eIF4G Dramatically Enhances the Binding of eIF4E to the mRNA 5′-Cap Structure

Haghighat, Ashkan; Sonenberg, Nahum

doi:10.1074/jbc.272.35.21677

Cited by 227 publications

(170 citation statements)

References 36 publications

(38 reference statements)

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“…have differed between the two preparations. This could have substantially influenced the binding of eIF4E to its ligand (21,24,25). Here we show, using the same fluorescence titration technique with well defined recombinant eIF4E preparations and an authentic kinase, that phosphorylation of eIF4E reduces its affinity for the cap structure about 3-fold.…”

Section: Discussionmentioning

confidence: 87%

Phosphorylation of Eukaryotic Initiation Factor 4E Markedly Reduces Its Affinity for Capped mRNA

Scheper¹,

Kollenburg²,

Hu³

et al. 2002

Journal of Biological Chemistry

230

198

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In eukaryotes, a key step in the initiation of translation is the binding of the eukaryotic initiation factor 4E (eIF4E) to the cap structure of the mRNA. Subsequent recruitment of several components, including the small ribosomal subunit, is thought to allow migration of initiation complexes and recognition of the initiation codon. Mitogens and cytokines stimulate the phosphorylation of eIF4E at Ser 209 , but the functional consequences of this modification have remained a major unresolved question. Using fluorescence spectroscopy and surface plasmon resonance techniques, we show that phosphorylation of eIF4E markedly reduces its affinity for capped RNA, primarily due to an increased rate of dissociation. Variant eIF4E proteins harboring negatively charged acidic residues at position 209 also showed decreased binding to capped RNA. Furthermore, a basic residue at position 159 was shown to be essential for cap binding. Although eIF4E-binding protein 1 greatly stabilized binding of phosphorylated eIF4E to capped RNA, in the presence of eIF4E-binding protein 1 the phosphorylated form still dissociated faster compared with nonphopshorylated eIF4E. The implications of our findings for the mechanism of translation initiation are discussed.In eukaryotic cells, all nucleus-encoded mRNAs possess a so-called "cap structure" at their 5Ј-end. This cap consists of a methylated 5Ј-5Ј bound guanosine triphosphate (m 7 GTP) moiety. The cap plays a key role in the translation of the mRNA by permitting recruitment of the eukaryotic initiation factors (eIFs) 1 required for the attachment of the ribosome and correct initiation of translation. The protein that interacts directly with the cap is eIF4E, which forms a complex with the scaffolding protein eIF4G, which in turn recruits other factors. These include eIF4A and eIF4B, which are involved in unwinding secondary structure in the 5Ј-untranslated region of the mRNA, and the poly(A)-binding protein, which by interacting with the 3Ј-tail of the mRNA circularizes it (1, 2). eIF4E also binds to small regulatory proteins termed eIF4E-binding proteins (4E-BPs). These compete with eIF4G for binding to overlapping sites on eIF4E and thus inhibit formation of initiation complexes (3, 4).It has long been known that eIF4E undergoes regulated phosphorylation, and the site has been identified as Ser 209 (5, 6). Phosphorylation of eIF4E is increased by mitogenic stimuli that activate translation (reviewed in Ref. 7) and by cytokines (8, 9). Recently, two kinases were identified that phosphorylate Ser 209 in eIF4E and are targets for the mitogen-activated extracellular signal-regulated kinase and stress/cytokine-activated p38 mitogen-activated protein kinase pathways (9 -13). These enzymes (Mnk1 and Mnk2) also associate with eIF4G in vivo (11,12,14). Despite these advances and the large number of studies on the changes of eIF4E phosphorylation in vivo, the key issue of the effect of phosphorylation on the function of eIF4E has received little attention and has remained a major question in the ...

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Section: Discussionmentioning

confidence: 87%

Phosphorylation of Eukaryotic Initiation Factor 4E Markedly Reduces Its Affinity for Capped mRNA

Scheper¹,

Kollenburg²,

Hu³

et al. 2002

Journal of Biological Chemistry

230

198

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“…Therefore, our data indicate the existence of signaling pathways that specifically affect eIF4GII-eIF4E interaction in addition to the 4E-BP-eIF4E interactions. A number of reports indicate that eIF4E binding to the cap is strongly enhanced in the presence of eIF4G (12,48). In addition, the effect of binding of full-length eIF4G on the cap affinity of eIF4E can be further enhanced through binding of the PABP to eIF4G (4,9,12,48).…”

Section: Discussionmentioning

confidence: 97%

“…A number of reports indicate that eIF4E binding to the cap is strongly enhanced in the presence of eIF4G (12,48). In addition, the effect of binding of full-length eIF4G on the cap affinity of eIF4E can be further enhanced through binding of the PABP to eIF4G (4,9,12,48). PABP can also modulate cap-dependent translation in the absence of a direct interaction with eIF4G, raising the possibility that PABP forms contacts with other factors at the 5Ј end of mRNA (30).…”

Section: Discussionmentioning

confidence: 99%

Selective Modification of Eukaryotic Initiation Factor 4F (eIF4F) at the Onset of Cell Differentiation: Recruitment of eIF4GII and Long-Lasting Phosphorylation of eIF4E

Caron

Charon

Cramer

et al. 2004

Molecular and Cellular Biology

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mRNA translation is mainly regulated at the level of initiation, a process that involves the synergistic action of the 5 cap structure and the 3 poly(A) tail at the ends of eukaryotic mRNA. The eukaryote initiation factor 4G(eIF4G) is a pivotal scaffold protein that forms a critical link between mRNA cap structure, poly(A) tail, and the small ribosomal subunit. There are two functional homologs of eIF4G in mammals, the original eIF4G, renamed eIF4GI, and eIF4GII that functionally complements eIF4GI. To date, biochemical and functional analysis have not identified differential activities for eIF4GI and eIF4GII. In this report, we demonstrate that eIF4GII, but not eIF4GI, is selectively recruited to capped mRNA at the onset of cell differentiation. This recruitment is coincident with a strong and long-lasting phosphorylation of eIF4E and the release of 4E-BP1, a suppressor of eIF4E function, from the cap structure, without a concomitant change in 4E-BP1's phosphorylation. Our data further indicate that cytokines such as thrombopoietin can differentially regulate eIF4GI/II activities. These results provide the first evidence that eIF4GI/II does fulfill selective roles in mammalian cells.

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“…15 Interaction of PABP with eIF4GI has been suggested to facilitate the functional association of the 3' end of an mRNA with the 5' end. 14 The association of eIF4G with eIF4E markedly enhances the binding of the latter to the mRNA cap 16 and is necessary to permit cap-dependent translation. It is also likely that the phosphorylation of eIF4E, which has been correlated with enhanced translational activity in cells treated with mitogens and growth factors, 17 ± 20 is facilitated by the binding of the eIF4E kinase Mnk1 to the C-terminal part of eIF4GI.…”

Section: Introductionmentioning

confidence: 99%

Cleavage of polypeptide chain initiation factor eIF4GI during apoptosis in lymphoma cells: characterisation of an internal fragment generated by caspase-3-mediated cleavage

et al. 2000

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Polypeptide chain initiation factor eIF4GI undergoes caspasemediated degradation during apoptosis to give characteristic fragments. The most prominent of these has an estimated mass of approximately 76 kDa (Middle-Fragment of Apoptotic cleavage of eIF4G; M-FAG). Subcellular fractionation of the BJAB lymphoma cell line after induction of apoptosis indicates that M-FAG occurs in both ribosome-bound and soluble forms. Affinity chromatography on m 7 GTP-Sepharose shows that M-FAG retains the ability of eIF4GI to associate with both the mRNA cap-binding protein eIF4E and initiation factor eIF4A and that the ribosome-bound form of M-FAG is also present as a complex with eIF4E and eIF4A. These data suggest that the binding sites for eIF4E, eIF4A and eIF3 on eIF4GI are retained in the caspase-generated fragment. M-FAG is also a substrate for cleavage by the Foot-and-MouthDisease Virus-encoded L protease. These properties, together with the pattern of recognition by a panel of antibodies, define the origin of the apoptotic cleavage fragment. N-terminal sequencing of the products of caspase-3-mediated eIF4GI cleavage has identified the major cleavage sites. The pattern of eIF4GI degradation and the possible roles of the individual cleavage products in cells undergoing apoptosis are discussed. Cell Death and Differentiation (2000) 7, 628 ± 636.

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eIF4G Dramatically Enhances the Binding of eIF4E to the mRNA 5′-Cap Structure

Cited by 227 publications

References 36 publications

Phosphorylation of Eukaryotic Initiation Factor 4E Markedly Reduces Its Affinity for Capped mRNA

Phosphorylation of Eukaryotic Initiation Factor 4E Markedly Reduces Its Affinity for Capped mRNA

Selective Modification of Eukaryotic Initiation Factor 4F (eIF4F) at the Onset of Cell Differentiation: Recruitment of eIF4GII and Long-Lasting Phosphorylation of eIF4E

Cleavage of polypeptide chain initiation factor eIF4GI during apoptosis in lymphoma cells: characterisation of an internal fragment generated by caspase-3-mediated cleavage

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