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Genes associated with translation and oxidative phosphorylation as components of the translational response in nodulated and water-restricted soybean.

BACKGROUND: Soybean primarily acquires nitrogen through symbiosis with nitrogen-fixing bacteria. Water deficit (WD) is a major stress limiting crop yield. Nodulation may enhance drought tolerance in legumes by modulating nitrogen and hormone metabolism, osmotic adjustment, and antioxidant defenses; however, the molecular basis underlying the differential WD responses between N-fix and N-fed plants remain unclear. Translational control of gene expression is a key regulatory mechanism during stress. RESULTS: We compared the transcriptome and translatome of soybean roots from N-fix and N-fed plants exposed to WD across four combined treatments. N-fix plants under WD exhibited more complex responses in terms of total differentially expressed genes (DEGs) compared to N-fed plants. This increased complexity was also evident among translationally regulated DEGs and differentially expressed transcription factors, whose involvement in WD responses of N-fix plants is novel. Co-expression network analysis identified modules associated with core biological processes encompassing nodulation, WD, and notably, their interplay was particularly prominent in Module 1, which was enriched in genes related to ribosomal protein synthesis and oxidative phosphorylation (OXPHOS). Guilt-by-Association analysis enabled the prediction of novel functions for differentially expressed, uncharacterized hub genes related to stress and/or nodulation responses. CONCLUSIONS: Translational regulation of genes involved in OXPHOS and translation initiation emerged as a central response in N-fix plants under WD. These findings reveal distinct molecular adaptations in N-fix soybean roots facing WD and highlight translational control as a key regulatory layer. We also identified promising candidate genes-including transcription factors and uncharacterized hub genes under translational regulation-that represent potential targets for improving drought tolerance in legumes once validated functionally.

Glycine max

Altered neuronal start codon stringency favors cap-independent repeat-associated non-AUG translation.

Intronic GGGGCC repeat expansions in C9orf72 cause amyotrophic lateral sclerosis (ALS) and frontotemporal dementia (FTD). This expansion supports a non-canonical form of translational initiation known as repeat-associated non-AUG (RAN) translation to produce toxic dipeptide repeat proteins that contribute to neurodegeneration. Here, we find that the efficiency of RAN translation and its dependency on the 5' 7-methylguanosine mRNA cap are variable across cell types, with both rodent neurons and human iNeurons favoring cap-independent RAN translation from two distinct repeats (CGG and GGGGCC) across multiple reading frames. Treatment with an eIF4E inhibitor that blocks cap-dependent translation enhances RAN translation specifically in neurons. Intriguingly, cap-independent RAN translation exhibits less reliance on near-cognate codons for initiation than cap-dependent RAN translation. This finding led us to identify a surprising global alteration in neuronal start codon stringency as a contributor to the relatively higher cap-independent RAN translation in this cell type. This effect correlates with cytoplasmic redistribution of eIF1 in neurons and is reversed with overexpression of the eukaryotic initiation factor eIF5, which relaxes start codon stringency and preferentially enhances cap-dependent RAN translation. Together, these findings reveal several neuron-specific features of translational regulation that favor cap-independent RAN translation with implications for nucleotide repeat expansion disorder pathogenesis.

Neurons

Acetic acid-induced translational repression involves eIF2B body formation and Ded1 sequestration into stress granules in yeast.

Elucidating the physiological impact of acetic acid stress and the corresponding yeast responses is essential for advancing fundamental biology and improving industrial alcoholic fermentation. Despite numerous genome-wide studies, information on the effects of acetic acid stress on yeast translational regulation remains limited. We found that a sublethal concentration of acetic acid (35 mM, 0.2% v/v) causes translational repression, accompanied by the formation of eIF2B bodies and the phosphorylation of eIF2α, both of which are involved in the regulation of translation initiation. Acetic acid also caused the sequestration of Ded1, a DEAD-box RNA helicase crucial for translation initiation, into stress granules. Removal of acetic acid restored translational activity and the proper localization of eIF2B and Ded1, indicating the reversibility of acetic acid-induced translational repression. Furthermore, when yeast cells were pretreated with 0.05% acetic acid, translational repression under subsequent 0.2% acetic acid stress was attenuated in wild-type cells but not in hrk1Δ cells. This indicates that Hrk1, a Pma1 activator, is required to sufficiently enhance tolerance to acetic acid-induced translational repression. These findings provide novel insights into the physiological effects of acetic acid stress on translational activity and translation-related factors in yeast cells.

Saccharomyces cerevisiae

Effects of light on chloroplast translation in Marchantia polymorpha are similar to those in angiosperms and are not influenced by light-independent chlorophyll synthesis.

Translation of the chloroplast psbA mRNA in angiosperms is activated by photodamage of its gene product, the D1 subunit of photosystem II (PSII), providing nascent D1 for PSII repair. The involvement of chlorophyll in the regulatory mechanism has been suggested due to the regulatory roles of proteins proposed to mediate chlorophyll/D1 transactions and the fact that chlorophyll is synthesized only in the light in angiosperms. We used ribosome profiling and RNA-seq to address whether the effects of light on chloroplast translation are conserved in the liverwort Marchantia (Marchantia polymorpha), which synthesizes chlorophyll in both the dark and the light. As in angiosperms, ribosome occupancy on psbA mRNA decreased rapidly upon shifting plants to the dark and was rapidly restored upon a transfer back to the light, whereas ribosome occupancy on other chloroplast mRNAs changed very little. The results were similar in a Marchantia mutant unable to synthesize chlorophyll in the dark. Those results, in conjunction with pulse-labeling data, suggest that light elicits a plastome-wide activation of translation elongation and a specific increase in psbA translation initiation in Marchantia, as in angiosperms. These findings show that light regulates chloroplast translation similarly in vascular and non-vascular plants, and that constitutive chlorophyll synthesis does not affect light-regulated psbA translation initiation. Additionally, the translational outputs of chloroplast genes are similar in Marchantia and angiosperms but result from differing contributions of mRNA abundance and translational efficiencies. This adds to the evidence that chloroplast mRNA abundance and translational efficiencies co-evolve under selection to maintain protein outputs.

Chloroplasts

An Intrinsically Disordered RNA Binding Protein Modulates mRNA Translation and Storage.

Proteins with intrinsically disordered regions (IDR) play diverse functions in regulating gene expression in the cell. Many of these proteins interact with cytoplasmic ribosomes. However, the molecular functions related to the interactions are largely unclear. In this study, using an abundant RNA-binding protein, Sbp1, with a structurally well-defined RNA recognition motif and an intrinsically disordered RGG domain as a model system, we investigated how an RNA binding protein with IDR modulates mRNA storage and translation. Using genomic and molecular approaches, we show that Sbp1 slows ribosome movement on cellular mRNAs and promotes polysome stacking or aggregation. Sbp1-associated polysomes display a ring-shaped structure in addition to a beads-on-string morphology visualized under the electron microscope, likely to be an intermediate slow translation state between actively translating polysomes and the translation-sequestered RNA granule. Moreover, the binding of Sbp1 to the 5'UTRs of mRNAs represses both cap-dependent and cap-independent translation initiation of proteins, many are functionally important for general protein synthesis in the cell. Finally, post-translational modifications at the arginine in the RGG motif change the Sbp1 protein interactome and play important roles in directing cellular mRNAs to either translation or storage. Taken together, our study demonstrates that under physiological conditions, intrinsically disordered RNA binding proteins promote polysome aggregation and regulate mRNA translation and storage using multiple distinctive mechanisms. This research also establishes a framework with which functions of other IDR-containing proteins can be investigated and defined.

RNA-Binding Proteins

Translation of the downstream ORF from bicistronic mRNAs by human cells: Impact of codon usage and splicing in the upstream ORF.

Biochemistry textbooks describe eukaryotic mRNAs as monocistronic. However, increasing evidence reveals the widespread presence and translation of upstream open reading frames preceding the "main" ORF. DNA and RNA viruses infecting eukaryotes often produce polycistronic mRNAs and viruses have evolved multiple ways of manipulating the host's translation machinery. Here, we introduce an experimental model to study gene expression regulation from virus-like bicistronic mRNAs in human cells. The model consists of a short upstream ORF and a reporter downstream ORF encoding a fluorescent protein. We have engineered synonymous variants of the upstream ORF to explore large parameter space, including codon usage preferences, mRNA folding features, and splicing propensity. We show that human translation machinery can translate the downstream ORF from bicistronic mRNAs, albeit reporter protein levels are thousand times lower than those from the upstream ORF. Furthermore, synonymous recoding of the upstream ORF exclusively during elongation significantly influences its own translation efficiency, reveals cryptic splice signals, and modulates the probability of downstream ORF translation. Our results are consistent with a leaky scanning mechanism facilitating downstream ORF translation from bicistronic mRNAs in human cells, offering new insights into the role of upstream ORFs in translation regulation.

Humans

Unbiased screen of human transcriptome reveals an unexpected role of 3'UTRs in translation initiation.

Although most eukaryotic mRNAs require a 5'-cap for translation initiation, some can also be translated through a poorly studied cap-independent pathway. Here we develop a circRNA-based system and unbiasedly identify more than 10,000 sequences in the human transcriptome that contain Cap-independent Translation Initiators (CiTIs). Surprisingly, most of the identified CiTIs are located in 3'UTRs, which mainly promote translation initiation in mRNAs bearing highly structured 5'UTR. Mechanistically, CiTI recruits several translation initiation factors including eIF3 and DHX29, which in turn unwind 5'UTR structures and facilitate ribosome scanning. Functionally, we show that the translation of HIF1A mRNA, an endogenous DHX29 target, is antagonistically regulated by its 5'UTR structure and a new 3'-CiTI in response to hypoxia. Consistently, deletion of 3'-CiTI suppresses cell growth in hypoxia and tumor progression in vivo. Collectively, our study uncovers a new regulatory mode for translation where the 3'UTR actively participate in the translation initiation.

Humans

Hexokinase 2 is an RNA-binding protein that regulates mRNA translation independently of glycolysis and induces melanoma cell proliferation.

Although metabolic benefits of glycolysis have been extensively described in tumor cells, the extra-metabolic functions linked to this energetic pathway in tumor growth and cell proliferation have not been clearly established yet. Recently, some key glycolytic enzymes, such as glyceraldehyde-3-phosphate dehydrogenase and pyruvate kinase 2, were reported to regulate mRNA translation. Translational control of gene expression is considered as a critical effector in cancer biology, representing a highly promising area of research. Here, we report that Hexokinase 2 (HK2), a glucose kinase that catalyzes the first step of glycolysis at the outer mitochondrial membrane (OMM), is an RNA-binding protein (RBP) that regulates mRNA translation in melanoma cell lines. Polysome profiling experiments followed by RNA sequencing indicate that the translational regulation exerted by HK2 is partly independent of the metabolic status or the glycolytic pathway. We found that HK2 specifically regulates translation of the mRNA encoding SOX10, a transcription factor implicated in the regulation of tumor initiation, maintenance, and progression in melanoma. RNA-protein interaction assays, including CrossLinking ImmunoPrecipitation (CLIP), indicate that HK2 is an RBP whose interaction with RNA is independent of its enzymatic activity, its ability to bind glucose or its association with the OMM. HK2 directly interacts with the 5' untranslated region (5'UTR) of the SOX10 mRNA through a stem-loop RNA secondary structure. Using RNA-protein proximity ligation assays and a fluorescence-based ribosome-bound mRNA mapping method, we found that high glucose conditions, which promote the release of HK2 from the OMM, induce an increase in HK2-SOX10 mRNA interaction and SOX10 mRNA translation in the cytoplasm. We further showed that HK2-dependent SOX10 mRNA translation is involved in melanoma cell proliferation and colony formation. Collectively, our data highlight a nonmetabolic function of HK2 acting as an RBP and translation regulator.

Hexokinase

Widespread release of translational repression across Plasmodium's host-to-vector transmission event.

Malaria parasites must respond quickly to environmental changes, including during their transmission between mammalian and mosquito hosts. Therefore, female gametocytes proactively produce and translationally repress mRNAs that encode essential proteins that the zygote requires to establish a new infection. While the release of translational repression of individual mRNAs has been documented, the details of the global release of translational repression have not. Moreover, changes in the spatial arrangement and composition of the DOZI/CITH/ALBA complex that contribute to translational control are also not known. Therefore, we have conducted the first quantitative, comparative transcriptomics and DIA-MS proteomics of Plasmodium parasites across the host-to-vector transmission event to document the global release of translational repression. Using female gametocytes and zygotes of P. yoelii, we found that ~200 transcripts are released for translation soon after fertilization, including those encoding essential functions. Moreover, we identified that many transcripts remain repressed beyond this point. TurboID-based proximity proteomics of the DOZI/CITH/ALBA regulatory complex revealed substantial spatial and/or compositional changes across this transmission event, which are consistent with recent, paradigm-shifting models of translational control. Together, these data provide a model for the essential translational control mechanisms that promote Plasmodium's efficient transmission from mammalian host to mosquito vector.

Animals

EV-D68 cleaves LARP1 and PABPC1 by 3Cpro to redirect host mRNA translation machinery toward its genomic RNA.

Enterovirus D68 (EV-D68) is an emerging pathogen associated with severe respiratory diseases and neurological complications, such as acute flaccid myelitis. EV-D68 has developed sophisticated mechanisms to hijack host translation machinery, facilitating its replication and impairing host mRNA translation. In this study, we demonstrate that EV-D68 cleaves La-related protein 1 (LARP1) and poly(A)-binding protein cytoplasmic 1 (PABPC1) through its proteases 3Cpro and 2Apro. Our results indicate that overexpressing LARP1 and PABPC1 significantly inhibits EV-D68 replication and reduces the virus-mediated suppression of host translation. While both LARP1 and PABPC1 regulate translation, they exert antiviral effects through distinct mechanisms. We found that LARP1 interacts with the 5'UTR of EV-D68 RNA through its LAM domain, and this interaction is crucial for its antiviral function. LARP1 translation modulation is also influenced by the mTOR and CDK1 signaling pathways. Viral infection inhibits mTOR and CDK1 phosphorylation, which enhances LARP1's binding to viral RNA and inhibits viral translation. To counteract this inhibition, EV-D68 cleaves LARP1 through 3Cpro, thereby promoting efficient viral translation. We also investigated other enteroviruses, such as EV-A71 and CV-A16, which similarly target LARP1 and PABPC1, indicating a conserved mechanism across enteroviruses. Our findings offer new insights into how EV-D68 manipulates host translation and highlight the potential of targeting LARP1 and PABPC1 for antiviral interventions.

Humans

Organoids in translation: a bench-to-bedside framework for pancreatic cancer precision medicine.

INTRODUCTION: Pancreatic ductal adenocarcinoma (PDAC) is one of the most lethal malignancies with a 5-year survival rate of < 13%. Standard treatments such as FOLFIRINOX or gemcitabine/nab-paclitaxel yield modest response rates, underscoring the urgent need for precision oncology approaches. Patient-derived organoids (PDOs) preserve the genomic, phenotypic, and histopathological features of the source tumor and offer a promising platform for drug screening, biomarker development, and personalized therapy. However, a systematic evaluation of their translational capacities is lacking. METHODS: A systematic review was conducted according to the PRISMA 2020 guidelines (PROSPERO registration pending) using PubMed, EMBASE, and Cochrane CENTRAL (December 10, 2024) to identify English-language PDAC PDO studies that incorporated therapeutic testing. Ninety-five studies met the inclusion criteria. Data extraction captured >75 variables per study, including spanning culture methodology, therapeutic profiling, biomarker integration, and clinical correlation. A 13-domain weighted Translatability Scoring Framework adapted from Wehling et al. assessed predictive validity, biomarker strength, pharmacogenetics, and clinical trial alignment. Scores ranged from 0 to 5 and were categorized as good (>4.0), moderate (3.0-4.0), or low (<3.0) translational potential. RESULTS: Of the 95 studies, 70.5% have been published since 2021, reflecting the rapid growth in this field. The mean PDO generation success rate was 89.7%, with the primary tumor tissue being the predominant source (48.4%). Only 24.8% were directly linked to clinical trials and 5.3% incorporated multi-omic profiling. The median translatability score was 3.13 (range, 1.72-4.59): 45.3% of the studies had low translatability, 50.5% moderate, and only 4.2% had good translational potential. High-scoring studies consistently combine multi-omic biomarker platforms, in vivo validation, clinical outcome correlation, and prospective trial integration. Conversely, the weakest domains were pharmacogenetics, endpoint strategies, and biomarker validation, limiting their overall clinical relevance. CONCLUSIONS: PDOs have demonstrated strong feasibility and in vitro clinical correlation in PDAC; however, their clinical translation remains constrained by limited multi-omic integration, absence of pharmacogenomic modeling, and sparse clinical trial embedding. Standardization of protocols, adoption of harmonized and clinically relevant endpoints, and systematic incorporation of biomarker-driven co-clinical trial frameworks are urgently needed to transition PDOs from promising experimental surrogates to validating precision oncology tools capable of informing therapeutic decision-making in PDAC.

Humans

Involvement of tRNA thiolation in uORF-mediated translational regulation during Xylogenesis in Arabidopsis thaliana.

Post-transcriptional modification of tRNAs is an important mechanism for regulating translation efficiency and cellular homeostasis, yet its contribution to upstream open reading frame (uORF)-mediated translational control remains largely unexplored. In this study, we investigated the role of tRNA thiolation in thermospermine-dependent regulation of xylem development in Arabidopsis thaliana. Using a suppressor screen of the thermospermine-deficient mutant acaulis5 (acl5), which exhibits dwarfism and excessive xylem differentiation, we identified suppressor-of-acl502 (sac502) as a recessive loss-of-function allele of CTU2, a gene encoding a key enzyme in the biosynthesis of the wobble uridine modification 5-methoxycarbonylmethyl-2-thiouridine. Mutations in other components of the same modification pathway, including ROL5 and TRM9, similarly suppressed the acl5 phenotype. Translational analyses using 5' leader-GUS reporter constructs revealed that the ctu2 mutation did not enhance translation of the mRNA containing a thermospermine-responsive uORF of SAC51, but instead significantly reduced translation of that of SACL3, a member of the SAC51 family, and that of LONESOME HIGHWAY (LHW), which contains another conserved uORF in the 5' leader region. Polysome profiling further demonstrated decreased association of SACL3 and LHW mRNAs with actively translating ribosomes in ctu2. Genetic interaction analyses supported the conclusion that the suppression of excessive xylem formation in acl5 by ctu2 is attributable to reduced LHW activity. In addition, ctu2 mutants displayed increased sensitivity to exogenous thermospermine, resembling the response of lhw mutants. Together, our results reveal that tRNA thiolation contributes to uORF-mediated translational regulation of key developmental regulators and identify tRNA modification as an important regulatory layer controlling vascular development.

Arabidopsis

Novel CDK-independent function of CDC25 phosphatases in mRNA translation.

Molecular and functional networks driving coordination between cell cycle and mRNA translation remain to be explored. Here, we use mass spectrometry-based proteomics to comprehensively investigate the interactome and phosphoproteome of the cell cycle regulator CDC25A. We identify actors of mRNA regulation, such as RNA-binding proteins and translation factors, as interacting partners of CDC25A. CDC25A overexpression increases global translation, whereas catalytic inactivation or pharmacological inhibition decreases protein synthesis. A Cyclin-Dependent Kinase (CDK) interaction-deficient mutant of CDC25A also enhances translation, indicating a CDK-independent role. Our results further reveal an interplay between CDC25A and CDC25B whereby downregulation of CDC25A leads to compensatory overexpression of CDC25B. The roles of CDC25A and CDC25B in mRNA translation are independent of their roles in the cell cycle, with CDC25A possibly regulating translation elongation and CDC25B rather involved in initiation. In acute myeloid leukemia cells, CDC25A depletion also inhibits translation, suggesting its potential relevance as a therapeutic target. We propose that CDC25 phosphatases might be signaling platforms coordinating cell cycle progression with protein synthesis.

cdc25 Phosphatases

Unconventional codon usage bias mediates mRNA translational dynamics in macrophages.

Macrophages require rapid and tightly controlled regulatory mechanisms to respond to environmental disruptions. While transcriptional regulation has been well characterized, the mechanisms underlying translational control in macrophages remain poorly understood. Here, we investigated the dynamics of mRNA translation in mouse macrophages during acute, intermediate, and prolonged LPS exposure. Our results reveal clear phase-specific translational regulation during macrophage polarization, which initially increases the synthesis of inflammatory mediators and cytokines, while simultaneously suppressing the expression of cell cycle-related genes. Mechanistically, we observed pervasive upstream translation in the 5' UTRs of cell cycle-related mRNAs, which contributes to cell cycle arrest during the early phase of inflammatory response. Notably, we identified a unique codon preference toward A/U in the third position of codons in macrophages, which contrasts with the G/C preference commonly observed in other tissues. AU codon preference increases the stability and translation efficiency of cell cycle-related mRNAs, promoting cell cycle restoration after extended LPS exposure. These findings reveal that uORF translation and codon usage bias are critical components of translational regulation during macrophage polarization, highlighting a potential therapeutic intervention for modulating immune activation via macrophage-specific codon optimization.

Animals

Polysomal Profiling Coupled to Allele-Specific Proteomics Reveals an EIF4H TranSNP Allele Possessing Higher mRNA Translation Potential.

To search for genetic sources of allele-specific mRNA translation, we leveraged heterozygous polymorphisms and variants present in the exome of HCT116 colorectal adenocarcinoma-derived cells, computing allelic fractions from both total and polysome-associated RNA from RNA-Seq data. Allelic imbalance in polysomal RNA led us to nominate 52 coding variants associated with allele-specific mRNA translation, of which 16 are nonsynonymous. To validate instances of allele-specific translation, a proteomics workflow was developed that combines label-free shotgun analysis, high-pH reversed-phase peptide fractionation, and targeted parallel reaction monitoring using isotope-labeled peptide standards. Using this approach, we provide proof-of-concept validation of the heterozygous G>A, R183H missense single-nucleotide variant rs1554710467 in the eukaryotic initiation factor 4H (EIF4H) gene. The variant is present in two EIF4H alternatively spliced variants, which showed equivalent translation efficiency in HCT116 cells but differ in abundance. The alternative peptide containing H183 was significantly more abundant than the corresponding reference peptide containing R183, consistent with the over-representation of the alternative allele in polysomal RNA in HCT116 cells. A dual-fluorescence ribosome-stalling assay confirmed the enhanced translation potential of the variant allele. The two EIF4H allelic proteins exhibited similar stability and subpolysomal localization. This study demonstrates the feasibility of using allele-specific proteomics at the endogenous protein levels by exploiting heterozygous coding variants. Overall, our approach extends the toolbox available to investigate allele-specific differences in mRNA translation potential, a relatively underexplored layer of gene expression regulation that could reveal interindividual differences in disease-relevant phenotypes.

Humans

Circadian clock control of ribosome composition promotes rhythmic translation and termination fidelity.

Ribosome composition is dynamic, shifting with cell state and stress, but whether it varies with circadian time is unknown. Here, we uncover circadian clock-driven changes in ribosome composition in Neurospora crassa. Mass spectrometry of ribosomes across circadian time identified six ribosomal proteins and one associated factor under clock control. Rhythms in eL31 abundance were validated in purified ribosomes, and deletion of el31 disrupted translation rhythms in nearly half of rhythmically translated mRNAs. N. crassa eL31 promotes circadian control of translation termination and impacts elongation fidelity while maintaining Mg homeostasis, a key determinant of translational accuracy. These findings reveal that the circadian clock reprograms ribosome composition to orchestrate rhythmic translation and fidelity, temporally expanding the proteome beyond the static genome to align cellular function with time of day.

Neurospora crassa

The Subtle Crisis: Public Domain Genomes and the Ethics of Translational Infrastructure.

Public domain human genomic resources are infrastructure: tools researchers use to ask basic biological questions whose answers are then translated into products and care. Translational science now asks them to support an expanding set of tasks, including clinical variant interpretation for diverse populations, pharmacogenomic prescribing, polygenic risk prediction, and the training of clinical artificial intelligence. The corpus of public domain genomes, due in large part to upstream recruitment choices, is not fit for these purposes, and the gap between discovery and translation is widening. This essay argues that closing the gap requires treating public domain genomic infrastructure as a particular object of translational bioethics rather than a technical precondition for it. The limited number of genomes in the public domain relative to the broader genomic record, and the typology-friendliness of how that record represents human variation, are two faces of the same set of upstream choices. Reversing them is not a matter of more sampling under existing terms; it is a matter of building infrastructure of a particular kind; infrastructure made from people. That category, common in genomics but absent from the rest of science, demands an ethical apparatus the field has not yet built. Here we consider the commitments such an apparatus requires, and argue that where, how, and with whom we build genomic infrastructure is itself an ethics question the field has largely declined to ask.

Humans

A-to-I RNA editing remodels 5'-UTR initiation codons to tune translational output.

A-to-I RNA editing is a prevalent post-transcriptional modification in higher eukaryotes that converts adenosine to inosine within RNA molecules. Because inosine is interpreted as guanosine during translation, editing can alter codon identity and potentially influence translation initiation signals. Here, we examined whether A-to-I editing within the 5' untranslated region (5'-UTR) can remodel upstream initiation codons and thereby tune downstream translation. Using luciferase-based reporter systems, we show that AUA-to-AUI editing generates an initiation-competent inosine-containing codon, whereas AUG-to-IUG editing markedly attenuates initiation and can relieve uORF-mediated repression. Quantitative in vitro and cellular assays establish the initiation hierarchy AUA&#x2009;<&#x2009;AUI&#x2009;<&#x2009;AUG, with IUG exhibiting strongly reduced initiation efficiency. Importantly, AUI-mediated upstream initiation did not behave like a canonical AUG-initiated uORF in the tested contexts; its effect on downstream ORF translation was modest and context-dependent. Transcriptome-wide bioinformatic analysis identified endogenous human transcripts whose 5'-UTRs harbor editing sites compatible with initiation-codon gain or attenuation. Reporter validation using native 5'-UTR sequences supports the possibility that editing-dependent initiation-codon remodeling can tune translational output in living cells, particularly through AUG-to-IUG-mediated derepression. Together, these findings establish a reporter-based framework in which A-to-I editing can remodel 5'-UTR initiation codons, while highlighting the need for endogenous protein-level and native-locus validation to determine physiological relevance.

RNA Editing