Oncogenic MYC induces a dependency on the spliceosome in human cancer
ABSTRACT: c-MYC (MYC) overexpression or hyperactivation is one of the most common drivers of human cancer. Despite intensive study, the MYC oncogene remains recalcitrant to therapeutic inhibition. Like other classic oncogenes, hyperactivation of MYC leads to collateral stresses onto cancer cells, suggesting that tumors harbor unique vulnerabilities arising from oncogenic activation of MYC. Herein, we discover the spliceosome as a new target of oncogenic stress in MYC-driven cancers. We identify BUD31 as a MYC-synthetic lethal gene, and demonstrate that BUD31 is a splicing factor required for the assembly and catalytic activity of the spliceosome. Core spliceosomal factors (SF3B1, U2AF1, and others) associate with BUD31 and are also required to tolerate oncogenic MYC. Notably, MYC hyperactivation induces an increase in total pre-mRNA synthesis, suggesting an increased burden on the core spliceosome to process pre-mRNA. In contrast to normal cells, partial inhibition of the spliceosome in MYC-hyperactivated cells leads to global intron retention, widespread defects in pre-mRNA maturation, and deregulation of many essential cell processes. Importantly, genetic or pharmacologic inhibition of the spliceosome in vivo impairs survival, tumorigenicity, and metastatic proclivity of MYC-dependent breast cancers. Collectively, these data suggest that oncogenic MYC confers a collateral stress on splicing and that components of the spliceosome may be therapeutic entry points for aggressive MYC-driven cancers. Examination of intron rentention in MYC-ER HMECs, in 4 conditions
Project description:Recent ChIP experiments indicate that spliceosome assembly and splicing can occur cotranscriptionally in S. cerevisiae. However, only a few genes have been examined, and all have long second exons. To extend these studies, we analyzed intron-containing genes with different second exon lengths, by ChIP as well as by whole-genome tiling arrays (ChIP-CHIP). The data indicate that U1 snRNP recruitment is independent of exon length. Recursive splicing constructs, which uncouple U1 recruitment from transcription, suggest that cotranscriptional U1 recruitment contributes to optimal splicing efficiency. In contrast, U2 snRNP recruitment as well as cotranscriptional splicing is deficient on short second exon-genes. We estimate that approximately 90% of endogenous yeast splicing is post-transcriptional, consistent with an analysis of post-transcriptional snRNP-associated pre-mRNA. Keywords: ChIP-CHIP Overall design: ChIP-CHIP was performed on tagged U1, U2, and U5 snRNPs to address spliceosome assembly on intron-containing genes in S. cerevisiae. Data expressed as log2 (immunoprecipitation/input) ratios.
Project description:There is good evidence for functional interactions between splicing and transcription in eukaryotes, but how and why these processes are coupled remain unknown. Prp5 is an RNA-stimulated ATPase required for pre-spliceosome formation in yeast. We demonstrate through in vivo RNA labelling that, in addition to a splicing defect, the prp5-1 mutation causes a defect in the transcription of intron-containing genes. We present chromatin immunoprecipitation evidence for a transcriptional elongation defect in which RNA polymerase that is phosphorylated at serine 5 of the largest subunit’s heptad repeat accumulates over introns, and that this defect requires the U2 snRNP-associated Cus2p. A similar accumulation of polymerase was observed when pre-spliceosome formation was blocked by a mutation in U2 snRNA. These results indicate the existence of a transcriptional elongation checkpoint that is associated with pre-spliceosome formation during co-transcriptional spliceosome assembly. We propose a role for Cus2p as a potential checkpoint factor in transcription. Examining the Pol II profile in MT strain and WT strain
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 Overall design: Splicing-specific microarrays were used to assay the phenotypes of 23 different conditional mutations in splicing and mRNA processing factors. The data includes time courses of shifts to the non-permissive temperature for each factor as well as dye-flipped technical replicates of each time point.
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:Intron-containing gene expression in eukaryotes proceeds through the process of RNA splicing to generate protein-coding messenger RNAs (mRNAs). Herein a large and dynamic ribonucleoprotein complex — the spliceosome — removes non-coding introns from pre-mRNAs and joins exons. Spliceosomes must also ensure accurate and timely removal of diverse and highly prevalent introns. Here we show that Sde2 is a conserved splicing regulator, contains a ubiquitin fold, and supports splicing of a subset of pre-mRNAs in an intron-specific manner in Schizosaccharomyces pombe. Its orthologs in S. pombe and humans are synthesized as precursors harboring a ubiquitin fold, followed by an invariant GGKGG motif and an uncharacterized C-terminal domain (referred to as Sde2-C). The precursor must be cleaved at GG^K by the ubiquitin specific proteases Ubp5 and Ubp15 to produce the Sde2-C protein containing a lysine residue at its C-terminus, and is a substrate of the N-end rule pathway of proteasomal degradation. The truncated Sde2-C functions as a component of the spliceosome, and loss of Sde2-C results in inefficient splicing of selected introns from target genes having functions in DNA replication, transcription and telomeric silencing. Thus, the ubiquitin-like processing of Sde2 — associated with its regulation by the N-end rule pathway — contributes to genomic stability in S. pombe through specific pre-mRNA splicing events. Overall design: Splicing sensitive microarrays for S. pombe (Agilent AMADID #: 027365) were used to monitor global changes in splicing in the background of temperature-sensitive variant of sde2 compared to wild type.
Project description:Resistance to proteasome inhibitors (PIs) is a ubiquitous clinical concern in multiple myeloma. We proposed that signaling-level responses after PI would reveal new means to enhance efficacy. Unbiased phosphoproteomics after the PI carfilzomib surprisingly demonstrated the most prominent phosphorylation changes on spliceosome components. Spliceosome modulation was invisible to RNA or protein abundance alone. Transcriptome analysis demonstrated broad-scale intron retention suggestive of PI-specific splicing interference. Direct spliceosome inhibition synergized with carfilzomib and showed potent anti-myeloma activity. Functional genomics and exome sequencing further supported the spliceosome as a specific vulnerability in myeloma. Our results propose splicing interference as an unrecognized modality of PI mechanism, reveal additional modes of spliceosome modulation, and suggest spliceosome targeting as a promising therapeutic strategy in myeloma.
Project description:Multiple lines of evidence implicate chromatin in the regulation of pre-mRNA splicing. However, the influence of chromatin factors on co-transcriptional splice-site usage remains unclear. Here we investigated the function of the highly conserved histone variant H2A.Z in pre-mRNA splicing using the intron-rich model yeast, Schizosaccharomyces pombe. Using Epistatic Mini-Array Profiles (EMAPs) to survey the genetic interaction landscape of the Swr1 nucleosome remodeling complex, which deposits H2A.Z, we uncovered evidence for functional interactions with components of the spliceosome. In support of these genetic connections, splicing-specific microarrays show that H2A.Z and the Swr1 ATPase are required during temperature stress for the efficient splicing of a sub-set of introns. Notably, affected introns are enriched for H2A.Z occupancy, and more likely to contain non-consensus splice sites. To test the significance of the latter correlation, we mutated the splice sites in an affected intron to consensus and found this suppressed the requirement for H2A.Z in splicing of that intron. These data suggest that H2A.Z occupancy promotes co-transcriptional splicing of sub-optimal introns that may otherwise be discarded via proofreading ATPases. Consistent with this model, we show that over-expression of splicing ATPase Prp16 suppresses both the growth and splicing defects seen in the absence of H2A.Z. Overall design: S. pombe splicing-specific microarrays (Agilent-027365) to compare multiple genotypes in Schizosaccharomyces pombe
Project description:Eukaryotic cells have to prevent the export of unspliced pre-mRNAs until intron removal is completed to avoid the expression of aberrant and potentially harmful proteins. Only mature RNAs associate with the export receptor Mex67 (mammalian TAP) and enter the cytoplasm. The underlying nuclear quality control mechanisms are still unclear. Here we show that two shuttling SR-proteins Gbp2 and Hrb1 are key surveillance factors for the selective export of spliced mRNAs in yeast. Their absence leads to the significant leakage of unspliced pre-mRNAs into the cytoplasm. They bind to pre-mRNAs and the spliceosome during splicing, where they are necessary for the surveillance of splicing and the stable binding of the TRAMP-complex to the spliceosome-bound transcripts. Faulty transcripts are marked for their degradation at the nuclear exosome. On correct mRNAs the SR-proteins recruit Mex67 upon completion of splicing to allow a quality controlled nuclear export. Altogether, these data identify a role for shuttling SR-proteins in mRNA surveillance and nuclear mRNA quality control. 6 samples, i.e. 2 replicates per protein Gbp2, Hrb1 and Npl3
Project description:Multiple lines of evidence implicate chromatin in the regulation of pre-mRNA splicing. However, the influence of chromatin factors on co-transcriptional splice-site usage remains unclear. Here we investigated the function of the highly conserved histone variant H2A.Z in pre-mRNA splicing using the intron-rich model yeast, Schizosaccharomyces pombe. Using Epistatic Mini-Array Profiles (EMAPs) to survey the genetic interaction landscape of the Swr1 nucleosome remodeling complex, which deposits H2A.Z, we uncovered evidence for functional interactions with components of the spliceosome. In support of these genetic connections, splicing-specific microarrays show that H2A.Z and the Swr1 ATPase are required during temperature stress for the efficient splicing of a sub-set of introns. Notably, affected introns are enriched for H2A.Z occupancy, and more likely to contain non-consensus splice sites. To test the significance of the latter correlation, we mutated the splice sites in an affected intron to consensus and found this suppressed the requirement for H2A.Z in splicing of that intron. These data suggest that H2A.Z occupancy promotes co-transcriptional splicing of sub-optimal introns that may otherwise be discarded via proofreading ATPases. Consistent with this model, we show that over-expression of splicing ATPase Prp16 suppresses both the growth and splicing defects seen in the absence of H2A.Z. Overall design: ChIP-Seq of H2A.Z association in Schizosaccharomyces pombe using the HiSeq 2500 platform
Project description:The splicing machinery associates with genes to facilitate efficient co-transcriptional mRNA processing. We have mapped these associations by genome localization analysis to ascertain how splicing is achieved and regulated on a system-wide scale. Our data show that factors important for intron recognition sample nascent mRNAs and are retained specifically at intron-containing genes via RNA-dependent interactions. Spliceosome assembly proceeds co-transcriptionally, but completes post-transcriptionally in most cases. Some intron-containing genes were not bound by the spliceosome, including several developmentally regulated genes. On this basis we predicted and verified regulated splicing, and observed a role for nuclear mRNA surveillance in monitoring those events. Finally, we present evidence that co-transcriptional processing events determine the recruitment of specific mRNA export factors. Broadly, our results provide mechanistic insights into the coordinated regulation of transcription, mRNA processing, and nuclear export in executing complex gene expression programs. Keywords: ChIP-chip Overall design: We analyzed the genomic localization of spliceosome components by chromatin IP followed by microarray analysis (ChIP-chip). All factors examined were C-terminally tagged at their genomic loci with either -myc or -HA epitopes. Between 3 and 6 biological replicates were performed for each factor. DNA from ChIPs and WCE input was amplified by linker-mediated PCR and labeled by Klenow incorporation of Cy3- or Cy-5 UTP using a random primer mix. In at least one replicate for each factor, fluorophores were swapped to control for bias during dye-labeling. ChIP and WCE fractions for each sample were competitively hybridized to the University Health Network (UNS) yeast ORF array (v6.4k), washed, and scanned using the GenePix 4000B scanner. Raw data was then uploaded onto Rosetta Resolver, and individual replicates were combined to give the raw data files submitted here.