High-throughput sequencing of mouse liver mRNA after treatment with the mRNA splicing inhibitor Pladienolide B
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ABSTRACT: RNA splicing is an essential step for expression of genes commonly altered in multiple liver diseases. However, how the spliceosomal components participate in the pathogenesis of acute liver failure (ALF) remains poorly defined. Here, we report that KH-type splicing regulatory protein (KSRP) which is downregulated in ALF, regulates RNA splicing in the liver through interacting with the Splicing factor 3b subunit 1 (SF3B1). Overexpression of KSRP resulted in marked amelioration of hepatic injury in vivo. Transcriptomic analysis reveals that KSRP depletion led to severe splicing defects in genes with significant intron retention. Such defects cause substantial loss of proliferation and apoptosis related genes such as EGFR, which further exaggerated liver injury. KSRP promotes RNA splicing of splicing related genes, including SF3B1, PHF5A, and SF3B4, indicating the existence of a positive feedback loop that regulates RNA splicing. Mechanistically, KSRP directly interacts with SF3B1 and enhances binding of SF3B1 to the branch sites located upstream of the exon. Overall, our findings demonstrate a novel mechanism by which KSPR protects against acute liver injury by promoting RNA splicing through interacting with the SF3B complex.
Project description:RNA splicing is an essential step for expression of genes commonly altered in multiple liver diseases. However, how the spliceosomal components participate in the pathogenesis of acute liver failure (ALF) remains poorly defined. Here, we report that KH-type splicing regulatory protein (KSRP) which is downregulated in ALF, regulates RNA splicing in the liver through interacting with the Splicing factor 3b subunit 1 (SF3B1). Overexpression of KSRP resulted in marked amelioration of hepatic injury in vivo. Transcriptomic analysis reveals that KSRP depletion led to severe splicing defects in genes with significant intron retention. Such defects cause substantial loss of proliferation and apoptosis related genes such as EGFR, which further exaggerated liver injury. KSRP promotes RNA splicing of splicing related genes, including SF3B1, PHF5A, and SF3B4, indicating the existence of a positive feedback loop that regulates RNA splicing. Mechanistically, KSRP directly interacts with SF3B1 and enhances binding of SF3B1 to the branch sites located upstream of the exon. Overall, our findings demonstrate a novel mechanism by which KSPR protects against acute liver injury by promoting RNA splicing through interacting with the SF3B complex.
Project description:RNA splicing is an essential step for expression of genes commonly altered in multiple liver diseases. However, how the spliceosomal components participate in the pathogenesis of acute liver failure (ALF) remains poorly defined. Here, we report that KH-type splicing regulatory protein (KSRP) which is downregulated in ALF, regulates RNA splicing in the liver through interacting with the Splicing factor 3b subunit 1 (SF3B1). Overexpression of KSRP resulted in marked amelioration of hepatic injury in vivo. Transcriptomic analysis reveals that KSRP depletion led to severe splicing defects in genes with significant intron retention. Such defects cause substantial loss of proliferation and apoptosis related genes such as EGFR, which further exaggerated liver injury. KSRP promotes RNA splicing of splicing related genes, including SF3B1, PHF5A, and SF3B4, indicating the existence of a positive feedback loop that regulates RNA splicing. Mechanistically, KSRP directly interacts with SF3B1 and enhances binding of SF3B1 to the branch sites located upstream of the exon. Overall, our findings demonstrate a novel mechanism by which KSPR protects against acute liver injury by promoting RNA splicing through interacting with the SF3B complex.
Project description:RNA splicing is an essential step for expression of genes commonly altered in multiple liver diseases. However, how the spliceosomal components participate in the pathogenesis of acute liver failure (ALF) remains poorly defined. Here, we report that KH-type splicing regulatory protein (KSRP) which is downregulated in ALF, regulates RNA splicing in the liver through interacting with the Splicing factor 3b subunit 1 (SF3B1). Overexpression of KSRP resulted in marked amelioration of hepatic injury in vivo. Transcriptomic analysis reveals that KSRP depletion led to severe splicing defects in genes with significant intron retention. Such defects cause substantial loss of proliferation and apoptosis related genes such as EGFR, which further exaggerated liver injury. KSRP promotes RNA splicing of splicing related genes, including SF3B1, PHF5A, and SF3B4, indicating the existence of a positive feedback loop that regulates RNA splicing. Mechanistically, KSRP directly interacts with SF3B1 and enhances binding of SF3B1 to the branch sites located upstream of the exon. Overall, our findings demonstrate a novel mechanism by which KSPR protects against acute liver injury by promoting RNA splicing through interacting with the SF3B complex.
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.
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.
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.
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.
Project description:A major impediment to studying the human spliceosome in vivo has been the inability to program point mutations in endogenous genes on a large scale. CRISPR-Cas9 technology now provides such opportunities. Due to its scalability and ability to introduce point mutations, we chose CRISPR-Cas9 base editing for a forward genetic screen of the spliceosome in an eHAP haploid human cell line background. We maintained eHAP FNLS cells as haploid so that we could subsequently assign genotype-phenotype relationships. We designed a single guide RNA (sgRNA) library targeting a hand-curated list of 153 human spliceosomal proteins which engage at various steps of the splicing cycle. After mutagenesis, we interrogated the spliceosome using the potent inhibitor pladienolide B (PB), which targets U2 snRNP by binding to a pocket between the SF3B1 and PHF5A subunits of the SF3b complex, preventing stabilization of the U2-branchpoint RNA duplex. Validation and genomic sequencing revealed resistance mutations in SF3B1 and PHF5A in residues adjacent to the compound binding pocket. We mapped hypersensitive mutants to U2 snRNP components, but also to factors that act as late as the second chemical step, after SF3b has dissociated. Strikingly, we obtained resistance mutants in SUGP1, a spliceosomal G-patch protein of unknown function that lacks orthologs in yeast and is also a newly proposed tumor suppressor whose loss underpins the splicing changes induced by cancer-associated SF3B1 mutations.
Project description:A major impediment to studying the human spliceosome in vivo has been the inability to program point mutations in endogenous genes on a large scale. CRISPR-Cas9 technology now provides such opportunities. Due to its scalability and ability to introduce point mutations, we chose CRISPR-Cas9 base editing for a forward genetic screen of the spliceosome in an eHAP haploid human cell line background. We maintained eHAP FNLS cells as haploid so that we could subsequently assign genotype-phenotype relationships. We designed a single guide RNA (sgRNA) library targeting a hand-curated list of 153 human spliceosomal proteins which engage at various steps of the splicing cycle. After mutagenesis, we interrogated the spliceosome using the potent inhibitor pladienolide B (PB), which targets U2 snRNP by binding to a pocket between the SF3B1 and PHF5A subunits of the SF3b complex, preventing stabilization of the U2-branchpoint RNA duplex. Validation and genomic sequencing revealed resistance mutations in SF3B1 and PHF5A in residues adjacent to the compound binding pocket. We mapped hypersensitive mutants to U2 snRNP components, but also to factors that act as late as the second chemical step, after SF3b has dissociated. Strikingly, we obtained resistance mutants in SUGP1, a spliceosomal G-patch protein of unknown function that lacks orthologs in yeast and is also a newly proposed tumor suppressor whose loss underpins the splicing changes induced by cancer-associated SF3B1 mutations.
Project description:A major impediment to studying the human spliceosome in vivo has been the inability to program point mutations in endogenous genes on a large scale. CRISPR-Cas9 technology now provides such opportunities. Due to its scalability and ability to introduce point mutations, we chose CRISPR-Cas9 base editing for a forward genetic screen of the spliceosome in an eHAP haploid human cell line background. We maintained eHAP FNLS cells as haploid so that we could subsequently assign genotype-phenotype relationships. We designed a single guide RNA (sgRNA) library targeting a hand-curated list of 153 human spliceosomal proteins which engage at various steps of the splicing cycle. After mutagenesis, we interrogated the spliceosome using the potent inhibitor pladienolide B (PB), which targets U2 snRNP by binding to a pocket between the SF3B1 and PHF5A subunits of the SF3b complex, preventing stabilization of the U2-branchpoint RNA duplex. Validation and genomic sequencing revealed resistance mutations in SF3B1 and PHF5A in residues adjacent to the compound binding pocket. We mapped hypersensitive mutants to U2 snRNP components, but also to factors that act as late as the second chemical step, after SF3b has dissociated. Strikingly, we obtained resistance mutants in SUGP1, a spliceosomal G-patch protein of unknown function that lacks orthologs in yeast and is also a newly proposed tumor suppressor whose loss underpins the splicing changes induced by cancer-associated SF3B1 mutations.