The CWC27/CWC22 heterodimer: a spliceosome building block linked to the inflammation response in retinal pigment epithelium
Ontology highlight
ABSTRACT: Human CWC27 is an uncharacterized splicing factor and mutations in its gene are linked to retinal degeneration and other developmental defects. We identify the splicing factor CWC22 as the major CWC27 partner. Both CWC27 and CWC22 are present in published Bact spliceosome structures, but no interacting domains are visible. Here, the structure of a CWC27/CWC22 heterodimer bound to the Exon Junction Complex (EJC) core component eIF4A3 is solved at 3Å-resolution. According to spliceosomal structures, the EJC is recruited in the C complex, once CWC27 has left. Our 3D structure of the eIF4A3/CWC22/CWC27 complex is compatible with the Bact spliceosome structure but not with that of the C complex, where a CWC27 loop would clash with the EJC core subunit Y14. A CWC27/CWC22 building block might thus form an intermediate landing platform for eIF4A3 onto the Bact complex prior to its conversion into C complex. Knock-down of either CWC27 or CWC22 in immortalized retinal pigment epithelial cells affects numerous common genes, indicating that these proteins cooperate, targeting the same pathways. As the most up-regulated genes encode factors involved in inflammation, our findings suggest a possible link to the retinal degeneration associated with CWC27 deficiencies.
Project description:We report that knockdown of EJC core proteins, eIF4A3, Y14, Magoh, causes a transcript-wide changes in alternative splicing, as well as some transcriptional changes. These changes are specific to EJC core proteins, and KD of UPF1 protein caused different sets of alterantive splicing changes. These changes are linked to the rate of transcription.
Project description:The exon junction complex is deposited at 24nt upstream of exon-exon junctions, but not at every junction. The core complex is comprosed of 4 proteins, eIF4A3, Magoh, Y14 and MLN51. Here we performed immunoprecipitation of Y14 with subsequent iCLIP of eIF4A3 in HeLa cells to identify the crosslink sites of the exon junction complex, in particular eIF4A3.
Project description:We report that knockdown of EJC core proteins, eIF4A3, Y14, Magoh, causes a transcript-wide changes in alternative splicing, as well as some transcriptional changes. These changes are specific to EJC core proteins, and KD of UPF1 protein caused different sets of alterantive splicing changes. These changes are linked to the rate of transcription. Examination of 4 different knockdown, as well as GFP knockdown in HeLa cells, 2 replicates each condition.
Project description:Using the TSG101 pre-mRNA, we previously discovered cancer-specific re-splicing of mature mRNA that generates aberrant transcripts/proteins. The fact that mRNA is aberrantly re-spliced in various cancer cells implies there must be an important mechanism to prevent deleterious re-splicing on the spliced mRNA in normal cells. We thus postulated that the mRNA re-splicing is controlled by specific repressors and we searched for repressor candidates by siRNA-based screening for mRNA re-splicing activity. We found that knock-down of EIF4A3, which is a core component of the exon junction complex (EJC), significantly promoted mRNA re-splicing. Remarkably, we could recapitulate cancer-specific mRNA re-splicing in normal cells by knock-down of any of the core EJC proteins, EIF4A3, MAGOH or RBM8A (Y14), implicating the EJC core as the repressor of mRNA re-splicing often observed in cancer cells. We propose that the EJC core is a critical mRNA quality control factor to prevent over-splicing of mature mRNA.
Project description:This experiment uses iCLIP to identify the binding pattern of the spliceosomal protein PRPF8 on RNA. The data shows that PRPF8 binds strongly and specifically in the region 12 to 14nt upstream of 5' splice sites (5ss). Due to PRPF8's role in the formation of the catalytically active spliceosome, this data can be used as a readout of 5ss selection. Here, we performed iCLIP on HeLa cells treated with control or EIF4A3 siRNA, with 4 replicate samples per condition and eIF4A3 protein levels reduced ~50% in knockdown. We investigated the role of the exon junction complex (EJC) in suppressing 5ss that are reconstituted at the junction of two canonical exons (RS-5ss) - selection of these splice sites would result in recursive splicing of canonical exons. We plotted the crosslink sites of reads that span an exon-exon junction, seperating reads that span RS-5ss from those that do not. We found that reads that span an RS-5ss are enriched at the 12-14nt window associated with 5ss selection, while reads that span other exon-exon junctions are not enriched. This effect is magnified greatly by knockdown of eIF4A3. The results indicate that RS-5ss can be used by the spliceosome, but that this process is usually repressed by the EJC. This data is evidence of recursive splicing of canonical exons and the role of the EJC in repressing recursive splicing.
Project description:The exon junction complex is involved in gene expression regulation on multiple co- and post-transcriptional levels. We aimed to investigate in HeLa Tet-Off cells which gene expression alterations can be observed upon knockdown of core EJC factors (EIF4A3, RBM8A and MAGOH) or upon EIF4A3 knockdown and rescue with EIF4A3 wild type construct by using RNA-Seq analyses. The rescue construct was stably integrated into the genome using the PiggyBac transposon system. As control Luciferase (Luc) siRNA was used.
Project description:The conserved SR-like protein Npl3 promotes the splicing of diverse pre-mRNAs. However, the RNA sequence(s) recognized by the RNA Recognition Motifs (RRM1 & RRM2) of Npl3 during the splicing reaction remain elusive. Here, we developed a split-iCRAC approach in vivo to determine the consensus sequence bound to each RRM in yeast. High-resolution NMR structures show that RRM2 recognizes a 5´-GNGG-3´ motif leading to an unusual mille-feuille topology. In addition, our data indicate a non-specific interaction of the RS domain with RNA. These structures reveal how RRM1 preferentially interacts with a CC-dinucleotide upstream of this motif, and how the inter-RRM linker and the region C-terminal to RRM2 contributes to cooperative RNA-binding. Structure-guided studies show that Npl3 genetically interacts with U2 snRNP specific factors and we provide evidence that Npl3 melts U2 snRNA stem-loop I, a prerequisite for U2/U6 duplex formation within the catalytic centre of the Bact spliceosomal complex. Our findings provide a mechanistic role for Npl3 during spliceosome active site formation.
Project description:RNA helicases are involved in multiple steps of RNA metabolism to direct their roles in gene expression, yet their functions in pluripotency control remain largely unexplored. Starting from an RNAi screen of RNA helicases, we identified that eIF4A3, a DEAD-box (Ddx) helicase component of the exon junction complex (EJC), is essential for the maintenance of embryonic stem cells (ESCs). We mapped the eIF4A3 interactomes in mouse ESCs, revealing that eIF4A3 is widely involved in the post-transcriptional regulation of gene expression. Mechanistically, we show that eIF4A3 post-transcriptionally controls the pluripotency-related cell cycle regulators and that its depletion causes cellular differentiation via cell cycle dysregulation. Specifically, eIF4A3 is required for the efficient nuclear export of Ccnb1 mRNA, which encodes Cyclin B1, a key component of the pluripotency-promoting pathway during cell cycle progression of ESCs. Our results reveal a previously unappreciated role of eIF4A3 and its associated EJC in the post-transcriptional cell cycle control in maintaining stem cell pluripotency.
Project description:In metazoans, mRNA quality is tightly monitored from transcription to translation. A key role lies with the exon junction complex (EJC) that is placed upstream of the exon-exon junction after splicing. The EJC inner core is composed of Magoh, Y14, eIF4AIII and BTZ and the outer core of proteins involved in mRNA splicing (CWC22), export (Yra1), translation (PYM) and non-sense mediated decay (NMD, UPF1/2/3). The protozoan parasite Trypanosoma brucei encodes only two genes with introns, but all mRNAs are processed by trans-splicing. The presence of the three core EJC proteins and a potential BTZ homologue (Rbp25) in trypanosomes has been suggested as an adaptation of the EJC function to mark trans-spliced mRNAs. Here we explore the interactome of Magoh, Y14, eIF4AIII in T. brucei by TurboID proximity labelling.
Project description:Regulated local translation, RNA transport and protein localization are critical for spatio-temporal gene expression in neurons. The localization of mRNA and subsequent local protein synthesis contribute to neuronal functions like synaptogenesis, synapse pruning, axon guidance, axonal regeneration and synaptic plasticity. Thus, mutations in motor proteins and subsequent cargo transport failure lead to motoneuron diseases. The kinesin family member 1 C has been shown to play a role in different cargo transport alongside the microtubule network, but the pathomechanisms behind KIF1C deficiency mediated motoneuron diseases has not been deciphered yet. Additionally, the exon junction complex has been suggested as a molecular link between splicing and cytoplasmic mRNA localization and local translation. Here we identified KIF1C as a EJC transporter in neuronal cells. We investigated the KIF1C proteome in differentiated SH-SY5Y cells and found an interaction of KIF1C with EJC components and other RNA-binding proteins in KIF1C overexpressing SH-SY5Y cells. The interaction could be validated via immunoprecipitation and an endogenous eIF4A3 co-immunoprecipitation. The co-localization of eIF4A3 and RBM8A with wildtpye KIF1C at protrusions of SH-SY5Ys further confirms the interaction. The mislocalization of eIF4A3 and RMB8A due to KIF1C mutation suggests a transport of the EJC by KIF1C. Furthermore, the interaction of KIF1C with PABPC1 and EJC components is RNA mediated. We additionally demonstrate via complex capture with KIF1C overexpressing HEK293 cells that KIF1C interacts with RNA itself. We therefore suggest the interaction of KIF1C not only with the EJC, but with a complex containing RNA and the EJC. Hence KIF1C is a transporter of mRNA and the EJC.