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Boerneke MA, Dibrov SM, Gu J, Wyles DL, Hermann T. Functional conservation despite structural divergence in ligand-responsive RNA switches. Proc Natl Acad Sci U S A 2014; 111:15952-7. [PMID: 25349403 PMCID: PMC4234586 DOI: 10.1073/pnas.1414678111] [Citation(s) in RCA: 37] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/25/2023] Open
Abstract
An internal ribosome entry site (IRES) initiates protein synthesis in RNA viruses, including the hepatitis C virus (HCV). We have discovered ligand-responsive conformational switches in viral IRES elements. Modular RNA motifs of greatly distinct sequence and local secondary structure have been found to serve as functionally conserved switches involved in viral IRES-driven translation and may be captured by identical cognate ligands. The RNA motifs described here constitute a new paradigm for ligand-captured switches that differ from metabolite-sensing riboswitches with regard to their small size, as well as the intrinsic stability and structural definition of the constitutive conformational states. These viral RNA modules represent the simplest form of ligand-responsive mechanical switches in nucleic acids.
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Affiliation(s)
| | | | - Jing Gu
- Department of Chemistry and Biochemistry
| | - David L Wyles
- Division of Infectious Diseases, Department of Medicine, and
| | - Thomas Hermann
- Department of Chemistry and Biochemistry, Center for Drug Discovery Innovation, University of California, San Diego, La Jolla, CA 92093
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52
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Othman Z, Sulaiman MK, Willcocks MM, Ulryck N, Blackbourn DJ, Sargueil B, Roberts LO, Locker N. Functional analysis of Kaposi's sarcoma-associated herpesvirus vFLIP expression reveals a new mode of IRES-mediated translation. RNA (NEW YORK, N.Y.) 2014; 20:1803-1814. [PMID: 25246653 PMCID: PMC4201831 DOI: 10.1261/rna.045328.114] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 03/17/2014] [Accepted: 08/26/2014] [Indexed: 06/03/2023]
Abstract
Kaposi's sarcoma-associated herpesvirus (KSHV) is an oncogenic virus, the etiological agent of Kaposi's sarcoma (KS) and primary effusion lymphoma (PEL). One of the key viral proteins that contributes to tumorigenesis is vFLIP, a viral homolog of the FLICE inhibitory protein. This KSHV protein interacts with the NFκB pathway to trigger the expression of antiapoptotic and proinflammatory genes and ultimately leads to tumor formation. The expression of vFLIP is regulated at the translational level by an internal ribosomal entry site (IRES) element. However, the precise mechanism by which ribosomes are recruited internally and the exact location of the IRES has remained elusive. Here we show that a 252-nt fragment directly upstream of vFLIP, within a coding region, directs translation. We have established its RNA structure and demonstrate that IRES activity requires the presence of eIF4A and an intact eIF4G. Furthermore, and unusually for an IRES, eIF4E is part of the complex assembled onto the vFLIP IRES to direct translation. These molecular interactions define a new paradigm for IRES-mediated translation.
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Affiliation(s)
- Zulkefley Othman
- Faculty of Health and Medical Sciences, School of Biosciences and Medicine, University of Surrey, Guildford GU27HE, United Kingdom
| | - Mariam K Sulaiman
- Faculty of Health and Medical Sciences, School of Biosciences and Medicine, University of Surrey, Guildford GU27HE, United Kingdom
| | - Margaret M Willcocks
- Faculty of Health and Medical Sciences, School of Biosciences and Medicine, University of Surrey, Guildford GU27HE, United Kingdom
| | - Nathalie Ulryck
- Faculté des Sciences Pharmaceutiques et Biologiques, UMR8015, Université Paris Descartes, 75270 Paris, France
| | - David J Blackbourn
- Faculty of Health and Medical Sciences, School of Biosciences and Medicine, University of Surrey, Guildford GU27HE, United Kingdom
| | - Bruno Sargueil
- Faculté des Sciences Pharmaceutiques et Biologiques, UMR8015, Université Paris Descartes, 75270 Paris, France
| | - Lisa O Roberts
- Faculty of Health and Medical Sciences, School of Biosciences and Medicine, University of Surrey, Guildford GU27HE, United Kingdom
| | - Nicolas Locker
- Faculty of Health and Medical Sciences, School of Biosciences and Medicine, University of Surrey, Guildford GU27HE, United Kingdom
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53
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Khawaja A, Vopalensky V, Pospisek M. Understanding the potential of hepatitis C virus internal ribosome entry site domains to modulate translation initiation via their structure and function. WILEY INTERDISCIPLINARY REVIEWS-RNA 2014; 6:211-24. [PMID: 25352252 PMCID: PMC4361049 DOI: 10.1002/wrna.1268] [Citation(s) in RCA: 24] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 06/14/2014] [Revised: 08/31/2014] [Accepted: 09/02/2014] [Indexed: 12/16/2022]
Abstract
Translation initiation in the hepatitis C virus (HCV) occurs through a cap-independent mechanism that involves an internal ribosome entry site (IRES) capable of interacting with and utilizing the eukaryotic translational machinery. In this review, we focus on the structural configuration of the different HCV IRES domains and the impact of IRES primary sequence variations on secondary structure conservation and function. In some cases, multiple mutations, even those scattered across different domains, led to restoration of the translational activity of the HCV IRES, although the individual occurrences of these mutations were found to be deleterious. We propose that such observation may be attributed to probable long-range inter- and/or intra-domain functional interactions. The precise functioning of the HCV IRES requires the specific interaction of its domains with ribosomal subunits and a subset of eukaryotic translation initiation factors (eIFs). The structural conformation, sequence preservation and variability, and translational machinery association with the HCV IRES regions are also thoroughly discussed, along with other factors that can affect and influence the formation of translation initiation complexes. WIREs RNA 2015, 6:211–224. doi: 10.1002/wrna.1268
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Affiliation(s)
- Anas Khawaja
- Department of Genetics and Microbiology, Faculty of Science, Charles University in Prague, Prague 2, Czech Republic
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54
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Base pairing between hepatitis C virus RNA and 18S rRNA is required for IRES-dependent translation initiation in vivo. Proc Natl Acad Sci U S A 2014; 111:15385-9. [PMID: 25313046 DOI: 10.1073/pnas.1413472111] [Citation(s) in RCA: 41] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
Degeneracy in eukaryotic translation initiation is evident in the initiation strategies of various viruses. Hepatitis C virus (HCV) provides an exceptional example--translation of the HCV RNA is facilitated by an internal ribosome entry site (IRES) that can autonomously bind a 40S ribosomal subunit and accurately position it at the initiation codon. This binding involves both ribosomal protein and 18S ribosomal RNA (rRNA) interactions. In this study, we evaluate the functional significance of the rRNA interaction and show that HCV IRES activity requires a 3-nt Watson-Crick base-pairing interaction between the apical loop of subdomain IIId in the IRES and helix 26 in 18S rRNA. Mutations of these nucleotides in either RNA dramatically disrupted IRES activity. The activities of the mutated HCV IRESs could be restored by compensatory mutations in the 18S rRNA. The effects of the 18S rRNA mutations appeared to be specific inasmuch as ribosomes containing these mutations did not support translation mediated by the wild-type HCV IRES, but did not block translation mediated by the cap structure or other viral IRESs. The present study provides, to our knowledge, the first functional demonstration of mRNA-rRNA base pairing in mammalian cells. By contrast with other rRNA-binding sites in mRNAs that can enhance translation as independent elements, e.g., the Shine-Dalgarno sequence in prokaryotes, the rRNA-binding site in the HCV IRES functions as an essential component of a more complex interaction.
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55
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Branilović MG, Tomić S. Computational study of the structural plasticity and the ligand binding affinity of the IRES subdomain IIa. MOLECULAR BIOSYSTEMS 2014; 10:3272-9. [PMID: 25308715 DOI: 10.1039/c4mb00469h] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/06/2023]
Abstract
The internal ribosome entry site (IRES) of hepatitis C virus (HCV) drives noncanonical initiation of protein synthesis necessary for viral replication. In order to fulfil its role in HCV translation initiation its subdomain IIa should adopt an L-shaped conformation. However, according to the present knowledge, the bent topology of IIa would prevent the progression of the ribosome from initiation to productive translation. In order to be released from the ribosome, IIa should transform from the bended to an extended form. With the purpose to study the plasticity and stability of the IRES subdomain IIa we performed detailed molecular dynamics (MD) simulations of the ligand free RNA and its (native and mutated) complexes with the potential HCV inhibitors. We have shown that upon ligand removal conformation of the IIa subdomain changed from an extended into an L-shaped one during several tens of ns. Differently, binding of the benzimidazole translation inhibitors locked IIa in the extended conformation. On the other hand, the newly discovered translation inhibitor diaminopiperidine (DAP), in agreement with the experimentally based assumptions, stabilized IIa RNA in the bent conformation during MD simulations. Apparently the efficient locking of subdomain IIa in one form is one of the requirements the HCV RNA targeting drugs should fulfil.
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Affiliation(s)
- Marina Grabar Branilović
- Laboratory for Chemical and Biological Crystallography, Division of Physical Chemistry, Ruđer Bošković Institute, HR 10002 Zagreb, P.O.B. 180, Croatia.
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56
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Interconversion between parallel and antiparallel conformations of a 4H RNA junction in domain 3 of foot-and-mouth disease virus IRES captured by dynamics simulations. Biophys J 2014; 106:447-58. [PMID: 24461020 DOI: 10.1016/j.bpj.2013.12.008] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/07/2013] [Revised: 11/23/2013] [Accepted: 12/03/2013] [Indexed: 01/31/2023] Open
Abstract
RNA junctions are common secondary structural elements present in a wide range of RNA species. They play crucial roles in directing the overall folding of RNA molecules as well as in a variety of biological functions. In particular, there has been great interest in the dynamics of RNA junctions, including conformational pathways of fully base-paired 4-way (4H) RNA junctions. In such constructs, all nucleotides participate in one of the four double-stranded stem regions, with no connecting loops. Dynamical aspects of these 4H RNAs are interesting because frequent interchanges between parallel and antiparallel conformations are thought to occur without binding of other factors. Gel electrophoresis and single-molecule fluorescence resonance energy transfer experiments have suggested two possible pathways: one involves a helical rearrangement via disruption of coaxial stacking, and the other occurs by a rotation between the helical axes of coaxially stacked conformers. Employing molecular dynamics simulations, we explore this conformational variability in a 4H junction derived from domain 3 of the foot-and-mouth disease virus internal ribosome entry site (IRES); this junction contains highly conserved motifs for RNA-RNA and RNA-protein interactions, important for IRES activity. Our simulations capture transitions of the 4H junction between parallel and antiparallel conformations. The interconversion is virtually barrier-free and occurs via a rotation between the axes of coaxially stacked helices with a transient perpendicular intermediate. We characterize this transition, with various interhelical orientations, by pseudodihedral angle and interhelical distance measures. The high flexibility of the junction, as also demonstrated experimentally, is suitable for IRES activity. Because foot-and-mouth disease virus IRES structure depends on long-range interactions involving domain 3, the perpendicular intermediate, which maintains coaxial stacking of helices and thereby consensus primary and secondary structure information, may be beneficial for guiding the overall organization of the RNA system in domain 3.
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57
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Malygin AA, Shatsky IN, Karpova GG. Proteins of the human 40S ribosomal subunit involved in hepatitis C IRES binding as revealed from fluorescent labeling. BIOCHEMISTRY (MOSCOW) 2014; 78:53-9. [PMID: 23379559 DOI: 10.1134/s0006297913010069] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/09/2023]
Abstract
Initiation of translation of genomic RNA (gRNA) of hepatitis C virus (HCV) is provided by a highly structured fragment in its 5'-untranslated region, the so-called Internal Ribosome Entry Site (IRES). In this work, the exposed NH2-groups of proteins in the 40S subunit of the human ribosome and in its binary complexes with RNA transcripts corresponding to the full-size HCV IRES or its fragments were probed using the N-hydroxysuccinimide derivative of the fluorescent dye Cy3. Comparison of efficiencies of modification of ribosomal proteins in free subunits and in their binary complexes with the RNA transcripts revealed ribosomal proteins involved in the HCV IRES binding. It was found that binding of the 40S subunits with the RNA transcript corresponding to full-size HCV IRES results in a decrease in modification levels of ribosomal protein (rp) S27 and, to a lesser extent of rpS10; also, a noticeable decrease in the efficiency of labeling of proteins RACK1/S2/S3a was observed. When a fragment of HCV IRES containing the initial part of the open reading frame (ORF) of the viral gRNA was deleted, the level of rpS10 modification became the same as in free subunits, whereas the levels of modification of rpS27 and the RACK1/S2/S3a group remained virtually unchanged compared to those observed in the complex of 40S subunit with the full-size HCV IRES. Binding of 40S subunits to a fragment of the HCV IRES lacking an ORF and domain II increased the modification level of the RACK1/S2/S3a proteins, while the efficiencies of labeling of rpS10 and rpS27 remained the same as upon the deletion of the ORF fragment. Comparison of these results with known structural and biochemical data on the organization of 40S subunit and the location of the HCV IRES on it revealed structural elements of the IRES contacting exposed lysine residues of the above-mentioned ribosomal proteins. Thus, it was found that the majority of exposed lysine residues of rpS27 are involved in the binding of the HCV IRES region formed by the junction of subdomains IIIa, IIIb, and IIIc with the central stalk of domain III, and that several lysine residues of rpS10 participate in the binding of the HCV IRES region corresponding to the initial part of the ORF of the viral gRNA. In addition, we concluded that lysine residues of rpS3a are involved in the binding of domains II and III of HCV IRES.
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Affiliation(s)
- A A Malygin
- Institute of Chemical Biology and Fundamental Medicine, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, 630090, Russia
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58
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Au HHT, Jan E. Novel viral translation strategies. WILEY INTERDISCIPLINARY REVIEWS-RNA 2014; 5:779-801. [PMID: 25045163 PMCID: PMC7169809 DOI: 10.1002/wrna.1246] [Citation(s) in RCA: 26] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 02/03/2014] [Revised: 05/03/2014] [Accepted: 05/08/2014] [Indexed: 01/06/2023]
Abstract
Viral genomes are compact and encode a limited number of proteins. Because they do not encode components of the translational machinery, viruses exhibit an absolute dependence on the host ribosome and factors for viral messenger RNA (mRNA) translation. In order to recruit the host ribosome, viruses have evolved unique strategies to either outcompete cellular transcripts that are efficiently translated by the canonical translation pathway or to reroute translation factors and ribosomes to the viral genome. Furthermore, viruses must evade host antiviral responses and escape immune surveillance. This review focuses on some recent major findings that have revealed unconventional strategies that viruses utilize, which include usurping the host translational machinery, modulating canonical translation initiation factors to specifically enhance or repress overall translation for the purpose of viral production, and increasing viral coding capacity. The discovery of these diverse viral strategies has provided insights into additional translational control mechanisms and into the viral host interactions that ensure viral protein synthesis and replication. WIREs RNA 2014, 5:779–801. doi: 10.1002/wrna.1246 This article is categorized under:
Translation > Translation Mechanisms Translation > Translation Regulation
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Affiliation(s)
- Hilda H T Au
- Department of Biochemistry and Molecular Biology, University of British Columbia, Vancouver, Canada
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59
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Measurement of the change in twist at a helical junction in RNA using the orientation dependence of FRET. Biophys J 2014; 105:2175-81. [PMID: 24209863 DOI: 10.1016/j.bpj.2013.09.042] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/05/2013] [Revised: 09/04/2013] [Accepted: 09/23/2013] [Indexed: 02/05/2023] Open
Abstract
Indocarbocyanine fluorophores attached via the 5' terminus of double-stranded nucleic acids have a strong propensity to stack onto the terminal basepair. We previously demonstrated that the efficiency of fluorescence resonance energy transfer between cyanine 3 and 5 terminally attached to duplex species exhibits a pronounced modulation with helix length. This results from a systematic variation in the orientation parameter κ(2) as the relative rotation of the fluorophore transition moments changes due to the helical geometry. Analysis of such profiles provides a rich source of orientational information. In this work, we applied this methodology to the structure of a three-way helical junction that plays an important role in the hepatitis C virus internal ribosome entry site. By comparing matched pairs of duplex and junction species, we were able to measure the change in rotation at the junction. The data reveal a 29.5° overwinding and a small axial extension. This shows the power of this approach for measuring orientational information in biologically important RNA junctions.
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60
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Karamichali E, Foka P, Tsitoura E, Kalliampakou K, Kazazi D, Karayiannis P, Georgopoulou U, Mavromara P. HCV NS5A co-operates with PKR in modulating HCV IRES-dependent translation. INFECTION GENETICS AND EVOLUTION 2014; 26:113-22. [PMID: 24815730 DOI: 10.1016/j.meegid.2014.04.015] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Subscribe] [Scholar Register] [Received: 02/10/2014] [Revised: 04/15/2014] [Accepted: 04/19/2014] [Indexed: 12/11/2022]
Abstract
Translation initiation of the Hepatitis C virus (HCV) genome is driven by an internal ribosome entry site (IRES), located within the 5' non-coding region. Several studies have suggested that different cellular non canonical proteins or viral proteins can regulate the HCV IRES activity. However, the role of the viral proteins on HCV translation remains controversial. In this report, we confirmed previous studies showing that NS5A down-regulates IRES activity in HepG2 but not in Huh7 cells suggesting that the NS5A effect on HCV IRES is cell-type dependent. Additionally, we provide strong evidence that activated PKR up-regulates the IRES activity while silencing of endogenous PKR had the opposite effect. Furthermore, we present data indicating that the NS5A-mediated inhibitory effect on IRES-dependent translation could be linked with the PKR inactivation. Finally, we show that NS5A from GBV-C but not from GBV-B down-regulates HCV IRES activity in the absence or the presence of PKR over expression. Notably, HCV and GBV-C but not GBV-B NS5A contains a previously identified PKR interacting protein domain.
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Affiliation(s)
- Eirini Karamichali
- Molecular Virology Laboratory, Hellenic Pasteur Institute, Athens, Greece; University of Patras, School of Health Sciences, Department of Pharmacy, Greece
| | - Pelagia Foka
- Molecular Virology Laboratory, Hellenic Pasteur Institute, Athens, Greece
| | - Eliza Tsitoura
- Molecular Virology Laboratory, Hellenic Pasteur Institute, Athens, Greece
| | | | - Dorothea Kazazi
- Molecular Virology Laboratory, Hellenic Pasteur Institute, Athens, Greece
| | - Peter Karayiannis
- Molecular Virology/Microbiology, University of Nicosia Medical School, Cyprus
| | | | - Penelope Mavromara
- Molecular Virology Laboratory, Hellenic Pasteur Institute, Athens, Greece.
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61
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Khan D, Bhat P, Das S. HCV-like IRESs sequester eIF3: advantage virus. Trends Microbiol 2014; 22:57-8. [DOI: 10.1016/j.tim.2013.12.009] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/12/2013] [Accepted: 12/19/2013] [Indexed: 02/05/2023]
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62
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Almasio PL, Ingrassia D, Vergara B, Filosto S. New therapeutic prospects in HCV treatment. Expert Rev Anti Infect Ther 2014; 6:775-9. [DOI: 10.1586/14787210.6.6.775] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/14/2022]
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63
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Dibrov SM, Parsons J, Carnevali M, Zhou S, Rynearson KD, Ding K, Garcia Sega E, Brunn ND, Boerneke MA, Castaldi MP, Hermann T. Hepatitis C virus translation inhibitors targeting the internal ribosomal entry site. J Med Chem 2013; 57:1694-707. [PMID: 24138284 DOI: 10.1021/jm401312n] [Citation(s) in RCA: 47] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
The internal ribosome entry site (IRES) in the 5' untranslated region (UTR) of the hepatitis C virus (HCV) genome initiates translation of the viral polyprotein precursor. The unique structure and high sequence conservation of the 5' UTR render the IRES RNA a potential target for the development of selective viral translation inhibitors. Here, we provide an overview of approaches to block HCV IRES function by nucleic acid, peptide, and small molecule ligands. Emphasis will be given to the IRES subdomain IIa, which currently is the most advanced target for small molecule inhibitors of HCV translation. The subdomain IIa behaves as an RNA conformational switch. Selective ligands act as translation inhibitors by locking the conformation of the RNA switch. We review synthetic procedures for inhibitors as well as structural and functional studies of the subdomain IIa target and its ligand complexes.
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Affiliation(s)
- Sergey M Dibrov
- Department of Chemistry and Biochemistry, University of California, San Diego , 9500 Gilman Drive, La Jolla, California 92093, United States
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64
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Hepatitis-C-virus-like internal ribosome entry sites displace eIF3 to gain access to the 40S subunit. Nature 2013; 503:539-43. [PMID: 24185006 DOI: 10.1038/nature12658] [Citation(s) in RCA: 142] [Impact Index Per Article: 12.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/19/2013] [Accepted: 09/13/2013] [Indexed: 12/12/2022]
Abstract
Hepatitis C virus (HCV) and classical swine fever virus (CSFV) messenger RNAs contain related (HCV-like) internal ribosome entry sites (IRESs) that promote 5'-end independent initiation of translation, requiring only a subset of the eukaryotic initiation factors (eIFs) needed for canonical initiation on cellular mRNAs. Initiation on HCV-like IRESs relies on their specific interaction with the 40S subunit, which places the initiation codon into the P site, where it directly base-pairs with eIF2-bound initiator methionyl transfer RNA to form a 48S initiation complex. However, all HCV-like IRESs also specifically interact with eIF3 (refs 2, 5-7, 9-12), but the role of this interaction in IRES-mediated initiation has remained unknown. During canonical initiation, eIF3 binds to the 40S subunit as a component of the 43S pre-initiation complex, and comparison of the ribosomal positions of eIF3 and the HCV IRES revealed that they overlap, so that their rearrangement would be required for formation of ribosomal complexes containing both components. Here we present a cryo-electron microscopy reconstruction of a 40S ribosomal complex containing eIF3 and the CSFV IRES. Remarkably, although the position and interactions of the CSFV IRES with the 40S subunit in this complex are similar to those of the HCV IRES in the 40S-IRES binary complex, eIF3 is completely displaced from its ribosomal position in the 43S complex, and instead interacts through its ribosome-binding surface exclusively with the apical region of domain III of the IRES. Our results suggest a role for the specific interaction of HCV-like IRESs with eIF3 in preventing ribosomal association of eIF3, which could serve two purposes: relieving the competition between the IRES and eIF3 for a common binding site on the 40S subunit, and reducing formation of 43S complexes, thereby favouring translation of viral mRNAs.
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65
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Structure of the full-length HCV IRES in solution. Nat Commun 2013; 4:1612. [PMID: 23511476 DOI: 10.1038/ncomms2611] [Citation(s) in RCA: 65] [Impact Index Per Article: 5.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/27/2012] [Accepted: 02/15/2013] [Indexed: 01/04/2023] Open
Abstract
The 5'-untranslated region of the hepatitis C virus genome contains an internal ribosome entry site (IRES) that initiates cap-independent translation of the viral RNA. Until now, the structural characterization of the entire (IRES) remained limited to cryo-electron microscopy reconstructions of the (IRES) bound to different cellular partners. Here we report an atomic model of free full-length hepatitis C virus (IRES) refined by selection against small-angle X-ray scattering data that incorporates the known structures of different fragments. We found that an ensemble of conformers reproduces small-angle X-ray scattering data better than a single structure suggesting in combination with molecular dynamics simulations that the hepatitis C virus (IRES) is an articulated molecule made of rigid parts that move relative to each other. Principal component analysis on an ensemble of physically accessible conformers of hepatitis C virus (IRES) revealed dominant collective motions in the molecule, which may underlie the conformational changes occurring in the (IRES) molecule upon formation of the initiation complex.
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66
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Malygin AA, Kossinova OA, Shatsky IN, Karpova GG. HCV IRES interacts with the 18S rRNA to activate the 40S ribosome for subsequent steps of translation initiation. Nucleic Acids Res 2013; 41:8706-14. [PMID: 23873958 PMCID: PMC3794592 DOI: 10.1093/nar/gkt632] [Citation(s) in RCA: 59] [Impact Index Per Article: 5.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022] Open
Abstract
Previous analyses of complexes of 40S ribosomal subunits with the hepatitis C virus (HCV) internal ribosome entry site (IRES) have revealed contacts made by the IRES with ribosomal proteins. Here, using chemical probing, we show that the HCV IRES also contacts the backbone and bases of the CCC triplet in the 18S ribosomal RNA (rRNA) expansion segment 7. These contacts presumably provide interplay between IRES domain II and the AUG codon close to ribosomal protein S5, which causes a rearrangement of 18S rRNA structure in the vicinity of the universally conserved nucleotide G1639. As a result, G1639 becomes exposed and the corresponding site of the 40S subunit implicated in transfer RNA discrimination can select . These data are the first demonstration at nucleotide resolution of direct IRES–rRNA interactions and how they induce conformational transition in the 40S subunit allowing the HCV IRES to function without AUG recognition initiation factors.
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Affiliation(s)
- Alexey A Malygin
- Institute of Chemical Biology and Fundamental Medicine, Siberian Branch of the Russian Academy of Sciences, Novosibirsk 630090, Russia and Belozersky Institute of Physico-Chemical Biology, Lomonosov Moscow State University, Moscow 119991, Russia
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67
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Bai Y, Zhou K, Doudna JA. Hepatitis C virus 3'UTR regulates viral translation through direct interactions with the host translation machinery. Nucleic Acids Res 2013; 41:7861-74. [PMID: 23783572 PMCID: PMC3763534 DOI: 10.1093/nar/gkt543] [Citation(s) in RCA: 56] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/11/2023] Open
Abstract
The 3′ untranslated region (3′UTR) of hepatitis C virus (HCV) messenger RNA stimulates viral translation by an undetermined mechanism. We identified a high affinity interaction, conserved among different HCV genotypes, between the HCV 3′UTR and the host ribosome. The 3′UTR interacts with 40S ribosomal subunit proteins residing primarily in a localized region on the 40S solvent-accessible surface near the messenger RNA entry and exit sites. This region partially overlaps with the site where the HCV internal ribosome entry site was found to bind, with the internal ribosome entry site-40S subunit interaction being dominant. Despite its ability to bind to 40S subunits independently, the HCV 3′UTR only stimulates translation in cis, without affecting the first round translation rate. These observations support a model in which the HCV 3′UTR retains ribosome complexes during translation termination to facilitate efficient initiation of subsequent rounds of translation.
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Affiliation(s)
- Yun Bai
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA, Howard Hughes Medical Institute, University of California, Berkeley, CA 94720, USA, Department of Chemistry, University of California, Berkeley, CA 94720, USA and Physical Biosciences Division, Lawrence Berkeley National Laboratory, Berkeley, CA 94720, USA
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68
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Roth JP, Li JKK, Morrey JD, Barnard DL, Vollmer AH. Deletion of the D domain of the human parainfluenza virus type 3 (HPIV3) PD protein results in decreased viral RNA synthesis and beta interferon (IFN-β) expression. Virus Genes 2013; 47:10-9. [PMID: 23686695 DOI: 10.1007/s11262-013-0919-x] [Citation(s) in RCA: 5] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/02/2013] [Accepted: 05/09/2013] [Indexed: 11/27/2022]
Abstract
The human parainfluenza virus type 3 (HPIV3) phosphoprotein (P) gene is unusual as it contains an editing site where nontemplated ribonucleotide residues can be inserted. This RNA editing can lead to the expression of the viral P, PD, putative W, and theoretical V protein from a single gene. Although the HPIV3 PD protein has been detected, its function and those of the W and V proteins are poorly understood. Therefore, we first used reverse genetics techniques to construct and rescue a recombinant (r)HPIV3 clone with a polyhistidine sequence at the 5' end of the P gene for tagged protein detection. Western blot analysis demonstrated the presence of the P, PD, and W proteins, but no V protein was detected. Then, we functionally studied the D domain of the PD protein by constructing two rHPIV3 knockout clones that are deficient in the expression of the D domain. Results from growth kinetic studies with infected MA-104 and A596 cells showed that viral replication of the two knockout viruses (rHPIV3-ΔES and rHPIV3-ΔD) was comparable to that of the parental virus in both cell lines. However, viral mRNA transcription and genomic replication was significantly reduced. Furthermore, cytokine/chemokine profiles of A549 cells infected with either knockout virus were unchanged or showed lower levels compared to those from cells infected with the parental virus. These data suggest that the D domain of the PD protein may play a luxury role in HPIV3 RNA synthesis and may also be involved in disrupting the expression of beta interferon.
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Affiliation(s)
- Jason P Roth
- Department of Animal, Dairy, and Veterinary Sciences, Institute for Antiviral Research, Utah State University, 5600 Old Main Hill, Logan, UT 84322-5600, USA
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69
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Structures of the human and Drosophila 80S ribosome. Nature 2013; 497:80-5. [DOI: 10.1038/nature12104] [Citation(s) in RCA: 410] [Impact Index Per Article: 37.3] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/09/2013] [Accepted: 03/19/2013] [Indexed: 12/19/2022]
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70
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Screening for inhibitors of the hepatitis C virus internal ribosome entry site RNA. Bioorg Med Chem 2013; 21:6139-44. [PMID: 23602522 DOI: 10.1016/j.bmc.2013.03.054] [Citation(s) in RCA: 27] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/06/2013] [Accepted: 03/21/2013] [Indexed: 01/09/2023]
Abstract
The highly conserved internal ribosome entry site (IRES) of hepatitis C virus (HCV) regulates translation of the viral RNA genome and is essential for the expression of HCV proteins in infected host cells. The structured subdomain IIa of the IRES element is the target site of recently discovered benzimidazole inhibitors that selectively block viral translation through capture of an extended conformation of an RNA internal loop. Here, we describe the development of a FRET-based screening assay for similarly acting HCV translation inhibitors. The assay relies on monitoring fluorescence changes that indicate rearrangement of the RNA target conformation upon ligand binding. Screening of a small pilot set of potential RNA binders identified a benzoxazole scaffold as a ligand that bound selectively to IIa IRES target and was confirmed as an inhibitor of in vitro viral translation. The screening approach outlined here provides an efficient method to discover HCV translation inhibitors that may provide leads for the development of novel antiviral therapies directed at the highly conserved IRES RNA.
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71
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Mauger DM, Siegfried NA, Weeks KM. The genetic code as expressed through relationships between mRNA structure and protein function. FEBS Lett 2013; 587:1180-1188. [PMID: 23499436 PMCID: PMC4269304 DOI: 10.1016/j.febslet.2013.03.002] [Citation(s) in RCA: 39] [Impact Index Per Article: 3.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/22/2013] [Revised: 02/28/2013] [Accepted: 03/01/2013] [Indexed: 02/05/2023]
Abstract
Structured RNA elements within messenger RNA often direct or modulate the cellular production of active proteins. As reviewed here, RNA structures have been discovered that govern nearly every step in protein production: mRNA production and stability; translation initiation, elongation, and termination; protein folding; and cellular localization. Regulatory RNA elements are common within RNAs from every domain of life. This growing body of RNA-mediated mechanisms continues to reveal new ways in which mRNA structure regulates translation. We integrate examples from several different classes of RNA structure-mediated regulation to present a global perspective that suggests that the secondary and tertiary structure of RNA ultimately constitutes an additional level of the genetic code that both guides and regulates protein biosynthesis.
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Affiliation(s)
- David M Mauger
- Department of Chemistry, University of North Carolina Chapel Hill, North Carolina, USA 25599-3290
| | - Nathan A Siegfried
- Department of Chemistry, University of North Carolina Chapel Hill, North Carolina, USA 25599-3290
| | - Kevin M Weeks
- Department of Chemistry, University of North Carolina Chapel Hill, North Carolina, USA 25599-3290
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72
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Mortimer SA, Doudna JA. Unconventional miR-122 binding stabilizes the HCV genome by forming a trimolecular RNA structure. Nucleic Acids Res 2013; 41:4230-40. [PMID: 23416544 PMCID: PMC3627571 DOI: 10.1093/nar/gkt075] [Citation(s) in RCA: 69] [Impact Index Per Article: 6.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
MicroRNAs (miRNAs) typically downregulate protein expression from target mRNAs through limited base-pairing interactions between the 5′ ‘seed’ region of the miRNA and the mRNA 3′ untranslated region (3′UTR). In contrast to this established mode of action, the liver-specific human miR-122 binds at two sites within the hepatitis C viral (HCV) 5′UTR, leading to increased production of infectious virions. We show here that two copies of miR-122 interact with the HCV 5′UTR at partially overlapping positions near the 5′ end of the viral transcript to form a stable ternary complex. Both miR-122 binding sites involve extensive base pairing outside of the seed sequence; yet, they have substantially different interaction affinities. Structural probing reveals changes in the architecture of the HCV 5′UTR that occur on interaction with miR-122. In contrast to previous reports, however, results using both the recombinant cytoplasmic exonuclease Xrn1 and liver cell extracts show that miR-122-mediated protection of the HCV RNA from degradation does not correlate with stimulation of viral propagation in vivo. Thus, the miR-122:HCV ternary complex likely functions at other steps critical to the viral life cycle.
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Affiliation(s)
- Stefanie A Mortimer
- Department of Molecular and Cell Biology, University of California, Berkeley, CA 94720, USA
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73
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Conrad KD, Giering F, Erfurth C, Neumann A, Fehr C, Meister G, Niepmann M. MicroRNA-122 dependent binding of Ago2 protein to hepatitis C virus RNA is associated with enhanced RNA stability and translation stimulation. PLoS One 2013; 8:e56272. [PMID: 23405269 PMCID: PMC3566042 DOI: 10.1371/journal.pone.0056272] [Citation(s) in RCA: 67] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2012] [Accepted: 01/08/2013] [Indexed: 01/16/2023] Open
Abstract
Translation of Hepatitis C Virus (HCV) RNA is directed by an internal ribosome entry site (IRES) in the 5′-untranslated region (5′-UTR). HCV translation is stimulated by the liver-specific microRNA-122 (miR-122) that binds to two binding sites between the stem-loops I and II near the 5′-end of the 5′-UTR. Here, we show that Argonaute (Ago) 2 protein binds to the HCV 5′-UTR in a miR-122-dependent manner, whereas the HCV 3′-UTR does not bind Ago2. miR-122 also recruits Ago1 to the HCV 5’-UTR. Only miRNA duplex precursors of the correct length stimulate HCV translation, indicating that the duplex miR-122 precursors are unwound by a complex that measures their length. Insertions in the 5′-UTR between the miR-122 binding sites and the IRES only slightly decrease translation stimulation by miR-122. In contrast, partially masking the miR-122 binding sites in a stem-loop structure impairs Ago2 binding and translation stimulation by miR-122. In an RNA decay assay, also miR-122-mediated RNA stability contributes to HCV translation stimulation. These results suggest that Ago2 protein is directly involved in loading miR-122 to the HCV RNA and mediating RNA stability and translation stimulation.
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Affiliation(s)
- K. Dominik Conrad
- Institute of Biochemistry, Faculty of Medicine, Justus-Liebig-University, Giessen, Germany
| | - Florian Giering
- Institute of Biochemistry, Faculty of Medicine, Justus-Liebig-University, Giessen, Germany
| | - Corinna Erfurth
- Institute of Biochemistry, Faculty of Medicine, Justus-Liebig-University, Giessen, Germany
| | - Angelina Neumann
- Institute of Biochemistry, Faculty of Medicine, Justus-Liebig-University, Giessen, Germany
| | - Carmen Fehr
- Institute of Biochemistry, Faculty of Medicine, Justus-Liebig-University, Giessen, Germany
| | - Gunter Meister
- Institute of Biochemistry, Faculty of Biology and Preclinical Medicine, University of Regensburg, Regensburg, Germany
| | - Michael Niepmann
- Institute of Biochemistry, Faculty of Medicine, Justus-Liebig-University, Giessen, Germany
- * E-mail:
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74
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Rapid purification of ribosomal particles assembled on histone H4 mRNA: a new method based on mRNA–DNA chimaeras. Biochem J 2013; 449:719-28. [DOI: 10.1042/bj20121211] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Detailed knowledge of the structure of the ribosomal particles during their assembly on mRNA is a prerequisite for understanding the intricate translation initiation process. In vitro preparation of eukaryotic translation initiation complexes is limited by the rather tricky assembly from individually purified ribosomal subunits, initiation factors and initiator tRNA. In order to directly isolate functional complexes from living cells, methods based on affinity tags have been developed which, however, often suffer from non-specific binding of proteins and/or RNAs. In the present study we present a novel method designed for the purification of high-quality ribosome/mRNA particles assembled in RRL (rabbit reticulocyte lysate). Chimaerical mRNA–DNA molecules, consisting of the full-length mRNA ligated to a biotinylated desoxy-oligonucleotide, are immobilized on streptavidin-coated beads and incubated with RRL to form initiation complexes. After a washing step, the complexes are eluted by specific DNase I digestion of the DNA moiety of the chimaera, releasing initiation complexes in native conditions. Using this simple and robust purification setup, 80S particles properly programmed with full-length histone H4 mRNA were isolated with the expected ribosome/mRNA molar ratio of close to 1. We show that by using this novel approach purified ribosomal particles can be obtained that are suitable for biochemical and structural studies, in particular single-particle cryo-EM (cryo-electron microscopy). This purification method thus is a versatile tool for the isolation of fully functional RNA-binding proteins and macromolecular RNPs.
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75
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de Vries S, Naarmann-de Vries IS, Urlaub H, Lue H, Bernhagen J, Ostareck DH, Ostareck-Lederer A. Identification of DEAD-box RNA helicase 6 (DDX6) as a cellular modulator of vascular endothelial growth factor expression under hypoxia. J Biol Chem 2013; 288:5815-27. [PMID: 23293030 DOI: 10.1074/jbc.m112.420711] [Citation(s) in RCA: 42] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023] Open
Abstract
Vascular endothelial growth factor A (VEGF) is a crucial proangiogenic factor, which regulates blood vessel supply under physiologic and pathologic conditions. The VEGF mRNA 5'-untranslated region (5'-UTR) bears internal ribosome entry sites (IRES), which confer sustained VEGF mRNA translation under hypoxia when 5'-cap-dependent mRNA translation is inhibited. VEGF IRES-mediated initiation of translation requires the modulated interaction of trans-acting factors. To identify trans-acting factors that control VEGF mRNA translation under hypoxic conditions we established an in vitro translation system based on human adenocarcinoma cells (MCF-7). Cytoplasmic extracts of MCF-7 cells grown under hypoxia (1% oxygen) recapitulate VEGF IRES-mediated reporter mRNA translation. Employing the VEGF mRNA 5'-UTR and 3'-UTR in an RNA affinity approach we isolated interacting proteins from translational active MCF-7 extract prepared from cells grown under normoxia or hypoxia. Interestingly, mass spectrometry analysis identified the DEAD-box RNA helicase 6 (DDX6) that interacts with the VEGF mRNA 5'-UTR. Recombinant DDX6 inhibits VEGF IRES-mediated translation in normoxic MCF-7 extract. Under hypoxia the level of DDX6 declines, and its interaction with VEGF mRNA is diminished in vivo. Depletion of DDX6 by RNAi further promotes VEGF expression in MCF-7 cells. Increased secretion of VEGF from DDX6 knockdown cells positively affects vascular tube formation of human umbilical vein endothelial cells (HUVEC) in vitro. Our results indicate that the decrease of DDX6 under hypoxia contributes to the activation of VEGF expression and promotes its proangiogenic function.
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Affiliation(s)
- Sebastian de Vries
- Experimental Research Unit, Department of Intensive Care and Intermediate Care, University Hospital, RWTH Aachen University, 52074 Aachen, Germany
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76
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77
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HCV IRES manipulates the ribosome to promote the switch from translation initiation to elongation. Nat Struct Mol Biol 2012; 20:150-8. [PMID: 23262488 PMCID: PMC3864654 DOI: 10.1038/nsmb.2465] [Citation(s) in RCA: 54] [Impact Index Per Article: 4.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/31/2012] [Accepted: 11/12/2012] [Indexed: 12/11/2022]
Abstract
The hepatitis C virus (HCV) internal ribosome entry site (IRES) drives non-canonical initiation of protein synthesis necessary for viral replication. HCV IRES functional studies have focused on 80S ribosome formation, but have not explored roles after the 80S ribosome is poised at the start codon. Here, we report that mutations of an IRES domain that docks in the 40S subunit’s decoding groove and cause only a local perturbation in IRES structure result in conformational changes in the IRES-rabbit 40S subunit complex. Functionally, we find the mutation decreases IRES activity by inhibiting the first ribosome translocation event, and modeling suggests that this effect is through an interaction with a single ribosomal protein. The HCV IRES’ ability to manipulate the ribosome provides insight into how the ribosome’s structure and function can be altered by bound RNAs, including those derived from cellular invaders.
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78
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Bhat P, Gnanasundram SV, Mani P, Ray PS, Sarkar DP, Das S. Targeting ribosome assembly on the HCV RNA using a small RNA molecule. RNA Biol 2012; 9:1110-9. [PMID: 22858675 DOI: 10.4161/rna.21208] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/03/2023] Open
Abstract
Translation initiation of hepatitis C Virus (HCV) RNA is the initial obligatory step of the viral life cycle, mediated through the Internal Ribosome Entry Site (IRES) present in the 5'-untranslated region (UTR). Initiation on the HCV IRES is mediated by multiple structure-specific interactions between IRES RNA and host 40S ribosomal subunit. In the present study we demonstrate that the SLIIIef domain, in isolation from other structural elements of HCV IRES, retain the ability to interact with 40S ribosome subunit. A small RNA SLRef, mimicking the SLIIIef domain was found to interact specifically with human La protein and the ribosomal protein S5 and selectively inhibit HCV RNA translation. More importantly, SLRef RNA showed significant suppression of replication in HCV monocistronic replicon and decrease of negative strand synthesis in HCV cell culture system. Finally, using Sendai virus based virosome, the targeted delivery of SLRef RNA into mice liver succeeded in selectively inhibiting HCV IRES mediated translation in vivo.
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Affiliation(s)
- Prasanna Bhat
- Department of Microbiology and Cell Biology, Indian Institute of Science, Bangalore, India
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79
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A new framework for understanding IRES-mediated translation. Gene 2012; 502:75-86. [PMID: 22555019 DOI: 10.1016/j.gene.2012.04.039] [Citation(s) in RCA: 70] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/30/2011] [Revised: 03/23/2012] [Accepted: 04/17/2012] [Indexed: 01/08/2023]
Abstract
Studies over the past 5 or so years have indicated that the traditional clustering of mechanisms for translation initiation in eukaryotes into cap-dependent and cap-independent (or IRES-mediated) is far too narrow. From individual studies of a number of mRNAs encoding proteins that are regulatory in nature (i.e. likely to be needed in small amounts such as transcription factors, protein kinases, etc.), it is now evident that mRNAs exist that blur these boundaries. This review seeks to set the basic ground rules for the analysis of different initiation pathways that are associated with these new mRNAs as well as related to the more traditional mechanisms, especially the cap-dependent translational process that is the major route of initiation of mRNAs for housekeeping proteins and thus, the bulk of protein synthesis in most cells. It will become apparent that a mixture of descriptions is likely to become the norm in the near future (i.e. m(7)G-assisted internal initiation).
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80
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Graifer D, Karpova G. Structural and functional topography of the human ribosome. Acta Biochim Biophys Sin (Shanghai) 2012; 44:281-99. [PMID: 22257731 DOI: 10.1093/abbs/gmr118] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
This review covers data on the structural organization of functional sites in the human ribosome, namely, the messenger RNA binding center, the binding site of the hepatitis C virus RNA internal ribosome entry site, and the peptidyl transferase center. The data summarized here have been obtained primarily by means of a site-directed cross-linking approach with application of the analogs of the respective ribosomal ligands bearing cross-linkers at the designed positions. These data are discussed taking into consideration available structural data on ribosomes from various kingdoms obtained with the use of cryo-electron microscopy, X-ray crystallography, and other approaches.
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Affiliation(s)
- Dmitri Graifer
- Laboratory of Ribosome Structure and Functions, Institute of Chemical Biology and Fundamental Medicine, Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
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81
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Structure of a hepatitis C virus RNA domain in complex with a translation inhibitor reveals a binding mode reminiscent of riboswitches. Proc Natl Acad Sci U S A 2012; 109:5223-8. [PMID: 22431596 DOI: 10.1073/pnas.1118699109] [Citation(s) in RCA: 81] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/19/2022] Open
Abstract
The internal ribosome entry site (IRES) in the hepatitis C virus (HCV) RNA genome is essential for the initiation of viral protein synthesis. IRES domains adopt well-defined folds that are potential targets for antiviral translation inhibitors. We have determined the three-dimensional structure of the IRES subdomain IIa in complex with a benzimidazole translation inhibitor at 2.2 Å resolution. Comparison to the structure of the unbound RNA in conjunction with studies of inhibitor binding to the target in solution demonstrate that the RNA undergoes a dramatic ligand-induced conformational adaptation to form a deep pocket that resembles the substrate binding sites in riboswitches. The presence of a well-defined ligand-binding pocket within the highly conserved IRES subdomain IIa holds promise for the development of unique anti-HCV drugs with a high barrier to resistance.
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82
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Plank TDM, Kieft JS. The structures of nonprotein-coding RNAs that drive internal ribosome entry site function. WILEY INTERDISCIPLINARY REVIEWS. RNA 2012; 3:195-212. [PMID: 22215521 PMCID: PMC3973487 DOI: 10.1002/wrna.1105] [Citation(s) in RCA: 49] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/14/2023]
Abstract
Internal ribosome entry sites (IRESs) are RNA sequences that can recruit the translation machinery independent of the 5' end of the messenger RNA. IRESs are found in both viral and cellular RNAs and are important for regulating gene expression. There is great diversity in the mechanisms used by IRESs to recruit the ribosome and this is reflected in a variety of RNA sequences that function as IRESs. The ability of an RNA sequence to function as an IRES is conferred by structures operating at multiple levels from primary sequence through higher-order three-dimensional structures within dynamic ribonucleoproteins (RNPs). When these diverse structures are compared, some trends are apparent, but overall it is not possible to find universal rules to describe IRES structure and mechanism. Clearly, many different sequences and structures have evolved to perform the function of recruiting, positioning, and activating a ribosome without using the canonical cap-dependent mechanism. However, as our understanding of the specific sequences, structures, and mechanisms behind IRES function improves, more common features may emerge to link these diverse RNAs.
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Affiliation(s)
- Terra-Dawn M. Plank
- Department of Biochemistry and Molecular Genetics, University of Colorado Denver School of Medicine, Aurora, Colorado, 80045, USA
| | - Jeffrey S. Kieft
- Howard Hughes Medical Institute and Department of Biochemistry and Molecular Genetics, University of Colorado Denver School of Medicine, Aurora, Colorado, 80045, USA
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83
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Berry KE, Waghray S, Mortimer SA, Bai Y, Doudna JA. Crystal structure of the HCV IRES central domain reveals strategy for start-codon positioning. Structure 2012; 19:1456-66. [PMID: 22000514 DOI: 10.1016/j.str.2011.08.002] [Citation(s) in RCA: 79] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/23/2011] [Revised: 07/29/2011] [Accepted: 08/02/2011] [Indexed: 01/11/2023]
Abstract
Translation of hepatitis C viral proteins requires an internal ribosome entry site (IRES) located in the 5' untranslated region of the viral mRNA. The core domain of the hepatitis C virus (HCV) IRES contains a four-way helical junction that is integrated within a predicted pseudoknot. This domain is required for positioning the mRNA start codon correctly on the 40S ribosomal subunit during translation initiation. Here, we present the crystal structure of this RNA, revealing a complex double-pseudoknot fold that establishes the alignment of two helical elements on either side of the four-helix junction. The conformation of this core domain constrains the open reading frame's orientation for positioning on the 40S ribosomal subunit. This structure, representing the last major domain of HCV-like IRESs to be determined at near-atomic resolution, provides the basis for a comprehensive cryoelectron microscopy-guided model of the intact HCV IRES and its interaction with 40S ribosomal subunits.
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Affiliation(s)
- Katherine E Berry
- Department of Chemistry, University of California, Berkeley, Berkeley, CA 94720, USA
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84
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Ben-Shem A, Garreau de Loubresse N, Melnikov S, Jenner L, Yusupova G, Yusupov M. The structure of the eukaryotic ribosome at 3.0 Å resolution. Science 2011; 334:1524-9. [PMID: 22096102 DOI: 10.1126/science.1212642] [Citation(s) in RCA: 855] [Impact Index Per Article: 65.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
Ribosomes translate genetic information encoded by messenger RNA into proteins. Many aspects of translation and its regulation are specific to eukaryotes, whose ribosomes are much larger and intricate than their bacterial counterparts. We report the crystal structure of the 80S ribosome from the yeast Saccharomyces cerevisiae--including nearly all ribosomal RNA bases and protein side chains as well as an additional protein, Stm1--at a resolution of 3.0 angstroms. This atomic model reveals the architecture of eukaryote-specific elements and their interaction with the universally conserved core, and describes all eukaryote-specific bridges between the two ribosomal subunits. It forms the structural framework for the design and analysis of experiments that explore the eukaryotic translation apparatus and the evolutionary forces that shaped it.
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Affiliation(s)
- Adam Ben-Shem
- Institut de Génétique et de Biologie Moléculaire et Cellulaire, Illkirch F-67400, France.
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85
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Burks JM, Zwieb C, Müller F, Wower IK, Wower J. Comparative structural studies of bovine viral diarrhea virus IRES RNA. Virus Res 2011; 160:136-42. [DOI: 10.1016/j.virusres.2011.06.002] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2011] [Revised: 05/28/2011] [Accepted: 06/01/2011] [Indexed: 02/03/2023]
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86
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Burks JM, Zwieb C, Müller F, Wower IK, Wower J. In silico analysis of IRES RNAs of foot-and-mouth disease virus and related picornaviruses. Arch Virol 2011; 156:1737-47. [PMID: 21681504 DOI: 10.1007/s00705-011-1043-7] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/17/2011] [Accepted: 05/26/2011] [Indexed: 02/05/2023]
Abstract
Foot-and-mouth disease virus (FMDV) uses an internal ribosome entry site (IRES), a highly structured segment of its genomic RNA, to hijack the translational apparatus of an infected host. Computational analysis of 162 type II picornavirus IRES RNA sequences yielded secondary structures that included only base pairs supported by comparative or experimental evidence. The deduced helical sections provided the foundation for a hypothetical three-dimensional model of FMDV IRES RNA. The model was further constrained by incorporation of data derived from chemical modification and enzymatic probing of IRES RNAs as well as high-resolution information about IRES RNA-bound proteins.
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Affiliation(s)
- Jody M Burks
- Department of Animal Sciences, Auburn University, 210 Upchurch Hall, Auburn, AL 36849-5415, USA
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87
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eIF2A mediates translation of hepatitis C viral mRNA under stress conditions. EMBO J 2011; 30:2454-64. [PMID: 21556050 DOI: 10.1038/emboj.2011.146] [Citation(s) in RCA: 92] [Impact Index Per Article: 7.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/17/2011] [Accepted: 04/13/2011] [Indexed: 02/08/2023] Open
Abstract
Translation of most mRNAs is suppressed under stress conditions. Phosphorylation of the α-subunit of eukaryotic translation initiation factor 2 (eIF2), which delivers initiator tRNA (Met-tRNA(i)) to the P site of the 40S ribosomal subunit, is responsible for such translational suppression. However, translation of hepatitis C viral (HCV) mRNA is refractory to the inhibitory effects of eIF2α phosphorylation, which prevents translation by disrupting formation of the eIF2-GTP-Met-tRNA(i) ternary complex. Here, we report that eIF2A, an alternative initiator tRNA-binding protein, has a key role in the translation of HCV mRNA during HCV infection, in turn promoting eIF2α phosphorylation by activating the eIF2α kinase PKR. Direct interaction of eIF2A with the IIId domain of the HCV internal ribosome entry site (IRES) is required for eIF2A-dependent translation. These data indicate that stress-independent translation of HCV mRNA occurs by recruitment of eIF2A to the HCV IRES via direct interaction with the IIId domain and subsequent loading of Met-tRNA(i) to the P site of the 40S ribosomal subunit.
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88
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Muhs M, Yamamoto H, Ismer J, Takaku H, Nashimoto M, Uchiumi T, Nakashima N, Mielke T, Hildebrand PW, Nierhaus KH, Spahn CMT. Structural basis for the binding of IRES RNAs to the head of the ribosomal 40S subunit. Nucleic Acids Res 2011; 39:5264-75. [PMID: 21378123 PMCID: PMC3130280 DOI: 10.1093/nar/gkr114] [Citation(s) in RCA: 44] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023] Open
Abstract
Some viruses exploit internal initiation for their propagation in the host cell. This type of initiation is facilitated by structured elements (internal ribosome entry site, IRES) upstream of the initiator AUG and requires only a reduced number of canonical initiation factors. An important example are IRES of the virus family Dicistroviridae that bind to the inter-subunit side of the small ribosomal 40S subunit and lead to the formation of elongation-competent 80S ribosomes without the help of any initiation factor. Here, we present a comprehensive functional and structural analysis of eukaryotic-specific ribosomal protein rpS25 in the context of this type of initiation and propose a structural model explaining the essential involvement of rpS25 for hijacking the ribosome.
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Affiliation(s)
- Margarita Muhs
- Institut für Medizinische Physik und Biophysik, Charite - Universitätsmedizin Berlin, Ziegelstrasse 5-9, 10117-Berlin, Germany
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89
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Mechanism of translation initiation by Dicistroviridae IGR IRESs. Virology 2011; 411:355-61. [PMID: 21284991 DOI: 10.1016/j.virol.2011.01.005] [Citation(s) in RCA: 34] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2010] [Accepted: 01/04/2011] [Indexed: 01/02/2023]
Abstract
The Dicistroviridae is a growing virus family characterized by a dicistronic genome, wherein each open reading frame (ORF) is translated from an independent internal ribosome entry site (IRES). The 5' IRES that translates the first open reading frame (ORF1) is similar to the picornaviral IRESs. However the second IRES, referred to as the intergenic region (IGR) IRES, - translates ORF2 by and uses an unusual mechanism of initiating protein synthesis. It folds into a compact RNA structure that can bind directly to 40S ribosomal subunits and form 80S complexes to initiate translation in the absence of any initiation factors. Despite its unusual mechanism, the IGR IRES has proven to be an elegant model for elucidating initiation mechanisms employed by IRESs, as well as making it a powerful research tool with diverse applications.
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90
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Armache JP, Jarasch A, Anger AM, Villa E, Becker T, Bhushan S, Jossinet F, Habeck M, Dindar G, Franckenberg S, Marquez V, Mielke T, Thomm M, Berninghausen O, Beatrix B, Söding J, Westhof E, Wilson DN, Beckmann R. Localization of eukaryote-specific ribosomal proteins in a 5.5-Å cryo-EM map of the 80S eukaryotic ribosome. Proc Natl Acad Sci U S A 2010; 107:19754-9. [PMID: 20974910 PMCID: PMC2993421 DOI: 10.1073/pnas.1010005107] [Citation(s) in RCA: 116] [Impact Index Per Article: 8.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/02/2023] Open
Abstract
Protein synthesis in all living organisms occurs on ribonucleoprotein particles, called ribosomes. Despite the universality of this process, eukaryotic ribosomes are significantly larger in size than their bacterial counterparts due in part to the presence of 80 r proteins rather than 54 in bacteria. Using cryoelectron microscopy reconstructions of a translating plant (Triticum aestivum) 80S ribosome at 5.5-Å resolution, together with a 6.1-Å map of a translating Saccharomyces cerevisiae 80S ribosome, we have localized and modeled 74/80 (92.5%) of the ribosomal proteins, encompassing 12 archaeal/eukaryote-specific small subunit proteins as well as the complete complement of the ribosomal proteins of the eukaryotic large subunit. Near-complete atomic models of the 80S ribosome provide insights into the structure, function, and evolution of the eukaryotic translational apparatus.
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Affiliation(s)
- Jean-Paul Armache
- Gene Center and Center for integrated Protein Science Munich, Department of Biochemistry, Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, 81377 Munich, Germany
| | - Alexander Jarasch
- Gene Center and Center for integrated Protein Science Munich, Department of Biochemistry, Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, 81377 Munich, Germany
| | - Andreas M. Anger
- Gene Center and Center for integrated Protein Science Munich, Department of Biochemistry, Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, 81377 Munich, Germany
| | - Elizabeth Villa
- Department of Molecular Structural Biology, Max Planck Institute of Biochemistry, Am Klopferspitz 18, 82152 Martinsried, Germany
| | - Thomas Becker
- Gene Center and Center for integrated Protein Science Munich, Department of Biochemistry, Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, 81377 Munich, Germany
| | - Shashi Bhushan
- Gene Center and Center for integrated Protein Science Munich, Department of Biochemistry, Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, 81377 Munich, Germany
| | - Fabrice Jossinet
- Université de Strasbourg, Institut de Biologie Moléculaire et Cellulaire du Centre National de la Recherche Scientifique, 15 Rue René Descartes, 67084 Strasbourg, France
| | - Michael Habeck
- Department of Empirical Inference, Max Planck Institute for Biological Cybernetics, Spemannstrasse 38, 72076 Tübingen, Germany
- Department of Protein Evolution, Max Planck Institute for Developmental Biology, Spemannstrasse 35, 72076 Tübingen, Germany
| | - Gülcin Dindar
- Gene Center and Center for integrated Protein Science Munich, Department of Biochemistry, Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, 81377 Munich, Germany
| | - Sibylle Franckenberg
- Gene Center and Center for integrated Protein Science Munich, Department of Biochemistry, Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, 81377 Munich, Germany
| | - Viter Marquez
- Gene Center and Center for integrated Protein Science Munich, Department of Biochemistry, Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, 81377 Munich, Germany
| | - Thorsten Mielke
- UltraStrukturNetzwerk, Max Planck Institute for Molecular Genetics, Ihnestrasse 73, 14195 Berlin, Germany
- Institut für Medizinische Physik und Biophysik, Charité, Ziegelstrasse 5-8, 10117 Berlin, Germany; and
| | - Michael Thomm
- Universität Regensburg, Lehrstuhl für Mikrobiologie, Universitätstrasse 31, 93053 Regensburg, Germany
| | - Otto Berninghausen
- Gene Center and Center for integrated Protein Science Munich, Department of Biochemistry, Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, 81377 Munich, Germany
| | - Birgitta Beatrix
- Gene Center and Center for integrated Protein Science Munich, Department of Biochemistry, Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, 81377 Munich, Germany
| | - Johannes Söding
- Gene Center and Center for integrated Protein Science Munich, Department of Biochemistry, Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, 81377 Munich, Germany
| | - Eric Westhof
- Université de Strasbourg, Institut de Biologie Moléculaire et Cellulaire du Centre National de la Recherche Scientifique, 15 Rue René Descartes, 67084 Strasbourg, France
| | - Daniel N. Wilson
- Gene Center and Center for integrated Protein Science Munich, Department of Biochemistry, Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, 81377 Munich, Germany
| | - Roland Beckmann
- Gene Center and Center for integrated Protein Science Munich, Department of Biochemistry, Ludwig-Maximilians-Universität München, Feodor-Lynen-Strasse 25, 81377 Munich, Germany
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91
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Carnevali M, Parsons J, Wyles DL, Hermann T. A modular approach to synthetic RNA binders of the hepatitis C virus internal ribosome entry site. Chembiochem 2010; 11:1364-7. [PMID: 20564282 DOI: 10.1002/cbic.201000177] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Affiliation(s)
- Maia Carnevali
- Department of Chemistry and Biochemistry, University of California San Diego, 9500 Gilman Drive, La Jolla, CA 92093 USA
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92
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Ouellet J, Melcher S, Iqbal A, Ding Y, Lilley DMJ. Structure of the three-way helical junction of the hepatitis C virus IRES element. RNA (NEW YORK, N.Y.) 2010; 16:1597-1609. [PMID: 20581129 PMCID: PMC2905758 DOI: 10.1261/rna.2158410] [Citation(s) in RCA: 20] [Impact Index Per Article: 1.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Received: 03/03/2010] [Accepted: 05/04/2010] [Indexed: 05/29/2023]
Abstract
The hepatitis C virus internal ribosome entry site (IRES) element contains a three-way junction that is important in the overall RNA conformation, and for its role in the internal initiation of translation. The junction also illustrates some important conformational principles in the folding of three-way helical junctions. It is formally a 3HS(4) junction, with the possibility of two alternative stacking conformers. However, in principle, the junction can also undergo two steps of branch migration that would form 2HS(1)HS(3) and 2HS(2)HS(2) junctions. Comparative gel electrophoresis and ensemble fluorescence resonance energy transfer (FRET) studies show that the junction is induced to fold by the presence of Mg(2+) ions in low micromolar concentrations, and suggest that the structure adopted is based on coaxial stacking of the two helices that do not terminate in a hairpin loop (i.e., helix IIId). Single-molecule FRET studies confirm this conclusion, and indicate that there is no minor conformer present based on an alternative choice of helical stacking partners. Moreover, analysis of single-molecule FRET data at an 8-msec resolution failed to reveal evidence for structural transitions. It seems probable that this junction adopts a single conformation as a unique and stable fold.
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Affiliation(s)
- Jonathan Ouellet
- Cancer Research UK Nucleic Acid Structure Research Group, MSI/WTB Complex, The University of Dundee, Dundee DD1 5EH, United Kingdom
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93
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Berry KE, Waghray S, Doudna JA. The HCV IRES pseudoknot positions the initiation codon on the 40S ribosomal subunit. RNA (NEW YORK, N.Y.) 2010; 16:1559-69. [PMID: 20584896 PMCID: PMC2905755 DOI: 10.1261/rna.2197210] [Citation(s) in RCA: 61] [Impact Index Per Article: 4.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/04/2023]
Abstract
The hepatitis C virus (HCV) genomic RNA contains an internal ribosome entry site (IRES) in its 5' untranslated region, the structure of which is essential for viral protein translation. The IRES includes a predicted pseudoknot interaction near the AUG start codon, but the results of previous studies of its structure have been conflicting. Using mutational analysis coupled with activity and functional assays, we verified the importance of pseudoknot base pairings for IRES-mediated translation and, using 35 mutants, conducted a comprehensive study of the structural tolerance and functional contributions of the pseudoknot. Ribosomal toeprinting experiments show that the entirety of the pseudoknot element positions the initiation codon in the mRNA binding cleft of the 40S ribosomal subunit. Optimal spacing between the pseudoknot and the start site AUG resembles that between the Shine-Dalgarno sequence and the initiation codon in bacterial mRNAs. Finally, we validated the HCV IRES pseudoknot as a potential drug target using antisense 2'-OMe oligonucleotides.
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Affiliation(s)
- Katherine E Berry
- Department of Chemistry, University of California at Berkeley, Berkeley, CA 94720, USA
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94
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Lavender CA, Ding F, Dokholyan NV, Weeks KM. Robust and generic RNA modeling using inferred constraints: a structure for the hepatitis C virus IRES pseudoknot domain. Biochemistry 2010; 49:4931-3. [PMID: 20545364 PMCID: PMC2889920 DOI: 10.1021/bi100142y] [Citation(s) in RCA: 25] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/29/2022]
Abstract
RNA function is dependent on its structure, yet three-dimensional folds for most biologically important RNAs are unknown. We develop a generic discrete molecular dynamics-based modeling system that uses long-range constraints inferred from diverse biochemical or bioinformatic analyses to create statistically significant (p < 0.01) nativelike folds for RNAs of known structure ranging from 45 to 158 nucleotides. We then predict the unknown structure of the hepatitis C virus internal ribosome entry site (IRES) pseudoknot domain. The resulting RNA model rationalizes independent solvent accessibility and cryo-electron microscopy structure information. The pseudoknot domain positions the AUG start codon near the mRNA channel and is tRNA-like, suggesting the IRES employs molecular mimicry as a functional strategy.
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Affiliation(s)
- Christopher A. Lavender
- Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290
| | - Feng Ding
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599-7260
| | - Nikolay V. Dokholyan
- Department of Biochemistry and Biophysics, University of North Carolina, Chapel Hill, North Carolina 27599-7260
| | - Kevin M. Weeks
- Department of Chemistry, University of North Carolina, Chapel Hill, North Carolina 27599-3290
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95
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Toroney R, Nallagatla SR, Boyer JA, Cameron CE, Bevilacqua PC. Regulation of PKR by HCV IRES RNA: importance of domain II and NS5A. J Mol Biol 2010; 400:393-412. [PMID: 20447405 DOI: 10.1016/j.jmb.2010.04.059] [Citation(s) in RCA: 40] [Impact Index Per Article: 2.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/29/2010] [Revised: 04/27/2010] [Accepted: 04/28/2010] [Indexed: 02/05/2023]
Abstract
Protein kinase R (PKR) is an essential component of the innate immune response. In the presence of double-stranded RNA (dsRNA), PKR is autophosphorylated, which enables it to phosphorylate its substrate, eukaryotic initiation factor 2alpha, leading to translation cessation. Typical activators of PKR are long dsRNAs produced during viral infection, although certain other RNAs can also activate. A recent study indicated that full-length internal ribosome entry site (IRES), present in the 5'-untranslated region of hepatitis C virus (HCV) RNA, inhibits PKR, while another showed that it activates. We show here that both activation and inhibition by full-length IRES are possible. The HCV IRES has a complex secondary structure comprising four domains. While it has been demonstrated that domains III-IV activate PKR, we report here that domain II of the IRES also potently activates. Structure mapping and mutational analysis of domain II indicate that while the double-stranded regions of the RNA are important for activation, loop regions contribute as well. Structural comparison reveals that domain II has multiple, non-Watson-Crick features that mimic A-form dsRNA. The canonical and noncanonical features of domain II cumulate to a total of approximately 33 unbranched base pairs, the minimum length of dsRNA required for PKR activation. These results provide further insight into the structural basis of PKR activation by a diverse array of RNA structural motifs that deviate from the long helical stretches found in traditional PKR activators. Activation of PKR by domain II of the HCV IRES has implications for the innate immune response when the other domains of the IRES may be inaccessible. We also study the ability of the HCV nonstructural protein 5A (NS5A) to bind various domains of the IRES and alter activation. A model is presented for how domain II of the IRES and NS5A operate to control host and viral translation during HCV infection.
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Affiliation(s)
- Rebecca Toroney
- Department of Chemistry, Pennsylvania State University, 104 Chemistry Building, University Park, PA 16802, USA
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96
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Malygin AA, Bochkaeva ZV, Bondarenko EI, Kossinova OA, Loktev VB, Shatsky IN, Karpova GG. Binding of the IRES of hepatitis C virus RNA to the 40S ribosomal subunit: Role of p40. Mol Biol 2009. [DOI: 10.1134/s0026893309060120] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
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97
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Landry DM, Hertz MI, Thompson SR. RPS25 is essential for translation initiation by the Dicistroviridae and hepatitis C viral IRESs. Genes Dev 2009; 23:2753-64. [PMID: 19952110 PMCID: PMC2788332 DOI: 10.1101/gad.1832209] [Citation(s) in RCA: 158] [Impact Index Per Article: 10.5] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/15/2009] [Accepted: 10/06/2009] [Indexed: 02/05/2023]
Abstract
Most eukaryotic mRNAs are translated using a cap-dependent mechanism of translation. However, approximately 10% of mammalian mRNAs initiate translation using a cap-independent mechanism that is not well understood. These mRNAs contain an internal ribosome entry site (IRES) located in the 5' untranslated region. The cricket paralysis virus (CrPV) intergenic region IRES (IGR IRES) functions in yeast, mammals, and plants, and does not require any translation initiation factors. We used yeast genetics to understand how ribosomes are recruited directly to the mRNA by an IRES. We found that Rps25p has an essential role in CrPV IGR IRES activity in yeast and mammalian cells but not in cap-dependent translation. Purified 40S ribosomal subunits lacking Rps25 are unable to bind to the IGR IRES in vitro. The hepatitis C virus (HCV) IRES also requires Rps25, demonstrating the function of Rps25 is conserved across IRES types. Yeast strains lacking Rps25 exhibit only slight defects in global translation, readthrough, ribosome biogenesis, and programmed ribosomal frameshifting. This work is the first demonstration of a ribosomal protein that is specifically required for IRES-mediated translation initiation. Our findings provide us with the beginnings of a model for the molecular interactions of an IRES with the ribosome.
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Affiliation(s)
- Dori M. Landry
- Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA
| | - Marla I. Hertz
- Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA
| | - Sunnie R. Thompson
- Department of Microbiology, University of Alabama at Birmingham, Birmingham, Alabama 35294, USA
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98
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Parsons J, Castaldi MP, Dutta S, Dibrov SM, Wyles DL, Hermann T. Conformational inhibition of the hepatitis C virus internal ribosome entry site RNA. Nat Chem Biol 2009; 5:823-5. [PMID: 19767736 PMCID: PMC2770845 DOI: 10.1038/nchembio.217] [Citation(s) in RCA: 118] [Impact Index Per Article: 7.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/28/2009] [Accepted: 07/10/2009] [Indexed: 01/14/2023]
Abstract
The internal ribosome entry site (IRES), a highly conserved structured element of the hepatitis C virus genomic RNA, is an attractive target for antiviral drugs. Here we show that benzimidazole inhibitors of the HCV replicon act by conformational induction of a widened interhelical angle in the IRES subdomain IIa which facilitates the undocking of subdomain IIb from the ribosome and ultimately leads to inhibition of IRES-driven translation in HCV-infected cells.
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Affiliation(s)
- Jerod Parsons
- Department of Chemistry and Biochemistry, University of California, San Diego, La Jolla, California, USA
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99
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Weinlich S, Hüttelmaier S, Schierhorn A, Behrens SE, Ostareck-Lederer A, Ostareck DH. IGF2BP1 enhances HCV IRES-mediated translation initiation via the 3'UTR. RNA (NEW YORK, N.Y.) 2009; 15:1528-42. [PMID: 19541769 PMCID: PMC2714754 DOI: 10.1261/rna.1578409] [Citation(s) in RCA: 65] [Impact Index Per Article: 4.3] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/02/2023]
Abstract
The positive-strand RNA genome of the Hepatitis C virus (HCV) contains an internal ribosome entry site (IRES) in the 5'untranslated region (5'UTR) and structured sequence elements within the 3'UTR, but no poly(A) tail. Employing a limited set of initiation factors, the HCV IRES coordinates the 5'cap-independent assembly of the 43S pre-initiation complex at an internal initiation codon located in the IRES sequence. We have established a Huh7 cell-derived in vitro translation system that shows a 3'UTR-dependent enhancement of 43S pre-initiation complex formation at the HCV IRES. Through the use of tobramycin (Tob)-aptamer affinity chromatography, we identified the Insulin-like growth factor-II mRNA-binding protein 1 (IGF2BP1) as a factor that interacts with both, the HCV 5'UTR and 3'UTR. We report that IGF2BP1 specifically enhances translation at the HCV IRES, but it does not affect 5'cap-dependent translation. RNA interference against IGF2BP1 in HCV replicon RNA-containing Huh7 cells reduces HCV IRES-mediated translation, whereas replication remains unaffected. Interestingly, we found that endogenous IGF2BP1 specifically co-immunoprecipitates with HCV replicon RNA, the ribosomal 40S subunit, and eIF3. Furthermore eIF3 comigrates with IGF2BP1 in 80S ribosomal complexes when a reporter mRNA bearing both the HCV 5'UTR and HCV 3'UTR is translated. Our data suggest that IGF2BP1, by binding to the HCV 5'UTR and/or HCV 3'UTR, recruits eIF3 and enhances HCV IRES-mediated translation.
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Affiliation(s)
- Susan Weinlich
- Institute of Biochemistry and Biotechnology, Martin-Luther-University Halle-Wittenberg, 06120 Halle (Saale), Germany
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100
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Hellen CUT. IRES-induced conformational changes in the ribosome and the mechanism of translation initiation by internal ribosomal entry. BIOCHIMICA ET BIOPHYSICA ACTA-GENE REGULATORY MECHANISMS 2009; 1789:558-70. [PMID: 19539793 DOI: 10.1016/j.bbagrm.2009.06.001] [Citation(s) in RCA: 63] [Impact Index Per Article: 4.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 05/06/2009] [Revised: 06/04/2009] [Accepted: 06/11/2009] [Indexed: 01/02/2023]
Abstract
Translation of the genomes of several positive-sense RNA viruses follows end-independent initiation on an internal ribosomal entry site (IRES) in the viral mRNA. There are four major IRES groups, and despite major differences in the mechanisms that they use, one unifying characteristic is that each mechanism involves essential non-canonical interactions of the IRES with components of the canonical translational apparatus. Thus the approximately 200nt.-long Type 4 IRESs (epitomized by Cricket paralysis virus) bind directly to the intersubunit space on the ribosomal 40S subunit, followed by joining to a 60S subunit to form active ribosomes by a factor-independent mechanism. The approximately 300nt.-long type 3 IRESs (epitomized by Hepatitis C virus) binds independently to eukaryotic initiation factor (eIF) 3, and to the solvent-accessible surface and E-site of the 40S subunit: addition of eIF2-GTP/initiator tRNA is sufficient to form a 48S complex that can join a 60S subunit in an eIF5/eIF5B-mediated reaction to form an active ribosome. Recent cryo-electron microscopy and biochemical analyses have revealed a second general characteristic of the mechanisms of initiation on Type 3 and Type 4 IRESs. Both classes of IRES induce similar conformational changes in the ribosome that influence entry, positioning and fixation of mRNA in the ribosomal decoding channel. HCV-like IRESs also stabilize binding of initiator tRNA in the peptidyl (P) site of the 40S subunit, whereas Type 4 IRESs induce changes in the ribosome that likely promote subsequent steps in the translation process, including subunit joining and elongation.
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Affiliation(s)
- Christopher U T Hellen
- Department of Cell Biology, State University of New York Downstate Medical Center, 450 Clarkson Avenue, Box 44, Brooklyn, NY 11203, USA.
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