The Experts below are selected from a list of 879 Experts worldwide ranked by ideXlab platform
Nahum Sonenberg - One of the best experts on this subject based on the ideXlab platform.
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control of paip1 eukayrotic translation Initiation Factor 3 interaction by amino acids through s6 kinase
Molecular and Cellular Biology, 2014Co-Authors: Yvan Martineau, Tommy Alain, Xiaoshan Wang, Emmanuel Petroulakis, David Shahbazian, Bertrand Fabre, Mariepierre Bousquetdubouch, Bernard Monsarrat, Stephane Pyronnet, Nahum SonenbergAbstract:The simultaneous interaction of poly(A)-binding protein (PABP) with eukaryotic translation Initiation Factor 4G (eIF4G) and the mRNA 3' poly(A) tail promotes translation Initiation. We previously showed that the interaction of PABP-interacting protein 1 (Paip1) with PABP and eukaryotic translation Initiation Factor 3 (eIF3; via the eIF3g subunit) further stimulates translation. Here, we demonstrate that the interaction of eIF3 with Paip1 is regulated by amino acids through the mTORC1 signaling pathway. The Paip1-eIF3 interaction is impaired by the mTORC1 inhibitors, rapamycin and PP242. We show that ribosomal protein S6 kinases 1 and 2 (S6K1/2) promote the interaction of eIF3 with Paip1. The enhancement of Paip1-eIF3 interaction by amino acids is abrogated by an S6K inhibitor or shRNA against S6K1/2. S6K1 interacts with eIF3f and, in vitro, phosphorylates eIF3. Finally, we show that S6K inhibition leads to a reduction in translation by Paip1. We propose that S6K1/2 phosphorylate eIF3 to stimulate Paip1-eIF3 interaction and consequent translation Initiation. Taken together, these data demonstrate that eIF3 is a new translation target of the mTOR/S6K pathway.
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control of translation and mirna dependent repression by a novel poly a binding protein hnrnp q
PLOS Biology, 2013Co-Authors: Yuri V Svitkin, Akiko Yanagiya, Alexey Karetnikov, Tommy Alain, Marc R Fabian, Arkady Khoutorsky, Sandra Perreault, Ivan Topisirovic, Nahum SonenbergAbstract:Translation control often operates via remodeling of messenger ribonucleoprotein particles. The poly(A) binding protein (PABP) simultaneously interacts with the 3′ poly(A) tail of the mRNA and the eukaryotic translation Initiation Factor 4G (eIF4G) to stimulate translation. PABP also promotes miRNA-dependent deadenylation and translational repression of target mRNAs. We demonstrate that isoform 2 of the mouse heterogeneous nuclear protein Q (hnRNP-Q2/SYNCRIP) binds poly(A) by default when PABP binding is inhibited. In addition, hnRNP-Q2 competes with PABP for binding to poly(A) in vitro. Depleting hnRNP-Q2 from translation extracts stimulates cap-dependent and IRES-mediated translation that is dependent on the PABP/poly(A) complex. Adding recombinant hnRNP-Q2 to the extracts inhibited translation in a poly(A) tail-dependent manner. The displacement of PABP from the poly(A) tail by hnRNP-Q2 impaired the association of eIF4E with the 5′ m7G cap structure of mRNA, resulting in the inhibition of 48S and 80S ribosome Initiation complex formation. In mouse fibroblasts, silencing of hnRNP-Q2 stimulated translation. In addition, hnRNP-Q2 impeded let-7a miRNA-mediated deadenylation and repression of target mRNAs, which require PABP. Thus, by competing with PABP, hnRNP-Q2 plays important roles in the regulation of global translation and miRNA-mediated repression of specific mRNAs.
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Structural Analysis of the DAP5 MIF4G Domain and Its Interaction with eIF4A.
Structure (London England : 1993), 2013Co-Authors: Geneviève Virgili, Nahum Sonenberg, Christopher S. Fraser, Filipp Frank, Kateryna Feoktistova, Maxime Sawicki, Bhushan NagarAbstract:Death-associated protein 5 (DAP5/p97) is a homolog of the eukaryotic Initiation Factor 4G (eIF4G) that promotes the IRES-driven translation of multiple cellular mRNAs. Central to its function is the middle domain (MIF4G), which recruits the RNA helicase eIF4A. The middle domain of eIF4G consists of tandem HEAT repeats that coalesce to form a solenoid-type structure. Here, we report the crystal structure of the DAP5 MIF4G domain. Its overall fold is very similar to that of eIF4G; however, significant conformational variations impart distinct surface properties that could explain the observed differences in IRES binding between the two proteins. Interestingly, quantitative analysis of the DAP5-eIF4A interaction using isothermal titration calorimetry reveals a 10-fold lower affinity than with the eIF4G-eIF4A interaction that appears to affect their ability to stimulate eIF4A RNA unwinding activity in vitro. This difference in stability of the complex may have functional implications in selecting the mode of translation Initiation.
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Poly(A)-binding protein-interacting protein 1 binds to eukaryotic translation Initiation Factor 3 to stimulate translation.
Molecular and cellular biology, 2008Co-Authors: Yvan Martineau, Akiko Yanagiya, Hiroaki Imataka, Xiaoshan Wang, Mélanie C. Derry, Juan José Berlanga, Ann-bin Shyu, Kalle Gehring, Nahum SonenbergAbstract:Poly(A)-binding protein (PABP) stimulates translation Initiation by binding simultaneously to the mRNA poly(A) tail and eukaryotic translation Initiation Factor 4G (eIF4G). PABP activity is regulated by PABP-interacting (Paip) proteins. Paip1 binds PABP and stimulates translation by an unknown mechanism. Here, we describe the interaction between Paip1 and eIF3, which is direct, RNA independent, and mediated via the eIF3g (p44) subunit. Stimulation of translation by Paip1 in vivo was decreased upon deletion of the N-terminal sequence containing the eIF3-binding domain and upon silencing of PABP or several eIF3 subunits. We also show the formation of ternary complexes composed of Paip1-PABP-eIF4G and Paip1-eIF3-eIF4G. Taken together, these data demonstrate that the eIF3-Paip1 interaction promotes translation. We propose that eIF3-Paip1 stabilizes the interaction between PABP and eIF4G, which brings about the circularization of the mRNA.
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RNA aptamers to mammalian Initiation Factor 4G inhibit cap-dependent translation by blocking the formation of Initiation Factor complexes.
RNA (New York N.Y.), 2006Co-Authors: Shin Miyakawa, Nahum Sonenberg, Hiroaki Imataka, Akihiro Oguro, Takashi Ohtsu, Yoshikazu NakamuraAbstract:Eukaryotic translation Initiation Factor 4G (eIF4G) plays a crucial multimodulatory role in mRNA translation and decay by interacting with other translation Factors and mRNA-associated proteins. In this study, we isolated eight different RNA aptamers with high affinity to mammalian eIF4G by in vitro RNA selection amplification. Of these, three aptamers (apt3, apt4, and apt5) inhibited the cap-dependent translation of two independent mRNAs in a rabbit reticulocyte lysate system. The cap-independent translation directed by an HCV internal ribosome entry site was not affected. Addition of exogenous eIF4G reversed the aptamer-mediated inhibition of translation. Even though apt3 and apt4 were selected independently, they differ only by two nucleotides. The use of truncated eIF4G variants in binding experiments indicated that apt4 (and probably apt3) bind to both the middle and C-terminal domains of eIF4G, while apt5 binds only to the middle domain of eIF4G. Corresponding to the difference in the binding sites in eIF4G, apt4, but not apt5, hindered eIF4G from binding to eIF4A and eIF3, in a purified protein solution system as well as in a crude lysate system. Therefore, the inhibition of translation by apt4 (and apt3) is due to the inhibition of formation of Initiation Factor complexes involving eIF4A and eIF3. On the other hand, apt5 had a much weaker affinity to eIF4G than apt4, but inhibited translation much more efficiently by an unknown mechanism. The five additional aptamers have sequences and predicted secondary structures that are largely different from each other and from apt3 through apt5. Therefore, we speculate that these seven sets of aptamers may bind to different regions in eIF4G in different fashions.
Daniel R. Gallie - One of the best experts on this subject based on the ideXlab platform.
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The Histone 3′-Terminal Stem-Loop-Binding Protein Enhances Translation through a Functional and Physical Interaction with Eukaryotic Initiation Factor 4G (eIF4G) and eIF3
Molecular and cellular biology, 2002Co-Authors: Jun Ling, Simon J. Morley, Virginia M. Pain, William F. Marzluff, Daniel R. GallieAbstract:Metazoan cell cycle-regulated histone mRNAs are unique cellular mRNAs in that they terminate in a highly conserved stem-loop structure instead of a poly(A) tail. Not only is the stem-loop structure necessary for 3'-end formation but it regulates the stability and translational efficiency of histone mRNAs. The histone stem-loop structure is recognized by the stem-loop-binding protein (SLBP), which is required for the regulation of mRNA processing and turnover. In this study, we show that SLBP is required for the translation of mRNAs containing the histone stem-loop structure. Moreover, we show that the translation of mRNAs ending in the histone stem-loop is stimulated in Saccharomyces cerevisiae cells expressing mammalian SLBP. The translational function of SLBP genetically required eukaryotic Initiation Factor 4E (eIF4E), eIF4G, and eIF3, and expressed SLBP coisolated with S. cerevisiae Initiation Factor complexes that bound the 5' cap in a manner dependent on eIF4G and eIF3. Furthermore, eIF4G coimmunoprecipitated with endogenous SLBP in mammalian cell extracts and recombinant SLBP and eIF4G coisolated. These data indicate that SLBP stimulates the translation of histone mRNAs through a functional interaction with both the mRNA stem-loop and the 5' cap that is mediated by eIF4G and eIF3.
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the histone 3 terminal stem loop binding protein enhances translation through a functional and physical interaction with eukaryotic Initiation Factor 4G eif4G and eif3
Molecular and Cellular Biology, 2002Co-Authors: Jun Ling, Simon J. Morley, Virginia M. Pain, William F. Marzluff, Daniel R. GallieAbstract:Metazoan cell cycle-regulated histone mRNAs are unique cellular mRNAs in that they terminate in a highly conserved stem-loop structure instead of a poly(A) tail. Not only is the stem-loop structure necessary for 3'-end formation but it regulates the stability and translational efficiency of histone mRNAs. The histone stem-loop structure is recognized by the stem-loop-binding protein (SLBP), which is required for the regulation of mRNA processing and turnover. In this study, we show that SLBP is required for the translation of mRNAs containing the histone stem-loop structure. Moreover, we show that the translation of mRNAs ending in the histone stem-loop is stimulated in Saccharomyces cerevisiae cells expressing mammalian SLBP. The translational function of SLBP genetically required eukaryotic Initiation Factor 4E (eIF4E), eIF4G, and eIF3, and expressed SLBP coisolated with S. cerevisiae Initiation Factor complexes that bound the 5' cap in a manner dependent on eIF4G and eIF3. Furthermore, eIF4G coimmunoprecipitated with endogenous SLBP in mammalian cell extracts and recombinant SLBP and eIF4G coisolated. These data indicate that SLBP stimulates the translation of histone mRNAs through a functional interaction with both the mRNA stem-loop and the 5' cap that is mediated by eIF4G and eIF3.
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Cap-Independent Translation Conferred by the 5′ Leader of Tobacco Etch Virus Is Eukaryotic Initiation Factor 4G Dependent
Journal of virology, 2001Co-Authors: Daniel R. GallieAbstract:The 5′ leader of tobacco etch virus (TEV) genomic RNA directs efficient translation from the naturally uncapped viral mRNA. Two distinct regions within the TEV 143-nucleotide leader confer cap-independent translation in vivo even when present in the intercistronic region of a discistronic mRNA, indicating that the TEV leader contains an internal ribosome entry site (IRES). In this study, the requirements for TEV IRES activity were investigated. The TEV IRES enhanced translation of monocistronic or dicistronic mRNAs in vitro under competitive conditions, i.e., at high RNA concentration or in lysate partially depleted of eukaryotic Initiation Factor 4F (eIF4F) and eIFiso4F, the two cap binding complexes in plants. The translational advantage conferred by the TEV IRES under these conditions was lost when the lysate reduced in eIF4F and eIFiso4F was supplemented with eIF4F (or, to a lesser extent, eIFiso4F) but not when supplemented with eIF4E, eIFiso4E, eIF4A, or eIF4B. eIF4G, the large subunit of eIF4F, was responsible for the competitive advantage conferred by the TEV IRES. TEV IRES activity was enhanced moderately by the poly(A)-binding protein. These observations suggest that the TEV IRES directs cap-independent translation through a mechanism that involves eIF4G specifically.
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cap independent translation conferred by the 5 leader of tobacco etch virus is eukaryotic Initiation Factor 4G dependent
Journal of Virology, 2001Co-Authors: Daniel R. GallieAbstract:The 5′ leader of tobacco etch virus (TEV) genomic RNA directs efficient translation from the naturally uncapped viral mRNA. Two distinct regions within the TEV 143-nucleotide leader confer cap-independent translation in vivo even when present in the intercistronic region of a discistronic mRNA, indicating that the TEV leader contains an internal ribosome entry site (IRES). In this study, the requirements for TEV IRES activity were investigated. The TEV IRES enhanced translation of monocistronic or dicistronic mRNAs in vitro under competitive conditions, i.e., at high RNA concentration or in lysate partially depleted of eukaryotic Initiation Factor 4F (eIF4F) and eIFiso4F, the two cap binding complexes in plants. The translational advantage conferred by the TEV IRES under these conditions was lost when the lysate reduced in eIF4F and eIFiso4F was supplemented with eIF4F (or, to a lesser extent, eIFiso4F) but not when supplemented with eIF4E, eIFiso4E, eIF4A, or eIF4B. eIF4G, the large subunit of eIF4F, was responsible for the competitive advantage conferred by the TEV IRES. TEV IRES activity was enhanced moderately by the poly(A)-binding protein. These observations suggest that the TEV IRES directs cap-independent translation through a mechanism that involves eIF4G specifically.
Hiroaki Imataka - One of the best experts on this subject based on the ideXlab platform.
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General RNA‐binding proteins have a function in poly(A)‐binding protein‐dependent translation
The EMBO journal, 2008Co-Authors: Yuri V Svitkin, Akiko Yanagiya, Hiroaki Imataka, Tatyana V. Pestova, Valentina Evdokimova, Ann Brasey, Daniel Fantus, Maxim A. Skabkin, Lev P. Ovchinnikov, William C. MerrickAbstract:The interaction between the poly(A)-binding protein (PABP) and eukaryotic translational Initiation Factor 4G (eIF4G), which brings about circularization of the mRNA, stimulates translation. General RNA-binding proteins affect translation, but their role in mRNA circularization has not been studied before. Here, we demonstrate that the major mRNA ribonucleoprotein YB-1 has a pivotal function in the regulation of eIF4F activity by PABP. In cell extracts, the addition of YB-1 exacerbated the inhibition of 80S ribosome Initiation complex formation by PABP depletion. Rabbit reticulocyte lysate in which PABP weakly stimulates translation is rendered PABP-dependent after the addition of YB-1. In this system, eIF4E binding to the cap structure is inhibited by YB-1 and stimulated by a nonspecific RNA. Significantly, adding PABP back to the depleted lysate stimulated eIF4E binding to the cap structure more potently if this binding had been downregulated by YB-1. Conversely, adding nonspecific RNA abrogated PABP stimulation of eIF4E binding. These data strongly suggest that competition between YB-1 and eIF4G for mRNA binding is required for efficient stimulation of eIF4F activity by PABP.
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Poly(A)-binding protein-interacting protein 1 binds to eukaryotic translation Initiation Factor 3 to stimulate translation.
Molecular and cellular biology, 2008Co-Authors: Yvan Martineau, Akiko Yanagiya, Hiroaki Imataka, Xiaoshan Wang, Mélanie C. Derry, Juan José Berlanga, Ann-bin Shyu, Kalle Gehring, Nahum SonenbergAbstract:Poly(A)-binding protein (PABP) stimulates translation Initiation by binding simultaneously to the mRNA poly(A) tail and eukaryotic translation Initiation Factor 4G (eIF4G). PABP activity is regulated by PABP-interacting (Paip) proteins. Paip1 binds PABP and stimulates translation by an unknown mechanism. Here, we describe the interaction between Paip1 and eIF3, which is direct, RNA independent, and mediated via the eIF3g (p44) subunit. Stimulation of translation by Paip1 in vivo was decreased upon deletion of the N-terminal sequence containing the eIF3-binding domain and upon silencing of PABP or several eIF3 subunits. We also show the formation of ternary complexes composed of Paip1-PABP-eIF4G and Paip1-eIF3-eIF4G. Taken together, these data demonstrate that the eIF3-Paip1 interaction promotes translation. We propose that eIF3-Paip1 stabilizes the interaction between PABP and eIF4G, which brings about the circularization of the mRNA.
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RNA aptamers to mammalian Initiation Factor 4G inhibit cap-dependent translation by blocking the formation of Initiation Factor complexes.
RNA (New York N.Y.), 2006Co-Authors: Shin Miyakawa, Nahum Sonenberg, Hiroaki Imataka, Akihiro Oguro, Takashi Ohtsu, Yoshikazu NakamuraAbstract:Eukaryotic translation Initiation Factor 4G (eIF4G) plays a crucial multimodulatory role in mRNA translation and decay by interacting with other translation Factors and mRNA-associated proteins. In this study, we isolated eight different RNA aptamers with high affinity to mammalian eIF4G by in vitro RNA selection amplification. Of these, three aptamers (apt3, apt4, and apt5) inhibited the cap-dependent translation of two independent mRNAs in a rabbit reticulocyte lysate system. The cap-independent translation directed by an HCV internal ribosome entry site was not affected. Addition of exogenous eIF4G reversed the aptamer-mediated inhibition of translation. Even though apt3 and apt4 were selected independently, they differ only by two nucleotides. The use of truncated eIF4G variants in binding experiments indicated that apt4 (and probably apt3) bind to both the middle and C-terminal domains of eIF4G, while apt5 binds only to the middle domain of eIF4G. Corresponding to the difference in the binding sites in eIF4G, apt4, but not apt5, hindered eIF4G from binding to eIF4A and eIF3, in a purified protein solution system as well as in a crude lysate system. Therefore, the inhibition of translation by apt4 (and apt3) is due to the inhibition of formation of Initiation Factor complexes involving eIF4A and eIF3. On the other hand, apt5 had a much weaker affinity to eIF4G than apt4, but inhibited translation much more efficiently by an unknown mechanism. The five additional aptamers have sequences and predicted secondary structures that are largely different from each other and from apt3 through apt5. Therefore, we speculate that these seven sets of aptamers may bind to different regions in eIF4G in different fashions.
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Translational Silencing of Ceruloplasmin Requires the Essential Elements of mRNA Circularization: Poly(A) Tail, Poly(A)-Binding Protein, and Eukaryotic Translation Initiation Factor 4G
Molecular and cellular biology, 2001Co-Authors: Barsanjit Mazumder, Nahum Sonenberg, Hiroaki Imataka, Vasudevan Seshadri, Paul L. FoxAbstract:Ceruloplasmin (Cp) is a glycoprotein secreted by the liver and monocytic cells and probably plays roles in inflammation and iron metabolism. We showed previously that gamma interferon (IFN-γ) induced Cp synthesis by human U937 monocytic cells but that the synthesis was subsequently halted by a transcript-specific translational silencing mechanism involving the binding of a cytosolic Factor(s) to the Cp mRNA 3′ untranslated region (UTR). To investigate how protein interactions at the Cp 3′-UTR inhibit translation Initiation at the distant 5′ end, we considered the “closed-loop” model of mRNA translation. In this model, the transcript termini are brought together by interactions of poly(A)-binding protein (PABP) with both the poly(A) tail and Initiation Factor eIF4G. The effect of these elements on Cp translational control was tested using chimeric reporter transcripts in rabbit reticulocyte lysates. The requirement for poly(A) was shown since the cytosolic inhibitor from IFN-γ-treated cells minimally inhibited the translation of a luciferase reporter upstream of the Cp 3′-UTR but almost completely blocked the translation of a transcript containing a poly(A) tail. Likewise, a requirement for poly(A) was shown for silencing of endogenous Cp mRNA. We considered the possibility that the cytosolic inhibitor blocked the interaction of PABP with the poly(A) tail or with eIF4G. We found that neither of these interactions were inhibited, as shown by immunoprecipitation of PABP followed by quantitation of the poly(A) tail by reverse transcription-PCR and of eIF4G by immunoblot analysis. We considered the alternate possibility that these interactions were required for translational silencing. When PABP was depleted from the reticulocyte lysate with anti-human PABP antibody, the cytosolic Factor did not inhibit translation of the chimeric reporter, thus showing the requirement for PABP. Similarly, in lysates treated with anti-human eIF4G antibody, the cytosolic extract did not inhibit the translation of the chimeric reporter, thereby showing a requirement for eIF4G. These data show that translational silencing of Cp requires interactions of three essential elements of mRNA circularization, poly(A), PABP, and eIF4G. We suggest that Cp mRNA circularization brings the cytosolic Cp 3′-UTR-binding Factor into the proximity of the translation Initiation site, where it silences translation by an undetermined mechanism. These results suggest that in addition to its important function in increasing the efficiency of translation, transcript circularization may serve as an essential structural determinant for transcript-specific translational control.
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Interaction of eIF4G with poly(A)-binding protein stimulates translation and is critical for Xenopus oocyte maturation
Current biology : CB, 2000Co-Authors: Motoaki Wakiyama, Hiroaki Imataka, Nahum SonenbergAbstract:The poly(A)-binding protein Pab1p interacts directly with the eukaryotic translation Initiation Factor 4G (eIF4G) to facilitate translation Initiation of polyadenylated mRNAs in yeast [1,2]. Although the eIF4G-PABP interaction has also been demonstrated in a mammalian system [3,4], its biological significance in vertebrates is unknown. In Xenopus oocytes, cytoplasmic polyadenylation of several mRNAs coincides with their translational activation and is critical for maturation [5-7]. Because the amount of PABP is very low in oocytes [8], it has been argued that the eIF4G-PABP interaction does not play a major role in translational activation during oocyte maturation. Also, overexpression of PABP in Xenopus oocytes has only a modest stimulatory effect on translation of polyadenylated mRNA and does not alter either the efficiency or the kinetics of progesterone-induced maturation [9]. Here, we report that the expression of an eIF4GI mutant defective in PABP binding in Xenopus oocytes reduces translation of polyadenylated mRNA and dramatically inhibits progesterone-induced maturation. Our results show that the eIF4G-PABP interaction is critical for translational control of maternal mRNAs during Xenopus development.
Simon J. Morley - One of the best experts on this subject based on the ideXlab platform.
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Multiple isoforms of the translation Initiation Factor eIF4GII are generated via use of alternative promoters, splice sites and a non-canonical Initiation codon.
The Biochemical journal, 2012Co-Authors: Mark J. Coldwell, Ulrike Sack, Joanne L. Cowan, Rachel M.a. Barrett, Markete Vlasak, Keiley Sivakumaran, Simon J. MorleyAbstract:During the Initiation stage of eukaryotic mRNA translation, the eIF4G (eukaryotic Initiation Factor 4G) proteins act as an aggregation point for recruiting the small ribosomal subunit to an mRNA. We previously used RNAi (RNA interference) to reduce expression of endogenous eIF4GI proteins, resulting in reduced protein synthesis rates and alterations in the morphology of cells. Expression of EIF4G1 cDNAs, encoding different isoforms (f-a) which arise through selection of alternative Initiation codons, rescued translation to different extents. Furthermore, overexpression of the eIF4GII paralogue in the eIF4GI-knockdown background was unable to restore translation to the same extent as eIF4GIf/e isoforms, suggesting that translation events governed by this protein are different. In the present study we show that multiple isoforms of eIF4GII exist in mammalian cells, arising from multiple promoters and alternative splicing events, and have identified a non-canonical CUG Initiation codon which extends the eIF4GII N-terminus. We further show that the rescue of translation in eIF4GI/eIF4GII double-knockdown cells by our novel isoforms of eIF4GII is as robust as that observed with either eIF4GIf or eIF4GIe, and more than that observed with the original eIF4GII. As the novel eIF4GII sequence diverges from eIF4GI, these data suggest that the eIF4GII N-terminus plays an alternative role in Initiation Factor assembly.
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Immunohistochemical mapping of total and phosphorylated eukaryotic Initiation Factor 4G in rat hippocampus following global brain ischemia and reperfusion.
Neuroscience, 2006Co-Authors: Donald J. Degracia, Simon J. Morley, José A. Rafols, Foaz KayaliAbstract:Partial proteolysis and phosphorylation of the translation Initiation Factor eukaryotic Initiation Factor 4G (eIF4G) occur in reperfused brain, but the contribution of eIF4G alterations to brain injury has not been established. A component of the complex delivering mRNA to the small ribosomal subunit, eIF4G is also found in stress granules. Stress granules sequester inactive 48S preInitiation complexes during stress-induced translation arrest. We performed double-labeling immunofluorescence histochemistry for total or ser 1108 phosphorylated eIF4G and the stress granule component T-cell internal antigen following normothermic, 10 min cardiac arrest-induced global brain ischemia and up to 4 h reperfusion in the rat. In cornu ammonis (Ammon?s horn; CA) 1 at 90 min and 4 h reperfusion, eIF4G staining transformed from a homogeneous to an aggregated distribution. The number of eIF4G-containing stress granules differed between CA1 and CA3 during reperfusion. In hippocampal pyramidal neurons, phosphorylated eIF4G appeared exclusively in stress granules. Supragranular interneurons of the dentate gyrus showed a large increase in cytoplasmic eIF4G(P) following reperfusion. Immunoblot analysis with antisera against different portions of eIF4G showed a large increase in phosphorylated C-terminal eIF4G fragments, suggesting these accumulate in the cytoplasm of dentate gyrus interneurons. Thus, altered eIF4G subcellular compartmentalization may contribute to prolonged translation arrest in CA1 pyramidal neurons. Accumulation of phosphorylated eIF4G fragments may contribute to the vulnerability of dentate interneurons. Ischemia and reperfusion invoke different translational control responses in distinct hippocampal neuron populations, which may contribute to the differential ischemic vulnerabilities of these cells.
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The Histone 3′-Terminal Stem-Loop-Binding Protein Enhances Translation through a Functional and Physical Interaction with Eukaryotic Initiation Factor 4G (eIF4G) and eIF3
Molecular and cellular biology, 2002Co-Authors: Jun Ling, Simon J. Morley, Virginia M. Pain, William F. Marzluff, Daniel R. GallieAbstract:Metazoan cell cycle-regulated histone mRNAs are unique cellular mRNAs in that they terminate in a highly conserved stem-loop structure instead of a poly(A) tail. Not only is the stem-loop structure necessary for 3'-end formation but it regulates the stability and translational efficiency of histone mRNAs. The histone stem-loop structure is recognized by the stem-loop-binding protein (SLBP), which is required for the regulation of mRNA processing and turnover. In this study, we show that SLBP is required for the translation of mRNAs containing the histone stem-loop structure. Moreover, we show that the translation of mRNAs ending in the histone stem-loop is stimulated in Saccharomyces cerevisiae cells expressing mammalian SLBP. The translational function of SLBP genetically required eukaryotic Initiation Factor 4E (eIF4E), eIF4G, and eIF3, and expressed SLBP coisolated with S. cerevisiae Initiation Factor complexes that bound the 5' cap in a manner dependent on eIF4G and eIF3. Furthermore, eIF4G coimmunoprecipitated with endogenous SLBP in mammalian cell extracts and recombinant SLBP and eIF4G coisolated. These data indicate that SLBP stimulates the translation of histone mRNAs through a functional interaction with both the mRNA stem-loop and the 5' cap that is mediated by eIF4G and eIF3.
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the histone 3 terminal stem loop binding protein enhances translation through a functional and physical interaction with eukaryotic Initiation Factor 4G eif4G and eif3
Molecular and Cellular Biology, 2002Co-Authors: Jun Ling, Simon J. Morley, Virginia M. Pain, William F. Marzluff, Daniel R. GallieAbstract:Metazoan cell cycle-regulated histone mRNAs are unique cellular mRNAs in that they terminate in a highly conserved stem-loop structure instead of a poly(A) tail. Not only is the stem-loop structure necessary for 3'-end formation but it regulates the stability and translational efficiency of histone mRNAs. The histone stem-loop structure is recognized by the stem-loop-binding protein (SLBP), which is required for the regulation of mRNA processing and turnover. In this study, we show that SLBP is required for the translation of mRNAs containing the histone stem-loop structure. Moreover, we show that the translation of mRNAs ending in the histone stem-loop is stimulated in Saccharomyces cerevisiae cells expressing mammalian SLBP. The translational function of SLBP genetically required eukaryotic Initiation Factor 4E (eIF4E), eIF4G, and eIF3, and expressed SLBP coisolated with S. cerevisiae Initiation Factor complexes that bound the 5' cap in a manner dependent on eIF4G and eIF3. Furthermore, eIF4G coimmunoprecipitated with endogenous SLBP in mammalian cell extracts and recombinant SLBP and eIF4G coisolated. These data indicate that SLBP stimulates the translation of histone mRNAs through a functional interaction with both the mRNA stem-loop and the 5' cap that is mediated by eIF4G and eIF3.
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interaction of eukaryotic translation Initiation Factor 4G with the nuclear cap binding complex provides a link between nuclear and cytoplasmic functions of the m7 guanosine cap
Molecular and Cellular Biology, 2001Co-Authors: Linda Mckendrick, Simon J. Morley, Elizabeth Thompson, Joao Ferreira, Joe D LewisAbstract:In eukaryotes the majority of mRNAs have an m7G cap that is added cotranscriptionally and that plays an important role in many aspects of mRNA metabolism. The nuclear cap-binding complex (CBC; consisting of CBP20 and CBP80) mediates the stimulatory functions of the cap in pre-mRNA splicing, 3' end formation, and U snRNA export. As little is known about how nuclear CBC mediates the effects of the cap in higher eukaryotes, we have characterized proteins that interact with CBC in HeLa cell nuclear extracts as potential mediators of its function. Using cross-linking and coimmunoprecipitation, we show that eukaryotic translation Initiation Factor 4G (eIF4G), in addition to its function in the cytoplasm, is a nuclear CBC-interacting protein. We demonstrate that eIF4G interacts with CBC in vitro and that, in addition to its cytoplasmic localization, there is a significant nuclear pool of eIF4G in mammalian cells in vivo. Immunoprecipitation experiments suggest that, in contrast to the cytoplasmic pool, much of the nuclear eIF4G is not associated with eIF4E (translation cap binding protein of eIF4F) but is associated with CBC. While eIF4G stably associates with spliceosomes in vitro and shows close association with spliceosomal snRNPs and splicing Factors in vivo, depletion studies show that it does not participate directly in the splicing reaction. Taken together the data indicate that nuclear eIF4G may be recruited to pre-mRNAs via its interaction with CBC and accompanies the mRNA to the cytoplasm, facilitating the switching of CBC for eIF4F. This may provide a mechanism to couple nuclear and cytoplasmic functions of the mRNA cap structure.
Tim Skern - One of the best experts on this subject based on the ideXlab platform.
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The leader proteinase of foot-and-mouth disease virus: structure-function relationships in a proteolytic virulence Factor.
Biological chemistry, 2014Co-Authors: Jutta Steinberger, Tim SkernAbstract:The leader proteinase (Lpro) of the foot-and-mouth disease virus inhibits the host innate immune response by at least three different mechanisms. The most well-characterised of these is the prevention of the synthesis of cytokines such as interferons immediately after infection, brought about by specific proteolytic cleavage of the eukaryotic Initiation Factor 4G. This prevents the recruitment of capped cellular mRNA; however, the viral RNA can be translated under these conditions. The two other mechanisms are the induction of NF-κB cleavage and the deubiquitination of immune signalling molecules. This review focuses on the structure-function relationships in Lpro responsible for these widely divergent activities.
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The Processing of eIF4GI by Human Rhinovirus Type 2 2Apro: Relationship to Self-Cleavage and Role of Zinc
Journal of virology, 2003Co-Authors: Walter Glaser, Andrea Triendl, Tim SkernAbstract:The 2A proteinase (2Apro) of human rhinoviruses (HRVs) is a cysteine protease containing a structurally important zinc ion. In the viral polyprotein, the enzyme cleaves between the C terminus of VP1 and its own N terminus. 2Apro also processes the two isoforms of the cellular protein, eukaryotic Initiation Factor 4G (eIF4G). We have shown that mature HRV2 2Apro, when translated in vitro in rabbit reticulocyte lysates, efficiently cleaves eIF4GI, although the enzyme was not immediately active upon synthesis. Here, we examine the relationship between self-processing and eIF4GI cleavage. The onset of both reactions first occurred at least 10 min after Initiation of protein synthesis. Furthermore, when self-processing was prevented by a specific mutation between VP1 and 2Apro, the VP1-2Apro precursor was essentially unable to cleave eIF4GI, implying that self-processing is a prerequisite for eIF4GI cleavage. 2Apro synthesized in the presence of a potent zinc chelator is inactive; however, upon addition of excess zinc, HRV2 2Apro rapidly gained activity. Finally, the presence of the zinc chelator in the culture medium can protect HeLa cells from HRV infection.
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Recognition of eukaryotic Initiation Factor 4G isoforms by picornaviral proteinases.
The Journal of biological chemistry, 2002Co-Authors: Nicole Foeger, Walter Glaser, Tim SkernAbstract:The leader proteinase (L(pro)) of foot and mouth disease virus is a papain-like cysteine proteinase. After processing itself from the polyprotein, L(pro) then cleaves the host protein eukaryotic Initiation Factor (eIf) 4GI, thus preventing protein synthesis from capped mRNA in the infected cell. We have investigated L(pro) interaction with eIF4GI and its isoform, eIF4GII. L(pro), expressed as a catalytically inactive fusion protein with glutathione S-transferase, binds specifically to eIF4G isomers in rabbit reticulocyte lysates. Deletion and specific mutagenesis were used to map the binding domain on L(pro) to residues 183-195 of the C-terminal extension and to residue Cys(133). These residues of the C-terminal extension and Cys(133) are adjacent in the crystal structure but lie about 25 A from the active site. The region on eIF4GI recognized by the L(pro) C-terminal extension was mapped to residues 640-669 using eIF4GI fragments generated by proteolysis or by in vitro translation. The L(pro) cleavage site at Gly(674) downward arrow Arg(675) was not necessary for binding. Similar experiments with human rhinovirus 2A proteinase (2A(pro)), a chymotrypsin-like cysteine proteinase that also cleaves eIF4G isoforms, revealed that 2A(pro) can also bind to eIF4GI fragments lacking its cleavage site. These experiments strongly suggest a novel interaction between picornaviral proteinases and eIF4G isoforms.
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Structure of the foot‐and‐mouth disease virus leader protease: a papain‐like fold adapted for self‐processing and eIF4G recognition
The EMBO journal, 1998Co-Authors: Alba Guarné, Regina Kirchweger, José Tormo, Doris M. Pfistermueller, Ignacio Fita, Tim SkernAbstract:The leader protease of foot-and-mouth disease virus, as well as cleaving itself from the nascent viral polyprotein, disables host cell protein synthesis by specific proteolysis of a cellular protein: the eukaryotic Initiation Factor 4G (eIF4G). The crystal structure of the leader protease presented here comprises a globular catalytic domain reminiscent of that of cysteine proteases of the papain superfamily, and a flexible C-terminal extension found intruding into the substrate-binding site of an adjacent molecule. Nevertheless, the relative disposition of this extension and the globular domain to each other supports intramolecular self-processing. The different sequences of the two substrates cleaved during viral replication, the viral polyprotein (at LysLeuLys/GlyAlaGly) and eIF4G (at AsnLeuGly/ArgThrThr), appear to be recognized by distinct features in a narrow, negatively charged groove traversing the active centre. The structure illustrates how the prototype papain fold has been adapted to the requirements of an RNA virus. Thus, the protein scaffold has been reduced to a minimum core domain, with the active site being modified to increase specificity. Furthermore, surface features have been developed which enable C-terminal self-processing from the viral polyprotein.
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Mapping of functional domains in eukaryotic protein synthesis Initiation Factor 4G (eIF4G) with picornaviral proteases. Implications for cap-dependent and cap-independent translational Initiation
The Journal of biological chemistry, 1995Co-Authors: Barry J. Lamphear, Regina Kirchweger, Tim Skern, Robert E. RhoadsAbstract:Abstract Cap-dependent binding of mRNA to the 40 S ribosomal subunit during translational Initiation requires the association of eukaryotic Initiation Factor 4G (eIF4G; formerly eIF-4γ and p220) with other Initiation Factors, notably eIF4E, eIF4A, and eIF3. Infection of cells by picornaviruses results in proteolytic cleavage of eIF4G and generation of a cap-independent translational state. Rhinovirus 2A protease and foot-and-mouth-disease virus L protease were used to analyze the association of eIF4G with eIF4A, eIF4E, and eIF3. Both proteases bisect eIF4G into N- and C-terminal fragments termed cpN and cpC·. cpN was shown to contain the eIF4E-binding site, as judged by retention on m7GTP-Sepharose, whereas cpC· was bound to eIF3 and eIF4A, based on ultracentrifugal co-sedimentation. Further proteolysis of cpN by L protease produced an 18-kDa polypeptide termed cpN2 which retained eIF4E binding activity and corresponded to amino acid residues 319-479 of rabbit eIF4G. Further proteolysis of cpC· yielded several smaller fragments. cpC2 (∼887-1402) contained the eIF4A binding site, whereas cpC3 (∼480-886) contained the eIF3 binding site. These results suggest that cleavage by picornaviral proteases at residues 479-486 separates eIF4G into two domains, one required for recruiting capped mRNAs and one for attaching mRNA to the ribosome and directing helicase activity. Only the latter would appear to be necessary for internal Initiation of picornaviral RNAs.