Protein synthesis is regulated in response to various environmental stresses by phosphorylation of the a subunit of the eukaryotic initiation factor 2 eif2. S51p results in sequestering eif2b in an inactive complex and as a result gdpgtp exchange can no longer occur and. Phosphorylation results in low availability of the eif2 ternary complex eif2gtptrnai by affecting the interaction of. However, the possibility that eif5b or eif2d participate in the initiation of hcv mrna in intact cells under stress conditions was not analyzed, and only in vitro observations were reported. This results in phosphorylation of eif2 and reduced eif2 availability, which inhibits.
In the absence of stress and low eif2 phosphorylation, translation of the uorf serves as a barrier that prevents translation of the downstream chop coding region. Phosphorylation of eif2 directs atf5 translational control in. One of the responses to stress by eukaryotic cells is the downregulation of protein synthesis by phosphorylation of translation initiation factor eif2. The removal of a phosphoryl group is called dephosphorylation. The primary role of eif2 in translation initiation, as depicted in fig. Enhanced eif2 phosphorylation during stress facilitates ribosome bypass of the uorf, and instead results in the translation of chop. Protein synthesis regulation modulates a variety of processes in eukaryotes. Eukaryotic cells respond to various forms of stress by blocking mrna translation initiation via the phosphorylation of the alpha.
Phosphorylation of eif2 causes a reduction in global translation, allowing cells to conserve energy and modify gene expression to effectively manage stress conditions. Phosphorylation of eif2 facilitates ribosomal bypass of an. View human phosphoeif2 alpha s52 antibody mab39971 validated in human. Structural basis for the inhibition of translation through. Iresmediated translation of cellular messenger rna.
Fertilization of the sea urchin eggs triggers a rapid increase in protein synthesis activity, which is necessary for the progress into embryonic cell cycles. Instead, eif2a functions by a separate mechanism in eukaryotic translation. Central to the eif2 kinase response is the preferential translation of atf4 mrna, encoding a transcriptional activator of genes involved in stress remediation. Although sv genomic and subgenomic mrnas appear to have different requirements for eif2 to initiate translation, phosphorylation of eif2. Phosphorylation of eif2 directs atf5 translational control. Il24 is an immunomodulatory cytokine that also displays broad cancerspecific suppressor effects. An eif2independent mode of translation initiation on csfv ires has been. During translation, regulation of protein synthesis by phosphorylation of eukaryotic translation initiation factor 2 eif2 is a common consequence of diverse stress stimuli, which leads to reprogramming of gene expression. An eif2 independent mode of translation initiation on csfv ires has been. Supraphysiologic activation andor overexpression of translation initiation factors are implicated in the initiation and progression of. In what is probably the bestcharacterized mechanism for the regulation of mrna translation, phosphorylation of eif2 on its smallest, or alpha, subunit converts eif2 from a substrate of eif2b into a competitive inhibitor.
Phosphorylation of eukaryotic initiation factor 2 eif2 is an important mechanism regulating global and genespecific translation in response to different environmental stresses. Phosphorylation of the translation initiation factor eif2. Fractionator and a 254nm ultraviolet monitor with data quest software. Enhanced eif2 phosphorylation during stress facilitates ribosome bypass of the uorf due to its poor start site context, and instead it allows scanning ribosomes to translate chop. The mtor nucleates two complexes, namely mtor complex 1 and 2 mtorc1 and mtorc2, which are implicated in cell growth, survival, metabolism, and cancer. Eif2a eukaryotic translation initiation factor 2a is a heterotrimer composed of three subunits alpha, beta, and gamma. Dependent elevation of bace1 and app levels or reduce amyloid pathology in a mouse model of alzheimers disease.
Selective mrna translation during eif2 phosphorylation induces. The structural basis of translational control by eif2 phosphorylation. Importance of eif2 phosphorylation and stress granule. On the other hand, excessive phosphorylation of ser51 of eif2. Previously, we identified isrib as a potent inhibitor of the integrated stress response isr and showed that isrib makes cells resistant to the effects of eif2. The heterotrimeric eif2 factor, associated with gtp, delivers the initiator methionyltrnai met to the 40s ribosomal subunit at each.
These are all responsible for the phosphorylation of the alpha subunit of eif2 at serine 51, one of the bestcharacterized mechanisms for downregulating protein synthesis in eukaryotes in response to various cellular stress responses. This translation initiation factor drives binding of initiator methionyltrna to the 40s ribosome in an augdependent manner to form the 43s preinitiation complex. Therefore, it makes sense to assume that both the phosphorylation of eif2. Inhibition of protein synthesis by phosphorylation of the. Frontiers the initiation factors eif2, eif2a, eif2d. We isolated a protein kinase from rabbit reticulocyte lysates on the basis of its ability to phosphorylate purified bacterially expressed recombinant rat eif5. The data collected includes not only links to publications in pubmed, but also provides information about sample types, species, and experimental conditions. Here, we show by genomewide in vivo ribosome profiling that translation of a restricted subset of mrnas is induced upon isr activation. Ribosome profiling uncovers selective mrna translation associated.
A few eif2independent modes of translation initiation have been proposed recently for the translation of viral rnas. This antibody reacts with human, mouse, yeast samples. Phosphorylation results in low availability of the eif2 ternary complex eif2 gtptrnai by affecting the interaction of eif2 with its gtpgdp exchange factor eif2b. Eukaryotic translation initiation factor 2a eif2a is a protein that in humans is encoded by the eif2a gene. The lollipop plot above illustrates recurrent observed in 3 or more out of 4440 tcga tumor samples from 15 cancer types and therefore potentially oncogenic missense mutations click on show cancer mutations. The intensities were quantified using licor image studio software. One key mechanism for regulating global translation is the phosphorylation of eukaryotic translation initiation factor eif2 sonenberg and hinnebusch, 2009. Oct 18, 2016 phosphorylation of eif2 causes a reduction in global translation, allowing cells to conserve energy and modify gene expression to effectively manage stress conditions. Perturbations in actin dynamics reconfigure protein complexes. Eukaryotic translation initiation factor 2 alpha subunit eif2 alpha is a subunit of the eif2 protein, an important regulator of translation initiation. Eukaryotic initiation factor eif2 is a key component of the ternary complex.
Luc mrnas by gadd34 or eif2 relative to buffer controls and the ratios of translation of n1m. It is required for most forms of eukaryotic translation initiation. Antibodies for proteins involved in regulation of eif2 alpha phosphorylation by dsrna pathways, according to their panthergene ontology classification. Activation of the integrated stress response isr by a variety of stresses triggers phosphorylation of the. P lowers translation initiation, which serves to conserve nutrients and energy. A core event in the integrated stress response, an adaptive pathway common to all eukaryotic cells in response to various stress stimuli, is the phosphorylation of eukaryotic translation initiation factor 2 eif2. Phosphorylated eif2, however, due to its stronger binding, acts as an inhibitor of its own gef eif2b. Translation initiation factor 2a eukaryotic translation initiation factor 2a.
A hallmark of huntingtons disease is the pronounced sensitivity of striatal neurons to polyglutamineexpanded huntingtin expression. Phosphorylation of eif2 during stress delays translation reinitiation, allowing scanning ribosomes to bypass uorf2, and instead translate the atf5 coding region. Anthony department of biochemistry and molecular biology, indiana university. Phosphorylation of the translation initiation factor eif2 alpha at a. Jun 14, 2019 one of the responses to stress by eukaryotic cells is the downregulation of protein synthesis by phosphorylation of translation initiation factor eif2. Phosphorylation of the translation initiation factor eif2 alpha at a conserved serine residue mediates translational control at the isr core. Eukaryotic initiation factor 2 eif2 is a eukaryotic initiation factor. Tested in western blot wb, immunofluorescence if and immunocytochemistry icc applications. Phosphorylation of the eukaryotic initiation factor 2 eif2. At the end of the initiation process, gtp bound to eif2 is hydrolyzed to gdp and the eif2. Initial studies using reconstituted translation systems indicated that eif2 was necessary for the translation of this viral mrna in vitro pestova et al. Tumor suppression by pten requires the activation of the. Automated data acquisition was done using the epu software thermo.
In various transformed cell lines treated with the mtorc1 inhibitor rapa mycin, eif2a phosphorylation was increased, an effect similar to that seen in cells treated with the nlinked gly cosylation inhibitor tunicamycin, an inducer of er stress and activator of the eif2 a kinase perk fig. Regulation of eif2 full description or abstract protein phosphorylation plays an important role in the control of translation by eukaryotic initiation factor2 eif2. May, 2019 protein synthesis in eukaryotes is controlled by signals and stresses via a common pathway, called the integrated stress response isr. In this step, eif2 binds gtp and mettrnai and transfers mettrnai to the 40s ribosomal subunit. Phosphorylation results in low availability of the eif2 ternary complex. The structural basis of translational control by eif2. Phosphorylation results in low availability of the eif2 ternary complex eif2gtptrnai by affecting the interaction of eif2 with its gtpgdp exchange factor eif2b. Phosphorylation is the chemical addition of a phosphoryl group po 3 to an organic molecule. Protein synthesis in eukaryotes is controlled by signals and stresses via a common pathway, called the integrated stress response isr. Perturbations in actin dynamics reconfigure protein. Diverse stress signals converge onto eif2 to integrate stress responses through phosphorylation of the. Translational resistance of late alphavirus mrna to eif2. Both phosphorylation and dephosphorylation are carried out by enzymes e.
Following the association of mrna with the 40s subunit and location of the subunit at the aug start codon, eif5 binds to eif2 and stimulates the hydrolysis of eif2 bound gtp. Consistent with previous findings, several inhibitors of eif2 activity, including sodium arsenite, thapsigargin, tunicamycin and salubrinal, had no inhibitory effect on the translation of an mrna bearing the hcv ires, and all induced the phosphorylation of eif2. Phosphorylation is important in the fields of biochemistry and molecular biology because its a key reaction in protein and. Iresmediated translation of cellular messenger rna operates. Phosphorylation of translation initiation factor eif2. N1methylpseudouridine in mrna enhances translation through. What links here related changes upload file special pages permanent link. Eukaryotic translation initiation factor 5 eif5 interacts with the 40s initiation complex 40seif3augmettrna f eif2gtp and, acting as a gtpase activating protein, promotes the hydrolysis of bound gtp. P is the regulation of redox homeostasis and adaptation of cells to oxidative stress. Automated data acquisition was done using the epu software fei on a.
In addition, eif2b activity is inhibited by phosphorylation of ser51, leading to global repression of translation and concomitant upregulation of several genes that are involved in stress responses. Functional characterization of the canine hemeregulated eif2. Inhibition of viral protein translation by indomethacin in. A few eif2 independent modes of translation initiation have been proposed recently for the translation of viral rnas. Disruption of protein folding in the endoplasmic reticulum triggers the unfolded protein response upr, a transcriptional and translational control network designed to restore protein homeostasis. Mediated by the protein kinase gcn2 eif2ak4, phosphorylation of eif2. Local translation is rapidly regulated by extrinsic signals during neural wiring, but its control mechanisms remain elusive. The small molecule isrib reverses the effects of eif2. Phosphorylation of mammalian translation initiation factor.
The perception of environmental stress in animal cells engineered to produce heterologous protein leads to the induction of stress signaling pathways and ultimately apoptosis and cell death. Regulation of arginine transport by gcn2 eif2 kinase is. Failsafe control of translation initiation by dissociation of eif2. This is because phosphorylated eif2 acts as a dominant inhibitor of the guanine exchange factor eif2b and prevents recycling of eif2 between successive rounds of protein synthesis 6. This process, known as the integrated stress response, is one of the most fundamental mechanisms of translational control conserved throughout eukaryotes. The involvement of eif2a for the translation of hcv mrna in place of eif2 in intact cells and in cell free systems. Abstracteukaryotic cells respond to various forms of stress by blocking mrna translation initiation via the. The eukaryotic initiation factor 2 eif2 is a key regulator of protein synthesis in eukaryotic cells, implicated in the initiation step of translation. The individual symbols represent individual data points.
Selective mrna translation during eif2 phosphorylation induces expression of ibtk. Phosphorylation of initiation factor eif2 in response to stress. Paradoxically, in cancer cells, the phosphorylation of eif2. The pattern of eef2 phosphorylation in mefs is markedly disturbed by the absence of eif2. Here we show that cultured striatal cells and murine brain striatum have remarkably low levels of phosphorylation of translation initiation factor eif2. Noncanonical modulation of the eif2 pathway controls an. Small molecule isrib suppresses the integrated stress. Genetic inhibition of phosphorylation of the translation. Phosphorylation of eif2 a triggered by mtorc1 inhibition.
Er stressinduced eif2alpha phosphorylation underlies. Here we show that the extracellular cue sema3a induces an initial burst in local translation that precisely controls phosphorylation of the translation initiation factor eif2. Frontiers the initiation factors eif2, eif2a, eif2d, eif4a. S51p is a key event of mrna translation initiation and a master regulator of cell fate during cellular stress. Phosphorylation of eif2 alpha on ser 52 increases the affinity of eif2 alpha for eif2b, a guanine. During nonstressed conditions, when eif2 phosphorylation is low, ribosomes reinitiate translation at the next orf, the inhibitory uorf2. Selective mrna translation during eif2 phosphorylation.
To provide insight into the mechanism of translational control we have determined the structures of eif2 both in phosphorylated and unphosphorylated forms bound with its nucleotide exchange factor eif2b by electron cryomicroscopy. The tumorsuppressor activities of il24 include inhibition of angiogenesis, sensitization to chemotherapy, and cancerspecific apoptosis. Indeed, genetic reduction of eif2 phosphorylation, either in gcn2 knockout mice costamattioli et al. Thus, phosphorylation of eif2 alpha effectively prevents formation of the eif2. The guanine nucleotide exchange factor eif2b replaces gdp by gtp in order to reconstitute a functional ternary complex for a new round of translation initiation 3.
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