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The mTORC1 complex has been implicated in tumorigenesis owing partially to its ability to increase protein translation; now, mTORC1 activity in the mouse intestine is shown not to be required for normal homeostasis but to be necessary for the triggering of tumorigenesis by APC mutations, suggesting that it could be a good target for the prevention of colorectal cancer in high-risk patients. How mTORC sustains tumour growth The mTORC1 complex, a protein kinase complex found in all eukaryotic cells, has been implicated in tumorigenesis because it is known to stimulate protein translation. The main effector pathway downstream of mTORC1 is thought to be 4EBP1, which promotes initiation of translation. William Faller et al . now show that in the mouse intestine, mTORC1 activity is not required for normal homeostasis, but is absolutely required for intestinal tumour formation triggered by APC tumour suppressor gene mutations. The authors identify increased translational elongation downstream of S6 kinase via the elongation factor eEF2 as a requirement for proliferation in APC-deficient but not normal cells. This suggests that translational elongation, rather than initiation, is limiting to cancer cell proliferation in vivo . These findings raise the possibility that targeting mTORC1 signalling may be beneficial in prevention of colorectal cancers in high-risk patients. Inactivation of APC is a strongly predisposing event in the development of colorectal cancer 1 , 2 , prompting the search for vulnerabilities specific to cells that have lost APC function. Signalling through the mTOR pathway is known to be required for epithelial cell proliferation and tumour growth 3 , 4 , 5 , and the current paradigm suggests that a critical function of mTOR activity is to upregulate translational initiation through phosphorylation of 4EBP1 (refs 6 , 7 ). This model predicts that the mTOR inhibitor rapamycin, which does not efficiently inhibit 4EBP1 (ref. 8 ), would be ineffective in limiting cancer progression in APC-deficient lesions. Here we show in mice that mTOR complex 1 (mTORC1) activity is absolutely required for the proliferation of Apc -deficient (but not wild-type) enterocytes, revealing an unexpected opportunity for therapeutic intervention. Although APC-deficient cells show the expected increases in protein synthesis, our study reveals that it is translation elongation, and not initiation, which is the rate-limiting component. Mechanistically, mTORC1-mediated inhibition of eEF2 kinase is required for the proliferation of APC-deficient cells. Importantly, treatment of established APC-deficient adenomas with rapamycin (which can target eEF2 through the mTORC1–S6K–eEF2K axis) causes tumour cells to undergo growth arrest and differentiation. Taken together, our data suggest that inhibition of translation elongation using existing, clinically approved drugs, such as the rapalogs, would provide clear therapeutic benefit for patients at high risk of developing colorectal cancer.

Translation of the genetic code into proteins is realized through repetitions of synchronous translocation of messenger RNA (mRNA) and transfer RNAs (tRNA) through the ribosome. In eukaryotes translocation is ensured by elongation factor 2 (eEF2), which catalyses the process and actively contributes to its accuracy 1 . Although numerous studies point to critical roles for both the conserved eukaryotic posttranslational modification diphthamide in eEF2 and tRNA modifications in supporting the accuracy of translocation, detailed molecular mechanisms describing their specific functions are poorly understood. Here we report a high-resolution X-ray structure of the eukaryotic 80S ribosome in a translocation-intermediate state containing mRNA, naturally modified eEF2 and tRNAs. The crystal structure reveals a network of stabilization of codon–anticodon interactions involving diphthamide 1 and the hypermodified nucleoside wybutosine at position 37 of phenylalanine tRNA, which is also known to enhance translation accuracy 2 . The model demonstrates how the decoding centre releases a codon–anticodon duplex, allowing its movement on the ribosome, and emphasizes the function of eEF2 as a ‘pawl’ defining the directionality of translocation 3 . This model suggests how eukaryote-specific elements of the 80S ribosome, eEF2 and tRNAs undergo large-scale molecular reorganizations to ensure maintenance of the mRNA reading frame during the complex process of translocation. Structural analysis of the Saccharomyces cerevisiae 80S ribosome trapped in an intermediate translocation state shows stabilization of codon–anticodon interactions by eukaryote-specific elements of the 80S ribosome, eEF2 and tRNA and demonstrates a major role for eEF2 in maintaining the directionality of translocation.

Nutrition is an important co-factor in exercise-induced training adaptations in muscle. We compared the effect of 6 weeks endurance training (3 days/week, 1–2 h at 75% VO 2peak ) in either the fasted state (F; n  = 10) or in the high carbohydrate state (CHO, n  = 10), on Ca 2+ -dependent intramyocellular signalling in young male volunteers. Subjects in CHO received a carbohydrate-rich breakfast before each training session, as well as ingested carbohydrates during exercise. Before ( pretest ) and after ( posttest ) the training period, subjects performed a 2 h constant-load exercise bout (~70% of pretest VO 2peak ) while ingesting carbohydrates (1 g/kg h −1 ). A muscle biopsy was taken from m. vastus lateralis immediately before and after the test, and after 4 h of recovery. Compared with pretest , in the posttest basal eukaryotic elongation factor 2 (eEF2) phosphorylation was elevated in CHO ( P  < 0.05), but not in F. In the pretest , exercise increased the degree of eEF2 phosphorylation about twofold ( P  < 0.05), and values returned to baseline within the 4 h recovery period in each group. However, in the posttest dephosphorylation of eEF2 was negated after recovery in CHO, but not in F. Independent of the dietary condition training enhanced the basal phosphorylation status of Phospholamban at Thr 17 , 5′-AMP-activated protein kinase α (AMPKα), and Acetyl CoA carboxylase β (ACCβ), and abolished the exercise-induced increase of AMPKα and ACCβ ( P  < 0.05). In conclusion, training in the fasted state, compared with identical training with ample carbohydrate intake, facilitates post-exercise dephosphorylation of eEF2. This may contribute to rapid re-activation of muscle protein translation following endurance exercise.

Molecular signaling mechanisms underlying Alzheimer's disease (AD) remain unclear. Maintenance of memory and synaptic plasticity depend on de novo protein synthesis, dysregulation of which is implicated in AD. Recent studies showed AD-associated hyperphosphorylation of mRNA translation factor eukaryotic elongation factor 2 (eEF2), which results in inhibition of protein synthesis. We tested to determine whether suppression of eEF2 phosphorylation could improve protein synthesis capacity and AD-associated cognitive and synaptic impairments. Genetic reduction of the eEF2 kinase (eEF2K) in 2 AD mouse models suppressed AD-associated eEF2 hyperphosphorylation and improved memory deficits and hippocampal long-term potentiation (LTP) impairments without altering brain amyloid β (Aβ) pathology. Furthermore, eEF2K reduction alleviated AD-associated defects in dendritic spine morphology, postsynaptic density formation, de novo protein synthesis, and dendritic polyribosome assembly. Our results link eEF2K/eEF2 signaling dysregulation to AD pathophysiology and therefore offer a feasible therapeutic target.

There is an urgent need for new drugs to treat malaria, with broad therapeutic potential and novel modes of action, to widen the scope of treatment and to overcome emerging drug resistance. Here we describe the discovery of DDD107498, a compound with a potent and novel spectrum of antimalarial activity against multiple life-cycle stages of the Plasmodium parasite, with good pharmacokinetic properties and an acceptable safety profile. DDD107498 demonstrates potential to address a variety of clinical needs, including single-dose treatment, transmission blocking and chemoprotection. DDD107498 was developed from a screening programme against blood-stage malaria parasites; its molecular target has been identified as translation elongation factor 2 (eEF2), which is responsible for the GTP-dependent translocation of the ribosome along messenger RNA, and is essential for protein synthesis. This discovery of eEF2 as a viable antimalarial drug target opens up new possibilities for drug discovery. The description of a compound (DDD107498) with antimalarial activity against multiple life-cycle stages of Plasmodium falciparum and good pharmacokinetic and safety properties, with potential for single-dose treatment, chemoprotection and prevention of transmission. A new antimalarial agent With artemisinin resistance spreading, there is an urgent need to develop new therapeutics to target Plasmodium falciparum , the causative agent of malaria. Here Ian Gilbert and colleagues report the discovery of a compound (DDD107498) with antimalarial activity against multiple life-cycle stages of the parasite and good pharmacokinetic and safety properties. It is non-mutagenic and has potential for both single-dose treatment and once-weekly chemoprotection. DDD107498 acts through inhibition of cytosolic protein synthesis, with translation elongation factor eEF2 as its target.

One of the most critical steps of protein synthesis is coupled translocation of messenger RNA (mRNA) and transfer RNAs (tRNAs) required to advance the mRNA reading frame by one codon. In eukaryotes, translocation is accelerated and its fidelity is maintained by elongation factor 2 (eEF2) 1 , 2 . At present, only a few snapshots of eukaryotic ribosome translocation have been reported 3 – 5 . Here we report ten high-resolution cryogenic-electron microscopy (cryo-EM) structures of the elongating eukaryotic ribosome bound to the full translocation module consisting of mRNA, peptidyl-tRNA and deacylated tRNA, seven of which also contained ribosome-bound, naturally modified eEF2. This study recapitulates mRNA–tRNA 2 -growing peptide module progression through the ribosome, from the earliest states of eEF2 translocase accommodation until the very late stages of the process, and shows an intricate network of interactions preventing the slippage of the translational reading frame. We demonstrate how the accuracy of eukaryotic translocation relies on eukaryote-specific elements of the 80S ribosome, eEF2 and tRNAs. Our findings shed light on the mechanism of translation arrest by the anti-fungal eEF2-binding inhibitor, sordarin. We also propose that the sterically constrained environment imposed by diphthamide, a conserved eukaryotic posttranslational modification in eEF2, not only stabilizes correct Watson–Crick codon–anticodon interactions but may also uncover erroneous peptidyl-tRNA, and therefore contribute to higher accuracy of protein synthesis in eukaryotes. The accuracy of eukaryotic ribosome translocation relies on eukaryote-specific elements of the 80S ribosome, elongation factor 2 and transfer RNAs, all of which contribute to the maintenance of the messenger RNA reading frame.

Gene expression is rapidly remodeled by infection and inflammation in part via transcription factor NF-κB activation and regulated protein synthesis. While protein synthesis is largely controlled by mRNA translation initiation, whether cellular translation elongation factors are responsive to inflammation and infection remains poorly understood. Here, we reveal a surprising mechanism whereby NF-κB restricts phosphorylation of the critical translation elongation factor eEF2, which catalyzes the protein synthesis translocation step. Upon exposure to NF-κB–activating stimuli, including TNFα, human cytomegalovirus infection, or double-stranded DNA, eEF2 phosphorylation on Thr56, which slows elongation to limit protein synthesis, and the overall abundance of eEF2 kinase (eEF2K) are reduced. Significantly, this reflected a p65 NF-κB subunit-dependent reduction in eEF2K pre-mRNA, indicating that NF-κB activation represses eEF2K transcription to decrease eEF2K protein levels. Finally, we demonstrate that reducing eEF2K abundance regulates protein synthesis in response to a bacterial toxin that inactivates eEF2. This establishes that NF-κB activation by diverse physiological effectors controls eEF2 activity via a transcriptional repression mechanism that reduces eEF2K polypeptide abundance to preclude eEF2 phosphorylation, thereby stimulating translation elongation and protein synthesis. Moreover, it illustrates how nuclear transcription regulation shapes translation elongation factor activity and exposes how eEF2 is integrated into innate immune response networks orchestrated by NF-κB.

Processing bodies (p-bodies) are a prototypical phase-separated RNA-containing granule. Their abundance is highly dynamic and has been linked to translation. Yet, the molecular mechanisms responsible for coordinate control of the two processes are unclear. Here, we uncover key roles for eEF2 kinase (eEF2K) in the control of ribosome availability and p-body abundance. eEF2K acts on a sole known substrate, eEF2, to inhibit translation. We find that the eEF2K agonist nelfinavir abolishes p-bodies in sensory neurons and impairs translation. To probe the latter, we used cryo-electron microscopy. Nelfinavir stabilizes vacant 80S ribosomes. They contain SERBP1 in place of mRNA and eEF2 in the acceptor site. Phosphorylated eEF2 associates with inactive ribosomes that resist splitting in vitro. Collectively, the data suggest that eEF2K defines a population of inactive ribosomes resistant to recycling and protected from degradation. Thus, eEF2K activity is central to both p-body abundance and ribosome availability in sensory neurons. Processing bodies are phase separated compartments enriched in translationally repressed mRNAs. Here, Smith et al. show that, in sensory neurons, eukaryotic elongation factor 2 kinase (eEF2K) plays key roles in the regulation of processing body abundance and the formation of translationally inactive ribosomes.

Diphthamide, a modification found only on translation elongation factor 2 (EF2), was proposed to suppress −1 frameshifting in translation. Although diphthamide is conserved among all eukaryotes, exactly what proteins are affected by diphthamide deletion is not clear in cells. Through genome-wide profiling for a potential −1 frameshifting site, we identified that the target of rapamycin complex 1 (TORC1)/mammalian TORC1 (mTORC1) signaling pathway is affected by deletion of diphthamide. Diphthamide deficiency in yeast suppresses the translation of TORC1-activating proteins Vam6 and Rtc1. Interestingly, TORC1 signaling also promotes diphthamide biosynthesis, suggesting that diphthamide forms a positive feedback loop to promote translation under nutrient-rich conditions. Our results provide an explanation for why diphthamide is evolutionarily conserved and why diphthamide deletion can cause severe developmental defects.

INTRODUCTION Cognitive impairment is a core feature of Down syndrome (DS), and the underlying neurobiological mechanisms remain unclear. Translation dysregulation is linked to multiple neurological disorders characterized by cognitive impairments. Phosphorylation of the translational factor eukaryotic elongation factor 2 (eEF2) by its kinase eEF2K results in inhibition of general protein synthesis. METHODS We used genetic and pharmacological methods to suppress eEF2K in two lines of DS mouse models. We further applied multiple approaches to evaluate the effects of eEF2K inhibition on DS pathophysiology. RESULTS We found that eEF2K signaling was overactive in the brain of patients with DS and DS mouse models. Inhibition of eEF2 phosphorylation through suppression of eEF2K in DS model mice improved multiple aspects of DS‐associated pathophysiology including de novo protein synthesis deficiency, synaptic morphological defects, long‐term synaptic plasticity failure, and cognitive impairments. DISCUSSION Our data suggested that eEF2K signaling dysregulation mediates DS‐associated synaptic and cognitive impairments. Highlights Phosphorylation of the translational factor eukaryotic elongation factor 2 (eEF2) is increased in the Down syndrome (DS) brain. Suppression of the eEF2 kinase (eEF2K) alleviates cognitive deficits in DS models. Suppression of eEF2K improves synaptic dysregulation in DS models. Cognitive and synaptic impairments in DS models are rescued by eEF2K inhibitors.