MRNA Deadenylation Is Coupled to Translation Rates by the Differential Activities of Ccr4-Not Nucleases.
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ABSTRACT:
SUBMITTER: Webster MW
PROVIDER: S-EPMC6024076 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:The biological significance of deadenylation in global gene expression is not fully understood. Here, we show that the CCR4-NOT deadenylase complex maintains expression of mRNAs, such as those encoding transcription factors, cell cycle regulators, DNA damage response-related proteins, and metabolic enzymes, at appropriate levels in the liver. Liver-specific disruption of Cnot1, encoding a scaffold subunit of the CCR4-NOT complex, leads to increased levels of mRNAs for transcription factors, cell cycle regulators, and DNA damage response-related proteins because of reduced deadenylation and stabilization of these mRNAs. CNOT1 suppression also results in an increase of immature, unspliced mRNAs (pre-mRNAs) for apoptosis-related and inflammation-related genes and promotes RNA polymerase II loading on their promoter regions. In contrast, mRNAs encoding metabolic enzymes become less abundant, concomitant with decreased levels of these pre-mRNAs. Lethal hepatitis develops concomitantly with abnormal mRNA expression. Mechanistically, the CCR4-NOT complex targets and destabilizes mRNAs mainly through its association with Argonaute 2 (AGO2) and butyrate response factor 1 (BRF1) in the liver. Therefore, the CCR4-NOT complex contributes to liver homeostasis by modulating the liver transcriptome through mRNA deadenylation.
| S-EPMC7119370 | biostudies-literature
Project description:Complete cytoplasmic polyadenosine tail (polyA-tail) deadenylation is thought to be essential for initiating mRNA decapping and subsequent degradation. To investigate this prevalent model, we conducted direct RNA sequencing of S. cerevisiae mRNAs derived from chase experiments under steady-state and stress condition. Subsequently, we developed a numerical model based on a modified gamma distribution function, which estimated the transcriptomic deadenylation rate at 10 A/min. A simplified independent method, based on the delineation of quantile polyA-tail values, showed a correlation between the decay and deadenylation rates of individual mRNAs, which appeared consistent within functional transcript groups and associated with codon optimality. Notably, these rates varied during the stress response. Detailed analysis of ribosomal protein-coding mRNAs (RPG mRNAs), constituting 40 % of the transcriptome, singled out this transcript group. While deadenylation and decay of RPG mRNAs accelerated under heat stress, their degradation could proceed even when deadenylation was blocked, depending entirely on ongoing nuclear export. Our findings support the general primary function of deadenylation in dictating the onset of decapping, while also demonstrating complex relations between these processes.
| S-SCDT-10_1038-S44318-024-00258-3 | biostudies-other
Project description:The earliest step in the mRNA degradation process is deadenylation, a progressive shortening of the mRNA poly(A) tail by deadenylases. The question of when deadenylation takes place remains open. MYC mRNA is one of the rare examples for which it was proposed a shortening of the poly(A) tail during ongoing translation. In this study, we analyzed the poly(A) tail length distribution of various mRNAs, including MYC mRNA. The mRNAs were isolated from the polysomal fractions of polysome profiling experiments and analyzed using ligase-mediated poly(A) test analysis. We show that, for all the mRNAs tested with the only exception of MYC, the poly(A) tail length distribution does not change in accordance with the number of ribosomes carried by the mRNA. Conversely, for MYC mRNA, we observed a poly(A) tail length decrease in the fractions containing the largest polysomes. Because the fractions with the highest number of ribosomes are also those for which translation termination is more frequent, we analyzed the poly(A) tail length distribution in polysomal fractions of cells depleted in translation termination factor eRF3. Our results show that the shortening of MYC mRNA poly(A) tail is alleviated by the silencing of translation termination factor eRF3. These findings suggest that MYC mRNA is co-translationally deadenylated and that the deadenylation process requires translation termination to proceed.
| S-EPMC5995228 | biostudies-literature
Project description:The CCR4-NOT complex is the major enzyme catalyzing mRNA deadenylation in Saccharomyces cerevisiae. We have identified homologs for almost all subunits of this complex in the Drosophila genome. Biochemical fractionation showed that the two likely catalytic subunits, CCR4 and CAF1, were associated with each other and with a poly(A)-specific 3' exonuclease activity. In Drosophila, the CCR4 and CAF1 proteins were ubiquitously expressed and present in cytoplasmic foci. Individual knock-down of several potential subunits of the Drosophila CCR4-NOT complex by RNAi in tissue culture cells led to a lengthening of bulk mRNA poly(A) tails. Knock-down of two individual subunits also interfered with the rapid deadenylation of Hsp70 mRNA during recovery from heat shock. Similarly, ccr4 mutant flies had elongated bulk poly(A) and a defect in Hsp70 mRNA deadenylation. A minor increase in bulk poly(A) tail length was also observed in Rga mutant flies, which are affected in the NOT2 subunit. The data show that the CCR4-NOT complex is conserved in Drosophila melanogaster and plays a role in general and regulated mRNA deadenylation.
| S-EPMC514940 | biostudies-literature
Project description:The CAF1 protein is a component of the CCR4-NOT deadenylase complex. While yeast CAF1 displays deadenylase activity, this activity is not required for its deadenylation function in vivo, and CCR4 is the primary deadenylase in the complex. In order to identify CAF1-specific functional regions required for deadenylation in vivo, we targeted for mutagenesis six regions of CAF1 that are specifically conserved among CAF1 orthologs. Defects in residues 213-215, found to be a site required for binding CCR4, reduced the rate of deadenylation to a lesser extent and resulted in in vivo phenotypes that were less severe than did defects in other regions of CAF1 that displayed greater contact to CCR4. These results imply that CAF1, while affecting deadenylation through its contact to CCR4, has functions in deadenylation separate from its contact to CCR4. Synthetic lethalities of caf1Delta, but not that of ccr4Delta, with defects in DHH1 or PAB1, both of which are involved in translation, further supports a role of CAF1 separate from that of CCR4. Importantly, other mutations in PAB1 that reduced translation, while not affecting deadenylation by themselves or when combined with ccr4Delta, severely blocked deadenylation when coupled with a caf1 deletion. These results indicate that both CAF1 and factors involved in translation are required for deadenylation.
| S-EPMC1888822 | biostudies-other
Project description:CSF-1 mRNA 3'UTR contains multiple unique motifs, including a common microRNA (miRNA) target in close proximity to a noncanonical G-quadruplex and AU-rich elements (AREs). Using a luciferase reporter system fused to CSF-1 mRNA 3'UTR, disruption of the miRNA target region, G-quadruplex, and AREs together dramatically increased reporter RNA levels, suggesting important roles for these cis-acting regulatory elements in the down-regulation of CSF-1 mRNA. We find that nucleolin, which binds both G-quadruplex and AREs, enhances deadenylation of CSF-1 mRNA, promoting CSF-1 mRNA decay, while having the capacity to increase translation of CSF-1 mRNA. Through interaction with the CSF-1 3'UTR miRNA common target, we find that miR-130a and miR-301a inhibit CSF-1 expression by enhancing mRNA decay. Silencing of nucleolin prevents the miRNA-directed mRNA decay, indicating a requirement for nucleolin in miRNA activity on CSF-1 mRNA. Downstream effects followed by miR-130a and miR-301a inhibition of directed cellular motility of ovarian cancer cells were found to be dependent on nucleolin. The paradoxical effects of nucleolin on miRNA-directed CSF-1 mRNA deadenylation and on translational activation were explored further. The nucleolin protein contains four acidic stretches, four RNA recognition motifs (RRMs), and nine RGG repeats. All three domains in nucleolin regulate CSF-1 mRNA and protein levels. RRMs increase CSF-1 mRNA, whereas the acidic and RGG domains decrease CSF-1 protein levels. This suggests that nucleolin has the capacity to differentially regulate both CSF-1 RNA and protein levels. Our finding that nucleolin interacts with Ago2 indirectly via RNA and with poly(A)-binding protein C (PABPC) directly suggests a nucleolin-Ago2-PABPC complex formation on mRNA. This complex is in keeping with our suggestion that nucleolin may work with PABPC as a double-edged sword on both mRNA deadenylation and translational activation. Our findings underscore the complexity of nucleolin's actions on CSF-1 mRNA and describe the dependence of miR-130a- and miR-301a-directed CSF-1 mRNA decay and inhibition of ovarian cancer cell motility on nucleolin.
| S-EPMC3675821 | biostudies-literature
Project description:How fragile X syndrome protein (FMRP) binds mRNAs and regulates mRNA metabolism remains unclear. Our previous work using human neuronal cells focused on mRNAs targeted for nonsense-mediated mRNA decay (NMD), which we showed are generally bound by FMRP and destabilized upon FMRP loss. Here, we identify >400 high-confidence FMRP-bound mRNAs, only ∼35% of which are NMD targets. Integrative transcriptomics together with SILAC-LC-MS/MS reveal that FMRP loss generally results in mRNA destabilization and more protein produced per FMRP target. We use our established RIP-seq technology to show that FMRP footprints are independent of protein-coding potential, target GC-rich and structured sequences, and are densest in 5' UTRs. Regardless of where within an mRNA FMRP binds, we find that FMRP protects mRNAs from deadenylation and directly binds the cytoplasmic poly(A)-binding protein. Our results reveal how FMRP sequesters polyadenylated mRNAs into stabilized and translationally repressed complexes, whose regulation is critical for neurogenesis and synaptic plasticity.
| S-EPMC9753132 | biostudies-literature
Project description:CCR4-NOT is a conserved multiprotein complex which regulates eukaryotic gene expression principally via shortening of poly(A) tails of messenger RNA or deadenylation. Here, we reconstitute a complete, recombinant human CCR4-NOT complex. Our reconstitution strategy permits strict compositional control to test mechanistic hypotheses with purified component variants. CCR4-NOT is more active and selective for poly(A) than the isolated exonucleases, CCR4a and CAF1, which have distinct deadenylation profiles in vitro. The exonucleases require at least two out of three conserved non-enzymatic modules (CAF40, NOT10:NOT11 or NOT) for full activity in CCR4-NOT. CAF40 and the NOT10:NOT11 module both bind RNA directly and stimulate deadenylation in a partially redundant manner. Linear motifs from different RNA-binding factors that recruit CCR4-NOT to specific mRNAs via protein-protein interactions with CAF40 can inhibit bulk deadenylation. We reveal an additional layer of regulatory complexity to the human deadenylation machinery, which may prime it either for general or target-specific degradation.
| S-EPMC6639331 | biostudies-literature
Project description:Because maturing oocytes and early embryos lack appreciable transcription, posttranscriptional regulatory processes control their development. To better understand this control, we profiled translational efficiencies and poly(A)-tail lengths throughout Drosophila oocyte maturation and early embryonic development. The correspondence between translational-efficiency changes and tail-length changes indicated that tail-length changes broadly regulate translation until gastrulation, when this coupling disappears. During egg activation, relative changes in poly(A)-tail length, and thus translational efficiency, were largely retained in the absence of cytoplasmic polyadenylation, which indicated that selective poly(A)-tail shortening primarily specifies these changes. Many translational changes depended on PAN GU and Smaug, and these changes were largely attributable to tail-length changes. Our results also revealed the presence of tail-length-independent mechanisms that maintained translation despite tail-length shortening during oocyte maturation, and prevented essentially all translation of bicoid and several other mRNAs before egg activation. In addition to these fundamental insights, our results provide valuable resources for future studies.
| S-EPMC4988829 | biostudies-literature
Project description:MicroRNAs (miRNAs) are ubiquitous regulators of eukaryotic gene expression. In addition to repressing translation, miRNAs can down-regulate the concentration of mRNAs that contain elements to which they are imperfectly complementary. Using miR-125b and let-7 as representative miRNAs, we show that in mammalian cells this reduction in message abundance is a consequence of accelerated deadenylation, which leads to rapid mRNA decay. The ability of miRNAs to expedite poly(A) removal does not result from decreased translation; nor does translational repression by miRNAs require a poly(A) tail, a 3' histone stem-loop being an effective substitute. These findings suggest that miRNAs use two distinct posttranscriptional mechanisms to down-regulate gene expression.
| S-EPMC1449641 | biostudies-literature