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Ribosome profiling analysis of Denr and Eif2d depleted cells reveals the absence of re-initiation function of EIF2D

ABSTRACT: Among the transcript features that regulate translation rate, upstream open reading frames (uORFs) have emerged as a major class of inhibitory elements which limit how many scanning ribosomes reach the start codon of the main protein coding sequence (CDS). Two processes are implicated in ensuring that CDS translation of uORF-containing transcripts can take place nevertheless: first, leaky-scanning, which involves the bypassing of uORF start codons by the scanning 40S ribosome, and second, re-initiation (REI), which allows the 40S subunit of the ribosome that terminated on the uORF stop codon to resume scanning to reach a downstream start codon. REI has remained particularly enigmatic, as it is at odds with generally accepted principles of conventional translation initiation, termination and post-termination subunit recycling. MCTS1-DENR is the first re-initiation-specific factor that has been identified. Its homolog, EIF2D, is assumed to act in uORF REI as well, yet formal proof of EIF2D-mediated REI has remained scarce. In our study, we present our in vivo analyses of DENR and EIF2D in translation re-initiation in mammalian cells. At the transcriptome-wide scale, ribosome profiling clearly identifies DENR-dependent REI, yet disproves the assumption that EIF2D also functions as a REI-factor.

ORGANISM(S): Mus musculus

PROVIDER: GSE263991 | GEO | 2024/10/30

REPOSITORIES: GEO

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Identification of DENR-interacting proteins in NIH3t3 cells using a co-IP MS-MS approach on endogenously tagged DENR.

Project description:Among the transcript features that regulate translation rate, upstream open reading frames (uORFs) have emerged as a major class of inhibitory elements which limit how many scanning ribosomes reach the start codon of the main protein coding sequence (CDS). Two processes are implicated in ensuring that CDS translation of uORF-containing transcripts can take place nevertheless: first, leaky-scanning, which involves the bypassing of uORF start codons by the scanning 40S ribosome, and second, re-initiation (REI), which allows the 40S subunit of the ribosome that terminated on the uORF stop codon to resume scanning to reach a downstream start codon. REI has remained particularly enigmatic, as it is at odds with generally accepted principles of conventional translation initiation, termination and post-termination subunit recycling. The heterodimer MCTS1-DENR is the first re-initiation-specific factor that has been identified. MCTS1 has been described as the only obligatory partner of DENR. Nevertheless, MCTS1 depletion phenotypes do not always copy the phenotype of DENR depletion in mammalian cells, suggesting that another partner could compensate for the lack of MCTS1. We performed co-immunoprecipitation followed by MS-MS analysis of endogenously FLAG-tagged DENR and identified MCTS2 as a new protein partner. MCTS2 is a homolog and retrogene copy of MCTS1. Downstream analyses demonstrated that MCTS2-DENR was able to promote re-initiation in vitro and showed that Mcts2 mRNA was highly abundant and the protein at least as efficiently synthesized as MCTS1 in NIH3t3 cells, implying that MCTS2 might be the main expressed variant in certain cell types.

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Charting DENR-dependent translation reinitiation uncovers predictive uORF features and links to circadian timekeeping via Clock

Project description:The non-canonical initiation factor DENR promotes translation reinitiation on uORF-containing mRNAs. Moreover, DENR depletion shortens circadian period in mouse fibroblasts, suggesting that uORF usage and reinitiation regulate clock function. To identify DENR-regulated translation events transcriptome-wide and, in particular, specific core clock transcripts affected by this mechanism, we have used ribosome profiling in DENR-deficient NIH3T3 cells. We found 240 transcripts with altered translation rate, and used linear regression analysis to extract uORF features predictive of DENR dependance. Among core clock genes, we identified Clock as a DENR target. Using Clock 5'UTR mutants, we mapped the specific uORF through which DENR acts to regulate CLOCK protein biosynthesis. Notably, these experiments identified an alternative downstream start codon, which likely represents the true CLOCK N-terminus. Our findings provide insights into uORF-mediated translational regulation that can regulate the mammalian circadian clock and gene expression at large.

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Charting DENR-dependent translation reinitiation uncovers predictive uORF features and links to circadian timekeeping via Clock

2019-04-01 | GSE124790 | GEO

Tma64 (eIF2D), Tma20 (MCT-1), and Tma22 (DENR) recycle post-termination 40S subunits in vivo

Project description:The recycling of ribosomal subunits after translation termination is critical for efficient gene expression. Tma64 (eIF2D), Tma20 (MCT-1), and Tma22 (DENR) function as 40S recycling factors in vitro, but it is unknown whether they perform this function in vivo or serve as alternative initiation factors. Ribosome profiling of strains missing these factors revealed 80S ribosomes queued behind the stop codon, consistent with a block in 40S recycling. We found that unrecycled ribosomes could reinitiate translation at AUG codons in the 3’UTR, as evidenced by peaks in the footprint data and 3’UTR reporter analysis. In vitro translation experiments using reporter mRNAs containing upstream ORFs (uORFs) further established that reinitiation increased in the absence of these proteins. In some cases, 40S ribosomes appeared to rejoin with 60S subunits and undergo an alternative 80S reinitiation process in 3’UTRs. These results support a crucial role for Tma64, Tma20, and Tma22 in the recycling of 40S ribosomal subunits at stop codons and translation reinitiation.

2018-08-30 | GSE108942 | GEO

Reprogramming of translation in yeast cells impaired for ribosome recycling favors short, efficiently translated mRNAs

Project description:Yeast strains lacking orthologs of mammalian eIF2D (Tma64), and either MCT-1 (Tma20) or DENR (Tma22) are broadly impaired for 40S recycling; however, it was unknown whether this defect leads to reduced 43S PIC levels with an impact on translation of particular mRNAs. To test this, we by combined ribosome footprint profiling with RNA-seq analysis of mRNA abundance.

2021-03-31 | GSE166987 | GEO

Bi-directional ribosome scanning controls the stringency of start codon selection

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2021-11-24 | GSE176058 | GEO

40S ribosome profiling reveals distinct roles for Tma20/Tma22 (MCT-1/DENR) and Tma64 (eIF2D) in 40S subunit recycling

Project description:The recycling of ribosomes at stop codons for use in further rounds of translation is critical for efficient protein synthesis. Removal of the 60S subunit is catalyzed by the ATPase Rli1 (ABCE1) while removal of the 40S is thought to require Tma64 (eIF2D), Tma20 (MCT-1), and Tma22 (DENR). However, it remains unclear how these Tma proteins cause 40S removal and control reinitiation of downstream translation. Here we developed an enhanced 40S ribosome footprinting strategy to directly observe intermediate steps of ribosome recycling in cells. Deletion of the genes encoding these Tma proteins resulted in broad accumulation of unrecycled 40S subunits at stop codons, directly establishing their role in 40S recycling. Furthermore, the Tma20/Tma22 heterodimer was responsible for a majority of 40S recycling events while Tma64 played a minor role. Introduction of an autism-associated mutation into TMA22 resulted in a loss of 40S recycling activity, linking ribosome recycling and neurological disease.

2021-03-01 | GSE145904 | GEO

Nuclear release of eIF1 restricts start-codon selection during mitosis

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2023-12-02 | GSE230189 | GEO

Master stress response gene ATF4 & other oncogenes are translated by DENR-dependent reinitiation

Project description:Translation efficiency varies 1000-fold between different mRNAs, thereby strongly impacting protein expression. Translation of the master stress response gene ATF4 increases in response to stress, but the molecular mechanisms are not well understood. We discover here that translation initiation factors DENR, MCTS1 and eIF2D are absolutely required to induce ATF4 translation upon stress, by promoting translation reinitiation on the ATF4 5’UTR. Hence DENR and MCTS1 are important players in the cellular Integrated Stress Response. We find DENR and MCTS1 promote reinitiation after long uORFs with specific penultimate codons, due to the tRNA that remains attached to 40S ribosomes after translation termination. This provides a model for how DENR and MCTS1 promote translation reinitiation. Since cancer cells are exposed to many stresses, they require ATF4 for survival and proliferation. We find a strong correlation between DENR•MCTS1 expression and ATF4 activity across cancers. Additional oncogenes including a-Raf, c-Raf and Cdk4 have long uORFs and are translated in a DENR•MCTS1 dependent manner. This explains in part why DENR and MCTS1 are oncogenes.

2020-07-18 | GSE140084 | GEO

eIF3 associates with 80S ribosomes to promote translation elongation, mitochondrial homeostasis, and muscle health

Project description:eIF3 is a multi-subunit complex thought to execute numerous functions in canonical translation initiation, including mRNA recruitment to the 40S ribosome, scanning for the start codon, and inhibition of 60S subunit joining 1–3. eIF3 was also found to interact with 40S and 60S ribosomal proteins and translation elongation factors 4, but a direct involvement in translation elongation has never been demonstrated. Using selective ribosome profiling, we made the unexpected observation that eIF3 remains bound to post-initiation 80S ribosomes, followed by release after translation of ~50 codons. Furthermore, eIF3 deficiency reduces early ribosomal elongation speed, particularly on mRNAs encoding proteins associated with membrane-associated functions, resulting in defective synthesis of their encoded proteins and abnormal mitochondrial and lysosomal physiology. Accordingly, heterozygous eIF3e+/- knockout mice accumulate giant mitochondria in skeletal muscle and show a progressive decline in muscle strength with age. Hence, in addition to its canonical role in translation initiation, eIF3 interacts with 80S ribosomes to enhance, at the level of early elongation, the synthesis of proteins with membrane-associated functions, an activity that is critical for normal muscle health.

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