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Abstract
The relevance of RNA-protein interactions in modulating mRNA and noncoding RNA function is increasingly appreciated and several methods have been recently developed to map them. The RNA immunoprecipitation (RIP) is a powerful method to study the physical association between individual proteins and RNA molecules in vivo. The basic principles of RIP are very similar to those of chromatin immunoprecipitation (ChIP), a largely used tool in the epigenetic field, but with some important caveats. The approach is based on the use of a specific antibody raised against the protein of interest to pull down the RNA-binding protein (RBP) and target-RNA complexes. Any RNA that is associated with this protein complex will also be isolated and can be further analyzed by polymerase chain reaction-based methods, hybridization, or sequencing.Several variants of this technique exist and can be divided into two main classes: native and cross-linked RNA immunoprecipitation. The native RIP allows to reveal the identity of RNAs directly bound by the protein and their abundance in the immunoprecipitated sample, while cross-linked RIP leads to precisely map the direct and indirect binding site of the RBP of interest to the RNA molecule.In this chapter both the protocols applied to mammalian cells are described taking into account the caveats and considerations required for designing, performing, and interpreting the results of these experiments.
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Cajigas I, Leib DE, Cochrane J, Luo H, Swyter KR, Chen S, Clark BS, Thompson J, Yates JR, Kingston RE, Kohtz JD. Evf2 lncRNA/BRG1/DLX1 interactions reveal RNA-dependent inhibition of chromatin remodeling. Development 2015; 142:2641-52. [PMID: 26138476 DOI: 10.1242/dev.126318] [Citation(s) in RCA: 70] [Impact Index Per Article: 7.8] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/09/2015] [Accepted: 06/09/2015] [Indexed: 01/12/2023]
Abstract
Transcription-regulating long non-coding RNAs (lncRNAs) have the potential to control the site-specific expression of thousands of target genes. Previously, we showed that Evf2, the first described ultraconserved lncRNA, increases the association of transcriptional activators (DLX homeodomain proteins) with key DNA enhancers but represses gene expression. In this report, mass spectrometry shows that the Evf2-DLX1 ribonucleoprotein (RNP) contains the SWI/SNF-related chromatin remodelers Brahma-related gene 1 (BRG1, SMARCA4) and Brahma-associated factor (BAF170, SMARCC2) in the developing mouse forebrain. Evf2 RNA colocalizes with BRG1 in nuclear clouds and increases BRG1 association with key DNA regulatory enhancers in the developing forebrain. While BRG1 directly interacts with DLX1 and Evf2 through distinct binding sites, Evf2 directly inhibits BRG1 ATPase and chromatin remodeling activities. In vitro studies show that both RNA-BRG1 binding and RNA inhibition of BRG1 ATPase/remodeling activity are promiscuous, suggesting that context is a crucial factor in RNA-dependent chromatin remodeling inhibition. Together, these experiments support a model in which RNAs convert an active enhancer to a repressed enhancer by directly inhibiting chromatin remodeling activity, and address the apparent paradox of RNA-mediated stabilization of transcriptional activators at enhancers with a repressive outcome. The importance of BRG1/RNA and BRG1/homeodomain interactions in neurodevelopmental disorders is underscored by the finding that mutations in Coffin-Siris syndrome, a human intellectual disability disorder, localize to the BRG1 RNA-binding and DLX1-binding domains.
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Affiliation(s)
- Ivelisse Cajigas
- Developmental Biology and Department of Pediatrics, Stanley Manne Children's Research Institute and Feinberg School of Medicine, Northwestern University, Box 204, 2430 N. Halsted, Chicago, IL 60614, USA
| | - David E Leib
- Developmental Biology and Department of Pediatrics, Stanley Manne Children's Research Institute and Feinberg School of Medicine, Northwestern University, Box 204, 2430 N. Halsted, Chicago, IL 60614, USA
| | - Jesse Cochrane
- Department of Molecular Biology, Harvard University, Boston, MA 02114, USA
| | - Hao Luo
- Developmental Biology and Department of Pediatrics, Stanley Manne Children's Research Institute and Feinberg School of Medicine, Northwestern University, Box 204, 2430 N. Halsted, Chicago, IL 60614, USA
| | - Kelsey R Swyter
- Developmental Biology and Department of Pediatrics, Stanley Manne Children's Research Institute and Feinberg School of Medicine, Northwestern University, Box 204, 2430 N. Halsted, Chicago, IL 60614, USA
| | - Sean Chen
- Developmental Biology and Department of Pediatrics, Stanley Manne Children's Research Institute and Feinberg School of Medicine, Northwestern University, Box 204, 2430 N. Halsted, Chicago, IL 60614, USA
| | - Brian S Clark
- Developmental Biology and Department of Pediatrics, Stanley Manne Children's Research Institute and Feinberg School of Medicine, Northwestern University, Box 204, 2430 N. Halsted, Chicago, IL 60614, USA
| | | | - John R Yates
- The Scripps Research Institute, La Jolla, CA 92037, USA
| | - Robert E Kingston
- Department of Molecular Biology, Harvard University, Boston, MA 02114, USA
| | - Jhumku D Kohtz
- Developmental Biology and Department of Pediatrics, Stanley Manne Children's Research Institute and Feinberg School of Medicine, Northwestern University, Box 204, 2430 N. Halsted, Chicago, IL 60614, USA
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Tacheny A, Dieu M, Arnould T, Renard P. Mass spectrometry-based identification of proteins interacting with nucleic acids. J Proteomics 2013; 94:89-109. [PMID: 24060998 DOI: 10.1016/j.jprot.2013.09.011] [Citation(s) in RCA: 22] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/27/2013] [Revised: 08/19/2013] [Accepted: 09/13/2013] [Indexed: 01/02/2023]
Abstract
The identification of the regulatory proteins that control DNA transcription as well as RNA stability and translation represents a key step in the comprehension of gene expression regulation. Those proteins can be purified by DNA- or RNA-affinity chromatography, followed by identification by mass spectrometry. Although very simple in the concept, this represents a real technological challenge due to the low abundance of regulatory proteins compared to the highly abundant proteins binding to nucleic acids in a nonsequence-specific manner. Here we review the different strategies that have been set up to reach this purpose, discussing the key parameters that should be considered to increase the chances of success. Typically, two categories of biological questions can be distinguished: the identification of proteins that specifically interact with a precisely defined binding site, mostly addressed by quantitative mass spectrometry, and the identification in a non-comparative manner of the protein complexes recruited by a poorly characterized long regulatory region of nucleic acids. Finally, beside the numerous studies devoted to in vitro-assembled nucleic acid-protein complexes, the scarce data reported on proteomic analyses of in vivo-assembled complexes are described, with a special emphasis on the associated challenges.
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Affiliation(s)
- A Tacheny
- Laboratory of Biochemistry and Cell Biology (URBC), NAmur Research Institute for LIfe Sciences (NARILIS), University of Namur, 61 rue de Bruxelles, 5000 Namur, Belgium
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Jain SS, Anderson CM, DiRienzo F, Taylor IR, Jain K, Guha S, Hoque N. RNA binding and inhibition of primer extension by a Ru(III)/Pt(II) metal complex. Chem Commun (Camb) 2013; 49:5031-3. [PMID: 23615723 DOI: 10.1039/c3cc40699g] [Citation(s) in RCA: 17] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023]
Abstract
AH197, a trinuclear Ru(III)/Pt(II) metal complex, is strikingly more effective than the hallmark anticancer drug cisplatin and the Ru(III) clinical candidate NAMI-A in its binding to RNA and inhibition of primer DNA synthesis. Heteromultinuclear complexes could potentially serve as far better chemotherapeutics than mononuclear complexes.
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Affiliation(s)
- Swapan S Jain
- Department of Chemistry, Bard College, 30 Campus Road, Annandale-on-Hudson, NY 12504, USA.
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Lakshmi GG, Ghosh S, Jones GP, Parikh R, Rawlins BA, Vaughn JC. An RNA electrophoretic mobility shift and mutational analysis of rnp-4f 5'-UTR intron splicing regulatory proteins in Drosophila reveals a novel new role for a dADAR protein isoform. Gene 2012; 511:161-8. [PMID: 23026215 PMCID: PMC4123196 DOI: 10.1016/j.gene.2012.09.088] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/04/2012] [Revised: 08/09/2012] [Accepted: 09/12/2012] [Indexed: 01/09/2023]
Abstract
Alternative splicing greatly enhances the diversity of proteins encoded by eukaryotic genomes, and is also important in gene expression control. In contrast to the great depth of knowledge as to molecular mechanisms in the splicing pathway itself, relatively little is known about the regulatory events behind this process. The 5'-UTR and 3'-UTR in pre-mRNAs play a variety of roles in controlling eukaryotic gene expression, including translational modulation, and nearly 4000 of the roughly 14,000 protein coding genes in Drosophila contain introns of unknown functional significance in their 5'-UTR. Here we report the results of an RNA electrophoretic mobility shift analysis of Drosophila rnp-4f 5'-UTR intron 0 splicing regulatory proteins. The pre-mRNA potential regulatory element consists of an evolutionarily-conserved 177-nt stem-loop arising from pairing of intron 0 with part of adjacent exon 2. Incubation of in vitro transcribed probe with embryo protein extract is shown to result in two shifted RNA-protein bands, and protein extract from a dADAR null mutant fly line results in only one shifted band. A mutated stem-loop in which the conserved exon 2 primary sequence is changed but secondary structure maintained by introducing compensatory base changes results in diminished band shifts. To test the hypothesis that dADAR plays a role in intron splicing regulation in vivo, levels of unspliced rnp-4f mRNA in dADAR mutant were compared to wild-type via real-time qRT-PCR. The results show that during embryogenesis unspliced rnp-4f mRNA levels fall by up to 85% in the mutant, in support of the hypothesis. Taken together, these results demonstrate a novel role for dADAR protein in rnp-4f 5'-UTR alternative intron splicing regulation which is consistent with a previously proposed model.
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Affiliation(s)
- G. Girija Lakshmi
- Department of Zoology, Cell Molecular and Structural Biology Program, Miami University, Oxford, OH 45056, United States
| | - Sushmita Ghosh
- Department of Zoology, Cell Molecular and Structural Biology Program, Miami University, Oxford, OH 45056, United States
| | - Gabriel P. Jones
- Department of Zoology, Cell Molecular and Structural Biology Program, Miami University, Oxford, OH 45056, United States
| | - Roshni Parikh
- Department of Zoology, Cell Molecular and Structural Biology Program, Miami University, Oxford, OH 45056, United States
| | - Bridgette A. Rawlins
- Department of Zoology, Cell Molecular and Structural Biology Program, Miami University, Oxford, OH 45056, United States
| | - Jack C. Vaughn
- Department of Zoology, Cell Molecular and Structural Biology Program, Miami University, Oxford, OH 45056, United States
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Janga SC. From specific to global analysis of posttranscriptional regulation in eukaryotes: posttranscriptional regulatory networks. Brief Funct Genomics 2012; 11:505-21. [PMID: 23124862 DOI: 10.1093/bfgp/els046] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Regulation of gene expression occurs at several levels in eukaryotic organisms and is a highly controlled process. Although RNAs have been traditionally viewed as passive molecules in the pathway from transcription to translation, there is mounting evidence that their metabolism is controlled by a class of proteins called RNA-binding proteins (RBPs), as well as a number of small RNAs. In this review, I provide an overview of the recent developments in our understanding of the repertoire of RBPs across diverse model systems, and discuss the computational and experimental approaches currently available for the construction of posttranscriptional networks governed by them. I also present an overview of the different roles played by RBPs in the cellular context, based on their cis-regulatory modules identified in the literature and discuss how their interplay can result in the dynamic, spatial and tissue-specific expression maps of RNAs. I finally present the concept of posttranscriptional network of RBPs and their cognate RNA targets and discuss their cross-talk with other important posttranscriptional regulatory molecules such as microRNAs s, resulting in diverse functional network motifs. I argue that with rapid developments in the genome-wide elucidation of posttranscriptional networks it would not only be possible to gain a deeper understanding of regulation at a level that has been under-appreciated in the past, but would also allow us to use the newly developed high-throughput approaches to interrogate the prevalence of these phenomena in different states, and thereby study their relevance to physiology and disease across organisms.
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Affiliation(s)
- Sarath Chandra Janga
- School of Informatics, Indiana University Purdue University, Indianapolis, Indiana, Center for Computational Biology and Bioinformatics, Indiana University School of Medicine, 719 Indiana Ave Ste 319, Walker Plaza Building, IN 46202, USA.
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Apoptosis-like programmed cell death induces antisense ribosomal RNA (rRNA) fragmentation and rRNA degradation in Leishmania. Cell Death Differ 2012; 19:1972-82. [PMID: 22767185 PMCID: PMC3504711 DOI: 10.1038/cdd.2012.85] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Few natural antisense (as) RNAs have been reported as yet in the unicellular protozoan Leishmania. Here, we describe that Leishmania produces natural asRNAs complementary to all ribosomal RNA (rRNA) species. Interestingly, we show that drug-induced apoptosis-like programmed cell death triggers fragmentation of asRNA complementary to the large subunit gamma (LSU-γ) rRNA, one of the six 28S rRNA processed fragments in Leishmania. Heat and oxidative stress also induce fragmentation of asrRNA, but to a lesser extent. Extensive asrRNA cleavage correlates with rRNA breakdown and translation inhibition. Indeed, overexpression of asLSU-γ rRNA accelerates rRNA degradation upon induction of apoptosis. In addition, we provide mechanistic insight into the regulation of apoptosis-induced asrRNA fragmentation by a 67 kDa ATP-dependent RNA helicase of the DEAD-box subfamily. This helicase binds both sense (s)LSU-γ and asLSU-γ rRNAs, and appears to have a key role in protecting rRNA from degradation by preventing asrRNA cleavage and thus cell death. Remarkably, the asrRNA fragmentation process operates not only in trypanosomatid protozoa but also in mammals. Our findings uncover a novel mechanism of regulation involving asrRNA fragmentation and rRNA breakdown, that is triggered by apoptosis and conditions of reduced translation under stress, and seems to be evolutionary conserved.
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Kouba T, Rutkai E, Karásková M, Valášek LS. The eIF3c/NIP1 PCI domain interacts with RNA and RACK1/ASC1 and promotes assembly of translation preinitiation complexes. Nucleic Acids Res 2011; 40:2683-99. [PMID: 22123745 PMCID: PMC3315329 DOI: 10.1093/nar/gkr1083] [Citation(s) in RCA: 56] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Several subunits of the multifunctional eukaryotic translation initiation factor 3 (eIF3) contain well-defined domains. Among them is the conserved bipartite PCI domain, typically serving as the principal scaffold for multisubunit 26S proteasome lid, CSN and eIF3 complexes, which constitutes most of the C-terminal region of the c/NIP1 subunit. Interestingly, the c/NIP1-PCI domain is exceptional in that its deletion, despite being lethal, does not affect eIF3 integrity. Here, we show that a short C-terminal truncation and two clustered mutations directly disturbing the PCI domain produce lethal or slow growth phenotypes and significantly reduce amounts of 40S-bound eIF3 and eIF5 in vivo. The extreme C-terminus directly interacts with blades 1–3 of the small ribosomal protein RACK1/ASC1, which is a part of the 40S head, and, consistently, deletion of the ASC1 coding region likewise affects eIF3 association with ribosomes. The PCI domain per se shows strong but unspecific binding to RNA, for the first time implicating this typical protein–protein binding domain in mediating protein–RNA interactions also. Importantly, as our clustered mutations severely reduce RNA binding, we conclude that the c/NIP1 C-terminal region forms an important intermolecular bridge between eIF3 and the 40S head region by contacting RACK1/ASC1 and most probably 18S rRNA.
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Affiliation(s)
- Tomáš Kouba
- Laboratory of Regulation of Gene Expression, Institute of Microbiology AVCR, v.v.i., Prague, the Czech Republic
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Epis MR, Barker A, Giles KM, Beveridge DJ, Leedman PJ. The RNA-binding protein HuR opposes the repression of ERBB-2 gene expression by microRNA miR-331-3p in prostate cancer cells. J Biol Chem 2011; 286:41442-41454. [PMID: 21971048 DOI: 10.1074/jbc.m111.301481] [Citation(s) in RCA: 78] [Impact Index Per Article: 6.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/16/2023] Open
Abstract
ERBB-2 overexpression is associated with the development and progression of cancer and mediates its resistance to therapy. It has been suggested that post-transcriptional mechanisms control the overexpression of ERBB-2 in prostate cancer (PCa). We recently demonstrated that the 3'-untranslated region (3'-UTR) of ERBB-2 mRNA contains two specific target sites for binding of the microRNA miR-331-3p and that miR-331-3p represses ERBB-2 expression and signaling in PCa cells. Here we investigate a U-rich element situated in close proximity to the distal miR-331-3p target site in the ERBB-2 3'-UTR. Specific binding of HuR to this U-rich element promotes ERBB-2 expression in PCa cells. We show that HuR antagonizes the repressive action of miR-331-3p on its distal ERBB-2 3'-UTR target site. These results support a model in which the interplay between RNA-binding proteins and microRNAs controls the post-transcriptional regulation of gene expression and suggest that both HuR and miR-331-3p participate in the overexpression of ERBB-2 observed in some PCas.
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Affiliation(s)
- Michael R Epis
- Laboratory for Cancer Medicine, Western Australian Institute for Medical Research and University of Western Australia Centre for Medical Research, Royal Perth Hospital, Perth, Western Australia 6000, Australia
| | - Andrew Barker
- Laboratory for Cancer Medicine, Western Australian Institute for Medical Research and University of Western Australia Centre for Medical Research, Royal Perth Hospital, Perth, Western Australia 6000, Australia
| | - Keith M Giles
- Laboratory for Cancer Medicine, Western Australian Institute for Medical Research and University of Western Australia Centre for Medical Research, Royal Perth Hospital, Perth, Western Australia 6000, Australia
| | - Dianne J Beveridge
- Laboratory for Cancer Medicine, Western Australian Institute for Medical Research and University of Western Australia Centre for Medical Research, Royal Perth Hospital, Perth, Western Australia 6000, Australia
| | - Peter J Leedman
- Laboratory for Cancer Medicine, Western Australian Institute for Medical Research and University of Western Australia Centre for Medical Research, Royal Perth Hospital, Perth, Western Australia 6000, Australia; School of Medicine and Pharmacology, University of Western Australia, Nedlands, Western Australia 6008, Australia.
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10
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Zheng Y, Miskimins WK. Far upstream element binding protein 1 activates translation of p27Kip1 mRNA through its internal ribosomal entry site. Int J Biochem Cell Biol 2011; 43:1641-8. [PMID: 21855647 DOI: 10.1016/j.biocel.2011.08.001] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2011] [Revised: 07/27/2011] [Accepted: 08/01/2011] [Indexed: 02/01/2023]
Abstract
The cyclin dependent kinase inhibitor p27 plays an important role in controlling the eukaryotic cell cycle by regulating progression through G1 and entry into S phase. It is often elevated during differentiation and under conditions of cellular stress. In contrast, it is commonly downregulated in cancer cells and its levels are generally inversely correlated with favorable prognosis. The cellular levels of p27 are regulated, in part, by translational control mechanisms. The 5'-untranslated region (5'-UTR) of the p27 mRNA harbors an internal ribosome entry site (IRES) which may facilitate synthesis of p27 in certain conditions. In this study, Far Upstream Element (FUSE) Binding Protein 1 (FBP1) was shown to directly bind to the human p27 5'-UTR and to promote IRES activity. An eight-nucleotide element downstream of a U-rich region within the 5'-UTR was important for FBP1 binding and p27 IRES activity. Overexpression of FBP1 enhanced endogenous p27 levels and stimulated translation initiation. In contrast, repression of FBP1 by siRNA transfection downregulated endogenous p27 protein levels. Using rabbit reticulocyte lysates, FBP1 stimulated p27 mRNA translation in vitro. The central domain of FBP1, containing four K homology motifs, was required for p27 5'-UTR RNA binding and the N terminal domain was important for translational activation. These findings indicate that FBP1 is a novel activator of p27 translation upon binding to the 5'-UTR.
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Affiliation(s)
- Yuhuan Zheng
- Cancer Biology Research Center, Sanford Research/USD, Sioux Falls, SD 57001, USA.
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Construction, Structure and Dynamics of Post-Transcriptional Regulatory Network Directed by RNA-Binding Proteins. ADVANCES IN EXPERIMENTAL MEDICINE AND BIOLOGY 2011; 722:103-17. [DOI: 10.1007/978-1-4614-0332-6_7] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
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12
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Gustin KM, Guan BJ, Dziduszko A, Brian DA. Bovine coronavirus nonstructural protein 1 (p28) is an RNA binding protein that binds terminal genomic cis-replication elements. J Virol 2009; 83:6087-97. [PMID: 19357173 PMCID: PMC2687364 DOI: 10.1128/jvi.00160-09] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/23/2009] [Accepted: 03/29/2009] [Indexed: 01/08/2023] Open
Abstract
Nonstructural protein 1 (nsp1), a 28-kDa protein in the bovine coronavirus (BCoV) and closely related mouse hepatitis coronavirus, is the first protein cleaved from the open reading frame 1 (ORF 1) polyprotein product of genome translation. Recently, a 30-nucleotide (nt) cis-replication stem-loop VI (SLVI) has been mapped at nt 101 to 130 within a 288-nt 5'-terminal segment of the 738-nt nsp1 cistron in a BCoV defective interfering (DI) RNA. Since a similar nsp1 coding region appears in all characterized groups 1 and 2 coronavirus DI RNAs and must be translated in cis for BCoV DI RNA replication, we hypothesized that nsp1 might regulate ORF 1 expression by binding this intra-nsp1 cistronic element. Here, we (i) establish by mutation analysis that the 72-nt intracistronic SLV immediately upstream of SLVI is also a DI RNA cis-replication signal, (ii) show by gel shift and UV-cross-linking analyses that cellular proteins of approximately 60 and 100 kDa, but not viral proteins, bind SLV and SLVI, (SLV-VI) and (iii) demonstrate by gel shift analysis that nsp1 purified from Escherichia coli does not bind SLV-VI but does bind three 5' untranslated region (UTR)- and one 3' UTR-located cis-replication SLs. Notably, nsp1 specifically binds SLIII and its flanking sequences in the 5' UTR with approximately 2.5 muM affinity. Additionally, under conditions enabling expression of nsp1 from DI RNA-encoded subgenomic mRNA, DI RNA levels were greatly reduced, but there was only a slight transient reduction in viral RNA levels. These results together indicate that nsp1 is an RNA-binding protein that may function to regulate viral genome translation or replication but not by binding SLV-VI within its own coding region.
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Affiliation(s)
- Kortney M Gustin
- Department of Microbiology, University of Tennessee, Knoxville, Tennessee 37996-0845, USA
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Gu L, Zhu N, Zhang H, Durden DL, Feng Y, Zhou M. Regulation of XIAP translation and induction by MDM2 following irradiation. Cancer Cell 2009; 15:363-75. [PMID: 19411066 PMCID: PMC2696306 DOI: 10.1016/j.ccr.2009.03.002] [Citation(s) in RCA: 133] [Impact Index Per Article: 8.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/22/2008] [Revised: 12/23/2008] [Accepted: 03/02/2009] [Indexed: 02/02/2023]
Abstract
Increases in protein levels of XIAP in cancer cells have been associated with resistance to apoptosis induced by cellular stress. Herein we demonstrate that the upregulation of XIAP protein levels is regulated by MDM2 at the translational level. MDM2 was found to physically interact with the IRES of the XIAP 5'-UTR, and to positively regulate XIAP IRES activity. This XIAP IRES-dependent translation was significantly increased in MDM2-transfected cells where MDM2 accumulated in the cytoplasm. Cellular stress and DNA damage triggered by irradiation induced the dephosphorylation and cytoplasmic localization of MDM2, which also led to an increase in IRES-dependent XIAP translation. Upregulation of XIAP in MDM2-overexpressing cancer cells in response to irradiation resulted in resistance of these cells to radiation-induced apoptosis.
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Affiliation(s)
- Lubing Gu
- Department of Pediatrics, Aflac Cancer Center and Blood Disorders Service, Emory University School of Medicine, Atlanta, GA 30322
| | - Ningxi Zhu
- Department of Pediatrics, Aflac Cancer Center and Blood Disorders Service, Emory University School of Medicine, Atlanta, GA 30322
| | - Hongying Zhang
- Department of Pediatrics, Aflac Cancer Center and Blood Disorders Service, Emory University School of Medicine, Atlanta, GA 30322
| | - Donald L. Durden
- Department of Pediatrics, Aflac Cancer Center and Blood Disorders Service, Emory University School of Medicine, Atlanta, GA 30322
| | - Yue Feng
- Department of Pharmacology, Aflac Cancer Center and Blood Disorders Service, Emory University School of Medicine, Atlanta, GA 30322
| | - Muxiang Zhou
- Department of Pediatrics, Aflac Cancer Center and Blood Disorders Service, Emory University School of Medicine, Atlanta, GA 30322
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Villaescusa JC, Buratti C, Penkov D, Mathiasen L, Planagumà J, Ferretti E, Blasi F. Cytoplasmic Prep1 interacts with 4EHP inhibiting Hoxb4 translation. PLoS One 2009; 4:e5213. [PMID: 19365557 PMCID: PMC2664923 DOI: 10.1371/journal.pone.0005213] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/12/2009] [Accepted: 03/19/2009] [Indexed: 11/18/2022] Open
Abstract
Background Homeobox genes are essential for embryonic patterning and cell fate determination. They are regulated mostly at the transcriptional level. In particular, Prep1 regulates Hox transcription in association with Pbx proteins. Despite its nuclear role as a transcription factor, Prep1 is located in the cytosol of mouse oocytes from primary to antral follicles. The homeodomain factor Bicoid (Bcd) has been shown to interact with 4EHP (eukaryotic translation initiation factor 4E homolog protein) to repress translation of Caudal mRNA and to drive Drosophila embryo development. Interestingly, Prep1 contains a putative binding motif for 4EHP, which may reflect a novel unknown function. Methodology/Principal Findings In this paper we show by confocal microscopy and deconvolution analysis that Prep1 and 4EHP co-localize in the cytosol of growing mouse oocytes, demonstrating their interaction by co-immunoprecipitation and pull-down experiments. A functional 4EHP-binding motif present in Prep1 has been also identified by mutagenesis analysis. Moreover, Prep1 inhibits (>95%) the in vitro translation of a luciferase reporter mRNA fused to the Hoxb4 3′UTR, in the presence of 4EHP. RNA electrophoretic mobility shift assay was used to demonstrate that Prep1 binds the Hoxb4 3′UTR. Furthermore, conventional histology and immunohistochemistry has shown a dramatic oocyte growth failure in hypomorphic mouse Prep1i/i females, accompanied by an increased production of Hoxb4. Finally, Hoxb4 overexpression in mouse zygotes showed a slow in vitro development effect. Conclusions Prep1 has a novel cytoplasmic, 4EHP-dependent, function in the regulation of translation. Mechanistically, the Prep1-4EHP interaction might bridge the 3′UTR of Hoxb4 mRNA to the 5′ cap structure. This is the first demonstration that a mammalian homeodomain transcription factor regulates translation, and that this function can be possibly essential for the development of female germ cells and involved in mammalian zygote development.
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Affiliation(s)
| | | | - Dmitry Penkov
- IFOM, FIRC Institute of Molecular Oncology, Milano, Italy
| | - Lisa Mathiasen
- IFOM, FIRC Institute of Molecular Oncology, Milano, Italy
| | - Jesús Planagumà
- Department of Biomedicine, University of Bergen, Bergen, Norway
| | - Elisabetta Ferretti
- Laboratory of Molecular Genetics, San Raffaele Scientific Institute and Università Vita Salute San Raffaele, Milano, Italy
| | - Francesco Blasi
- IFOM, FIRC Institute of Molecular Oncology, Milano, Italy
- Laboratory of Molecular Genetics, San Raffaele Scientific Institute and Università Vita Salute San Raffaele, Milano, Italy
- * E-mail:
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15
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Ing NH, Massuto DA, Jaeger LA. Estradiol up-regulates AUF1p45 binding to stabilizing regions within the 3'-untranslated region of estrogen receptor alpha mRNA. J Biol Chem 2007; 283:1764-1772. [PMID: 18029355 DOI: 10.1074/jbc.m704745200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Estradiol up-regulates expression of the estrogen receptor alpha gene in the uterus by stabilizing estrogen receptor alpha mRNA. Previously, we defined two discrete minimal estradiol-modulated stability sequences (MEMSS) within the extensive 3'-untranslated region of estrogen receptor alpha mRNA with an in vitro stability assay using cytosolic extracts from sheep uterus. We report here that excess MEMSS RNA inhibited the enhanced stability of estrogen receptor alpha mRNA in extracts from estradiol-treated ewes compared with those from control ewes. Several estradiol-induced MEMSS-binding proteins were characterized by UV cross-linking in uterine extracts from ewes in a time course study (0, 8, 16, and 24 h after estradiol injection). The pattern of binding proteins changed at 16 h post-injection, concurrent with enhanced estrogen receptor alpha mRNA stability and the highest rate of accumulation of estrogen receptor alpha mRNA. The predominant MEMSS-binding protein induced by estradiol treatment was identified as AUF1 (A + U-rich RNA-binding factor 1) protein isoform p45 (a product of the heterogeneous nuclear ribonucleoprotein D gene). Immunoblot analysis indicated that only two of four AUF1 protein isoforms were present in the uterine cytosolic extracts and that estradiol treatment strongly increased the ratio of AUF1 isoforms p45 to p37. Nonphosphorylated recombinant AUF1p45 protected estrogen receptor alpha mRNA in vitro in a dose-dependent manner. These studies describe estrogenic induction of AUF1p45 binding to the estrogen receptor alpha mRNA as a molecular mechanism for post-transcriptional up-regulation of gene expression.
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Affiliation(s)
- Nancy H Ing
- Department of Animal Science, Texas A & M University, College Station, Texas 77843; Veterinary Integrative Biosciences, Texas A & M University, College Station, Texas 77843.
| | - Dana A Massuto
- Veterinary Integrative Biosciences, Texas A & M University, College Station, Texas 77843
| | - Laurie A Jaeger
- Veterinary Integrative Biosciences, Texas A & M University, College Station, Texas 77843
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16
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Butcher NJ, Broadhurst GM, Minchin RF. Polyamine-dependent Regulation of Spermidine-Spermine N1-Acetyltransferase mRNA Translation. J Biol Chem 2007; 282:28530-28539. [PMID: 17690107 DOI: 10.1074/jbc.m701265200] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Spermidine-spermine N(1)-acetyltransferase (SSAT) is induced in response to an elevation in intracellular polyamine pools. The increased enzyme activity is the result of an increase in gene transcription, mRNA translation, and protein stability. Induction of SSAT by polyamine analogues can lead to intracellular polyamine depletion and apoptosis. The mechanism by which polyamines alter the translational efficiency of SSAT mRNA is not well understood. In this study, we investigated the regulation of SSAT translation by the polyamine analogue N(1),N(11)-diethylnorspermine (DENSPM). DENSPM induced expression of both FLAG-tagged SSAT and SSAT fused to Renilla luciferase in a time- and concentration-dependent manner. This effect was not inhibited by actinomycin D indicating that changes in gene transcription did not explain the enhanced expression in the presence of DENSPM. Furthermore, because FLAG-SSAT did not contain the 5'- or 3'-untranslated regions of SSAT, translational regulation involved the coding sequence only. By contrast, cycloheximide completely inhibited induction by DENSPM, indicating a requirement for new protein synthesis. Deletion constructs identified two regions of the SSAT protein-coding RNA sequence that conferred polyamine responsiveness. Using these regions as probes in RNA electrophoretic mobility shift assays, we observed specific binding of a cytoplasmic protein. In addition, we found that the interaction between the RNA probes and the binding protein could be inhibited by DENSPM in a concentration-dependent manner. These results suggest that polyamines regulate SSAT mRNA translational efficiency by inhibiting a repressor protein from binding to regions of the coding sequence of the SSAT transcript.
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Affiliation(s)
- Neville J Butcher
- Department of Physiology and Pharmacology, School of Biomedical Sciences, University of Queensland, St. Lucia, Queensland 4072, Australia.
| | - Gysell M Broadhurst
- Department of Physiology and Pharmacology, School of Biomedical Sciences, University of Queensland, St. Lucia, Queensland 4072, Australia
| | - Rodney F Minchin
- Department of Physiology and Pharmacology, School of Biomedical Sciences, University of Queensland, St. Lucia, Queensland 4072, Australia
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17
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Chang JS, Santhanam R, Trotta R, Neviani P, Eiring AM, Briercheck E, Ronchetti M, Roy DC, Calabretta B, Caligiuri MA, Perrotti D. High levels of the BCR/ABL oncoprotein are required for the MAPK-hnRNP-E2 dependent suppression of C/EBPalpha-driven myeloid differentiation. Blood 2007; 110:994-1003. [PMID: 17475908 PMCID: PMC1924762 DOI: 10.1182/blood-2007-03-078303] [Citation(s) in RCA: 80] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/05/2007] [Accepted: 04/24/2007] [Indexed: 12/21/2022] Open
Abstract
The inability of myeloid chronic myelogenous leukemia blast crisis (CML-BC) progenitors to undergo neutrophil differentiation depends on suppression of C/EBPalpha expression through the translation inhibitory activity of the RNA-binding protein hnRNP-E2. Here we show that "oncogene dosage" is a determinant factor for suppression of differentiation in CML-BC. In fact, high levels of p210-BCR/ABL are required for enhanced hnRNP-E2 expression, which depends on phosphorylation of hnRNP-E2 serines 173, 189, and 272 and threonine 213 by the BCR/ABL-activated MAPK(ERK1/2). Serine/threonine to alanine substitution abolishes hnRNP-E2 phosphorylation and markedly decreases its stability in BCR/ABL-expressing myeloid precursors. Similarly, pharmacologic inhibition of MAPK(ERK1/2) activity decreases hnRNP-E2 binding to the 5'UTR of C/EBPalpha mRNA by impairing hnRNP-E2 phosphorylation and stability. This, in turn, restores in vitro and/or in vivo C/EBPalpha expression and G-CSF-driven neutrophilic maturation of differentiation-arrested BCR/ABL(+) cell lines, primary CML-BC(CD34+) patient cells and lineage-negative mouse bone marrow cells expressing high levels of p210-BCR/ABL. Thus, increased BCR/ABL oncogenic tyrosine kinase activity is essential for suppression of myeloid differentiation of CML-BC progenitors as it is required for sustained activation of the MAPK(ERK1/2)-hnRNP-E2-C/EBPalpha differentiation-inhibitory pathway. Furthermore, these findings suggest the inclusion of clinically relevant MAPK inhibitors in the therapy of CML-BC.
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MESH Headings
- Animals
- Blast Crisis/drug therapy
- Blast Crisis/metabolism
- Blast Crisis/pathology
- CCAAT-Enhancer-Binding Protein-alpha/biosynthesis
- Cell Differentiation/drug effects
- Enzyme Inhibitors/pharmacology
- Enzyme Inhibitors/therapeutic use
- Fusion Proteins, bcr-abl/biosynthesis
- Gene Expression Regulation, Leukemic/drug effects
- Heterogeneous-Nuclear Ribonucleoproteins/metabolism
- Humans
- K562 Cells
- Leukemia, Myelogenous, Chronic, BCR-ABL Positive/drug therapy
- Leukemia, Myelogenous, Chronic, BCR-ABL Positive/metabolism
- Leukemia, Myelogenous, Chronic, BCR-ABL Positive/pathology
- Mice
- Mitogen-Activated Protein Kinase 1/antagonists & inhibitors
- Mitogen-Activated Protein Kinase 1/metabolism
- Mitogen-Activated Protein Kinase 3/antagonists & inhibitors
- Mitogen-Activated Protein Kinase 3/metabolism
- Myeloid Progenitor Cells/metabolism
- Myeloid Progenitor Cells/pathology
- Neutrophils/metabolism
- Neutrophils/pathology
- Phosphorylation/drug effects
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Affiliation(s)
- Ji Suk Chang
- Human Cancer Genetics Program, Department of Molecular Virology, Immunology and Medical Genetics, Ohio State University, Columbus, OH 23240, USA
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18
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Emerald BS, Chen Y, Zhu T, Zhu Z, Lee KO, Gluckman PD, Lobie PE. AlphaCP1 mediates stabilization of hTERT mRNA by autocrine human growth hormone. J Biol Chem 2006; 282:680-90. [PMID: 17085453 DOI: 10.1074/jbc.m600224200] [Citation(s) in RCA: 25] [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
We herein demonstrate that autocrine human growth hormone production in human mammary carcinoma cells results in increased telomerase activity as a result of specific up-regulation of telomerase catalytic subunit (human telomerase reverse transcriptase (hTERT)) mRNA and protein. This increase in hTERT gene expression is not due to increased transcriptional activation of the hTERT promoter but is the result of increased stability of hTERT mRNA exerted by CU-rich cis-regulatory sequences present in the 3'-untranslated region of TERT mRNA. Autocrine human growth hormone up-regulates two poly(C)-binding proteins, alphaCP1 and alphaCP2, which bind to these cis-regulatory elements and stabilize hTERT mRNA. We have therefore demonstrated that post-transcriptional modulation of the level of hTERT mRNA is one mechanism for regulation of cellular telomerase activity.
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Affiliation(s)
- B Starling Emerald
- Liggins Institute and the National Research Centre for Growth and Development, University of Auckland, Auckland, New Zealand
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19
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Hatchell EC, Colley SM, Beveridge DJ, Epis MR, Stuart LM, Giles KM, Redfern AD, Miles LEC, Barker A, MacDonald LM, Arthur PG, Lui JCK, Golding JL, McCulloch RK, Metcalf CB, Wilce JA, Wilce MCJ, Lanz RB, O'Malley BW, Leedman PJ. SLIRP, a small SRA binding protein, is a nuclear receptor corepressor. Mol Cell 2006; 22:657-68. [PMID: 16762838 DOI: 10.1016/j.molcel.2006.05.024] [Citation(s) in RCA: 99] [Impact Index Per Article: 5.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/23/2005] [Revised: 03/21/2006] [Accepted: 05/19/2006] [Indexed: 10/24/2022]
Abstract
Steroid receptor RNA activator (SRA), the only known RNA coactivator, augments transactivation by nuclear receptors (NRs). We identified SLIRP (SRA stem-loop interacting RNA binding protein) binding to a functional substructure of SRA, STR7. SLIRP is expressed in normal and tumor tissues, contains an RNA recognition motif (RRM), represses NR transactivation in a SRA- and RRM-dependent manner, augments the effect of Tamoxifen, and modulates association of SRC-1 with SRA. SHARP, a RRM-containing corepressor, also binds STR7, augmenting repression with SLIRP. SLIRP colocalizes with SKIP (Chr14q24.3), another NR coregulator, and reduces SKIP-potentiated NR signaling. SLIRP is recruited to endogenous promoters (pS2 and metallothionein), the latter in a SRA-dependent manner, while NCoR promoter recruitment is dependent on SLIRP. The majority of the endogenous SLIRP resides in the mitochondria. Our data demonstrate that SLIRP modulates NR transactivation, suggest it may regulate mitochondrial function, and provide mechanistic insight into interactions between SRA, SLIRP, SRC-1, and NCoR.
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Affiliation(s)
- Esme C Hatchell
- Laboratory for Cancer Medicine, The University of Western Australia Centre for Medical Research, Western Australian Institute for Medical Research, Western Australia
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20
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Zhang H, Barnoski BL, Sol-Church K, Stabley DL, Martin-Deleon PA. Murine Spam1 mRNA: involvement of AU-rich elements in the 3'UTR and antisense RNA in its tight post-transcriptional regulation in spermatids. Mol Reprod Dev 2006; 73:247-55. [PMID: 16250006 DOI: 10.1002/mrd.20400] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/26/2022]
Abstract
Sperm adhesion molecule1 (SPAM1), the best characterized hyaluronidase gene, is abundantly expressed in the testis. We attempted to overexpress mouse Spam1 via transgenesis using either the endogenous promoter in a BAC or a heterologous Protamine1 promoter for a Spam1 cDNA transgene. Although transgene-copy numbers ranged from 2 to 15 and transgenic transcripts were expressed, there was a general failure of overexpression of the RNA and protein in the testis of all seven founders. Also, three transgenic lines showed a modest downregulation or co-suppression of the RNA for Spam1 and Hyal5, present on the BAC. We provide evidence for the potential involvement of two co-ordinating post-transcriptional regulatory processes in the failure of overexpression: abundant endogenous antisense RNA and adenosine-uridine (AU)-rich element-mediated regulation of RNA turnover. We demonstrate that AU-rich elements (AREs) in the 3'UTR of mRNAs, well-known to interact with trans-acting proteins to target the RNA for (in)stability, are present in Spam1 RNA and specifically bind to six testicular cytoplasmic proteins. These AU-binding proteins (AUBPs) were virtually absent from the kidney where transcripts are rare, and were shown to interact with the cytoskeleton, which modulates mRNA turnover. In addition to a role in the RNAi pathway, antisense RNA can also modulate ARE-mediated regulation of mRNA by hybridizing to the AREs and specifically silencing their function. This potentially links the two processes in the regulation of Spam1 expression. We hypothesize that testicular Spam1 RNA is regulated post-transcriptionally by cis-acting ARE(s) in the 3'UTR which recognize AUBPs and which are modulated by antisense transcripts.
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Affiliation(s)
- Hong Zhang
- Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA
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21
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Harris D, Zhang Z, Chaubey B, Pandey VN. Identification of cellular factors associated with the 3'-nontranslated region of the hepatitis C virus genome. Mol Cell Proteomics 2006; 5:1006-18. [PMID: 16500930 DOI: 10.1074/mcp.m500429-mcp200] [Citation(s) in RCA: 75] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
Chronic infection by hepatitis C virus (HCV) is the leading cause of severe hepatitis that often develops into liver cirrhosis and hepatocellular carcinoma. The molecular mechanisms underlying HCV replication and pathogenesis are poorly understood. Similarly, the role(s) of host factors in the replication of HCV remains largely undefined. Based on our knowledge of other RNA viruses, it is likely that a number of cellular factors may be involved in facilitating HCV replication. It has been demonstrated that elements within the 3'-nontranslated region (3'-NTR) of the (+) strand HCV genome are essential for initiation of (-) strand synthesis. The RNA signals within the highly conserved 3'-NTR may be the site for recruiting cellular factors that mediate virus replication/pathogenesis. However, the identities of putative cellular factors interacting with these RNA signals remain unknown. In this report, we demonstrate that an RNA affinity capture system developed in our laboratory used in conjunction with LC/MS/MS allowed us to positively identify more than 70 cellular proteins that interact with the 3'-NTR (+) of HCV. Binding of these cellular proteins was not competed out by a 10-fold excess of nonspecific competitor RNA. With few exceptions, all of the identified cellular proteins are RNA-binding proteins whose reported cellular functions provide unique insights into host cell-virus interactions and possible mechanisms influencing HCV replication and HCV-associated pathogenesis. Small interfering RNA-mediated silencing of selected 3'-NTR-binding proteins in an HCV replicon cell line reduced replicon RNA to undetectable levels, suggesting important roles for these cellular factors in HCV replication.
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Affiliation(s)
- Dylan Harris
- Department of Biochemistry and Molecular Biology and Centre for the Study of Emerging and Re-emerging Pathogens, University of Medicine and Dentistry of New Jersey--New Jersey Medical School, Newark, New Jersey 07103, USA
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22
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Patel GP, Ma S, Bag J. The autoregulatory translational control element of poly(A)-binding protein mRNA forms a heteromeric ribonucleoprotein complex. Nucleic Acids Res 2005; 33:7074-89. [PMID: 16356927 PMCID: PMC1316114 DOI: 10.1093/nar/gki1014] [Citation(s) in RCA: 65] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/14/2022] Open
Abstract
Repression of poly(A)-binding protein (PABP) mRNA translation involves the binding of PABP to the adenine-rich autoregulatory sequence (ARS) in the 5′-untranslated region of its own mRNA. In this report, we show that the ARS forms a complex in vitro with PABP, and two additional polypeptides of 63 and 105 kDa. The 63 and 105 kDa polypeptides were identified, as IMP1, an ortholog of chicken zip-code binding polypeptide, and UNR, a PABP binding polypeptide, respectively, by mass spectrometry of the ARS RNA affinity purified samples. Using a modified ribonucleoprotein (RNP) immunoprecipitation procedure we further show that indeed, both IMP1 and UNR bind to the ARS containing reporter RNA in vivo. Although both IMP1 and UNR could bind independently to the ARS RNA in vitro, their RNA-binding ability was stimulated by PABP. Mutational analyses of the ARS show that the presence of four of the six oligo(A) regions of the ARS was sufficient to repress translation and the length of the conserved pyrimidine spacers between the oligo(A) sequences was important for ARS function. The ability of mutant ARS RNAs to form the PABP, IMP1 and UNR containing RNP complex correlates well with the translational repressor activity of the ARS. There is also a direct relationship between the length of the poly(A) RNAs and their ability to form a trimeric complex with PABP, and to repress mRNA translation. UV crosslinking studies suggest that the ARS is less efficient than a poly(A) RNA of similar length, to bind to PABP. We show here that the ARS cannot efficiently form a trimeric complex with PABP; therefore, additional interactions with IMP1 and UNR to form a heteromeric RNP complex may be required for maximal repression of PABP mRNA translation under physiological conditions.
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Affiliation(s)
| | | | - Jnanankur Bag
- To whom correspondence should be addressed. Tel: +1 519 824 4120 (Ext. 53390); Fax: +1 519 837 2075;
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23
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Ma S, Musa T, Bag J. Reduced stability of mitogen-activated protein kinase kinase-2 mRNA and phosphorylation of poly(A)-binding protein (PABP) in cells overexpressing PABP. J Biol Chem 2005; 281:3145-56. [PMID: 16332685 DOI: 10.1074/jbc.m508937200] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/24/2022] Open
Abstract
The poly(A)-binding protein (PABP) is an important regulator of mRNA translation and stability. The cellular level of PABP is controlled by regulating its mRNA translation by a feedback mechanism. The important aspect of this mechanism is that PABP binds to an adenosine-rich cis-element at the 5'-untranslated region of its own mRNA and inhibits its translation. To assess the importance of controlling the PABP level, we studied the effect of PABP overexpression on the transcription profile using the microarray technique. In PABP-overexpressing cells, 19 mRNAs showed a reduction in cellular levels due to reduced mRNA stability, and one showed an increase due to increased mRNA stability. Among these mRNAs, the MKK-2 mRNA encodes the protein kinase activator of ERK1/2 kinase, which is involved in the phosphorylation of eukaryotic initiation factor (eIF) 4E. As a result, mRNA translation may be regulated by the cellular level of MKK-2. In this study, we show that the abundance of the MKK-2 polypeptide is reduced in PABP-overexpressing cells. In these cells, the levels of phosphorylated PABP, eIF4E, and ERK2 are also reduced. Treatment of HeLa cells with the MKK-2 inhibitor U0126 reduced PABP phosphorylation, suggesting that the phosphorylation of PABP is mediated by the MKK-2/ERK signaling pathway. Thus, a novel signaling pathway involving MKK-2 and ERK1/2 may down-regulate the activity of PABP and eIF4E by controlling their phosphorylation and compensates for the effect of excess cellular PABP.
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Affiliation(s)
- Shuhua Ma
- Department of Molecular and Cellular Biology, University of Guelph, Guelph, Ontario N1G 2W1, Canada
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24
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Raman S, Brian DA. Stem-loop IV in the 5' untranslated region is a cis-acting element in bovine coronavirus defective interfering RNA replication. J Virol 2005; 79:12434-46. [PMID: 16160171 PMCID: PMC1211515 DOI: 10.1128/jvi.79.19.12434-12446.2005] [Citation(s) in RCA: 51] [Impact Index Per Article: 2.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The 210-nucleotide (nt) 5' untranslated region (UTR) in the positive-strand bovine coronavirus (BCoV) genome is predicted to contain four higher-order structures identified as stem-loops I to IV, which may function as cis-acting elements in genomic RNA replication. Here, we describe evidence that stem-loop IV, a bulged stem-loop mapping at nt 186 through 215, (i) is phylogenetically conserved among group 2 coronaviruses and may have a homolog in groups 1 and 3, (ii) exists as a higher-order structure on the basis of enzyme probing, (iii) is required as a higher-order element for replication of a BCoV defective interfering (DI) RNA in the positive but not the negative strand, and (iv) as a higher-order structure in wild-type (wt) and mutant molecules that replicate, specifically binds six cellular proteins in the molecular mass range of 25 to 58 kDa as determined by electrophoretic mobility shift and UV cross-linking assays; binding to viral proteins was not detected. Interestingly, the predicted stem-loop IV homolog in the severe acute respiratory syndrome (SARS) coronavirus appears to be group 1-like in that it is in part duplicated with a group 1-like conserved loop sequence and is not group 2-like, as would be expected by the SARS coronavirus group 2-like 3' UTR structure. These results together indicate that stem-loop IV in the BCoV 5' UTR is a cis-acting element for DI RNA replication and that it might function through interactions with cellular proteins. It is postulated that stem-loop IV functions similarly in the virus genome.
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Affiliation(s)
- Sharmila Raman
- Department of Microbiology, University of Tennessee College of Veterinary Medicine, Knoxville, TN 37996-0845, USA
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25
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Blum JL, Samarel AM, Mestril R. Phosphorylation and binding of AUF1 to the 3'-untranslated region of cardiomyocyte SERCA2a mRNA. Am J Physiol Heart Circ Physiol 2005; 289:H2543-50. [PMID: 16113063 DOI: 10.1152/ajpheart.00545.2005] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Experimental animals and patients with cardiac hypertrophy and heart failure display abnormally slowed myocardial relaxation, which is associated with downregulation of sarco(endo)plasmic reticulum calcium ATPase 2a (SERCA2a), the cardiomyocyte sarcoplasmic reticulum Ca2+ pump. We previously showed that SERCA2a downregulation can be simulated in cultured neonatal rat ventricular myocytes (NRVM) by treatment with the hypertrophic agonist phorbol myristate acetate (PMA) or by overexpression of the novel protein kinase C (PKC) isoenzymes PKCdelta and PKCepsilon. PKC activation, in turn, decreased SERCA2a promoter activity and destabilized the SERCA2a mRNA. Here we demonstrate by using an RSV beta-galactosidase reporter system that a 609-nt fragment of the SERCA2a mRNA 3'-untranslated region (UTR), containing five adenylate-uridylate (AU)-rich regions, may be responsible for destabilizing the message following PMA treatment. UV cross-linking analysis demonstrated that several proteins found in the NRVM cell extracts bind to the 609-nt fragment. In addition, protein binding was transiently increased in response to PMA stimulation. 3'-UTR mRNA pull-down assays and Western blot analysis indicated that the AU binding protein AUF1 interacted with the SERCA2a 3'-UTR. AUF1 binding activity was predominantly found in the nuclear fraction, and PMA-induced AUF1 binding was associated with increased threonine phosphorylation of AUF1. These data suggest that the phosphorylation, binding, and location of AUF1 affect the posttranscriptional regulation of the SERCA2a message in NRVM.
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Affiliation(s)
- Juliana L Blum
- The Cardiovascular Institute, Loyola Univ. Medical Center, Bldg 110, Rm. 5222, 2160 South First Ave., Maywood, IL 60153, USA
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26
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Archambault D, St-Louis MC, Martin S. Binding of cellular proteins to the leader RNA of equine arteritis virus. Virus Genes 2005; 30:121-5. [PMID: 15744570 PMCID: PMC7088659 DOI: 10.1007/s11262-004-4589-6] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2004] [Accepted: 08/10/2004] [Indexed: 02/05/2023]
Abstract
The genome of equine arteritis virus (EAV) produces a 3' coterminal-nested set of six subgenomic (sg) viral RNAs during virus replication cycle, and each set possesses a common leader sequence of 206 nucleotides (nt) in length derived from the 5' end of the viral genome. Given the presence of the leader region within both genomic and sg mRNAs, it is likely to contain cis-acting signals that may interact with cellular or viral proteins for RNA synthesis. Gel mobility shift assays indicated that proteins in Vero cell cytoplasmic extracts formed complexes with the positive (+) and negative (-) strands of the EAV leader RNA. Several cell proteins with molecular masses ranging from 74 to 31 kDa and 58 to 32 kDa were detected in UV-induced cross-linking assays with the EAV leader RNA (+) and (-) strands, respectively. In both cases, intense bands were observed at the 58-52 kDa molecular weight markers. Results from competition gel mobility shift assays using overlapping cold RNA probes spanning the leader RNA (+) strand indicated that nt 140-206 are not necessary for binding to cell proteins.
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Affiliation(s)
- Denis Archambault
- Department of Biological Sciences, University of Québec at Montréal, P.O. Box 8888, Succursale Centre-Ville, Montréal, Québec, H3C 3P8, Canada.
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27
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Mohanty BK, Maples VF, Kushner SR. The Sm-like protein Hfq regulates polyadenylation dependent mRNA decay in Escherichia coli. Mol Microbiol 2005; 54:905-20. [PMID: 15522076 DOI: 10.1111/j.1365-2958.2004.04337.x] [Citation(s) in RCA: 184] [Impact Index Per Article: 9.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
In Escherichia coli, the post-transcriptional addition of poly(A) tails by poly(A) polymerase I (PAP I, pcnB) plays a significant role in cellular RNA metabolism. However, many important features of this system, including its regulation and the selection of polyadenylation sites, are still poorly understood. Here we show that the inactivation of Hfq (hfq), an abundant RNA-binding protein, leads to the reduction in the ability of PAP I to add poly(A) tails at the 3' termini of mRNAs containing Rho-independent transcription terminators even though PAP I protein levels remain unchanged. Those poly(A) tails that are synthesized in the absence of Hfq are shorter in length, even in the absence of polynucleotide phosphorylase (PNPase), RNase II and RNase E. In fact, the biosynthetic activity of PNPase in the hfq single mutant is enhanced and it becomes the primary polynucleotide polymerase, adding heteropolymeric tails almost exclusively to 3' truncated mRNAs. Surprisingly, both PNPase and Hfq co-purified with His-tagged PAP I under native conditions indicating a potential complex among these proteins. Immunoprecipitation experiments using PNPase- and Hfq-specific antibodies confirmed the protein-protein interactions among PAP I, PNPase and Hfq. Analysis of mRNA half-lives in hfq, deltapcnB and hfq deltapcnB mutants suggests that Hfq and PAP I function in the same mRNA decay pathway.
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Affiliation(s)
- Bijoy K Mohanty
- Department of Genetics, University of Georgia, Athens, GA 30602, USA
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28
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Martin-DeLeon PA, Zhang H, Morales CR, Zhao Y, Rulon M, Barnoski BL, Chen H, Galileo DS. Spam1-associated transmission ratio distortion in mice: elucidating the mechanism. Reprod Biol Endocrinol 2005; 3:32. [PMID: 16092963 PMCID: PMC1201170 DOI: 10.1186/1477-7827-3-32] [Citation(s) in RCA: 27] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 05/02/2005] [Accepted: 08/10/2005] [Indexed: 11/20/2022] Open
Abstract
BACKGROUND While transmission ratio distortion, TRD, (a deviation from Mendelian ratio) is extensive in humans and well-documented in mice, the underlying mechanisms are unknown. Our earlier studies on carriers of spontaneous mutations of mouse Sperm Adhesion Molecule 1 (Spam1) suggested that TRD results from biochemically different sperm, due to a lack of transcript sharing through the intercellular cytoplasmic bridges of spermatids. These bridges usually allow transcript sharing among genetically different spermatids which develop into biochemically and functionally equivalent sperm. OBJECTIVES The goals of the study were to provide support for the lack of sharing (LOS) hypothesis, using transgene and null carriers of Spam1, and to determine the mechanism of Spam1-associated TRD. METHODS Carriers of Spam1-Hyal5 BAC transgenes were mated with wild-type female mice and the progeny analyzed for TRD by PCR genotyping. Sperm from transgene and Spam1 null carriers were analyzed using flow cytometry and immunocytochemistry to detect quantities of Spam1 and/or Hyal5. Transgene-bearing sperm with Spam1 overexpression were detected by fluorescence in situ hybridization. In wild-type animals, EM studies of in situ transcript hybridization of testis sections and Northern analysis of biochemically fractionated testicular RNA were performed to localize Spam1 transcript. Finally, AU-rich motifs identified in the 3' UTR of Spam1 RNA were assayed by UV cross-linking to determine their ability to interact with testicular RNA binding proteins. RESULTS The Tg8 line of transgene carriers had a significant (P < 0.001) TRD, due to reduced fertilizing ability of transgene-bearing sperm. These sperm retained large cytoplasmic droplets engorged with overexpressed Spam1 or Hyal5 protein. Caudal sperm from transgene carriers and caput sperm of null carriers showed a bimodal distribution of Spam1, indicating that the sperm in a male were biochemically different with respect to Spam1 quantities. Spam1 RNA was absent from the bridges, associated exclusively with the ER, and was shown to be anchored to the cytoskeleton. This compartmentalization of the transcript, mediated by cytoskeletal binding, occurs via protein interactions with 3' UTR AU-rich sequences that are likely involved in its stabilization. CONCLUSION We provide strong support for the LOS hypothesis, and have elucidated the mechanism of Spam1-associated TRD.
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Affiliation(s)
| | - Hong Zhang
- Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA
| | - Carlos R Morales
- Department of Anatomy and Cell Biology, McGill University, Montreal, Quebec, Canada
| | - Yutong Zhao
- Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA
| | - Michelle Rulon
- Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA
| | - Barry L Barnoski
- Department of Genetics, Thomas Jefferson University, Philadelphia, PA, USA
| | - Hong Chen
- Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA
| | - Deni S Galileo
- Department of Biological Sciences, University of Delaware, Newark, DE 19716, USA
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Thomson AM, Cahill CM, Cho HH, Kassachau KD, Epis MR, Bridges KR, Leedman PJ, Rogers JT. The acute box cis-element in human heavy ferritin mRNA 5'-untranslated region is a unique translation enhancer that binds poly(C)-binding proteins. J Biol Chem 2005; 280:30032-45. [PMID: 15967798 DOI: 10.1074/jbc.m502951200] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Intracellular levels of the light (L) and heavy (H) ferritin subunits are regulated by iron at the level of message translation via a modulated interaction between the iron regulatory proteins (IRP1 and IRP2) and a 5'-untranslated region. Iron-responsive element (IRE). Here we show that iron and interleukin-1beta (IL-1beta) act synergistically to increase H- and L-ferritin expression in hepatoma cells. A GC-rich cis-element, the acute box (AB), located downstream of the IRE in the H-ferritin mRNA 5'-untranslated region, conferred a substantial increase in basal and IL-1beta-stimulated translation over a similar time course to the induction of endogenous ferritin. A scrambled version of the AB was unresponsive to IL-1. Targeted mutation of the AB altered translation; reverse orientation and a deletion of the AB abolished the wild-type stem-loop structure and abrogated translational enhancement, whereas a conservative structural mutant had little effect. Labeled AB transcripts formed specific complexes with hepatoma cell extracts that contained the poly(C)-binding proteins, iso-alphaCP1 and -alphaCP2, which have well defined roles as translation regulators. Iron influx increased the association of alphaCP1 with ferritin mRNA and decreased the alphaCP2-ferritin mRNA interaction, whereas IL-1beta reduced the association of alphaCP1 and alphaCP2 with H-ferritin mRNA. In summary, the H-ferritin mRNA AB is a key cis-acting translation enhancer that augments H-subunit expression in Hep3B and HepG2 hepatoma cells, in concert with the IRE. The regulated association of H-ferritin mRNA with the poly(C)-binding proteins suggests a novel role for these proteins in ferritin translation and iron homeostasis in human liver.
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Affiliation(s)
- Andrew M Thomson
- Laboratory for Cancer Medicine, School of Medicine and Pharmacology, UWA Centre for Medical Research, Western Australian Institute for Medical Research and University of Western Australia, Royal Perth Hospital
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30
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Sidiqi M, Wilce JA, Porter CJ, Barker A, Leedman PJ, Wilce MCJ. Formation of an alphaCP1-KH3 complex with UC-rich RNA. EUROPEAN BIOPHYSICS JOURNAL: EBJ 2005; 34:423-9. [PMID: 15756586 DOI: 10.1007/s00249-005-0467-y] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/18/2004] [Revised: 01/14/2005] [Accepted: 01/28/2005] [Indexed: 11/29/2022]
Abstract
The alphaCP family of proteins [also known as poly(C)-binding or heterogeneous nuclear ribonucleoprotein E proteins] are involved in the regulation of messenger RNA (mRNA) stability and translational efficiency. They bind via their triple heterologous nuclear ribonucleoprotein K homology (KH) domain structures to C-rich mRNA, and are thought to interact with other mRNA-binding proteins as well as provide direct nuclease protection. In particular, alphaCP1 and alphaCP2 have been shown to bind to a specific region of androgen receptor (AR) mRNA, resulting in its increased stability. The roles of each of the KH motifs in the binding affinity and the specificity is not yet understood. We report the beginning of a systematic study of each of the alphaCP KH domains, with the cloning and expression of alphaCP1-KH2 and alphaCP1-KH3. We report the ability of alphaCP1-KH3, but not alphaCP1-KH2, to bind the target AR mRNA sequence using an RNA electrophoretic mobility gel shift assay. We also report the preparation of an alphaCP1-KH3/AR mRNA complex for structural studies. (1)H-(15)N heteronuclear single quantum correlation NMR spectra of (15)N-labelled alphaCP1-KH3 verified the integrity and good solution behaviour of the purified domain. The titration of the 11-nucleotide RNA target sequence from AR mRNA resulted in a rearrangement of the (1)H-(15)N correlations, demonstrating the complete binding of the protein to form a homogeneous protein/RNA complex suitable for future structural studies.
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Affiliation(s)
- M Sidiqi
- School of Biomedical and Chemical Sciences, The University of Western Australia, 35 Stirling Highway, Crawley, Perth, WA 6009, Australia
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31
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Reddy KK, Oitomen FM, Patel GP, Bag J. Perinuclear localization of slow troponin C m RNA in muscle cells is controlled by a cis-element located at its 3' untranslated region. RNA (NEW YORK, N.Y.) 2005; 11:294-307. [PMID: 15701732 PMCID: PMC1370719 DOI: 10.1261/rna.5460105] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/07/2003] [Accepted: 12/07/2004] [Indexed: 05/24/2023]
Abstract
The process of mRNA localization within a specific cytoplasmic region is an integral aspect of the regulation of gene expression. Furthermore, colocalization of mRNAs and their respective translation products may facilitate the proper assembly of multi-subunit complexes like the thick and thin filaments of muscle. This postulate was tested by investigating the cytoplasmic localization of three mRNAs-the alpha-actin, slow troponin C (sTnC), and slow troponin I (sTnI), which encode different poly-peptide partners of the thin filament. Using in situ hybridization we showed that all three thin filament mRNAs are localized in the perinuclear cytoplasm of cultured C2C12 muscle cells. Their localization differs from that of the nonmuscle beta-actin mRNA, which is localized in the peripheral region of both proliferating nondifferentiated myoblasts and the differentiated myocytes. Analysis of the localization signal of the sTnC mRNA showed that a 40-nucleotide-long region of the sTnC mRNA 3' UTR is sufficient to confer the perinuclear localization on a heterologous reporter beta-Gal mRNA. This localization signal showed tissue specificity and worked only in the differentiated myocytes, but not in the proliferating myoblasts or in HeLa cells. The predicted secondary structure of the localization signal suggests the presence of multiple stem and loop structures in this region of the 3' UTR. Mutations within the stem region of the localization signal, which abolish the base pairing in this region, significantly reduced its perinuclear mRNA localization activity. Using UV-induced photo-cross-linking of RNA and proteins we found that a myotube-specific 42-kDa polypeptide binds to the localization signal.
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Affiliation(s)
- Kishore K Reddy
- Department of Molecular Biology and Genetics, University of Guelph, Guelph, Ontario, N1G 2W1, Canada
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32
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Lee JH, Jeon MH, Seo YJ, Lee YJ, Ko JH, Tsujimoto Y, Lee JH. CA repeats in the 3'-untranslated region of bcl-2 mRNA mediate constitutive decay of bcl-2 mRNA. J Biol Chem 2004; 279:42758-64. [PMID: 15294893 DOI: 10.1074/jbc.m407357200] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/15/2023] Open
Abstract
An AU-rich element (ARE) in the 3'-untranslated region (UTR) of bcl-2 mRNA has previously been shown to be responsible for destabilizing bcl-2 mRNA during apoptosis through increasing AUF1 binding. In the present study, we investigated the effect of the region upstream of the ARE on bcl-2 mRNA stability using serial deletion constructs of the 3'-UTR of bcl-2. Deletion of 30 nucleotides mostly consisting of the CA repeats, located upstream of the ARE, resulted in the stabilization of bcl-2 mRNA abundance, in the absence or presence of the ARE. The specificity of the CA repeats in terms of destabilizing bcl-2 mRNA was proven by the substituting the CA repeats with other alternative repeats of purine/pyrimidine, but this had no effect on the stability of bcl-2 mRNA. CA repeats alone, however, failed to confer instability to bcl-2 or gfp reporter mRNAs, indicating a requirement for additional sequences in the upstream region of the 3'-UTR. Serial deletion and replacement of a part of the region upstream of the CA repeats revealed that the entire 131-nucleotide upstream region is an essential prerequisite for the CA repeat-dependent destabilization of bcl-2 mRNA. Unlike the ARE, CA repeat-mediated degradation of bcl-2 mRNA was not accelerated upon apoptotic stimulus. Moreover, the upstream sequences and CA repeats are conserved among mammals. Collectively, CA repeats contribute to the constitutive decay of bcl-2 mRNA in the steady states, thereby maintaining appropriate bcl-2 levels in mammalian cells.
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Affiliation(s)
- Jung-Hee Lee
- Department of Biochemistry, The Catholic University of Korea, Seoul 137-701, Korea
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33
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Abstract
Androgens (testosterone), acting via the androgen receptor (AR) a nuclear transcription factor, regulate male sexual development and body composition. In addition, AR expression plays an important role in the proliferation of human prostate cancer and confers a better prognosis in breast cancer. AR mRNA stability is central to the regulation of AR expression in prostate and breast cancer cells, and recent studies have demonstrated binding by members of the ELAV/Hu and poly(C) RNA-binding protein families to a highly conserved UC-rich element in the 3'-untranslated region of AR mRNA, with functional impact on AR protein expression. Remarkably, a CAG trinucleotide repeat in exon 1 of the AR, the length of which has been linked to prostate cancer survival, is also a target for multiple RNA-binding proteins from a variety of human and murine tissues. In this review, we will detail the current knowledge of the mechanisms involved in regulating AR mRNA stability, the nature, potential role and structural biology of several novel AR mRNA-protein interactions, and the implications for novel therapeutics in human prostate cancer.
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Affiliation(s)
- Bu B Yeap
- School of Medicine and Pharmacology, The University of Western Australia, Fremantle and Royal Perth Hospitals, Perth, Western Australia, Australia
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34
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Adams DJ, Beveridge DJ, van der Weyden L, Mangs H, Leedman PJ, Morris BJ. HADHB, HuR, and CP1 bind to the distal 3'-untranslated region of human renin mRNA and differentially modulate renin expression. J Biol Chem 2003; 278:44894-903. [PMID: 12933794 DOI: 10.1074/jbc.m307782200] [Citation(s) in RCA: 49] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Production of renin is critically dependent on modulation of REN mRNA stability. Here we sought to elucidate the molecular mechanisms involved. Transfections of renin-expressing Calu-6 cells with reporter constructs showed that a cis-acting 34-nucleotide AU-rich "renin stability regulatory element" in the REN 3'-untranslated region (3'-UTR) contributes to basal REN mRNA instability. Yeast three-hybrid screening with the REN 3'-UTR as bait isolated HADHB (hydroxyacyl-CoA dehydrogenase/3-ketoacyl-CoA thiolase/enoyl-CoA hydratase (trifunctional protein) beta-subunit) as a novel REN mRNA-binding protein. Recombinant HADHB bound specifically to the 3'-UTR of REN mRNA, as did the known mRNA stabilizers HuR and CP1 (poly(C)-binding protein-1). This required the renin stability regulatory element. Forskolin, which augments REN mRNA stability in Calu-6 cells, increased binding of several proteins, including HuR and CP1, to the REN 3'-UTR, whereas 4-bromocrotonic acid, a specific thiolase inhibitor, decreased binding and elevated renin protein levels. Upon decreasing HADHB mRNA with RNA interference, renin protein and mRNA stability increased, whereas RNA interference against HuR caused these to decrease. Immunoprecipitation and reverse transcription-PCR of Calu-6 extracts confirmed that HADHB, HuR, and CP1 each associate with REN mRNA in vivo. Intracellular imaging revealed distinct localization of HADHB to mitochondria, HuR to nuclei, and CP1 throughout the cell. Immunohistochemistry demonstrated enrichment of HADHB in renin-producing renal juxtaglomerular cells. In conclusion, HADHB, HuR, and CP1 are novel REN mRNA-binding proteins that target a cis-element in the 3'-UTR of REN mRNA and regulate renin production. cAMP-mediated increased REN mRNA stability may involve stimulation of HuR and CP1, whereas REN mRNA decay may involve thiolase-dependent pathways.
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Affiliation(s)
- David J Adams
- Basic & Clinical Genomics Laboratory, School of Medical Sciences and Institute for Biomedical Research, The University of Sydney, New South Wales 2006, Australia
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35
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Giles KM, Daly JM, Beveridge DJ, Thomson AM, Voon DC, Furneaux HM, Jazayeri JA, Leedman PJ. The 3'-untranslated region of p21WAF1 mRNA is a composite cis-acting sequence bound by RNA-binding proteins from breast cancer cells, including HuR and poly(C)-binding protein. J Biol Chem 2003; 278:2937-46. [PMID: 12431987 DOI: 10.1074/jbc.m208439200] [Citation(s) in RCA: 97] [Impact Index Per Article: 4.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Despite promoting growth in many cell types, epidermal growth factor (EGF) induces growth inhibition in a variety of cancer cells that overexpress its receptor. The cyclin-dependent kinase inhibitor p21(WAF1) is a central component of this pathway. We found in human MDA-468 breast cancer cells that EGF up-regulates p21(WAF1) mRNA and protein, through a combination of increased mRNA stability and transcription. The decay rate of a hybrid luciferase reporter full-length p21(WAF1) 3'-untranslated region (UTR) mRNA was significantly faster than that of a control mRNA. Transfections with a variety of p21(WAF1) 3'-UTR constructs identified multiple cis-acting elements capable of reducing basal reporter activity. Short wavelength ultraviolet light induced reporter activity in constructs containing the 5' region of the p21(WAF1) 3'-UTR, whereas EGF induced reporter activity in constructs containing sequences 3' of the UVC-responsive region. These cis-elements bound multiple proteins from MDA-468 cells, including HuR and poly(C)-binding protein 1 (CP1). Immunoprecipitation studies confirmed that HuR and CP1 associate with p21(WAF1) mRNA in MDA-468 cells. Over- and underexpression of HuR in MDA-468 cells did not affect EGF-induced p21(WAF1) protein expression or growth inhibition. However, binding of HuR to its target 3'-UTR cis-element was regulated by UVC but not by EGF, suggesting that these stimuli modulate the stability of p21(WAF1) mRNA via different mechanisms. We conclude that EGF-induced p21(WAF1) protein expression is mediated largely by stabilization of p21(WAF1) mRNA elicited via multiple 3'-UTR cis-elements. Although HuR binds at least one of these elements, it does not appear to be a major modulator of p21(WAF1) expression or growth inhibition in this system. CP1 is a novel p21(WAF1) mRNA-binding protein that may function cooperatively with other mRNA-binding proteins to regulate p21(WAF1) mRNA stability.
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Affiliation(s)
- Keith M Giles
- Laboratory for Cancer Medicine and University Department of Medicine, Western Australian Institute for Medical Research and Centre for Medical Research, the University of Western Australia, Perth, Western Australia 6001, Australia
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36
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Abstract
In neurons, local protein synthesis in synaptodendritic microdomains has been implicated in the growth and plasticity of synapses. Prerequisites for local translation are the targeted transport of RNAs to distal sites of synthesis in dendrites and translational control mechanisms to limit synthesis to times of demand. Here we identify dendritic BC1 RNA as a specific repressor of translation. Experimental use of internal ribosome entry mechanisms and sucrose density gradient centrifugation showed that BC1-mediated repression targets translation at the level of initiation. Specifically, BC1 RNA inhibited formation of the 48S preinitiation complex, i.e., recruitment of the small ribosomal subunit to the messenger RNA (mRNA). However, 48S complex formation that is independent of the eukaryotic initiation factor 4 (eIF4) family of initiation factors was found to be refractory to inhibition by BC1 RNA, a result that implicates at least one of these factors in the BC1 repression pathway. Biochemical experiments indicated a specific interaction of BC1 RNA with eIF4A, an RNA unwinding factor, and with poly(A)-binding protein. Both proteins were found enriched in synaptodendritic microdomains. Significantly, BC1-mediated repression was shown to be effective not only in cap-dependent translation initiation but also in eIF4-dependent internal initiation. The results suggest a functional role of BC1 RNA as a mediator of translational control in local protein synthesis in nerve cells.
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37
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Rogers JT, Randall JD, Cahill CM, Eder PS, Huang X, Gunshin H, Leiter L, McPhee J, Sarang SS, Utsuki T, Greig NH, Lahiri DK, Tanzi RE, Bush AI, Giordano T, Gullans SR. An iron-responsive element type II in the 5'-untranslated region of the Alzheimer's amyloid precursor protein transcript. J Biol Chem 2002; 277:45518-28. [PMID: 12198135 DOI: 10.1074/jbc.m207435200] [Citation(s) in RCA: 380] [Impact Index Per Article: 17.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/19/2023] Open
Abstract
Iron-responsive elements (IREs) are the RNA stem loops that control cellular iron homeostasis by regulating ferritin translation and transferrin receptor mRNA stability. We mapped a novel iron-responsive element (IRE-Type II) within the 5'-untranslated region (5'-UTR) of the Alzheimer's amyloid precursor protein (APP) transcript (+51 to +94 from the 5'-cap site). The APP mRNA IRE is located immediately upstream of an interleukin-1 responsive acute box domain (+101 to +146). APP 5'-UTR conferred translation was selectively down-regulated in response to intracellular iron chelation using three separate reporter assays (chloramphenicol acetyltransferase, luciferase, and red fluorescent protein reflecting an inhibition of APP holoprotein translation in response to iron chelation. Iron influx reversed this inhibition. As an internal control to ensure specificity, a viral internal ribosome entry sequence was unresponsive to intracellular iron chelation with desferrioxamine. Using RNA mobility shift assays, the APP 5'-UTRs, encompassing the IRE, bind specifically to recombinant iron-regulatory proteins (IRP) and to IRP from neuroblastoma cell lysates. IRP binding to the APP 5'-UTR is reduced after treatment of cells with desferrioxamine and increased after interleukin-1 stimulation. IRP binding is abrogated when APP cRNA probe is mutated in the core IRE domain (Delta4 bases:Delta83AGAG86). Iron regulation of APP mRNA through the APP 5'-UTR points to a role for iron in the metabolism of APP and confirms that this RNA structure can be a target for the selection of small molecule drugs, such as desferrioxamine (Fe chelator) and clioquinol (Fe, Cu, and Zn chelator), which reduce Abeta peptide burden during Alzheimer's disease.
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Affiliation(s)
- Jack T Rogers
- Genetics and Aging Research Unit, Department of Psychiatry, Massachusetts General Hospital, Charlestown, Massachusetts 02129-4404, USA
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Hollams EM, Giles KM, Thomson AM, Leedman PJ. MRNA stability and the control of gene expression: implications for human disease. Neurochem Res 2002; 27:957-80. [PMID: 12462398 DOI: 10.1023/a:1020992418511] [Citation(s) in RCA: 165] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023]
Abstract
Regulation of gene expression is essential for the homeostasis of an organism, playing a pivotal role in cellular proliferation, differentiation, and response to specific stimuli. Multiple studies over the last two decades have demonstrated that the modulation of mRNA stability plays an important role in regulating gene expression. The stability of a given mRNA transcript is determined by the presence of sequences within an mRNA known as cis-elements, which can be bound by trans-acting RNA-binding proteins to inhibit or enhance mRNA decay. These cis-trans interactions are subject to a control by a wide variety of factors including hypoxia, hormones, and cytokines. In this review, we describe mRNA biosynthesis and degradation, and detail the cis-elements and RNA-binding proteins known to affect mRNA turnover. We present recent examples in which dysregulation of mRNA stability has been associated with human diseases including cancer, inflammatory disease, and Alzheimer's disease.
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Affiliation(s)
- Elysia M Hollams
- Laboratory for Cancer Medicine and University Department of Medicine, Western Australian Institute for Medical Research and University of Western Australia, Perth, Australia
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39
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Yeap BB, Voon DC, Vivian JP, McCulloch RK, Thomson AM, Giles KM, Czyzyk-Krzeska MF, Furneaux H, Wilce MCJ, Wilce JA, Leedman PJ. Novel binding of HuR and poly(C)-binding protein to a conserved UC-rich motif within the 3'-untranslated region of the androgen receptor messenger RNA. J Biol Chem 2002; 277:27183-92. [PMID: 12011088 DOI: 10.1074/jbc.m202883200] [Citation(s) in RCA: 114] [Impact Index Per Article: 5.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The androgen receptor (AR) mediates androgen action and plays a central role in the proliferation of specific cancer cells. We demonstrated recently that AR mRNA stability is a major determinant of AR gene expression in prostate and breast cancer cells and that androgens differentially regulate AR mRNA decay dependent on cell type (Yeap, B. B., Kreuger, R. G., Leedman, P. J. (1999) Endocrinology 140, 3282-3291). Here, we have identified a highly conserved UC-rich region in the 3-untranslated region of AR mRNA that contains a 5'-C(U)(n)C motif and a 3'-CCCUCCC poly(C)-binding protein motif. In transfection studies with LNCaP human prostate cancer cells, the AR UC-rich region reduced expression of a luciferase reporter gene. The AR UC-rich region was a target for cytoplasmic and nuclear RNA-binding proteins from human prostate and breast cancer cells as well as human testicular and breast cancer tissue. One of these proteins is HuR, a ubiquitously expressed member of the Elav/Hu family of RNA-binding proteins involved in the stabilization of several mRNAs. Poly(C)-binding protein-1 and -2 (CP1 and CP2), previously implicated in the control of mRNA turnover and translation, also bound avidly to the UC-rich region. Mutational analysis of the UC-rich region identified specific binding motifs for both HuR and the CPs. HuR and CP1 bound simultaneously to the UC-rich RNA and in a cooperative manner. Immunoprecipitation studies confirmed that each of these proteins associated with AR mRNA in prostate cancer cells. In summary, we have identified and characterized a novel complex of AR mRNA-binding proteins that target the highly conserved UC-rich region. The binding of HuR, CP1, and CP2 to AR mRNA suggests a role for each of these proteins in the post-transcriptional regulation of AR expression in cancer cells.
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Affiliation(s)
- Bu B Yeap
- Laboratory for Cancer Medicine, Western Australian Institute for Medical Research, University Department of Medicine, University of Western Australia, 50 Murray Street, Perth, WA 6000, Australia
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Hartley R, Le Meuth-Metzinger V, Osborne HB. Screening for sequence-specific RNA-BPs by comprehensive UV crosslinking. BMC Mol Biol 2002; 3:8. [PMID: 12067421 PMCID: PMC116595 DOI: 10.1186/1471-2199-3-8] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/14/2002] [Accepted: 06/07/2002] [Indexed: 11/10/2022] Open
Abstract
BACKGROUND Specific cis-elements and the associated trans-acting factors have been implicated in the post-transcriptional regulation of gene expression. In the era of genome wide analyses identifying novel trans-acting factors and cis-regulatory elements is a step towards understanding coordinated gene expression. UV-crosslink analysis is a standard method used to identify RNA-binding proteins. Uridine is traditionally used to radiolabel substrate RNAs, however, proteins binding to cis-elements particularly uridine poor will be weakly or not detected. We evaluate here the possibility of using UV-crosslinking with RNA substrates radiolabeled with each of the four ribonucleotides as an approach for screening for novel sequence specific RNA-binding proteins. RESULTS The radiolabeled RNA substrates were derived from the 3'UTRs of the cloned Eg and c-mos Xenopus laevis maternal mRNAs. Specific, but not identical, uv-crosslinking signals were obtained, some of which corresponded to already identified proteins. A signal for a novel 90 kDa protein was observed with the c-mos 3'UTR radiolabeled with both CTP and GTP but not with UTP. The binding site of the 90 kDa RNA-binding protein was localised to a 59-nucleotide portion of the c-mos 3'UTR. CONCLUSION That the 90 kDa signal was detected with RNAs radiolabeled with CTP or GTP but not UTP illustrates the advantage of radiolabeling all four nucleotides in a UV-crosslink based screen. This method can be used for both long and short RNAs and does not require knowledge of the cis-acting sequence. It should be amenable to high throughput screening for RNA binding proteins.
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Affiliation(s)
- Rebecca Hartley
- Department of Anatomy and Cell Biology, College of Medicine, University of Iowa, Iowa City, Iowa 52242, USA.
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Perrotti D, Cesi V, Trotta R, Guerzoni C, Santilli G, Campbell K, Iervolino A, Condorelli F, Gambacorti-Passerini C, Caligiuri MA, Calabretta B. BCR-ABL suppresses C/EBPalpha expression through inhibitory action of hnRNP E2. Nat Genet 2002; 30:48-58. [PMID: 11753385 DOI: 10.1038/ng791] [Citation(s) in RCA: 230] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/05/2023]
Abstract
The arrest of differentiation is a feature of both chronic myelogenous leukemia cells in myeloid blast crisis and myeloid precursors that ectopically express the p210BCR-ABL oncoprotein; however, its underlying mechanisms remain poorly understood. Here we show that expression of BCR-ABL in myeloid precursor cells leads to transcriptional suppression of the granulocyte colony-stimulating factor receptor G-CSF-R (encoded by CSF3R), possibly through down-modulation of C/EBPalpha-the principal regulator of granulocytic differentiation. Expression of C/EBPalpha protein is barely detectable in primary marrow cells taken from individuals affected with chronic myeloid leukemia in blast crisis. In contrast, CEBPA RNA is clearly present. Ectopic expression of C/EBPalpha induces granulocytic differentiation of myeloid precursor cells expressing BCR-ABL. Expression of C/EBPalpha is suppressed at the translational level by interaction of the poly(rC)-binding protein hnRNP E2 with CEBPA mRNA, and ectopic expression of hnRNP E2 in myeloid precursor cells down-regulates both C/EBPalpha and G-CSF-R and leads to rapid cell death on treatment with G-CSF (encoded by CSF3). Our results indicate that BCR-ABL regulates the expression of C/EBPalpha by inducing hnRNP E2-which inhibits the translation of CEBPA mRNA.
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MESH Headings
- Animals
- Apoptosis/genetics
- Apoptosis/physiology
- Benzamides
- Blast Crisis/metabolism
- Blast Crisis/pathology
- CCAAT-Enhancer-Binding Protein-alpha/biosynthesis
- CCAAT-Enhancer-Binding Protein-alpha/genetics
- CCAAT-Enhancer-Binding Proteins
- Carrier Proteins/metabolism
- Cells, Cultured/metabolism
- DNA-Binding Proteins
- Down-Regulation
- Fusion Proteins, bcr-abl/antagonists & inhibitors
- Fusion Proteins, bcr-abl/physiology
- Gene Expression Regulation
- Gene Expression Regulation, Leukemic
- Hematopoietic Stem Cells/metabolism
- Heterogeneous-Nuclear Ribonucleoproteins
- Humans
- Imatinib Mesylate
- K562 Cells
- Leukemia, Myelogenous, Chronic, BCR-ABL Positive/metabolism
- Leukemia, Myelogenous, Chronic, BCR-ABL Positive/pathology
- Mice
- Myeloid Cells/metabolism
- Neoplasm Proteins/antagonists & inhibitors
- Neoplasm Proteins/biosynthesis
- Neoplasm Proteins/genetics
- Neoplasm Proteins/physiology
- Neoplastic Stem Cells/metabolism
- Oligodeoxyribonucleotides/chemistry
- Oligodeoxyribonucleotides/pharmacology
- Piperazines/pharmacology
- Protein Biosynthesis
- Protein Isoforms/biosynthesis
- Protein Isoforms/genetics
- Pyrimidines/pharmacology
- RNA, Messenger/biosynthesis
- RNA, Messenger/genetics
- RNA-Binding Proteins/genetics
- RNA-Binding Proteins/isolation & purification
- RNA-Binding Proteins/physiology
- Receptors, Granulocyte Colony-Stimulating Factor/biosynthesis
- Receptors, Granulocyte Colony-Stimulating Factor/genetics
- Sequence Alignment
- Sequence Homology, Nucleic Acid
- Transcription Factors
- Transcription, Genetic
- Transfection
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Affiliation(s)
- Danilo Perrotti
- Department of Microbiology and Immunology, Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, Pennsylvania 19107, USA.
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Bunse AA, Nickelsen J, Kück U. Intron-specific RNA binding proteins in the chloroplast of the green alga Chlamydomonas reinhardtii. BIOCHIMICA ET BIOPHYSICA ACTA 2001; 1519:46-54. [PMID: 11406270 DOI: 10.1016/s0167-4781(01)00211-1] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/18/2022]
Abstract
Mitochondria and chloroplasts both contain group II introns which are believed to be the ancestors of nuclear spliceosomal introns. We used the mitochondrial group II intron rI1 from the green alga Scenedesmus obliquus for biochemical characterization of intron-specific RNA binding proteins. rI1 is correctly spliced from a chloroplast precursor RNA when integrated into the chloroplast genome of Chlamydomonas reinhardtii. Glycerol gradients revealed the sedimentation profile of transcripts containing intron rI1 in native C. reinhardtii extracts and in deproteinized RNA preparations, thus indicating the association of rI1 containing transcripts with high molecular weight ribonucleoprotein complexes in vivo. Furthermore, the specific binding of a 61 kDa protein and a 31 kDa protein with the conserved domain IV was demonstrated using a set of intron derivatives for in vitro RNA binding experiments. We propose that we have biochemically characterized 'general splicing factors', which enable the successful splicing even of mitochondrial introns in chloroplasts.
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Affiliation(s)
- A A Bunse
- Lehrstuhl für Allgemeine und Molekulare Botanik, Fakultät für Biologie, Ruhr-Universität Bochum, D-44780 Bochum, Germany
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43
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Balmer LA, Beveridge DJ, Jazayeri JA, Thomson AM, Walker CE, Leedman PJ. Identification of a novel AU-Rich element in the 3' untranslated region of epidermal growth factor receptor mRNA that is the target for regulated RNA-binding proteins. Mol Cell Biol 2001; 21:2070-84. [PMID: 11238942 PMCID: PMC86815 DOI: 10.1128/mcb.21.6.2070-2084.2001] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The epidermal growth factor receptor (EGF-R) plays an important role in the growth and progression of estrogen receptor-negative human breast cancers. EGF binds with high affinity to the EGF-R and activates a variety of second messenger pathways that affect cellular proliferation. However, the underlying mechanisms involved in the regulation of EGF-R expression in breast cancer cells are yet to be described. Here we show that the EGF-induced upregulation of EGF-R mRNA in two human breast cancer cell lines that overexpress EGF-R (MDA-MB-468 and BT-20) is accompanied by stabilization (>2-fold) of EGF-R mRNA. Transient transfections using a luciferase reporter identified a novel EGF-regulated approximately 260-nucleotide (nt) cis-acting element in the 3' untranslated region (3'-UTR) of EGF-R mRNA. This cis element contains two distinct AU-rich sequences (~75 nt), EGF-R1A with two AUUUA pentamers and EGF-R2A with two AUUUUUA extended pentamers. Each independently regulated the mRNA stability of the heterologous reporter. Analysis of mutants of the EGF-R2A AU-rich sequence demonstrated a role for the 3' extended pentamer in regulating basal turnover. RNA gel shift analysis identified cytoplasmic proteins (~55 to 80 kDa) from breast cancer cells that bound specifically to the EGF-R1A and EGF-R2A cis-acting elements and whose binding activity was rapidly downregulated by EGF and phorbol esters. RNA gel shift analysis of EGF-R2A mutants identified a role for the 3' extended AU pentamer, but not the 5' extended pentamer, in binding proteins. These EGF-R mRNA-binding proteins were present in multiple human breast and prostate cancer cell lines. In summary, these data demonstrate a central role for mRNA stabilization in the control of EGF-R gene expression in breast cancer cells. EGF-R mRNA contains a novel complex AU-rich 260-nt cis-acting destabilizing element in the 3'-UTR that is bound by specific and EGF-regulated trans-acting factors. Furthermore, the 3' extended AU pentamer of EGF-R2A plays a central role in regulating EGF-R mRNA stability and the binding of specific RNA-binding proteins. These findings suggest that regulated RNA-protein interactions involving this novel cis-acting element will be a major determinant of EGF-R mRNA stability.
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Affiliation(s)
- L A Balmer
- Laboratory for Cancer Medicine, Royal Perth Hospital, University of Western Australia, Perth, Western Australia, Australia 6000
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44
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Thomson AM, Rogers JT, Leedman PJ. Thyrotropin-releasing hormone and epidermal growth factor regulate iron-regulatory protein binding in pituitary cells via protein kinase C-dependent and -independent signaling pathways. J Biol Chem 2000; 275:31609-15. [PMID: 10889193 DOI: 10.1074/jbc.m002354200] [Citation(s) in RCA: 36] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Intracellular iron homeostasis is regulated, in part, by interactions between iron-regulatory proteins (IRP1 and IRP2) and iron-responsive elements (IREs) in ferritin and transferrin receptor mRNAs. In addition to iron, cellular oxidative stress induced by H(2)O(2), nitric oxide, and hypoxia, and hormonal activation by thyroid hormone and erythropoeitin have each been shown to regulate IRP binding to IREs. Hormonal signals, in particular mediated through protein kinase C (PKC), play a central role in the modulation of IRP/IRE interactions since phorbol esters were shown to activate IRP binding (Eisenstein, R. S., Tuazon, P. T., Schalinske, K. L., Anderson, S. A., and Traugh, J. A. (1993) J. Biol. Chem. 268, 27363-27370). In pituitary thyrotrophs (TtT97), we found that thyrotropin releasing hormone (TRH) and epidermal growth factor (EGF) increased IRP binding to a ferritin IRE, dependent on PKC and mitogen-activated protein kinase (MAPK) activity. In contrast, TRH and EGF decreased IRP binding in pituitary lactotrophs (GH3), despite activation of PKC and MAPK. IRP1 and IRP2 levels remained constant and IRP2 binding was predominant throughout. TRH and EGF markedly decreased IRP binding in MAPK kinase inhibitor-treated GH3 cells, whereas, they increased IRP binding in phosphatase inhibitor-treated GH3 cells. IRE-dependent CAT reporter translational expression closely reflected IRP binding to the ferritin IRE in both GH3 and TtT97 cells. Interestingly, ferritin protein levels were regulated similarly by TRH in both cell lines. These data link two different cell receptor systems to common signaling pathways that regulate IRP binding and ferritin expression. Remarkably, for TRH and EGF, these effects may be PKC-dependent or -independent determined by the cell type.
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Affiliation(s)
- A M Thomson
- Laboratory for Cancer Medicine and University Department of Medicine, University of Western Australia, Western Australian Institute for Medical Research, Royal Perth Hospital, Perth, Western Australia 6000, Australia
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45
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Holcik M, Korneluk RG. Functional characterization of the X-linked inhibitor of apoptosis (XIAP) internal ribosome entry site element: role of La autoantigen in XIAP translation. Mol Cell Biol 2000; 20:4648-57. [PMID: 10848591 PMCID: PMC85872 DOI: 10.1128/mcb.20.13.4648-4657.2000] [Citation(s) in RCA: 185] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/09/2000] [Accepted: 04/11/2000] [Indexed: 12/14/2022] Open
Abstract
X-linked inhibitor of apoptosis protein (XIAP) is a key regulator of programmed cell death triggered by various apoptotic triggers. Translation of XIAP is controlled by a 162-nucleotide (nt) internal ribosome entry site (IRES) element located in the 5' untranslated region of XIAP mRNA. XIAP IRES mediates efficient translation of XIAP under physiological stress and enhances cell protection against serum deprivation and radiation-induced apoptosis. In the present report we describe the assembly of a sequence-specific RNA-protein complex consisting of at least four cytosolic proteins on the XIAP IRES element. We determine that the core binding sequence is approximately 28 nt long and is located 34 nt upstream of the initiation site. Moreover, we identify the La autoantigen as a protein that specifically binds XIAP IRES in vivo and in vitro. The biological relevance of this interaction is further demonstrated by the inhibition of XIAP IRES-mediated translation in the absence of functional La protein. The results suggest an important role for the La protein in the regulation of XIAP expression, possibly by facilitating ribosome recruitment to the XIAP IRES.
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Affiliation(s)
- M Holcik
- Apoptogen Inc.; Solange Gauthier Karsh Molecular Genetics Laboratory, Children's Hospital of Eastern Ontario, Ottawa, Canada
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