Mutational landscape of splicing genes and functional consequences across 33 cancer types
Ontology highlight
ABSTRACT: Hotspot mutations in the spliceosome component genes have been recently reported at high frequency in hematological malignancies, suggesting the importance of this pathway in cancer. However, a comprehensive survey of splicing factor mutations across tumor types has not yet been performed. We analyzed whole-exome sequencing data across 33 tumor types in The Cancer Genome Atlas (TCGA) in order to discover recurrent mutations in spliceosome components, identifying 119 genes with significant non-silent mutation patterns, including mutation overrepresentation, recurrent loss of function (tumor suppressor-like), or hotspot mutation profile (oncogene-like). We used RNA sequencing data to identify altered splicing events associated with these spliceosome mutations. In addition, we were able to discover common gene pathway profiles associated with the presence of these mutations. Our analysis suggests that somatic alteration of the splicing pathway is common in solid tumors and may represent an underappreciated hallmark of tumorigenesis.
Project description:Myelodysplastic syndromes (MDS) are characterized by recurrent somatic alterations often affecting components of RNA splicing machinery. Mutations of splice factors SF3B1, SRSF2, ZRSR2 and U2AF1 occur in >50% of MDS. To assess the impact of spliceosome mutations on splicing and to identify common pathways/genes affected by distinct mutations, we performed RNA-sequencing of 24 MDS bone marrow samples harboring spliceosome mutations (including hotspot alterations of SF3B1, SRSF2 and U2AF1; small deletions of SRSF2 and truncating mutations of ZRSR2), and devoid of other common co-occurring mutations. We uncover the landscape of splicing alterations in each splice factor mutant MDS and demonstrate that SRSF2 deletions cause highest number of splicing alterations compared with other spliceosome mutations. Although the mis-spliced events observed in different splice factor mutations were largely non-overlapping, a subset of genes, including EZH2, were aberrantly spliced in multiple mutant groups. Pathway analysis revealed that the mis-spliced genes in different mutant groups were enriched in RNA splicing and transport as well as several signaling cascades, suggesting converging biological consequences downstream of distinct spliceosome mutations.
Project description:Recurrent mutations in RNA splicing factors SF3B1, U2AF1, and SRSF2 have been reported in hematologic cancers including myelodysplastic syndromes (MDS) and chronic lymphocytic leukemia (CLL). However, SF3B1 is the only splicing associated gene to be found mutated in CLL and has been shown to induce aberrant splicing. To investigate if any other genomic aberration caused similar transcriptome changes, we clustered RNASeq samples based on an alternative 3’ splice site (ss) pattern previously identified in SF3B1-mutant CLL patients. Out of 215 samples, we identified 37 (17%) with alternative 3’ ss usage, the majority of which harbored known SF3B1 hotspot mutations. Interestingly, 3 patient samples carried previously unreported in-frame deletions in SF3B1 around K700, the most frequent mutation hotspot. To study the functional effects of these deletions, we used various minigenes demonstrating that recognition of canonical 3’ ss and alternative branchsite are required for aberrant splicing, as observed for SF3B1 p.K700E. The common mechanism of action of these deletions and substitutions result in similar sensitivity of primary cells towards splicing inhibitor E7107. Altogether, these data demonstrate that novel SF3B1 in-frame deletion events identified in CLL result in aberrant splicing, a common biomarker in spliceosome-mutant cancers.
Project description:Recurrent mutations in the spliceosome are observed in several human cancers but their functional and therapeutic significance remain elusive. SF3B1, the most frequently mutated component of the spliceosome in cancer, is involved in the recognition of the branch point sequence (BPS) during selection of the 3’ splice site (ss) in RNA splicing. Here, we report that common and tumor-specific splicing aberrations are induced by SF3B1 mutations and establish aberrant 3’ ss selection as the most frequent splicing defect. Strikingly, mutant SF3B1 utilizes a BPS that differs from that used by wild-type SF3B1 and requires the canonical 3’ ss to enable aberrant splicing during the second step. Approximately 50% of the aberrantly spliced mRNAs are subjected to nonsense-mediated decay resulting in downregulation of gene and protein expression. These findings ascribe functional significance to the consequences of SF3B1 mutations in cancer. 72 samples, including two sets of patient data and cell lines with two additional technical replicates each
Project description:DICER1 plays a critical role in microRNA (miRNA) biogenesis. Recurrent somatic “hotspot” mutations at four mental binding sites within the RNase IIIb domain of DICER1, were identified in ovarian sex cord-stromal tumors and have since been described in other pediatric tumors. In this study, we identified and characterized DICER1 hotspot mutations in endometrial cancers derived from The Cancer Genome Atlas (TCGA) and our local tumor bank. DICER1 hotspot mutations are found in ~2% of endometrial tumors. Using Illumina and Sanger targeted resequencing we observed biallelic DICER1 mutations in more than 50% of cases with hotspot mutations and identified an additional recurrent mutation G1809R in 2 cases. Through small RNA deep sequencing and real-time PCR, we demonstrated mutations that add a positively charged side chain to residue 1809 have similar detrimental effects on 5p miRNA production as mutations at metal binding sites. In one case G1809R was compound heterozygous with a germline S839F mutation, which contributes to loss of DICER1 expression by promoting protein degradation. As expected, 5p miRNAs are globally reduced in tumors and cell lines with hotspot mutations. Pathway analysis of gene expression profiles indicated that genes derepressed due to loss of 5p miRNAs are strongly associated with cell cycle related pathways. Using a Dicer null cell line model, we demonstrated that DICER1 hotspot mutants abolished the inhibitory effects of wildtype DICER1 on cell proliferation upon re-expression. Furthermore, targets of let-7 family miRNAs are enriched among the upregulated genes, suggesting loss of let-7 may be impacting downstream pathways.
Project description:RNA splicing dysregulation is a hallmark of cancers, promoting the onset and progression of disease. In chronic lymphocytic leukemia (CLL), spliceosome mutations leading to aberrant splicing occur in ~20% of patients. However, the underlying mechanism for splicing defects in spliceosome unmutated CLL cases remains elusive. Through an integrative transcriptomic and proteomic analysis, we discover proteins involved in RNA splicing are post-transcriptionally upregulated in CLL cells, resulting in splicing dysregulation. The abundance of splicing (factors) complexes is an independent risk factor and associated with poor prognosis in CLL. Moreover, increased splicing factor expression is highly correlated with METTL3, an RNA methyltransferase that modifies N6-methyladenosine (m6A) on mRNA. METTL3 is essential for cell growth in vitro and in vivo, and controls splicing factor protein expression in a methyltransferase-dependent manner through m6A modification mediated ribosome recycling and decoding process. Our results uncover a novel regulatory axis of METTL3 for splicing dysregulation in CLL and highlight m6A modification as a major contributor to spliceosome mutation-independent splicing defects that lead to CLL progression.
Project description:RNA splicing dysregulation is a hallmark of cancers, promoting the onset and progression of disease. In chronic lymphocytic leukemia (CLL), spliceosome mutations leading to aberrant splicing occur in ~20% of patients. However, the underlying mechanism for splicing defects in spliceosome unmutated CLL cases remains elusive. Through an integrative transcriptomic and proteomic analysis, we discover proteins involved in RNA splicing are post-transcriptionally upregulated in CLL cells, resulting in splicing dysregulation. The abundance of splicing (factors) complexes is an independent risk factor and associated with poor prognosis in CLL. Moreover, increased splicing factor expression is highly correlated with METTL3, an RNA methyltransferase that modifies N6-methyladenosine (m6A) on mRNA. METTL3 is essential for cell growth in vitro and in vivo, and controls splicing factor protein expression in a methyltransferase-dependent manner through m6A modification mediated ribosome recycling and decoding process. Our results uncover a novel regulatory axis of METTL3 for splicing dysregulation in CLL and highlight m6A modification as a major contributor to spliceosome mutation-independent splicing defects that lead to CLL progression.
Project description:RNA splicing dysregulation is a hallmark of cancers, promoting the onset and progression of disease. In chronic lymphocytic leukemia (CLL), spliceosome mutations leading to aberrant splicing occur in ~20% of patients. However, the underlying mechanism for splicing defects in spliceosome unmutated CLL cases remains elusive. Through an integrative transcriptomic and proteomic analysis, we discover proteins involved in RNA splicing are post-transcriptionally upregulated in CLL cells, resulting in splicing dysregulation. The abundance of splicing (factors) complexes is an independent risk factor and associated with poor prognosis in CLL. Moreover, increased splicing factor expression is highly correlated with METTL3, an RNA methyltransferase that modifies N6-methyladenosine (m6A) on mRNA. METTL3 is essential for cell growth in vitro and in vivo, and controls splicing factor protein expression in a methyltransferase-dependent manner through m6A modification mediated ribosome recycling and decoding process. Our results uncover a novel regulatory axis of METTL3 for splicing dysregulation in CLL and highlight m6A modification as a major contributor to spliceosome mutation-independent splicing defects that lead to CLL progression.
Project description:Recurrent mutations in the spliceosome are observed in several human cancers but their functional and therapeutic significance remain elusive. SF3B1, the most frequently mutated component of the spliceosome in cancer, is involved in the recognition of the branch point sequence (BPS) during selection of the 3’ splice site (ss) in RNA splicing. Here, we report that common and tumor-specific splicing aberrations are induced by SF3B1 mutations and establish aberrant 3’ ss selection as the most frequent splicing defect. Strikingly, mutant SF3B1 utilizes a BPS that differs from that used by wild-type SF3B1 and requires the canonical 3’ ss to enable aberrant splicing during the second step. Approximately 50% of the aberrantly spliced mRNAs are subjected to nonsense-mediated decay resulting in downregulation of gene and protein expression. These findings ascribe functional significance to the consequences of SF3B1 mutations in cancer.
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:Genomic analyses of cancer have identified recurrent point mutations in the RNA splicing factors SF3B1, U2AF1, and SRSF2 that confer an alteration of function. Although cells bearing these mutations are preferentially dependent on wild-type (WT) spliceosome function, clinical means to therapeutically target the spliceosome do not currently exist. Here, we describe an orally available modulator of the SF3b complex, H3B-8800, which potently and selectively kills spliceosome-mutant epithelial and hematologic malignancies. The effects of H3B-8800 are entirely selective for the Sf3b complex, as evidenced by the identification of drug-resistant cells bearing mutations in Sf3b components. Although H3B-8800 modulates RNA splicing mediated by WT or cancer-associated SF3B1 mutants, its preferential effects on spliceosome-mutant cells is due to preferred retention of short, GC-rich introns, which are enriched in genes encoding a substantial number of spliceosome components. These data demonstrate the therapeutic potential of splicing modulation in spliceosome-mutant cancers.