A Defective Splicing Machinery Promotes Senescence through MDM4 Alternative Splicing
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ABSTRACT: Defects in the splicing machinery have been implicated in various diseases, including cancer. We identified a general reduction in the expression spliceosome components and splicing regulators in human cell lines undergoing replicative, stress-induced and telomere uncapping-induced senescence. Supporting the notion that defective splicing contributes to senescence, we showed that the splicing inhibitors herboxidiene and pladienolide B induce senescence both in normal and cancer cell lines. Furthermore, the individual depletion of several spliceosome components also promoted senescence. We noted an alternative splicing shift in MDM4, from the full-length MDM4-FL variant to MDM4-S during replicative and stress-induced senescence. This shift was replicated by splicing inhibition and the depletion of individual spliceosome components. Importantly, decreasing the level of MDM4-FL promoted senescence, while cell survival was improved both by reducing the level of MDM4-FL and by overexpressing MDM4-S. Overall, our work establishes that defects in the splicing machinery alter the alternative splicing of MDM4 to promote senescence.
Project description:Precursor messenger RNA (pre-mRNA) splicing is catalyzed by the spliceosome, a highly dynamic machinery with sequentially assembled small nuclear ribonucleoproteins (snRNPs) and splicing factors. Aberrant spliceosome composition and function result in the dysregulation of pre-mRNA alternative splicing, which may cause cellular stresses and diseases such as cancer. Here, we identify a splicing factor, E2F-associated phosphoprotein (EAPP), that directly binds to the U4/U6. U5 tri-snRNP and PRPF19 complex. Notably, the C-terminal “bucket” domain in EAPP composed of several beta-sheets is required for its interaction with the tri-snRNP. EAPP is prominently located at Cajal bodies within the nucleus where it colocalizes with the spliceosome. Loss of EAPP impedes the assembly and homeostasis of the tri-snRNP complex in Cajal bodies and increases the frequency of splicing abnormalities, mostly exon skipping. Moreover, EAPP depletion promotes MDM4 exon 6 skipping, which suppresses cell growth and tumor progression via p53 overactivation. Our study demonstrates a previously uncharacterized function of EAPP in spliceosome regulation and reveals that EAPP-mediated alternative splicing of MDM4 is a critical determinant of cell fate and tumor growth.
Project description:Pre-mRNA splicing relies on the still poorly understood dynamic interplay between more than 150 protein components of the Spliceosome, and the steps at which splicing can be regulated remain largely unknown. Here we systematically analyze the effect of knocking down the components of the splicing machinery on alternative splicing events relevant for cell proliferation and apoptosis and use this information to reconstruct a network of functional interactions. The network accurately captures well-established physical and functional associations and identifies new, revealing remarkable regulatory potential of core spliceosomal components, related to the order and duration of their recruitment during Spliceosome assembly. In contrast with standard models of regulation at early events of splice site recognition, factors involved in catalytic activation of the Spliceosome display regulatory properties. The network also sheds light on the antagonism between hnRNP C and U2AF and on targets of anti-tumor drugs, and can be widely used to identify mechanisms of splicing regulation. RNA from 3 biological replicates of 72 hours knockdowns of human IK or SMU1 and a control set were used. Changes between the control and knockdowns were measured based on using a splice-junction array (Affymetrix HJAY).
Project description:Identification of novel vulnerabilities in the context of therapeutic resistance is emerging as key challenge for cancer treatment. Recent studies have detected pervasive aberrant splicing in cancer cells, supporting its targeting for treatment of hematological malignancies.We here evaluated the expression of several spliceosome machinery components in primary multiple myeloma (MM) cells and the impact of splicing modulations on MM cell growth and viability.Our comprehensive gene expression analysis confirmed deregulation of spliceosome machinery components in MM cells compared to normal plasma cells (PCs) from healthy donors, while pharmacological and genetic modulation of splicing confirmed significant impact on growth and survival of MM cell lines and patient-derived malignant PCs. Transcriptomic analysis revealed deregulation of BCL2 family membersincluding decrease of proapoptotic long form of myeloid cell leukemia-1 (MCL1) expression in cells treated with splicing inhibitors. This caused a shift in the apoptotic priming resulting in improved BCL2-dependenceand increased sensitivity to Venetoclax, a BCL2 small molecule inhibitor, in vitro and in vivo. Overall, our data provide a rationale for supporting clinical use of splicing modulators as strategy to reprogram apoptotic dependencies, making MM patients more vulnerable to BCL2 inhibitors.
Project description:Pre-mRNA splicing relies on the still poorly understood dynamic interplay between more than 150 protein components of the Spliceosome, and the steps at which splicing can be regulated remain largely unknown. Here we systematically analyze the effect of knocking down the components of the splicing machinery on alternative splicing events relevant for cell proliferation and apoptosis and use this information to reconstruct a network of functional interactions. The network accurately captures well-established physical and functional associations and identifies new, revealing remarkable regulatory potential of core spliceosomal components, related to the order and duration of their recruitment during Spliceosome assembly. In contrast with standard models of regulation at early events of splice site recognition, factors involved in catalytic activation of the Spliceosome display regulatory properties. The network also sheds light on the antagonism between hnRNP C and U2AF and on targets of anti-tumor drugs, and can be widely used to identify mechanisms of splicing regulation.
Project description:Splicing is catalyzed by the spliceosome, a compositionally dynamic complex assembled stepwise on pre-mRNA. We reveal links between splicing machinery components and the intrinsically disordered ciliopathy protein SANS. Pathogenic mutations in SANS/USH1G lead to Usher syndrome––the most common cause of deaf-blindness. Previously, SANS was shown to function only in the cytosol and primary cilia. Here, we have uncovered molecular links between SANS and pre-mRNA splicing catalyzed by the spliceosome in the nucleus. We show that SANS is found in Cajal bodies and nuclear speckles, where it interacts with components of spliceosomal subcomplexes such as SF3B1 and the large splicing cofactor SON but also with PRPFs and snRNAs related to the tri-snRNP complex. SANS is required for the transfer of tri-snRNPs between Cajal bodies and nuclear speckles for spliceosome assembly and may also participate in snRNP recycling back to Cajal bodies. SANS depletion alters the kinetics of spliceosome assembly, leading to accumulation of complex A. SANS deficiency and USH1G pathogenic mutations affects splicing of genes related to cell proliferation and USH. Thus, we provide the first evidence that splicing dysregulation may participate in the pathophysiology of Usher syndrome.
Project description:During meiosis in yeast, global splicing efficiency increases. The mechanism for this is relief of competition for the splicing machinery by repression of intron-containing ribosomal protein genes (RPGs). Repression of RPGs with rapamycin also increases splicing efficiency in vegetative cells. Reducing levels of an RPG-dedicated transcription factor globally improves splicing and suppresses the temperature-sensitive growth defect of a spliceosome mutation. These results indicate that the spliceosome is limiting and pre-mRNAs compete with each other. Under these conditions, splicing efficiency of a given pre-mRNA therefore depends on both its concentration and affinity for the limiting splicing factor(s) as well as those of the competing pre-mRNAs. We propose that trans-competition control of splicing helps repress meiotic gene expression in vegetative cells, and promotes efficient meiosis. Competition between RNAs for a limiting factor may be a general condition important for function of a variety of post-transcriptional control mechanisms. Splicing and gene expression profiles of 1) wild type yeast cells treated with rapamycin (2 biological replicates) relative to untreated cells and 2) prp4-1 pGAL-IFH1 (down-regulated expression of IFH1 transcription factor(specific for ribosomal protein genes)) relative to prp4-1 yeast.
Project description:The investigation of spliceosomal processes is currently a topic of intense research in molecular biology. In the molecular mechanism of alternative splicing, a multi-protein–RNA complex – the spliceosome – plays a crucial role. To understand the biological processes of alternative splicing, it is essential to comprehend the biogenesis of the spliceosome.
In this paper, we propose the first abstract model of the regulatory assembly pathway of the human spliceosomal subunit U1. Using Petri nets, we describe its highly ordered assembly that takes place in a stepwise manner.
Project description:Appropriate expression of most eukaryotic genes requires the removal of introns from their pre-messenger RNAs (pre-mRNAs), a process catalyzed by the spliceosome. In higher eukaryotes a large family of auxiliary factors known as SR proteins can improve the splicing efficiency of transcripts containing suboptimal splice sites by interacting with distinct sequences present in those pre-mRNAs. The yeast Saccharomyces cerevisiae lacks functional equivalents of most of these factors; thus, it has been unclear whether the spliceosome could effectively distinguish among transcripts. To address this question, we have used a microarray-based approach to examine the effects of mutations in 18 highly conserved core components of the spliceosomal machinery. The kinetic profiles reveal clear differences in the splicing defects of particular pre-mRNA substrates. Most notably, the behaviors of ribosomal protein gene transcripts are generally distinct from other intron-containing transcripts in response to several spliceosomal mutations. However, dramatically different behaviors can be seen for some pairs of transcripts encoding ribosomal protein gene paralogs, suggesting that the spliceosome can readily distinguish between otherwise highly similar pre-mRNAs. The ability of the spliceosome to distinguish among its different substrates may therefore offer an important opportunity for yeast to regulate gene expression in a transcript-dependent fashion. Given the high level of conservation of core spliceosomal components across eukaryotes, we expect that these results will significantly impact our understanding of how regulated splicing is controlled in higher eukaryotes as well. Keywords: time course, splicing mutant, splicing-specific microarray
Project description:Protein Arginine MethylTransferase 5 (PRMT5) is known to mediate epigenetic control on chromatin and to functionally regulate components of the splicing machinery. In this study we show that selective deletion of PRMT5 in different organs leads to cell cycle arrest and apoptosis. At the molecular level, PRMT5 depletion results in reduced methylation of Sm proteins, aberrant constitutive splicing and in the Alternative Splicing (AS) of specific mRNAs. We identify Mdm4 as one of these mRNAs, which due to its weak 5’-Donor site, acts as a sensor of splicing defects and transduces the signal to activate the p53 response, providing a mechanistic explanation of the phenotype observed in PRMT5 conditional knockout mice. Our data demonstrate a key role of PRMT5, together with p53, as guardians of the transcriptome. This will have fundamental implications in our understanding of PRMT5 activity, both in physiological conditions, as well as pathological conditions, including cancer and neurological diseases. Total RNA was extracted from control Prmt5F/F, and Prmt5 depleted Prmt5F/FNes (Nestin-Cre) Neural Stem/Progenitors Cells (NPCs). The final cRNA samples were hybridized to Illumina MouseRef-8 V2 arrays in quadruplicates.