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Alagar Boopathy L, Beadle E, Xiao A, Garcia-Bueno Rico A, Alecki C, Garcia de-Andres I, Edelmeier K, Lazzari L, Amiri M, Vera M. The ribosome quality control factor Asc1 determines the fate of HSP70 mRNA on and off the ribosome. Nucleic Acids Res 2023; 51:6370-6388. [PMID: 37158240 PMCID: PMC10325905 DOI: 10.1093/nar/gkad338] [Citation(s) in RCA: 3] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/12/2022] [Revised: 04/16/2023] [Accepted: 04/20/2023] [Indexed: 05/10/2023] Open
Abstract
Cells survive harsh environmental conditions by potently upregulating molecular chaperones such as heat shock proteins (HSPs), particularly the inducible members of the HSP70 family. The life cycle of HSP70 mRNA in the cytoplasm is unique-it is translated during stress when most cellular mRNA translation is repressed and rapidly degraded upon recovery. Contrary to its 5' untranslated region's role in maximizing translation, we discovered that the HSP70 coding sequence (CDS) suppresses its translation via the ribosome quality control (RQC) mechanism. The CDS of the most inducible Saccharomyces cerevisiae HSP70 gene, SSA4, is uniquely enriched with low-frequency codons that promote ribosome stalling during heat stress. Stalled ribosomes are recognized by the RQC components Asc1p and Hel2p and two novel RQC components, the ribosomal proteins Rps28Ap and Rps19Bp. Surprisingly, RQC does not signal SSA4 mRNA degradation via No-Go-Decay. Instead, Asc1p destabilizes SSA4 mRNA during recovery from heat stress by a mechanism independent of ribosome binding and SSA4 codon optimality. Therefore, Asc1p operates in two pathways that converge to regulate the SSA4 mRNA life cycle during stress and recovery. Our research identifies Asc1p as a critical regulator of the stress response and RQC as the mechanism tuning HSP70 synthesis.
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Affiliation(s)
| | - Emma Beadle
- Department of Biochemistry. McGill University, Montreal, QuebecH3G 1Y6, Canada
| | - Alan RuoChen Xiao
- Department of Biochemistry. McGill University, Montreal, QuebecH3G 1Y6, Canada
| | | | - Celia Alecki
- Department of Biochemistry. McGill University, Montreal, QuebecH3G 1Y6, Canada
| | | | - Kyla Edelmeier
- Department of Biochemistry. McGill University, Montreal, QuebecH3G 1Y6, Canada
| | - Luca Lazzari
- Department of Biochemistry. McGill University, Montreal, QuebecH3G 1Y6, Canada
| | - Mehdi Amiri
- Department of Biochemistry. McGill University, Montreal, QuebecH3G 1Y6, Canada
| | - Maria Vera
- Department of Biochemistry. McGill University, Montreal, QuebecH3G 1Y6, Canada
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Alagar Boopathy LR, Jacob-Tomas S, Alecki C, Vera M. Mechanisms tailoring the expression of heat shock proteins to proteostasis challenges. J Biol Chem 2022; 298:101796. [PMID: 35248532 PMCID: PMC9065632 DOI: 10.1016/j.jbc.2022.101796] [Citation(s) in RCA: 35] [Impact Index Per Article: 17.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/29/2021] [Revised: 02/23/2022] [Accepted: 02/25/2022] [Indexed: 12/14/2022] Open
Abstract
All cells possess an internal stress response to cope with environmental and pathophysiological challenges. Upon stress, cells reprogram their molecular functions to activate a survival mechanism known as the heat shock response, which mediates the rapid induction of molecular chaperones such as the heat shock proteins (HSPs). This potent production overcomes the general suppression of gene expression and results in high levels of HSPs to subsequently refold or degrade misfolded proteins. Once the damage or stress is repaired or removed, cells terminate the production of HSPs and resume regular functions. Thus, fulfillment of the stress response requires swift and robust coordination between stress response activation and completion that is determined by the status of the cell. In recent years, single-cell fluorescence microscopy techniques have begun to be used in unravelling HSP-gene expression pathways, from DNA transcription to mRNA degradation. In this review, we will address the molecular mechanisms in different organisms and cell types that coordinate the expression of HSPs with signaling networks that act to reprogram gene transcription, mRNA translation, and decay and ensure protein quality control.
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3
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Choi Y, Jeong K, Shin S, Lee JW, Lee YS, Kim S, Kim SA, Jung J, Kim KP, Kim VN, Kim JS. MS1-Level Proteome Quantification Platform Allowing Maximally Increased Multiplexity for SILAC and In Vitro Chemical Labeling. Anal Chem 2020; 92:4980-4989. [PMID: 32167278 DOI: 10.1021/acs.analchem.9b05148] [Citation(s) in RCA: 1] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/23/2022]
Abstract
Quantitative proteomic platforms based on precursor intensity in mass spectrometry (MS1-level) uniquely support in vivo metabolic labeling with superior quantification accuracy but suffer from limited multiplexity (≤3-plex) and frequent missing quantities. Here we present a new MS1-level quantification platform that allows maximal multiplexing with high quantification accuracy and precision for the given labeling scheme. The platform currently comprises 6-plex in vivo SILAC or in vitro diethylation labeling with a dedicated algorithm and is also expandable to higher multiplexity (e.g., nine-plex for SILAC). For complex samples with broad dynamic ranges such as total cell lysates, our platform performs highly accurately and free of missing quantities. Furthermore, we successfully applied our method to measure protein synthesis rate under heat shock response in human cells by 6-plex pulsed SILAC experiments, demonstrating the unique biological merits of our in vivo platform to disclose translational regulations for cellular response to stress.
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Affiliation(s)
- Yeon Choi
- Center for RNA Research, Institute for Basic Science, Seoul 08826, Korea.,School of Biological Sciences, Seoul National University, Seoul 08826, Korea
| | - Kyowon Jeong
- Center for RNA Research, Institute for Basic Science, Seoul 08826, Korea.,School of Biological Sciences, Seoul National University, Seoul 08826, Korea
| | - Sanghee Shin
- Center for RNA Research, Institute for Basic Science, Seoul 08826, Korea.,School of Biological Sciences, Seoul National University, Seoul 08826, Korea
| | - Joon Won Lee
- Department of Applied Chemistry, Kyung Hee University, Yongin 17104, Korea
| | - Young-Suk Lee
- Center for RNA Research, Institute for Basic Science, Seoul 08826, Korea.,School of Biological Sciences, Seoul National University, Seoul 08826, Korea
| | - Sangtae Kim
- Illumina, Inc., San Diego, California 92122, United States
| | - Sun Ah Kim
- Center for RNA Research, Institute for Basic Science, Seoul 08826, Korea.,School of Biological Sciences, Seoul National University, Seoul 08826, Korea
| | - Jaehun Jung
- Department of Applied Chemistry, Kyung Hee University, Yongin 17104, Korea
| | - Kwang Pyo Kim
- Department of Applied Chemistry, Kyung Hee University, Yongin 17104, Korea
| | - V Narry Kim
- Center for RNA Research, Institute for Basic Science, Seoul 08826, Korea.,School of Biological Sciences, Seoul National University, Seoul 08826, Korea
| | - Jong-Seo Kim
- Center for RNA Research, Institute for Basic Science, Seoul 08826, Korea.,School of Biological Sciences, Seoul National University, Seoul 08826, Korea
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Obi S, Nakajima T, Hasegawa T, Nakamura F, Sakuma M, Toyoda S, Tei C, Inoue T. Heat induces myogenic transcription factors of myoblast cells via transient receptor potential vanilloid 1 (Trpv1). FEBS Open Bio 2018; 9:101-113. [PMID: 30652078 PMCID: PMC6325605 DOI: 10.1002/2211-5463.12550] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/13/2018] [Revised: 09/25/2018] [Accepted: 10/30/2018] [Indexed: 12/17/2022] Open
Abstract
Exercise generates heat, blood flow, and metabolic changes, thereby inducing hypertrophy of skeletal muscle cells. However, the mechanism by which heat incudes hypertrophy in response to heat is not well known. Here, we hypothesized that heat would induce differentiation of myoblast cells. We investigated the underlying mechanism by which myoblast cells respond to heat. When mouse myoblast cells were exposed to 42 °C for over 30 min, the phosphorylation level of protein kinase C (PKC) and heat shock factor 1 (Hsf1) increased, and the mRNA and protein expression level of heat shock protein 70 (Hsp70) increased. Inhibitors of transient receptor potential vanilloid 1 (Trpv1), calmodulin, PKC, and Hsf1, and the small interfering RNA‐mediated knockdown of Trpv1 diminished those heat responses. Heat exposure increased the phosphorylation levels of thymoma viral proto‐oncogene 1 (Akt), mammalian target of rapamycin (mTOR), eukaryotic translation initiation factor 4E binding protein 1 (Eif4ebp1), and ribosomal protein S6 kinase, polypeptide 1 (S6K1). The knockdown of Trpv1 decreased these heat‐induced responses. Antagonists of Hsp70 inhibited the phosphorylation level of Akt. Finally, heat increased the protein expression level of skeletal muscle markers such as myocyte enhancer factor 2D, myogenic factor 5, myogenic factor 6, and myogenic differentiation 1. Heat also increased myotube formation. Knockdown of Trpv1 diminished heat‐induced increases of those proteins and myotube formation. These results indicate that heat induces myogenic transcription factors of myoblast cells through the Trpv1, calmodulin, PKC, Hsf1, Hsp70, Akt, mTOR, Eif4ebp1, and S6K1 pathway. Moreover, heat increases myotube formation through Trpv1.
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Affiliation(s)
- Syotaro Obi
- Research Support Center Dokkyo Medical University Tochigi Japan.,Department of Cardiovascular Medicine Dokkyo Medical University Tochigi Japan
| | - Toshiaki Nakajima
- Department of Cardiovascular Medicine Dokkyo Medical University Tochigi Japan.,Heart Center Dokkyo Medical University Hospital Tochigi Japan
| | - Takaaki Hasegawa
- Department of Cardiovascular Medicine Dokkyo Medical University Tochigi Japan
| | - Fumitaka Nakamura
- Third Department of Internal Medicine Teikyo University Chiba Medical Center Japan
| | - Masashi Sakuma
- Department of Cardiovascular Medicine Dokkyo Medical University Tochigi Japan
| | - Shigeru Toyoda
- Department of Cardiovascular Medicine Dokkyo Medical University Tochigi Japan.,Heart Center Dokkyo Medical University Hospital Tochigi Japan
| | - Chuwa Tei
- Department of Cardiovascular Medicine Dokkyo Medical University Tochigi Japan
| | - Teruo Inoue
- Research Support Center Dokkyo Medical University Tochigi Japan.,Department of Cardiovascular Medicine Dokkyo Medical University Tochigi Japan.,Heart Center Dokkyo Medical University Hospital Tochigi Japan
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Nayak S, Siddiqui JK, Varner JD. Modelling and analysis of an ensemble of eukaryotic translation initiation models. IET Syst Biol 2016; 5:2. [PMID: 21261397 DOI: 10.1049/iet-syb.2009.0065] [Citation(s) in RCA: 19] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/04/2023] Open
Abstract
Programmed protein synthesis plays an important role in the cell cycle. Deregulated translation has been observed in several cancers. In this study, the authors constructed an ensemble of mathematical models describing the integration of growth factor signals with translation initiation. Using these models, the authors estimated critical structural features of the translation architecture. Sensitivity and robustness analysis with and without growth factors suggested that a balance between competing regulatory programmes governed translation initiation. Proteins such as Akt and mTor promoted initiation by integrating growth factor signals with the assembly of the 80S initiation complex. However, negative regulators such as PTEN and 4EBP1 restrained initiation in the absence of stimulation. Other proteins such as eIF4E were also found to be structurally critical as deletion of amplification of these components resulted in a network incapable of nominal operation. These findings could help understand the molecular basis of translation deregulation observed in cancer and perhaps lead to new anti-cancer therapeutic strategies. [Includes supplementary material].
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Affiliation(s)
- S Nayak
- Cornell University, School of Chemical and Biomolecular Engineering, Ithaca, USA
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7
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Chang CY, Lin WD, Tu SL. Genome-Wide Analysis of Heat-Sensitive Alternative Splicing in Physcomitrella patens. PLANT PHYSIOLOGY 2014; 165:826-840. [PMID: 24777346 PMCID: PMC4044832 DOI: 10.1104/pp.113.230540] [Citation(s) in RCA: 93] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 05/11/2023]
Abstract
Plant growth and development are constantly influenced by temperature fluctuations. To respond to temperature changes, different levels of gene regulation are modulated in the cell. Alternative splicing (AS) is a widespread mechanism increasing transcriptome complexity and proteome diversity. Although genome-wide studies have revealed complex AS patterns in plants, whether AS impacts the stress defense of plants is not known. We used heat shock (HS) treatments at nondamaging temperature and messenger RNA sequencing to obtain HS transcriptomes in the moss Physcomitrella patens. Data analysis identified a significant number of novel AS events in the moss protonema. Nearly 50% of genes are alternatively spliced. Intron retention (IR) is markedly repressed under elevated temperature but alternative donor/acceptor site and exon skipping are mainly induced, indicating differential regulation of AS in response to heat stress. Transcripts undergoing heat-sensitive IR are mostly involved in specific functions, which suggests that plants regulate AS with transcript specificity under elevated temperature. An exonic GAG-repeat motif in these IR regions may function as a regulatory cis-element in heat-mediated AS regulation. A conserved AS pattern for HS transcription factors in P. patens and Arabidopsis (Arabidopsis thaliana) reveals that heat regulation for AS evolved early during land colonization of green plants. Our results support that AS of specific genes, including key HS regulators, is fine-tuned under elevated temperature to modulate gene regulation and reorganize metabolic processes.
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Affiliation(s)
- Chiung-Yun Chang
- Institute of Plant and Microbial Biology (C.-Y.C., W.-D.L., S.-L.T.) and Molecular and Biological Agricultural Sciences Program, Taiwan International Graduate Program (C.-Y.C., S.-L.T.), Academia Sinica, Taipei 11529, Taiwan; andGraduate Institute of Biotechnology (C.-Y.C.) and Biotechnology Center (S.-L.T.), National Chung-Hsing University, Taichung 402, Taiwan
| | - Wen-Dar Lin
- Institute of Plant and Microbial Biology (C.-Y.C., W.-D.L., S.-L.T.) and Molecular and Biological Agricultural Sciences Program, Taiwan International Graduate Program (C.-Y.C., S.-L.T.), Academia Sinica, Taipei 11529, Taiwan; andGraduate Institute of Biotechnology (C.-Y.C.) and Biotechnology Center (S.-L.T.), National Chung-Hsing University, Taichung 402, Taiwan
| | - Shih-Long Tu
- Institute of Plant and Microbial Biology (C.-Y.C., W.-D.L., S.-L.T.) and Molecular and Biological Agricultural Sciences Program, Taiwan International Graduate Program (C.-Y.C., S.-L.T.), Academia Sinica, Taipei 11529, Taiwan; andGraduate Institute of Biotechnology (C.-Y.C.) and Biotechnology Center (S.-L.T.), National Chung-Hsing University, Taichung 402, Taiwan
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Howard A, Rogers AN. Role of translation initiation factor 4G in lifespan regulation and age-related health. Ageing Res Rev 2014; 13:115-24. [PMID: 24394551 DOI: 10.1016/j.arr.2013.12.008] [Citation(s) in RCA: 20] [Impact Index Per Article: 2.0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/11/2013] [Revised: 12/18/2013] [Accepted: 12/23/2013] [Indexed: 01/04/2023]
Abstract
Inhibiting expression of eukaryotic translation initiation factor 4G (eIF4G) arrests normal development but extends lifespan when suppressed during adulthood. In addition to reducing overall translation, inhibition alters the stoichiometry of mRNA translation in favor of genes important for responding to stress and against those associated with growth and reproduction in C. elegans. In humans, aberrant expression of eIF4G is associated with certain forms of cancer and neurodegeneration. Here we review what is known about the roles of eIF4G in molecular, cellular, and organismal contexts. Also discussed are the gaps in understanding of this factor, particularly with regard to the roles of specific forms of expression in individual tissues and the importance of understanding eIF4G for development of potential therapeutic applications.
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9
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Shalgi R, Hurt JA, Krykbaeva I, Taipale M, Lindquist S, Burge CB. Widespread regulation of translation by elongation pausing in heat shock. Mol Cell 2013; 49:439-52. [PMID: 23290915 DOI: 10.1016/j.molcel.2012.11.028] [Citation(s) in RCA: 226] [Impact Index Per Article: 20.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/27/2012] [Revised: 09/27/2012] [Accepted: 11/30/2012] [Indexed: 10/27/2022]
Abstract
Global repression of protein synthesis is a hallmark of the cellular stress response and has been attributed primarily to inhibition of translation initiation, although this mechanism may not always explain the full extent of repression. Here, using ribosome footprinting, we show that 2 hr of severe heat stress triggers global pausing of translation elongation at around codon 65 on most mRNAs in both mouse and human cells. The genome-wide nature of the phenomenon, its location, and features of protein N termini suggested the involvement of ribosome-associated chaperones. After severe heat shock, Hsp70's interactions with the translational machinery were markedly altered and its association with ribosomes was reduced. Pretreatment with mild heat stress or overexpression of Hsp70 protected cells from heat shock-induced elongation pausing, while inhibition of Hsp70 activity triggered elongation pausing without heat stress. Our findings suggest that regulation of translation elongation in general, and by chaperones in particular, represents a major component of cellular stress responses.
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Affiliation(s)
- Reut Shalgi
- Department of Biology, Massachusetts Institute of Technology, Cambridge, MA 02142, USA
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10
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Lee ECH, Strange K. GCN-2 dependent inhibition of protein synthesis activates osmosensitive gene transcription via WNK and Ste20 kinase signaling. Am J Physiol Cell Physiol 2012; 303:C1269-77. [PMID: 23076791 DOI: 10.1152/ajpcell.00294.2012] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Abstract
Increased gpdh-1 transcription is required for accumulation of the organic osmolyte glycerol and survival of Caenorhabditis elegans during hypertonic stress. Our previous work has shown that regulators of gpdh-1 (rgpd) gene knockdown constitutively activates gpdh-1 expression. Fifty-five rgpd genes play essential roles in translation suggesting that inhibition of protein synthesis is an important signal for regulating osmoprotective gene transcription. We demonstrate here that translation is reduced dramatically by hypertonic stress or knockdown of rgpd genes encoding aminoacyl-tRNA synthetases and eukaryotic translation initiation factors (eIFs). Toxin-induced inhibition of translation also activates gpdh-1 expression. Hypertonicity-induced translation inhibition is mediated by general control nonderepressible (GCN)-2 kinase signaling and eIF-2α phosphoryation. Loss of gcn-1 or gcn-2 function prevents eIF-2α phosphorylation, completely blocks reductions in translation, and inhibits gpdh-1 transcription. gpdh-1 expression is regulated by the highly conserved with-no-lysine kinase (WNK) and Ste20 kinases WNK-1 and GCK-3, which function in the GCN-2 signaling pathway downstream from eIF-2α phosphorylation. Our previous work has shown that hypertonic stress causes rapid and dramatic protein damage in C. elegans and that inhibition of translation reduces this damage. The current studies demonstrate that reduced translation also serves as an essential signal for activation of WNK-1/GCK-3 kinase signaling and subsequent transcription of gpdh-1 and possibly other osmoprotective genes.
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Affiliation(s)
- Elaine Choung-Hee Lee
- Boylan Center for Cellular and Molecular Physiology, Mount Desert Island Biological Laboratory, Salisbury Cove, ME 04672, USA
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11
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Silver JT, Noble EG. Regulation of survival gene hsp70. Cell Stress Chaperones 2012; 17:1-9. [PMID: 21874533 PMCID: PMC3227850 DOI: 10.1007/s12192-011-0290-6] [Citation(s) in RCA: 104] [Impact Index Per Article: 8.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2011] [Revised: 08/15/2011] [Accepted: 08/16/2011] [Indexed: 12/31/2022] Open
Abstract
Rapid expression of the survival gene, inducible heat shock protein 70 (hsp70), is critical for mounting cytoprotection against severe cellular stress, like elevated temperature. Hsp70 protein chaperones the refolding of heat-denatured peptides to minimize proteolytic degradation as a part of an eukaryotically conserved phenomenon referred to as the heat shock response. The physiologic stress associated with exercise, which can include elevated temperature, mechanical damage, hypoxia, lowered pH, and reactive oxygen species generation, may promote protein unfolding, leading to hsp70 gene expression in skeletal myofibers. Although the pre-transcriptional activation of hsp70 gene expression has been thoroughly reviewed, discussion of downstream hsp70 gene regulation is less extensive. The purpose of this brief review was to examine all levels of hsp70 gene regulation in response to heat stress and exercise with a special focus on skeletal myofibers where data are available. In general, while heat stress represses bulk gene expression, hsp70 mRNA expression is enhanced. Post-transcriptionally, intronless hsp70 mRNA circumvents a host of decay pathways, as well as heat stress-repressed pre-mRNA splicing and nuclear export. Pre-translationally, hsp70 mRNA is excluded from stress granules and preferentially translated during heat stress-repressed global cap-dependent translation. Post-translationally, nascent Hsp70 protein is thermodynamically stable at elevated temperatures, allowing for the commencement of chaperoning activity early after synthesis to attenuate the heat shock response and protect against subsequent injury. This review demonstrates that hsp70 mRNA expression is closely coupled with functional protein translation.
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Affiliation(s)
- Jordan Thomas Silver
- School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, ON Canada N6A 3K7
| | - Earl G. Noble
- School of Kinesiology, Faculty of Health Sciences, The University of Western Ontario, London, ON Canada N6A 3K7
- Lawson Health Research Institute, The University of Western Ontario, London, ON Canada N6A 3K7
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12
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Lequieu J, Chakrabarti A, Nayak S, Varner JD. Computational modeling and analysis of insulin induced eukaryotic translation initiation. PLoS Comput Biol 2011; 7:e1002263. [PMID: 22102801 PMCID: PMC3213178 DOI: 10.1371/journal.pcbi.1002263] [Citation(s) in RCA: 15] [Impact Index Per Article: 1.2] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/09/2011] [Accepted: 09/23/2011] [Indexed: 11/18/2022] Open
Abstract
Insulin, the primary hormone regulating the level of glucose in the bloodstream, modulates a variety of cellular and enzymatic processes in normal and diseased cells. Insulin signals are processed by a complex network of biochemical interactions which ultimately induce gene expression programs or other processes such as translation initiation. Surprisingly, despite the wealth of literature on insulin signaling, the relative importance of the components linking insulin with translation initiation remains unclear. We addressed this question by developing and interrogating a family of mathematical models of insulin induced translation initiation. The insulin network was modeled using mass-action kinetics within an ordinary differential equation (ODE) framework. A family of model parameters was estimated, starting from an initial best fit parameter set, using 24 experimental data sets taken from literature. The residual between model simulations and each of the experimental constraints were simultaneously minimized using multiobjective optimization. Interrogation of the model population, using sensitivity and robustness analysis, identified an insulin-dependent switch that controlled translation initiation. Our analysis suggested that without insulin, a balance between the pro-initiation activity of the GTP-binding protein Rheb and anti-initiation activity of PTEN controlled basal initiation. On the other hand, in the presence of insulin a combination of PI3K and Rheb activity controlled inducible initiation, where PI3K was only critical in the presence of insulin. Other well known regulatory mechanisms governing insulin action, for example IRS-1 negative feedback, modulated the relative importance of PI3K and Rheb but did not fundamentally change the signal flow.
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Affiliation(s)
- Joshua Lequieu
- School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York, United States of America
| | - Anirikh Chakrabarti
- School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York, United States of America
| | - Satyaprakash Nayak
- School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York, United States of America
| | - Jeffrey D. Varner
- School of Chemical and Biomolecular Engineering, Cornell University, Ithaca, New York, United States of America
- * E-mail:
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13
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de Nadal E, Ammerer G, Posas F. Controlling gene expression in response to stress. Nat Rev Genet 2011; 12:833-45. [PMID: 22048664 DOI: 10.1038/nrg3055] [Citation(s) in RCA: 450] [Impact Index Per Article: 34.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Acute stress puts cells at risk, and rapid adaptation is crucial for maximizing cell survival. Cellular adaptation mechanisms include modification of certain aspects of cell physiology, such as the induction of efficient changes in the gene expression programmes by intracellular signalling networks. Recent studies using genome-wide approaches as well as single-cell transcription measurements, in combination with classical genetics, have shown that rapid and specific activation of gene expression can be accomplished by several different strategies. This article discusses how organisms can achieve generic and specific responses to different stresses by regulating gene expression at multiple stages of mRNA biogenesis from chromatin structure to transcription, mRNA stability and translation.
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Affiliation(s)
- Eulàlia de Nadal
- Cell Signaling Unit, Departament de Ciències Experimentals i de la Salut, Universitat Pompeu Fabra, Barcelona, Spain
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14
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Heldens L, Hensen SMM, Onnekink C, van Genesen ST, Dirks RP, Lubsen NH. An atypical unfolded protein response in heat shocked cells. PLoS One 2011; 6:e23512. [PMID: 21853144 PMCID: PMC3154502 DOI: 10.1371/journal.pone.0023512] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/20/2011] [Accepted: 07/19/2011] [Indexed: 11/18/2022] Open
Abstract
Background The heat shock response (HSR) and the unfolded protein response (UPR) are both activated by proteotoxic stress, although in different compartments, and share cellular resources. How these resources are allocated when both responses are active is not known. Insight in possible crosstalk will help understanding the consequences of failure of these systems in (age-related) disease. Results In heat stressed HEK293 cells synthesis of the canonical UPR transcription factors XBP1s and ATF4 was detected as well as HSF1 independent activation of the promoters of the ER resident chaperones HSPA5 (BiP) and DNAJB9 (ERdj4). However, the heat stress activation of the DNAJB9 promoter, a XBP1s target, was not blocked in cells expressing a dominant negative IRE1α mutant, and thus did not require XBP1s. Furthermore, the DNA element required for heat stress activation of the DNAJB9 promoter is distinct from the ATF4 and ATF6 target elements; even though inhibition of eIF2α phosphorylation resulted in a decreased activation of the DNAJB9 promoter upon heat stress, suggesting a role for an eIF2α phosphorylation dependent product. Conclusions The initial step in the UPR, synthesis of transcription factors, is activated by heat stress but the second step, transcriptional transactivation by these factors, is blocked and these pathways of the UPR are thus not productive. Expression of canonical ER chaperones is part of the response of heat stressed cells but another set of transcription factors has been recruited to regulate expression of these ER chaperones.
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Affiliation(s)
- Lonneke Heldens
- Department of Biomolecular Chemistry, Radboud University Nijmegen, Nijmegen, The Netherlands
| | - Sanne M. M. Hensen
- Department of Biomolecular Chemistry, Radboud University Nijmegen, Nijmegen, The Netherlands
| | - Carla Onnekink
- Department of Biomolecular Chemistry, Radboud University Nijmegen, Nijmegen, The Netherlands
| | - Siebe T. van Genesen
- Department of Biomolecular Chemistry, Radboud University Nijmegen, Nijmegen, The Netherlands
| | - Ron P. Dirks
- Department of Biomolecular Chemistry, Radboud University Nijmegen, Nijmegen, The Netherlands
| | - Nicolette H. Lubsen
- Department of Biomolecular Chemistry, Radboud University Nijmegen, Nijmegen, The Netherlands
- * E-mail:
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15
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Spriggs KA, Bushell M, Willis AE. Translational regulation of gene expression during conditions of cell stress. Mol Cell 2010; 40:228-37. [PMID: 20965418 DOI: 10.1016/j.molcel.2010.09.028] [Citation(s) in RCA: 523] [Impact Index Per Article: 37.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/08/2010] [Revised: 09/10/2010] [Accepted: 09/28/2010] [Indexed: 01/17/2023]
Abstract
A number of stresses, including nutrient stress, temperature shock, DNA damage, and hypoxia, can lead to changes in gene expression patterns caused by a general shutdown and reprogramming of protein synthesis. Each of these stress conditions results in selective recruitment of ribosomes to mRNAs whose protein products are required for responding to stress. This recruitment is regulated by elements within the 5' and 3' untranslated regions of mRNAs, including internal ribosome entry segments, upstream open reading frames, and microRNA target sites. These elements can act singly or in combination and are themselves regulated by trans-acting factors. Translational reprogramming can result in increased life span, and conversely, deregulation of these translation pathways is associated with disease including cancer and diabetes.
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Affiliation(s)
- Keith A Spriggs
- Centre for Biomolecular Sciences, School of Pharmacy, University of Nottingham, University Park, Nottingham NG7 2RD, UK
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16
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Sukarieh R, Sonenberg N, Pelletier J. The eIF4E-binding proteins are modifiers of cytoplasmic eIF4E relocalization during the heat shock response. Am J Physiol Cell Physiol 2009; 296:C1207-17. [PMID: 19244480 DOI: 10.1152/ajpcell.00511.2008] [Citation(s) in RCA: 22] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Stress granules (SGs) arise as a consequence of cellular stress, contain stalled translation preinitiation complexes, and are associated with cell survival during environmental insults. SGs are dynamic entities with proteins relocating into and out of them during stress. Among the repertoire of proteins present in SGs is eukaryotic initiation factor 4E (eIF4E), a translation factor required for cap-dependent translation and that regulates a rate-limiting step for protein synthesis. Herein, we demonstrate that localization of eIF4E to SGs is dependent on the presence of a family of repressor proteins, eIF4E-binding proteins (4E-BPs). Our results demonstrate that 4E-BPs regulate the SG localization of eIF4E.
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Affiliation(s)
- R Sukarieh
- McGill University, Montreal, Quebec, Canada H3G 1Y6
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17
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Martin J, Masri J, Bernath A, Nishimura RN, Gera J. Hsp70 associates with Rictor and is required for mTORC2 formation and activity. Biochem Biophys Res Commun 2008; 372:578-83. [PMID: 18505677 DOI: 10.1016/j.bbrc.2008.05.086] [Citation(s) in RCA: 53] [Impact Index Per Article: 3.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 05/01/2008] [Accepted: 05/14/2008] [Indexed: 10/22/2022]
Abstract
mTORC2 is a multiprotein kinase composed of mTOR, mLST8, PRR5, mSIN1 and Rictor. The complex is insensitive to rapamycin and has demonstrated functions controlling cell growth, motility, invasion and cytoskeletal assembly. mTORC2 is the major hydrophobic domain kinase which renders Akt fully active via phosphorylation on serine 473. We isolated Hsp70 as a putative Rictor interacting protein in a yeast two-hybrid assay and confirmed this interaction via co-immunoprecipitation and colocalization experiments. In cells expressing an antisense RNA targeting Hsp70, mTORC2 formation and activity were impaired. Moreover, in cells lacking Hsp70 expression, mTORC2 activity was inhibited following heat shock while controls demonstrated increased mTORC2 activity. These differential effects on mTORC2 activity were specific, in that mTORC1 did not demonstrate Hsp70-dependent alterations under these conditions. These data suggest that Hsp70 is a component of mTORC2 and is required for proper assembly and activity of the kinase both constitutively and following heat shock.
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Affiliation(s)
- Jheralyn Martin
- Department of Research & Development, Greater Los Angeles Veterans Affairs Healthcare System, 16111 Plummer Street (151), Building 1, Room C111A, Los Angeles, CA 91343, USA
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18
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Meyuhas O. Physiological roles of ribosomal protein S6: one of its kind. INTERNATIONAL REVIEW OF CELL AND MOLECULAR BIOLOGY 2008; 268:1-37. [PMID: 18703402 DOI: 10.1016/s1937-6448(08)00801-0] [Citation(s) in RCA: 170] [Impact Index Per Article: 10.6] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/13/2022]
Abstract
The phosphorylation of ribosomal protein S6 (rpS6), which occurs in response to a wide variety of stimuli on five evolutionarily conserved serine residues, has attracted much attention since its discovery more than three decades ago. However, despite a large body of information on the respective kinases and the signal transduction pathways, the role of this phosphorylation remained obscure. It is only recent that targeting the genes encoding rpS6, the phosphorylatable serine residues or the respective kinases that the unique role of rpS6 and its posttranslational modification have started to be elucidated. This review focuses primarily on the critical role of rpS6 for mouse development, the pathways that transduce various signals into rpS6 phosphorylation, and the physiological functions of this modification. The mechanism(s) underlying the diverse effects of rpS6 phosphorylation on cellular and organismal physiology has yet to be determined. However, a model emerging from the currently available data suggests that rpS6 phosphorylation operates, at least partly, by counteracting positive signals simultaneously induced by rpS6 kinase, and thus might be involved in fine-tuning of the cellular response to these signals.
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Affiliation(s)
- Oded Meyuhas
- Department of Biochemistry, Hebrew University-Hadassah Medical School, Jerusalem 91120, Israel
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19
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Halaby MJ, Yang DQ. p53 translational control: a new facet of p53 regulation and its implication for tumorigenesis and cancer therapeutics. Gene 2007; 395:1-7. [PMID: 17395405 DOI: 10.1016/j.gene.2007.01.029] [Citation(s) in RCA: 57] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/20/2006] [Revised: 01/26/2007] [Accepted: 01/26/2007] [Indexed: 01/09/2023]
Abstract
While posttranslational regulation of p53 levels by its interaction with the ubiquitin ligase MDM2 is widely accepted, it has recently become clear that regulation of p53 translation also contributes to p53 induction following DNA damage. However, the mechanisms underlying the translational control of p53 are still poorly understood. In this review, we will focus on the translational regulation of p53 through the 5'- and 3'-untranslated regions of its mRNA. We will also discuss in detail the recent discovery of the p53 internal ribosome entry site (IRES), its role in p53 translation in response to DNA damage, and how it might lead to a better understanding of the process of oncogenesis and provide new avenues for cancer therapeutics.
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Affiliation(s)
- Marie-Jo Halaby
- Sanford School of Medicine, The University of South Dakota, Division of Basic Biomedical Sciences, 414 East Clark Street, Lee Medicine Building, Vermillion, South Dakota 57069, USA
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20
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Marín-Vinader L, van Genesen ST, Lubsen NH. mRNA made during heat shock enters the first round of translation. ACTA ACUST UNITED AC 2006; 1759:535-42. [PMID: 17118471 DOI: 10.1016/j.bbaexp.2006.10.003] [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] [Received: 06/21/2006] [Revised: 10/12/2006] [Accepted: 10/16/2006] [Indexed: 11/26/2022]
Abstract
To determine whether mRNA synthesized during a heat shock is translated at least once in spite of the strong inhibition of translation by heat shock, we used nonsense-mediated decay (NMD) as an assay since NMD requires a round of translation. As NMD substrate we used the human psigammaE-crystallin gene, which contains a premature termination codon, and as control, its close relative, the human gammaD-crystallin gene, both placed under control of the Hsp70 promoter. We show that no spliced psigammaE-crystallin mRNA can be detected in heat shocked cells, suggesting that NMD resumes as soon as splicing is restored. We further show that newly synthesized mRNAs co-sediment with the 40S ribosomal subunits, indicating that the transcripts are recruited to the translation machinery but are stalled at the translation initiation stage. Using fluorescence loss in photobleaching (FLIP) we show that cytoplasmic EGFP-CBP20 is immobile in heat shocked cells. CBP20 is part of the cap binding complex which is thought to direct the first round of translation. Together our data suggest that all mRNAs made during heat shock enter the pioneer round of translation.
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Affiliation(s)
- Laura Marín-Vinader
- Department of Biochemistry 271, Radboud University of Nijmegen. P.O. Box 9101, 6500 HB Nijmegen, The Netherlands
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21
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Abstract
The TOR (target of rapamycin) pathway is an evolutionarily conserved signaling module regulating cell growth (accumulation of mass) in response to a variety of environmental cues such as nutrient availability, hypoxia, DNA damage and osmotic stress. Its pivotal role in cellular and organismal homeostasis is reflected in the fact that unrestrained signaling activity in mammals is associated with the occurrence of disease states including inflammation, cancer and diabetes. The existence of TOR homologs in unicellular organisms whose growth is affected by environmental factors, such as temperature, nutrients and osmolarity, suggests an ancient role for the TOR signaling network in the surveillance of stress conditions. Here, we will summarize recent advances in the TOR signaling field with special emphasis on how stress conditions impinge on insulin/insulin-like growth factor signaling/TOR signaling.
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Affiliation(s)
- J H Reiling
- Whitehead Institute for Biomedical Research, Massachusetts Institute of Technology, Cambridge, MA 02142-1479, USA
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22
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Murata T, Shimotohno K. Ubiquitination and proteasome-dependent degradation of human eukaryotic translation initiation factor 4E. J Biol Chem 2006; 281:20788-20800. [PMID: 16720573 DOI: 10.1074/jbc.m600563200] [Citation(s) in RCA: 62] [Impact Index Per Article: 3.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/20/2022] Open
Abstract
Translation initiation factor 4E (eIF4E) is a cytoplasmic cap-binding protein that is required for cap-dependent translation initiation. Here, we have shown that eIF4E is ubiquitinated primarily at Lys-159 and incubation of cells with a proteasome inhibitor leads to increased eIF4E levels, suggesting the proteasome-dependent proteolysis of ubiquitinated eIF4E. Ubiquitinated eIF4E retained its cap binding ability, whereas eIF4E phosphorylation and eIF4G binding were reduced by ubiquitination. The W73A mutant of eIF4E exhibited enhanced ubiquitination/degradation, and 4E-BP overexpression protected eIF4E from ubiquitination/degradation. Because heat shock or the expression of the carboxyl terminus of heat shock cognate protein 70-interacting protein (Chip) dramatically increased eIF4E ubiquitination, Chip may be at least one ubiquitin E3 ligase responsible for eIF4E ubiquitination.
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Affiliation(s)
- Takayuki Murata
- Department of Viral Oncology, Institute for Virus Research, Kyoto University, Sakyo-ku, Kyoto 606-8507, Japan
| | - Kunitada Shimotohno
- Department of Viral Oncology, Institute for Virus Research, Kyoto University, Sakyo-ku, Kyoto 606-8507, Japan.
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23
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O'Loghlen A, Pérez-Morgado MI, Salinas M, Martín ME. N-acetyl-cysteine abolishes hydrogen peroxide-induced modification of eukaryotic initiation factor 4F activity via distinct signalling pathways. Cell Signal 2006; 18:21-31. [PMID: 15907373 DOI: 10.1016/j.cellsig.2005.03.013] [Citation(s) in RCA: 33] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 02/21/2005] [Revised: 03/10/2005] [Accepted: 03/10/2005] [Indexed: 12/16/2022]
Abstract
During the oxidative stress generated by hydrogen peroxide (H2O2) in nerve growth factor (NGF)-differentiated PC12 cells, eIF4E binding protein (4E-BP1) and initiation factor 4E (eIF4E) phosphorylated levels decrease significantly, and an enhancement of the association of 4E-BP1 to eIF4E, which in turn decreases eIF4F formation is observed. The treatment with N-acetyl-cysteine (NAC) completely abolishes the H2O2-induced decrease in eIF4E phosphorylated levels, whereas the decrease in 4E-BP1 phosphorylated levels and eIF4F activity inhibition are significantly but not fully reversed. Rapamycin, the mammalian target of rapamycin (FRAP/mTOR) inhibitor, prevents the effect of NAC on H2O2-induced eIF4F complex formation inhibition. Besides the inhibitor induces a similar decrease in 4E-BP1 phosphorylated levels to that promote by H2O2. However, rapamycin has no effect on the NAC-induced recovery in phosphorylated eIF4E levels. Neither the MAP kinase inhibitors, PD98056 and SB203580, or the protein phosphatase 2A inhibitor, okadaic acid, mimic NAC effect on the H2O2-induced eIF4E dephosphorylation. Altogether our findings suggest that the effects caused by oxidative stress on eIF4s factors depends on two MAP kinase-independent signal transduction pathways, being at least one of them rapamycin-dependent.
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Affiliation(s)
- A O'Loghlen
- Servicio de Bioquímica, Departamento de Investigación, Hospital Ramón y Cajal, Ctra. Colmenar Km. 9, 28034 Madrid, Spain
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24
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Rolfe M, McLEOD L, Pratt P, Proud C. Activation of protein synthesis in cardiomyocytes by the hypertrophic agent phenylephrine requires the activation of ERK and involves phosphorylation of tuberous sclerosis complex 2 (TSC2). Biochem J 2005; 388:973-84. [PMID: 15757502 PMCID: PMC1183479 DOI: 10.1042/bj20041888] [Citation(s) in RCA: 101] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
The hypertrophic Gq-protein-coupled receptor agonist PE (phenylephrine) activates protein synthesis. We showed previously that activation of protein synthesis by PE requires MEK [MAPK (mitogen-activated protein kinase)/ERK (extracellular-signal-regulated kinase) kinase] and mTOR (mammalian target of rapamycin). However, it remained unclear whether ERK activation was required and which downstream components were involved in activating mTOR and protein synthesis. Using an adenovirus encoding the MKP3 (MAPK phosphatase 3) to inhibit ERK activity, we demonstrate that ERK is essential for the activation of protein synthesis by PE. Activation and phosphorylation of S6K1 (ribosomal protein S6 kinase 1) and phosphorylation of eIF4E (eukaryotic initiation factor 4E)-binding protein (both are mTOR targets) were also inhibited by MKP3, suggesting that ERK is also required for the activation of mTOR signalling. PE stimulation of cardiomyocytes induced the phosphorylation of TSC2 (tuberous sclerosis complex 2), a negative regulator of mTOR activity. TSC2 was phosphorylated only weakly at Thr1462, but phosphorylated at additional sites within the sequence RXRXX(S/T). This differs from the phosphorylation induced by insulin, indicating that MEK/ERK signalling targets distinct sites in TSC2. This phosphorylation may be mediated by p90RSK (90 kDa ribosomal protein S6K), which is activated by ERK, and appears to involve phosphorylation at Ser1798. Activation of protein synthesis by PE is partially insensitive to the mTOR inhibitor rapamycin. Inhibition of the MAPK-interacting kinases by CGP57380 decreases the phosphorylation of eIF4E and PE-induced protein synthesis. Moreover, CGP57380+rapamycin inhibited protein synthesis to the same extent as blocking ERK activation, suggesting that MAPK-interacting kinases and regulation of mTOR each contribute to the activation of protein synthesis by PE in cardiomyocytes.
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Affiliation(s)
- Mark Rolfe
- *Division of Molecular Physiology, School of Life Sciences, University of Dundee, MSI/WTB Complex, Dow Street, Dundee DD1 5EH, U.K
| | - Laura E. McLEOD
- *Division of Molecular Physiology, School of Life Sciences, University of Dundee, MSI/WTB Complex, Dow Street, Dundee DD1 5EH, U.K
| | - Phillip F. Pratt
- †Department of Medicine, Medical College of Wisconsin, Milwaukee, WI 53226, U.S.A
| | - Christopher G. Proud
- *Division of Molecular Physiology, School of Life Sciences, University of Dundee, MSI/WTB Complex, Dow Street, Dundee DD1 5EH, U.K
- To whom correspondence should be addressed (email )
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25
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Niedzwiecka A, Darzynkiewicz E, Stolarski R. Thermodynamics of mRNA 5' cap binding by eukaryotic translation initiation factor eIF4E. Biochemistry 2004; 43:13305-17. [PMID: 15491137 DOI: 10.1021/bi0491651] [Citation(s) in RCA: 38] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
Translation of mRNA in eukaryotes begins with specific recognition of the 5' cap structure by the highly conserved protein, eIF4E. The thermodynamics of eIF4E interaction with nine chemical cap analogues has been studied by means of emission spectroscopy. High-sensitivity measurements of intrinsic protein fluorescence quenching upon cap binding provided equilibrium association constants in the temperature range of 279 to 314 K. A van't Hoff analysis yielded the negative binding enthalpies for the entire cap analogue series, -16.6 to -81 kJ mol(-1), and the entropies covering the range of +40.3 to -136 J mol(-1) K(-1) at 293 K. The main enthalpic contributions come from interactions of the phosphate chains and positively charged amino acids and the cation-pi stacking of 7-methylguanine with tryptophans. A nontrivial, statistically important isothermal enthalpy-entropy compensation has been detected (T(c) = 399 +/- 24 K), which points to significant fluctuations of apo-eIF4E and indicates that the cap-binding microstate lies 9.66 +/- 1.7 kJ mol(-1) below the mean energy of all available conformational states. For five cap analogues, large and positive heat capacity changes have been found. The values of DeltaC(p) degrees correlate with the free energies of eIF4E binding due to stiffening of the protein upon interaction with cap analogues. At biological temperatures, binding of the natural caps has both favorable enthalpy and favorable entropy. Thermodynamic coupling of cap-eIF4E association to intramolecular self-stacking of dinucleotide cap analogues strongly influences the enthalpies and entropies of the binding, but has a negligible effect on the resultant DeltaG degrees and DeltaC(p) degrees values.
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Affiliation(s)
- Anna Niedzwiecka
- Department of Biophysics, Institute of Experimental Physics, Warsaw University, 02-089 Warszawa, Poland
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26
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Stephenson AH, Christian JF, Seidel ER. Polyamines regulate eukaryotic initiation factor 4E-binding protein 1 gene transcription. Biochem Biophys Res Commun 2004; 323:204-12. [PMID: 15351722 DOI: 10.1016/j.bbrc.2004.08.076] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/09/2004] [Indexed: 11/26/2022]
Abstract
Difluoromethylornithine-induced polyamine depletion produced a significant fall in the rate of 4E-BP1 gene transcription in IEC-6 cells, without a change in stability of the 4E-BP1 message. The effect was reversed by the addition of exogenous putrescine. Decreased 4E-BP1 gene transcription produced a concomitant fall in steady-state concentration of the 4E-BP1 protein. Segments of the 4E-BP1 gene 5' flanking sequence were inserted into a GFP reporter construct. While all the segments containing the first 500 nucleotides 5' to exon 1 were capable of driving GFP expression, two regions (between -2465 and -1965, and between -896 and 511) did so in a polyamine-dependent manner. Steady-state concentration of ornithine decarboxylase (ODC), the first enzyme in the polyamine biosynthetic pathway, was increased in response to polyamine depletion. These data provide a mechanism by which polyamines affect transcription of the 4E-BP1 gene, which in turn affect translation of ODC and perhaps other cap-dependent proteins.
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Affiliation(s)
- A H Stephenson
- Department of Physiology, Brody School of Medicine, East Carolina University, Greenville, NC 27858, USA
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27
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Orton KC, Ling J, Waskiewicz AJ, Cooper JA, Merrick WC, Korneeva NL, Rhoads RE, Sonenberg N, Traugh JA. Phosphorylation of Mnk1 by caspase-activated Pak2/gamma-PAK inhibits phosphorylation and interaction of eIF4G with Mnk. J Biol Chem 2004; 279:38649-57. [PMID: 15234964 DOI: 10.1074/jbc.m407337200] [Citation(s) in RCA: 29] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
The mitogen-activated protein kinase-interacting kinase 1 (Mnk1) is phosphorylated by caspase-cleaved protein kinase Pak2/gamma-PAK but not by Cdc42-activated Pak2. Phosphorylation of Mnk1 is rapid, reaching 1 mol/mol within 15 min of incubation with Pak2. A kinetic analysis of the phosphorylation of Mnk1 by Pak2 yields a K(m) of 0.6 microm and a V(max) of 14.9 pmol of (32)P/min/microg of Pak2. Two-dimensional tryptic phosphopeptide mapping of Mnk1 phosphorylated by Pak2 yields two distinct phosphopeptides. Analysis of the phosphopeptides by automated microsequencing and manual Edman degradation identified the sites in Mnk1 as Thr(22) and Ser(27). Mnk1, activated by phosphorylation with Erk2, phosphorylates the eukaryotic initiation factor (eIF) 4E and the eIF4G components of eIF4F. Phosphorylation of Mnk1 by Pak2 does not activate Mnk1, as measured with either eIF4E or eIF4F as substrate. Phosphorylation of Erk2-activated Mnk1 by Pak2 has no effect on phosphorylation of eIF4E but reduces phosphorylation of eIF4G by Mnk1 by up to 50%. Phosphorylation of Mnk1 by Pak2 inhibits binding of eIF4G peptides containing the Mnk1 binding site by up to 80%. When 293T cells are subjected to apoptotic induction by hydrogen peroxide, Mnk1 is phosphorylated at both Thr(22) and Ser(27). These results indicate a role for Pak2 in the down-regulation of translation initiation in apoptosis by phosphorylation of Mnk1.
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Affiliation(s)
- Kevin C Orton
- Department of Biochemistry, University of California, Riverside, Riverside, California 92521, USA
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28
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Preiss T, W Hentze M. Starting the protein synthesis machine: eukaryotic translation initiation. Bioessays 2004; 25:1201-11. [PMID: 14635255 DOI: 10.1002/bies.10362] [Citation(s) in RCA: 150] [Impact Index Per Article: 7.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/11/2022]
Abstract
The final assembly of the protein synthesis machinery occurs during translation initiation. This delicate process involves both ends of eukaryotic messenger RNAs as well as multiple sequential protein-RNA and protein-protein interactions. As is expected from its critical position in the gene expression pathway between the transcriptome and the proteome, translation initiation is a selective and highly regulated process. This synopsis summarises the current status of the field and identifies intriguing open questions.
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Affiliation(s)
- Thomas Preiss
- Victor Chang Cardiac Research Institute (VCCRI), Molecular Genetics Program, Sydney, Australia.
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29
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Arsham AM, Howell JJ, Simon MC. A novel hypoxia-inducible factor-independent hypoxic response regulating mammalian target of rapamycin and its targets. J Biol Chem 2003; 278:29655-60. [PMID: 12777372 DOI: 10.1074/jbc.m212770200] [Citation(s) in RCA: 357] [Impact Index Per Article: 17.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/15/2022] Open
Abstract
Hypoxia triggers a reversible inhibition of protein synthesis thought to be important for energy conservation in O2-deficient environments. The mammalian target of rapamycin (mTOR) pathway integrates multiple environmental cues to regulate translation in response to nutrient availability and stress, suggesting it as a candidate for O2 regulation. We show here that hypoxia rapidly and reversibly triggers hypophosphorylation of mTOR and its effectors 4E-BP1, p70S6K, rpS6, and eukaryotic initiation factor 4G. Hypoxic regulation of these translational control proteins is dominant to activation via multiple distinct signaling pathways such as insulin, amino acids, phorbol esters, and serum and is independent of Akt/protein kinase B and AMP-activated protein kinase phosphorylation, ATP levels, ATP:ADP ratios, and hypoxia-inducible factor-1 (HIF-1). Finally, hypoxia appears to repress phosphorylation of translational control proteins in a manner analogous to rapamycin and independent of phosphatase 2A (PP2A) activity. These data demonstrate a new mode of regulation of the mTOR pathway and position this pathway as a powerful point of control by O2 of cellular metabolism and energetics.
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Affiliation(s)
- Andrew M Arsham
- Committee on Genetics, University of Chicago, Chicago, Illinois 60615, USA
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30
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Wang L, Rolfe M, Proud CG. Ca(2+)-independent protein kinase C activity is required for alpha1-adrenergic-receptor-mediated regulation of ribosomal protein S6 kinases in adult cardiomyocytes. Biochem J 2003; 373:603-11. [PMID: 12720544 PMCID: PMC1223514 DOI: 10.1042/bj20030454] [Citation(s) in RCA: 24] [Impact Index Per Article: 1.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 03/24/2003] [Revised: 04/29/2003] [Accepted: 04/30/2003] [Indexed: 02/04/2023]
Abstract
The alpha(1)-adrenergic agonist, phenylephrine (PE), exerts hypertrophic effects in the myocardium and activates protein synthesis. Both Ca(2+)-dependent protein kinase C (PKC, PKCalpha) and Ca(2+)-independent PKC isoforms (PKCdelta and epsilon ) are detectably expressed in adult rat cardiomyocytes. Stimulation of the alpha(1)-adrenergic receptor by PE results in activation of Ca(2+)-independent PKCs, as demonstrated by translocation of the delta and epsilon isoenzymes from cytosol to membrane fractions. PE also induces activation of p70 ribosomal protein S6 kinases (S6K1 and 2) in adult cardiomyocytes. We have studied the role of Ca(2+)-independent PKCs in the regulation of S6K activity by PE. Activation of S6K1/2 by PE was blocked by the broad-spectrum PKC inhibitor bisindolylmaleimide (BIM) I, whereas Gö6976, a compound that only inhibits Ca(2+)-dependent PKCs, did not inhibit S6K activation. Rottlerin, which selectively inhibits PKCdelta, also prevented PE-induced S6K activation. The isoform-specific PKC inhibitors had similar effects on the phosphorylation of eukaryotic initiation factor 4E (eIF4E)-binding protein 1, a translation repressor that, like the S6Ks, lies downstream of the mammalian target of rapamycin (mTOR). Infection of cells with adenoviruses encoding dominant-negative PKCdelta or epsilon inhibited the activation of extracellular-signal-regulated kinase (ERK) by PE, and also inhibited the activation and/or phosphorylation of S6Ks 1 and 2. The PE-induced activation of protein synthesis was abolished by BIM I and markedly attenuated by rottlerin. Our data thus suggest that Ca(2+)-independent PKC isoforms play an important role in coupling the alpha(1)-adrenergic receptor to mTOR signalling and protein synthesis in adult cardiomyocytes.
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Affiliation(s)
- Lijun Wang
- Division of Molecular Physiology, School of Life Sciences, University of Dundee, Dundee DD1 5EH, UK
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31
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Rubtsova MP, Sizova DV, Dmitriev SE, Ivanov DS, Prassolov VS, Shatsky IN. Distinctive properties of the 5'-untranslated region of human hsp70 mRNA. J Biol Chem 2003; 278:22350-6. [PMID: 12682055 DOI: 10.1074/jbc.m303213200] [Citation(s) in RCA: 77] [Impact Index Per Article: 3.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
A relaxed cap-dependence of translation of the mRNA-encoding mammalian heat shock protein Hsp70 may suggest that its 5'-untranslated region (UTR) possesses an internal ribosome entry site (IRES). In this study, this possibility has been tested in transfected cells using plasmids that express dicistronic mRNAs. Using a reporter gene construct, Renilla luciferase/Photinus pyralis luciferase, we show that the 216-nt long 5'-UTR of Hsp70 mRNA acts as an IRES that directs ribosomes to the downstream start codon by a cap-independent mechanism. The relative activity of this IRES (100-fold over the empty vector) is similar to that of the classical picornaviral IRESs. Additional controls indicate that this high expression of the downstream reporter is not due to readthrough from the upstream cistron, nor is it due to translation of cryptic monocistronic transcripts. The effect of small deletions within the 5'-UTR of Hsp70 mRNA on the IRES activity varies in dependence on their position within the 5'-UTR sequence. With the exception of deletion of nt 33-50, it is small for the 5'-terminal half of the 5'-UTR and rather strong for the 3'-terminal section. However, neither of these small deletions abolishes the IRES activity completely. Excision of larger sections (>50 nt) by truncation of the 5'-UTR from the 5'-end or by internal deleting results in a dramatic impairment of the IRES function. Taken together, these data suggest that the IRES activity of the 5'-UTR of Hsp70 mRNA requires integrity of almost the entire sequence of the 5'-UTR. The data are discussed in terms of a model that allows a three-dimensional rather than linear mode of selection of the initiation region surrounding the start codon of Hsp70 mRNA.
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Affiliation(s)
- Maria P Rubtsova
- A. N. Belozersky Institute of Physico-Chemical Biology, Moscow State University, Moscow 119899, Russia
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32
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Wang L, Proud CG. Ras/Erk signaling is essential for activation of protein synthesis by Gq protein-coupled receptor agonists in adult cardiomyocytes. Circ Res 2002; 91:821-9. [PMID: 12411397 DOI: 10.1161/01.res.0000041029.97988.e9] [Citation(s) in RCA: 104] [Impact Index Per Article: 4.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/16/2022]
Abstract
The Gq protein-coupled receptor agonists phenylephrine (PE) and endothelin-1 (ET-1) induce cardiac hypertrophy and stimulate protein synthesis in cardiomyocytes. This study aims to investigate how they activate mRNA translation in adult cardiomyocytes. PE and ET-1 do not activate protein kinase B but stimulate Ras and Erk, and their ability to activate protein synthesis was blocked by inhibition of Ras or MEK and by rapamycin, which inhibits mTOR (mammalian target of rapamycin). These agonists activated ribosomal protein S6 kinase 1 (S6K1) and induced phosphorylation of eIF4E-binding protein-1 (4E-BP1) and its release from eIF4E. These effects were blocked by inhibitors of MEK. Furthermore, adenovirus-mediated expression of constitutively-active MEK1 caused activation of S6K1, phosphorylation of 4E-BP1, and activation of protein synthesis in a rapamycin-sensitive manner. Expression of N17Ras inhibited the regulation of S6K1 and protein synthesis by GqPCR agonists. These data point to a signaling pathway involving Ras and MEK that acts, with mTOR, to control regulatory translation factors and activate protein synthesis. This study provides new insights into the mechanisms underlying the stimulation of protein synthesis by hypertrophic agents in heart.
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Affiliation(s)
- Lijun Wang
- Division of Molecular Physiology, Faculty of Life Sciences, University of Dundee, Dundee, UK
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Niedzwiecka A, Stepinski J, Darzynkiewicz E, Sonenberg N, Stolarski R. Positive heat capacity change upon specific binding of translation initiation factor eIF4E to mRNA 5' cap. Biochemistry 2002; 41:12140-8. [PMID: 12356315 DOI: 10.1021/bi0258142] [Citation(s) in RCA: 58] [Impact Index Per Article: 2.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/30/2022]
Abstract
Specific recognition of the mRNA 5' cap by eukaryotic initiation factor eIF4E is a rate-limiting step in the translation initiation. Fluorescence spectroscopy and high-sensitivity isothermal titration calorimetry were used to examine the thermodynamics of eIF4E binding to a cap-analogue, 7-methylGpppG. A van't Hoff plot revealed nonlinearity characterized by an unexpected, large positive molar heat capacity change (DeltaC(degree)(p) = +1.92 +/- 0.93 kJ.mol(-1).K(-1)), which was confirmed by direct ITC measurements (DeltaC(degree)(p) = +1.941 +/- 0.059 kJ.mol(-1).K(-1)). This unique result appears to come from an extensive additional hydration upon binding and charge-related interactions within the binding site. As a consequence of the positive DeltaC(degree)(p), the nature of the thermodynamic driving force changes with increasing temperature, from enthalpy-driven and entropy-opposed, through enthalpy- and entropy-driven in the range of biological temperatures, into entropy-driven and enthalpy-opposed. Comparison of the van't Hoff and calorimetric enthalpy values provided proof for the ligand protonation at N(1) upon binding, which is required for tight stabilization of the cap-eIF4E complex. Intramolecular self-stacking of the dinucleotide cap-analogue was analyzed to reveal the influence of this coupled process on the thermodynamic parameters of the eIF4E-mRNA 5' cap interaction. The temperature-dependent change in the conformation of 7-methylGpppG shifts significantly the intrinsic DeltaH(degree)(0) = -72.9 +/- 4.2 kJ.mol(-1) and DeltaS(degree)(0) = -116 +/- 58 J.mol(-1).K(-1) of binding to the less negative resultant values, by DeltaH(degree)(sst) = +9.76 +/- 1.15 kJ.mol(-1) and DeltaS(degree)(sst) = +24.8 +/- 2.1 J.mol(-1).K(-1) (at 293 K), while the corresponding DeltaC(degree)(p)(sst) = -0.0743 +/- 0.0083 kJ.mol(-1).K(-1) is negligible in comparison with the total DeltaC(degree)(p) .
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Affiliation(s)
- Anna Niedzwiecka
- Department of Biophysics, Institute of Experimental Physics, Warsaw University, 93 Zwirki & Wigury Street, 02-089 Warsaw, Poland
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Connor JH, Lyles DS. Vesicular stomatitis virus infection alters the eIF4F translation initiation complex and causes dephosphorylation of the eIF4E binding protein 4E-BP1. J Virol 2002; 76:10177-87. [PMID: 12239292 PMCID: PMC136556 DOI: 10.1128/jvi.76.20.10177-10187.2002] [Citation(s) in RCA: 127] [Impact Index Per Article: 5.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/20/2022] Open
Abstract
Vesicular stomatitis virus (VSV) modulates protein synthesis in infected cells in a way that allows the translation of its own 5'-capped mRNA but inhibits the translation of host mRNA. Previous data have shown that inactivation of eIF2alpha is important for VSV-induced inhibition of host protein synthesis. We tested whether there is a role for eIF4F in this inhibition. The multisubunit eIF4F complex is involved in the regulation of protein synthesis via phosphorylation of cap-binding protein eIF4E, a subunit of eIF4F. Translation of host mRNA is significantly reduced under conditions in which eIF4E is dephosphorylated. To determine whether VSV infection alters the eIF4F complex, we analyzed eIF4E phosphorylation and the association of eIF4E with other translation initiation factors, such as eIF4G and the translation inhibitor 4E-BP1. VSV infection of HeLa cells resulted in the dephosphorylation of eIF4E at serine 209 between 3 and 6 h postinfection. This time course corresponded well to that of the inhibition of host protein synthesis induced by VSV infection. Cells infected with a VSV mutant that is delayed in the ability to inhibit host protein synthesis were also delayed in dephosphorylation of eIF4E. In addition to decreasing eIF4E phosphorylation, VSV infection also resulted in the dephosphorylation and activation of eIF4E-binding protein 4E-BP1 between 3 and 6 h postinfection. Analysis of cap-binding complexes showed that VSV infection reduced the association of eIF4E with the eIF4G scaffolding subunit at the same time as its association with 4E-BP1 increased and that these time courses correlated with the dephosphorylation of eIF4E. These changes in the eIF4F complex occurred over the same time period as the onset of viral protein synthesis, suggesting that activation of 4E-BP1 does not inhibit translation of viral mRNAs. In support of this idea, VSV protein synthesis was not affected by the presence of rapamycin, a drug that blocks 4E-BP1 phosphorylation. These data show that VSV infection results in modifications of the eIF4F complex that are correlated with the inhibition of host protein synthesis and that translation of VSV mRNAs occurs despite lowered concentrations of the active cap-binding eIF4F complex. This is the first noted modification of both eIF4E and 4E-BP1 phosphorylation levels among viruses that produce capped mRNA for protein translation.
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Affiliation(s)
- John H Connor
- Department of Microbiology and Immunology, Wake Forest University School of Medicine, Winston-Salem, NC 27157, USA.
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Patel J, McLeod LE, Vries RGJ, Flynn A, Wang X, Proud CG. Cellular stresses profoundly inhibit protein synthesis and modulate the states of phosphorylation of multiple translation factors. EUROPEAN JOURNAL OF BIOCHEMISTRY 2002; 269:3076-85. [PMID: 12071973 DOI: 10.1046/j.1432-1033.2002.02992.x] [Citation(s) in RCA: 134] [Impact Index Per Article: 6.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/20/2022]
Abstract
We have examined the effects of widely used stress-inducing agents on protein synthesis and on regulatory components of the translational machinery. The three stresses chosen, arsenite, hydrogen peroxide and sorbitol, exert their effects in quite different ways. Nonetheless, all three rapidly ( approximately 30 min) caused a profound inhibition of protein synthesis. In each case this was accompanied by dephosphorylation of the eukaryotic initiation factor (eIF) 4E-binding protein 1 (4E-BP1) and increased binding of this repressor protein to eIF4E. Binding of 4E-BP1 to eIF4E correlated with loss of eIF4F complexes. Sorbitol and hydrogen peroxide each caused inhibition of the 70-kDa ribosomal protein S6 kinase, while arsenite activated it. The effects of stresses on the phosphorylation of eukaryotic elongation factor 2 also differed: oxidative stress elicited a marked increase in eEF2 phosphorylation, which is expected to contribute to inhibition of translation, while the other stresses did not have this effect. Although all three proteins (4E-BP1, p70 S6 kinase and eEF2) can be regulated through the mammalian target of rapamycin (mTOR), our data imply that stresses do not interfere with mTOR function but act in different ways on these three proteins. All three stresses activate the p38 MAP kinase pathway but we were able to exclude a role for this in their effects on 4E-BP1. Our data reveal that these stress-inducing agents, which are widely used to study stress-signalling in mammalian cells, exert multiple and complex inhibitory effects on the translational machinery.
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Affiliation(s)
- Jashmin Patel
- Department of Biosciences, University of Kent at Canterbury, Canterbury, UK
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Clemens MJ. Initiation factor eIF2 alpha phosphorylation in stress responses and apoptosis. PROGRESS IN MOLECULAR AND SUBCELLULAR BIOLOGY 2002; 27:57-89. [PMID: 11575161 DOI: 10.1007/978-3-662-09889-9_3] [Citation(s) in RCA: 169] [Impact Index Per Article: 7.7] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/29/2022]
Abstract
The alpha subunit of polypeptide chain initiation factor eIF2 can be phosphorylated by a number of related protein kinases which are activated in response to cellular stresses. Physiological conditions which result in eIF2 alpha phosphorylation include virus infection, heat shock, iron deficiency, nutrient deprivation, changes in intracellular calcium, accumulation of unfolded or denatured proteins and the induction of apoptosis. Phosphorylated eIF2 acts as a dominant inhibitor of the guanine nucleotide exchange factor eIF2B and prevents the recycling of eIF2 between successive rounds of protein synthesis. Extensive phosphorylation of eIF2 alpha and strong inhibition of eIF2B activity can result in the downregulation of the overall rate of protein synthesis; less marked changes may lead to alterations in the selective translation of alternative open reading frames in polycistronic mRNAs, as demonstrated in yeast. These mechanisms can provide a signal transduction pathway linking eukaryotic cellular stress responses to alterations in the control of gene expression at the translational level.
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Affiliation(s)
- M J Clemens
- Department of Biochemistry and Immunology, St George's Hospital Medical School, University of London, Cranmer Terrace, London SW17 0RE, UK
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Morley SJ. The regulation of eIF4F during cell growth and cell death. PROGRESS IN MOLECULAR AND SUBCELLULAR BIOLOGY 2002; 27:1-37. [PMID: 11575157 DOI: 10.1007/978-3-662-09889-9_1] [Citation(s) in RCA: 19] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/18/2023]
Affiliation(s)
- S J Morley
- Biochemistry Laboratory, School of Biological Sciences, University of Sussex, Falmer, Brighton BN1 9QG, UK
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Pham FH, Cole SM, Clerk A. Regulation of cardiac myocyte protein synthesis through phosphatidylinositol 3' kinase and protein kinase B. ADVANCES IN ENZYME REGULATION 2001; 41:73-86. [PMID: 11384738 DOI: 10.1016/s0065-2571(00)00007-8] [Citation(s) in RCA: 18] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 01/08/2023]
Affiliation(s)
- F H Pham
- Division of Biomedical Sciences, Imperial College School of Medicine, South Kensington, SW7 2AZ, London, UK
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Saghir AN, Tuxworth WJ, Hagedorn CH, McDermott PJ. Modifications of eukaryotic initiation factor 4F (eIF4F) in adult cardiocytes by adenoviral gene transfer: differential effects on eIF4F activity and total protein synthesis rates. Biochem J 2001; 356:557-66. [PMID: 11368785 PMCID: PMC1221869 DOI: 10.1042/0264-6021:3560557] [Citation(s) in RCA: 13] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
In adult feline cardiocytes, increases in eukaryotic initiation factor 4F (eIF4F) activity are correlated with accelerated rates of total protein synthesis produced in response to increased load. Adenoviral gene transfer was employed to increase either eIF4F complex formation or the phosphorylation of eIF4E on Ser-209. To simulate load,cardiocytes were electrically stimulated to contract (2 Hz,5 ms pulses). Non-stimulated cardiocytes were used as controls.Adenovirus-mediated overexpression of wild-type eIF4E increased the total eIF4E pool by 120-140% above endogenous levels after 24 h and produced a corresponding increase in eIF4F content.However, it did not accelerate total protein synthesis rates inquiescent cardiocytes; neither did it potentiate the increase produced by contraction. To modify the affinity of eIF4F, cardiocytes were infected with a mutant (eIF4E/W56F) with a decreased binding affinity for the mRNA cap. Overexpression of eIF4E/W56F increased the quantity of eIF4F but the rate of total protein synthesis was decreased inquiescent and contracting cardiocytes. Overexpression of a mutant that blocked eIF4E phosphorylation (eIF4E/S209A) increased the quantity ofeIF4F without any significant effect on total protein synthesis rates in quiescent or contracting cardiocytes. Overexpression of the eIF4Ekinase Mnk-1 increased eIF4E phosphorylation without a corresponding increase in eIF4F complex formation or in the rate of total protein synthesis. We conclude the following: (1) eIF4F assembly is increased by raising eIF4E levels via adenoviral gene transfer; (2) the capbinding affinity of eIF4F is a rate-limiting determinant for total protein synthesis rates; and (3) increases in the quantity of eIF4Falone or in eIF4E phosphorylation are not sufficient to accelerate total protein synthesis rates.
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Affiliation(s)
- A N Saghir
- Department of Medicine, Strom Thurmond Biomedical ResearchBuilding, Room 303, 114 Doughty Street, Charleston, SC 29403, USA
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40
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Hasday JD, Bannerman D, Sakarya S, Cross AS, Singh IS, Howard D, Drysdale BE, Goldblum SE. Exposure to febrile temperature modifies endothelial cell response to tumor necrosis factor-alpha. J Appl Physiol (1985) 2001; 90:90-8. [PMID: 11133897 DOI: 10.1152/jappl.2001.90.1.90] [Citation(s) in RCA: 34] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/22/2022] Open
Abstract
Fever is an important regulator of inflammation that modifies expression and bioactivity of cytokines, including tumor necrosis factor (TNF)-alpha. Pulmonary vascular endothelium is an important target of TNF-alpha during the systemic inflammatory response. In this study, we analyzed the effect of a febrile range temperature (39.5 degrees C) on TNF-alpha-stimulated changes in endothelial barrier function, capacity for neutrophil binding and transendothelial migration (TEM), and cytokine secretion in human pulmonary artery endothelial cells (EC). Permeability for [(14)C]BSA tracer was increased by treatment with TNF-alpha, and this effect was augmented by incubating EC at 39.5 degrees C. Treating EC with 2. 5 U/ml TNF-alpha stimulated an increase in subsequent neutrophil adherence and TEM. Incubating EC at 39.5 degrees C caused a 30% increase in TEM but did not modify the enhancement of neutrophil adherence or TEM by TNF-alpha treatment. Analysis of cytokine expression in EC cultures exposed to TNF-alpha at either 37 degrees or 39.5 degrees C revealed three patterns of temperature and TNF-alpha responsiveness. Granulocyte-macrophage colony stimulating factor (GM-CSF) and interleukin (IL)-8 were not detectable in untreated EC but were increased after TNF-alpha exposure, and this increase was enhanced at 39.5 degrees C. IL-6 expression was also increased with TNF-alpha exposure, but IL-6 expression was lower in 39.5 degrees C EC cultures. Transforming growth factor-beta(1) was constitutively expressed, and its expression was not influenced either by TNF-alpha or exposure to 39.5 degrees C. These data demonstrate that clinically relevant shifts in body temperature might cause important changes in the effects of proinflammatory cytokines on the endothelium.
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Affiliation(s)
- J D Hasday
- Divisions of Pulmonary and Critical Care Medicine, Department of Medicine, University of Maryland School of Medicine, University of Maryland, USA
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41
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Scheper GC, Van Wijk R, Thomas AAM. Regulation of the Activity of Eukaryotic Initiation Factors in Stressed Cells. SIGNALING PATHWAYS FOR TRANSLATION 2001. [DOI: 10.1007/978-3-662-09889-9_2] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 12/09/2022]
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Gingras AC, Raught B, Sonenberg N. eIF4 initiation factors: effectors of mRNA recruitment to ribosomes and regulators of translation. Annu Rev Biochem 2000; 68:913-63. [PMID: 10872469 DOI: 10.1146/annurev.biochem.68.1.913] [Citation(s) in RCA: 1630] [Impact Index Per Article: 67.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Eukaryotic translation initiation factor 4F (eIF4F) is a protein complex that mediates recruitment of ribosomes to mRNA. This event is the rate-limiting step for translation under most circumstances and a primary target for translational control. Functions of the constituent proteins of eIF4F include recognition of the mRNA 5' cap structure (eIF4E), delivery of an RNA helicase to the 5' region (eIF4A), bridging of the mRNA and the ribosome (eIF4G), and circularization of the mRNA via interaction with poly(A)-binding protein (eIF4G). eIF4 activity is regulated by transcription, phosphorylation, inhibitory proteins, and proteolytic cleavage. Extracellular stimuli evoke changes in phosphorylation that influence eIF4F activity, especially through the phosphoinositide 3-kinase (PI3K) and Ras signaling pathways. Viral infection and cellular stresses also affect eIF4F function. The recent determination of the structure of eIF4E at atomic resolution has provided insight about how translation is initiated and regulated. Evidence suggests that eIF4F is also implicated in malignancy and apoptosis.
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Affiliation(s)
- A C Gingras
- Department of Biochemistry McGill University, Montréal, Québec, Canada.
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43
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Abstract
Stimulation of phosphatidylinositol 3'-kinase (PI3K) and protein kinase B (PKB) is implicated in the regulation of protein synthesis in various cells. One mechanism involves PI3K/PKB-dependent phosphorylation of 4E-BP1, which dissociates from eIF4E, allowing initiation of translation from the 7-methylGTP cap of mRNAs. We examined the effects of insulin and H(2)O(2) on this pathway in neonatal cardiac myocytes. Cardiac myocyte protein synthesis was increased by insulin, but was inhibited by H(2)O(2). PI3K inhibitors attenuated basal levels of protein synthesis and inhibited the insulin-induced increase in protein synthesis. Insulin or H(2)O(2) increased the phosphorylation (activation) of PKB through PI3K, but, whereas insulin induced a sustained response, the response to H(2)O(2) was transient. 4E-BP1 was phosphorylated in unstimulated cells, and 4E-BP1 phosphorylation was increased by insulin. H(2)O(2) stimulated dephosphorylation of 4E-BP1 by increasing protein phosphatase (PP1/PP2A) activity. This increased the association of 4E-BP1 with eIF4E, consistent with H(2)O(2) inhibition of protein synthesis. The effects of H(2)O(2) were sufficient to override the stimulation of protein synthesis and 4E-BP1 phosphorylation induced by insulin. These results indicate that PI3K and PKB are important regulators of protein synthesis in cardiac myocytes, but other factors, including phosphatase activity, modulate the overall response.
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Affiliation(s)
- F H Pham
- Division of Biomedical Sciences (Molecular Pathology), Imperial College School of Medicine, London, UK
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Tee AR, Proud CG. DNA-damaging agents cause inactivation of translational regulators linked to mTOR signalling. Oncogene 2000; 19:3021-31. [PMID: 10871854 DOI: 10.1038/sj.onc.1203622] [Citation(s) in RCA: 99] [Impact Index Per Article: 4.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/09/2022]
Abstract
Treatment of cells with DNA-damaging agents, such as etoposide, can cause growth arrest or apoptosis. Treatment of Swiss 3T3 or RAT-1 cells with etoposide led to the dephosphorylation of both p70 S6 kinase and eukaryotic initiation factor (eIF) 4E-binding protein 1 (4E-BP1), resulting in decreased p70 S6 kinase activity and an increase in 4E-BP1 binding to eIF4E. These effects were not prevented by the general caspase inhibitor, Z-VAD.FMK. These findings indicate caspase-independent inhibition of signalling pathways that involve the mammalian target of rapamycin (mTOR). Similar effects were observed in response to two other DNA-damaging agents, cisplatin and mitomycin-C. These events preceded apoptosis, which was assessed by caspase-3 activity assays and FACS analysis. This shows that inhibition of mTOR signalling is not a consequence of apoptosis, although it may play a role in the events that precede cell death. 4E-BP1 was cleaved during apoptosis yielding a fragment that retained the ability to bind eIF4E. Cleavage of 4E-BP1 was inhibited by treatment of the cells with Z-VAD.FMK, indicating it is caspase-dependent. Insulin elicited full activation of p70 S6 kinase and phosphorylation of 4E-PB1 in etoposide-treated cells prior to the onset of apoptosis, but not during cell death. This suggests that mTOR signalling becomes irreversibly inhibited only after entry into apoptosis. Oncogene (2000).
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Affiliation(s)
- A R Tee
- Department of Anatomy & Physiology, Medical Sciences Institute/Wellcome Trust Building Complex, University of Dundee, Dow Street, Dundee, DD1 5EH, UK
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45
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Cuesta R, Laroia G, Schneider RJ. Chaperone Hsp27 inhibits translation during heat shock by binding eIF4G and facilitating dissociation of cap-initiation complexes. Genes Dev 2000. [DOI: 10.1101/gad.14.12.1460] [Citation(s) in RCA: 93] [Impact Index Per Article: 3.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/24/2022]
Abstract
Inhibition of protein synthesis during heat shock limits accumulation of unfolded proteins that might damage eukaryotic cells. We demonstrate that chaperone Hsp27 is a heat shock-induced inhibitor of cellular protein synthesis. Translation of most mRNAs requires formation of a cap-binding initiation complex known as eIF4F, consisting of factors eIF4E, eIF4A, eIF4E kinase Mnk1, poly(A)-binding protein, and adaptor protein eIF4G. Hsp27 specifically bound eIF4G during heat shock, preventing assembly of the cap-initiation/eIF4F complex and trapping eIF4G in insoluble heat shock granules. eIF4G is a specific target of Hsp27, as eIF4E, eIF4A, Mnk1, poly(A)-binding protein, eIF4B, and eIF3 were not bound by Hsp27 and were not recruited into insoluble complexes. Dissociation of eIF4F was enhanced during heat shock by ectopic overexpression of Hsp25, the murine homolog of human Hsp27. Overexpression of Hsc70, a constitutive homolog of Hsp70, prevented loss of cap-initiation complexes and maintained eIF4G solubility. Purified Hsp27 specifically bound purified eIF4G in vitro, prevented in vitro translation, eliminated eIF4G interaction with protein binding factors, and promoted eIF4G insolubilization. These results therefore demonstrate that Hsp27 is a heat-induced inhibitor of eIF4F-dependent mRNA translation.
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Martín ME, Pérez MI, Redondo C, Alvarez MI, Salinas M, Fando JL. 4E binding protein 1 expression is inversely correlated to the progression of gastrointestinal cancers. Int J Biochem Cell Biol 2000; 32:633-42. [PMID: 10785360 DOI: 10.1016/s1357-2725(00)00007-8] [Citation(s) in RCA: 71] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/17/2022]
Abstract
Several components of the eukaryotic protein synthesis apparatus have been associated with oncogenic transformation of cells. Overexpression of the initiation factor eIF4E occurs in a variety of human tumours. The aim of this study was to determine the level of expression and the phosphorylation state of eIF4E and 4E-binding protein 1 (4E-BP1) in gastrointestinal cancer, and to ascertain whether or not these factors can be used as diagnostic or prognostic markers within this type of cancer. The eIF4E levels were significantly higher in tumours compared with normal tissue (51. 5+/-4.4 vs 30.9+/-2.5 arbitrary units (A.U.)/mg of protein, p<0.001). However, phosphorylated eIF4E did not change in stomach cancers and decreased in colorectal cancers (67.1+/-1.2 vs 60.8+/-2.8%, p<0.05). 4E-BP1 expression increased in most of the gastrointestinal cancers studied. In addition, an inverse correlation between 4E-BP1 elevation and N and M stages was found, showing significant higher elevation of 4E-BP1 in Node-negative patients (11.21+/-5.74 vs 4. 03+/-2.36 n-fold, p<0.05) as well as in patients without distant metastasis (8.41+/-3.29 vs 0.97+/-0.35 n-fold, p<0.05). These results suggest that 4E-BP1 could function as a tumour suppressor. Moreover, the data show a significant dephosphorylation of 4E-BP1 in gastrointestinal tumours that correlated with an increase in the association of 4E-BP1 and eIF4E indicating a lower availability to eIF4E to recruit to the ribosomes. Our results support a possible role of 4E-BP1 as a prognostic factor in gastrointestinal carcinoma.
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Affiliation(s)
- M E Martín
- Departamento de Bioquímica y Biología Molecular, Universidad de Alcalá, Alcalá de Henares, 28871, Madrid, Spain.
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Bernal A, Kimbrell DA. Drosophila Thor participates in host immune defense and connects a translational regulator with innate immunity. Proc Natl Acad Sci U S A 2000; 97:6019-24. [PMID: 10811906 PMCID: PMC18551 DOI: 10.1073/pnas.100391597] [Citation(s) in RCA: 115] [Impact Index Per Article: 4.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/18/2022] Open
Abstract
Thor has been identified as a new type of gene involved in Drosophila host immune defense. Thor is a member of the 4E-binding protein (4E-BP) family, which in mammals has been defined as critical regulators in a pathway that controls initiation of translation through binding eukaryotic initiation factor 4E (eIF4E). Without an infection, Thor is expressed during all developmental stages and transcripts localize to a wide variety of tissues, including the reproductive system. In response to bacterial infection and, to a lesser extent, by wounding, Thor is up-regulated. The Thor promoter has the canonical NFkappaB and associated GATA recognition sequences that have been shown to be essential for immune induction, as well as other sequences commonly found for Drosophila immune response genes, including interferon-related regulatory sequences. In survival tests, Thor mutants show symptoms of being immune compromised, indicating that Thor may be critical in host defense. In contrast to Thor, Drosophila eIF4E is not induced by bacterial infection. These findings for Thor provide the first evidence that a 4E-BP family member has a role in immune induction in any organism. Further, no gene in the translation initiation pathway that includes 4E-BP has been previously found to be immune induced. Our results suggest either a role for translational regulation in humoral immunity or a new, nontranslational function for 4E-BP type genes.
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Affiliation(s)
- A Bernal
- Department of Biochemistry and Cell Biology, Rice University, 6100 Main Street, Houston, TX 77005, USA
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48
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Herbert TP, Kilhams GR, Batty IH, Proud CG. Distinct signalling pathways mediate insulin and phorbol ester-stimulated eukaryotic initiation factor 4F assembly and protein synthesis in HEK 293 cells. J Biol Chem 2000; 275:11249-56. [PMID: 10753934 DOI: 10.1074/jbc.275.15.11249] [Citation(s) in RCA: 96] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Stimulation of serum-starved human embryonic kidney (HEK) 293 cells with either the phorbol ester, 12-O-tetradecanoylphorbol-13-acetate (TPA), or insulin resulted in increases in the phosphorylation of 4E-BP1 and p70 S6 kinase, eIF4F assembly, and protein synthesis. All these effects were blocked by rapamycin, a specific inhibitor of mTOR. Phosphatidylinositol 3-kinase and protein kinase B were activated by insulin but not by TPA. Therefore TPA can induce eIF4F assembly, protein synthesis, and the phosphorylation of p70 S6 kinase and 4E-BP1 independently of both phosphatidylinositol 3-kinase and protein kinase B. Using two structurally unrelated inhibitors of MEK (PD098059 and U0126), we provide evidence that Erk activation is important in TPA stimulation of eIF4F assembly and the phosphorylation of p70 S6 kinase and 4E-BP1 and that basal MEK activity is important for basal, insulin, and TPA-stimulated protein synthesis. Transient transfection of constitutively active mitogen-activated protein kinase interacting kinase 1 (the eIF4E kinase) indicated that inhibition of protein synthesis and eIF4F assembly by PD098059 is not through inhibition of eIF4E phosphorylation but of other signals emanating from MEK. This report also provides evidence that increased eIF4E phosphorylation alone does not affect the assembly of the eIF4F complex or general protein synthesis.
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Affiliation(s)
- T P Herbert
- Department of Anatomy, The Medical Sciences Institute, University of Dundee, Dow Street, Dundee DD1 5EH, United Kingdom.
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Wang L, Wang X, Proud CG. Activation of mRNA translation in rat cardiac myocytes by insulin involves multiple rapamycin-sensitive steps. Am J Physiol Heart Circ Physiol 2000; 278:H1056-68. [PMID: 10749698 DOI: 10.1152/ajpheart.2000.278.4.h1056] [Citation(s) in RCA: 95] [Impact Index Per Article: 4.0] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
Insulin acutely activates protein synthesis in ventricular cardiomyocytes from adult rats. In this study, we have established the methodology for studying the regulation of the signaling pathways and translation factors that may be involved in this response and have examined the effects of acute insulin treatment on them. Insulin rapidly activated the 70-kDa ribosomal S6 kinase (p70 S6k), and this effect was inhibited both by rapamycin and by inhibitors of phosphatidylinositol 3-kinase. The activation of p70 S6k is mediated by a signaling pathway involving the mammalian target of rapamycin (mTOR), which also modulates other translation factors. These include the eukaryotic initiation factor (eIF) 4E binding proteins (4E-BPs) and eukaryotic elongation factor 2 (eEF2). Insulin caused phosphorylation of 4E-BP1 and induced its dissociation from eIF4E, and these effects were also blocked by rapamycin. Concomitant with this, insulin increased the binding of eIF4E to eIF4G. Insulin also activated protein kinase B (PKB), which may lie upstream of p70 S6k and 4E-BP1, with the activation of the different isoforms being in the order alpha>beta>gamma. Insulin also caused inhibition of glycogen synthase kinase 3, which lies downstream of PKB, and of eEF2 kinase. The phosphorylation of eEF2 itself was also decreased by insulin, and this effect and the inactivation of eEF2 kinase were attenuated by rapamycin. The activation of overall protein synthesis by insulin in cardiomyocytes was substantially inhibited by rapamycin (but not by inhibitors of other specific signaling pathways, e.g., mitogen-activated protein kinase), showing that signaling events linked to mTOR play a major role in the control of translation by insulin in this cell type.
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Affiliation(s)
- L Wang
- Department of Anatomy and Physiology, Medical Sciences Institute, University of Dundee, Dundee DD1 5EH, United Kingdom
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Tuxworth WJ, Wada H, Ishibashi Y, McDermott PJ. Role of load in regulating eIF-4F complex formation in adult feline cardiocytes. THE AMERICAN JOURNAL OF PHYSIOLOGY 1999; 277:H1273-82. [PMID: 10516161 DOI: 10.1152/ajpheart.1999.277.4.h1273] [Citation(s) in RCA: 9] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 11/22/2022]
Abstract
This study examined whether cardiocyte load increases eIF-4F complex formation. To increase load in vitro, adult feline cardiocytes were electrically stimulated to contract (1 Hz, 5-ms pulses). eIF-4F complex formation, measured by eIF-4G association with eIF-4E, increased 57 +/- 16% after 4 h of contraction compared with controls. eIF-4F complex formation did not increase on electrical stimulation with 2,3-butanedione monoxime (BDM), an inhibitor of active tension. Both insulin and phorbol ester increased eIF-4F complex formation, but these increases were unaffected by BDM. Insulin caused a shift of eIF-4E binding proteins (4E-BPs) into their hyperphosphorylated gamma-isoforms and dissociation of 4E-BPs from eIF-4E. Rapamycin inhibited 4E-BP phosphorylation in response to insulin but had no effect on eIF-4F complex formation. Electrically stimulated contraction caused a partial shift of 4E-BP1 and 4E-BP2 into the gamma-isoforms, but it had no effect on 4E-BP association with eIF-4E. Rapamycin blocked the increase in eIF-4F complex formation in electrically stimulated cardiocytes and depressed contractility. These data indicate that cardiocyte load causes a tension-dependent increase in eIF-4F complex formation that does not require dissociation of 4E-BPs from eIF-4E.
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Affiliation(s)
- W J Tuxworth
- Department of Medicine, Medical University of South Carolina, Charleston, 29425, USA
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