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Cap-proximal nucleotides via differential eIF4E binding and alternative promoter usage mediate translational response to energy stress

ABSTRACT: Transcription and translation are highly energy consuming processes and both are modulated by the intracellular energy status. Transcription start site (TSS) selection and alternative promoter (AP) usage contribute to the complexity of gene expression but little is known about their impact on translation in response to metabolic deficiencies. Here we performed TSS mapping of the translatome following energy stress. We assessed the contribution of cap-proximal TSS nucleotides and strikingly found dramatic effect on translation only upon stress. As eIF4E levels were reduced, we analyzed its binding to capped-RNAs with different initiating nucleotides and found differential affinity, the lowest being for 5’cytidine, in correlation with the translational response. In addition the number of differentially translated APs was highly elevated following energy stress, suggesting that AP usage is central to the stress response. These include novel glucose-starvation-induced downstream promoters for the translation regulators eIF4A and Pabp which are translationally-induced despite the general translational inhibition. The resultant eIF4A protein is N-terminally truncated and acts as eIF4A inhibitor. The induced Pabp isoform has shorter 5'UTR removing an auto-inhibitory element. These findings uncovered several levels of coordination of transcription and translation responses to energy stress.

ORGANISM(S): Mus musculus

PROVIDER: GSE93981 | GEO | 2017/01/25

SECONDARY ACCESSION(S): PRJNA362999

REPOSITORIES: GEO

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Project description:DEAD-box RNA helicases eIF4A and Ded1 are believed to promote translation initiation by resolving mRNA secondary structures that impede ribosome attachment at the mRNA 5’ end or subsequent scanning of the 5’UTR, but whether they perform distinct functions or act redundantly in vivo is poorly understood. We compared the effects of mutations in Ded1 or eIF4A on global translational efficiencies (TEs) in yeast by ribosome footprint profiling. Despite similar reductions in bulk translation, inactivation of a cold-sensitive Ded1 mutant substantially reduced the TEs of >600 mRNAs, whereas inactivation of a temperature-sensitive eIF4A mutant yielded <40 similarly impaired mRNAs. The broader requirement for Ded1 did not reflect more pervasive secondary structures at low temperature, as inactivation of temperature-sensitive and cold-sensitive ded1 mutants gave highly correlated results. Interestingly, Ded1-dependent mRNAs exhibit greater than average 5’UTR length and propensity for secondary structure, implicating Ded1 in scanning though structured 5' UTRs. Reporter assays confirmed that cap- distal stem-loop insertions increase dependence on Ded1 but not eIF4A for efficient translation. While only a small fraction of mRNAs is strongly dependent on eIF4A, this dependence is significantly correlated with requirements for Ded1 and 5’UTR features characteristic of Ded1- dependent mRNAs. Our findings suggest that Ded1 is critically required to promote scanning through secondary structures within 5’UTRs; and while eIF4A cooperates with Ded1 in this function, it also promotes a step of initiation common to virtually all yeast mRNAs. We compared the effects of mutations in Ded1 or eIF4A on global translational efficiencies (TEs) in yeast by ribosome footprint profiling.The study includes 32 samples, comprised of 16 mRNA-Seq samples and 16 ribosome footprint profiling samples, derived from biological replicates of 3 mutant strains, ded1-cs, ded1-ts and tif1-ts, and the corresponding wild-type strains. The tif1-ts mutant and its wild-type counterpart were analyzed at 30°C and 37°C.

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Cap-proximal nucleotides via differential eIF4E binding and alternative promoter usage mediate translational response to energy stress

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