Translation Elongation and Recoding in Eukaryotes

The RNA Helicase Ded1 from Yeast Is Associated with the Signal Recognition Particle and Is Regulated by SRP21

The DEAD-box RNA helicase Ded1 is an essential yeast protein involved in translation initiation that belongs to the DDX3 subfamily. The purified Ded1 protein is an ATP-dependent RNA-binding protein and an RNA-dependent ATPase, but it was previously found to lack substrate specificity and enzymatic regulation. Here we demonstrate through yeast genetics, yeast extract pull-down experiments, in situ localization, and in vitro biochemical approaches that Ded1 is associated with, and regulated by, the signal recognition particle (SRP), which is a universally conserved ribonucleoprotein complex required for the co-translational translocation of polypeptides into the endoplasmic reticulum lumen and membrane. Ded1 is physically associated with SRP components in vivo and in vitro. Ded1 is genetically linked with SRP proteins. Finally, the enzymatic activity of Ded1 is inhibited by SRP21 in the presence of SCR1 RNA. We propose a model where Ded1 actively participates in the translocation of proteins during translation. Our results provide a new understanding of the role of Ded1 during translation.

The eEF1A protein in cancer: Clinical significance, oncogenic mechanisms, and targeted therapeutic strategies

Eukaryotic elongation factor 1A (eEF1A) is among the most abundant proteins in eukaryotic cells. Evolutionarily conserved across species, eEF1A is in charge of translation elongation for protein biosynthesis as well as a plethora of non-translational moonlighting functions for cellular homeostasis. In malignant cells, however, eEF1A becomes a pleiotropic driver of cancer progression via a broad diversity of pathways, which are not limited to hyperactive translational output. In the past decades, mounting studies have demonstrated the causal link between eEF1A and carcinogenesis, gaining deeper insights into its multifaceted mechanisms and corroborating its value as a prognostic marker in various cancers. On the other hand, an increasing number of natural and synthetic compounds were discovered as anticancer eEF1A-targeting inhibitors. Among them, plitidepsin was approved for the treatment of multiple myeloma whereas metarrestin was currently under clinical development. Despite significant achievements in these two interrelated fields, hitherto there lacks a systematic examination of the eEF1A protein in the context of cancer research. Therefore, the present work aims to delineate its clinical implications, molecular oncogenic mechanisms, and targeted therapeutic strategies as reflected in the ever expanding body of literature, so as to deepen mechanistic understanding of eEF1A-involved tumorigenesis and inspire the development of eEF1A-targeted chemotherapeutics and biologics.

Differential effects of translation inhibitors on Plasmodium berghei liver stage parasites

Increasing numbers of antimalarial compounds are being identified that converge mechanistically at inhibition of cytoplasmic translation, regardless of the molecular target or mechanism. A deeper understanding of how their effectiveness as liver stage translation inhibitors relates to their chemoprotective potential could prove useful. Here, we probed that relationship using the Plasmodium berghei-HepG2 liver stage infection model. After determining translation inhibition EC50s for five compounds, we tested them at equivalent effective concentrations to compare the parasite response to, and recovery from, a brief period of translation inhibition in early schizogony, followed by parasites to 120 h post-infection to assess antiplasmodial effects of the treatment. We show compound-specific heterogeneity in single parasite and population responses to translation inhibitor treatment, with no single metric strongly correlated to the release of hepatic merozoites for all compounds. We also demonstrate that DDD107498 is capable of exerting antiplasmodial effects on translationally arrested liver stage parasites and uncover unexpected growth dynamics during the liver stage. Our results demonstrate that translation inhibition efficacy does not determine antiplasmodial efficacy for these compounds.

Cellular energy regulates mRNA degradation in a codon-specific manner

Codon optimality is a major determinant of mRNA translation and degradation rates. However, whether and through which mechanisms its effects are regulated remains poorly understood. Here we show that codon optimality associates with up to 2-fold change in mRNA stability variations between human tissues, and that its effect is attenuated in tissues with high energy metabolism and amplifies with age. Mathematical modeling and perturbation data through oxygen deprivation and ATP synthesis inhibition reveal that cellular energy variations non-uniformly alter the effect of codon usage. This new mode of codon effect regulation, independent of tRNA regulation, provides a fundamental mechanistic link between cellular energy metabolism and eukaryotic gene expression.

Transcript-specific induction of stop codon readthrough using a CRISPR-dCas13 system

Stop codon readthrough (SCR) is the process where translation continues beyond a stop codon on an mRNA. Here, we describe a strategy to enhance or induce SCR in a transcript-selective manner using a CRISPR-dCas13 system. Using specific guide RNAs, we target dCas13 to the region downstream of canonical stop codons of mammalian AGO1 and VEGFA mRNAs, known to exhibit natural SCR. Readthrough assays reveal enhanced SCR of these mRNAs (both exogenous and endogenous) caused by the dCas13-gRNA complexes. This effect is associated with ribosomal pausing, which has been reported for several SCR events. Our data show that CRISPR-dCas13 can also induce SCR across premature termination codons (PTCs) in the mRNAs of green fluorescent protein and TP53. We demonstrate the utility of this strategy in the induction of readthrough across the thalassemia-causing PTC in HBB mRNA and hereditary spherocytosis-causing PTC in SPTA1 mRNA. Thus, CRISPR-dCas13 can be programmed to enhance or induce SCR in a transcript-selective and stop codon-specific manner.

RNA-binding proteins in pain

RNAs are meticulously controlled by proteins. Through direct and indirect associations, every facet in the brief life of an mRNA is subject to regulation. RNA-binding proteins (RBPs) permeate biology. Here, we focus on their roles in pain. Chronic pain is among the largest challenges facing medicine and requires new strategies. Mounting pharmacologic and genetic evidence obtained in pre-clinical models suggests fundamental roles for a broad array of RBPs. We describe their diverse roles that span RNA modification, splicing, stability, translation, and decay. Finally, we highlight opportunities to expand our understanding of regulatory interactions that contribute to pain signaling. This article is categorized under: RNA Interactions with Proteins and Other Molecules > Protein-RNA Interactions: Functional Implications Translation > Regulation RNA in Disease and Development > RNA in Disease.

METTL3 as a master regulator of translation in cancer: mechanisms and implications

Translational regulation is an important step in the control of gene expression. In cancer cells, the orchestration of both global control of protein synthesis and selective translation of specific mRNAs promote tumor cell survival, angiogenesis, transformation, invasion and metastasis. N6-methyladenosine (m6A), the most prevalent mRNA modification in higher eukaryotes, impacts protein translation. Over the past decade, the development of m6A mapping tools has facilitated comprehensive functional investigations, revealing the involvement of this chemical mark, together with its writer METTL3, in promoting the translation of both oncogenes and tumor suppressor transcripts, with the impact being context-dependent. This review aims to consolidate our current understanding of how m6A and METTL3 shape translation regulation in the realm of cancer biology. In addition, it delves into the role of cytoplasmic METTL3 in protein synthesis, operating independently of its catalytic activity. Ultimately, our goal is to provide critical insights into the interplay between m6A, METTL3 and translational regulation in cancer, offering a deeper comprehension of the mechanisms sustaining tumorigenesis.

Protein translation: biological processes and therapeutic strategies for human diseases

Protein translation is a tightly regulated cellular process that is essential for gene expression and protein synthesis. The deregulation of this process is increasingly recognized as a critical factor in the pathogenesis of various human diseases. In this review, we discuss how deregulated translation can lead to aberrant protein synthesis, altered cellular functions, and disease progression. We explore the key mechanisms contributing to the deregulation of protein translation, including functional alterations in translation factors, tRNA, mRNA, and ribosome function. Deregulated translation leads to abnormal protein expression, disrupted cellular signaling, and perturbed cellular functions- all of which contribute to disease pathogenesis. The development of ribosome profiling techniques along with mass spectrometry-based proteomics, mRNA sequencing and single-cell approaches have opened new avenues for detecting diseases related to translation errors. Importantly, we highlight recent advances in therapies targeting translation-related disorders and their potential applications in neurodegenerative diseases, cancer, infectious diseases, and cardiovascular diseases. Moreover, the growing interest lies in targeted therapies aimed at restoring precise control over translation in diseased cells is discussed. In conclusion, this comprehensive review underscores the critical role of protein translation in disease and its potential as a therapeutic target. Advancements in understanding the molecular mechanisms of protein translation deregulation, coupled with the development of targeted therapies, offer promising avenues for improving disease outcomes in various human diseases. Additionally, it will unlock doors to the possibility of precision medicine by offering personalized therapies and a deeper understanding of the molecular underpinnings of diseases in the future.

PRFect: a tool to predict programmed ribosomal frameshifts in prokaryotic and viral genomes

BACKGROUND

One of the stranger phenomena that can occur during gene translation is where, as a ribosome reads along the mRNA, various cellular and molecular properties contribute to stalling the ribosome on a slippery sequence and shifting the ribosome into one of the other two alternate reading frames. The alternate frame has different codons, so different amino acids are added to the peptide chain. More importantly, the original stop codon is no longer in-frame, so the ribosome can bypass the stop codon and continue to translate the codons past it. This produces a longer version of the protein, a fusion of the original in-frame amino acids, followed by all the alternate frame amino acids. There is currently no automated software to predict the occurrence of these programmed ribosomal frameshifts (PRF), and they are currently only identified by manual curation.

RESULTS

Here we present PRFect, an innovative machine-learning method for the detection and prediction of PRFs in coding genes of various types. PRFect combines advanced machine learning techniques with the integration of multiple complex cellular properties, such as secondary structure, codon usage, ribosomal binding site interference, direction, and slippery site motif. Calculating and incorporating these diverse properties posed significant challenges, but through extensive research and development, we have achieved a user-friendly approach. The code for PRFect is freely available, open-source, and can be easily installed via a single command in the terminal. Our comprehensive evaluations on diverse organisms, including bacteria, archaea, and phages, demonstrate PRFect's strong performance, achieving high sensitivity, specificity, and an accuracy exceeding 90%. The code for PRFect is freely available and installs with a single terminal command.

CONCLUSION

PRFect represents a significant advancement in the field of PRF detection and prediction, offering a powerful tool for researchers and scientists to unravel the intricacies of programmed ribosomal frameshifting in coding genes.

Making sense of mRNA translational "noise"

The importance of translation fidelity has been apparent since the discovery of genetic code. It is commonly believed that translation deviating from the main coding region is to be avoided at all times inside cells. However, ribosome profiling and mass spectrometry have revealed pervasive noncanonical translation. Both the scope and origin of translational "noise" are just beginning to be appreciated. Although largely overlooked, those translational "noises" are associated with a wide range of cellular functions, such as producing unannotated protein products. Furthermore, the dynamic nature of translational "noise" is responsive to stress conditions, highlighting the beneficial effect of translational "noise" in stress adaptation. Mechanistic investigation of translational "noise" will provide better insight into the mechanisms of translational regulation. Ultimately, they are not "noise" at all but represent a signature of cellular activities under pathophysiological conditions. Deciphering translational "noise" holds the therapeutic and diagnostic potential in a wide spectrum of human diseases.

Systematic analysis of nonprogrammed frameshift suppression in E. coli via translational tiling proteomics

The synthesis of proteins as encoded in the genome depends critically on translational fidelity. Nevertheless, errors inevitably occur, and those that result in reading frame shifts are particularly consequential because the resulting polypeptides are typically nonfunctional. Despite the generally maladaptive impact of such errors, the proper decoding of certain mRNAs, including many viral mRNAs, depends on a process known as programmed ribosomal frameshifting. The fact that these programmed events, commonly involving a shift to the -1 frame, occur at specific evolutionarily optimized "slippery" sites has facilitated mechanistic investigation. By contrast, less is known about the scope and nature of error (i.e., nonprogrammed) frameshifting. Here, we examine error frameshifting by monitoring spontaneous frameshift events that suppress the effects of single base pair deletions affecting two unrelated test proteins. To map the precise sites of frameshifting, we developed a targeted mass spectrometry-based method called "translational tiling proteomics" for interrogating the full set of possible -1 slippage events that could produce the observed frameshift suppression. Surprisingly, such events occur at many sites along the transcripts, involving up to one half of the available codons. Only a subset of these resembled canonical "slippery" sites, implicating alternative mechanisms potentially involving noncognate mispairing events. Additionally, the aggregate frequency of these events (ranging from 1 to 10% in our test cases) was higher than we might have anticipated. Our findings point to an unexpected degree of mechanistic diversity among ribosomal frameshifting events and suggest that frameshifted products may contribute more significantly to the proteome than generally assumed.

Methylation of elongation factor 1A by yeast Efm4 or human eEF1A-KMT2 involves a beta-hairpin recognition motif and crosstalks with phosphorylation

Translation elongation factor 1A (eEF1A) is an essential and highly conserved protein required for protein synthesis in eukaryotes. In both Saccharomyces cerevisiae and human, five different methyltransferases methylate specific residues on eEF1A, making eEF1A the eukaryotic protein targeted by the highest number of dedicated methyltransferases after histone H3. eEF1A methyltransferases are highly selective enzymes, only targeting eEF1A and each targeting just one or two specific residues in eEF1A. However, the mechanism of this selectivity remains poorly understood. To reveal how S. cerevisiae elongation factor methyltransferase 4 (Efm4) specifically methylates eEF1A at K316, we have used AlphaFold-Multimer modeling in combination with crosslinking mass spectrometry (XL-MS) and enzyme mutagenesis. We find that a unique beta-hairpin motif, which extends out from the core methyltransferase fold, is important for the methylation of eEF1A K316 in vitro. An alanine mutation of a single residue on this beta-hairpin, F212, significantly reduces Efm4 activity in vitro and in yeast cells. We show that the equivalent residue in human eEF1A-KMT2 (METTL10), F220, is also important for its activity towards eEF1A in vitro. We further show that the eEF1A guanine nucleotide exchange factor, eEF1Bα, inhibits Efm4 methylation of eEF1A in vitro, likely due to competitive binding. Lastly, we find that phosphorylation of eEF1A at S314 negatively crosstalks with Efm4-mediated methylation of K316. Our findings demonstrate how protein methyltransferases can be highly selective towards a single residue on a single protein in the cell.

Diphthamide - a conserved modification of eEF2 with clinical relevance

Diphthamide, a complex modification on eukaryotic translation elongation factor 2 (eEF2), assures reading-frame fidelity during translation. Diphthamide and enzymes for its synthesis are conserved in eukaryotes and archaea. Originally identified as target for diphtheria toxin (DT) in humans, its clinical relevance now proves to be broader than the link to pathogenic bacteria. Diphthamide synthesis enzymes (DPH1 and DPH3) are associated with cancer, and DPH gene mutations can cause diphthamide deficiency syndrome (DDS). Finally, new analyses provide evidence that diphthamide may restrict propagation of viruses including SARS-CoV-2 and HIV-1, and that DPH enzymes are targeted by viruses for degradation to overcome this restriction. This review describes how diphthamide is synthesized and functions in translation, and covers its clinical relevance in human development, cancer, and infectious diseases.

Autoantibodies against eukaryotic translation elongation factor 1 delta in two patients with autoimmune cerebellar ataxia

Background

Autoantibodies are useful biomarkers for the early detection and diagnosis of autoimmune cerebellar ataxia (ACA).

Objective

To identify novel autoantibody candidates in ACA patients.

Methods

Patients with cerebellar ataxia of unknown cause were recruited from July 2018 to February 2023. Anti-neural autoantibodies in patient samples were detected by tissue-based indirect immunofluorescence assay (TBA) on rat cerebellum sections. TBA-positive samples were further screened for well-established anti-neural autoantibodies using commercial kits. Tissue-immunoprecipitation (TIP) and subsequent mass spectrometric (MS) analysis were used to explore the target antigens of autoantibodies in samples that were TBA-positive but negative for known autoantibodies. The specific binding between autoantibodies and the identified target antigen was confirmed by neutralization experiments, recombinant cell-based indirect immunofluorescence assay (CBA), and western blotting experiments.

Results

The eukaryotic translation elongation factor 1 delta (EEF1D) protein was identified as a target antigen of autoantibodies in samples from a 43-year-old female ACA patient, while the specific binding of autoantibodies and EEF1D was confirmed by subsequent experiments. A second anti-EEF1D autoantibody-positive ACA patient, a 59-year-old female, was detected in simultaneous screening. The main clinical manifestations in each of the two patients were cerebellar syndrome, such as unsteady walking and limb ataxia. Both patients received immunotherapy, including corticosteroids, intravenous immunoglobulin, and mycophenolate mofetil. Their outcomes provided evidence to support the effectiveness of immunotherapy, but the cerebellar atrophy that occurred before treatment may be irreversible.

Conclusion

In the current study, we identified anti-EEF1D autoantibody as a novel autoantibody candidate in ACA. Its pathological roles and diagnostic value need to be further verified in larger-scale studies.

mRNA reading frame maintenance during eukaryotic ribosome translocation

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 reported3-5. 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-tRNA2-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 Integral Role of Magnesium in Muscle Integrity and Aging: A Comprehensive Review

Aging is characterized by significant physiological changes, with the degree of decline varying significantly among individuals. The preservation of intrinsic capacity over the course of an individual's lifespan is fundamental for healthy aging. Locomotion, which entails the capacity for independent movement, is intricately connected with various dimensions of human life, including cognition, vitality, sensory perception, and psychological well-being. Notably, skeletal muscle functions as a pivotal nexus within this intricate framework. Any perturbation in its functionality can manifest as compromised physical performance and an elevated susceptibility to frailty. Magnesium is an essential mineral that plays a central role in approximately 800 biochemical reactions within the human body. Its distinctive physical and chemical attributes render it an indispensable stabilizing factor in the orchestration of diverse cellular reactions and organelle functions, thereby rendering it irreplaceable in processes directly impacting muscle health. This narrative review offers a comprehensive exploration of the pivotal role played by magnesium in maintaining skeletal muscle integrity, emphasizing the critical importance of maintaining optimal magnesium levels for promoting healthy aging.

Programmable modulation of ribosomal frameshifting by mRNA targeting CRISPR-Cas12a system

Minus 1 programmed ribosomal frameshifting (-1 PRF) is a conserved translational regulation event essential for critical biological processes, including the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) replication. Efficient trans-modulation of the structured RNA element crucial to -1 PRF will endow the therapeutic application. Here, we demonstrate that CRISPR RNA can stimulate efficient -1 PRF. Assembled CRISPR-Cas12a, but not CRISPR-Cas9, complex further enhances -1 PRF efficiency through its higher capacity to stall translating ribosomes. We additionally perform CRISPR-Cas12a targeting to impair the SARS-CoV-2 frameshifting pseudoknot structure via a focused screening. We demonstrate that targeting CRISPR-Cas12a results in more than 70% suppression of -1 PRF in vitro and about 50% suppression in mammalian cells. Our results show the expanded function of the CRISPR-Cas12 system in modulating -1 PRF efficiency through stalling ribosomes and deforming frameshifting stimulatory signals, which could serve as a new strategy for future coronavirus pandemics.

Translation inhibition efficacy does not determine the Plasmodium berghei liver stage antiplasmodial efficacy of protein synthesis inhibitors

Protein synthesis is a core cellular process, necessary throughout the complex lifecycle of Plasmodium parasites, thus specific translation inhibitors would be a valuable class of antimalarial drugs, capable of both treating symptomatic infections in the blood and providing chemoprotection by targeting the initial parasite population in the liver, preventing both human disease and parasite transmission back to the mosquito host. As increasing numbers of antiplasmodial compounds are identified that converge mechanistically at inhibition of cytoplasmic translation, regardless of molecular target or mechanism, it would be useful to gain deeper understanding of how their effectiveness as liver stage translation inhibitors relates to their chemoprotective potential. Here, we probed that relationship using the P. berghei-HepG2 liver stage infection model. Using o-propargyl puromycin-based labeling of the nascent proteome in P. berghei-infected HepG2 monolayers coupled with automated confocal feedback microscopy to generate unbiased, single parasite image sets of P. berghei liver stage translation, we determined translation inhibition EC50s for five compounds, encompassing parasite-specific aminoacyl tRNA synthetase inhibitors, compounds targeting the ribosome in both host and parasite, as well as DDD107498, which targets Plasmodium eEF2, and is a leading antimalarial candidate compound being clinically developed as cabamiquine. Compounds were then tested at equivalent effective concentrations to compare the parasite response to, and recovery from, a brief period of translation inhibition in early schizogony, with parasites followed up to 120 hours post-infection to assess liver stage antiplasmodial effects of the treatment. Our data conclusively show that translation inhibition efficacy per se does not determine a translation inhibitor's antiplasmodial efficacy. DDD107498 was the least effective translation inhibitor, yet exerted the strongest antimalarial effects at both 5x- and 10x EC50 concentrations. We show compound-specific heterogeneity in single parasite and population responses to translation inhibitor treatment, with no single metric strongly correlated to release of hepatic merozoites for all compound, demonstrate that DDD107498 is capable of exerting antiplasmodial effects on translationally arrested liver stage parasites, and uncover unexpected growth dynamics during the liver stage. Our results demonstrate that translation inhibition efficacy cannot function as a proxy for antiplasmodial effectiveness, and highlight the importance of exploring the ultimate, as well as proximate, mechanisms of action of these compounds on liver stage parasites.

YfmR is a translation factor that prevents ribosome stalling and cell death in the absence of EF-P

Protein synthesis is performed by the ribosome and a host of highly conserved elongation factors. Elongation factor P (EF-P) prevents ribosome stalling at difficult-to-translate sequences, particularly polyproline tracts. In bacteria, phenotypes associated with efp deletion range from modest to lethal, suggesting that some species encode an additional translation factor that has similar function to EF-P. Here we identify YfmR as a translation factor that is essential in the absence of EF-P in B. subtilis. YfmR is an ABCF ATPase that is closely related to both Uup and EttA, ABCFs that bind the ribosomal E-site and are conserved in more than 50% of bacterial genomes. We show that YfmR associates with actively translating ribosomes and that depleting YfmR from Δefp cells causes severe ribosome stalling at a polyproline tract in vivo. YfmR depletion from Δefp cells was lethal, and caused reduced levels of actively translating ribosomes. Our results therefore identify YfmR as an important translation factor that is essential in B. subtilis in the absence of EF-P.

A highly efficient human cell-free translation system

Cell-free protein synthesis (CFPS) systems enable easy in vitro expression of proteins with many scientific, industrial, and therapeutic applications. Here we present an optimized, highly efficient human cell-free translation system that bypasses many limitations of currently used in vitro systems. This CFPS system is based on extracts from human HEK293T cells engineered to endogenously express GADD34 and K3L proteins, which suppress phosphorylation of translation initiation factor eIF2α. Overexpression of GADD34 and K3L proteins in human cells before cell lysate preparation significantly simplifies lysate preparation. We find that expression of the GADD34 and K3L accessory proteins before cell lysis maintains low levels of phosphorylation of eIF2α in the extracts. During in vitro translation reactions, eIF2α phosphorylation increases moderately in a GCN2-dependent fashion that can be inhibited by GCN2 kinase inhibitors. This new CFPS system should be useful for exploring human translation mechanisms in more physiological conditions outside the cell.

Shiftless Is a Novel Member of the Ribosome Stress Surveillance Machinery That Has Evolved to Play a Role in Innate Immunity and Cancer Surveillance

A longstanding paradox in molecular biology has centered on the question of how very long proteins are synthesized, despite numerous measurements indicating that ribosomes spontaneously shift reading frame at rates that should preclude their ability completely translate their mRNAs. Shiftless (SFL; C19orf66) was originally identified as an interferon responsive gene encoding an antiviral protein, indicating that it is part of the innate immune response. This activity is due to its ability to bind ribosomes that have been programmed by viral sequence elements to shift reading frame. Curiously, Shiftless is constitutively expressed at low levels in mammalian cells. This study examines the effects of altering Shiftless homeostasis, revealing how it may be used by higher eukaryotes to identify and remove spontaneously frameshifted ribosomes, resolving the apparent limitation on protein length. Data also indicate that Shiftless plays a novel role in the ribosome-associated quality control program. A model is proposed wherein SFL recognizes and arrests frameshifted ribosomes, and depending on SFL protein concentrations, either leads to removal of frameshifted ribosomes while leaving mRNAs intact, or to mRNA degradation. We propose that SFL be added to the growing pantheon of proteins involved in surveilling translational fidelity and controlling gene expression in higher eukaryotes.

Conserved 5-methyluridine tRNA modification modulates ribosome translocation

While the centrality of post-transcriptional modifications to RNA biology has long been acknowledged, the function of the vast majority of modified sites remains to be discovered. Illustrative of this, there is not yet a discrete biological role assigned for one the most highly conserved modifications, 5-methyluridine at position 54 in tRNAs (m 5 U54). Here, we uncover contributions of m 5 U54 to both tRNA maturation and protein synthesis. Our mass spectrometry analyses demonstrate that cells lacking the enzyme that installs m 5 U in the T-loop (TrmA in E. coli , Trm2 in S. cerevisiae ) exhibit altered tRNA modifications patterns. Furthermore, m 5 U54 deficient tRNAs are desensitized to small molecules that prevent translocation in vitro. This finding is consistent with our observations that, relative to wild-type cells, trm2 Δ cell growth and transcriptome-wide gene expression are less perturbed by translocation inhibitors. Together our data suggest a model in which m 5 U54 acts as an important modulator of tRNA maturation and translocation of the ribosome during protein synthesis.

Establishing chromosomal design-build-test-learn through a synthetic chromosome and its combinatorial reconfiguration

Chromosome-level design-build-test-learn cycles (chrDBTLs) allow systematic combinatorial reconfiguration of chromosomes with ease. Here, we established chrDBTL with a redesigned synthetic Saccharomyces cerevisiae chromosome XV, synXV. We designed and built synXV to harbor strategically inserted features, modified elements, and synonymously recoded genes throughout the chromosome. Based on the recoded chromosome, we developed a method to enable chrDBTL: CRISPR-Cas9-mediated mitotic recombination with endoreduplication (CRIMiRE). CRIMiRE allowed the creation of customized wild-type/synthetic combinations, accelerating genotype-phenotype mapping and synthetic chromosome redesign. We also leveraged synXV as a "build-to-learn" model organism for translation studies by ribosome profiling. We conducted a locus-to-locus comparison of ribosome occupancy between synXV and the wild-type chromosome, providing insight into the effects of codon changes and redesigned features on translation dynamics in vivo. Overall, we established synXV as a versatile reconfigurable system that advances chrDBTL for understanding biological mechanisms and engineering strains.

The role of dysregulated mRNA translation machinery in cancer pathogenesis and therapeutic value of ribosome-inactivating proteins

Dysregulated protein synthesis is a hallmark of tumors. mRNA translation reprogramming contributes to tumorigenesis, which is fueled by abnormalities in ribosome formation, tRNA abundance and modification, and translation factors. Not only malignant cells but also stromal cells within tumor microenvironment can undergo transformation toward tumorigenic phenotypes during translational reprogramming. Ribosome-inactivating proteins (RIPs) have garnered interests for their ability to selectively inhibit protein synthesis and suppress tumor growth. This review summarizes the role of dysregulated translation machinery in tumor development and explores the potential of RIPs in cancer treatment.

Gelation of cytoplasmic expanded CAG RNA repeats suppresses global protein synthesis

RNA molecules with the expanded CAG repeat (eCAGr) may undergo sol-gel phase transitions, but the functional impact of RNA gelation is completely unknown. Here, we demonstrate that the eCAGr RNA may form cytoplasmic gel-like foci that are rapidly degraded by lysosomes. These RNA foci may significantly reduce the global protein synthesis rate, possibly by sequestering the translation elongation factor eEF2. Disrupting the eCAGr RNA gelation restored the global protein synthesis rate, whereas enhanced gelation exacerbated this phenotype. eEF2 puncta were significantly enhanced in brain slices from a knock-in mouse model and from patients with Huntington's disease, which is a CAG expansion disorder expressing eCAGr RNA. Finally, neuronal expression of the eCAGr RNA by adeno-associated virus injection caused significant behavioral deficits in mice. Our study demonstrates the existence of RNA gelation inside the cells and reveals its functional impact, providing insights into repeat expansion diseases and functional impacts of RNA phase transition.

Post-transcriptional regulation of myeloid cell-mediated inflammatory responses

Myeloid cells, particularly macrophages, act as the frontline responders to infectious agents and initiate inflammation. While the molecular mechanisms driving inflammatory responses have primarily focused on pattern recognition by myeloid cells and subsequent transcriptional events, it is crucial to note that post-transcriptional regulation plays a pivotal role in this process. In addition to the transcriptional regulation of innate immune responses, additional layers of intricate network of post-transcriptional mechanisms critically determine the quantity and duration of key inflammatory products and thus the outcome of immune responses. A multitude of mechanisms governing post-transcriptional regulation in innate immunity have been uncovered, encompassing RNA alternative splicing, mRNA stability, and translational regulation. This review encapsulates the current insights into the post-transcriptional regulation of inflammatory genes within myeloid cells, with particular emphasis on translational regulation during inflammation. While acknowledging the advancements, we also shed light on the existing gaps in immunological research pertaining to post-transcriptional levels and propose perspectives that controlling post-transcriptional process may serve as potential targets for therapeutic interventions in inflammatory diseases.

DPH1 and DPH2 variants that confer susceptibility to diphthamide deficiency syndrome in human cells and yeast models

The autosomal-recessive diphthamide deficiency syndrome presents as intellectual disability with developmental abnormalities, seizures, craniofacial and additional morphological phenotypes. It is caused by reduced activity of proteins that synthesize diphthamide on human translation elongation factor 2. Diphthamide synthesis requires seven proteins (DPH1-DPH7), with clinical deficiency described for DPH1, DPH2 and DPH5. A limited set of variant alleles from syndromic patients has been functionally analyzed, but databases (gnomAD) list additional so far uncharacterized variants in human DPH1 and DPH2. Because DPH enzymes are conserved among eukaryotes, their functionality can be assessed in yeast and mammalian cells. Our experimental assessment of known and uncharacterized DPH1 and DPH2 missense alleles showed that six variants are tolerated despite inter-species conservation. Ten additional human DPH1 (G113R, A114T, H132P, H132R, S136R, C137F, L138P, Y152C, S221P, H240R) and two DPH2 (H105P, C341Y) variants showed reduced functionality and hence are deficiency-susceptibility alleles. Some variants locate close to the active enzyme center and may affect catalysis, while others may impact on enzyme activation. In sum, our study has identified functionally compromised alleles of DPH1 and DPH2 genes that likely cause diphthamide deficiency syndrome.

Translation dysregulation in neurodegenerative diseases: a focus on ALS

RNA translation is tightly controlled in eukaryotic cells to regulate gene expression and maintain proteome homeostasis. RNA binding proteins, translation factors, and cell signaling pathways all modulate the translation process. Defective translation is involved in multiple neurological diseases including amyotrophic lateral sclerosis (ALS). ALS is a progressive neurodegenerative disorder and poses a major public health challenge worldwide. Over the past few years, tremendous advances have been made in the understanding of the genetics and pathogenesis of ALS. Dysfunction of RNA metabolisms, including RNA translation, has been closely associated with ALS. Here, we first introduce the general mechanisms of translational regulation under physiological and stress conditions and review well-known examples of translation defects in neurodegenerative diseases. We then focus on ALS-linked genes and discuss the recent progress on how translation is affected by various mutant genes and the repeat expansion-mediated non-canonical translation in ALS.

In vitro Analysis of Stalled Ribosomes Using Puromycin Incorporation

Ribosome footprint profiling has demonstrated that ribosomes can be slowed or stalled on select mRNAs, often due to the presence of rare codons, stalling motifs, or via a ribosome-binding protein (e.g., FMRP). Stalled ribosomes can act as physical roadblocks for trailing ribosomes and ultimately can cause ribosome collisions that stimulate no-go mRNA decay. Detecting stalled or slowed ribosomes in cells by ribosome footprint profiling or classic polysome profiling is laborious, technically challenging, and low throughput. Here, we present a protocol to assay for stalled ribosomes on in vitro-transcribed reporter mRNAs using a robust, commercially available mammalian in vitro translation lysate and an optimized low-speed sucrose cushion. In short, we take advantage of the ability of puromycin to incorporate into the nascent polypeptide and cause the ribosome to dissociate from the mRNA during active elongation, as well as the ability to selectively pellet ribosomes through a low-speed sucrose cushion due to their large molecular weight. Stalled ribosomes are not actively elongating and do not incorporate puromycin, allowing the ribosome-bound mRNA to pellet in the low-speed sucrose cushion. RT-qPCR is used to quantify the amount of ribosome-bound reporter mRNA in the pellet. This workflow allows for direct assessment of stalled ribosomes and is fully amendable to insertion of putative stalling motifs in the target mRNA, as well as supplementation with recombinant proteins or small molecule inhibitors that target translation elongation. Key features This protocol is optimized for cap-dependent in vitro translation in the dynamic linear range. Details for generating capped reporter mRNA in one day are provided. Requires as little as one day to complete if starting with in vitro-transcribed mRNA. This protocol requires access to an ultracentrifuge and a real-time PCR system.

The central role of translation elongation in response to stress

Protein synthesis is essential to support homeostasis, and thus, must be highly regulated during cellular response to harmful environments. All stages of translation are susceptible to regulation under stress, however, the mechanisms involved in translation regulation beyond initiation have only begun to be elucidated. Methodological advances enabled critical discoveries on the control of translation elongation, highlighting its important role in translation repression and the synthesis of stress-response proteins. In this article, we discuss recent findings on mechanisms of elongation control mediated by ribosome pausing and collisions and the availability of tRNAs and elongation factors. We also discuss how elongation intersects with distinct modes of translation control, further supporting cellular viability and gene expression reprogramming. Finally, we highlight how several of these pathways are reversibly regulated, emphasizing the dynamics of translation control during stress-response progression. A comprehensive understanding of translation regulation under stress will produce fundamental knowledge of protein dynamics while opening new avenues and strategies to overcome dysregulated protein production and cellular sensitivity to stress.

Interaction of the La-related protein Slf1 with colliding ribosomes maintains translation of oxidative-stress responsive mRNAs

In response to oxidative stress cells reprogram gene expression to enhance levels of antioxidant enzymes and promote survival. In Saccharomyces cerevisiae the polysome-interacting La-related proteins (LARPs) Slf1 and Sro9 aid adaptation of protein synthesis during stress by undetermined means. To gain insight in their mechanisms of action in stress responses, we determined LARP mRNA binding positions in stressed and unstressed cells. Both proteins bind within coding regions of stress-regulated antioxidant enzyme and other highly translated mRNAs in both optimal and stressed conditions. LARP interaction sites are framed and enriched with ribosome footprints suggesting ribosome-LARP-mRNA complexes are identified. Although stress-induced translation of antioxidant enzyme mRNAs is attenuated in slf1Δ, these mRNAs remain on polysomes. Focusing further on Slf1, we find it binds to both monosomes and disomes following RNase treatment. slf1Δ reduces disome enrichment during stress and alters programmed ribosome frameshifting rates. We propose that Slf1 is a ribosome-associated translational modulator that stabilises stalled/collided ribosomes, prevents ribosome frameshifting and so promotes translation of a set of highly-translated mRNAs that together facilitate cell survival and adaptation to stress.

Translation and mRNA Stability Control

Messenger RNA (mRNA) stability and translational efficiency are two crucial aspects of the post-transcriptional process that profoundly impact protein production in a cell. While it is widely known that ribosomes produce proteins, studies during the past decade have surprisingly revealed that ribosomes also control mRNA stability in a codon-dependent manner, a process referred to as codon optimality. Therefore, codons, the three-nucleotide words read by the ribosome, have a potent effect on mRNA stability and provide cis-regulatory information that extends beyond the amino acids they encode. While the codon optimality molecular mechanism is still unclear, the translation elongation rate appears to trigger mRNA decay. Thus, transfer RNAs emerge as potential master gene regulators affecting mRNA stability. Furthermore, while few factors related to codon optimality have been identified in yeast, the orthologous genes in vertebrates do not necessary share the same functions. Here, we discuss codon optimality findings and gene regulation layers related to codon composition in different eukaryotic species.

Translation Arrest: A Key Player in Plant Antiviral Response

Plants evolved several mechanisms to protect themselves against viruses. Besides recessive resistance, where compatible host factors required for viral proliferation are absent or incompatible, there are (at least) two types of inducible antiviral immunity: RNA silencing (RNAi) and immune responses mounted upon activation of nucleotide-binding domain leucine-rich repeat (NLR) receptors. RNAi is associated with viral symptom recovery through translational repression and transcript degradation following recognition of viral double-stranded RNA produced during infection. NLR-mediated immunity is induced upon (in)direct recognition of a viral protein by an NLR receptor, triggering either a hypersensitive response (HR) or an extreme resistance response (ER). During ER, host cell death is not apparent, and it has been proposed that this resistance is mediated by a translational arrest (TA) of viral transcripts. Recent research indicates that translational repression plays a crucial role in plant antiviral resistance. This paper reviews current knowledge on viral translational repression during viral recovery and NLR-mediated immunity. Our findings are summarized in a model detailing the pathways and processes leading to translational arrest of plant viruses. This model can serve as a framework to formulate hypotheses on how TA halts viral replication, inspiring new leads for the development of antiviral resistance in crops.

A highly efficient human cell-free translation system

Cell-free protein synthesis (CFPS) systems enable easy in vitro expression of proteins with many scientific, industrial, and therapeutic applications. Here we present an optimized, highly efficient human cell-free translation system that bypasses many limitations of currently used in vitro systems. This CFPS system is based on extracts from human HEK293T cells engineered to endogenously express GADD34 and K3L proteins, which suppress phosphorylation of translation initiation factor eIF2α. Overexpression of GADD34 and K3L proteins in human cells significantly simplifies cell lysate preparation. The new CFPS system improves the translation of 5' cap-dependent mRNAs as well as those that use internal ribosome entry site (IRES) mediated translation initiation. We find that expression of the GADD34 and K3L accessory proteins before cell lysis maintains low levels of phosphorylation of eIF2α in the extracts. During in vitro translation reactions, eIF2α phosphorylation increases moderately in a GCN2-dependent fashion that can be inhibited by GCN2 kinase inhibitors. We also find evidence for activation of regulatory pathways related to eukaryotic elongation factor 2 (eEF2) phosphorylation and ribosome quality control in the extracts. This new CFPS system should be useful for exploring human translation mechanisms in more physiological conditions outside the cell.

Methylated guanosine and uridine modifications in S. cerevisiae mRNAs modulate translation elongation

Chemical modifications to protein encoding messenger RNAs (mRNAs) influence their localization, translation, and stability within cells. Over 15 different types of mRNA modifications have been observed by sequencing and liquid chromatography coupled to tandem mass spectrometry (LC-MS/MS) approaches. While LC-MS/MS is arguably the most essential tool available for studying analogous protein post-translational modifications, the high-throughput discovery and quantitative characterization of mRNA modifications by LC-MS/MS has been hampered by the difficulty of obtaining sufficient quantities of pure mRNA and limited sensitivities for modified nucleosides. We have overcome these challenges by improving the mRNA purification and LC-MS/MS pipelines. The methodologies we developed result in no detectable non-coding RNA modifications signals in our purified mRNA samples, quantify 50 ribonucleosides in a single analysis, and provide the lowest limit of detection reported for ribonucleoside modification LC-MS/MS analyses. These advancements enabled the detection and quantification of 13 S. cerevisiae mRNA ribonucleoside modifications and reveal the presence of four new S. cerevisiae mRNA modifications at low to moderate levels (1-methyguanosine, N2-methylguanosine, N2,N2-dimethylguanosine, and 5-methyluridine). We identified four enzymes that incorporate these modifications into S. cerevisiae mRNAs (Trm10, Trm11, Trm1, and Trm2, respectively), though our results suggest that guanosine and uridine nucleobases are also non-enzymatically methylated at low levels. Regardless of whether they are incorporated in a programmed manner or as the result of RNA damage, we reasoned that the ribosome will encounter the modifications that we detect in cells. To evaluate this possibility, we used a reconstituted translation system to investigate the consequences of modifications on translation elongation. Our findings demonstrate that the introduction of 1-methyguanosine, N2-methylguanosine and 5-methyluridine into mRNA codons impedes amino acid addition in a position dependent manner. This work expands the repertoire of nucleoside modifications that the ribosome must decode in S. cerevisiae. Additionally, it highlights the challenge of predicting the effect of discrete modified mRNA sites on translation de novo because individual modifications influence translation differently depending on mRNA sequence context.

Decoding and Recoding of mRNA Sequences by the Ribosome

Faithful translation of messenger RNA (mRNA) into protein is essential to maintain protein homeostasis in the cell. Spontaneous translation errors are very rare due to stringent selection of cognate aminoacyl transfer RNAs (tRNAs) and the tight control of the mRNA reading frame by the ribosome. Recoding events, such as stop codon readthrough, frameshifting, and translational bypassing, reprogram the ribosome to make intentional mistakes and produce alternative proteins from the same mRNA. The hallmark of recoding is the change of ribosome dynamics. The signals for recoding are built into the mRNA, but their reading depends on the genetic makeup of the cell, resulting in cell-specific changes in expression programs. In this review, I discuss the mechanisms of canonical decoding and tRNA-mRNA translocation; describe alternative pathways leading to recoding; and identify the links among mRNA signals, ribosome dynamics, and recoding.

Molecular mechanisms of eukaryotic translation fidelity and their associations with diseases

Converting genetic information into functional proteins is a complex, multi-step process, with each step being tightly regulated to ensure the accuracy of translation, which is critical to cellular health. In recent years, advances in modern biotechnology, especially the development of cryo-electron microscopy and single-molecule techniques, have enabled a clearer understanding of the mechanisms of protein translation fidelity. Although there are many studies on the regulation of protein translation in prokaryotes, and the basic elements of translation are highly conserved in prokaryotes and eukaryotes, there are still great differences in the specific regulatory mechanisms. This review describes how eukaryotic ribosomes and translation factors regulate protein translation and ensure translation accuracy. However, a certain frequency of translation errors does occur in translation, so we describe diseases that arise when the rate of translation errors reaches or exceeds a threshold of cellular tolerance.

A novel de novo variant in CASK causes a severe neurodevelopmental disorder that masks the phenotype of a novel de novo variant in EEF2

We report a 9-year-old Spanish boy with severe psychomotor developmental delay, short stature, microcephaly and abnormalities of the brain morphology, including cerebellar atrophy. Whole-exome sequencing (WES) uncovered two novel de novo variants, a hemizygous variant in CASK (Calcium/Calmodulin Dependent Serine Protein Kinase) and a heterozygous variant in EEF2 (Eukaryotic Translation Elongation Factor 2). CASK gene encodes the peripheral plasma membrane protein CASK that is a scaffold protein located at the synapses in the brain. The c.2506-6 A > G CASK variant induced two alternative splicing events that account for the 80% of the total transcripts, which are likely to be degraded by NMD. Pathogenic variants in CASK have been associated with severe neurological disorders such as mental retardation with or without nystagmus also called FG syndrome 4 (FGS4), and intellectual developmental disorder with microcephaly and pontine and cerebellar hypoplasia (MICPCH). Heterozygous variants in EEF2, which encodes the elongation factor 2 (eEF2), have been associated to Spinocerebellar ataxia 26 (SCA26) and more recently to a childhood-onset neurodevelopmental disorder with benign external hydrocephalus. The yeast model system used to investigate the functional consequences of the c.34 A > G EEF2 variant supported its pathogenicity by demonstrating it affects translational fidelity. In conclusion, the phenotype associated with the CASK variant is more severe and masks the milder phenotype of EEF2 variant.

Anticancer Small-Molecule Agents Targeting Eukaryotic Elongation Factor 1A: State of the Art

Eukaryotic elongation factor 1A (eEF1A) canonically delivers amino acyl tRNA to the ribosomal A site during the elongation stage of protein biosynthesis. Yet paradoxically, the oncogenic nature of this instrumental protein has long been recognized. Consistently, eEF1A has proven to be targeted by a wide assortment of small molecules with excellent anticancer activity, among which plitidepsin has been granted approval for the treatment of multiple myeloma. Meanwhile, metarrestin is currently under clinical development for metastatic cancers. Bearing these exciting advances in mind, it would be desirable to present a systematic up-to-date account of the title topic, which, to the best of our knowledge, has thus far been unavailable in the literature. The present review summarizes recent advances in eEF1A-targeting anticancer agents, both naturally occurring and synthetically crafted, with regard to their discovery or design, target identification, structure–activity relationship, and mode of action. Their structural diversity and differential eEF1A-targeting mechanisms warrant continuing research in pursuit of curing eEF1A-driven malignancy.

Mammalian proteome expansion by stop codon readthrough

Recognition of a stop codon by translation machinery as a sense codon results in translational readthrough instead of termination. This recoding process, termed stop codon readthrough (SCR) or translational readthrough, is found in all domains of life including mammals. The context of the stop codon, local mRNA topology, and molecules that interact with the mRNA region downstream of the stop codon determine SCR. The products of SCR can have localization, stability, and function different from those of the canonical isoforms. In this review, we discuss how recent technological and computational advances have increased our understanding of the SCR process in the mammalian system. Based on the known molecular events that occur during SCR of multiple mRNAs, we propose transient molecular roadblocks on an mRNA downstream of the stop codon as a possible mechanism for the induction of SCR. We argue, with examples, that the insights gained from the natural SCR events can guide us to develop novel strategies for the treatment of diseases caused by premature stop codons. This article is categorized under: Translation > Regulation.

Plant translational reprogramming for stress resilience

Organisms regulate gene expression to produce essential proteins for numerous biological processes, from growth and development to stress responses. Transcription and translation are the major processes of gene expression. Plants evolved various transcription factors and transcriptome reprogramming mechanisms to dramatically modulate transcription in response to environmental cues. However, even the genome-wide modulation of a gene's transcripts will not have a meaningful effect if the transcripts are not properly biosynthesized into proteins. Therefore, protein translation must also be carefully controlled. Biotic and abiotic stresses threaten global crop production, and these stresses are seriously deteriorating due to climate change. Several studies have demonstrated improved plant resistance to various stresses through modulation of protein translation regulation, which requires a deep understanding of translational control in response to environmental stresses. Here, we highlight the translation mechanisms modulated by biotic, hypoxia, heat, and drought stresses, which are becoming more serious due to climate change. This review provides a strategy to improve stress tolerance in crops by modulating translational regulation.

Zinc-finger protein Zpr1 is a bespoke chaperone essential for eEF1A biogenesis

The conserved regulon of heat shock factor 1 in budding yeast contains chaperones for general protein folding as well as zinc-finger protein Zpr1, whose essential role in archaea and eukaryotes remains unknown. Here, we show that Zpr1 depletion causes acute proteotoxicity driven by biosynthesis of misfolded eukaryotic translation elongation factor 1A (eEF1A). Prolonged Zpr1 depletion leads to eEF1A insufficiency, thereby inducing the integrated stress response and inhibiting protein synthesis. Strikingly, we show by using two distinct biochemical reconstitution approaches that Zpr1 enables eEF1A to achieve a conformational state resistant to protease digestion. Lastly, we use a ColabFold model of the Zpr1-eEF1A complex to reveal a folding mechanism mediated by the Zpr1's zinc-finger and alpha-helical hairpin structures. Our work uncovers the long-sought-after function of Zpr1 as a bespoke chaperone tailored to the biogenesis of one of the most abundant proteins in the cell.

Translation factor eIF5a is essential for IFNγ production and cell cycle regulation in primary CD8+ T lymphocytes

Control of mRNA translation adjusts protein production rapidly and facilitates local cellular responses to environmental conditions. Traditionally initiation of translation is considered to be a major translational control point, however, control of peptide elongation is also important. Here we show that the function of the elongation factor, eIF5a, is regulated dynamically in naïve CD8+ T cells upon activation by post-translational modification, whereupon it facilitates translation of specific subsets of proteins. eIF5a is essential for long-term survival of effector CD8+ T cells and sequencing of nascent polypeptides indicates that the production of proteins which regulate proliferation and key effector functions, particularly the production of IFNγ and less acutely TNF production and cytotoxicity, is dependent on the presence of functional eIF5a. Control of translation in multiple immune cell lineages is required to co-ordinate immune responses and these data illustrate that translational elongation contributes to post-transcriptional regulons important for the control of inflammation.

Pathogenesis of bronchopulmonary dysplasia in preterm neonates revealed by an RNA sequencing interaction network analysis

BACKGROUND

The chronic lung condition known as bronchopulmonary dysplasia (BPD), which primarily affects newborns, especially preterm neonates, is brought on by prolonged oxygen consumption and mechanical ventilation. This case-control study sought to investigate the pathogenesis of BPD in preterm neonates by RNA sequencing (RNA-seq).

METHODS

First, RNA-seq samples were collected from 3 BPD and 3 healthy preterm neonates. Based on the sequencing data and microarray data sets, MERGE.57185.1, the key long non-coding RNA (lncRNA), was identified from the differentially expressed lncRNAs and the key module by a weighted gene co-expression network analysis (WGCNA), a Venn diagram, and an expression analysis. Next, the differentially expressed messenger RNAs (mRNAs) and microRNAs (miRNAs) that were strongly correlated to MERGE.57185.1 were identified in the protein-protein interaction networks and underwent a functional enrichment analysis and Spearman correlation analysis. Finally, the mRNA [i.e., eukaryotic translation initiation factor 5A (EIF5A)] and miRNA (i.e., hsa-miR-6833-5p) with the strongest correlations to MERGE.57185.1 were identified as the downstream targets.

RESULTS

Among the 32 genes in the dark-red module and the 158 differentially expressed lncRNAs, 21 overlapping genes were identified. In the gene expression analysis, MERGE.57185.1 (an oncogene) was identified as the key lncRNA in BPD. The results of the multiple bioinformatics analysis showed that the mRNA and the miRNA with the strongest correlations to MERGE.57185.1 were hsa-miR-6833-5p (a suppressor gene) and EIF5A (an oncogene), respectively. Hsa-miR-6833-5p was lowly expressed in the BPD group, while EIF5A was highly expressed in the BPD group.

CONCLUSIONS

This study identified 1 key upregulated lncRNA (i.e., MERGE.57185.1) in preterm neonatal BPD, and revealed the MERGE.57185.1/hsa-miR-6833-5p/EIF5A mechanism in preterm neonatal BPD from the lncRNA-miRNA-mRNA network. This key lncRNA gene could serve as a promising diagnostic biomarker for prenatal examinations.

Biomotors, viral assembly, and RNA nanobiotechnology: Current achievements and future directions

The International Society of RNA Nanotechnology and Nanomedicine (ISRNN) serves to further the development of a wide variety of functional nucleic acids and other related nanotechnology platforms. To aid in the dissemination of the most recent advancements, a biennial discussion focused on biomotors, viral assembly, and RNA nanobiotechnology has been established where international experts in interdisciplinary fields such as structural biology, biophysical chemistry, nanotechnology, cell and cancer biology, and pharmacology share their latest accomplishments and future perspectives. The results summarized here highlight advancements in our understanding of viral biology and the structure-function relationship of frame-shifting elements in genomic viral RNA, improvements in the predictions of SHAPE analysis of 3D RNA structures, and the understanding of dynamic RNA structures through a variety of experimental and computational means. Additionally, recent advances in the drug delivery, vaccine design, nanopore technologies, biomotor and biomachine development, DNA packaging, RNA nanotechnology, and drug delivery are included in this critical review. We emphasize some of the novel accomplishments, major discussion topics, and present current challenges and perspectives of these emerging fields.

Features and factors that dictate if terminating ribosomes cause or counteract nonsense-mediated mRNA decay

Nonsense-mediated mRNA decay (NMD) is a quality control pathway in eukaryotes that continuously monitors mRNA transcripts to ensure truncated polypeptides are not produced. The expression of many normal mRNAs that encode full-length polypeptides is also regulated by this pathway. Such transcript surveillance by NMD is intimately linked to translation termination. When a ribosome terminates translation at a normal termination codon, NMD is not activated, and mRNA can undergo repeated rounds of translation. On the other hand, when translation termination is deemed abnormal, such as that on a premature termination codon, it leads to a series of poorly understood events involving the NMD pathway, which destabilizes the transcript. In this review, we summarize our current understanding of how the NMD machinery interfaces with the translation termination factors to initiate NMD. We also discuss a variety of cis-acting sequence contexts and trans-acting factors that can cause readthrough, ribosome reinitiation, or ribosome frameshifting at stop codons predicted to induce NMD. These alternative outcomes can lead to the ribosome translating downstream of such stop codons and hence the transcript escaping NMD. NMD escape via these mechanisms can have wide-ranging implications on human health, from being exploited by viruses to hijack host cell systems to being harnessed as potential therapeutic possibilities to treat genetic diseases.

The Arabidopsis ATP-Binding Cassette E protein ABCE2 is a conserved component of the translation machinery

ATP-Binding Cassette E (ABCE) proteins dissociate cytoplasmic ribosomes after translation terminates, and contribute to ribosome recycling, thus linking translation termination to initiation. This function has been demonstrated to be essential in animals, fungi, and archaea, but remains unexplored in plants. In most species, ABCE is encoded by a single-copy gene; by contrast, Arabidopsis thaliana has two ABCE paralogs, of which ABCE2 seems to conserve the ancestral function. We isolated apiculata7-1 (api7-1), the first viable, hypomorphic allele of ABCE2, which has a pleiotropic morphological phenotype reminiscent of mutations affecting ribosome biogenesis factors and ribosomal proteins. We also studied api7-2, a null, recessive lethal allele of ABCE2. Co-immunoprecipitation experiments showed that ABCE2 physically interacts with components of the translation machinery. An RNA-seq study of the api7-1 mutant showed increased responses to iron and sulfur starvation. We also found increased transcript levels of genes related to auxin signaling and metabolism. Our results support for the first time a conserved role for ABCE proteins in translation in plants, as previously shown for the animal, fungal, and archaeal lineages. In Arabidopsis, the ABCE2 protein seems important for general growth and vascular development, likely due to an indirect effect through auxin metabolism.

Overexpressing eukaryotic elongation factor 1 alpha (eEF1A) proteins to promote corticospinal axon repair after injury

Although protein synthesis is hypothesized to have a pivotal role in axonal repair after central nervous system (CNS) injury, the role of core components of the protein synthesis machinery has not been examined. Notably, some elongation factors possess non-canonical functions that may further impact axonal repair. Here, we examined whether overexpressing eukaryotic elongation factor 1 alpha (eEF1A) proteins enhances the collateral sprouting of corticospinal tract (CST) neurons after unilateral pyramidotomy, along with the underlying molecular mechanisms. We found that overexpressing eEF1A proteins in CST neurons increased the levels of pS6, an indicator for mTOR activity, but not pSTAT3 and pAKT levels, in neuronal somas. Strikingly, overexpressing eEF1A2 alone, but neither eEF1A1 alone nor both factors simultaneously, increased protein synthesis and actin rearrangement in CST neurons. While eEF1A1 overexpression only slightly enhanced CST sprouting after pyramidotomy, eEF1A2 overexpression substantially enhanced this sprouting. Surprisingly, co-overexpression of both eEF1A1 and eEF1A2 led to a sprouting phenotype similar to wild-type controls, suggesting an antagonistic effect of overexpressing both proteins. These data provide the first evidence that overexpressing a core component of the translation machinery, eEF1A2, enhances CST sprouting, likely by a combination of increased protein synthesis, mTOR signaling and actin cytoskeleton rearrangement.

Translational regulation by ribosome-associated quality control in neurodegenerative disease, cancer, and viral infection

Translational control at the initiation, elongation, and termination steps exerts immediate effects on the rate as well as the spatiotemporal dynamics of new protein synthesis, shaping the composition of the proteome. Translational control is particularly important for cells under stress as during viral infection or in disease conditions such as cancer and neurodegenerative diseases. Much has been learned about the control mechanisms acting at the translational initiation step under normal or pathological conditions. However, problems during the elongation or termination steps of translation can lead to ribosome stalling and ribosome collision, which will trigger ribosome-associated quality control (RQC) mechanism. Inadequate RQC may lead to the accumulation of faulty translation products that perturb protein homeostasis (proteostasis). Proteostasis signifies a cellular state in which the synthesis, folding, and degradation of proteins are maintained at a homeostatic state such that an intact proteome is preserved. Cellular capacity to preserve proteostasis declines with age, which is thought to contribute to age-related diseases. Proteostasis failure manifested as formation of aberrant protein aggregates, epitomized by the amyloid plaques in Alzheimer’s disease (AD), is a defining feature of neurodegenerative diseases. The root cause of the proteostasis failure and protein aggregation is still enigmatic. Here I will review recent studies supporting that faulty translation products resulting from inadequate RQC of translational stalling and ribosome collision during the translation of problematic mRNAs can be the root cause of proteostasis failure and may represent novel therapeutic targets for neurodegenerative diseases. I will also review evidence that translation regulation by RQC is operative in cancer cells and during viral infection. Better understanding of RQC mechanism may lead to novel therapeutic strategies against neurodegenerative diseases, cancer, and viral infections, including the ongoing COVID-19 pandemic.