Glucocorticoid resistance in pediatric leukemia is associated with altered splicing profiles and vulnerability to spliceosome modulation
Ontology highlight
ABSTRACT:
ORGANISM(S): Homo sapiens
PROVIDER: GSE133499 | GEO | 2020/03/24
REPOSITORIES: GEO
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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.
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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.
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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.
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Project description:Drug resistance remains a major obstacle to successful cancer treatment. Here we use a novel approach to identify rapamycin as a glucocorticoid resistance reversal agent. A database of drug-associated gene expression profiles was screened for molecules whose profile overlapped with a gene expression signature of glucocorticoid (GC) sensitivity/resistance in Acute Lymphoblastic Leukemia (ALL) cells. The screen indicated the mTOR inhibitor rapamycin profile matched the signature of GC-sensitivity. We thus tested the hypothesis that rapamycin would induce GC sensitivity in lymphoid malignancy cells, and found that it sensitized cells to glucocorticoid induced apoptosis via modulation of antiapoptotic MCL1. These data indicate that MCL1 is an important regulator of GC-induced apoptosis, and that the combination of rapamycin and glucocorticoids has potential utility in ALL. Furthermore this approach represents a novel strategy for identification of promising combination therapies for cancer. This SuperSeries is composed of the following subset Series:; GSE5820: Gene expression-based chemical genomics identifies rapamycin as a modulator of MCL-1 and glucocorticoid resistance; GSE5821: Rapamycin treatment of CEM_C1 cells 24 hours; GSE5822: Rapamycin treated CEM-C1 cells 3 hours Experiment Overall Design: Refer to individual Series
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