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Disease-associated mutation in SRSF2 misregulates splicing by altering RNA binding affinities

ABSTRACT: SRSF2 is an RNA binding protein that plays important roles in splicing of mRNA precursors. Mutations in SRSF2 are frequently found in patients with myelodysplastic syndromes and certain leukemias, but how they affect SRSF2 function has only begun to be examined. Here we used CRISPR/Cas9 to introduce the P95H mutation to SRSF2 in K562 leukemia cells, generating an isogenic model so that splicing alterations can be attributed solely to mutant SRSF2. We found that SRSF2 (P95H) misregulates 548 splicing events (<1% of total). Of these, 374 involve the inclusion of cassette exons, and the inclusion was either increased (206) or decreased (168). We detected a specific motif (UCCA/UG) enriched in the more included exons and a distinct motif (UGGA/UG) in the more excluded exons. RNA gel shift assays showed that a mutant SRSF2 derivative bound more tightly than its wild-type counterpart to RNA sites containing UCCAG, but less tightly to UGGAG sites. The pattern of exon inclusion or exclusion thus correlated in most cases with stronger or weaker RNA binding, respectively. We further show that the P95H mutation does not affect other functions of SRSF2, i.e., protein-protein interactions with key splicing factors. Our results thus demonstrate that the P95H mutation positively or negatively alters the binding affinity of SRSF2 for cognate RNA sites in target transcripts, leading to misregulation of exon inclusion. Our findings not only shed light on the mechanism of the disease-associated SRSF2 mutation in splicing regulation, but also reveal a group of mis-spliced mRNA isoforms for potential therapeutic targeting.

ORGANISM(S): Homo sapiens

PROVIDER: GSE71299 | GEO | 2015/08/10

SECONDARY ACCESSION(S): PRJNA290859

REPOSITORIES: GEO

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Project description:Mutations in spliceosomal genes are commonly found in patients with myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML). These mutations occur at highly restricted amino acid residues and perturb normal splice site and exon recognition. Spliceosomal mutations are always heterozygous and rarely co-occur with one another, suggesting that cells may only tolerate a partial deviation from normal splicing activity. To test this hypothesis, we generated mice with inducible hemizygous expression of the commonly occurring SRSF2P95H mutation in the hematopoietic system. These mice rapidly developed lethal bone marrow failure upon activation of the Srsf2P95H mutation with concomitant deletion of the wildtype Srsf2 allele, demonstrating that Srsf2-mutant cells depend on the wildtype Srsf2 allele for survival. We next tested whether spliceosomal-mutant leukemias display greater sensitivity to pharmacologic splicing inhibition induced by the small molecule E7107. Treatment of isogenic murine leukemias as well as patient-derived xenograft (PDX) AMLs showed significant reductions in leukemic burden specifically in samples carrying spliceosomal mutations. Collectively, these data provide genetic and pharmacologic evidence that leukemias with spliceosomal mutations are preferentially susceptible to additional splicing perturbations in vivo compared with wildtype counterparts. Modulation of spliceosome function may provide a novel therapeutic avenue in genetically defined subsets of MDS/AML patients. We created an isogenic murine leukemia model by retroviral overexpression of the MLL-AF9 fusion oncogene in Vav-Cre Srsf2+/+ or Vav-Cre Srsf2P95H/+ BM cells followed by transplantation into lethally irradiated recipient mice. In order to determine the mechanistic origins of the Srsf2 mutant-selective effects of E7107, we analyzed transcriptional changes after five consecutive days of E7107 or vehicle treatment in vivo. GFP+ Cd11b+ cells were purified from the BM of recipient mice exactly three hours after the last dose of E7107 and were subjected to paired-end 2x50bp RNA-seq. For the knock-in/knock-out experiments, we generated inducible, hemizygous Srsf2P95H mice to study the effects of wildtype Srsf2 deletion with concomitant activation of the Srsf2P95H allele. Mx1-cre Srsf2fl/+ mice were crossed to Srsf2P95H/+ mice to generate Srsf2 wildtype (Mx1-cre Srsf2+/+), Srsf2 heterozygous knockout (Mx1-Cre Srsf2+/-), Srsf2 heterozygous P95H mutant (Mx1-Cre Srsf2P95H/+), and Srsf2 hemizygous P95H mutant (Mx1-Cre Srsf2P95H/-) mice, which were subjected to single-end 101bp RNA-seq.

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Disease-associated mutation in SRSF2 misregulates splicing by altering RNA binding affinities

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