This gene is downstream of the mTOR pathway.
Tomek W, et al 2002 reported the regulation of translation during in vitro maturation of bovine
oocytes and the role of MAP kinase, eIF4E (cap binding protein)
phosphorylation, and eIF4E-BP1.
Meiotic maturation of mammalian oocytes (transition from prophase I to
metaphase II) is accompanied by complex changes in the protein phosphorylation
pattern. At least two major protein kinases are involved in these events;
namely, cdc2 kinase and mitogen-activated protein (MAP) kinase, because the
inhibition of these kinases arrest mammalian oocytes in the germinal vesicle
(GV) stage. The authors show that during meiotic maturation of bovine oocytes, the
translation initiation factor, eIF4E (the cap binding protein), gradually
becomes phosphorylated. This substantial phosphorylation begins at the time of
germinal vesicle breakdown (GVBD and continues to the metaphase II stage. The
onset of eIF4E phosphorylation occurs in parallel with a significant increase
in overall protein synthesis. However, although eIF4E is nearly fully
phosphorylated in metaphase II oocytes, protein synthesis reaches only basal
levels at this stage, similar to that of prophase I oocytes, in which the
factor remains unphosphorylated. A specific repressor
of eIF4E, the binding protein 4E-BP1, is present and could be involved in
preventing eIF4E function in metaphase 11 stage oocytes. Recently, two protein
kinases, called Mnk1 and Mnk2, have been identified in somatic cells as eIF4E
kinases, both of which are substrates of MAP kinase in vivo. In bovine
oocytes, a specific inhibitor of cdk kinases, butyrolactone I, arrests oocytes
in GV stage and prevents activation of both cdc2 and MAP kinase. Under these
conditions, the phosphorylation of eIF4E is also blocked, and its function in
initiation of translation is impaired. In contrast, PD 098059, a specific
inhibitor of the MAP kinase activation pathway, which inhibits the MAP kinase
kinase, called MEK function, leads only to a postponed GVBD, and a delay in
MAP kinase and eIF4E phosphorylation. These results indicate that in bovine
oocytes, 1) MAP kinase activation is only partially dependent on MEK kinase,
2) MAP kinase is involved in eIF4E phosphorylation, and 3) the abundance of
fully phosphorylated eIF4E does not necessarily directly stimulate protein
synthesis. A possible MEK kinase-independent pathway of MAP kinase
phosphorylation and the role of 4E-BP1 in repressing translation in metaphase
II oocytes are discussed.
NCBI Summary:
This gene encodes one member of a family of translation repressor proteins. The protein directly interacts with eukaryotic translation initiation factor 4E (eIF4E), which is a limiting component of the multisubunit complex that recruits 40S ribosomal subunits to the 5' end of mRNAs. Interaction of this protein with eIF4E inhibits complex assembly and represses translation. This protein is phosphorylated in response to various signals including UV irradiation and insulin signaling, resulting in its dissociation from eIF4E and activation of mRNA translation. [provided by RefSeq, Jul 2008]
General function
Apoptosis
Comment
Cellular localization
Cytoplasmic
Comment
Ovarian function
Oogenesis, Oocyte maturation, Early embryo development
Comment
Regulation of 4E-BP1 activity in the mammalian oocyte. Jansova D et al. (2017) Fully grown mammalian oocytes utilize transcripts synthetized and stored during earlier development. RNA localization followed by a local translation is a mechanism responsible for the regulation of spatial and temporal gene expression. Here we show that the mouse oocyte contains three forms of cap-dependent translational repressor expressed on the mRNA level: 4E-BP1, 4E-BP2 and 4E-BP3. However, only 4E-BP1 is present as a protein in oocytes, it becomes inactivated by phosphorylation after nuclear envelope breakdown and as such it promotes cap-dependent translation after NEBD. Phosphorylation of 4E-BP1 can be seen in the oocytes after resumption of meiosis but it is not detected in the surrounding cumulus cells, indicating that 4E-BP1 promotes translation at a specific cell cycle stage. Our immunofluorescence analyses of 4E-BP1 in oocytes during meiosis I showed an even localization of global 4E-BP1, as well as of its 4E-BP1 (Thr37/46) phosphorylated form. On the other hand, 4E-BP1 phosphorylated on Ser65 is localized at the spindle poles, and 4E-BP1 phosphorylated on Thr70 localizes on the spindle. We further show that the main positive regulators of 4E-BP1 phosphorylation after NEBD are mTOR and CDK1 kinases, but not PLK1 kinase. CDK1 exerts its activity towards 4E-BP1 phosphorylation via phosphorylation and activation of mTOR. Moreover, both CDK1 and phosphorylated mTOR co-localize with 4E-BP1 phosphorylated on Thr70 on the spindle at the onset of meiotic resumption. Expression of the dominant negative 4E-BP1 mutant adversely affects translation and results in spindle abnormality. Taken together, our results show that the phosphorylation of 4E-BP1 promotes translation at the onset of meiosis in order to support the spindle assembly and suggest an important role of CDK1 and mTOR kinases in this process. We also show that the mTOR regulatory pathway is present in human oocytes and is likely to function in a similar way as in mouse oocytes.//////////////////
Expression regulated by
Comment
Ovarian localization
Oocyte
Comment
Association of Maternal mRNA and Phosphorylated EIF4EBP1 Variants with the Spindle in Mouse Oocytes: Localized Translational Control Supporting Female Meiosis in Mammals. Romasko EJ 2013 et al.
The oocytes of many species, both invertebrate and vertebrate, contain a large collection of localized determinants in the form of proteins and translationally inactive maternal mRNAs. However, it is unknown whether mammalian oocytes contain localized mRNA determinants and what mechanisms might be responsible for their control. We find by cDNA microarray analysis enrichment for maternal mRNAs encoding spindle and other proteins on the mouse oocyte MII spindle. We also find that the key translational regulator, EIF4EBP1, undergoes a dynamic and complex spatially regulated pattern of phosphorylation at sites that regulate its association with EIF4E and its ability to repress translation. These phosphorylation variants appear at different positions along the spindle at different stages of meiosis. These results indicate that dynamic spatially restricted patterns of EIF4EBP1 phosphorylation may promote localized mRNA translation to support spindle formation, maintenance, function, and other nearby processes. Regulated EIF4EBP1 phosphorylation at the spindle may help coordinate spindle formation with progression through the cell cycle. The discovery that EIF4EBP1 may be part of an overall mechanism that integrates and couples cell cycle progression to mRNA translation and subsequent spindle formation and function may be relevant to understanding mechanisms leading to diminished oocyte quality, and potential means of avoiding such defects. The localization of maternal mRNAs at the spindle is evolutionarily conserved between mammals and other vertebrates, and is also seen in mitotic cells, indicating that EIF4EBP1 control of localized mRNA translation is likely key to correct segregation of genetic material across cell types.
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