1
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Vaughn LS, Chukwurah E, Patel RC. Opposite actions of two dsRNA-binding proteins PACT and TRBP on RIG-I mediated signaling. Biochem J 2021; 478:493-510. [PMID: 33459340 PMCID: PMC7919947 DOI: 10.1042/bcj20200987] [Citation(s) in RCA: 6] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2020] [Revised: 01/13/2021] [Accepted: 01/18/2021] [Indexed: 02/07/2023]
Abstract
An integral aspect of innate immunity is the ability to detect foreign molecules of viral origin to initiate antiviral signaling via pattern recognition receptors (PRRs). One such receptor is the RNA helicase retinoic acid inducible gene 1 (RIG-I), which detects and is activated by 5'triphosphate uncapped double stranded RNA (dsRNA) as well as the cytoplasmic viral mimic dsRNA polyI:C. Once activated, RIG-I's CARD domains oligomerize and initiate downstream signaling via mitochondrial antiviral signaling protein (MAVS), ultimately inducing interferon (IFN) production. Another dsRNA binding protein PACT, originally identified as the cellular protein activator of dsRNA-activated protein kinase (PKR), is known to enhance RIG-I signaling in response to polyI:C treatment, in part by stimulating RIG-I's ATPase and helicase activities. TAR-RNA-binding protein (TRBP), which is ∼45% homologous to PACT, inhibits PKR signaling by binding to PKR as well as by sequestration of its' activators, dsRNA and PACT. Despite the extensive homology and similar structure of PACT and TRBP, the role of TRBP has not been explored much in RIG-I signaling. This work focuses on the effect of TRBP on RIG-I signaling and IFN production. Our results indicate that TRBP acts as an inhibitor of RIG-I signaling in a PACT- and PKR-independent manner. Surprisingly, this inhibition is independent of TRBP's post-translational modifications that are important for other signaling functions of TRBP, but TRBP's dsRNA-binding ability is essential. Our work has major implications on viral susceptibility, disease progression, and antiviral immunity as it demonstrates the regulatory interplay between PACT and TRBP IFN production.
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Affiliation(s)
- Lauren S. Vaughn
- Department of Biology, University of South Carolina, Columbia, SC 29210
| | | | - Rekha C Patel
- Department of Biology, University of South Carolina, Columbia, SC 29210
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2
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Recombinant hTRBP and hPACT Modulate hAgo2-Catalyzed siRNA-Mediated Target RNA Cleavage In Vitro. PLoS One 2016; 11:e0146814. [PMID: 26784517 PMCID: PMC4718636 DOI: 10.1371/journal.pone.0146814] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/16/2015] [Accepted: 12/21/2015] [Indexed: 11/19/2022] Open
Abstract
The human TAR RNA-binding protein (hTRBP) and protein activator of protein kinase R (hPACT) are important players in RNA interference (RNAi). Together with hArgonaute2 (hAgo2) and hDicer they have been reported to form the RISC-loading complex (RLC). Among other functions, hTRBP was suggested to assist the loading of hAgo2 with small interfering RNAs (siRNAs) within the RLC. Although several studies have been conducted to evaluate the specific functions of hTRBP and hPACT in RNAi, exact mechanisms and modes of action are still unknown. Here, we present a biochemical study further evaluating the role of hTRBP and hPACT in hAgo2-loading. We found that both proteins enhance hAgo2-mediated RNA cleavage significantly; even a hAgo2 mutant impaired in siRNA binding shows full cleavage activity in the presence of hTRBP or hPACT. Pre-steady state binding studies reveal that the assembly of wildtype-hAgo2 (wt-hAgo2) and siRNAs remains largely unaffected, whereas the binding of mutant hAgo2-PAZ9 to siRNA is restored by adding either hTRBP or hPACT. We conclude that both proteins assist in positioning the siRNA within hAgo2 to ensure optimal binding and cleavage. Overall, our data indicate that hTRBP and hPACT are part of a regulative system of RNAi that is important for efficient target RNA cleavage.
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3
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Daniels SM, Sinck L, Ward NJ, Melendez-Peña CE, Scarborough RJ, Azar I, Rance E, Daher A, Pang KM, Rossi JJ, Gatignol A. HIV-1 RRE RNA acts as an RNA silencing suppressor by competing with TRBP-bound siRNAs. RNA Biol 2015; 12:123-35. [PMID: 25668122 DOI: 10.1080/15476286.2015.1014759] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/23/2022] Open
Abstract
Several proteins and RNAs expressed by mammalian viruses have been reported to interfere with RNA interference (RNAi) activity. We investigated the ability of the HIV-1-encoded RNA elements Trans-Activation Response (TAR) and Rev-Response Element (RRE) to alter RNAi. MicroRNA let7-based assays showed that RRE is a potent suppressor of RNAi activity, while TAR displayed moderate RNAi suppression. We demonstrate that RRE binds to TAR-RNA Binding Protein (TRBP), an essential component of the RNA Induced Silencing Complex (RISC). The binding of TAR and RRE to TRBP displaces small interfering (si)RNAs from binding to TRBP. Several stem-deleted RRE mutants lost their ability to suppress RNAi activity, which correlated with a reduced ability to compete with siRNA-TRBP binding. A lentiviral vector expressing TAR and RRE restricted RNAi, but RNAi was restored when Rev or GagPol were coexpressed. Adenoviruses are restricted by RNAi and encode their own suppressors of RNAi, the Virus-Associated (VA) RNA elements. RRE enhanced the replication of wild-type and VA-deficient adenovirus. Our work describes RRE as a novel suppressor of RNAi that acts by competing with siRNAs rather than by disrupting the RISC. This function is masked in lentiviral vectors co-expressed with viral proteins and thus will not affect their use in gene therapy. The potent RNAi suppressive effects of RRE identified in this study could be used to enhance the expression of RNAi restricted viruses used in oncolysis such as adenoviruses.
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Key Words
- Ago2, Argonaute-2
- EGFP, enhanced green fluorescent protein
- EMSA, electrophoresis mobility shift assay
- FL, firefly luciferase
- GAPDH, glyceraldehyde-3-phosphate dehydrogenase
- HIV, human immunodeficiency virus
- HIV-1
- IP, immunoprecipitation
- NC, nucleocapsid
- PAGE, polyacrylamide gel electrophoresis
- RISC, RNA-Induced Silencing Complex
- RL, Renilla luciferase
- RNA interference
- RNA silencing suppressor
- RNAi, RNA interference
- RRE, Rev Response Element
- RSS, RNA silencing suppressor
- RT, reverse transcription
- Rev-Response Element RNA
- TAR RNA Binding Protein (TRBP)
- TAR, trans-activation responsive element
- TRBP, TAR RNA Binding Protein
- Trans-Activation Response Element
- UTR, untranslated region
- VA, virus-associated
- WT, wild-type
- adenovirus
- ds, double-stranded
- lentiviral vectors
- miRNA, micro RNA
- pre-miRNA, precursor miRNA
- siRNA, small interfering RNA
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Affiliation(s)
- Sylvanne M Daniels
- a Virus-Cell Interactions Laboratory ; Lady Davis Institute for Medical Research ; Montréal , Québec , Canada
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4
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Ding J, Chen J, Wang Y, Kataoka M, Ma L, Zhou P, Hu X, Lin Z, Nie M, Deng ZL, Pu WT, Wang DZ. Trbp regulates heart function through microRNA-mediated Sox6 repression. Nat Genet 2015; 47:776-83. [PMID: 26029872 PMCID: PMC4485565 DOI: 10.1038/ng.3324] [Citation(s) in RCA: 50] [Impact Index Per Article: 5.6] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/28/2015] [Accepted: 05/07/2015] [Indexed: 12/18/2022]
Abstract
Cardiomyopathy is associated with altered expression of genes encoding contractile proteins. Here we show that Trbp (Tarbp2), an RNA binding protein, is required for normal heart function. Cardiac-specific inactivation of Trbp (TrbpcKO) caused progressive cardiomyopathy and lethal heart failure. Trbp loss of function resulted in upregulation of Sox6, repression of genes encoding normal cardiac slow-twitch myofiber proteins, and pathologically increased expression of skeletal fast-twitch myofiber genes. Remarkably, knockdown of Sox6 fully rescued the Trbp mutant phenotype, whereas Sox6 overexpression phenocopied the TrbpcKO phenotype. Trbp inactivation was mechanistically linked to Sox6 upregulation through altered processing of miR-208a, which is a direct inhibitor of Sox6. Transgenic overexpression of miR-208a sufficiently repressed Sox6, restored the balance of fast- and slow- twitch myofiber gene expression, and rescued cardiac function in TrbpcKO mice. Together, our studies reveal a novel Trbp-mediated microRNA processing mechanism in regulating a linear genetic cascade essential for normal heart function.
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Affiliation(s)
- Jian Ding
- Department of Cardiology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | - Jinghai Chen
- Department of Cardiology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | - Yanqun Wang
- Departmant of Genetics, Harvard Medical School, Boston, Massachusetts, USA
| | - Masaharu Kataoka
- 1] Department of Cardiology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA. [2] Department of Cardiology, Keio University School of Medicine, Tokyo, Japan
| | - Lixin Ma
- 1] Department of Cardiology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA. [2] College of Life Sciences, Hubei University, Wuhan, China
| | - Pingzhu Zhou
- Department of Cardiology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | - Xiaoyun Hu
- Department of Cardiology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | - Zhiqiang Lin
- Department of Cardiology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA
| | - Mao Nie
- 1] Department of Cardiology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA. [2] Department of Orthopaedic Surgery, The Second Affiliated Hospital, Chongqing Medical University, Chongqing, China
| | - Zhong-Liang Deng
- Department of Orthopaedic Surgery, The Second Affiliated Hospital, Chongqing Medical University, Chongqing, China
| | - William T Pu
- 1] Department of Cardiology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA. [2] Harvard Stem Cell Institute, Harvard University, Cambridge, Massachusetts, USA
| | - Da-Zhi Wang
- 1] Department of Cardiology, Boston Children's Hospital, Harvard Medical School, Boston, Massachusetts, USA. [2] Harvard Stem Cell Institute, Harvard University, Cambridge, Massachusetts, USA
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5
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Piñeiro D, Fernandez-Chamorro J, Francisco-Velilla R, Martinez-Salas E. Gemin5: A Multitasking RNA-Binding Protein Involved in Translation Control. Biomolecules 2015; 5:528-44. [PMID: 25898402 PMCID: PMC4496684 DOI: 10.3390/biom5020528] [Citation(s) in RCA: 28] [Impact Index Per Article: 3.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/23/2015] [Revised: 04/01/2015] [Accepted: 04/09/2015] [Indexed: 12/31/2022] Open
Abstract
Gemin5 is a RNA-binding protein (RBP) that was first identified as a peripheral component of the survival of motor neurons (SMN) complex. This predominantly cytoplasmic protein recognises the small nuclear RNAs (snRNAs) through its WD repeat domains, allowing assembly of the SMN complex into small nuclear ribonucleoproteins (snRNPs). Additionally, the amino-terminal end of the protein has been reported to possess cap-binding capacity and to interact with the eukaryotic initiation factor 4E (eIF4E). Gemin5 was also shown to downregulate translation, to be a substrate of the picornavirus L protease and to interact with viral internal ribosome entry site (IRES) elements via a bipartite non-canonical RNA-binding site located at its carboxy-terminal end. These features link Gemin5 with translation control events. Thus, beyond its role in snRNPs biogenesis, Gemin5 appears to be a multitasking protein cooperating in various RNA-guided processes. In this review, we will summarise current knowledge of Gemin5 functions. We will discuss the involvement of the protein on translation control and propose a model to explain how the proteolysis fragments of this RBP in picornavirus-infected cells could modulate protein synthesis.
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Affiliation(s)
- David Piñeiro
- Medical Research Council Toxicology Unit, Lancaster Rd, Leicester LE1 9HN, UK.
| | - Javier Fernandez-Chamorro
- Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Nicolas Cabrera 1, Madrid 28049, Spain.
| | - Rosario Francisco-Velilla
- Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Nicolas Cabrera 1, Madrid 28049, Spain.
| | - Encarna Martinez-Salas
- Centro de Biología Molecular Severo Ochoa, Consejo Superior de Investigaciones Científicas-Universidad Autónoma de Madrid, Nicolas Cabrera 1, Madrid 28049, Spain.
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6
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Acevedo R, Orench-Rivera N, Quarles KA, Showalter SA. Helical defects in microRNA influence protein binding by TAR RNA binding protein. PLoS One 2015; 10:e0116749. [PMID: 25608000 PMCID: PMC4301919 DOI: 10.1371/journal.pone.0116749] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/18/2014] [Accepted: 12/12/2014] [Indexed: 01/19/2023] Open
Abstract
Background MicroRNAs (miRNAs) are critical post-transcriptional regulators of gene expression. Their precursors have a globally A-form helical geometry, which prevents most proteins from identifying their nucleotide sequence. This suggests the hypothesis that local structural features (e.g., bulges, internal loops) play a central role in specific double-stranded RNA (dsRNA) selection from cellular RNA pools by dsRNA binding domain (dsRBD) containing proteins. Furthermore, the processing enzymes in the miRNA maturation pathway require tandem-dsRBD cofactor proteins for optimal function, suggesting that dsRBDs play a key role in the molecular mechanism for precise positioning of the RNA within these multi-protein complexes. Here, we focus on the tandem-dsRBDs of TRBP, which have been shown to bind dsRNA tightly. Methodology/Principal Findings We present a combination of dsRNA binding assays demonstrating that TRBP binds dsRNA in an RNA-length dependent manner. Moreover, circular dichroism data shows that the number of dsRBD moieties bound to RNA at saturation is different for a tandem-dsRBD construct than for constructs with only one dsRBD per polypeptide, revealing another reason for the selective pressure to maintain multiple domains within a polypeptide chain. Finally, we show that helical defects in precursor miRNA alter the apparent dsRNA size, demonstrating that imperfections in RNA structure influence the strength of TRBP binding. Conclusion/Significance We conclude that TRBP is responsible for recognizing structural imperfections in miRNA precursors, in the sense that TRBP is unable to bind imperfections efficiently and thus is positioned around them. We propose that once positioned around structural defects, TRBP assists Dicer and the rest of the RNA-induced silencing complex (RISC) in providing efficient and homogenous conversion of substrate precursor miRNA into mature miRNA downstream.
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Affiliation(s)
- Roderico Acevedo
- Department of Chemistry and Center for RNA Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, United States of America
| | - Nichole Orench-Rivera
- Department of Chemistry and Center for RNA Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, United States of America
| | - Kaycee A. Quarles
- Department of Chemistry and Center for RNA Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, United States of America
| | - Scott A. Showalter
- Department of Chemistry and Center for RNA Molecular Biology, The Pennsylvania State University, University Park, Pennsylvania, United States of America
- * E-mail:
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7
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Goodarzi H, Zhang S, Buss CG, Fish L, Tavazoie S, Tavazoie SF. Metastasis-suppressor transcript destabilization through TARBP2 binding of mRNA hairpins. Nature 2014; 513:256-60. [PMID: 25043050 DOI: 10.1038/nature13466] [Citation(s) in RCA: 65] [Impact Index Per Article: 6.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/16/2013] [Accepted: 05/12/2014] [Indexed: 01/30/2023]
Abstract
Aberrant regulation of RNA stability has an important role in many disease states. Deregulated post-transcriptional modulation, such as that governed by microRNAs targeting linear sequence elements in messenger RNAs, has been implicated in the progression of many cancer types. A defining feature of RNA is its ability to fold into structures. However, the roles of structural mRNA elements in cancer progression remain unexplored. Here we performed an unbiased search for post-transcriptional modulators of mRNA stability in breast cancer by conducting whole-genome transcript stability measurements in poorly and highly metastatic isogenic human breast cancer lines. Using a computational framework that searches RNA sequence and structure space, we discovered a family of GC-rich structural cis-regulatory RNA elements, termed sRSEs for structural RNA stability elements, which are significantly overrepresented in transcripts displaying reduced stability in highly metastatic cells. By integrating computational and biochemical approaches, we identified TARBP2, a double-stranded RNA-binding protein implicated in microRNA processing, as the trans factor that binds the sRSE family and similar structural elements--collectively termed TARBP2-binding structural elements (TBSEs)--in transcripts. TARBP2 is overexpressed in metastatic cells and metastatic human breast tumours and destabilizes transcripts containing TBSEs. Endogenous TARBP2 promotes metastatic cell invasion and colonization by destabilizing amyloid precursor protein (APP) and ZNF395 transcripts, two genes previously associated with Alzheimer's and Huntington's disease, respectively. We reveal these genes to be novel metastasis suppressor genes in breast cancer. The cleavage product of APP, extracellular amyloid-α peptide, directly suppresses invasion while ZNF395 transcriptionally represses a pro-metastatic gene expression program. The expression levels of TARBP2, APP and ZNF395 in human breast carcinomas support their experimentally uncovered roles in metastasis. Our findings establish a non-canonical and direct role for TARBP2 in mammalian gene expression regulation and reveal that regulated RNA destabilization through protein-mediated binding of mRNA structural elements can govern cancer progression.
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Affiliation(s)
- Hani Goodarzi
- Laboratory of Systems Cancer Biology, Rockefeller University, 1230 York Avenue, New York, New York 10065, USA
| | - Steven Zhang
- Laboratory of Systems Cancer Biology, Rockefeller University, 1230 York Avenue, New York, New York 10065, USA
| | - Colin G Buss
- Laboratory of Systems Cancer Biology, Rockefeller University, 1230 York Avenue, New York, New York 10065, USA
| | - Lisa Fish
- Laboratory of Systems Cancer Biology, Rockefeller University, 1230 York Avenue, New York, New York 10065, USA
| | - Saeed Tavazoie
- Department of Biochemistry and Molecular Biophysics, and Department of Systems Biology, Columbia University, New York, New York 10032, USA
| | - Sohail F Tavazoie
- Laboratory of Systems Cancer Biology, Rockefeller University, 1230 York Avenue, New York, New York 10065, USA
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8
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Zimmermann J, Latta L, Beck A, Leidinger P, Fecher-Trost C, Schlenstedt G, Meese E, Wissenbach U, Flockerzi V. Trans-activation response (TAR) RNA-binding protein 2 is a novel modulator of transient receptor potential canonical 4 (TRPC4) protein. J Biol Chem 2014; 289:9766-80. [PMID: 24563462 DOI: 10.1074/jbc.m114.557066] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
TRPC4 proteins function as Ca(2+) conducting, non-selective cation channels in endothelial, smooth muscle, and neuronal cells. To further characterize the roles of TRPC4 in vivo, detailed information about the molecular composition of native channel complexes and their association with cellular signaling networks is needed. Therefore, a mouse brain cDNA library was searched for novel TRPC4-interacting proteins using a modified yeast two-hybrid assay. This screen identified Trans-activation Response RNA-binding protein 2 (Tarpb2), a protein that recruits the Dicer complex to Ago2 for microRNA processing and gene silencing. Tarbp2 was found to bind to the C terminus of TRPC4 and TRPC5 and to modulate agonist-dependent TRPC4-induced Ca(2+) entry. A stretch of basic residues within the Tarbp2 protein is required for these actions. Tarbp2 binding to and modulation of TRPC4 occurs in the presence of endogenously expressed Dicer but is no longer detectable when the Dicer cDNA is overexpressed. Dicer activity in crude cell lysates is increased in the presence of Ca(2+), most probably by Ca(2+)-dependent proteolytic activation of Dicer. Apparently, Tarbp2 binding to TRPC4 promotes changes of cytosolic Ca(2+) and, thereby, leads to a dynamic regulation of Dicer activity, essentially at low endogenous Dicer concentrations.
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Affiliation(s)
- Jasmin Zimmermann
- From the Institut für Experimentelle und Klinische Pharmakologie und Toxikologie
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9
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Maticzka D, Lange SJ, Costa F, Backofen R. GraphProt: modeling binding preferences of RNA-binding proteins. Genome Biol 2014; 15:R17. [PMID: 24451197 PMCID: PMC4053806 DOI: 10.1186/gb-2014-15-1-r17] [Citation(s) in RCA: 182] [Impact Index Per Article: 18.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/07/2013] [Accepted: 01/22/2014] [Indexed: 12/01/2022] Open
Abstract
We present GraphProt, a computational framework for learning sequence- and structure-binding preferences of RNA-binding proteins (RBPs) from high-throughput experimental data. We benchmark GraphProt, demonstrating that the modeled binding preferences conform to the literature, and showcase the biological relevance and two applications of GraphProt models. First, estimated binding affinities correlate with experimental measurements. Second, predicted Ago2 targets display higher levels of expression upon Ago2 knockdown, whereas control targets do not. Computational binding models, such as those provided by GraphProt, are essential for predicting RBP binding sites and affinities in all tissues. GraphProt is freely available at http://www.bioinf.uni-freiburg.de/Software/GraphProt.
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10
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Distinguishable in vitro binding mode of monomeric TRBP and dimeric PACT with siRNA. PLoS One 2013; 8:e63434. [PMID: 23658827 PMCID: PMC3642127 DOI: 10.1371/journal.pone.0063434] [Citation(s) in RCA: 19] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/15/2013] [Accepted: 04/01/2013] [Indexed: 01/14/2023] Open
Abstract
RNA interference (RNAi) is an evolutionally conserved posttranscriptional gene-silencing mechanism whereby small interfering RNA (siRNA) triggers sequence-specific cleavage of its cognate mRNA. Dicer, Argonaute (Ago), and either TAR-RNA binding protein (TRBP) or a protein activator of PKR (PACT) are the primary components of the RNAi pathway, and they comprise the core of a complex termed the RNA-induced silencing complex (RISC)-loading complex (RLC). TRBP and PACT share similar structural features including three dsRNA binding domains (dsRBDs), and a complex containing Dicer and either TRBP or PACT is considered to sense thermodynamic asymmetry of siRNA ends for guide strand selection. Thus, both TRBP and PACT are thought to participate in the RNAi pathway in an indistinguishable manner, but the differences in siRNA binding mode and the functional involvement of TRBP and PACT are poorly understood. Here, we show in vitro binding patterns of human TRBP and PACT to siRNA using electrophoresis mobility shift analysis and gel filtration chromatography. Our results clearly showed that TRBP and PACT have distinct in vitro siRNA binding patterns from each other. The results suggest that monomeric TRBP binds to siRNA at the higher affinity compared to the affinity for own homodimerization. In contrast, the affinity between PACT and siRNA is lower than that of homodimerization or that between TRBP and siRNA. Thus, siRNA may be more readily incorporated into RLC, interacting with TRBP (instead of PACT) in vivo.
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11
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The multiple functions of TRBP, at the hub of cell responses to viruses, stress, and cancer. Microbiol Mol Biol Rev 2013; 76:652-66. [PMID: 22933564 DOI: 10.1128/mmbr.00012-12] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023] Open
Abstract
The TAR RNA binding protein (TRBP) has emerged as a key player in many cellular processes. First identified as a cellular protein that facilitates the replication of human immunodeficiency virus, TRBP has since been shown to inhibit the activation of protein kinase R (PKR), a protein involved in innate immune responses and the cellular response to stress. It also binds to the PKR activator PACT and regulates its function. TRBP also contributes to RNA interference as an integral part of the minimal RNA-induced silencing complex with Dicer and Argonaute proteins. Due to its multiple functions in the cell, TRBP is involved in oncogenesis when its sequence is mutated or its expression is deregulated. The depletion or overexpression of TRBP results in malignancy, suggesting that the balance of TRBP expression is key to normal cellular function. These studies show that TRBP is multifunctional and mediates cross talk between different pathways. Its activities at the molecular level impact the cellular function from normal development to cancer and the response to infections.
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12
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Abstract
The proteins harboring double-stranded RNA binding domains (dsRBDs) play diverse functional roles such as RNA localization, splicing, editing, export, and translation, yet mechanistic basis and functional significance of dsRBDs remain unclear. To unravel this enigma, we investigated transactivation response RNA binding protein (TRBP) consisting of three dsRBDs, which functions in HIV replication, protein kinase R(PKR)-mediated immune response, and RNA silencing. Here we report an ATP-independent diffusion activity of TRBP exclusively on dsRNA in a length-dependent manner. The first two dsRBDs of TRBP are essential for diffusion, whereas the third dsRBD is dispensable. Two homologs of TRBP, PKR activator and R3D1-L, displayed the same diffusion, implying a universality of the diffusion activity among this protein family. Furthermore, a Dicer-TRBP complex on dsRNA exhibited dynamic diffusion, which was correlated with Dicer's catalytic activity. These results implicate the dsRNA-specific diffusion activity of TRBP that contributes to enhancing siRNA and miRNA processing by Dicer.
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13
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Wang S, Chen AJ, Shi LJ, Zhao XF, Wang JX. TRBP and eIF6 homologue in Marsupenaeus japonicus play crucial roles in antiviral response. PLoS One 2012; 7:e30057. [PMID: 22279564 PMCID: PMC3261181 DOI: 10.1371/journal.pone.0030057] [Citation(s) in RCA: 35] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/01/2011] [Accepted: 12/09/2011] [Indexed: 11/30/2022] Open
Abstract
Plants and invertebrates can suppress viral infection through RNA silencing, mediated by RNA-induced silencing complex (RISC). Trans-activation response RNA-binding protein (TRBP), consisting of three double-stranded RNA-binding domains, is a component of the RISC. In our previous paper, a TRBP homologue in Fenneropenaeus chinensis (Fc-TRBP) was reported to directly bind to eukaryotic initiation factor 6 (Fc-eIF6). In this study, we further characterized the function of TRBP and the involvement of TRBP and eIF6 in antiviral RNA interference (RNAi) pathway of shrimp. The double-stranded RNA binding domains (dsRBDs) B and C of the TRBP from Marsupenaeus japonicus (Mj-TRBP) were found to mediate the interaction of TRBP and eIF6. Gel-shift assays revealed that the N-terminal of Mj-TRBP dsRBD strongly binds to double-stranded RNA (dsRNA) and that the homodimer of the TRBP mediated by the C-terminal dsRBD increases the affinity to dsRNA. RNAi against either Mj-TRBP or Mj-eIF6 impairs the dsRNA-induced sequence-specific RNAi pathway and facilitates the proliferation of white spot syndrome virus (WSSV). These results further proved the important roles of TRBP and eIF6 in the antiviral response of shrimp.
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Affiliation(s)
- Shuai Wang
- The Key Laboratory of Plant Cell Engineering and Germplasm Innovation of Ministry of Education, School of Life Sciences, Shandong University, Jinan, Shandong, People's Republic of China
- Wuhan Institute of Virology, Chinese Academy of Science, Wuchang, Hubei, People's Republic of China
| | - An-Jing Chen
- The Key Laboratory of Plant Cell Engineering and Germplasm Innovation of Ministry of Education, School of Life Sciences, Shandong University, Jinan, Shandong, People's Republic of China
| | - Li-Jie Shi
- The Key Laboratory of Plant Cell Engineering and Germplasm Innovation of Ministry of Education, School of Life Sciences, Shandong University, Jinan, Shandong, People's Republic of China
| | - Xiao-Fan Zhao
- The Key Laboratory of Plant Cell Engineering and Germplasm Innovation of Ministry of Education, School of Life Sciences, Shandong University, Jinan, Shandong, People's Republic of China
| | - Jin-Xing Wang
- The Key Laboratory of Plant Cell Engineering and Germplasm Innovation of Ministry of Education, School of Life Sciences, Shandong University, Jinan, Shandong, People's Republic of China
- * E-mail:
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14
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Yamashita S, Nagata T, Kawazoe M, Takemoto C, Kigawa T, Güntert P, Kobayashi N, Terada T, Shirouzu M, Wakiyama M, Muto Y, Yokoyama S. Structures of the first and second double-stranded RNA-binding domains of human TAR RNA-binding protein. Protein Sci 2011; 20:118-30. [PMID: 21080422 DOI: 10.1002/pro.543] [Citation(s) in RCA: 47] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The TAR RNA-binding Protein (TRBP) is a double-stranded RNA (dsRNA)-binding protein, which binds to Dicer and is required for the RNA interference pathway. TRBP consists of three dsRNA-binding domains (dsRBDs). The first and second dsRBDs (dsRBD1 and dsRBD2, respectively) have affinities for dsRNA, whereas the third dsRBD (dsRBD3) binds to Dicer. In this study, we prepared the single domain fragments of human TRBP corresponding to dsRBD1 and dsRBD2 and solved the crystal structure of dsRBD1 and the solution structure of dsRBD2. The two structures contain an α-β-β-β-α fold, which is common to the dsRBDs. The overall structures of dsRBD1 and dsRBD2 are similar to each other, except for a slight shift of the first α helix. The residues involved in dsRNA binding are conserved. We examined the small interfering RNA (siRNA)-binding properties of these dsRBDs by isothermal titration colorimetry measurements. The dsRBD1 and dsRBD2 fragments both bound to siRNA, with dissociation constants of 220 and 113 nM, respectively. In contrast, the full-length TRBP and its fragment with dsRBD1 and dsRBD2 exhibited much smaller dissociation constants (0.24 and 0.25 nM, respectively), indicating that the tandem dsRBDs bind simultaneously to one siRNA molecule. On the other hand, the loop between the first α helix and the first β strand of dsRBD2, but not dsRBD1, has a Trp residue, which forms hydrophobic and cation-π interactions with the surrounding residues. A circular dichroism analysis revealed that the thermal stability of dsRBD2 is higher than that of dsRBD1 and depends on the Trp residue.
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Affiliation(s)
- Seisuke Yamashita
- RIKEN Systems and Structural Biology Center, 1-7-22 Suehiro-cho, Tsurumi, Yokohama 230-0045, Japan
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15
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Chi YH, Semmes OJ, Jeang KT. A proteomic study of TAR-RNA binding protein (TRBP)-associated factors. Cell Biosci 2011; 1:9. [PMID: 21711701 PMCID: PMC3125213 DOI: 10.1186/2045-3701-1-9] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2011] [Accepted: 02/25/2011] [Indexed: 12/24/2022] Open
Abstract
Background The human TAR RNA-binding protein, TRBP, was first identified and cloned based on its high affinity binding to the small hairpin trans-activation responsive (TAR) RNA of HIV-1. TRBP has more recently been found to be a constituent of the RNA-induced silencing complex (RISC) serving as a Dicer co-factor in the processing of the ~70 nucleotide pre-microRNAs(miRNAs) to 21-25 nucleotide mature miRNAs. Findings Using co-immunoprecipitation and protein-identification by mass spectrometry, we characterized intracellular proteins that complex with TRBP. These interacting proteins include those that have been described to act in protein synthesis, RNA modifications and processing, DNA transcription, and cell proliferation. Conclusions Our findings provide a proteome of factors that may cooperate with TRBP in activities such as miRNA processing and in RNA interference by the RISC complex.
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Affiliation(s)
- Ya-Hui Chi
- Molecular Virology Section, Laboratory of Molecular Microbiology, National Institute of Allergy and Infectious Diseases, National Institutes of Health, Bethesda, MD, USA.
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16
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Lever AML, Jeang KT. Insights into cellular factors that regulate HIV-1 replication in human cells. Biochemistry 2011; 50:920-31. [PMID: 21218853 DOI: 10.1021/bi101805f] [Citation(s) in RCA: 28] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
Retroviruses integrate into the host cell's chromosome. Accordingly, many aspects of the life cycle of retroviruses like HIV-1 are intimately linked to the functions of cellular proteins and RNAs. In this review, we discuss in brief recent genomewide screens for the identification of cellular proteins that assist HIV-1 replication in human cells. We also review findings for other cellular moieties that help or restrict the viral life cycle.
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Affiliation(s)
- Andrew M L Lever
- Addenbrooke's Hospital, University of Cambridge, Cambridge CB2 0QQ, U.K
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17
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Chakravarthy S, Sternberg SH, Kellenberger CA, Doudna JA. Substrate-specific kinetics of Dicer-catalyzed RNA processing. J Mol Biol 2010; 404:392-402. [PMID: 20932845 DOI: 10.1016/j.jmb.2010.09.030] [Citation(s) in RCA: 108] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2010] [Revised: 09/07/2010] [Accepted: 09/14/2010] [Indexed: 12/21/2022]
Abstract
The specialized ribonuclease Dicer plays a central role in eukaryotic gene expression by producing small regulatory RNAs-microRNAs (miRNAs) and short interfering RNAs (siRNAs)-from larger double-stranded RNA (dsRNA) substrates. Although Dicer will cleave both imperfectly base-paired hairpin structures (pre-miRNAs) and perfect duplexes (pre-siRNAs) in vitro, it has not been clear whether these are mechanistically equivalent substrates and how dsRNA binding proteins such as trans-activation response (TAR) RNA binding protein (TRBP) influence substrate selection and RNA processing efficiency. We show here that human Dicer is much faster at processing a pre-miRNA substrate compared to a pre-siRNA substrate under both single and multiple turnover conditions. Maximal cleavage rates (V(max)) calculated by Michaelis-Menten analysis differed by more than 100-fold under multiple turnover conditions. TRBP was found to enhance dicing of both substrates to similar extents, and this stimulation required the two N-terminal dsRNA binding domains of TRBP. These results demonstrate that multiple factors influence dicing kinetics. While TRBP stimulates dicing by enhancing the stability of Dicer-substrate complexes, Dicer itself generates product RNAs at rates determined at least in part by the structural properties of the substrate.
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18
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Watashi K, Yeung ML, Starost MF, Hosmane RS, Jeang KT. Identification of small molecules that suppress microRNA function and reverse tumorigenesis. J Biol Chem 2010; 285:24707-16. [PMID: 20529860 DOI: 10.1074/jbc.m109.062976] [Citation(s) in RCA: 92] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022] Open
Abstract
MicroRNAs (miRNAs) act in post-transcriptional gene silencing and are proposed to function in a wide spectrum of pathologies, including cancers and viral diseases. Currently, to our knowledge, no detailed mechanistic characterization of small molecules that interrupt miRNA pathways have been reported. In screening a small chemical library, we identified compounds that suppress RNA interference activity in cultured cells. Two compounds were characterized; one impaired Dicer activity while the other blocked small RNA-loading into an Argonaute 2 (AGO2) complex. We developed a cell-based model of miRNA-dependent tumorigenesis, and using this model, we observed that treatment of cells with either of the two compounds effectively neutralized tumor growth. These findings indicate that miRNA pathway-suppressing small molecules could potentially reverse tumorigenesis.
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Affiliation(s)
- Koichi Watashi
- Molecular Virology Section, Laboratory of Molecular Microbiology, NIAID, National Institutes of Health, Bethesda, Maryland 20892, USA
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19
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Gredell JA, Dittmer MJ, Wu M, Chan C, Walton SP. Recognition of siRNA asymmetry by TAR RNA binding protein. Biochemistry 2010; 49:3148-55. [PMID: 20184375 DOI: 10.1021/bi902189s] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
The recognition of small interfering RNAs (siRNAs) by the RNA-induced silencing complex (RISC) and its precursor, the RISC loading complex (RLC), is a key step in the RNA interference pathway that controls the subsequent sequence-specific mRNA degradation. In Drosophila, selection of the guide strand has been shown to be mediated by RLC protein R2D2, which senses the relative hybridization stability between the two ends of the siRNA. A protein with similar function has yet to be conclusively identified in humans. We show here that human TAR RNA binding protein (TRBP) alone can bind siRNAs in vitro and sense their asymmetry. We also show that TRBP can bind 21-nucleotide single-stranded RNAs, though with far lower affinity than for double-stranded siRNA, and that TRBP cross-links preferentially to the 3'-ends of the guide strands of siRNAs. This suggests that TRBP binding depends both on the sequences of the siRNA strands and on the relative hybridization stability of the ends of the duplex. Together, these results demonstrate the importance of the siRNA-TRBP interaction in the selection of the siRNA guide strand in RNAi.
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Affiliation(s)
- Joseph A Gredell
- Department of Chemical Engineering and Materials Science, Michigan State University, East Lansing, Michigan 48824-1226, USA
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20
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Daniels SM, Melendez-Peña CE, Scarborough RJ, Daher A, Christensen HS, El Far M, Purcell DFJ, Lainé S, Gatignol A. Characterization of the TRBP domain required for dicer interaction and function in RNA interference. BMC Mol Biol 2009; 10:38. [PMID: 19422693 PMCID: PMC2685382 DOI: 10.1186/1471-2199-10-38] [Citation(s) in RCA: 106] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/30/2008] [Accepted: 05/07/2009] [Indexed: 01/26/2023] Open
Abstract
BACKGROUND Dicer, Ago2 and TRBP are the minimum components of the human RNA-induced silencing complex (RISC). While Dicer and Ago2 are RNases, TRBP is the double-stranded RNA binding protein (dsRBP) that loads small interfering RNA into the RISC. TRBP binds directly to Dicer through its C-terminal domain. RESULTS We show that the TRBP binding site in Dicer is a 165 amino acid (aa) region located between the ATPase and the helicase domains. The binding site in TRBP is a 69 aa domain, called C4, located at the C-terminal end of TRBP. The TRBP1 and TRBP2 isoforms, but not TRBPs lacking the C4 site (TRBPsDeltaC4), co-immunoprecipitated with Dicer. The C4 domain is therefore necessary to bind Dicer, irrespective of the presence of RNA. Immunofluorescence shows that while full-length TRBPs colocalize with Dicer, TRBPsDeltaC4 do not. tarbp2-/- cells, which do not express TRBP, do not support RNA interference (RNAi) mediated by short hairpin or micro RNAs against EGFP. Both TRBPs, but not TRBPsDeltaC4, were able to rescue RNAi function. In human cells with low RNAi activity, addition of TRBP1 or 2, but not TRBPsDeltaC4, rescued RNAi function. CONCLUSION The mapping of the interaction sites between TRBP and Dicer show unique domains that are required for their binding. Since TRBPsDeltaC4 do not interact or colocalize with Dicer, we suggest that TRBP and Dicer, both dsRBPs, do not interact through bound dsRNA. TRBPs, but not TRBPsDeltaC4, rescue RNAi activity in RNAi-compromised cells, indicating that the binding of Dicer to TRBP is critical for RNAi function.
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Affiliation(s)
- Sylvanne M Daniels
- Virus-Cell Interactions Laboratory, Lady Davis Institute for Medical Research, Montréal, Québec, Canada.
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21
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TRBP control of PACT-induced phosphorylation of protein kinase R is reversed by stress. Mol Cell Biol 2008; 29:254-65. [PMID: 18936160 DOI: 10.1128/mcb.01030-08] [Citation(s) in RCA: 94] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The TAR RNA binding Protein, TRBP, inhibits the activity of the interferon-induced protein kinase R (PKR), whereas the PKR activator, PACT, activates its function. TRBP and PACT also bind to each other through their double-stranded RNA binding domains (dsRBDs) and their Medipal domains, which may influence their activity on PKR. In a human immunodeficiency virus (HIV) long terminal repeat-luciferase assay, PACT unexpectedly reversed PKR-mediated inhibition of gene expression. In a translation inhibition assay in HeLa cells, PACT lacking the 13 C-terminal amino acids (PACTDelta13), but not full-length PACT, activated PKR and enhanced interferon-mediated repression. In contrast, in the astrocytic U251MG cells that express low TRBP levels, both proteins activate PKR, but PACTDelta13 is stronger. Immunoprecipitation assays and yeast two-hybrid assays show that TRBP and PACTDelta13 interact very weakly due to a loss of binding in the Medipal domain. PACT-induced PKR phosphorylation was restored in Tarbp2(-/-) murine tail fibroblasts and in HEK293T or HeLa cells when TRBP expression was reduced by RNA interference. In HEK293T and HeLa cells, arsenite, peroxide, and serum starvation-mediated stresses dissociated the TRBP-PACT interaction and increased PACT-induced PKR activation, demonstrating the relevance of this control in a physiological context. Our results demonstrate that in cells, TRBP controls PACT activation of PKR, an activity that is reversed by stress.
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22
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Parker GS, Maity TS, Bass BL. dsRNA binding properties of RDE-4 and TRBP reflect their distinct roles in RNAi. J Mol Biol 2008; 384:967-79. [PMID: 18948111 DOI: 10.1016/j.jmb.2008.10.002] [Citation(s) in RCA: 61] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/20/2008] [Revised: 08/29/2008] [Accepted: 10/01/2008] [Indexed: 11/18/2022]
Abstract
Double-stranded RNA (dsRNA)-binding proteins facilitate Dicer functions in RNA interference. Caenorhabditis elegans RDE-4 facilitates cleavage of long dsRNA to small interfering RNA (siRNA), while human trans-activation response RNA-binding protein (TRBP) functions downstream to pass siRNA to the RNA-induced silencing complex. We show that these distinct in vivo roles are reflected in in vitro binding properties. RDE-4 preferentially binds long dsRNA, while TRBP binds siRNA with an affinity that is independent of dsRNA length. These properties are mechanistically based on the fact that RDE-4 binds cooperatively, via contributions from multiple domains, while TRBP binds noncooperatively. Our studies offer a paradigm for how dsRNA-binding proteins, which are not sequence specific, discern dsRNA length. Additionally, analyses of the ability of RDE-4 deletion constructs and RDE-4/TRBP chimeras to reconstitute Dicer activity suggest RDE-4 promotes activity using its dsRNA-binding motif 2 to bind dsRNA, its linker region to interact with Dicer, and its C-terminus for Dicer activation.
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Affiliation(s)
- Greg S Parker
- University of Utah, Department of Biochemistry/HHMI, Salt Lake City, UT 84112-5650, USA
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23
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HIV-1 TAR element is processed by Dicer to yield a viral micro-RNA involved in chromatin remodeling of the viral LTR. BMC Mol Biol 2007; 8:63. [PMID: 17663774 PMCID: PMC1955452 DOI: 10.1186/1471-2199-8-63] [Citation(s) in RCA: 196] [Impact Index Per Article: 11.5] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/12/2007] [Accepted: 07/30/2007] [Indexed: 12/27/2022] Open
Abstract
Background RNA interference (RNAi) is a regulatory mechanism conserved in higher eukaryotes. The RNAi pathway generates small interfering RNA (siRNA) or micro RNA (miRNA) from either long double stranded stretches of RNA or RNA hairpins, respectively. The siRNA or miRNA then guides an effector complex to a homologous sequence of mRNA and regulates suppression of gene expression through one of several mechanisms. The suppression of gene expression through these mechanisms serves to regulate endogenous gene expression and protect the cell from foreign nucleic acids. There is growing evidence that many viruses have developed in the context of RNAi and express either a suppressor of RNAi or their own viral miRNA. Results In this study we investigated the possibility that the HIV-1 TAR element, a hairpin structure of ~50 nucleotides found at the 5' end of the HIV viral mRNA, is recognized by the RNAi machinery and processed to yield a viral miRNA. We show that the protein Dicer, the enzyme responsible for cleaving miRNA and siRNA from longer RNA sequences, is expressed in CD4+ T-cells. Interestingly, the level of expression of Dicer in monocytes is sub-optimal, suggesting a possible role for RNAi in maintaining latency in T-cells. Using a biotin labeled TAR element we demonstrate that Dicer binds to this structure. We show that recombinant Dicer is capable of cleaving the TAR element in vitro and that TAR derived miRNA is present in HIV-1 infected cell lines and primary T-cell blasts. Finally, we show that a TAR derived miRNA is capable of regulating viral gene expression and may be involved in repressing gene expression through transcriptional silencing. Conclusion HIV-1 TAR element is processed by the Dicer enzyme to create a viral miRNA. This viral miRNA is detectable in infected cells and appears to contribute to viral latency.
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Fenner BJ, Goh W, Kwang J. Dissection of double-stranded RNA binding protein B2 from betanodavirus. J Virol 2007; 81:5449-59. [PMID: 17376906 PMCID: PMC1900263 DOI: 10.1128/jvi.00009-07] [Citation(s) in RCA: 32] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Betanodaviruses are small RNA viruses that infect teleost fish and pose a considerable threat to marine aquaculture production. These viruses possess a small protein, termed B2, which binds to and protects double-stranded RNA. This prevents cleavage of virus-derived double-stranded RNAs (dsRNAs) by Dicer and subsequent production of small interfering RNA (siRNA), which would otherwise induce an RNA-silencing response against the virus. In this work, we have performed charged-to-alanine scanning mutagenesis of the B2 protein in order to identify residues required for dsRNA binding and protection. While the majority of the 19 mutated B2 residues were required for maximal dsRNA binding and protection in vitro, residues R53 and R60 were essential for both activities. Subsequent experiments in fish cells confirmed these findings by showing that mutations in these residues abolished accumulation of both the RNA1 and RNA2 components of the viral genome, in addition to preventing any significant induction of the host interferon gene, Mx. Moreover, an obvious positive correlation was found between dsRNA binding and protection in vitro and RNA1, RNA2, and Mx accumulation in fish cells, further validating the importance of the selected amino acid residues. The same trend was also demonstrated using an RNA silencing system in HeLa cells, with residues R53 and R60 being essential for suppression of RNA silencing. Importantly, we found that siRNA-mediated knockdown of Dicer dramatically enhanced the accumulation of a B2 mutant. In addition, we found that B2 is able to induce apoptosis in fish cells but that this was not the result of dsRNA binding.
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Affiliation(s)
- Beau J Fenner
- Animal Health Biotechnology, Temasek Life Sciences Laboratory, 1 Research Link, National University of Singapore, Singapore 117604, Singapore
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25
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Christensen HS, Daher A, Soye KJ, Frankel LB, Alexander MR, Lainé S, Bannwarth S, Ong CL, Chung SWL, Campbell SM, Purcell DFJ, Gatignol A. Small interfering RNAs against the TAR RNA binding protein, TRBP, a Dicer cofactor, inhibit human immunodeficiency virus type 1 long terminal repeat expression and viral production. J Virol 2007; 81:5121-31. [PMID: 17360756 PMCID: PMC1900231 DOI: 10.1128/jvi.01511-06] [Citation(s) in RCA: 50] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
RNA interference (RNAi) is now widely used for gene silencing in mammalian cells. The mechanism uses the RNA-induced silencing complex, in which Dicer, Ago2, and the human immunodeficiency virus type 1 (HIV-1) TAR RNA binding protein (TRBP) are the main components. TRBP is a protein that increases HIV-1 expression and replication by inhibition of the interferon-induced protein kinase PKR and by increasing translation of viral mRNA. After HIV infection, TRBP could restrict the viral RNA through its activity in RNAi or could contribute more to the enhancement of viral replication. To determine which function will be predominant in the virological context, we analyzed whether the inhibition of its expression could enhance or decrease HIV replication. We have generated small interfering RNAs (siRNAs) against TRBP and found that they decrease HIV-1 long terminal repeat (LTR) basal expression 2-fold, and the LTR Tat transactivated level up to 10-fold. In the context of HIV replication, siRNAs against TRBP decrease the expression of viral genes and inhibit viral production up to fivefold. The moderate increase in PKR expression and activation indicates that it contributes partially to viral gene inhibition. The moderate decrease in micro-RNA (miRNA) biogenesis by TRBP siRNAs suggests that in the context of HIV replication, TRBP functions other than RNAi are predominant. In addition, siRNAs against Dicer decrease viral production twofold and impede miRNA biogenesis. These results suggest that, in the context of HIV replication, TRBP contributes mainly to the enhancement of virus production and that Dicer does not mediate HIV restriction by RNAi.
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Affiliation(s)
- Helen S Christensen
- Department of Microbiology and Immunology, University of Melbourne, Parkville, Australia
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26
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Abstract
Viruses are replication competent genomes which are relatively gene-poor. Even the largest viruses (i.e. Herpesviruses) encode only slightly >200 open reading frames (ORFs). However, because viruses replicate obligatorily inside cells, and considering that evolution may be driven by a principle of economy of scale, it is reasonable to surmise that many viruses have evolved the ability to co-opt cell-encoded proteins to provide needed surrogate functions. An in silico survey of viral sequence databases reveals that most positive-strand and double-stranded RNA viruses have ORFs for RNA helicases. On the other hand, the genomes of retroviruses are devoid of virally-encoded helicase. Here, we review in brief the notion that the human immunodeficiency virus (HIV-1) has adopted the ability to use one or more cellular RNA helicases for its replicative life cycle.
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Affiliation(s)
- Kuan-Teh Jeang
- Molecular Virology Section, Laboratory of Molecular Medicine, NIAID, NIH, Bethesda, MD 20892, USA.
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27
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Ong CL, Thorpe JC, Gorry PR, Bannwarth S, Jaworowski A, Howard JL, Chung S, Campbell S, Christensen HS, Clerzius G, Mouland AJ, Gatignol A, Purcell DFJ. Low TRBP levels support an innate human immunodeficiency virus type 1 resistance in astrocytes by enhancing the PKR antiviral response. J Virol 2005; 79:12763-72. [PMID: 16188979 PMCID: PMC1235869 DOI: 10.1128/jvi.79.20.12763-12772.2005] [Citation(s) in RCA: 64] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Acute human immunodeficiency virus type 1 (HIV-1) replication in astrocytes produces minimal new virus particles due, in part, to inefficient translation of viral structural proteins despite high levels of cytoplasmic viral mRNA. We found that a highly reactive double-stranded (ds) RNA-binding protein kinase (PKR) response in astrocytes underlies this inefficient translation of HIV-1 mRNA. The dsRNA elements made during acute replication of HIV-1 in astrocytes triggers PKR activation and the specific inhibition of HIV-1 protein translation. The heightened PKR response results from relatively low levels of the cellular antagonist of PKR, the TAR RNA binding protein (TRBP). Efficient HIV-1 production was restored in astrocytes by inhibiting the innate PKR response to HIV-1 dsRNA with dominant negative PKR mutants, or PKR knockdown by siRNA gene silencing. Increasing the expression of TRBP in astrocytes restored acute virus production to levels comparable to those observed in permissive cells. Therefore, the robust innate PKR antiviral response in astrocytes results from relatively low levels of TRBP expression and contributes to their restricted infection. Our findings highlight TRBP as a novel cellular target for therapeutic interventions to block productive HIV-1 replication in cells that are fully permissive for HIV-1 infection.
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Affiliation(s)
- Chi L Ong
- Department of Microbiology and Immunology, University of Melbourne, Parkville, Victoria, Australia
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28
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Gatignol A, Lainé S, Clerzius G. Dual role of TRBP in HIV replication and RNA interference: viral diversion of a cellular pathway or evasion from antiviral immunity? Retrovirology 2005; 2:65. [PMID: 16253139 PMCID: PMC1282568 DOI: 10.1186/1742-4690-2-65] [Citation(s) in RCA: 69] [Impact Index Per Article: 3.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/28/2005] [Accepted: 10/27/2005] [Indexed: 11/10/2022] Open
Abstract
Increasing evidence indicates that RNA interference (RNAi) may be used to provide antiviral immunity in mammalian cells. Human micro (mi)RNAs can inhibit the replication of a primate virus, whereas a virally-encoded miRNA from HIV inhibits its own replication. Indirect proof comes from RNAi suppressors encoded by mammalian viruses. Influenza NS1 and Vaccinia E3L proteins can inhibit RNAi in plants, insects and worms. HIV-1 Tat protein and Adenovirus VA RNAs act as RNAi suppressors in mammalian cells. Surprisingly, many RNAi suppressors are also inhibitors of the interferon (IFN)-induced protein kinase R (PKR) but the potential overlap between the RNAi and the IFN pathways remains to be determined. The link between RNAi as an immune response and the IFN pathway may be formed by a cellular protein, TRBP, which has a dual role in HIV replication and RNAi. TRBP has been isolated as an HIV-1 TAR RNA binding protein that increases HIV expression and replication by inhibiting PKR and by increasing translation of structured RNAs. A recent report published in the Journal of Virology shows that the poor replication of HIV in astrocytes is mainly due to a heightened PKR response that can be overcome by supplying TRBP exogenously. In two recent papers published in Nature and EMBO Reports, TRBP is now shown to interact with Dicer and to be required for RNAi mediated by small interfering (si) and micro (mi)RNAs. The apparent discrepancy between TRBP requirement in RNAi and in HIV replication opens the hypotheses that RNAi may be beneficial for HIV-1 replication or that HIV-1 may evade the RNAi restriction by diverting TRBP from Dicer and use it for its own benefit.
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Affiliation(s)
- Anne Gatignol
- Virus-Cell Interactions Laboratory, Lady Davis Institute for Medical Research, and Department of Medicine and Microbiology & Immunology, McGill University, Montréal, Québec, Canada
| | - Sébastien Lainé
- Virus-Cell Interactions Laboratory, Lady Davis Institute for Medical Research, and Department of Medicine and Microbiology & Immunology, McGill University, Montréal, Québec, Canada
| | - Guerline Clerzius
- Virus-Cell Interactions Laboratory, Lady Davis Institute for Medical Research, and Department of Medicine and Microbiology & Immunology, McGill University, Montréal, Québec, Canada
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29
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Huang X, Hutchins B, Patel RC. The C-terminal, third conserved motif of the protein activator PACT plays an essential role in the activation of double-stranded-RNA-dependent protein kinase (PKR). Biochem J 2002; 366:175-86. [PMID: 11985496 PMCID: PMC1222748 DOI: 10.1042/bj20020204] [Citation(s) in RCA: 57] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/31/2002] [Revised: 04/16/2002] [Accepted: 05/02/2002] [Indexed: 11/17/2022]
Abstract
One of the key mediators of the antiviral and antiproliferative actions of interferon is double-stranded-RNA-dependent protein kinase (PKR). PKR activity is also involved in the regulation of cell proliferation, apoptosis and signal transduction. We have recently identified PACT, a novel protein activator of PKR, as an important modulator of PKR activity in cells in the absence of viral infection. PACT heterodimerizes with PKR and activates it by direct protein-protein interactions. Endogenous PACT acts as an activator of PKR in response to diverse stress signals, such as serum starvation and peroxide or arsenite treatment, and is therefore a novel, stress-modulated physiological activator of PKR. In this study, we have characterized the functional domains of PACT that are required for PKR activation. Our results have shown that, unlike the N-terminal conserved domains 1 and 2, the third conserved domain of PACT is dispensable for its binding of double-stranded RNA and inter action with PKR. However, a deletion of domain 3 results in a loss of PKR activation ability, in spite of a normal interaction with PKR, thereby indicating that domain 3 plays an essential role in PKR activation. Purified recombinant domain 3 could also activate PKR efficiently in vitro. Our results indicate that, although dispensable for PACT's high-affinity interaction with PKR, the third motif is essential for PKR activation. In addition, domain 3 and eukaryotic initiation factor 2alpha both interact with PKR through the same region within PKR, which we have mapped to lie between amino acid residues 318 and 551.
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Affiliation(s)
- Xu Huang
- Department of Biological Sciences, University of South Carolina, 700 Sumter Street, Columbia, SC 29208, U.S.A
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30
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Yang C, Maiguel DA, Carrier F. Identification of nucleolin and nucleophosmin as genotoxic stress-responsive RNA-binding proteins. Nucleic Acids Res 2002; 30:2251-60. [PMID: 12000845 PMCID: PMC115285 DOI: 10.1093/nar/30.10.2251] [Citation(s) in RCA: 105] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2001] [Revised: 03/15/2002] [Accepted: 03/15/2002] [Indexed: 01/25/2023] Open
Abstract
Genotoxic stress (DNA damage) can elicit multiple responses in mammalian cells, including the activation of numerous cascades of signal transduction that result in the activation of cellular genes involved in growth control, DNA repair and apoptosis. In an earlier report, we have shown that DNA-damaging agents can also induce the RNA-binding activity of several specific proteins that favor a double stem-loop RNA structure. Here we report the purification and identification of nucleophosmin (NPM) and nucleolin as two genotoxic stress-responsive RNA-binding proteins. UV radiation induces the protein expression levels and RNA-binding activity of NPM while nucleolin RNA-binding activity increases after UV or ionizing radiation exposure. Moreover, we have identified 40 mRNA ligands that are potentially regulated by nucleolin, several of which are stress-responsive transcripts. In addition, our data indicate that activation of nucleolin RNA-binding activity by genotoxic stress is mediated by stress-activated protein kinase p38. Our findings suggest that activation of the RNA-binding properties of nucleolin and NPM is part of the cellular response to genotoxic stress.
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Affiliation(s)
- Chonglin Yang
- University of Maryland, Baltimore, School of Medicine, Biochemistry and Molecular Biology Department, 108 North Greene Street, Baltimore, MD 21201-1503, USA
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Mohr SE, Dillon ST, Boswell RE. The RNA-binding protein Tsunagi interacts with Mago Nashi to establish polarity and localize oskar mRNA during Drosophila oogenesis. Genes Dev 2001; 15:2886-99. [PMID: 11691839 PMCID: PMC312802 DOI: 10.1101/gad.927001] [Citation(s) in RCA: 102] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/11/2001] [Accepted: 09/12/2001] [Indexed: 11/24/2022]
Abstract
In Drosophila melanogaster, formation of the axes and the primordial germ cells is regulated by interactions between the germ line-derived oocyte and the surrounding somatic follicle cells. This reciprocal signaling results in the asymmetric localization of mRNAs and proteins critical for these oogenic processes. Mago Nashi protein interprets the posterior follicle cell-to-oocyte signal to establish the major axes and to determine the fate of the primordial germ cells. Using the yeast two-hybrid system we have identified an RNA-binding protein, Tsunagi, that interacts with Mago Nashi protein. The proteins coimmunoprecipitate and colocalize, indicating that they form a complex in vivo. Immunolocalization reveals that Tsunagi protein is localized within the posterior oocyte cytoplasm during stages 1-5 and 8-9, and that this localization is dependent on wild-type mago nashi function. When tsunagi function is removed from the germ line, egg chambers develop in which the oocyte nucleus fails to migrate, oskar mRNA is not localized within the posterior pole, and dorsal-ventral pattern abnormalities are observed. These results show that a Mago Nashi-Tsunagi protein complex is required for interpreting the posterior follicle cell-to-oocyte signal to define the major body axes and to localize components necessary for determination of the primordial germ cells.
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Affiliation(s)
- S E Mohr
- Department of Molecular, Cellular, and Developmental Biology, University of Colorado, Boulder, Colorado 80309-0347, USA
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32
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Mouland AJ, Mercier J, Luo M, Bernier L, DesGroseillers L, Cohen EA. The double-stranded RNA-binding protein Staufen is incorporated in human immunodeficiency virus type 1: evidence for a role in genomic RNA encapsidation. J Virol 2000; 74:5441-51. [PMID: 10823848 PMCID: PMC112028 DOI: 10.1128/jvi.74.12.5441-5451.2000] [Citation(s) in RCA: 126] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/09/2023] Open
Abstract
Human Staufen (hStau), a double-stranded RNA (dsRNA)-binding protein that is involved in mRNA transport, is incorporated in human immunodeficiency virus type 1 (HIV-1) and in other retroviruses, including HIV-2 and Moloney murine leukemia virus. Sucrose and Optiprep gradient analyses reveal cosedimentation of hStau with purified HIV-1, while subtilisin assays demonstrate that it is internalized. hStau incorporation in HIV-1 is selective, is dependent on an intact functional dsRNA-binding domain, and quantitatively correlates with levels of encapsidated HIV-1 genomic RNA. By coimmunoprecipitation and reverse transcription-PCR analyses, we demonstrate that hStau is associated with HIV-1 genomic RNA in HIV-1-expressing cells and purified virus. Overexpression of hStau enhances virion incorporation levels, and a corresponding, threefold increase in HIV-1 genomic RNA encapsidation levels. This coordinated increase in hStau and genomic RNA packaging had a significant negative effect on viral infectivity. This study is the first to describe hStau within HIV-1 particles and provides evidence that hStau binds HIV-1 genomic RNA, indicating that it may be implicated in retroviral genome selection and packaging into assembling virions.
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MESH Headings
- Binding Sites
- Cell Line
- Centrifugation, Density Gradient
- Cloning, Molecular
- Drosophila Proteins
- Gene Expression
- Gene Products, gag/genetics
- Gene Products, gag/metabolism
- Genome, Viral
- HIV-1/chemistry
- HIV-1/genetics
- HIV-1/metabolism
- HIV-1/pathogenicity
- HIV-2/chemistry
- HIV-2/metabolism
- Humans
- Moloney murine leukemia virus/chemistry
- Moloney murine leukemia virus/metabolism
- Mutation/genetics
- Precipitin Tests
- Protein Precursors/genetics
- Protein Precursors/metabolism
- RNA, Double-Stranded/genetics
- RNA, Double-Stranded/metabolism
- RNA, Viral/analysis
- RNA, Viral/genetics
- RNA, Viral/metabolism
- RNA-Binding Proteins/analysis
- RNA-Binding Proteins/chemistry
- RNA-Binding Proteins/genetics
- RNA-Binding Proteins/metabolism
- Reverse Transcriptase Polymerase Chain Reaction
- Substrate Specificity
- Subtilisin/metabolism
- Transfection
- Virus Assembly
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Affiliation(s)
- A J Mouland
- Departments of Microbiology & Immunology, Université de Montréal, Montreal, Quebec H3C 3J7, Canada
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33
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Coolidge CJ, Patton JG. A new double-stranded RNA-binding protein that interacts with PKR. Nucleic Acids Res 2000; 28:1407-17. [PMID: 10684936 PMCID: PMC111047 DOI: 10.1093/nar/28.6.1407] [Citation(s) in RCA: 26] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/24/1999] [Revised: 01/26/2000] [Accepted: 01/26/2000] [Indexed: 11/13/2022] Open
Abstract
We have identified a 74 kDa double-stranded (ds)RNA-binding protein that shares extensive homology with the mouse spermatid perinuclear RNA-binding (Spnr) protein. p74 contains two dsRNA-binding motifs (dsRBMs) that are essential for preferential binding to dsRNA. Previously, dsRNA-binding proteins were shown to undergo homo- and heterodimerization, raising the possibility that regulation of activity could be controlled by interactions between different family members. Homodimerization is required to activate the dsRNA-dependent protein kinase PKR, whereas hetero-dimerization between PKR and other dsRNA-binding proteins can inhibit kinase activity. We have found that p74 also interacts with PKR, both the wild-type enzyme and a catalytically defective mutant (K296R). While co-expression of p74 and wild-type PKR in the yeast Saccharomyces cerevisiae did not alter PKR activity, co-expression of p74 and the catalytically defective K296R mutant surprisingly resulted in abnormal morphology and cell death in transformants that maintained a high level of p74 expression. These transformants could be rescued by overexpression of the alpha-subunit of wild-type eukaryotic translation initiation factor 2 (eIF2alpha), one of the known substrates for PKR. We hypothesize that competing heterodimers between p74-K296R PKR and eIF2alpha-K296R PKR may control cell growth such that stabilization of the p74-K296R PKR heterodimer induces abnormal morphology and cell death.
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Affiliation(s)
- C J Coolidge
- Department of Molecular Biology, Box 1820, Station B, Vanderbilt University, Nashville, TN 37235, USA
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34
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Ben-Asouli Y, Banai Y, Hauser H, Kaempfer R. Recognition of 5'-terminal TAR structure in human immunodeficiency virus-1 mRNA by eukaryotic translation initiation factor 2. Nucleic Acids Res 2000; 28:1011-8. [PMID: 10648795 PMCID: PMC102579 DOI: 10.1093/nar/28.4.1011] [Citation(s) in RCA: 15] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/26/1999] [Revised: 12/06/1999] [Accepted: 12/15/1999] [Indexed: 11/13/2022] Open
Abstract
TAR, a 59 nt 5'-terminal hairpin in human immuno-deficiency virus 1 (HIV-1) mRNA, binds viral Tat and several cellular proteins. We report that eukaryotic translation initiation factor 2 (eIF2) recognizes TAR. TAR and the AUG initiation codon domain, located well downstream from TAR, both contribute to the affinity of HIV-1 mRNA for eIF2. The affinity of TAR for eIF2 was insensitive to lower stem mutations that modify sequence and structure or to sequence changes throughout the remainder that leave the TAR secondary structure intact. Hence, eIF2 recognizes structure rather than sequence in TAR. The affinity for eIF2 was severely reduced by a 3 nt change that converts the single A bulge into a 7 nt internal loop. T1 footprinting showed that eIF2 protects nucleotides in the loop as well as in the strand opposite the A bulge. Thus, eIF2 recognizes the TAR loop and lower part of the sub-apical stem. Though not contiguous, these regions are brought into proximity in TAR by a bend in the helical structure induced by the UCU bulge; binding of eIF2 opens up the bulge context and apical stem. The ability to bind eIF2 suggests a function for TAR in HIV-1 mRNA translation. Indeed, the 3 nt change that reduces the affinity of TAR for eIF2 impairs the ability of reporter mRNA to compete in translation. Interaction of TAR with eIF2 thus allows HIV-1 mRNA to compete more effectively during protein synthesis.
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Affiliation(s)
- Y Ben-Asouli
- Department of Molecular Virology, The Hebrew University-Hadassah Medical School, 91120 Jerusalem, Israel
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35
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Marión RM, Fortes P, Beloso A, Dotti C, Ortín J. A human sequence homologue of Staufen is an RNA-binding protein that is associated with polysomes and localizes to the rough endoplasmic reticulum. Mol Cell Biol 1999; 19:2212-9. [PMID: 10022908 PMCID: PMC84014 DOI: 10.1128/mcb.19.3.2212] [Citation(s) in RCA: 148] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
In the course of a two-hybrid screen with the NS1 protein of influenza virus, a human clone capable of coding for a protein with high homology to the Staufen protein from Drosophila melanogaster (dmStaufen) was identified. With these sequences used as a probe, cDNAs were isolated from a lambda cDNA library. The encoded protein (hStaufen-like) contained four double-stranded RNA (dsRNA)-binding domains with 55% similarity and 38% identity to those of dmStaufen, including identity at all residues involved in RNA binding. A recombinant protein containing all dsRNA-binding domains was expressed in Escherichia coli as a His-tagged polypeptide. It showed dsRNA binding activity in vitro, with an apparent Kd of 10(-9) M. Using a specific antibody, we detected in human cells a major form of the hStaufen-like protein with an apparent molecular mass of 60 to 65 kDa. The intracellular localization of hStaufen-like protein was investigated by immunofluorescence using a series of markers for the cell compartments. Colocalization was observed with the rough endoplasmic reticulum but not with endosomes, cytoskeleton, or Golgi apparatus. Furthermore, sedimentation analyses indicated that hStaufen-like protein associates with polysomes. These results are discussed in relation to the possible functions of the protein.
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Affiliation(s)
- R M Marión
- Centro Nacional de Biotecnología (CSIC), Cantoblanco, 28049 Madrid, Spain
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36
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Wickham L, Duchaîne T, Luo M, Nabi IR, DesGroseillers L. Mammalian staufen is a double-stranded-RNA- and tubulin-binding protein which localizes to the rough endoplasmic reticulum. Mol Cell Biol 1999; 19:2220-30. [PMID: 10022909 PMCID: PMC84015 DOI: 10.1128/mcb.19.3.2220] [Citation(s) in RCA: 204] [Impact Index Per Article: 8.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Staufen (Stau) is a double-stranded RNA (dsRNA)-binding protein involved in mRNA transport and localization in Drosophila. To understand the molecular mechanisms of mRNA transport in mammals, we cloned human (hStau) and mouse (mStau) staufen cDNAs. In humans, four transcripts arise by differential splicing of the Stau gene and code for two proteins with different N-terminal extremities. In vitro, hStau and mStau bind dsRNA via each of two full-length dsRNA-binding domains and tubulin via a region similar to the microtubule-binding domain of MAP-1B, suggesting that Stau cross-links cytoskeletal and RNA components. Immunofluorescent double labeling of transfected mammalian cells revealed that Stau is localized to the rough endoplasmic reticulum (RER), implicating this RNA-binding protein in mRNA targeting to the RER, perhaps via a multistep process involving microtubules. These results are the first demonstration of the association of an RNA-binding protein in addition to ribosomal proteins, with the RER, implicating this class of proteins in the transport of RNA to its site of translation.
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Affiliation(s)
- L Wickham
- Departments of Biochemistry, University of Montreal, Montreal, Quebec, Canada H3C 3J7
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37
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Kumar M, Carmichael GG. Antisense RNA: function and fate of duplex RNA in cells of higher eukaryotes. Microbiol Mol Biol Rev 1998; 62:1415-34. [PMID: 9841677 PMCID: PMC98951 DOI: 10.1128/mmbr.62.4.1415-1434.1998] [Citation(s) in RCA: 222] [Impact Index Per Article: 8.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
There is ample evidence that cells of higher eukaryotes express double-stranded RNA molecules (dsRNAs) either naturally or as the result of viral infection or aberrant, bidirectional transcriptional readthrough. These duplex molecules can exist in either the cytoplasmic or nuclear compartments. Cells have evolved distinct ways of responding to dsRNAs, depending on the nature and location of the duplexes. Since dsRNA molecules are not thought to exist naturally within the cytoplasm, dsRNA in this compartment is most often associated with viral infections. Cells have evolved defensive strategies against such molecules, primarily involving the interferon response pathway. Nuclear dsRNA, however, does not induce interferons and may play an important posttranscriptional regulatory role. Nuclear dsRNA appears to be the substrate for enzymes which deaminate adenosine residues to inosine residues within the polynucleotide structure, resulting in partial or full unwinding. Extensively modified RNAs are either rapidly degraded or retained within the nucleus, whereas transcripts with few modifications may be transported to the cytoplasm, where they serve to produce altered proteins. This review summarizes our current knowledge about the function and fate of dsRNA in cells of higher eukaryotes and its potential manipulation as a research and therapeutic tool.
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Affiliation(s)
- M Kumar
- Department of Microbiology, University of Connecticut Health Center, Farmington, Connecticut 06030-3205, USA.
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38
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Wilson SA, Brown EC, Kingsman AJ, Kingsman SM. TRIP: a novel double stranded RNA binding protein which interacts with the leucine rich repeat of flightless I. Nucleic Acids Res 1998; 26:3460-7. [PMID: 9671805 PMCID: PMC147727 DOI: 10.1093/nar/26.15.3460] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/13/2022] Open
Abstract
A northwestern screen of a CHO-K1 cell line cDNA library with radiolabelled HIV-1 TAR RNA identified a novel TAR RNA interacting protein, TRIP. The human trip cDNA was also cloned and its expression is induced by phorbol esters. The N-terminus of TRIP shows high homology to the coiled coil domain of FLAP, a protein which binds the leucine-rich repeat (LRR) of Flightless I (FLI) and the interaction of TRIP with the FLI LRR has been confirmed in vitro . TRIP does not bind single stranded DNA or RNA significantly and binds double stranded DNA weakly. In contrast, TRIP binds double stranded RNA with high affinity and two molecules of TRIP bind the TAR stem. The RNA binding domain has been identified and encompasses a lysine-rich motif. A TRIP-GFP fusion is localised in the cytoplasm and excluded from the nucleus. FLI has a C-terminal gelsolin-like domain which binds actin and therefore the association of TRIP with the FLI LRR may provide a link between the actin cytoskeleton and RNA in mammalian cells.
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Affiliation(s)
- S A Wilson
- Department of Biochemistry, University of Oxford, South Parks Road, Oxford OX1 3QU, UK
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39
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Cerritelli SM, Fedoroff OY, Reid BR, Crouch RJ. A common 40 amino acid motif in eukaryotic RNases H1 and caulimovirus ORF VI proteins binds to duplex RNAs. Nucleic Acids Res 1998; 26:1834-40. [PMID: 9512560 PMCID: PMC147478 DOI: 10.1093/nar/26.7.1834] [Citation(s) in RCA: 43] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/06/2023] Open
Abstract
Eukaryotic RNases H from Saccharomyces cerevisiae , Schizosaccharomyces pombe and Crithidia fasciculata , unlike the related Escherichia coli RNase HI, contain a non-RNase H domain with a common motif. Previously we showed that S.cerevisiae RNase H1 binds to duplex RNAs (either RNA-DNA hybrids or double-stranded RNA) through a region related to the double-stranded RNA binding motif. A very similar amino acid sequence is present in caulimovirus ORF VI proteins. The hallmark of the RNase H/caulimovirus nucleic acid binding motif is a stretch of 40 amino acids with 11 highly conserved residues, seven of which are aromatic. Point mutations, insertions and deletions indicated that integrity of the motif is important for binding. However, additional amino acids are required because a minimal peptide containing the motif was disordered in solution and failed to bind to duplex RNAs, whereas a longer protein bound well. Schizosaccharomyces pombe RNase H1 also bound to duplex RNAs, as did proteins in which the S.cerevisiae RNase H1 binding motif was replaced by either the C.fasciculata or by the cauliflower mosaic virus ORF VI sequence. The similarity between the RNase H and the caulimovirus domain suggest a common interaction with duplex RNAs of these two different groups of proteins.
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Affiliation(s)
- S M Cerritelli
- Laboratory of Molecular Genetics, National Institute of Child Health and Human Development, National Institutes of Health, Bethesda, MD 20892, USA
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40
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Abstract
Escherichia coli ribonucleases (RNases) HII, III, II, PH and D have been used to characterise new and known viral, bacterial, archaeal and eucaryotic sequences similar to these endo- (HII and III) and exoribonucleases (II, PH and D). Statistical models, hidden Markov models (HMMs), were created for the RNase HII, III, II and PH and D families as well as a double-stranded RNA binding domain present in RNase III. Results suggest that the RNase D family, which includes Werner syndrome protein and the 100 kDa antigenic component of the human polymyositis scleroderma (PMSCL) autoantigen, is a 3'-->5' exoribonuclease structurally and functionally related to the 3'-->5' exodeoxyribonuclease domain of DNA polymerases. Polynucleotide phosphorylases and the RNase PH family, which includes the 75 kDa PMSCL autoantigen, possess a common domain suggesting similar structures and mechanisms of action for these 3'-->5' phosphorolytic enzymes. Examination of HMM-generated multiple sequences alignments for each family suggest amino acids that may be important for their structure, substrate binding and/or catalysis.
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Affiliation(s)
- I S Mian
- Sinsheimer Laboratories, University of California Santa Cruz, Santa Cruz, CA 95064, USA.
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41
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Donzeau M, Winnacker EL, Meisterernst M. Specific repression of Tax trans-activation by TAR RNA-binding protein TRBP. J Virol 1997; 71:2628-35. [PMID: 9060615 PMCID: PMC191384 DOI: 10.1128/jvi.71.4.2628-2635.1997] [Citation(s) in RCA: 12] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
The human T-cell leukemia virus type 1 (HTLV-1)-encoded Tax protein activates transcription from the long terminal repetition via association with host cellular factors. In this study, we searched for cellular proteins that interact with Tax and modulate its activity by using the yeast two-hybrid system. One of the strongest interactors was found to be identical with TRBP, which was previously shown to bind to the RNA encoded by the Tat response element of human immunodeficiency virus type 1. Interactions are demonstrated with Escherichia coli-expressed proteins in vitro and in mammalian cells, using one- and two-hybrid systems, and with antibodies that coprecipitate Tax and TRBP at physiological TRBP concentrations. Moreover, TRBP, when directed into the cytoplasm, is capable of preventing transport of Tax into the nucleus. A 60-amino-acid polypeptide suffices for binding to Tax. TRBP inhibits activation of transcription by both Tax and GAL4-Tax fusion proteins. Inhibition is specific for Tax and is not seen with the other activators tested. Our data are consistent with the interpretation that TRBP inhibits the interplay of Tax with the transcription machinery or accessory factors.
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Affiliation(s)
- M Donzeau
- Laboratorium für Molekulare Biologie-Genzentrum der Ludwig-Maximilians-Universität München, Munich, Germany
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42
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Benkirane M, Neuveut C, Chun RF, Smith SM, Samuel CE, Gatignol A, Jeang KT. Oncogenic potential of TAR RNA binding protein TRBP and its regulatory interaction with RNA-dependent protein kinase PKR. EMBO J 1997; 16:611-24. [PMID: 9034343 PMCID: PMC1169664 DOI: 10.1093/emboj/16.3.611] [Citation(s) in RCA: 187] [Impact Index Per Article: 6.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
TAR RNA binding protein (TRBP) belongs to an RNA binding protein family that includes the double-stranded RNA-activated protein kinase (PKR), Drosophila Staufen and Xenopus xlrbpa. One member of this family, PKR, is a serine/threonine kinase which has anti-viral and anti-proliferative effects. In this study we show that TRBP is a cellular down-regulator of PKR function. Assaying expression from an infectious HIV-1 molecular clone, we found that PKR inhibited viral protein synthesis and that over-expression of TRBP effectively countered this inhibition. In intracellular and in cell-free assays we show that TRBP directly inhibits PKR autophosphorylation through an RNA binding-independent pathway. Biologically, TRBP serves a growth-promoting role; cells that overexpress TRBP exhibit transformed phenotypes. Our results demonstrate the oncogenic potential of TRBP and are consistent with the notion that intracellular PKR function contributes physiologically towards regulating cellular proliferation.
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Affiliation(s)
- M Benkirane
- Laboratory of Molecular Microbiology, NIAID, NIH, Bethesda, MD 20892-0460, USA
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43
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Lee K, Fajardo MA, Braun RE. A testis cytoplasmic RNA-binding protein that has the properties of a translational repressor. Mol Cell Biol 1996; 16:3023-34. [PMID: 8649414 PMCID: PMC231297 DOI: 10.1128/mcb.16.6.3023] [Citation(s) in RCA: 78] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
Translation of the mouse protamine 1 (Prm-1) mRNA is repressed for several days during male germ cell differentiation. With the hope of cloning genes that regulate the translational repression of Prm-1, we screened male germ cell cDNA expression libraries with the 3' untranslated region of the Prm-1 RNA. From this screen we obtained two independent clones that encode Prbp, a Prm-1 RNA-binding protein. Prbp contains two copies of a double-stranded-RNA-binding domain. In vitro, the protein binds to a portion of the Prm-1 3' untranslated region previously shown to be sufficient for translational repression in transgenic mice, as well as to poly(I). poly(C). Prbp protein is present in multiple forms in cytoplasmic extracts prepared from wild-type mouse testes and is absent from testes of germ cell-deficient mouse mutants, suggesting that Prbp is restricted to the germ cells of the testis. Immunocytochemical localization confirmed that Prbp is present in the cytoplasmic compartment of late-stage meiotic cells and haploid round spermatids. Recombinant Prbp protein inhibits the translation of multiple mRNAs in a wheat germ lysate, suggesting that Prbp acts to repress translation in round spermatids. While this protein lacks complete specificity for Prm-1-containing RNAs in vitro, the properties of Prbp are consistent with it acting as a general repressor of translation.
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Affiliation(s)
- K Lee
- Department of Genetics, University of Washington, Seattle 98195, USA
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44
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Liu Y, Samuel CE. Mechanism of interferon action: functionally distinct RNA-binding and catalytic domains in the interferon-inducible, double-stranded RNA-specific adenosine deaminase. J Virol 1996; 70:1961-8. [PMID: 8627722 PMCID: PMC190025 DOI: 10.1128/jvi.70.3.1961-1968.1996] [Citation(s) in RCA: 64] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/01/2023] Open
Abstract
The 1,226-amino-acid sequence of the interferon-inducible double-stranded RNA-specific adenosine deaminase (dsRAD) contains three copies (RI, RII, and RIII) of the highly conserved subdomain R motif commonly found in double-stranded RNA-binding proteins. We have examined the effects of equivalent site-directed mutations in each of the three R-motif copies of dsRAD on RNA-binding activity and adenosine deaminase enzyme activity. Mutations of the R motifs were analyzed alone as single mutants and in combination with each other. The results suggest that the RIII copy is the most important of the three R motifs for dsRAD activity and that the RII copy is the least important. The RIII mutant lacked detectable enzymatic activity and displayed greatly diminished RNA-binding activity. Site-directed mutations within the highly conserved CHAE sequence of the postulated C-terminal deaminase catalytic domain destroyed enzymatic activity but did not affect RNA-binding activity. These results indicate that the three copies of the RNA-binding R subdomain are likely functionally distinct from each other and also from the catalytic domain of dsRAD.
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Affiliation(s)
- Y Liu
- Department of Molecular, Cellular and Developmental Biology, University of California, Santa Barbara 93106, USA
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45
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Cosentino GP, Venkatesan S, Serluca FC, Green SR, Mathews MB, Sonenberg N. Double-stranded-RNA-dependent protein kinase and TAR RNA-binding protein form homo- and heterodimers in vivo. Proc Natl Acad Sci U S A 1995; 92:9445-9. [PMID: 7568151 PMCID: PMC40818 DOI: 10.1073/pnas.92.21.9445] [Citation(s) in RCA: 146] [Impact Index Per Article: 5.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The yeast two-hybrid system and far-Western protein blot analysis were used to demonstrate dimerization of human double-stranded RNA (dsRNA)-dependent protein kinase (PKR) in vivo and in vitro. A catalytically inactive mutant of PKR with a single amino acid substitution (K296R) was found to dimerize in vivo, and a mutant with a deletion of the catalytic domain of PKR retained the ability to dimerize. In contrast, deletion of the two dsRNA-binding motifs in the N-terminal regulatory domain of PKR abolished dimerization. In vitro dimerization of the dsRNA-binding domain required the presence of dsRNA. These results suggest that the binding of dsRNA by PKR is necessary for dimerization. The mammalian dsRNA-binding protein TRBP, originally identified on the basis of its ability to bind the transactivation region (TAR) of human immunodeficiency virus RNA, also dimerized with itself and with PKR in the yeast assay. Taken together, these results suggest that complexes consisting of different combinations of dsRNA-binding proteins may exist in vivo. Such complexes could mediate differential effects on gene expression and control of cell growth.
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Affiliation(s)
- G P Cosentino
- Department of Biochemistry, McGill University, Montreal, QC Canada
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Rotondo G, Gillespie M, Frendewey D. Rescue of the fission yeast snRNA synthesis mutant snm1 by overexpression of the double-strand-specific Pac1 ribonuclease. MOLECULAR & GENERAL GENETICS : MGG 1995; 247:698-708. [PMID: 7616961 DOI: 10.1007/bf00290401] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/26/2023]
Abstract
The Schizosaccharomyces pombe temperature-sensitive mutant snm1 maintains reduced steady-state quantities of the spliceosomal small nuclear RNAs (snRNAs) and the RNA subunit of the tRNA processing enzyme RNase P. We report here the isolation of the pac1+ gene as a multi-copy suppressor of snm1. The pac1+ gene was previously identified as a suppressor of the ran1 mutant and by its ability to cause sterility when overexpressed. The pac1+ gene encodes a double-strand-specific ribonuclease that is similar to RNase III, an RNA processing and turnover enzyme in Escherichia coli. To investigate the essential structural features of the Pac1 RNase, we altered the pac1+ gene by deletion and point mutation and tested the mutant constructs for their ability to complement the snm1 and ran1 mutants and to cause sterility. These experiments identified four essential amino acids in the Pac1 sequence: glycine 178, glutamic acid 251, and valines 346 and 347. These amino acids are conserved in all RNase III-like proteins. The glycine and glutamic acid residues were previously identified as essential for E. coli RNase III activity. The valines are conserved in an element found in a family of double-stranded RNA binding proteins. Our results support the hypothesis that the Pac1 RNase is an RNase III homolog and suggest a role for the Pac1 RNase in snRNA metabolism.
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Affiliation(s)
- G Rotondo
- Department of Microbiology, New York University Medical Center, NY 10016, USA
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47
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Atreya CD, Singh NK, Nakhasi HL. The rubella virus RNA binding activity of human calreticulin is localized to the N-terminal domain. J Virol 1995; 69:3848-51. [PMID: 7745733 PMCID: PMC189103 DOI: 10.1128/jvi.69.6.3848-3851.1995] [Citation(s) in RCA: 30] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
The rubella virus RNA 3' cis-acting element, which is essential for viral negative-strand RNA synthesis, is specifically bound by autophosphorylated calreticulin. Autophosphorylation in recombinant human calreticulin occurs on serine and threonine residues. The RNA-binding and autophosphorylation activities were localized to the N-terminal 180 amino acids. Furthermore, N-terminal deletions revealed that the RNA-binding activity of calreticulin is abrogated upon deletion of the first 10 residues, whereas the autophosphorylation activity resides between amino acids 60 and 180. These results indicate that both the rubella virus RNA-binding and autophosphorylation activities of calreticulin are present in the N-terminal domain.
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Affiliation(s)
- C D Atreya
- Laboratory of Molecular Pharmacology, Food and Drug Administration, Bethesda, Maryland 20892, USA
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48
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Schumacher JM, Lee K, Edelhoff S, Braun RE. Spnr, a murine RNA-binding protein that is localized to cytoplasmic microtubules. J Cell Biol 1995; 129:1023-32. [PMID: 7744952 PMCID: PMC2120489 DOI: 10.1083/jcb.129.4.1023] [Citation(s) in RCA: 76] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/26/2023] Open
Abstract
Previous studies in transgenic mice have established the importance of the 3' untranslated region (UTR) of the spermatid-specific protamine-1 (Prm-1) mRNA in its translational control during male germ cell development. To clone genes that mediate the translational repression or activation of the Prm-1 mRNA, we screened cDNA expression libraries made with RNA from pachytene spermatocytes and round spermatids, with an RNA probe corresponding to the 3' UTR of Prm-1. We obtained six independent clones that encode Spnr, a spermatid perinuclear RNA-binding protein. Spnr is a 71-kD protein that contains two previously described RNA binding domains. The Spnr mRNA is expressed at high levels in the testis, ovary, and brain, and is present in multiple forms in those tissues. Immunolocalization of the Spnr protein within the testis shows that it is expressed exclusively in postmeiotic germ cells and that it is localized to the manchette, a spermatid-specific microtubular array. Although the Spnr protein is expressed too late to be directly involved in the translational repression of Prm-1 specifically, we suggest that the Spnr protein may be involved in other aspects of spermatid RNA metabolism, such as RNA transport or translational activation.
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Affiliation(s)
- J M Schumacher
- Department of Genetics, University of Washington, Seattle 98195, USA
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49
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O'Connell MA, Krause S, Higuchi M, Hsuan JJ, Totty NF, Jenny A, Keller W. Cloning of cDNAs encoding mammalian double-stranded RNA-specific adenosine deaminase. Mol Cell Biol 1995; 15:1389-97. [PMID: 7862132 PMCID: PMC230363 DOI: 10.1128/mcb.15.3.1389] [Citation(s) in RCA: 210] [Impact Index Per Article: 7.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
Double-stranded RNA (dsRNA)-specific adenosine deaminase converts adenosine to inosine in dsRNA. The protein has been purified from calf thymus, and here we describe the cloning of cDNAs encoding both the human and rat proteins as well as a partial bovine clone. The human and rat clones are very similar at the amino acid level except at their N termini and contain three dsRNA binding motifs, a putative nuclear targeting signal, and a possible deaminase motif. Antibodies raised against the protein encoded by the partial bovine clone specifically recognize the calf thymus dsRNA adenosine deaminase. Furthermore, the antibodies can immunodeplete a calf thymus extract of dsRNA adenosine deaminase activity, and the activity can be restored by addition of pure bovine deaminase. Staining of HeLa cells confirms the nuclear localization of the dsRNA-specific adenosine deaminase. In situ hybridization in rat brain slices indicates a widespread distribution of the enzyme in the brain.
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Affiliation(s)
- M A O'Connell
- Department of Cell Biology, University of Basel, Switzerland
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50
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Chang YN, Kenan DJ, Keene JD, Gatignol A, Jeang KT. Direct interactions between autoantigen La and human immunodeficiency virus leader RNA. J Virol 1994; 68:7008-20. [PMID: 7933083 PMCID: PMC237138 DOI: 10.1128/jvi.68.11.7008-7020.1994] [Citation(s) in RCA: 99] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/27/2023] Open
Abstract
We have characterized the in vivo and in vitro binding of human La protein to the human immunodeficiency virus type 1 (HIV-1) leader RNA, the trans-activation response element (TAR). In immunoprecipitation studies using anti-La serum, La-TAR ribonucleoproteins were recovered from HIV-1-infected lymphocytes. Further characterization of this interaction revealed that La has preference for the TAR stem. However, TAR RNA recognition tolerated changes in the primary sequence of the stem as long as the secondary structure was conserved. This structural aspect of La-TAR recognition was confirmed in competition studies in which certain homopolymers influenced complex formation while other single-stranded and double-stranded RNAs had no effect. Deletion mutants of recombinant La protein were used to demonstrate that the residues responsible for binding to polymerase III precursor transcripts overlapped the binding domain for the TAR leader RNA. This finding of a direct interaction between La and TAR has functional implications for translational regulation of HIV-1 mRNAs as demonstrated in the accompanying report (Y. V. Svitkin, A. Pause, and N. Sonenberg, J. Virol. 68:7001-7007, 1994).
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Affiliation(s)
- Y N Chang
- Molecular Virology Section, National Institute of Allergy and Infectious Diseases, NIH, Bethesda, MD 20892
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