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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.

2024-11-01 | PXD051482 | Pride

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.

2019-04-01 | GSE124790 | GEO

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

2019-04-01 | GSE116221 | 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

Project description:The fidelity of start codon recognition by ribosomes is paramount during protein synthesis. The textbook knowledge of eukaryotic translation initiation depicts 5’→3’ unidirectional migration of the pre-initiation complex (PIC) along the 5’UTR. In probing translation initiation from ultra-short 5’UTR, we report that an AUG triplet near the 5’ end can be selected via PIC backsliding. The bi-directional ribosome scanning is supported by competitive selection of closely spaced AUG codons and recognition of two initiation sites flanking an internal ribosome entry site. Transcriptome-wide PIC profiling reveals footprints with an oscillation pattern near the 5’ end and start codons. Depleting the RNA helicase eIF4A leads to reduced PIC oscillations and impaired selection of 5’ end start codons. Enhancing the ATPase activity of eIF4A promotes nonlinear PIC scanning and stimulates upstream translation initiation. The helicase-mediated PIC conformational switch may provide an operational mechanism that unifies ribosome recruitment, scanning, and start codon selection.

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

Project description:Regulated start-codon selection has the potential to reshape the proteome through the differential production of upstream open reading frames, canonical proteins, and alternative translational isoforms. However, conditions under which start codon selection is altered remain poorly defined. Here, using transcriptome-wide translation-initiation-site profiling, we reveal a global increase in the stringency of start-codon selection during mammalian mitosis. Low-efficiency initiation sites are preferentially repressed in mitosis, resulting in pervasive changes in the translation of thousands of start sites and their corresponding protein products. This enhanced stringency of start-codon selection during mitosis results from increased association between the 40S ribosome and the key regulator of start-codon selection, eIF1. We find that increased eIF1–40S ribosome interaction during mitosis is mediated by the release of a nuclear pool of eIF1 upon nuclear envelope breakdown. Selectively depleting the nuclear pool of eIF1 eliminates the change to translational stringency during mitosis, resulting in altered synthesis of thousands of protein isoforms. In addition, preventing mitotic translational rewiring results in substantially increased cell death and decreased mitotic slippage in cells that experience a mitotic delay induced by anti-mitotic chemotherapies. Thus, cells globally control stringency of translation initiation, which has critical roles during the mammalian cell cycle in preserving mitotic cell physiology.

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

eIF1 discriminates against suboptimal initiation sites to prevent excessive uORF translation genome-wide

Project description:The translation pre-initiation complex (PIC) scans the mRNA for an AUG codon in favorable context. Previous findings suggest that the factor eIF1 discriminates against non-AUG start codons by impeding full accommodation of Met-tRNAi in the P site of the 40S ribosomal subunit, necessitating eIF1 dissociation for start codon selection. Consistent with this, yeast eIF1 substitutions that weaken its binding to the PIC increase initiation at UUG codons on a mutant his4 mRNA and particular synthetic mRNA reporters; and also at the AUG start codon of the mRNA for eIF1 itself owing to its poor Kozak context. It was not known however whether such eIF1 mutants increase initiation at suboptimal start codons genome-wide. By ribosome profiling, we show that the eIF1-L96P variant confers increased translation of numerous upstream open reading frames (uORFs) initiating with either near-cognate codons (NCCs) or AUGs in poor context. The increased uORF translation is frequently associated with reduced translation of the downstream main coding sequences (CDS). Initiation is also elevated at the NCCs initiating N-terminal extensions on GRS1 and ALA1 mRNAs, and at a small set of main CDS AUG codons with especially poor context, including that of eIF1 itself. Thus, eIF1 acts throughout the yeast translatome to discriminate against NCC start codons and AUGs in poor context; and impairing this function enhances the repressive effects of uORFs on CDS translation and alters the ratios of protein isoforms translated from near-cognate versus AUG start codons.

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