Upstream open reading frames cause widespread reduction of protein expression and are polymorphic among humans.
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ABSTRACT:
SUBMITTER: Calvo SE
PROVIDER: S-EPMC2669787 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:Upstream open reading frames (uORFs) latent in mRNA transcripts are thought to modify translation of coding sequences by altering ribosome activity. Not all uORFs are thought to be active in such a process. To estimate the impact of uORFs on the regulation of translation in humans, we first circumscribed the universe of all possible uORFs based on coding gene sequence motifs and identified 1.3 million unique uORFs. To determine which of these are likely to be biologically relevant, we built a simple Bayesian classifier using 89 attributes of uORFs labeled as active in ribosome profiling experiments. This allowed us to extrapolate to a comprehensive catalog of likely functional uORFs. We validated our predictions using in vivo protein levels and ribosome occupancy from 46 individuals. This is a substantially larger catalog of functional uORFs than has previously been reported. Our ranked list of likely active uORFs allows researchers to test their hypotheses regarding the role of uORFs in health and disease. We demonstrate several examples of biological interest through the application of our catalog to somatic mutations in cancer and disease-associated germline variants in humans.
| S-EPMC6283423 | biostudies-literature
Project description:We engineered short ORFs and used them to control the expression level of recombinant proteins. These short ORFs, encoding a two-amino acid peptide, were placed upstream of an ORF encoding a protein of interest. Insertion of these upstream ORFs (uORFs) resulted in suppression of protein expression. By varying the base sequence preceding the uORF, we sought to vary the translation initiation rate of the uORF and subsequently control the degree of this suppression. Using this strategy, we generated a library of RNA sequence elements that can specify protein expression over a broad range of levels. By also using multiple uORFs in series and non-AUG start codons, we were able to generate particularly low expression levels, allowing us to achieve expression levels spanning three orders of magnitude. Modeling supported a mechanism where uORFs shunt the flow of ribosomes away from the downstream protein-coding ORF. With a lower translation initiation rate at the uORF, more ribosomes "leak" past the uORF; consequently, more ribosomes are able to reach and translate the downstream ORF. We report expression control by engineering uORFs and translation initiation to be robust, predictable, and reproducible across all cell types tested. We propose control of translation initiation as a primary method of choice for tuning expression in mammalian systems.
| S-EPMC3710870 | biostudies-other
Project description:BACKGROUND: Upstream open reading frames (uORFs) can down-regulate the translation of the main open reading frame (mORF) through two broad mechanisms: ribosomal stalling and reducing reinitiation efficiency. In distantly related plants, such as rice and Arabidopsis, it has been found that conserved uORFs are rare in these transcriptomes with approximately 100 loci. It is unclear how prevalent conserved uORFs are in closely related plants. RESULTS: We used a homology-based approach to identify conserved uORFs in five cereals (monocots) that could potentially regulate translation. Our approach used a modified reciprocal best hit method to identify putative orthologous sequences that were then analysed by a comparative R-nomics program called uORFSCAN to find conserved uORFs. CONCLUSION: This research identified new genes that may be controlled at the level of translation by conserved uORFs. We report that conserved uORFs are rare (<150 loci contain them) in cereal transcriptomes, are generally short (less than 100 nt), highly conserved (50% median amino acid sequence similarity), position independent in their 5'-UTRs, and their start codon context and the usage of rare codons for translation does not appear to be important.
| S-EPMC2527020 | biostudies-literature
Project description:Post-transcriptional control has emerged as a major regulatory event in gene expression and often occurs at the level of translation initiation. Although overexpression or constitutive activation of tyrosine kinases (TKs) through gene amplification, translocation or mutation are well-characterized oncogenic events, current knowledge about translational mechanisms of TK activation is scarce. Here, we report the presence of translational cis-regulatory upstream open reading frames (uORFs) in the majority of transcript leader sequences of human TK mRNAs. Genetic ablation of uORF initiation codons in TK transcripts resulted in enhanced translation of the associated downstream main protein-coding sequences (CDSs) in all cases studied. Similarly, experimental removal of uORF start codons in additional non-TK proto-oncogenes, and naturally occurring loss-of-uORF alleles of the c-met proto-oncogene (MET) and the kinase insert domain receptor (KDR), was associated with increased CDS translation. Based on genome-wide sequence analyses we identified polymorphisms in 15.9% of all human genes affecting uORF initiation codons, associated Kozak consensus sequences or uORF-related termination codons. Together, these data suggest a comprehensive role of uORF-mediated translational control and delineate how aberrant induction of proto-oncogenes through loss-of-function mutations at uORF initiation codons may be involved in the etiology of cancer. We provide a detailed map of uORFs across the human genome to stimulate future research on the pathogenic role of uORFs.
| S-EPMC4820681 | biostudies-literature
Project description:Specific sequences of certain nascent peptides cause programmed ribosomal arrest during mRNA translation to control gene expression. In eukaryotes, most known regulatory arrest peptides are encoded by upstream open reading frames (uORFs) present in the 5'-untranslated region of mRNAs. However, to date, a limited number of eukaryotic uORFs encoding arrest peptides have been reported. Here, we searched for arrest peptide-encoding uORFs among Arabidopsis thaliana uORFs with evolutionarily conserved peptide sequences. Analysis of in vitro translation products of 22 conserved uORFs identified three novel uORFs causing ribosomal arrest in a peptide sequence-dependent manner. Stop codon-scanning mutagenesis, in which the effect of changing the uORF stop codon position on the ribosomal arrest was examined, and toeprint analysis revealed that two of the three uORFs cause ribosomal arrest during translation elongation, whereas the other one causes ribosomal arrest during translation termination. Transient expression assays showed that the newly identified arrest-causing uORFs exerted a strong sequence-dependent repressive effect on the expression of the downstream reporter gene in A. thaliana protoplasts. These results suggest that the peptide sequences of the three uORFs identified in this study cause ribosomal arrest in the uORFs, thereby repressing the expression of proteins encoded by the main ORFs.
| S-EPMC5587730 | biostudies-literature
Project description:BackgroundSome upstream open reading frames (uORFs) regulate gene expression (i.e., they are functional) and can play key roles in keeping organisms healthy. However, how uORFs are involved in gene regulation is not yet fully understood. In order to get a complete view of how uORFs are involved in gene regulation, it is expected that a large number of experimentally verified functional uORFs are needed. Unfortunately, wet-experiments to verify that uORFs are functional are expensive.ResultsIn this paper, a new computational approach to predicting functional uORFs in the yeast Saccharomyces cerevisiae is presented. Our approach is based on inductive logic programming and makes use of a novel combination of knowledge about biological conservation, Gene Ontology annotations and genes' responses to different conditions. Our method results in a set of simple and informative hypotheses with an estimated sensitivity of 76%. The hypotheses predict 301 further genes to have 398 novel functional uORFs. Three (RPC11, TPK1, and FOL1) of these 301 genes have been hypothesised, following wet-experiments, by a related study to have functional uORFs. A comparison with another related study suggests that eleven of the predicted functional uORFs from genes LDB17, HEM3, CIN8, BCK2, PMC1, FAS1, APP1, ACC1, CKA2, SUR1, and ATH1 are strong candidates for wet-lab experimental studies.ConclusionsLearning based prediction of functional uORFs can be done with a high sensitivity. The predictions made in this study can serve as a list of candidates for subsequent wet-lab verification and might help to elucidate the regulatory roles of uORFs.
| S-EPMC2813248 | biostudies-literature
Project description:BACKGROUND:RNA secondary structures in the 5'-untranslated regions (5'-UTR) of mRNAs are key to the post-transcriptional regulation of gene expression. While it is evident that non-canonical Hoogsteen-paired G-quadruplex (rG4) structures somehow contribute to the regulation of translation initiation, the nature and extent of human mRNAs that are regulated by rG4s is not known. Here, we provide new insights into a mechanism by which rG4 formation modulates translation. RESULTS:Using transcriptome-wide ribosome profiling, we identify rG4-driven mRNAs in HeLa cells and reveal that rG4s in the 5'-UTRs of inefficiently translated mRNAs associate with high ribosome density and the translation of repressive upstream open reading frames (uORF). We demonstrate that depletion of the rG4-unwinding helicases DHX36 and DHX9 promotes translation of rG4-associated uORFs while reducing the translation of coding regions for transcripts that comprise proto-oncogenes, transcription factors and epigenetic regulators. Transcriptome-wide identification of DHX9 binding sites shows that reduced translation is mediated through direct physical interaction between the helicase and its rG4 substrate. CONCLUSION:This study identifies human mRNAs whose translation efficiency is modulated by the DHX36- and DHX9-dependent folding/unfolding of rG4s within their 5'-UTRs. We reveal a previously unknown mechanism for translation regulation in which unresolved rG4s within 5'-UTRs promote 80S ribosome formation on upstream start codons, causing inhibition of translation of the downstream main open reading frames. Our findings suggest that the interaction of helicases with rG4s could be targeted for future therapeutic intervention.
| S-EPMC6307142 | biostudies-literature
Project description:Upstream open reading frames (uORFs) initiate translation within mRNA 5’ leaders,and have the potential to altermain coding sequence(CDS) translationontranscripts in which they reside. Ribosome profiling(RP)studies suggest that translating ribosomes are pervasive within 5’ leadersacross model systems. However, the significance of this observationremains unclear. To explore a role for uORF usage in neuronal differentiation, we performed RP on undifferentiated and differentiated human neuroblastoma cells. Using a spectral coherence algorithm (SPECtre),we identify4,954uORFsacross31%of all neuroblastoma transcripts. These uORFspredominantly utilize non-AUG initiationcodonsand exhibit translational efficiencies(TE)comparable to annotated coding regions. Usage of both AUG initiated uORFs and aconservedandconsistently translated subset of non-AUG initiated uORFs correlateswith repressed CDS translation. Ribosomal protein transcripts are enriched in uORFs, and select uORFs on such transcripts were validated for expression. Withneuronal differentiation, we observedan overall positive correlation between translational shifts in uORF/CDSpairs. However,a subset of transcripts exhibit inverse shifts in translation of uORF/CDSpairs. TheseuORFsare enriched in AUG initiation sites, non-overlapping, and shorterin length. Cumulatively, CDSs downstream of uORFs characterized by persistent translation show smaller shifts in TE withneuronal differentiation relative to CDSs without a predicted uORF, suggesting that fluctuations in CDS translation are buffered by uORF translation. In sum, this work provides insights into the dynamic relationshipsand potential regulatory functionsof uORF/CDS pairs in a model of neuronal differentiation.
2018-09-07 | GSE119615 | GEO
Project description:Translational control is a key determinant of protein abundance, which in turns defines the physiology and pathology of human cells. Initiation of translation is highly regulated in eukaryotes and is considered as the rate-limiting step of protein synthesis. mRNA secondary structures in 5’ untranslated region (UTR) and associated helicases have been characterised as key determinants of translation initiation. Nevertheless the transcriptome-wide contribution of non-canonical secondary structures, such as RNA G-quadruplexes (rG4s), to the translation of human mRNAs remains largely unappreciated. Here we use a ribosome profiling strategy to investigate the translational landscape associated to rG4s-containing mRNAs and the contribution of two rG4s-specialised DExH-box helicases, DHX9 and DHX36, to translation initiation in human cells. We show that rG4-forming sequences in 5’-UTR is associated with decreased translation efficiency which correlate with an increased ribosome density within the 5’-UTRs. We found that rG4s contribute to the translation of upstream open reading frames, and as a consequence, thwart the translation of the associated protein coding sequences (CDS). Depletion of the DHX36 and DHX9 helicases demonstrated that the formation of the rG4 structural motif rather than its nucleotide sequence mediate translation initiation. Our findings unveil a role for non-canonical structures in defining alternative 5’ starts for human mRNAs translation initiation.
2018-04-30 | GSE105082 | GEO
Project description:BackgroundUpstream open reading frames (uORFs) initiate translation within mRNA 5' leaders, and have the potential to alter main coding sequence (CDS) translation on transcripts in which they reside. Ribosome profiling (RP) studies suggest that translating ribosomes are pervasive within 5' leaders across model systems. However, the significance of this observation remains unclear. To explore a role for uORF usage in a model of neuronal differentiation, we performed RP on undifferentiated and differentiated human neuroblastoma cells.ResultsUsing a spectral coherence algorithm (SPECtre), we identify 4954 consistently translated uORFs across 31% of all neuroblastoma transcripts. These uORFs predominantly utilize non-AUG initiation codons and exhibit translational efficiencies (TE) comparable to annotated coding regions. On a population basis, the global impact of both AUG and non-AUG initiated uORFs on basal CDS translation were small, even when analysis is limited to conserved and consistently translated uORFs. However, uORFs did alter the translation of a subset of genes, including the Diamond-Blackfan Anemia associated ribosomal gene RPS24. With retinoic acid induced differentiation, we observed an overall positive correlation in translational shifts between uORF/CDS pairs. However, CDSs downstream of uORFs show smaller shifts in TE with differentiation relative to CDSs without a predicted uORF, suggesting that uORF translation buffers cell state dependent fluctuations in CDS translation.ConclusionThis work provides insights into the dynamic relationships and potential regulatory functions of uORF/CDS pairs in a model of neuronal differentiation.
| S-EPMC6528255 | biostudies-literature