codon (PTC) is present. NMD requires translation to read the frame of the mRNA and detect the PTC. During pre-mRNA splicing, the exon-exon junction complex (EJC) is recruited to a region 20-24 nt upstream of the exon junction on the mature mRNA. The presence of a PTC upstream from the EJC elicits NMD. Eukaryotic initiation factor 4A (eIF4A) III is a nuclear protein that interacts physically or functionally with translation initiation factors eIF4G and eIF4B, respectively, and shares strikingly high identity with the initiation factors eIF4AI/II. Here we show that siRNA against eIF4AIII, but not against eIF4AI/II, inhibits NMD. Moreover, eIF4AIII, but not eIF4AI, is specifically recruited to the EJC during splicing. The observations that eIF4AIII is loaded onto the mRNA during splicing in the nucleus, has properties related to a translation initiation factor, and functions in NMD raises the possibility that eIF4AIII substitutes for eIF4AI/II during NMD.
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Affiliation(s)
- Maria A Ferraiuolo
- Department of Biochemistry, McGill University, 3655 Promenade Sir William Osler, Montreal, Quebec, Canada H3G 1Y6
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16
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Shibuya T, Tange TØ, Sonenberg N, Moore MJ. eIF4AIII binds spliced mRNA in the exon junction complex and is essential for nonsense-mediated decay. Nat Struct Mol Biol 2004; 11:346-51. [PMID: 15034551 DOI: 10.1038/nsmb750] [Citation(s) in RCA: 205] [Impact Index Per Article: 10.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2004] [Accepted: 03/03/2004] [Indexed: 11/09/2022]
Abstract
The exon junction complex (EJC), a set of proteins deposited on mRNAs as a consequence of pre-mRNA splicing, is a key effector of downstream mRNA metabolism. We have identified eIF4AIII, a member of the eukaryotic translation initiation factor 4A family of RNA helicases (also known as DExH/D box proteins), as a novel EJC core component. Crosslinking and antibody inhibition studies suggest that eIF4AIII constitutes at least part of the platform anchoring other EJC components to spliced mRNAs. A nucleocytoplasmic shuttling protein, eIF4AIII associates in vitro and in vivo with two other EJC core factors, Y14 and Magoh. In mammalian cells, eIF4AIII is essential for nonsense-mediated mRNA decay (NMD). Finally, a model is proposed by which eIF4AIII represents a new functional class of DExH/D box proteins that act as RNA clamps or 'place holders' for the sequence-independent attachment of additional factors to RNAs.
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Affiliation(s)
- Toshiharu Shibuya
- Howard Hughes Medical Institute, Department of Biochemistry, Brandeis University, Waltham, Massachusetts 02454, USA
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17
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Chan CC, Dostie J, Diem MD, Feng W, Mann M, Rappsilber J, Dreyfuss G. eIF4A3 is a novel component of the exon junction complex. RNA (NEW YORK, N.Y.) 2004; 10:200-9. [PMID: 14730019 PMCID: PMC1370532 DOI: 10.1261/rna.5230104] [Citation(s) in RCA: 195] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/13/2003] [Accepted: 11/19/2003] [Indexed: 05/19/2023]
Abstract
The exon junction complex (EJC) is a protein complex that assembles near exon-exon junctions of mRNAs as a result of splicing. EJC proteins play important roles in postsplicing events including mRNA export, cytoplasmic localization, and nonsense-mediated decay. Recent evidence suggests that mRNA translation is also influenced by the splicing history of the transcript. Here we identify eIF4A3, a DEAD-box RNA helicase and a member of the eIF4A family of translation initiation factors, as a novel component of the EJC. We show that eIF4A3 associates preferentially with nuclear complexes containing the EJC proteins magoh and Y14. Furthermore, eIF4A3, but not the highly related eIF4A1 or eIF4A2, preferentially associates with spliced mRNA. In vitro splicing and mapping experiments demonstrate that eIF4A3 binds mRNAs at the position of the EJC. Using monoclonal antibodies, we show that eIF4A3 is found in the nucleus whereas eIF4A1 and eIF4A2 are found in the cytoplasm. Thus, eIF4A3 likely provides a splicing-dependent influence on the translation of mRNAs.
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Affiliation(s)
- Chia C Chan
- Howard Hughes Medical Institute and Department of Biochemistry & Biophysics, University of Pennsylvania School of Medicine, Philadelphia, Pennsylvania 19104-6148, USA
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18
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Abstract
The eukaryotic nucleus has been proposed to be organized by two interdependent nucleoprotein structures, the DNA-based chromatin and the RNA-dependent nuclear matrix. The functional composition and molecular organization of the second component have not yet been resolved. Here, we describe the isolation of the nuclear matrix from the model plant Arabidopsis, its initial characterization by confocal and electron microscopy, and the identification of 36 proteins by mass spectrometry. Electron microscopy of resinless samples confirmed a structure very similar to that described for the animal nuclear matrix. Two-dimensional gel electrophoresis resolved approximately 300 protein spots. Proteins were identified in batches by ESI tandem mass spectrometry after resolution by 1D SDS-PAGE. Among the identified proteins were a number of demonstrated or predicted Arabidopsis homologs of nucleolar proteins such as IMP4, Nop56, Nop58, fibrillarins, nucleolin, as well as ribosomal components and a putative histone deacetylase. Others included homologs of eEF-1, HSP/HSC70, and DnaJ, which have also been identified in the nucleolus or nuclear matrix of human cells, as well as a number of novel proteins with unknown function. This study is the first proteomic approach towards the characterization of a higher plant nuclear matrix. It demonstrates the striking similarities both in structure and protein composition of the operationally defined nuclear matrix across kingdoms whose unicellular ancestors have separated more than one billion years ago.
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Affiliation(s)
- Tomasz T Calikowski
- Department of Plant Biology and Plant Biotechnology Center, Ohio State University, Columbus, Ohio 43210, USA
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19
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Nicoll JB, Gwinn BL, Iwig JS, Garcia PP, Bunn CF, Allison LA. Compartment-specific phosphorylation of rat thyroid hormone receptor alpha1 regulates nuclear localization and retention. Mol Cell Endocrinol 2003; 205:65-77. [PMID: 12890568 DOI: 10.1016/s0303-7207(03)00199-0] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
Abstract
The thyroid hormone receptor alpha1 (TRalpha1) is a transcription factor, which can activate or repress gene expression in response to thyroid hormone. In addition, some of its actions, including DNA binding and transcriptional activation, are thought to be regulated by phosphorylation. Results presented here, using Xenopus oocyte microinjection assays, demonstrate that a phosphorylated form of rat TRalpha1 is present in the nucleus, whereas unphosphorylated TRalpha1 remains cytoplasmic. Changes in the phosphorylation state of TRalpha1 occur rapidly and point to the possibility that phosphorylation occurs in the nucleus. Furthermore, increasing the overall phosphorylation state of the cell leads to enhanced nuclear retention of TRalpha1, suggesting that compartment-specific phosphorylation regulates nuclear localization of TRalpha1. Enhanced nuclear retention of TRalpha1 is not dependent on phosphorylation of serine 12, a well-characterized casein kinase II site, nor is phosphorylation of this site necessary for import of TRalpha1 into the Xenopus oocyte nucleus. Similarly, mutational analysis in mammalian cells shows that nuclear localization and partitioning of TRalpha1 to the nuclear matrix are independent of serine 12 phosphorylation. Taken together, these studies suggest that phosphorylation of one or more sites in TRalpha1, excluding serine 12, enhances nuclear retention and/or inhibits nuclear export but is not directly involved in nuclear import.
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Affiliation(s)
- James B Nicoll
- Department of Biology, College of William and Mary, PO Box 8795, Williamsburg, VA 23187, USA
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20
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Gerner C, Gotzmann J, Fröhwein U, Schamberger C, Ellinger A, Sauermann G. Proteome analysis of nuclear matrix proteins during apoptotic chromatin condensation. Cell Death Differ 2002; 9:671-81. [PMID: 12032676 DOI: 10.1038/sj.cdd.4401010] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/26/2001] [Revised: 12/20/2001] [Accepted: 01/08/2002] [Indexed: 11/08/2022] Open
Abstract
The nuclear matrix (NM) is considered a proteinaceous scaffold spatially organizing the interphase nucleus, the integrity of which is affected during apoptosis. Caspase-mediated degradation of NM proteins, such as nuclear lamins, precedes apoptotic chromatin condensation (ACC). Nevertheless, other NM proteins remain unaffected, which most likely maintain a remaining nuclear structure devoid of chromatin. We, therefore, screened various types of apoptotic cells for changes of the nuclear matrix proteome during the process of apoptotic ACC. Expectedly, we observed fundamental alterations of known chromatin-associated proteins, comprising both degradation and translocation to the cytosol. Importantly, a consistent set of abundant NM proteins, some (e.g. hNMP 200) of which displaying structural features, remained unaffected during apoptosis and might therefore represent constituents of an elementary scaffold. In addition, proteins involved in DNA replication and DNA repair were found accumulated in the NM fraction before cells became irreversibly committed to ACC, a time point characterized in detail by inhibitor studies with orthovanadate. In general, protein alterations of a consistent set of NM proteins (67 of which were identified), were reproducibly detectable in Fas-induced Jurkat cells, in UV-light treated U937 cells and also in staurosporine-treated HeLa cells. Our data indicate that substantial alterations of proteins linking chromatin to an elementary nuclear protein scaffold might play an intriguing role for the process of ACC.
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Affiliation(s)
- C Gerner
- Institute of Cancer Research, University of Vienna, A-1090 Vienna, Austria.
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21
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Abstract
The emerging field of nuclear eIF research has yielded many surprises and led to the dissolution of some dogmatic/ideological viewpoints of the place of translation in the regulation of gene expression. Eukaryotic initiation factors (eIFs) are classically defined by their cytoplasmic location and ability to regulate the initiation phase of protein synthesis. For instance, in the cytoplasm, the m7G cap-binding protein eIF4E plays a distinct role in cap-dependent translation initiation. Disruption of eIF4E's regulatory function drastically effects cell growth and may lead to oncogenic transformation. A growing number of studies indicate that many eIFs, including a substantial fraction of eIF4E, are found in the nucleus. Indeed, nuclear eIF4E participates in a variety of important RNA-processing events including the nucleocytoplasmic transport of specific, growth regulatory mRNAs. Although unexpected, it is possible that some eIFs regulate protein synthesis within the nucleus. This review will focus on the novel, nuclear functions of eIF4E and how they contribute to eIF4E's growth-activating and oncogenic properties. Both the cytoplasmic and nuclear functions of eIF4E appear to be dependent on its intrinsic ability to bind to the 5' m7G cap of mRNA. For example, Promyelocytic Leukemia Protein (PML) potentially acts as a negative regulator of nuclear eIF4E function by decreasing eIF4E's affinity for the m7G cap. Therefore, eIF4E protein is flexible enough to utilize a common biochemical activity, such as m7G cap binding, to participate in divergent processes in different cellular compartments.
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Affiliation(s)
- Stephen Strudwick
- Structural Biology Program, Department of Physiology & Biophysics, Mount Sinai School of Medicine, New York University, One Gustave Levy Place, New York, NY 10029, USA
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22
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Sacco-Bubulya P, Spector DL. Disassembly of interchromatin granule clusters alters the coordination of transcription and pre-mRNA splicing. J Cell Biol 2002; 156:425-36. [PMID: 11827980 PMCID: PMC2173333 DOI: 10.1083/jcb.200107017] [Citation(s) in RCA: 115] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
To examine the involvement of interchromatin granule clusters (IGCs) in transcription and pre-mRNA splicing in mammalian cell nuclei, the serine-arginine (SR) protein kinase cdc2-like kinase (Clk)/STY was used as a tool to manipulate IGC integrity in vivo. Both immunofluorescence and transmission electron microscopy analyses of cells overexpressing Clk/STY indicate that IGC components are completely redistributed to a diffuse nuclear localization, leaving no residual structure. Conversely, overexpression of a catalytically inactive mutant, Clk/STY(K190R), causes retention of hypophosphorylated SR proteins in nuclear speckles. Our data suggest that the protein-protein interactions responsible for the clustering of interchromatin granules are disrupted when SR proteins are hyperphosphorylated and stabilized when SR proteins are hypophosphorylated. Interestingly, cells without intact IGCs continue to synthesize nascent transcripts. However, both the accumulation of splicing factors at sites of pre-mRNA synthesis as well as pre-mRNA splicing are dramatically reduced, demonstrating that IGC disassembly perturbs coordination between transcription and pre-mRNA splicing in mammalian cell nuclei.
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23
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Li W, Belsham GJ, Proud CG. Eukaryotic initiation factors 4A (eIF4A) and 4G (eIF4G) mutually interact in a 1:1 ratio in vivo. J Biol Chem 2001; 276:29111-5. [PMID: 11408474 DOI: 10.1074/jbc.c100284200] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
mRNA translation in eukaryotic cells involves a set of proteins termed translation initiation factors (eIFs), several of which are involved in the binding of ribosomes to mRNA. These include eIF4G, a modular scaffolding protein, and eIF4A, an RNA helicase, of which two closely related forms are known in mammals, eIF4A(I) and eIF4A(II). In mammals, eIF4G possesses two independent sites for binding eIF4A, whereas in other eukaryotes (e.g. yeast) only one site appears to be present, thus raising the issue of the stoichiometry of eIF4G.eIF4A complexes in different eukaryotes. We show that in human embryonic kidney cells eIF4G is associated with eIF4A(I) or eIF4A(II) but not with both simultaneously, suggesting a stoichiometry of 1:1 rather than 1:2. To confirm this, eIF4A(I) or eIF4A(II) was expressed in a tagged form in these cells, and complexes with eIF4G were again isolated. Complexes containing tagged eIF4A(I) or eIF4A(II) contained no endogenous eIF4A, supporting the notion that eIF4G binds only one molecule of eIF4A. Each binding site in eIF4G can bind either eIF4A(I) or eIF4A(II). The data imply that the second binding site in mammalian eIF4A does not bind an additional eIF4A molecule and that initiation factor complexes in different eukaryotes contain one eIF4A per eIF4G.
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Affiliation(s)
- W Li
- Division of Molecular Physiology, School of Life Sciences, University of Dundee, Dow Street, Dundee DD1 5EH, United Kingdom
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24
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Gotzmann J, Gerner C, Meissner M, Holzmann K, Grimm R, Mikulits W, Sauermann G. hNMP 200: a novel human common nuclear matrix protein combining structural and regulatory functions. Exp Cell Res 2000; 261:166-79. [PMID: 11082287 DOI: 10.1006/excr.2000.5025] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
Previously we have reported about human nuclear matrix proteins (hNMPs) with increased reassembling and potential filament-forming capability [C. Gerner et al., 1999, J. Cell. Biochem. 74, 145-151]. Here, we cloned the cDNA of one of these proteins, hNMP 200, following partial amino acid sequencing of the novel 56-kDa nuclear protein. Sequence alignments show hNMP 200-related proteins in metazoans, plants, and yeast, the homologous Saccharomyces cerevisiae protein prp19 being an accessory, but essential, factor for pre-mRNA processing. Evidence for any enzymatic activity was not detected. However, the hNMP 200 primary sequence contained five consensus WD-repeat sequences, indicative of participation and regulatory function in larger protein assemblies. Northern blot analysis and 2D protein electrophoresis showed ubiquitous expression of hNMP 200 in a variety of cell types. (35)S labeling studies indicated a high metabolic stability of the protein. The hNMP 200 gene was assigned to chromosomal region 11q12.2. Confocal laser scanning microscopy revealed that the intracellular localization conformed with that reported for other structural nuclear proteins. In interphase cells, green fluorescent protein-tagged hNMP 200 was predominantly nucleoplasmic. Structures with speckled appearance extended through several sections of in situ-isolated nuclear matrices. During cell division hNMP 200 became irregularly distributed in prophase, sparing regions of condensing chromatin. In anaphase it was concentrated in the spindle midzone. The putative dual function of the novel NMP is discussed. Being a component of the nuclear framework, it may provide structural support for components of the RNA-processing machinery, thereby also modulating splicing activities.
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Affiliation(s)
- J Gotzmann
- Institute of Cancer Research, University of Vienna, Borschkegasse 8a, Vienna, A-1090, Austria.
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