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Christopher G Proud - One of the best experts on this subject based on the ideXlab platform.
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analysis of the regulatory motifs in eukaryotic Initiation Factor 4E binding protein 1
FEBS Journal, 2008Co-Authors: Timothy M Healy, Bruno D Fonseca, Amanda Hayashi, Christopher G ProudAbstract:Mammalian target of rapamycin complex 1 (mTORC1) phosphorylates proteins such as eukaryotic Initiation Factor 4E-binding protein 1 (4E-BP1) and the S6 kinases. These substrates contain short sequences, termed TOR signalling (TOS) motifs, which interact with the mTORC1 component raptor. Phosphorylation of 4E-BP1 requires an additional feature, termed the RAIP motif (Arg-Ala-Ile-Pro). We have analysed the interaction of 4E-BP1 with raptor and the amino acid residues required for functional RAIP and TOS motifs, as assessed by raptor binding and the phosphorylation of 4E-BP1 in human cells. Binding of 4E-BP1 to raptor strongly depends on an intact TOS motif, but the RAIP motif and additional C-terminal features of 4E-BP1 also contribute to this interaction. Mutational analysis of 4E-BP1 reveals that isoleucine is a key feature of the RAIP motif, that proline is also very important and that there is greater tolerance for substitution of the first two residues. Within the TOS motif, the first position (phenylalanine in the known motifs) is most critical, whereas a wider range of residues function in other positions (although an uncharged aliphatic residue is preferred at position three). These data provide important information on the structural requirements for efficient signalling downstream of mTORC1.
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regulation of cyclin d1 expression by mtorc1 signaling requires eukaryotic Initiation Factor 4E binding protein 1
Oncogene, 2008Co-Authors: J Averous, Bruno D Fonseca, Christopher G ProudAbstract:Regulation of cyclin D1 expression by mTORC1 signaling requires eukaryotic Initiation Factor 4E-binding protein 1
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distinct signaling events downstream of mtor cooperate to mediate the effects of amino acids and insulin on Initiation Factor 4E binding proteins
Molecular and Cellular Biology, 2005Co-Authors: Xuemin Wang, Anne Beugnet, Mirei Murakami, Shinya Yamanaka, Christopher G ProudAbstract:Signaling through the mammalian target of rapamycin (mTOR) controls cell size and growth as well as other functions, and it is a potential therapeutic target for graft rejection, certain cancers, and disorders characterized by inappropriate cell or tissue growth. mTOR signaling is positively regulated by hormones or growth Factors and amino acids. mTOR signaling regulates the phosphorylation of several proteins, the best characterized being ones that control mRNA translation. Eukaryotic Initiation Factor 4E-binding protein 1 (4E-BP1) undergoes phosphorylation at multiple sites. Here we show that amino acids regulate the N-terminal phosphorylation sites in 4E-BP1 through the RAIP motif in a rapamycin-insensitive manner. Several criteria indicate this reflects a rapamycin-insensitive output from mTOR. In contrast, the insulin-stimulated phosphorylation of the C-terminal site Ser64/65 is generally sensitive to rapamycin, as is phosphorylation of another well-characterized target for mTOR signaling, S6K1. Our data imply that it is unlikely that mTOR directly phosphorylates Thr69/70 in 4E-BP1. Although 4E-BP1 and S6K1 bind the mTOR partner, raptor, our data indicate that the outputs from mTOR to 4E-BP1 and S6K1 are distinct. In cells, efficient phosphorylation of 4E-BP1 requires it to be able to bind to eIF4E, whereas phosphorylation of 4E-BP1 by mTOR in vitro shows no such preference. These data have important implications for understanding signaling downstream of mTOR and the development of new strategies to impair mTOR signaling.
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the c terminus of Initiation Factor 4E binding protein 1 contains multiple regulatory features that influence its function and phosphorylation
Molecular and Cellular Biology, 2003Co-Authors: Xuemin Wang, Wei Li, Joseplluis Parra, Anne Beugnet, Christopher G ProudAbstract:Eukaryotic Initiation Factor 4E (eIF4E) binds the mRNA cap structure and forms eIF4F complexes that recruit 40S subunits to the mRNA. Formation of eIF4F is blocked by eIF4E-binding proteins such as 4E-BP1, which interacts with eIF4E via a motif in the center of its 118-residue sequence. 4E-BP1 plays key roles in cell proliferation, growth, and survival. Binding of 4E-BP1 to eIF4E is regulated by hierarchical multisite phosphorylation. Here we demonstrate that three different features in the C terminus of 4E-BP1 play distinct roles in regulating its phosphorylation and function. Firstly, we identify a new phosphorylation site in its C terminus (S101). A serine or glutamate at this position is required for efficient phosphorylation at Ser65. A second C-terminal site, S112, directly affects binding of 4E-BP1 to eIF4E without influencing phosphorylation of other sites. Thirdly, a conserved C-terminal motif influences phosphorylation of multiple residues, including rapamycin-insensitive sites. These relatively long-range effects are surprising given the reportedly unstructured nature of 4E-BP1 and may imply that phosphorylation of 4E-BP1 and/or binding to eIF4E induces a more-ordered structure. 4E-BP2 and -3 lack phosphorylatable residues corresponding to both S101 and S112. However, in 4E-BP3, replacement of the alanine at the position corresponding to S112 by serine or glutamate did not confer the ability to be released from eIF4E in response to insulin.
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caspase cleavage of Initiation Factor 4E binding protein 1 yields a dominant inhibitor of cap dependent translation and reveals a novel regulatory motif
Molecular and Cellular Biology, 2002Co-Authors: Christopher G ProudAbstract:Eukaryotic Initiation Factor 4E (eIF4E) binding proteins (4E-BPs) regulate the assembly of Initiation complexes required for cap-dependent mRNA translation. 4E-BP1 undergoes insulin-stimulated phosphorylation, resulting in its release from eIF4E, allowing Initiation complex assembly. 4E-BP1 undergoes caspase-dependent cleavage in cells undergoing apoptosis. Here we show that cleavage occurs after Asp24, giving rise to the N-terminally truncated polypeptide Δ4E-BP1, which possesses the eIF4E-binding site and all the known phosphorylation sites. Δ4E-BP1 binds to eIF4E and fails to become sufficiently phosphorylated upon insulin stimulation to bring about its release from eIF4E. Therefore, Δ4E-BP1 acts as a potent inhibitor of cap-dependent translation. Using a mutagenesis approach, we identify a novel regulatory motif of four amino acids (RAIP) which lies within the first 24 residues of 4E-BP1 and which is necessary for efficient phosphorylation of 4E-BP1. This motif is conserved among sequences of 4E-BP1 and 4E-BP2 but is absent from 4E-BP3. Insulin increased the phosphorylation of 4E-BP3 but not sufficiently to cause its release from eIF4E. However, a chimeric protein that was generated by replacing the N terminus of 4E-BP3 with the N-terminal sequence of 4E-BP1 (containing this RAIP motif) underwent a higher degree of phosphorylation and was released from eIF4E. This suggests that the N-terminal sequence of 4E-BP1 is required for optimal regulation of 4E-BPs by insulin.
Nahum Sonenberg - One of the best experts on this subject based on the ideXlab platform.
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Abstract 321: Deletion Of The Translational Repressors Eukaryotic Translation Initiation Factor 4E Binding Proteins 1 And 2 Protects Against Pressure Overload Induced Heart Failure
Circulation Research, 2013Co-Authors: Zhongbing Lu, Vitaly A. Polunovsky, Mark Peterson, Xinli Hu, Yimin Huang, Xin Xu, Nahum Sonenberg, Robert J. Bache, Ping Zhang, Peter B. BittermanAbstract:Assembly of the translation Initiation machinery is negatively regulated by the eukaryotic translation Initiation Factor 4E binding proteins, which sequester the mRNA cap-binding protein eIF4E, thus preventing assembly of an intact Initiation complex. However, the role of translational control on the development of congestive heart failure (CHF) has not been systematically examined. Here we perturbed translational control in mice by knockout of both 4E binding protein 1 (Eif4Ebp1) and 2 (Eif4Ebp2) (designated as Eif4Ebp1/2 double knockout) to study its impact on left ventricular hypertrophy and CHF resulting from transverse aortic constriction. Eif4Ebp1/2 double knockout caused a modest increase in left ventricular mass under basal conditions. However, following transverse aortic constriction, Eif4Ebp1/2 double knockout profoundly attenuated the development of CHF and its attendant mortality. Examination of candidate genes involved in the mechanism revealed increased expression of transcription Factors for genes governing energy metabolism and mitochondrial biogenesis with corresponding increases in the expression of their target genes. Our data indicate that removing physiological restraints on translation Initiation exerts a profound cardiac protective effect against pressure overload induced CHF, suggesting that method(s) to disrupt the function of the 4E binding proteins may be a novel therapeutic approach for preventing or treating CHF.
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eukaryotic Initiation Factor 4E 3 is essential for meiotic chromosome segregation cytokinesis and male fertility in drosophila
Development, 2012Co-Authors: Greco Hernandez, Nahum Sonenberg, Hong Han, Valentina Gandin, Lacramioara Fabian, Tiago A Ferreira, Joanna Zuberek, Julie A Brill, Paul LaskoAbstract:Gene expression is translationally regulated during many cellular and developmental processes. Translation can be modulated by affecting the recruitment of mRNAs to the ribosome, which involves recognition of the 5′ cap structure by the cap-binding protein eIF4E. Drosophila has several genes encoding eIF4E-related proteins, but the biological role of most of them remains unknown. Here, we report that Drosophila eIF4E-3 is required specifically during spermatogenesis. Males lacking eIF4E-3 are sterile, showing defects in meiotic chromosome segregation, cytokinesis, nuclear shaping and individualization. We show that eIF4E-3 physically interacts with both eIF4G and eIF4G-2, the latter being a Factor crucial for spermatocyte meiosis. In eIF4E-3 mutant testes, many proteins are present at different levels than in wild type, suggesting widespread effects on translation. Our results imply that eIF4E-3 forms specific eIF4F complexes that are essential for spermatogenesis.
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regulation of eukaryotic Initiation Factor 4E by converging signaling pathways during metabotropic glutamate receptor dependent long term depression
The Journal of Neuroscience, 2006Co-Authors: Jessica L Banko, Francis Poulin, Nahum Sonenberg, Eric KlannAbstract:Long-term depression (LTD) is an activity-dependent decrease in synaptic efficacy that can be induced in hippocampal area CA1 by pharmacological application of the selective group I metabotropic glutamate receptor (mGluR) agonist 3,5-diyhroxyphenylglycine (DHPG). Recent work has demonstrated that DHPG-induced LTD recruits at least two signal transduction pathways known to couple to translation, the mitogen-activated protein kinase kinase (MEK)–extracellular signal-regulated kinase (ERK) signaling pathway and the phosphoinositide 3-kinase (PI3K)–Akt–mammalian target of rapamycin (mTOR) signaling pathway. However, it remains unclear which translation Factors are engaged by these two signaling pathways during mGluR-LTD. In this study, we investigated whether the group I mGluRs couple to the cap-dependent translation proteins: Mnk1, eIF4E, and 4E-BP. We found that both the MEK–ERK and PI3K–mTOR signaling pathways are critical for the DHPG-induced regulation of these translation Factors. Furthermore, we demonstrate that increasing eIF4F complex availability via the genetic elimination of 4E-BP2 can enhance the degree of LTD achieved by DHPG application in an ERK-dependent manner. Our results provide direct evidence that cap-dependent translation is engaged during mGluR-LTD and demonstrate that the MEK–ERK and PI3K–mTOR signaling pathways converge to regulate eIF4E activity after induction of DHPG-LTD.
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a rapamycin sensitive signaling pathway contributes to long term synaptic plasticity in the hippocampus
Proceedings of the National Academy of Sciences of the United States of America, 2002Co-Authors: Shaojun Tang, Nahum Sonenberg, Anne-claude Gingras, Gerald Reis, Hyejin Kang, Erin M SchumanAbstract:Many forms of long-lasting behavioral and synaptic plasticity require the synthesis of new proteins. For example, long-term potentiation (LTP) that endures for more than an hour requires both transcription and translation. The signal-transduction mechanisms that couple synaptic events to protein translational machinery during long-lasting synaptic plasticity, however, are not well understood. One signaling pathway that is stimulated by growth Factors and results in the translation of specific mRNAs includes the rapamycin-sensitive kinase mammalian target of rapamycin (mTOR, also known as FRAP and RAFT-1). Several components of this translational signaling pathway, including mTOR, eukaryotic Initiation Factor-4E-binding proteins 1 and 2, and eukaryotic Initiation Factor-4E, are present in the rat hippocampus as shown by Western blot analysis, and these proteins are detected in the cell bodies and dendrites in the hippocampal slices by immunostaining studies. In cultured hippocampal neurons, these proteins are present in dendrites and are often found near the presynaptic protein, synapsin I. At synaptic sites, their distribution completely overlaps with a postsynaptic protein, PSD-95. These observations suggest the postsynaptic localization of these proteins. Disruption of mTOR signaling by rapamycin results in a reduction of late-phase LTP expression induced by high-frequency stimulation; the early phase of LTP is unaffected. Rapamycin also blocks the synaptic potentiation induced by brain-derived neurotrophic Factor in hippocampal slices. These results demonstrate an essential role for rapamycin-sensitive signaling in the expression of two forms of synaptic plasticity that require new protein synthesis. The localization of this translational signaling pathway at postsynaptic sites may provide a mechanism that controls local protein synthesis at potentiated synapses.
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tumstatin an endothelial cell specific inhibitor of protein synthesis
Science, 2002Co-Authors: Yohei Maeshima, Akulapalli Sudhaka, Julie C Lively, Kohjiro Ueki, Surende Kharbanda, Nahum Sonenberg, Richard O Hynes, Roberta C Kah, Raghu KalluriAbstract:Tumstatin is a 28-kilodalton fragment of type IV collagen that displays both anti-angiogenic and proapoptotic activity. Here we show that tumstatin functions as an endothelial cell-specific inhibitor of protein synthesis. Through a requisite interaction with alphaVbeta3 integrin, tumstatin inhibits activation of focal adhesion kinase (FAK), phosphatidylinositol 3-kinase (PI3-kinase), protein kinase B (PKB/Akt), and mammalian target of rapamycin (mTOR), and it prevents the dissociation of eukaryotic Initiation Factor 4E protein (eIF4E) from 4E-binding protein 1. These results establish a role for integrins in mediating cell-specific inhibition of cap-dependent protein synthesis and suggest a potential mechanism for tumstatin's selective effects on endothelial cells.
Thierry Candresse - One of the best experts on this subject based on the ideXlab platform.
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a eukaryotic translation Initiation Factor 4E eif4E is responsible for the va tobacco recessive resistance to potyviruses
Plant Molecular Biology Reporter, 2015Co-Authors: Emilie Julio, J Cotucheau, C Decorps, R Volpatti, C Sentenac, Thierry Candresse, Dorlhac F De BorneAbstract:Potato virus Y (PVY), the type member of the genus Potyvirus, is transmitted by aphids and can cause severe damage in several solanaceous family crops. In Nicotiana tabacum, a large genome deletion conferring resistance to PVY, the va gene, is commonly used. This resistance is unfortunately associated with lower tobacco quality parameters, potentially due to the presence of several other important genes in the deleted region. In the present study, we have used next-generation sequencing to analyze the transcriptome of a dozen of tobacco F7 recombinant inbred lines (RILs) segregating for PVY resistance. After comparison with a reference transcriptome, genes differentially expressed between resistant and susceptible plants were identified. About 30 candidate sequences were selected, including a sequence annotated as encoding an eukaryotic translation Initiation Factor 4E (eIF4E), which was strongly expressed in susceptible plants but not in resistant ones. Other differentially expressed candidates are mostly related to photosynthesis. A complete correlation between susceptibility and expression of this eIF4E sequence was confirmed by amplification in 91 F8 RILs and in a segregating F2 population. The gene was mapped on chromosome 21 of the tobacco genetic map and corresponds to an eIF4E isoform derived from the N. sylvestris parent of tobacco. Final confirmation of the identification of the va gene came from the analysis of two tobacco lines with missense mutations in the eIF4E gene and which correspondingly showed resistance to PVY infection. Screening of a large collection of tobacco accessions revealed a strong correlation between the status of this eIF4 gene and PVY resistance, but the identification of a few resistant accessions with an apparently intact gene suggests the possible existence of alternative resistance sources. The identification of the va gene and of molecular markers linked to it or to the large deletion associated with it opens the way to breeding efforts aimed at breaking the linkage drag associated with this valuable resistance gene.
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The C terminus of lettuce mosaic potyvirus cylindrical inclusion helicase interacts with the viral VPg and with lettuce translation eukaryotic Initiation Factor 4E
Journal of General Virology, 2012Co-Authors: Genevieve Tavert-roudet, Anas Abdul Razzak, Bénédicte Doublet, Jocelyne Walter, Thierry Delaunay, Thierry Michon, Olivier Le Gall, Thierry CandresseAbstract:Recessive resistance to lettuce mosaic virus (LMV) is conferred in lettuce by the mo1 gene, encoding the eukaryotic translation Initiation Factor 4E (eIF4E). The C terminus of the viral cylindrical inclusion helicase (CI-Cter), together with the VPg, is involved directly in overcoming mo1 resistance. In this study, recombinant LMV VPg and CI-Cter proteins from wild-type or resistance-breaking isolates were expressed and purified from Escherichia coli. The allelic forms of eIF4E from susceptible or resistant lettuce cultivars were produced similarly and these proteins were used in ELISA-based assays to demonstrate the in vitro binding of the various forms of LMV CI-Cter to both lettuce eIF4E and LMV VPg proteins. All combinations tested displayed significant and specific interactions, and the interaction between the C-terminal part of the LMV CI and eIF4E was confirmed in vivo in bimolecular fluorescence complementation assays. Higher interaction signals for both CI–eIF4E and CI–VPg were observed for LMV-E, indicating that the eIF4E interaction network involving CI and VPg appears to be stronger in the case of this resistance-breaking isolate. This could suggest the need for a minimal interaction threshold for infection success in resistant lettuce, but more precise measurement of the interaction parameters linking eIF4E, VPg and CI is needed in order to reinforce such a hypothesis.
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involvement of the cylindrical inclusion ci protein in the overcoming of an eif4E mediated resistance against lettuce mosaic potyvirus
Molecular Plant Pathology, 2009Co-Authors: Anas Abdulrazzak, Thierry Candresse, Thomas Guiraud, Martine Peypelut, Jocel Ne Y Walter, Mariechristine Houvenaghel, Olivier Le Gall, Sylvie GermanretanaAbstract:SUMMARY The capacity of Lettuce mosaic virus to overcome the lettuce resistance conferred by the mo1 1 and mo1 2 alleles of the gene for eukaryotic translation Initiation Factor 4E (eIF4E) was analysed using reverse genetics. Mutations in the virus genome-linked protein (VPg) allowed mo1 1 only to be overcome, but mutations in the C-terminal portion of the cylindrical inclusion (CI) protein allowed both alleles to be overcome. Site-directed mutagenesis pinpointed a key role of the amino acid at position 621 in the virulence. This is the first example of the involvement of a potyviral CI protein in the breaking of an eIF4E-mediated resistance.
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the eukaryotic translation Initiation Factor 4E controls lettuce susceptibility to the potyvirus lettuce mosaic virus
Plant Physiology, 2003Co-Authors: Valerie Nicaise, Carole Caranta, Thierry Candresse, Sylvie Germanretana, Raquel Sanjuan, Mariepierre Dubrana, Marianne Mazier, Brigitte Maisonneuve, Olivier LegallAbstract:The eIF4E and eIF(iso)4E cDNAs from several genotypes of lettuce ( Lactuca sativa ) that are susceptible, tolerant, or resistant to infection by Lettuce mosaic virus (LMV; genus Potyvirus ) were cloned and sequenced. Although Ls-eIF(iso)4E was monomorphic in sequence, three types of Ls-eIF4E differed by point sequence variations, and a short in-frame deletion in one of them. The amino acid variations specific to Ls-eIF4E 1 and Ls-eIF4E 2 were predicted to be located near the cap recognition pocket in a homology-based tridimensional protein model. In 19 lettuce genotypes, including two near-isogenic pairs, there was a strict correlation between these three allelic types and the presence or absence of the recessive LMV resistance genes mo1 1 and mo1 2 . Ls-eIF4E 1 and mo1 1 cosegregated in the progeny of two separate crosses between susceptible genotypes and an mo1 1 genotype. Finally, transient ectopic expression of Ls-eIF4E restored systemic accumulation of a green fluorescent protein-tagged LMV in LMV-resistant mo1 2 plants and a recombinant LMV expressing Ls-eIF4E° from its genome, but not Ls-eIF4E 1 or Ls-eIF(iso)4E, accumulated and produced symptoms in mo1 1 or mo1 2 genotypes. Therefore, sequence correlation, tight genetic linkage, and functional complementation strongly suggest that eIF4E plays a role in the LMV cycle in lettuce and that mo1 1 and mo1 2 are alleles coding for forms of eIF4E unable or less effective to fulfill this role. More generally, the isoforms of eIF4E appear to be host Factors involved in the cycle of potyviruses in plants, probably through a general mechanism yet to be clarified.
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the eukaryotic translation Initiation Factor 4E controls lettuce susceptibility to the potyvirus lettuce mosaic virus
Plant Physiology, 2003Co-Authors: Valerie Nicaise, Carole Caranta, Thierry Candresse, Sylvie Germanretana, Raquel Sanjuan, Mariepierre Dubrana, Marianne Mazier, Brigitte Maisonneuve, Olivier LegallAbstract:The eIF4E and eIF(iso)4E cDNAs from several genotypes of lettuce (Lactuca sativa) that are susceptible, tolerant, or resistant to infection by Lettuce mosaic virus (LMV; genus Potyvirus) were cloned and sequenced. Although Ls-eIF(iso)4E was monomorphic in sequence, three types of Ls-eIF4E differed by point sequence variations, and a short in-frame deletion in one of them. The amino acid variations specific to Ls-eIF4E(1) and Ls-eIF4E(2) were predicted to be located near the cap recognition pocket in a homology-based tridimensional protein model. In 19 lettuce genotypes, including two near-isogenic pairs, there was a strict correlation between these three allelic types and the presence or absence of the recessive LMV resistance genes mo1(1) and mo1(2). Ls-eIF4E(1) and mo1(1) cosegregated in the progeny of two separate crosses between susceptible genotypes and an mo1(1) genotype. Finally, transient ectopic expression of Ls-eIF4E restored systemic accumulation of a green fluorescent protein-tagged LMV in LMV-resistant mo1(2) plants and a recombinant LMV expressing Ls-eIF4E degrees from its genome, but not Ls-eIF4E(1) or Ls-eIF(iso)4E, accumulated and produced symptoms in mo1(1) or mo1(2) genotypes. Therefore, sequence correlation, tight genetic linkage, and functional complementation strongly suggest that eIF4E plays a role in the LMV cycle in lettuce and that mo1(1) and mo1(2) are alleles coding for forms of eIF4E unable or less effective to fulfill this role. More generally, the isoforms of eIF4E appear to be host Factors involved in the cycle of potyviruses in plants, probably through a general mechanism yet to be clarified.
Lynne E. Maquat - One of the best experts on this subject based on the ideXlab platform.
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cap binding protein 1 mediated and eukaryotic translation Initiation Factor 4E mediated pioneer rounds of translation in yeast
Proceedings of the National Academy of Sciences of the United States of America, 2005Co-Authors: Fred Sherman, Lynne E. MaquatAbstract:Abstract Nonsense-mediated mRNA decay (NMD) in mammalian cells is restricted to newly synthesized mRNA that is bound at the 5′ cap by the major nuclear cap-binding complex and at splicing-generated exon–exon junctions by exon junction complexes. This messenger ribonucleoprotein has been called the pioneer translation Initiation complex and, accordingly, NMD occurs as a consequence of nonsense codon recognition during a pioneer round of translation. Here, we characterize the nature of messenger ribonucleoprotein that is targeted for NMD in Saccharomyces cerevisiae. Data indicate that NMD targets both cap-binding complex (Cbc)1p- and eukaryotic translation Initiation Factor (eIF)4E-bound mRNAs, unlike in mammalian cells, where NMD does not detectably target eIF4E-bound mRNA. First, intron-containing pre-mRNAs in yeast are detectably bound by either Cbc1p, or, unlike in mammalian cells, eIF4E, indicating that mRNAs can be derived from either Cbc1p- or eIF4E-bound pre-mRNAs. Second, the ratio of nonsense-containing Cbc1p-bound mRNA to nonsense-free Cbc1p-bound mRNA, which was < 0.4 for those mRNAs tested here, is essentially identical to the ratio of the corresponding nonsense-containing eIF4E-bound mRNA to nonsense-free eIF4E-bound mRNA, and both ratios increase in cells treated with the translational inhibitor cycloheximide (CHX). These data, together with data presented here and elsewhere showing that Cbc1p-bound transcripts are precursors to eIF4E-bound transcripts, demonstrate that Cbc1p-bound mRNA is targeted for NMD. In support of the idea that eIF4E-bound mRNA is also targeted for NMD, eIF4E-bound mRNA is targeted for NMD in strains that lack Cbc1p. These results suggest that both Cbc1p- and eIF4E-mediated pioneer rounds of translation occur in yeast. messenger ribonucleoprotein nonsense-mediated mRNA decay premature termination codon
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cap binding protein 1 mediated and eukaryotic translation Initiation Factor 4E mediated pioneer rounds of translation in yeast
Proceedings of the National Academy of Sciences of the United States of America, 2005Co-Authors: Qinshan Gao, Fred Sherman, Biswadip Das, Lynne E. MaquatAbstract:Abstract Nonsense-mediated mRNA decay (NMD) in mammalian cells is restricted to newly synthesized mRNA that is bound at the 5′ cap by the major nuclear cap-binding complex and at splicing-generated exon–exon junctions by exon junction complexes. This messenger ribonucleoprotein has been called the pioneer translation Initiation complex and, accordingly, NMD occurs as a consequence of nonsense codon recognition during a pioneer round of translation. Here, we characterize the nature of messenger ribonucleoprotein that is targeted for NMD in Saccharomyces cerevisiae. Data indicate that NMD targets both cap-binding complex (Cbc)1p- and eukaryotic translation Initiation Factor (eIF)4E-bound mRNAs, unlike in mammalian cells, where NMD does not detectably target eIF4E-bound mRNA. First, intron-containing pre-mRNAs in yeast are detectably bound by either Cbc1p, or, unlike in mammalian cells, eIF4E, indicating that mRNAs can be derived from either Cbc1p- or eIF4E-bound pre-mRNAs. Second, the ratio of nonsense-containing Cbc1p-bound mRNA to nonsense-free Cbc1p-bound mRNA, which was < 0.4 for those mRNAs tested here, is essentially identical to the ratio of the corresponding nonsense-containing eIF4E-bound mRNA to nonsense-free eIF4E-bound mRNA, and both ratios increase in cells treated with the translational inhibitor cycloheximide (CHX). These data, together with data presented here and elsewhere showing that Cbc1p-bound transcripts are precursors to eIF4E-bound transcripts, demonstrate that Cbc1p-bound mRNA is targeted for NMD. In support of the idea that eIF4E-bound mRNA is also targeted for NMD, eIF4E-bound mRNA is targeted for NMD in strains that lack Cbc1p. These results suggest that both Cbc1p- and eIF4E-mediated pioneer rounds of translation occur in yeast. messenger ribonucleoprotein nonsense-mediated mRNA decay premature termination codon
Katherine L B Borden - One of the best experts on this subject based on the ideXlab platform.
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molecular dissection of the eukaryotic Initiation Factor 4E eif4E export competent rnp
The EMBO Journal, 2009Co-Authors: Ivan Topisirovic, Nadeem Siddiqui, Vincent Leroux Lapointe, Matthias Trost, Pierre Thibault, Catherine Bangeranye, Serafin Pinolroma, Katherine L B BordenAbstract:The eukaryotic translation Initiation Factor 4E (eIF4E) controls gene expression through its effects on mRNA export and cap-dependent translation, both of which contribute to its oncogenic potential. In contrast to its translation function, the mRNA export function of eIF4E is poorly understood. Using an RNP isolation/mass spectrometry approach, we identified candidate coFactors of eIF4E mRNA export including LRPPRC. This protein associates with mRNAs containing the eIF4E-sensitivity element (4E-SE), and its overexpression alters the nuclear export of several eIF4E-sensitive mRNAs. LRPPRC-mediated alteration of eIF4E's mRNA export function requires the integrity of its eIF4E-binding site and it coincides with the subcellular re-distribution of eIF4E. The eIF4E export RNP is distinct in composition from the bulk mRNA export pathway, in that eIF4E- and eIF4E-sensitive mRNAs do not associate with general mRNA export Factors such as TAP/NXF1 or REF/Aly. Our data indicate that mRNA export pathways have evolved for specific mRNAs enabling the differential regulation of biochemical pathways by modulating the expression of groups of genes at the level of their export.
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homeodomain proteins and eukaryotic translation Initiation Factor 4E eif4E an unexpected relationship
Histology and Histopathology, 2005Co-Authors: Ivan Topisirovic, Katherine L B BordenAbstract:The central role of post-transcriptional modification of the expression of several genes involved in tumorigenesis implicates eIF4E as a pivotal Factor in the regulation of cell survival, growth and proliferation. Overexpression of eIF4E leads to malignant transformation in vitro and induces tumor formation in vivo. Furthermore, upregulated expression of eIF4E has been reported in a variety of human malignancies. Consequently, studies over the last ten years have sought to better characterize the molecular mechanisms and cellular Factors that control eIF4E activity. These efforts have revealed a role for eIF4E in diverse biological processes including embryonic development, cell cycle progression, synaptic plasticity and cancer. In this review we focus on several members of the homeodomain protein family, which have recently been identified as a novel class of eIF4E regulators
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eukaryotic translation Initiation Factor 4E activity is modulated by hoxa9 at multiple levels
Molecular and Cellular Biology, 2005Co-Authors: Ivan Topisirovic, Alex Kentsis, Jacqueline M Perez, Monica L Guzman, Craig T Jordan, Katherine L B BordenAbstract:The eukaryotic translation Initiation Factor 4E (eIF4E) alters gene expression on multiple levels. In the cytoplasm, eIF4E acts in the rate-limiting step of translation Initiation. In the nucleus, eIF4E facilitates nuclear export of a subset of mRNAs. Both of these functions contribute to eIF4E's ability to oncogenically transform cells. We report here that the homeodomain protein, HOXA9, is a positive regulator of eIF4E. HOXA9 stimulates eIF4E-dependent export of cyclin D1 and ornithine decarboxylase (ODC) mRNAs in the nucleus, as well as increases the translation efficiency of ODC mRNA in the cytoplasm. These activities depend on direct interactions of HOXA9 with eIF4E and are independent of the role of HOXA9 in transcription. At the biochemical level, HOXA9 mediates these effects by competing with Factors that repress eIF4E function, in particular the proline-rich homeodomain PRH/Hex. This competitive mechanism of eIF4E regulation is disrupted in a subset of leukemias, where HOXA9 displaces PRH from eIF4E, thereby contributing to eIF4E's dysregulation. In regard to these results and our previous finding that approximately 200 homeodomain proteins contain eIF4E binding sites, we propose that homeodomain modulation of eIF4E activity is a novel means through which this family of proteins implements their effects on growth and development.
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aberrant eukaryotic translation Initiation Factor 4E dependent mrna transport impedes hematopoietic differentiation and contributes to leukemogenesis
Molecular and Cellular Biology, 2003Co-Authors: Ivan Topisirovic, Monica L Guzman, Craig T Jordan, Melanie J Mcconnell, Jonathan D Licht, Biljana Culjkovic, Sarah J Neering, Katherine L B BordenAbstract:The eukaryotic translation Initiation Factor 4E (eIF4E) acts as both a key translation Factor and as a promoter of nucleocytoplasmic transport of specific transcripts. Traditionally, its transformation capacity in vivo is attributed to its role in translation Initiation in the cytoplasm. Here, we demonstrate that elevated eIF4E impedes granulocytic and monocytic differentiation. Our subsequent mutagenesis studies indicate that this block is a result of dysregulated eIF4E-dependent mRNA transport. These studies indicate that the RNA transport function of eIF4E could contribute to leukemogenesis. We extended our studies to provide the first evidence that the nuclear transport function of eIF4E contributes to human malignancy, specifically in a subset of acute and chronic myelogenous leukemia patients. We observe an increase in eIF4E-dependent cyclin D1 mRNA transport and a concomitant increase in cyclin D1 protein levels. The aberrant nuclear function of eIF4E is due to abnormally large eIF4E bodies and the loss of regulation by the proline-rich homeodomain PRH. We developed a novel tool to modulate this transport activity. The introduction of IκB, the repressor of NF-κB, leads to suppression of eIF4E, elevation of PRH, reorganization of eIF4E nuclear bodies, and subsequent downregulation of eIF4E-dependent mRNA transport. Thus, our findings indicate that this nuclear function of eIF4E can contribute to leukemogenesis by promoting growth and by impeding differentiation.
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the lymphocytic choriomeningitis virus ring protein z associates with eukaryotic Initiation Factor 4E and selectively represses translation in a ring dependent manner
Journal of Virology, 2000Co-Authors: Elizabeth Campbell J Dwyer, Katherine L B Borden, Huikang Lai, Rhea C Macdonald, Maria S SalvatoAbstract:Only a few host cell proteins that associate with arenaviruses have been identified. To date, the arenavirus Z protein associates with the promyelocytic leukemia protein PML and the ribosomal P proteins. The majority of PML is present in nuclear bodies which are translocated to the cytoplasm by infection with the arenavirus, lymphocytic choriomeningitis virus (LCMV). The Z protein is a small zinc-binding RING protein with an unknown function which is required for the viral life cycle. Here, we demonstrate an association between Z and the host cell translation Factor, eukaryotic Initiation Factor 4E (eIF-4E) in infected and transfected cells. Z's association with both ribosomal proteins and this translation Factor led us to investigate whether Z could modulate host cell translation. In cell culture, Z selectively represses protein production in an eIF-4E-dependent manner. Specifically, we see reduction in cyclin D1 protein production with no effect on glyceraldehyde-3-phosphate dehydrogenase (GAPDH) in cells transfected with Z. Previous reports indicate that cyclin D1 is sensitive to eIF-4E levels, whereas GAPDH is not. Consistent with this, we observe preferential downregulation of cyclin D1 during infection and no effect on GAPDH. Further, no changes in RNA levels were observed for cyclin D1 or GAPDH transcripts. The interaction between eIF-4E and Z may provide a mechanism for slower growth observed in infected cells and a viral strategy for establishing chronic infection.