Paradoxically, in cancer cells, the phosphorylation of eif2. Phosphorylation of eif2 directs atf5 translational control. View human phosphoeif2 alpha s52 antibody mab39971 validated in human. 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. Instead, eif2a functions by a separate mechanism in eukaryotic translation. Functional characterization of the canine hemeregulated eif2. Phosphorylation of the translation initiation factor eif2 alpha at a. Enhanced eif2 phosphorylation during stress facilitates ribosome bypass of the uorf, and instead results in the translation of chop. Perturbations in actin dynamics reconfigure protein complexes. An analysis of the stressinduced phosphorylation of the alphasubunit of eukaryotic initiation factor eif2. 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. Selective mrna translation during eif2 phosphorylation induces expression of ibtk. 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. Selective mrna translation during eif2 phosphorylation induces.
Phosphorylation of the translation initiation factor eif2 alpha at a conserved serine residue mediates translational control at the isr core. The mtor nucleates two complexes, namely mtor complex 1 and 2 mtorc1 and mtorc2, which are implicated in cell growth, survival, metabolism, and cancer. One of the responses to stress by eukaryotic cells is the downregulation of protein synthesis by phosphorylation of translation initiation factor eif2. 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. Eukaryotic cells respond to various forms of stress by blocking mrna translation initiation via the phosphorylation of the alpha. Fertilization of the sea urchin eggs triggers a rapid increase in protein synthesis activity, which is necessary for the progress into embryonic cell cycles. Eukaryotic translation initiation factor 2a eif2a is a protein that in humans is encoded by the eif2a gene. May, 2019 protein synthesis in eukaryotes is controlled by signals and stresses via a common pathway, called the integrated stress response isr. Ribosome profiling uncovers selective mrna translation associated.
Supraphysiologic activation andor overexpression of translation initiation factors are implicated in the initiation and progression of. 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. Central to the eif2 kinase response is the preferential translation of atf4 mrna, encoding a transcriptional activator of genes involved in stress remediation. Phosphorylation of eukaryotic initiation factor 2 eif2 is an important mechanism regulating global and genespecific translation in response to different environmental stresses. Phosphorylation of eif2 facilitates ribosomal bypass of an. Both phosphorylation and dephosphorylation are carried out by enzymes e. 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. Eif2a eukaryotic translation initiation factor 2a is a heterotrimer composed of three subunits alpha, beta, and gamma. P is the regulation of redox homeostasis and adaptation of cells to oxidative stress. 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.
Mediated by the protein kinase gcn2 eif2ak4, phosphorylation of eif2. Frontiers the initiation factors eif2, eif2a, eif2d. Phosphorylation results in low availability of the eif2 ternary complex eif2gtptrnai by affecting the interaction of. 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 of eif2 directs atf5 translational control in. Protein synthesis is regulated in response to various environmental stresses by phosphorylation of the a subunit of the eukaryotic initiation factor 2 eif2. Structural basis for the inhibition of translation through. Phosphorylation is important in the fields of biochemistry and molecular biology because its a key reaction in protein and. Phosphorylation of mammalian translation initiation factor. Aug 15, 2019 phosphorylation is the chemical addition of a phosphoryl group po 3 to an organic molecule. Iresmediated translation of cellular messenger rna operates. 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. 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. 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.
Frontiers the initiation factors eif2, eif2a, eif2d, eif4a. 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. Importance of eif2 phosphorylation and stress granule. Phosphorylation of eif2 causes a reduction in global translation, allowing cells to conserve energy and modify gene expression to effectively manage stress conditions.
Eukaryotic translation initiation factor 2 alpha subunit eif2 alpha is a subunit of the eif2 protein, an important regulator of translation initiation. P lowers translation initiation, which serves to conserve nutrients and energy. Therefore, it makes sense to assume that both the phosphorylation of eif2. Phosphorylation is the chemical addition of a phosphoryl group po 3 to an organic molecule. In this step, eif2 binds gtp and mettrnai and transfers mettrnai to the 40s ribosomal subunit.
The involvement of eif2a for the translation of hcv mrna in place of eif2 in intact cells and in cell free systems. Phosphorylation results in low availability of the eif2 ternary complex. Phosphorylation results in low availability of the eif2 ternary complex eif2 gtptrnai by affecting the interaction of eif2 with its gtpgdp exchange factor eif2b. Diverse stress signals converge onto eif2 to integrate stress responses through phosphorylation of the. Phosphorylation results in low availability of the eif2 ternary complex eif2gtptrnai by affecting the interaction of eif2 with its gtpgdp exchange factor eif2b. Automated data acquisition was done using the epu software thermo. Protein synthesis regulation modulates a variety of processes in eukaryotes. We isolated a protein kinase from rabbit reticulocyte lysates on the basis of its ability to phosphorylate purified bacterially expressed recombinant rat eif5. Moreover, analyses using mrnas bearing hcv ires in cell free systems revealed the presence of eif2 in the initiation complexes otto and puglisi, 2004. Thus, phosphorylation of eif2 alpha effectively prevents formation of the eif2. On the other hand, excessive phosphorylation of ser51 of eif2. Genetic inhibition of phosphorylation of the translation. The eukaryotic initiation factor 2 eif2 is a key regulator of protein synthesis in eukaryotic cells, implicated in the initiation step of translation. Regulation of eif2 full description or abstract protein phosphorylation plays an important role in the control of translation by eukaryotic initiation factor2 eif2.
At the end of the initiation process, gtp bound to eif2 is hydrolyzed to gdp and the eif2. 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. Fractionator and a 254nm ultraviolet monitor with data quest software. Tested in western blot wb, immunofluorescence if and immunocytochemistry icc applications. Activation of the integrated stress response isr by a variety of stresses triggers phosphorylation of the. Phosphorylation of eif2 during stress delays translation reinitiation, allowing scanning ribosomes to bypass uorf2, and instead translate the atf5 coding region.
Selective mrna translation during eif2 phosphorylation. The pattern of eef2 phosphorylation in mefs is markedly disturbed by the absence of eif2. Iresmediated translation of cellular messenger rna. S51p is a key event of mrna translation initiation and a master regulator of cell fate during cellular stress. Failsafe control of translation initiation by dissociation of eif2. Small molecule isrib suppresses the integrated stress. Anthony department of biochemistry and molecular biology, indiana university. N1methylpseudouridine in mrna enhances translation through. Phosphorylation of the eukaryotic initiation factor 2 eif2. The individual symbols represent individual data points. Translation initiation factor 2a eukaryotic translation initiation factor 2a. 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. Phosphorylation of initiation factor eif2 in response to stress. Phosphorylated eif2, however, due to its stronger binding, acts as an inhibitor of its own gef eif2b.
A hallmark of huntingtons disease is the pronounced sensitivity of striatal neurons to polyglutamineexpanded huntingtin expression. A few eif2 independent modes of translation initiation have been proposed recently for the translation of viral rnas. During nonstressed conditions, when eif2 phosphorylation is low, ribosomes reinitiate translation at the next orf, the inhibitory uorf2. Regulation of chop translation in response to eif2. Antibodies for proteins involved in regulation of eif2 alpha phosphorylation by dsrna pathways, according to their panthergene ontology classification. Abstracteukaryotic cells respond to various forms of stress by blocking mrna translation initiation via the. Il24 is an immunomodulatory cytokine that also displays broad cancerspecific suppressor effects. Perturbations in actin dynamics reconfigure protein. Phosphorylation of eif2 a triggered by mtorc1 inhibition. Not only is eef2 phosphorylation triggered at lower doses of h 2 o 2 0. It is required for most forms of eukaryotic translation initiation. Eukaryotic initiation factor 2 eif2 is a eukaryotic initiation factor. 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.
The small molecule isrib reverses the effects of eif2. One key mechanism for regulating global translation is the phosphorylation of eukaryotic translation initiation factor eif2 sonenberg and hinnebusch, 2009. Phosphorylated translation initiation factor eif2, a potent inhibitor of. Tumor suppression by pten requires the activation of the. The heterotrimeric eif2 factor, associated with gtp, delivers the initiator methionyltrnai met to the 40s ribosomal subunit at each. Initial studies using reconstituted translation systems indicated that eif2 was necessary for the translation of this viral mrna in vitro pestova et al.
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. Dependent elevation of bace1 and app levels or reduce amyloid pathology in a mouse model of alzheimers disease. Phosphorylation of translation initiation factor eif2. Translational resistance of late alphavirus mrna to eif2. Inhibition of viral protein translation by indomethacin in. 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. The intensities were quantified using licor image studio software. Noncanonical modulation of the eif2 pathway controls an. An eif2 independent mode of translation initiation on csfv ires has been. Protein synthesis in eukaryotes is controlled by signals and stresses via a common pathway, called the integrated stress response isr.
Regulation of arginine transport by gcn2 eif2 kinase is. An eif2independent mode of translation initiation on csfv ires has been. 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. The data collected includes not only links to publications in pubmed, but also provides information about sample types, species, and experimental conditions. 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. Here, we show by genomewide in vivo ribosome profiling that translation of a restricted subset of mrnas is induced upon isr activation. The structural basis of translational control by eif2. This results in phosphorylation of eif2 and reduced eif2 availability, which inhibits. Er stressinduced eif2alpha phosphorylation underlies. Genetic inhibition of phosphorylation of the translation initiation factor eif2. This translation initiation factor drives binding of initiator methionyltrna to the 40s ribosome in an augdependent manner to form the 43s preinitiation complex.
Local translation is rapidly regulated by extrinsic signals during neural wiring, but its control mechanisms remain elusive. The removal of a phosphoryl group is called dephosphorylation. Here we show that cultured striatal cells and murine brain striatum have remarkably low levels of phosphorylation of translation initiation factor eif2. Inhibition of protein synthesis by phosphorylation of the. Automated data acquisition was done using the epu software fei on a. The structural basis of translational control by eif2 phosphorylation. Indeed, genetic reduction of eif2 phosphorylation, either in gcn2 knockout mice costamattioli et al. This process, known as the integrated stress response, is one of the most fundamental mechanisms of translational control conserved throughout eukaryotes. Luc mrnas by gadd34 or eif2 relative to buffer controls and the ratios of translation of n1m. The tumorsuppressor activities of il24 include inhibition of angiogenesis, sensitization to chemotherapy, and cancerspecific apoptosis. Phosphorylation of the translation initiation factor eif2.
This antibody reacts with human, mouse, yeast samples. 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. Central to the upr is perk phosphorylation of the alpha subunit of eif2 eif2p, which represses global translation coincident with preferential translation of mrnas, such as atf4 and. Although sv genomic and subgenomic mrnas appear to have different requirements for eif2 to initiate translation, phosphorylation of eif2. The primary role of eif2 in translation initiation, as depicted in fig.
Eukaryotic initiation factor eif2 is a key component of the ternary complex. S51p results in sequestering eif2b in an inactive complex and as a result gdpgtp exchange can no longer occur and. 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. What links here related changes upload file special pages permanent link. Phosphorylation of eif2 alpha on ser 52 increases the affinity of eif2 alpha for eif2b, a guanine. A few eif2independent modes of translation initiation have been proposed recently for the translation of viral rnas. Various forms of stress induce pathways that converge on the phosphorylation of the alpha.
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