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Modulation of SF3B1 causes global intron retention and downregulation of the B-cell receptor pathway in chronic lymphocytic leukemia

ABSTRACT: Splicing factor SF3B1 is frequently mutated in chronic lymphocytic leukemia (CLL) patients and has been suggested as a potential therapeutic target. In this study, we performed RNA-seq analysis to evaluate the global impact of SF3B1 modulator sudemycin D6 (SD6) on alternative splicing. Our analysis revealed significant increases in global intron-retention in SD6-treated CLL cells. Pathway analysis of the genes associated with increased intron-retention suggested that B-cell receptor (BCR), protein ubiquitination, and PI3K signaling pathways were among the top canonical pathways being affected by SD6. The increases in intron-retention were inversely correlated with deceases in mRNA and protein levels of the affected BCR/PI3K pathway molecules such as BLNK, BTK, AKT1, PLCγ2 and PI3Kδ. SD6 also induced a time-dependent exon-skipping event in mRNA of MCL1 and resulted in significant down-regulation of another anti-apoptotic gene TRAF1, which may contribute to the SD6-induced apoptosis. Finally, SD6 can overcome the pro-survival and pro-growth signals and synergize with ibrutinib, idelalisib and venetoclax to induce apoptosis in primary CLL cells co-cultured with bone marrow stromal cells and in the presence of T-cell-derived cytokines. Cumulatively, these results provide a strong rationale for future clinical development of spliceosome modulators and combinatory therapies based on spliceosome modulators in CLL.

ORGANISM(S): Homo sapiens

PROVIDER: GSE114514 | GEO | 2018/05/17

REPOSITORIES: GEO

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Splicing Modulators Act at the Branch Point Adenosine Binding Pocket Defined by the PHF5A-SF3b Complex

Project description:Developing small-molecule splicing modulators represents a promising therapeutic approach for various diseases. Natural products such as pladienolide, herboxidiene, and spliceostatin have been identified as potent splicing modulators that target SF3B1 in the SF3b subcomplex. Using integrated chemogenomic, structural and biochemical approaches, we show that PHF5A, another core component of the SF3b complex, is also targeted by these compounds. Mutations in PHF5A-Y36, SF3B1-K1071, SF3B1-R1074, and SF3B1-V1078 confer resistance to these modulators, suggesting a common site of interaction. Whole-transcriptome RNA-seq analysis reveals that PHF5A-Y36C has minimal effect on basal splicing but alters the action of splicing modulators from inducing intron-retention to exon-skipping. Relative intron strength to splicing inhibition correlates with the differential in GC content between adjacent introns and exons, leading to this differential global splicing pattern. We determine the crystal structure of human PHF5A and find that Y36 is located on the surface in a region of high sequence conservation. Structural analysis of the cryo-EM spliceosome Bact complex shows that these mutations cluster in a well-defined pocket surrounding the branch point adenosine suggesting a possible competitive mode of action for these splicing modulators, which interact with the aromatic side-chain of PHF5A-Y36. Collectively, we propose that PHF5A-SF3B1 forms a central node for binding to these small-molecule splicing modulators, offering insights to modulate splicing.

2017-05-25 | GSE96917 | GEO

CDK11 phosphorylates SF3B1 and is essential for constitutive splicing (RNA-seq)

Project description:Pre-mRNA splicing is a highly regulated process catalyzing intron excision by spliceosome. Spliceosome activation is a major control step requiring dramatic protein and RNA rearrangements leading to a catalytically active complex. Prior research has linked hyperphosphorylation of SF3B1, a subunit of U2 snRNP, with spliceosome activation and catalytically active spliceosome, rendering a relevant kinase a key player for pre-mRNA splicing. Here we use OTS964, the first potent inhibitor of cyclin-dependent kinase 11 (CDK11), to show rapid and selective dephosphorylation of SF3B1 on threonines required for spliceosome activation. CDK11 associates with SF3B1 and its inhibition causes massive intron retention, block in precatalytic spliceosome complex B to activated spliceosome complex Bact transition and accumulation of non-functional spliceosomes on pre-mRNA and chromatin. These studies reveal crucial regulatory role of CDK11 in human pre-mRNA splicing and define the compound OTS964 as a quality chemical biology probe for CDK11.

2022-07-09 | GSE185809 | GEO

CDK11 phosphorylates SF3B1 and is essential for constitutive splicing (iCLIP)

2022-07-09 | GSE185811 | GEO

CDK11 phosphorylates SF3B1 and is essential for constitutive splicing (4sU-seq)

2022-07-09 | GSE185810 | GEO

CDK11 phosphorylates SF3B1 and is essential for constitutive splicing (ChIP-seq)

2022-07-09 | GSE185812 | GEO

CDK11 regulates pre-mRNA splicing by phosphorylation of SF3B1

Project description:RNA splicing, the process of intron removal from pre-mRNA, is essential for the regulation of gene expression. It is controlled by the spliceosome, a megadalton RNA-protein complex that assembles de novo on each pre-mRNA intron via an ordered assembly of intermediate complexes. Spliceosome activation is a major control step requiring dramatic protein and RNA rearrangements leading to a catalytically active complex. Splicing factor 3B subunit 1 (SF3B1) protein, a subunit of the U2 snRNP, is phosphorylated during spliceosome activation, but the responsible kinase has not been identified. Here we show that cyclin-dependent kinase 11 (CDK11) associates with SF3B1 and phosphorylates threonine residues at its N-terminus during spliceosome activation. The phosphorylation is important for association of SF3B1 with U5 and U6 snRNAs in spliceosome activated Bact complex and it can be blocked by OTS964, a potent and selective inhibitor of CDK11. CDK11 inhibition prevents spliceosomal transition from the precatalytic complex B to the activated complex Bact and leads to widespread intron retention and accumulation of non-functional spliceosomes on pre-mRNAs and chromatin. We characterize OTS964 as a quality chemical biology probe for CDK11 and demonstrate a central role of CDK11 in spliceosome assembly and splicing regulation.

2022-07-09 | MSV000089855 | MassIVE

Oncogenic MYC induces a dependency on the spliceosome in human cancer

Project description: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

2015-09-03 | E-GEOD-66182 | biostudies-arrayexpress

Overlapping roles of spliceosomal components SF3B1 and PHF5A in rice splicing regulation

Project description:The SF3B complex, a multiprotein component of the U2 snRNP of the spliceosome, mediates branch point selection and facilitates spliceosome assembly and activation. Several splicing modulators bind the SF3B1 and PHF5A subunits of the SF3B complex and globally inhibit splicing. Engineered mutant variants of SF3B1 and PHF5A conferred tolerance to splicing inhibitors with only minor effects on gene expression and AS.

2021-04-11 | GSE153234 | GEO

Novel SF3B1 Deletion Mutations Result in Aberrant RNA Splicing in CLL Patients

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.

2017-06-27 | GSE95352 | GEO

A genetic murine model of CLL based on B cell-restricted expression of Sf3b1 mutation and Atm deletion

Project description:The RNA splicing factor SF3B1 is recurrently mutated in chronic lymphocytic leukemia (CLL), but its functional role in the pathogenesis of this disease has not been firmly established. Here, we show that conditional expression of heterozygous Sf3b1-K700E mutation in mouse B lineage cells disrupts pre-mRNA splicing, alters B-cell development and function, and induces a state of cellular senescence. B-cell restricted expression of this mutation combined with Atm deletion led to the overcoming of cellular senescence, together with enhanced genome instability and the development of clonal B220+CD5+ CLL cells in elderly mice at low penetrance. Mice with CLL-like disease were found to have amplifications of chromosomes 15 and 17. Integrated transcriptome and proteome analysis of the CLL-like cells revealed coordinated dysregulation of multiple CLL-associated cellular processes. This included an unexpected signature of deregulated B-cell receptor (BCR) signaling, which we could also identify in SF3B1-mutated CLL samples from two independent patient cohorts. Notably, human CLLs harboring SF3B1 mutations exhibited greater sensitivity and altered response kinetics to BTK kinase ibrutinib. Our genetically faithful murine model of CLL thus reveals fresh insights regarding the impact of SF3B1 mutation on CLL pathogenesis and suggests a system for identifying vulnerabilities related to this mutation that can be further exploited for the treatment of CLLs with this common mutation.

2018-11-20 | GSE122668 | GEO

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