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Role of DDX3X in translation regulation in acute ER stress

ABSTRACT: In eukaryotes, regulation of mRNA translation initiation greatly impacts gene expression, and is critical for cellular stress responses. DDX3X is a ubiquitous DEAD-box RNA helicase whose precise role in 5´ UTR scanning and start codon decoding in non-stressed and stressed cells is still elusive. Here we show that DDX3X engages with thousands of mRNAs as part of the 48S scanning complex, simultaneously acting to promote or suppress translation of select mRNAs in non-stressed conditions, and switches this regulation in opposite directions to establish a stress response translational program upon acute ER stress. We find distinct DDX3X binding patterns of differentially regulated mRNAs, which lead us to identify N4-acetylation of cytidines surrounding the start codon as a crucial feature for DDX3X-mediated selective regulation. Our findings highlight a novel co-dependence between an RNA helicase and a post-transcriptional modification in regulating mRNA translation

ORGANISM(S): Homo sapiens

PROVIDER: GSE282245 | GEO | 2025/06/09

REPOSITORIES: GEO

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Role of DDX3X in translation regulation in acute ER stress [mouse]

Project description:In eukaryotes, regulation of mRNA translation initiation greatly impacts gene expression, and is critical for cellular stress responses. DDX3X is a ubiquitous DEAD-box RNA helicase whose precise role in 5´ UTR scanning and start codon decoding in non-stressed and stressed cells is still elusive. Here we show that DDX3X engages with thousands of mRNAs as part of the 48S scanning complex, simultaneously acting to promote or suppress translation of select mRNAs in non-stressed conditions, and switches this regulation in opposite directions to establish a stress response translational program upon acute ER stress. We find distinct DDX3X binding patterns of differentially regulated mRNAs, which lead us to identify N4-acetylation of cytidines surrounding the start codon as a crucial feature for DDX3X-mediated selective regulation. Our findings highlight a novel co-dependence between an RNA helicase and a post-transcriptional modification in regulating mRNA translation

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Project description:We have developed a deep sequencing-based approach, Rec-Seq, that allows simultaneous monitoring of ribosomal 48S pre-initiation complex (PIC) formation on every mRNA in the translatome in an in vitro reconstituted system. Rec-Seq isolates key early steps in translation initiation in the absence of all other cellular components and processes. Using this approach we show that the DEAD-box ATPase Ded1 promotes 48S PIC formation on the start codons of >1000 native mRNAs, most of which have long, structured 5’-untranslated regions (5’UTRs). Remarkably, initiation measured in Rec-Seq was enhanced by Ded1 for most mRNAs previously shown to be highly Ded1-dependent by ribosome profiling of ded1 mutants in vivo, demonstrating that the core translation functions of the factor are recapitulated in the purified system. Our data do not support a model in which Ded1acts by reducing initiation at start codons in 5’UTRs and instead indicate it functions by directly promoting mRNA recruitment to the 43S PIC and scanning to locate the start codon. We also provide evidence that eIF4A, another essential DEAD-box initiation factor, is required for efficient PIC assembly on almost all mRNAs, regardless of their structural complexity, in contrast to the preferential stimulation by Ded1 of initiation on mRNAs with long, structured 5’UTRs.

2023-10-03 | GSE244093 | GEO

The DEAD-box RNA helicase Ded1 is a translation-elongation factor

Project description:DEAD-box RNA helicases are ATP-dependent RNA binding proteins and RNA-dependent ATPases that possess weak, nonprocessive unwinding activity in vitro, but they can form long-lived complexes on RNAs when the ATPase activity is inhibited. Ded1 is a yeast DEAD-box protein, the functional ortholog of mammalian DDX3, that is considered important for the scanning efficiency of the 48S pre-initiation complex ribosomes to the AUG start codon. We used a modified PAR-CLIP technique, which we call quicktime PAR-CLIP (qtPAR-CLIP) to crosslink Ded1 to 4-thiouridine-incorported RNAs in vivo using UV light centered at 365 nm. The irradiation conditions are largely benign to the yeast cells and to Ded1, and we are able to obtain a high efficiency of crosslinking under physiological conditions. We find that Ded1 forms crosslinks on the open reading frames of many different mRNAs, but it forms the most extensive interactions on a relatively few mRNAs, and particularly on mRNAs encoding certain ribosomal proteins and translation factors. Under glucose-depletion conditions the crosslinking pattern shifts to mRNAs encoding metabolic and stress-related proteins, which reflects the altered translation. These data are consistent with Ded1 functioning in the regulation of translation elongation, perhaps by pausing or stabilizing the ribosomes through its ATP-dependent binding.

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Project description:Aberrant translation initiation at non-AUG start codons is associated with multiple cancers and neurodegenerative diseases. Nevertheless, how non-AUG translation is regulated differently from canonical translation is poorly understood. We thus used start codon-selective reporters and ribosome profiling to characterize how translation from non-AUG start codons responds to protein synthesis inhibitors in human cells. These analyses surprisingly revealed that translation of non-AUG reporters and the endogenous GUG-encoded DAP5 (eIF4G2/p97) mRNA are resistant to cycloheximide (CHX), a translation inhibitor which slows but does not completely abrogate elongation. Our data suggest that slowly elongating ribosomes cause queuing of scanning pre-initiation complexes (PIC), preferentially enhancing otherwise poor recognition of non-AUG start codons. Consistent with this model, limiting PIC formation or scanning sensitizes non-AUG translation to CHX. Moreover, PIC queuing can cause translation from an AUG codon in a poor context to become less sensitive to CHX. We further find that non-AUG translation is resistant to other inhibitors that target ribosomes within the coding sequence, but not those targeting newly initiated ribosomes. In total, these data indicate that ribosome queuing enables mRNAs with poor initiation context, namely those from non-AUG start codons, to be resistant to pharmacological inhibitors.

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DDX3X regulation of global translation is impaired by medulloblastoma-associated mutations [CLIP-Seq]

Project description:Whole-genome sequencing recently identified recurrent missense mutations in the RNA helicase DDX3X in pediatric medulloblastoma (MB) and other tumors. The normal function of DDX3X is poorly understood, and the consequences of its cancer-associated mutations have not been explored. Here we used genomic, biochemical, cell biological, and animal modeling approaches to investigate normal DDX3X function and the impact of cancer-associated DDX3X mutations. Cross-linking immunoprecipitation–high-throughput sequencing (CLIPseq) analyses revealed that DDX3X binds primarily to ~1000 mature mRNA targets at binding sites spanning the full mRNA length; their enrichment in the coding regions suggests that DDX3X plays a role in translational elongation. The association of wild-type DDX3X with polysomes is consistent with this observation. Cancer-associated mutations result in loss of DDX3X from polysomes and accumulation of mutant DDX3X in stress granules (cytoplasmic accumulations of translationally arrested mRNAs). Mutation-dependent redistribution of DDX3X to stress granules is also observed in a Drosophila model system and in MB tumor cells from patients carrying DDX3X mutations. Importantly, mRNAs targeted by DDX3X are enriched in translation factors, suggesting that DDX3X regulates translation both directly and indirectly. Indeed, depletion of DDX3X by RNAi or over-expression of mutant DDX3X significantly impairs global protein synthesis. Ribosome profiling confirmed this observation and showed a 5’ bias in ribosomal occupancy, further confirming the role of DDX3X in translational elongation. Together, our data show that DDX3X is a key regulator of translation and that this function is impaired by cancer-associated mutations. Finally, we found that medulloblastoma-related mutant DDX3X can efficiently bind the wild-type form suggesting that mutant DDX3X could exert a dominant negative effect in vivo.

2016-05-20 | GSE59094 | GEO

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