mTORC1 regulates cell survival under glucose starvation through 4EBP1/2-mediated translational reprogramming of fatty acid metabolism.

Energetic stress compels cells to evolve adaptive mechanisms to adjust their metabolism. Inhibition of mTOR kinase complex 1 (mTORC1) is essential for cell survival during glucose starvation. How mTORC1 controls cell viability during glucose starvation is not well understood. Here we show that the mTORC1 effectors eukaryotic initiation factor 4E binding proteins 1/2 (4EBP1/2) confer protection to mammalian cells and budding yeast under glucose starvation. Mechanistically, 4EBP1/2 promote NADPH homeostasis by preventing NADPH-consuming fatty acid synthesis via translational repression of Acetyl-CoA Carboxylase 1 (ACC1), thereby mitigating oxidative stress. This has important relevance for cancer, as oncogene-transformed cells and glioma cells exploit the 4EBP1/2 regulation of ACC1 expression and redox balance to combat energetic stress, thereby supporting transformation and tumorigenicity in vitro and in vivo. Clinically, high EIF4EBP1 expression is associated with poor outcomes in several cancer types. Our data reveal that the mTORC1-4EBP1/2 axis provokes a metabolic switch essential for survival during glucose starvation which is exploited by transformed and tumor cells.

A Novel Inhibitor of Translation Initiation Factor eIF5B in Saccharomyces cerevisiae.

The eukaryotic translation initiation factor eIF5B is a bacterial IF2 ortholog that plays an important role in ribosome joining and stabilization of the initiator tRNA on the AUG start codon during the initiation of translation. We identified the fluorophenyl oxazole derivative 2,2-dibromo-1-(2-(4-fluorophenyl)benzo[d]oxazol-5-yl)ethanone quinolinol as an inhibitor of fungal protein synthesis using an in vitro translation assay in a fungal system. Mutants resistant to this compound were isolated in Saccharomyces cerevisiae and were demonstrated to contain amino acid substitutions in eIF5B that conferred the resistance. These results suggest that eIF5B is a target of potential antifungal compound and that mutation of eIF5B can confer resistance. Subsequent identification of 16 other mutants revealed that primary mutations clustered mainly on domain 2 of eIF5B and secondarily mainly on domain 4. Domain 2 has been implicated in the interaction with the small ribosomal subunit during initiation of translation. The tested translation inhibitor could act by weakening the functional contact between eIF5B and the ribosome complex. This data provides the basis for the development of a new family of antifungals.

Poly(A)-binding protein promotes VPg-dependent translation of potyvirus through enhanced binding of phosphorylated eIFiso4F and eIFiso4F∙eIF4B.

The phosphorylation of eukaryotic translational initiation factors has been shown to play a significant role in controlling the synthesis of protein. Viral infection, environmental stress, and growth circumstances cause phosphorylation or dephosphorylation of plant initiation factors. Our findings indicate that casein kinase 2 can phosphorylate recombinant wheat eIFiso4E and eIFiso4G generated from E. coli in vitro. For wheat eIFiso4E, Ser-207 was found to be the in vitro phosphorylation site. eIFiso4E lacks an amino acid that can be phosphorylated at the position corresponding to Ser-209, the phosphorylation site in mammalian eIF4E, yet phosphorylation of eIFiso4E has effects on VPg binding affinity that are similar to those of phosphorylation of mammalian eIF4E. The addition of VPg and phosphorylated eIFiso4F to depleted wheat germ extract (WGE) leads to enhancement of translation of both uncapped and capped viral mRNA. The addition of PABP together with eIFiso4Fp and eIF4B to depleted WGE increases both uncapped and capped mRNA translation. However, it exhibits a translational advantage specifically for uncapped mRNA, implying that the phosphorylation of eIFiso4F hinders cap binding while promoting VPg binding, thereby facilitating uncapped translation. These findings indicate TEV virus mediates VPg-dependent translation by engaging a mechanism entailing phosphorylated eIFiso4Fp and PABP. To elucidate the molecular mechanisms underlying these observed effects, we studied the impact of PABP and/or eIF4B on the binding of VPg with eIFiso4Fp. The inclusion of PABP and eIF4B with eIFiso4Fp resulted in about 2-fold increase in affinity for VPg (Kd = 24 ± 1.7 nM), as compared to the affinity of eIFiso4Fp alone (Kd = 41.0 ± 3.1 nM). The interactions between VPg and eIFiso4Fp were determined to be both enthalpically and entropically favorable, with the enthalpic contribution accounting for 76-97% of the ΔG at 25°C, indicating a substantial role of hydrogen bonding in enhancing the stability of the complex. The binding of PABP to eIFiso4Fp·4B resulted in a conformational alteration, leading to a significant enhancement in the binding affinity to VPg. These observations suggest PABP enhances the affinity between eIFiso4Fp and VPg, leading to an overall conformational change that provides a stable platform for efficient viral translation.

To initiate or not to initiate: A critical assessment of eIF2A, eIF2D, and MCT-1·DENR to deliver initiator tRNA to ribosomes.

Selection of the correct start codon is critical for high-fidelity protein synthesis. In eukaryotes, this is typically governed by a multitude of initiation factors (eIFs), including eIF2·GTP that directly delivers the initiator tRNA (Met-tRNAi Met ) to the P site of the ribosome. However, numerous reports, some dating back to the early 1970s, have described other initiation factors having high affinity for the initiator tRNA and the ability of delivering it to the ribosome, which has provided a foundation for further work demonstrating non-canonical initiation mechanisms using alternative initiation factors. Here we provide a critical analysis of current understanding of eIF2A, eIF2D, and the MCT-1·DENR dimer, the evidence surrounding their ability to initiate translation, their implications in human disease, and lay out important key questions for the field. This article is categorized under: RNA Interactions with Proteins and Other Molecules > RNA-Protein Complexes Translation > Mechanisms Translation > Regulation.

Methionyl-Methionine Dipeptide Enhances Mammogenesis and Lactogenesis by Suppressing the Expression of a Novel Long Noncoding RNA MGPNCR to Inhibit eIF4B Dephosphorylation.

Previous research has demonstrated that in pregnant mice deficient in l-methionine (Met), the mixture of the dipeptide l-methionyl-l-methionine (Met-Met) with Met was more effective than Met alone in promoting mammogenesis and lactogenesis. This study aimed to investigate the role of a novel long noncoding RNA (lncRNA), named mammary gland proliferation-associated lncRNA (MGPNCR), in these processes. Transcriptomic analysis of mammary tissues from Met-deficient mice, supplemented either with a Met-Met/Met mixture or with Met alone, revealed significantly higher MGPNCR expression in the Met group compared to the mixture group, a finding recapitulated in a mammary epithelial cell model. Our findings suggested that MGPNCR hindered mammogenesis and milk protein synthesis by binding to eukaryotic initiation factor 4B (eIF4B). This interaction promoted the dephosphorylation of eIF4B at serine-422 by enhancing its association with protein phosphatase 2A (PP2A). Our study sheds light on the regulatory mechanisms of lncRNA-mediated dipeptide effects on mammary cell proliferation and milk protein synthesis. These insights underscore the potential benefits of utilizing dipeptides to improve milk protein in animals and potentially in humans.

AGO1 controls protein folding in mouse embryonic stem cell fate decisions.

Argonaute (AGO) proteins are evolutionarily conserved RNA-binding proteins that control gene expression through the small RNAs they interact with. Whether AGOs have regulatory roles independent of RNAs, however, is unknown. Here, we show that AGO1 controls cell fate decisions through facilitating protein folding. We found that in mouse embryonic stem cells (mESCs), while AGO2 facilitates differentiation via the microRNA (miRNA) pathway, AGO1 controls stemness independently of its binding to small RNAs. We determined that AGO1 specifically interacts with HOP, a co-chaperone for the HSP70 and HSP90 chaperones, and enhances the folding of a set of HOP client proteins with intrinsically disordered regions. This AGO1-mediated facilitation of protein folding is important for maintaining stemness in mESCs. Our results demonstrate divergent functions between AGO1 and AGO2 in controlling cellular states and identify an RNA-independent function of AGO1 in controlling gene expression and cell fate decisions.

Identification of SV2C and DENR as Key Biomarkers for Parkinson's Disease Based on Bioinformatics, Machine Learning, and Experimental Verification.

The objective of this study is to investigate the potential biomarkers and therapeutic target genes for Parkinson's disease (PD). We analyzed four datasets (GSE8397, GSE20292, GSE20163, GSE20164) from the Gene Expression Omnibus database. We employed weighted gene co-expression network analysis and differential expression analysis to select genes and perform functional analysis. We applied three algorithms, namely, random forest, support vector machine recursive feature elimination, and least absolute shrinkage and selection operator, to identify hub genes, perform functional analysis, and assess their clinical diagnostic potential using receiver operating characteristic (ROC) curve analysis. We employed the xCell website to evaluate differences in the composition patterns of immune cells in the GEO datasets. We also collected serum samples from PD patients and established PD cell model to validate the expression of hub genes using enzyme-linked immunosorbent assay and quantitative real-time polymerase chain reaction. Our findings identified SV2C and DENR as two hub genes for PD and decreased in PD brain tissue compared with controls. ROC analysis showed effectively value of SV2C and DENR to diagnose PD, and they were downregulated in the serum of PD patients and cell model. Functional analysis revealed that dopamine vesicle transport and synaptic vesicle recycling are crucial pathways in PD. Besides, the differences in the composition of immune cells, especially basophils and T cells, were discovered between PD and controls. In summary, our study identifies SV2C and DENR as potential biomarkers for diagnosing PD and provides a new perspective for exploring the molecular mechanisms of PD.

A Translational Regulatory Mechanism Mediated by Hypusinated Eukaryotic Initiation Factor 5A Facilitates ß-Cell Identity and Function.

As professional secretory cells, ß-cells require adaptable mRNA translation to facilitate a rapid synthesis of proteins, including insulin, in response to changing metabolic cues. Specialized mRNA translation programs are essential drivers of cellular development and differentiation. However, in the pancreatic ß-cell, the majority of factors identified to promote growth and development function primarily at the level of transcription. Therefore, despite its importance, the regulatory role of mRNA translation in the formation and maintenance of functional ß-cells is not well defined. In this study, we have identified a translational regulatory mechanism mediated by the specialized mRNA translation factor eukaryotic initiation factor 5A (eIF5A), which facilitates the maintenance of ß-cell identity and function. The mRNA translation function of eIF5A is only active when it is posttranslationally modified ("hypusinated") by the enzyme deoxyhypusine synthase (DHPS). We have discovered that the absence of ß-cell DHPS in mice reduces the synthesis of proteins critical to ß-cell identity and function at the stage of ß-cell maturation, leading to a rapid and reproducible onset of diabetes. Therefore, our work has revealed a gatekeeper of specialized mRNA translation that permits the ß-cell, a metabolically responsive secretory cell, to maintain the integrity of protein synthesis necessary during times of induced or increased demand.

The intrinsically disordered region of eIF5B stimulates IRES usage and nucleates biological granule formation.

Cells activate stress response pathways to survive adverse conditions. Such responses involve the inhibition of global cap-dependent translation. This inhibition is a block that essential transcripts must escape via alternative methods of translation initiation, e.g., an internal ribosome entry site (IRES). IRESs have distinct structures and generally require a limited repertoire of translation factors. Cellular IRESs have been identified in many critical cellular stress response transcripts. We previously identified cellular IRESs in the murine insulin receptor (Insr) and insulin-like growth factor 1 receptor (Igf1r) transcripts and demonstrated their resistance to eukaryotic initiation factor 4F (eIF4F) inhibition. Here, we find that eIF5B preferentially promotes Insr, Igf1r, and hepatitis C virus IRES activity through a non-canonical mechanism that requires its highly charged and disordered N terminus. We find that the N-terminal region of eIF5B can drive cytoplasmic granule formation. This eIF5B granule is triggered by cellular stress and is sufficient to specifically promote IRES activity.

Kinetics of Translating Ribosomes Determine the Efficiency of Programmed Stop Codon Readthrough.

During translation, a stop codon on the mRNA signals the ribosomes to terminate the process. In certain mRNAs, the termination fails due to the recoding of the canonical stop codon, and ribosomes continue translation to generate C-terminally extended protein. This process, termed stop codon readthrough (SCR), regulates several cellular functions. SCR is driven by elements/factors that act immediately downstream of the stop codon. Here, we have analysed the process of SCR using a simple mathematical model to investigate how the kinetics of translating ribosomes influences the efficiency of SCR. Surprisingly, the analysis revealed that the rate of translation inversely regulates the efficiency of SCR. We tested this prediction experimentally in mammalian AGO1 and MTCH2 mRNAs. Reduction in translation either globally by harringtonine or locally by rare codons caused an increase in the efficiency of SCR. Thus, our study has revealed a hitherto unknown mode of regulation of SCR.

Allele mining of eukaryotic translation initiation factor genes in Prunus for the identification of new sources of resistance to sharka.

Members of the eukaryotic translation initiation complex are co-opted in viral infection, leading to susceptibility in many crop species, including stone fruit trees (Prunus spp.). Therefore, modification of one of those eukaryotic translation initiation factors or changes in their gene expression may result in resistance. We searched the crop and wild Prunus germplasm from the Armeniaca and Amygdalus taxonomic sections for allelic variants in the eIF4E and eIFiso4E genes, to identify alleles potentially linked to resistance to Plum pox virus (PPV). Over one thousand stone fruit accessions (1397) were screened for variation in eIF4E and eIFiso4E transcript sequences which are in single copy within the diploid Prunus genome. We identified new alleles for both genes differing from haplotypes associated with PPV susceptible accessions. Overall, analyses showed that eIFiso4E is genetically more constrained since it displayed less polymorphism than eIF4E. We also demonstrated more variations at both loci in the related wild species than in crop species. As the eIFiso4E translation initiation factor was identified as indispensable for PPV infection, a selection of ten different eIFiso4E haplotypes along 13 accessions were tested by infection with PPV and eight of them displayed a range of reduced susceptibility to resistance, indicating new potential sources of resistance to sharka.

Backbone resonance assignments of the C-terminal region of human translation initiation factor eIF4B.

Translation initiation in eukaryotes is an early step in protein synthesis, requiring multiple factors to recruit the ribosomal small subunit to the mRNA 5' untranslated region. One such protein factor is the eukaryotic translation initiation factor 4B (eIF4B), which increases the activity of the eIF4A RNA helicase, and is linked to cell survival and proliferation. We report here the protein backbone chemical shift assignments corresponding to the C-terminal 279 residues of human eIF4B. Analysis of the chemical shift values identifies one main helical region in the area previously linked to RNA binding, and confirms that the overall C-terminal region is intrinsically disordered.

Dihydropyrimidinase-Related Protein 2 Is a New Partner in the Binding between 4E-BP2 and eIF4E Related to Neuronal Death after Cerebral Ischemia.

Transient cerebral ischemia induces neuronal degeneration, followed in time by secondary delayed neuronal death that is strongly correlated with a permanent inhibition of protein synthesis in vulnerable brain regions, while protein translational rates are recovered in resistant areas. In the translation-regulation initiation step, the eukaryotic initiation factor (eIF) 4E is a key player regulated by its association with eIF4E-binding proteins (4E-BPs), mostly 4E-BP2 in brain tissue. In a previous work, we identified dihydropyrimidinase-related protein 2 (DRP2) as a 4E-BP2-interacting protein. Here, using a proteomic approach in a model of transient cerebral ischemia, a detailed study of DRP2 was performed in order to address the challenge of translation restoration in vulnerable regions. In this report, several DRP2 isoforms that have a specific interaction with both 4E-BP2 and eIF4E were identified, showing significant and opposite differences in this association, and being differentially detected in resistant and vulnerable regions in response to ischemia reperfusion. Our results provide the first evidence of DRP2 isoforms as potential regulators of the 4E-BP2-eIF4E association that would have consequences in the delayed neuronal death under ischemic-reperfusion stress. The new knowledge reported here identifies DRP2 as a new target to promote neuronal survival after cerebral ischemia.

Comparison of Human Eukaryotic Translation Initiation Factors 5A1 and 5AL1: Identification of Amino Acid Residues Important for EIF5A1 Lysine 50 Hypusination and Its Protein Stability.

The human eukaryotic translation initiation factor 5A (EIF5A) family consists of three members, namely EIF5A1, EIF5A2, and EIF5AL1. Recent studies have shown that the expression of EIF5As is related to many human diseases, such as diabetes, viral infection, central nervous system injury, and cancer. Among them, EIF5A1 plays different functions in various cancers, possibly as a tumor-suppressor or oncogene, while EIF5A2 promotes the occurrence and development of cancer. Yet, the biological function of EIF5AL1 is not being studied so far. Interestingly, although there are only three amino acid (at residues 36, 45, and 109) differences between EIF5A1 and EIF5AL1, we demonstrate that only EIF5A1 can be hypusinated while EIF5AL1 cannot, and EIF5AL1 has a tumor-suppressor-like function by inhibiting cell proliferation and migration. We also show that EIF5AL1 protein turnover is mediated through the proteasomal pathway, and EIF5AL1 protein turnover is much faster than that of EIF5A1, which may explain their differential protein expression level in cells. By engineering single and double mutations on these three amino acids, we pinpoint which of these amino acids are critical for hypusination and protein stability. The data of this work should fill in the gaps in EIF5As research and pave the way for future studies on EIF5AL1.

The eukaryotic translation initiation factor eIF4E reprograms alternative splicing.

Aberrant splicing is typically attributed to splice-factor (SF) mutation and contributes to malignancies including acute myeloid leukemia (AML). Here, we discovered a mutation-independent means to extensively reprogram alternative splicing (AS). We showed that the dysregulated expression of eukaryotic translation initiation factor eIF4E elevated selective splice-factor production, thereby impacting multiple spliceosome complexes, including factors mutated in AML such as SF3B1 and U2AF1. These changes generated a splicing landscape that predominantly supported altered splice-site selection for ~800 transcripts in cell lines and ~4,600 transcripts in specimens from high-eIF4E AML patients otherwise harboring no known SF mutations. Nuclear RNA immunoprecipitations, export assays, polysome analyses, and mutational studies together revealed that eIF4E primarily increased SF production via its nuclear RNA export activity. By contrast, eIF4E dysregulation did not induce known SF mutations or alter spliceosome number. eIF4E interacted with the spliceosome and some pre-mRNAs, suggesting its direct involvement in specific splicing events. eIF4E induced simultaneous effects on numerous SF proteins, resulting in a much larger range of splicing alterations than in the case of mutation or dysregulation of individual SFs and providing a novel paradigm for splicing control and dysregulation.

Neuronal RNA-Binding Protein HuD Interacts with Translation Initiation Factor eIF3.

Translation initiation is the rate-limiting step of protein synthesis and is the main target of translation regulation. RNA-binding proteins (RBPs) are key mediators of the spatiotemporal control of translation and are critical for cell proliferation, development, and differentiation. We have previously shown that HuD, one of the neuronal RBPs, enhances cap-dependent translation through the direct interaction with eukaryotic initiation factor 4A (eIF4A) and poly(A) tail using a HeLa-derived in vitro translation system. We have also found that translation stimulation of HuD is essential for HuD-induced neurite outgrowth in PC12 cells. However, it remains unclear how HuD is involved in the regulation of translation initiation. Here, we report that HuD binds to eukaryotic initiation factor 3 (eIF3) via the eIF3b subunit, which belongs to the functional core of mammalian eIF3. eIF3 plays an essential role in recruiting the 40S ribosomal subunit onto mRNA in translation initiation. We hypothesize that the interaction between HuD and eIF3 stabilizes the translation initiation complex and increases translation efficiency. We also showed that the linker region of HuD is required for the interaction with eIF3b. Moreover, we found that eIF3b-binding region of HuD is conserved in all Hu proteins (HuB, HuC, HuD, and HuR). These data might also help to explain how Hu proteins stimulate translation in a cap- and poly(A)-dependent way.

Renal venous density in the arterial phase of contrast-enhanced CT predicts prognosis in septic shock.

OBJECTIVE: To evaluate a series of vascular parameters derived from abdominal dual-phase contrast-enhanced CT as predictors of 14-day mortality and AKI within 7 days in septic shock. METHODS: 144 patients with septic shock and 60 negative cases were included. The vascular parameters from CT were measured and calculated, including aortic density in arterial (Dena-A) and venous phase (Dena-V), renal vein density in arterial (Denrv-A) and venous phase (Denrv-V), and renal vein-to-aortic density ratio in arterial (DenRrv/a-A) and venous phase (DenRrv/a-V). The parameters were compared between patients and controls, and between patients with different clinical outcomes, and assessed for predictive value of 14-day mortality and AKI within 7 days. RESULTS: Patients with septic shock presented significantly lower Denrv-A (p < 0.001) and DenRrv/a-A (p = 0.002) levels than the controls. In the septic shock group, patients who died had significantly lower Denrv-A (p = 0.001) and lower DenRrv/a-A (p < 0.001) than those who survived. Patients who developed AKI had significantly lower Denrv-A (p < 0.001) and DenRrv/a-A (p = 0.011) than those who did not. Multivariate analysis suggested DenRrv/a-A as an independent predictor of 14-day mortality (OR 0.012; 95% confidence interval [CI]:0.002,0.086; p < 0.001) and Denrv-A as an independent predictor of AKI (OR 0.989;95% CI:0.982,0.997; p = 0.006). CONCLUSION: In septic shock, significant decreases in Denrv-A and DenRrv/a-A were associated with the onset of AKI and predicted higher 14-day mortality. ADVANCES IN KNOWLEDGE: The renal vein density and renal vein-aortic density ratio in arterial phase of dual-phase contrast-enhanced CT may serve as good predictors of AKI and mortality in septic shock.

Dynamic states of eIF6 and SDS variants modulate interactions with uL14 of the 60S ribosomal subunit.

Assembly of ribosomal subunits into active ribosomal complexes is integral to protein synthesis. Release of eIF6 from the 60S ribosomal subunit primes 60S to associate with the 40S subunit and engage in translation. The dynamics of eIF6 interaction with the uL14 (RPL23) interface of 60S and its perturbation by somatic mutations acquired in Shwachman-Diamond Syndrome (SDS) is yet to be clearly understood. Here, by using a modified strategy to obtain high yields of recombinant human eIF6 we have uncovered the critical interface entailing eight key residues in the C-tail of uL14 that is essential for physical interactions between 60S and eIF6. Disruption of the complementary binding interface by conformational changes in eIF6 disease variants provide a mechanism for weakened interactions of variants with the 60S. Hydrogen-deuterium exchange mass spectrometry (HDX-MS) analyses uncovered dynamic configurational rearrangements in eIF6 induced by binding to uL14 and exposed an allosteric interface regulated by the C-tail of eIF6. Disrupting key residues in the eIF6-60S binding interface markedly limits proliferation of cancer cells, which highlights the significance of therapeutically targeting this interface. Establishing these key interfaces thus provide a therapeutic framework for targeting eIF6 in cancers and SDS.

A noncanonical function of EIF4E limits ALDH1B1 activity and increases susceptibility to ferroptosis.

Ferroptosis is a type of lipid peroxidation-dependent cell death that is emerging as a therapeutic target for cancer. However, the mechanisms of ferroptosis during the generation and detoxification of lipid peroxidation products remain rather poorly defined. Here, we report an unexpected role for the eukaryotic translation initiation factor EIF4E as a determinant of ferroptotic sensitivity by controlling lipid peroxidation. A drug screening identified 4EGI-1 and 4E1RCat (previously known as EIF4E-EIF4G1 interaction inhibitors) as powerful inhibitors of ferroptosis. Genetic and functional studies showed that EIF4E (but not EIF4G1) promotes ferroptosis in a translation-independent manner. Using mass spectrometry and subsequent protein-protein interaction analysis, we identified EIF4E as an endogenous repressor of ALDH1B1 in mitochondria. ALDH1B1 belongs to the family of aldehyde dehydrogenases and may metabolize the aldehyde substrate 4-hydroxynonenal (4HNE) at high concentrations. Supraphysiological levels of 4HNE triggered ferroptosis, while low concentrations of 4HNE increased the cell susceptibility to classical ferroptosis inducers by activating the NOX1 pathway. Accordingly, EIF4E-dependent ALDH1B1 inhibition enhanced the anticancer activity of ferroptosis inducers in vitro and in vivo. Our results support a key function of EIF4E in orchestrating lipid peroxidation to ignite ferroptosis.

[Effect of eIF4B knockout on apoptosis of mouse fetal liver cells].

Eukaryotic translation initiation factor 4B (eIF4B) plays an important role in mRNA translation initiation, cell survival and proliferation in vitro, but the in vivo function is poorly understood. In this study, via various experimental techniques such as hematoxylin-eosin (HE) staining, flow cytometry, Western blotting, and immunohistochemistry, we investigated the role of eIF4B in mouse embryo development using an eIF4B knockout (KO) mouse model and explored the mechanism. We found that the livers, but not lungs, brain, stomach, or pancreas, derived from eIF4B KO mouse embryos displayed severe pathological changes characterized by enhanced apoptosis and necrosis. Accordingly, high expression of cleaved-caspase 3, and excessive activation of mTOR signaling as evidenced by increased expression and phosphorylation of p70S6K and enhanced phosphorylation of 4EBP1, were observed in mouse embryonic fibroblasts and fetal livers from eIF4B KO mice. These results uncover a critical role of eIF4B in mouse embryo development and provide important insights into the biological functions of eIF4B in vivo.