151
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Abstract
Pateamine A inhibits translation by preventing proper translational initiation complex formation. In the December issue of Chemistry & Biology, Bordeleau et al. demonstrated that the effects of Patemine A on translation are mediated through the interaction between the RNA helicase eIF4A and mRNA .
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Affiliation(s)
- Nadejda L Korneeva
- Department of Biochemistry and Molecular Biology, Louisiana State University Health Sciences Center, 1501 Kings Highway, Shreveport, LA 71130-3932, USA.
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152
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Anderson P, Kedersha N. Stress granules: the Tao of RNA triage. Trends Biochem Sci 2008; 33:141-50. [PMID: 18291657 DOI: 10.1016/j.tibs.2007.12.003] [Citation(s) in RCA: 839] [Impact Index Per Article: 52.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/21/2007] [Revised: 12/07/2007] [Accepted: 12/11/2007] [Indexed: 12/12/2022]
Abstract
Cytoplasmic RNA structures such as stress granules (SGs) and processing bodies (PBs) are functional byproducts of mRNA metabolism, sharing substrate mRNA, dynamic properties and many proteins, but also housing separate components and performing independent functions. Each can exist independently, but when coordinately induced they are often tethered together in a cytosolic dance. Although both self-assemble in response to stress-induced perturbations in translation, several recent reports reveal novel proteins and RNAs that are components of these structures but also perform other cellular functions. Proteins that mediate splicing, transcription, adhesion, signaling and development are all integrated with SG and PB assembly. Thus, these ephemeral bodies represent more than just the dynamic sorting of mRNA between translation and decay.
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Affiliation(s)
- Paul Anderson
- Division of Rheumatology, Immunology and Allergy, Brigham and Women's Hospital and Harvard Medical School, One Jimmy Fund Way, Boston, MA 02115, USA.
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153
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Gruber-Olipitz M, Ströbel T, Chen WQ, Grotzer MA, Quehenberger F, Slavc I, Lubec G. Synthesis, chaperoning, and metabolism of proteins are regulated by NT-3/TrkC signaling in the medulloblastoma cell line DAOY. J Proteome Res 2008; 7:1932-44. [PMID: 18336001 DOI: 10.1021/pr700724a] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/27/2022]
Abstract
The human medulloblastoma cell line DAOY was transfected with Tropomyosin receptor kinase (TrkC), a marker for good prognostic outcome. Following TrkC-activation by its ligand neurotrophin-3, protein extracts from DAOY cells were run on 2DE with subsequent MALDI-TOF-TOF analysis and quantification in order to detect downstream effectors. Protein levels of translational, splicing, processing, chaperone, protein handling, and metabolism machineries were shown to depend on neurotrophin-3-induced TrkC activation probably representing pharmacological targets.
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154
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Lindqvist L, Oberer M, Reibarkh M, Cencic R, Bordeleau ME, Vogt E, Marintchev A, Tanaka J, Fagotto F, Altmann M, Wagner G, Pelletier J. Selective pharmacological targeting of a DEAD box RNA helicase. PLoS One 2008; 3:e1583. [PMID: 18270573 PMCID: PMC2216682 DOI: 10.1371/journal.pone.0001583] [Citation(s) in RCA: 102] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/18/2007] [Accepted: 01/13/2008] [Indexed: 01/19/2023] Open
Abstract
RNA helicases represent a large family of proteins implicated in many biological processes including ribosome biogenesis, splicing, translation and mRNA degradation. However, these proteins have little substrate specificity, making inhibition of selected helicases a challenging problem. The prototypical DEAD box RNA helicase, eIF4A, works in conjunction with other translation factors to prepare mRNA templates for ribosome recruitment during translation initiation. Herein, we provide insight into the selectivity of a small molecule inhibitor of eIF4A, hippuristanol. This coral-derived natural product binds to amino acids adjacent to, and overlapping with, two conserved motifs present in the carboxy-terminal domain of eIF4A. Mutagenesis of amino acids within this region allowed us to alter the hippuristanol-sensitivity of eIF4A and undertake structure/function studies. Our results provide an understanding into how selective targeting of RNA helicases for pharmacological intervention can be achieved.
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Affiliation(s)
- Lisa Lindqvist
- Department of Biochemistry, McGill University, Montreal, Quebec, Canada
| | - Monika Oberer
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Mikhail Reibarkh
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Regina Cencic
- Department of Biochemistry, McGill University, Montreal, Quebec, Canada
| | | | - Emily Vogt
- Department of Biology, McGill University, Montreal, Quebec, Canada
| | - Assen Marintchev
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Junichi Tanaka
- Department of Chemistry, Biology, and Marine Sciences, University of the Ryukyus, Nishihara, Okinawa, Japan
| | - Francois Fagotto
- Department of Biology, McGill University, Montreal, Quebec, Canada
| | - Michael Altmann
- Institut für Biochemie und Molekulare Medizin, Universität Bern, Bern, Switzerland
| | - Gerhard Wagner
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, Massachusetts, United States of America
| | - Jerry Pelletier
- Department of Biochemistry, McGill University, Montreal, Quebec, Canada
- McGill Cancer Center, McGill University, Montreal, Quebec, Canada
- *E-mail:
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155
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Godbout R, Li L, Liu RZ, Roy K. Role of DEAD box 1 in retinoblastoma and neuroblastoma. Future Oncol 2008; 3:575-87. [PMID: 17927523 DOI: 10.2217/14796694.3.5.575] [Citation(s) in RCA: 28] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/07/2023] Open
Abstract
Analysis of hereditary and nonhereditary retinoblastoma led to the formulation of the two-hit hypothesis of cancer in the early 1970s. The two-hit hypothesis was validated in the 1980s when both copies of the RB1 gene were shown to be mutated in hereditary and nonhereditary retinoblastoma. However, consistent genetic abnormalities other than RB1 mutations suggest that additional events may be required for the formation of these malignant tumors. For example, MYCN amplification has long been known to occur in both retinoblastoma and neuroblastoma tumors and is strongly associated with poor prognosis in neuroblastoma. The DEAD box gene, DEAD box 1 (DDX1), is often coamplified with MYCN in both these childhood tumors. Here, we examine possible roles for DDX1 overexpression in retinoblastoma and neuroblastoma.
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Affiliation(s)
- Roseline Godbout
- Cross Cancer Institute, 11560 University Avenue, Edmonton, Alberta T6G 1Z2, Canada.
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156
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Low WK, Dang Y, Schneider-Poetsch T, Shi Z, Choi NS, Rzasa RM, Shea HA, Li S, Park K, Ma G, Romo D, Liu JO. Isolation and identification of eukaryotic initiation factor 4A as a molecular target for the marine natural product Pateamine A. Methods Enzymol 2007; 431:303-24. [PMID: 17923240 DOI: 10.1016/s0076-6879(07)31014-8] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 03/01/2023]
Abstract
Natural products continue to demonstrate their utility both as therapeutics and as molecular probes for the discovery and mechanistic deconvolution of various cellular processes. However, this utility is dampened by the inherent difficulties involved in isolating and characterizing new bioactive natural products, in obtaining sufficient quantities of purified compound for further biological studies, and in developing bioactive probes. Key to characterizing the biological activity of natural products is the identification of the molecular target(s) within the cell. The marine sponge-derived natural product Pateamine A (PatA) has been found to be an inhibitor of eukaryotic translation initiation. Herein, we describe the methods utilized for identification of the eukaryotic translation initiation factor 4A (eIF4A) as one of the primary protein targets of PatA. We begin by describing the synthesis of an active biotin conjugate of PatA (B-PatA), made possible by total synthesis, followed by its use for affinity purification of PatA binding proteins from cellular lysates. We have attempted to present the methodology as a general technique for the identification of protein targets for small molecules including natural products.
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Affiliation(s)
- Woon-Kai Low
- Department of Pharmacology, Johns Hopkins School of Medicine, Baltimore, Maryland, USA
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157
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Lan CC, Laurenson S, Copp BR, Cattin PM, Love DR. Whole organism approaches to chemical genomics: the promising role of zebrafish (Danio rerio). Expert Opin Drug Discov 2007; 2:1389-401. [PMID: 23484534 DOI: 10.1517/17460441.2.10.1389] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.2] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/05/2022]
Abstract
Chemical genomics is a new and rapidly developing field. It refers to the use of cell-permeable small molecules, which are highly specific for their protein targets, in order to dissect biological pathways and to discover new drug leads. Small-molecule screening is usually limited to high-throughput approaches that use defined cell lines; however, whole organism screening is gaining increasing attention. This review addresses the latter concept and highlights the advances in whole organism-based screening, with an emphasis on the use of the zebrafish (Danio rerio).
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Affiliation(s)
- Chuan-Ching Lan
- University of Auckland, School of Biological Sciences, Private Bag 92019, Auckland Mail Centre, Auckland 1142, New Zealand +64 9 3737599 ; ext: 87228; +64 9 3737417 ;
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158
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Low WK, Dang Y, Bhat S, Romo D, Liu JO. Substrate-dependent targeting of eukaryotic translation initiation factor 4A by pateamine A: negation of domain-linker regulation of activity. ACTA ACUST UNITED AC 2007; 14:715-27. [PMID: 17584618 DOI: 10.1016/j.chembiol.2007.05.012] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/27/2007] [Revised: 05/07/2007] [Accepted: 05/21/2007] [Indexed: 12/15/2022]
Abstract
Central to cap-dependent eukaryotic translation initiation is the eIF4F complex, which is composed of the three eukaryotic initiation factors eIF4E, eIF4G, and eIF4A. eIF4A is an RNA-dependent ATPase and an ATP-dependent helicase that unwinds local secondary structure in mRNA to allow binding of the 43S ribosomal complex. The marine natural product pateamine A (PatA) has been demonstrated to inhibit cap-dependent initiation by targeting eIF4A and disrupting its protein-protein interactions while increasing its enzymatic activities. Here we demonstrate that the increased activity is caused by the induction of global conformational changes within eIF4A. Furthermore, binding of PatA is dependent on substrate (RNA and ATP) binding, and the increased activity upon PatA binding is caused by relief of a negative regulatory function of the eIF4A unique domain linker.
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Affiliation(s)
- Woon-Kai Low
- Department of Pharmacology and Molecular Sciences, Johns Hopkins School of Medicine, Baltimore, MD 21205, USA
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159
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Bordeleau ME, Cencic R, Lindqvist L, Oberer M, Northcote P, Wagner G, Pelletier J. RNA-mediated sequestration of the RNA helicase eIF4A by Pateamine A inhibits translation initiation. ACTA ACUST UNITED AC 2007; 13:1287-95. [PMID: 17185224 DOI: 10.1016/j.chembiol.2006.10.005] [Citation(s) in RCA: 113] [Impact Index Per Article: 6.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/05/2006] [Revised: 10/05/2006] [Accepted: 10/17/2006] [Indexed: 11/28/2022]
Abstract
Eukaryotic initiation factor 4A (eIF4A) is a member of the DEAD-box family of putative RNA helicases whose members are involved in many aspects of RNA metabolism. eIF4A is thought to facilitate binding of 43S preinitiation complexes to mRNAs by unwinding secondary structures present in the 5' untranslated region. Pateamine A, a small-molecule inhibitor of translation initiation, acts in an unusual manner by stimulating eIF4A activity. Herein, we report the elucidation of pateamine's mode of action. We demonstrate that Pateamine A is a chemical inducer of dimerization that forces an engagement between eIF4A and RNA and prevents eIF4A from participating in the ribosome-recruitment step of translation initiation.
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Affiliation(s)
- Marie-Eve Bordeleau
- Department of Biochemistry, McGill University, McIntyre Medical Sciences Building, 3655 Promenade Sir William Osler, Montreal, Quebec H3G 1Y6, Canada
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160
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Moerke NJ, Aktas H, Chen H, Cantel S, Reibarkh MY, Fahmy A, Gross JD, Degterev A, Yuan J, Chorev M, Halperin JA, Wagner G. Small-molecule inhibition of the interaction between the translation initiation factors eIF4E and eIF4G. Cell 2007; 128:257-67. [PMID: 17254965 DOI: 10.1016/j.cell.2006.11.046] [Citation(s) in RCA: 424] [Impact Index Per Article: 24.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/06/2006] [Revised: 09/15/2006] [Accepted: 11/23/2006] [Indexed: 12/21/2022]
Abstract
Assembly of the eIF4E/eIF4G complex has a central role in the regulation of gene expression at the level of translation initiation. This complex is regulated by the 4E-BPs, which compete with eIF4G for binding to eIF4E and which have tumor-suppressor activity. To pharmacologically mimic 4E-BP function we developed a high-throughput screening assay for identifying small-molecule inhibitors of the eIF4E/eIF4G interaction. The most potent compound identified, 4EGI-1, binds eIF4E, disrupts eIF4E/eIF4G association, and inhibits cap-dependent translation but not initiation factor-independent translation. While 4EGI-1 displaces eIF4G from eIF4E, it effectively enhances 4E-BP1 association both in vitro and in cells. 4EGI-1 inhibits cellular expression of oncogenic proteins encoded by weak mRNAs, exhibits activity against multiple cancer cell lines, and appears to have a preferential effect on transformed versus nontransformed cells. The identification of this compound provides a new tool for studying translational control and establishes a possible new strategy for cancer therapy.
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MESH Headings
- Animals
- Antineoplastic Agents/chemistry
- Antineoplastic Agents/isolation & purification
- Antineoplastic Agents/pharmacology
- Cell Line, Transformed
- Cell Line, Tumor
- Cell Transformation, Neoplastic/drug effects
- Cell Transformation, Neoplastic/genetics
- Cell Transformation, Neoplastic/metabolism
- Drug Evaluation, Preclinical/methods
- Eukaryotic Initiation Factor-4E/drug effects
- Eukaryotic Initiation Factor-4E/genetics
- Eukaryotic Initiation Factor-4E/metabolism
- Eukaryotic Initiation Factor-4G/drug effects
- Eukaryotic Initiation Factor-4G/genetics
- Eukaryotic Initiation Factor-4G/metabolism
- Feedback, Physiological/drug effects
- Feedback, Physiological/physiology
- Fluorescence Polarization Immunoassay/methods
- Gene Expression Regulation, Neoplastic/drug effects
- Gene Expression Regulation, Neoplastic/genetics
- Humans
- Hydrazones
- Jurkat Cells
- Mice
- Models, Molecular
- Nitro Compounds/chemistry
- Nitro Compounds/isolation & purification
- Nitro Compounds/pharmacology
- Oncogenes/drug effects
- Oncogenes/genetics
- Peptide Fragments/genetics
- Peptide Fragments/metabolism
- Peptide Fragments/pharmacology
- Protein Binding/drug effects
- Protein Binding/genetics
- Protein Biosynthesis/drug effects
- Protein Biosynthesis/genetics
- RNA, Messenger/drug effects
- RNA, Messenger/genetics
- Thiazoles/chemistry
- Thiazoles/isolation & purification
- Thiazoles/pharmacology
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Affiliation(s)
- Nathan J Moerke
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, Boston, MA 02115, USA
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161
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Prabhu S, Saadat D, Zhang M, Halbur L, Fruehauf JP, Ong ST. A novel mechanism for Bcr-Abl action: Bcr-Abl-mediated induction of the eIF4F translation initiation complex and mRNA translation. Oncogene 2007; 26:1188-200. [PMID: 16936779 PMCID: PMC2527622 DOI: 10.1038/sj.onc.1209901] [Citation(s) in RCA: 41] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/09/2006] [Revised: 06/26/2006] [Accepted: 07/11/2006] [Indexed: 12/30/2022]
Abstract
The oncogenic kinase Bcr-Abl is thought to cause chronic myelogenous leukemia (CML) by altering the transcription of specific genes with growth- and survival-promoting functions. Recently, Bcr-Abl has also been shown to activate an important regulator of protein synthesis, the mammalian target of rapamycin (mTOR), which suggests that dysregulated translation may also contribute to CML pathogenesis. In this study, we found that both Bcr-Abl and the rapamycin-sensitive mTORC1 complex contribute to the phosphorylation (inactivation) of 4E-BP1, an inhibitor of the eIF4E translation initiation factor. Experiments with rapamycin and the Bcr-Abl inhibitor, imatinib mesylate, in Bcr-Abl-expressing cell lines and primary CML cells indicated that Bcr-Abl and mTORC1 induced formation of the translation initiation complex, eIF4F. This was characterized by reduced 4E-BP1 binding and increased eIF4G binding to eIF4E, two events that lead to the assembly of eIF4F. One target transcript is cyclin D3, which is regulated in Bcr-Abl-expressing cells by both Bcr-Abl and mTORC1 in a translational manner. In addition, the combination of imatinib and rapamycin was found to act synergistically against committed CML progenitors from chronic and blast phase patients. These experiments establish a novel mechanism of action for Bcr-Abl, and they provide insights into the modes of action of imatinib mesylate and rapamycin in treatment of CML. They also suggest that aberrant cap-dependent mRNA translation may be a therapeutic target in Bcr-Abl-driven malignancies.
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MESH Headings
- Adaptor Proteins, Signal Transducing
- Animals
- Antibiotics, Antineoplastic
- Benzamides
- Carrier Proteins/metabolism
- Cell Cycle Proteins
- Cyclin D3
- Cyclins/metabolism
- Eukaryotic Initiation Factor-4F/metabolism
- Eukaryotic Initiation Factor-4G/metabolism
- Eukaryotic Initiation Factors
- Fusion Proteins, bcr-abl/antagonists & inhibitors
- Fusion Proteins, bcr-abl/physiology
- Humans
- Imatinib Mesylate
- Leukemia, Myelogenous, Chronic, BCR-ABL Positive/genetics
- Leukemia, Myelogenous, Chronic, BCR-ABL Positive/metabolism
- Mechanistic Target of Rapamycin Complex 1
- Mice
- Multiprotein Complexes
- Phosphoproteins/metabolism
- Phosphorylation
- Piperazines/pharmacology
- Protein Biosynthesis/drug effects
- Proteins
- Pyrimidines/pharmacology
- Sirolimus/pharmacology
- TOR Serine-Threonine Kinases
- Transcription Factors/antagonists & inhibitors
- Transcription Factors/metabolism
- Tumor Cells, Cultured
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Affiliation(s)
- S Prabhu
- The Division of Hematology/Oncology, University of California, Irvine, CA 92697, USA
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162
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Abstract
This review covers the literature published in 2005 for marine natural products, with 704 citations (493 for the period January to December 2005) referring to compounds isolated from marine microorganisms and phytoplankton, green algae, brown algae, red algae, sponges, coelenterates, bryozoans, molluscs, tunicates and echinoderms. The emphasis is on new compounds (812 for 2005), together with their relevant biological activities, source organisms and country of origin. Biosynthetic studies, first syntheses, and syntheses that lead to the revision of structures or stereochemistries, have been included.
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Affiliation(s)
- John W Blunt
- Department of Chemistry, University of Canterbury, Christchurch, New Zealand.
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163
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Cencic R, Robert F, Pelletier J. Identifying small molecule inhibitors of eukaryotic translation initiation. Methods Enzymol 2007; 431:269-302. [PMID: 17923239 DOI: 10.1016/s0076-6879(07)31013-6] [Citation(s) in RCA: 16] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/18/2022]
Abstract
In eukaryotes, translation initiation is rate-limiting with much regulation exerted at the ribosome recruitment and ternary complex (eIF2.GTP.Met-tRNA(i)(Met)) formation steps. Although small molecule inhibitors have been extremely useful for chemically dissecting translation, there is a dearth of compounds available to study the initiation phase in vitro and in vivo. In this chapter, we describe reverse and forward chemical genetic screens developed to identify new inhibitors of translation. The ability to manipulate cell extracts biochemically, and to compare the activity of small molecules on translation of mRNA templates that differ in their factor requirements for ribosome recruitment, facilitates identification of the relevant target.
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Affiliation(s)
- Regina Cencic
- Department of Biochemistry, McGill University, Montreal, Quebec, Canada
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164
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Merrick WC, Barth-Baus D. Use of Reticulocyte Lysates for Mechanistic Studies of Eukaryotic Translation Initiation. Methods Enzymol 2007; 429:1-21. [PMID: 17913616 DOI: 10.1016/s0076-6879(07)29001-9] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/22/2023]
Abstract
This chapter describes how commercially available, nuclease-treated rabbit reticulocyte lysates can be used to study different types of translation initiation (cap-dependent initiation, reinitiation, internal ribosome entry site-mediated initiation) and the influence of different initiation factors on these translation mechanisms. Additionally, with the use of sucrose gradients, it is possible to use nuclease-treated reticulocyte lysates to monitor the formation of ribosomal complexes for their content of mRNA, initiator met-tRNA(i), and initiation factors. The advantage of using nuclease-treated lysates rather than purified initiation factors is that reactions occur at or near the in vivo rate in contrast to rates observed in reactions with purified components, which are generally 10- to 1000-fold lower. The disadvantage is not being able to accurately control the amount of individual initiation factors, although the use of either factor additions or specific inhibitors can be helpful in assessing the role of specific individual initiation factors.
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Affiliation(s)
- William C Merrick
- Department of Biochemistry, School of Medicine, Case Western Reserve University, Cleveland, Ohio, USA
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165
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Dixon N, Wong LS, Geerlings TH, Micklefield J. Cellular targets of natural products. Nat Prod Rep 2007; 24:1288-310. [DOI: 10.1039/b616808f] [Citation(s) in RCA: 47] [Impact Index Per Article: 2.8] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/21/2022]
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166
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Dang Y, Kedersha N, Low WK, Romo D, Gorospe M, Kaufman R, Anderson P, Liu JO. Eukaryotic Initiation Factor 2α-independent Pathway of Stress Granule Induction by the Natural Product Pateamine A. J Biol Chem 2006; 281:32870-8. [PMID: 16951406 DOI: 10.1074/jbc.m606149200] [Citation(s) in RCA: 206] [Impact Index Per Article: 11.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Stress granules are aggregates of small ribosomal subunits, mRNA, and numerous associated RNA-binding proteins that include several translation initiation factors. Stress granule assembly occurs in the cytoplasm of higher eukaryotic cells under a wide variety of stress conditions, including heat shock, UV irradiation, hypoxia, and exposure to arsenite. Thus far, a unifying principle of eukaryotic initiation factor 2alpha phosphorylation prior to stress granule formation has been observed from the majority of experimental evidence. Pateamine A, a natural product isolated from marine sponge, was recently reported to inhibit eukaryotic translation initiation and induce the formation of stress granules. In this report, the protein composition and fundamental progression of stress granule formation and disassembly induced by pateamine A was found to be similar to that for arsenite. However, pateamine A-induced stress granules were more stable and less prone to disassembly than those formed in the presence of arsenite. Most significantly, pateamine A induced stress granules independent of eukaryotic initiation factor 2alpha phosphorylation, suggesting an alternative mechanism of formation from that previously described for other cellular stresses. Taking into account the known inhibitory effect of pateamine A on eukaryotic translation initiation, a model is proposed to account for the induction of stress granules by pateamine A as well as other stress conditions through perturbation of any steps prior to the rejoining of the 60S ribosomal subunit during the entire translation initiation process.
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Affiliation(s)
- Yongjun Dang
- Department of Pharmacology and Molecular Sciences, Solomon H. Snyder Department of Neuroscience, and Department of Oncology, Johns Hopkins School of Medicine, Baltimore, MD 21205, USA
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167
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Linder P. Dead-box proteins: a family affair--active and passive players in RNP-remodeling. Nucleic Acids Res 2006; 34:4168-80. [PMID: 16936318 PMCID: PMC1616962 DOI: 10.1093/nar/gkl468] [Citation(s) in RCA: 347] [Impact Index Per Article: 19.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/03/2006] [Revised: 06/19/2006] [Accepted: 06/20/2006] [Indexed: 11/23/2022] Open
Abstract
DEAD-box proteins are characterized by nine conserved motifs. According to these criteria, several hundreds of these proteins can be identified in databases. Many different DEAD-box proteins can be found in eukaryotes, whereas prokaryotes have small numbers of different DEAD-box proteins. DEAD-box proteins play important roles in RNA metabolism, and they are very specific and cannot mutually be replaced. In vitro, many DEAD-box proteins have been shown to have RNA-dependent ATPase and ATP-dependent RNA helicase activities. From the genetic and biochemical data obtained mainly in yeast, it has become clear that these proteins play important roles in remodeling RNP complexes in a temporally controlled fashion. Here, I shall give a general overview of the DEAD-box protein family.
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Affiliation(s)
- Patrick Linder
- Department of Microbiology and Molecular Medicine, CMU 1, rue Michel Servet, CH-1211 Genève 4, Switzerland.
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168
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Mazroui R, Sukarieh R, Bordeleau ME, Kaufman RJ, Northcote P, Tanaka J, Gallouzi I, Pelletier J. Inhibition of ribosome recruitment induces stress granule formation independently of eukaryotic initiation factor 2alpha phosphorylation. Mol Biol Cell 2006; 17:4212-9. [PMID: 16870703 PMCID: PMC1635342 DOI: 10.1091/mbc.e06-04-0318] [Citation(s) in RCA: 258] [Impact Index Per Article: 14.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022] Open
Abstract
Cytoplasmic aggregates known as stress granules (SGs) arise as a consequence of cellular stress and contain stalled translation preinitiation complexes. These foci are thought to serve as sites of mRNA storage or triage during the cell stress response. SG formation has been shown to require induction of eukaryotic initiation factor (eIF)2alpha phosphorylation. Herein, we investigate the potential role of other initiation factors in this process and demonstrate that interfering with eIF4A activity, an RNA helicase required for the ribosome recruitment phase of translation initiation, induces SG formation and that this event is not dependent on eIF2alpha phosphorylation. We also show that inhibition of eIF4A activity does not impair the ability of eIF2alpha to be phosphorylated under stress conditions. Furthermore, we observed SG assembly upon inhibition of cap-dependent translation after poliovirus infection. We propose that SG modeling can occur via both eIF2alpha phosphorylation-dependent and -independent pathways that target translation initiation.
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Affiliation(s)
| | | | | | - Randal J. Kaufman
- Howard Hughes Medical Institute and
- Departments of Biological Chemistry and Internal Medicine, University of Michigan, Ann Arbor, MI 48109
| | - Peter Northcote
- School of Chemical and Physical Sciences, Victoria University of Wellington, Wellington 6140, New Zealand; and
| | - Junichi Tanaka
- Department of Chemistry, Biology, and Marine Sciences, University of the Ryukyus, Nishihara, Okinawa 903-0213, Japan
| | | | - Jerry Pelletier
- *Department of Biochemistry and
- McGill Cancer Center, McIntyre Medical Sciences Building, McGill University, Montreal, Quebec, Canada H3G 1Y6
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169
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Chaudhry Y, Nayak A, Bordeleau ME, Tanaka J, Pelletier J, Belsham GJ, Roberts LO, Goodfellow IG. Caliciviruses differ in their functional requirements for eIF4F components. J Biol Chem 2006; 281:25315-25. [PMID: 16835235 DOI: 10.1074/jbc.m602230200] [Citation(s) in RCA: 111] [Impact Index Per Article: 6.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Two classes of viruses, namely members of the Potyviridae and Caliciviridae, use a novel mechanism for the initiation of protein synthesis that involves the interaction of translation initiation factors with a viral protein covalently linked to the viral RNA, known as VPg. The calicivirus VPg proteins can interact directly with the initiation factors eIF4E and eIF3. Translation initiation on feline calicivirus (FCV) RNA requires eIF4E because it is inhibited by recombinant 4E-BP1. However, to date, there have been no functional studies carried out with respect to norovirus translation initiation, because of a lack of a suitable source of VPg-linked viral RNA. We have now used the recently identified murine norovirus (MNV) as a model system for norovirus translation and have extended our previous studies with FCV RNA to examine the role of the other eIF4F components in translation initiation. We now demonstrate that, as with FCV, MNV VPg interacts directly with eIF4E, although, unlike FCV RNA, translation of MNV RNA is not sensitive to 4E-BP1, eIF4E depletion, or foot-and-mouth disease virus Lb protease-mediated cleavage of eIF4G. We also demonstrate that both FCV and MNV RNA translation require the RNA helicase component of the eIF4F complex, namely eIF4A, because translation was sensitive (albeit to different degrees) to a dominant negative form and to a small molecule inhibitor of eIF4A (hippuristanol). These results suggest that calicivirus RNAs differ with respect to their requirements for the components of the eIF4F translation initiation complex.
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Affiliation(s)
- Yasmin Chaudhry
- Department of Virology, Faculty of Medicine, Imperial College London, St. Mary's Campus, Norfolk Place, London W2 1PG, United Kingdom
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170
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Marsden S, Nardelli M, Linder P, McCarthy JEG. Unwinding single RNA molecules using helicases involved in eukaryotic translation initiation. J Mol Biol 2006; 361:327-35. [PMID: 16828800 DOI: 10.1016/j.jmb.2006.06.016] [Citation(s) in RCA: 59] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/30/2006] [Revised: 06/07/2006] [Accepted: 06/09/2006] [Indexed: 02/07/2023]
Abstract
The small (40 S) subunit of the eukaryotic ribosome may have to scan more than 2000 nucleotides (>600 nm) from its 5'cap recruiting point on an mRNA molecule before initiating on a translation start codon. As with many other processes in living cells, including transcription, editing, mRNA splicing, pre-rRNA processing, RNA transport and RNA decay, scanning is facilitated by helicase activity. However, precise quantitative data on the molecular mechanism of scanning, including the roles of helicases, are lacking. Here, we describe a novel atomic force microscopy (AFM)-based procedure to examine the roles of two yeast helicases, eIF4A and Ded1, previously implicated in translation initiation by genetic and biochemical studies. Our results show that eIF4A, especially in the presence of its "cofactor" eIF4B, promotes ATP-dependent unwinding of localised secondary structure in long RNA molecules under tensional loading, albeit only at high protein:RNA ratios. Thus eIF4A can act to separate only a limited number of base-pairs, possibly via a steric unwinding mechanism. In contrast, Ded1 is more effective in reducing (by up to 50 pN at an AFM loading rate of 14 nNs(-1)) the force necessary to disrupt an RNA stem-loop, and thus shows significant kinetic competence to facilitate fast unwinding. These single molecule experiments indicate that Ded1 is likely to act as the more potent unwinding factor on natural mRNA substrates.
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Affiliation(s)
- Steven Marsden
- Manchester Interdisciplinary Biocentre, University of Manchester, 131 Princess Street, Manchester M1 7ND, UK
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171
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172
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Robert F, Gao HQ, Donia M, Merrick WC, Hamann MT, Pelletier J. Chlorolissoclimides: new inhibitors of eukaryotic protein synthesis. RNA (NEW YORK, N.Y.) 2006; 12:717-25. [PMID: 16540697 PMCID: PMC1440909 DOI: 10.1261/rna.2346806] [Citation(s) in RCA: 43] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/07/2023]
Abstract
Lissoclimides are cytotoxic compounds produced by shell-less molluscs through chemical secretions to deter predators. Chlorinated lissoclimides were identified as the active component of a marine extract from Pleurobranchus forskalii found during a high-throughput screening campaign to characterize new protein synthesis inhibitors. It was demonstrated that these compounds inhibit protein synthesis in vitro, in extracts prepared from mammalian and plant cells, as well as in vivo against mammalian cells. Our results suggest that they block translation elongation by inhibiting translocation, leading to an accumulation of ribosomes on mRNA. These data provide a rationale for the cytotoxic nature of this class of small molecule natural products.
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Affiliation(s)
- Francis Robert
- Department of Biochemistry, McGill University, Montreal, Quebec, Canada
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173
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Mazan-Mamczarz K, Lal A, Martindale JL, Kawai T, Gorospe M. Translational repression by RNA-binding protein TIAR. Mol Cell Biol 2006; 26:2716-27. [PMID: 16537914 PMCID: PMC1430315 DOI: 10.1128/mcb.26.7.2716-2727.2006] [Citation(s) in RCA: 123] [Impact Index Per Article: 6.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
The RNA-binding protein TIAR has been proposed to inhibit protein synthesis transiently by promoting the formation of translationally silent stress granules. Here, we report the selective binding of TIAR to several mRNAs encoding translation factors such as eukaryotic initiation factor 4A (eIF4A) and eIF4E (translation initiation factors), eEF1B (a translation elongation factor), and c-Myc (which transcriptionally controls the expression of numerous translation regulatory proteins). TIAR bound the 3'-untranslated regions of these mRNAs and potently suppressed their translation, particularly in response to low levels of short-wavelength UV (UVC) irradiation. The UVC-imposed global inhibition of the cellular translation machinery was significantly relieved after silencing of TIAR expression. We propose that the TIAR-mediated inhibition of translation factor expression elicits a sustained repression of protein biosynthesis in cells responding to stress.
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Affiliation(s)
- Krystyna Mazan-Mamczarz
- Laboratory of Cellular and Molecular Biology, Box 12, LCMB, National Institute on Aging-Intramural Research Program, National Institutes of Health, 5600 Nathan Shock Dr., Baltimore, Maryland 21224, USA
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174
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Mazan-Mamczarz K, Lal A, Martindale JL, Kawai T, Gorospe M. Translational repression by RNA-binding protein TIAR. Mol Cell Biol 2006. [PMID: 16537914 DOI: 10.1128/mcb.26.7.2716] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 04/17/2023] Open
Abstract
The RNA-binding protein TIAR has been proposed to inhibit protein synthesis transiently by promoting the formation of translationally silent stress granules. Here, we report the selective binding of TIAR to several mRNAs encoding translation factors such as eukaryotic initiation factor 4A (eIF4A) and eIF4E (translation initiation factors), eEF1B (a translation elongation factor), and c-Myc (which transcriptionally controls the expression of numerous translation regulatory proteins). TIAR bound the 3'-untranslated regions of these mRNAs and potently suppressed their translation, particularly in response to low levels of short-wavelength UV (UVC) irradiation. The UVC-imposed global inhibition of the cellular translation machinery was significantly relieved after silencing of TIAR expression. We propose that the TIAR-mediated inhibition of translation factor expression elicits a sustained repression of protein biosynthesis in cells responding to stress.
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Affiliation(s)
- Krystyna Mazan-Mamczarz
- Laboratory of Cellular and Molecular Biology, Box 12, LCMB, National Institute on Aging-Intramural Research Program, National Institutes of Health, 5600 Nathan Shock Dr., Baltimore, Maryland 21224, USA
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175
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Bordeleau ME, Mori A, Oberer M, Lindqvist L, Chard LS, Higa T, Belsham GJ, Wagner G, Tanaka J, Pelletier J. Functional characterization of IRESes by an inhibitor of the RNA helicase eIF4A. Nat Chem Biol 2006; 2:213-20. [PMID: 16532013 DOI: 10.1038/nchembio776] [Citation(s) in RCA: 285] [Impact Index Per Article: 15.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/08/2005] [Accepted: 02/13/2006] [Indexed: 11/09/2022]
Abstract
RNA helicases are molecular motors that are involved in virtually all aspects of RNA metabolism. Eukaryotic initiation factor (eIF) 4A is the prototypical member of the DEAD-box family of RNA helicases. It is thought to use energy from ATP hydrolysis to unwind mRNA structure and, in conjunction with other translation factors, it prepares mRNA templates for ribosome recruitment during translation initiation. In screening marine extracts for new eukaryotic translation initiation inhibitors, we identified the natural product hippuristanol. We show here that this compound is a selective and potent inhibitor of eIF4A RNA-binding activity that can be used to distinguish between eIF4A-dependent and -independent modes of translation initiation in vitro and in vivo. We also show that poliovirus replication is delayed when infected cells are exposed to hippuristanol. Our study demonstrates the feasibility of selectively targeting members of the DEAD-box helicase family with small-molecule inhibitors.
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Affiliation(s)
- Marie-Eve Bordeleau
- Department of Biochemistry, McIntyre Medical Sciences Building Rm. 810, 3655 Promenade Sir William Osler, McGill University, Montreal, Quebec H3G 1Y6, Canada
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176
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Abstract
A recent publication revealing that the cytotoxic marine natural product pateamine A targets eukaryotic initiation factor eIF4A continues a story with lessons for both chemists and biologists, that is, the significance of natural products, the importance of synthetic organic chemistry, the small molecule regulation of eukaryotic translation machinery, and possibly a new approach to cancer chemotherapy.
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Affiliation(s)
- Jon Clardy
- Department of Biological Chemistry and Molecular Pharmacology, Harvard Medical School, 240 Longwood Avenue, Boston, Massachusetts 02115, USA.
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177
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Holz MK, Ballif BA, Gygi SP, Blenis J. mTOR and S6K1 mediate assembly of the translation preinitiation complex through dynamic protein interchange and ordered phosphorylation events. Cell 2006; 123:569-80. [PMID: 16286006 DOI: 10.1016/j.cell.2005.10.024] [Citation(s) in RCA: 857] [Impact Index Per Article: 47.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/20/2005] [Revised: 09/05/2005] [Accepted: 10/31/2005] [Indexed: 11/29/2022]
Abstract
In response to nutrients, energy sufficiency, hormones, and mitogenic agents, S6K1 phosphorylates several targets linked to translation. However, the molecular mechanisms whereby S6K1 is activated, encounters substrate, and contributes to translation initiation are poorly understood. We show that mTOR and S6K1 maneuver on and off the eukaryotic initiation factor 3 (eIF3) translation initiation complex in a signal-dependent, choreographed fashion. When inactive, S6K1 associates with the eIF3 complex, while the S6K1 activator mTOR/raptor does not. Cell stimulation promotes mTOR/raptor binding to the eIF3 complex and phosphorylation of S6K1 at its hydrophobic motif. Phosphorylation results in S6K1 dissociation, activation, and subsequent phosphorylation of its translational targets, including eIF4B, which is then recruited into the complex in a phosphorylation-dependent manner. Thus, the eIF3 preinitiation complex acts as a scaffold to coordinate a dynamic sequence of events in response to stimuli that promote efficient protein synthesis.
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Affiliation(s)
- Marina K Holz
- Department of Cell Biology, Harvard Medical School, Boston, Massachusetts 02115, USA
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178
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Low WK, Dang Y, Schneider-Poetsch T, Shi Z, Choi NS, Merrick WC, Romo D, Liu JO. Inhibition of Eukaryotic Translation Initiation by the Marine Natural Product Pateamine A. Mol Cell 2005; 20:709-22. [PMID: 16337595 DOI: 10.1016/j.molcel.2005.10.008] [Citation(s) in RCA: 186] [Impact Index Per Article: 9.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/26/2005] [Revised: 07/14/2005] [Accepted: 10/07/2005] [Indexed: 11/19/2022]
Abstract
Translation initiation in eukaryotes is accomplished through the coordinated and orderly action of a large number of proteins, including the eIF4 initiation factors. Herein, we report that pateamine A (PatA), a potent antiproliferative and proapoptotic marine natural product, inhibits cap-dependent eukaryotic translation initiation. PatA bound to and enhanced the intrinsic enzymatic activities of eIF4A, yet it inhibited eIF4A-eIF4G association and promoted the formation of a stable ternary complex between eIF4A and eIF4B. These changes in eIF4A affinity for its partner proteins upon binding to PatA caused the stalling of initiation complexes on mRNA in vitro and induced stress granule formation in vivo. These results suggest that PatA will be a valuable molecular probe for future studies of eukaryotic translation initiation and may serve as a lead compound for the development of anticancer agents.
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Affiliation(s)
- Woon-Kai Low
- Department of Pharmacology, Johns Hopkins School of Medicine, Baltimore, Maryland 21205, USA
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