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 ...

Vanishing white matter disease (VWM) is a genetic leukoencephalopathy linked to mutations in the eukaryotic translation initiation factor 2B (eIF2B). It is a disease of infants, children and adults, who experience a slowly progressive neurological deterioration with episodes of rapid clinical worsening triggered by stress and eventually leading to death. Characteristic neuropathological findings include cystic degeneration of the white matter with scarce reactive gliosis, dysmorphic astrocytes, and paucity of myelin despite an increase in oligodendrocytic density. To assess whether a defective maturation of macroglia may be responsible for the feeble gliosis and lack of myelin, we investigated the maturation status of astrocytes and oligodendrocytes in the brains of 8 VWM patients, 4 patients with other white matter disorders and 6 age-matched controls with a combination of immunocytochemistry, histochemistry, scratch-wound assays, Western blot and quantitative PCR. We observed increased proliferation and a defect in the maturation of VWM astrocytes. They show an anomalous composition of their intermediate filament network with predominance of the δ-isoform of the glial fibrillary acidic protein and an increase in the heat shock protein αB-crystallin, supporting the possibility that a deficiency in astrocyte function may contribute to the loss of white matter in VWM. We also demonstrated a significant increase in numbers of pre-myelinating oligodendrocyte progenitors in VWM, which may explain the co-existence of oligodendrocytosis and myelin paucity in the patients’ white matter.