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SF3B1 mutant-induced missplicing of MAP3K7 causes anemia in myelodysplastic syndromes

ABSTRACT: SF3B1 is the most frequently mutated RNA splicing factor in cancer, including in ~25% of myelodysplastic syndromes (MDS) patients. SF3B1-mutated MDS, which is strongly associated with ringed sideroblast morphology, is characterized by ineffective erythropoiesis, leading to severe, often fatal, anemia. However, functional evidence linking SF3B1 mutations to the anemia described in MDS patients harboring this genetic aberration is weak, and the underlying mechanism is completely unknown. Using isogenic SF3B1 wild-type and mutant cell lines, normal human CD34 cells and MDS patient cells, we define a previously unrecognized role of the kinase MAP3K7, encoded by a known mutant SF3B1-targeted transcript, in controlling proper terminal erythroid differentiation, and show how MAP3K7 missplicing leads to the anemia characteristic of SF3B1-mutated MDS, although not to ringed sideroblast formation. We found that p38 MAPK is deactivated in SF3B1 mutant isogenic and patient cells and that MAP3K7 is an upstream positive effector of p38 MAPK. We demonstrate that disruption of this MAP3K7-p38 MAPK pathway leads to premature downregulation of GATA1, a master regulator of erythroid differentiation, and that this is sufficient to trigger accelerated differentiation, erythroid hyperplasia and ultimately apoptosis. Our findings thus define the mechanism leading to the severe anemia found in MDS patients harboring SF3B1 mutations.

ORGANISM(S): Homo sapiens

PROVIDER: GSE187356 | GEO | 2021/11/06

REPOSITORIES: GEO

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Expression data from Sf3b1 heterozygous Lineage-c-Kit+Sca-1+ (LSK) bone marrow cells

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Expression data from Sf3b1 heterozygous Lineage-c-Kit+Sca-1+ (LSK) bone marrow cells

Project description:Recent studies have shown that multiple components of the mRNA splicing machinery are mutated in myelodysplastic syndrome (MDS) patients. SF3B1 is frequently mutated in refractory anemia with ringed sideroblasts (RARS)-MDS patients, however, the pathophysiological role of SF3B1 mutations has not been elucidated yet. In this study, we examined the function of Sf3b1 in murine hematopoiesis. Since Sf3b1 null homozygotes died during preimplantation development, in this study, we utilized Sf3b1 heterozygous mice showing grossly normal growth. We harvested bone marrow stem/progenitor (LSK) cells from wild type (WT) and Sf3b1+/- mice (n=4) at 20 weeks old. In addition, to exclude the possibility of indirect effect from bone marrow environment, we transplanted total bone marrow cells from WT or Sf3b1+/- (CD45.2+) mice into lethally irradiated CD45.1+ recipient mice, and then harvested (CD45.2+) LSK cells from the recipients (n=5) at 9 months-post transplantation.

2013-09-20 | E-GEOD-51038 | biostudies-arrayexpress

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Physiologic expression of Sf3b1K700E causes impaired erythropoieses, aberrant splicing, and sensitivity to pharmacologic spliceosome modulation

Project description:Over 80% of patients with the refractory anemia with ring sideroblasts subtype of myelodysplastic syndrome (MDS) have mutations in Splicing Factor 3B, Subunit 1 (SF3B1). We generated a conditional knock-in mouse model of the most common SF3B1 mutation, Sf3b1K700E. Sf3b1K700E mice develop macrocytic anemia due to a terminal erythroid maturation defect, erythroid dysplasia, and long-term hematopoietic stem cell (LT-HSC) expansion. Sf3b1K700E myeloid progenitors and SF3B1-mutant MDS patient samples demonstrate aberrant 3' splice-site selection associated with increased nonsense-mediated decay. Tet2 loss cooperates with Sf3b1K700E to cause a more severe erythroid and LT-HSC phenotype. Furthermore, the spliceosome modulator, E7017, selectively kills Sf3b1K700E-expressing cells. Thus, Sf3b1K700E expression reflects the phenotype of the mutation in MDS and may be a therapeutic target in MDS.

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RNA sequencing of bone marrow CD34+ cells from myelodysplastic syndrome patients with and without SF3B1 mutation and from healthy controls

Project description:The splicing factor SF3B1 is the most commonly mutated gene in the myelodysplastic syndromes (MDS), particularly in patients with refractory anemia with ring sideroblasts (RARS). MDS is a disorder of the hematopoietic stem cell and we thus studied the transcriptome of CD34+ cells from MDS patients with SF3B1 mutations using RNA-sequencing. Genes significantly differentially expressed at the transcript and/or exon level in SF3B1 mutant compared to wildtype cases include genes involved in MDS pathogenesis (ASXL1, CBL), iron homeostasis and mitochondrial metabolism (ALAS2, ABCB7, SLC25A37) and RNA splicing/processing (PRPF8, HNRNPD). Many genes regulated by a DNA damage-induced BRCA1-BCLAF1-SF3B1 protein complex showed differential expression/splicing in SF3B1 mutant cases. Our data indicate that SF3B1 plays a critical role in MDS by affecting the expression and splicing of genes involved in specific cellular processes/pathways, many of which are relevant to the known RARS pathophysiology, suggesting a causal link. RNA-Seq was performed to compare the transcriptome of bone marrow CD34+ cells from eight MDS patients with SF3B1 mutation, four MDS patients with no known splicing mutation and five healthy controls.

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Project description:SF3B1 mutations, which occur in 20% of patients with myelodysplastic syndromes (MDS), are the hallmarks of a specific MDS subtype, MDS with ringed sideroblasts (MDS-RS), which is characterized by the accumulation of erythroid precursors in the bone marrow and affects the elderly population. Here, using single-cell technologies and functional validation studies of primary SF3B1-mutant MDS-RS samples (MDS-RS-3-bis, MDS-RS-13, and MDS-RS-14), we show that SF3B1 mutations lead to the activation of the EIF2AK1 pathway in response to heme deficiency and that targeting this pathway rescues aberrant erythroid differentiation and enables the red blood cell maturation of MDS-RS erythroblasts. These data support the development of EIF2AK1 inhibitors to overcome transfusion dependency in patients with SF3B1-mutant MDS-RS with impaired red blood cell production. MACS-purified CD34+ cells were subjected to a 3-phase in vitro culture as described previously (Huang et al., 2020a). Cells were maintained in phase 1 from the day of collection until day 8, at which time the cells underwent ribonucleoprotein-based gene editing and were transitioned to phase 2 medium. On day 13 of culture, the cells were transitioned to phase 3 medium. Samples for Western blot and cytospin analyses, and sample for flow cytometry were harvested on day 13 or 15 of culture, respectively.

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DNA Replication Stress Due to Loss of R-Loops in Myelodysplastic Syndromes with SF3B1 Mutation

Project description:Myelodysplastic syndromes (MDS) with mutated SF3B1 gene have many features including a favorable outcome that are distinct from MDS with mutations in other splicing factor genes SRSF2 or U2AF1. Molecular bases of these divergences are poorly understood. Here we show that SF3B1-mutated MDS are characterized by a dramatically reduced R-loop formation predominating in gene bodies, which tightly associates with reduced retention of introns specifically found in SF3B1-mutated, but not in U2AF1- or SRSF2-mutated MDS. Compared to erythroblasts from SRSF2- or U2AF1-mutated patients, SF3B1-mutated erythroblasts exhibited augmented DNA synthesis, accelerated replication forks, and single-stranded DNA exposure upon differentiation, which were recapitulated in murine Sf3b1K700E/+ proerythroblasts. Importantly, R-loop formation was restored by histone deacetylase inhibition using SAHA/vorinostat, which improved Sf3b1K700E/+ erythroblast differentiation. In conclusion, loss of R-loops with associated DNA replication stress is a hallmark of SF3B1- mutated MDS ineffective erythropoiesis, which could be used as a new therapeutic target.

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A variant erythroferrone disrupts iron homeostasis in SF3B1-mutated myelodysplastic syndrome (RNA-Seq)

Project description:Myelodysplastic syndromes (MDS) with ring sideroblasts are hematopoietic stem celldisorders with erythroid dysplasia and mutations in the SF3B1 splicing factor gene. MDS patientswith SF3B1 mutations often accumulate excessive tissue iron, even in the absence oftransfusions, but the mechanisms that are responsible for their parenchymal iron overload areunknown. Body iron content, tissue distribution, and the supply of iron for erythropoiesis arecontrolled by the hormone hepcidin, which is regulated by erythroblasts through secretion of theerythroid hormone erythroferrone (ERFE). Here, we identified an alternative ERFE transcript inMDS patients with the SF3B1 mutation. Induction of this ERFE transcript in primary SF3B1-mutated bone marrow erythroblasts generated a variant protein that maintained the capacity tosuppress hepcidin transcription. Plasma concentrations of ERFE were higher in MDS patientswith a SF3B1 gene mutation than in patients with SF3B1 wild-type MDS. Thus, hepcidinsuppression by a variant erythroferrone is likely responsible for the increased iron loading inpatients with SF3B1-mutated MDS, suggesting that ERFE could be targeted to prevent ironmediated toxicity. The expression of the variant ERFE transcript that was restricted to SF3B1-mutated erythroblasts decreased in lenalidomide-responsive anemic patients, identifying variantERFE as a specific biomarker of clonal erythropoiesis.

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RNA sequencing of bone marrow CD34+ cells from myelodysplastic syndrome patients with and without SF3B1 mutation and from healthy controls

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Accelerated DNA replication fork speed due to Loss of R-Loops in Myelodysplastic Syndromes with SF3B1 Mutation [RNAseq_CMNhuman]

Project description:Myelodysplastic syndromes (MDS) with mutated SF3B1 gene have many features including a favorable outcome that are distinct from MDS with mutations in other splicing factor genes SRSF2 or U2AF1. Molecular bases of these divergences are poorly understood. Here we show that SF3B1-mutated MDS are characterized by a dramatically reduced R-loop formation predominating in gene bodies, which associates with intron retention reduction specifically found in SF3B1-mutated, but not in U2AF1- or SRSF2-mutated MDS. Compared to erythroblasts from SRSF2- or U2AF1-mutated patients, SF3B1-mutated erythroblasts exhibited augmented DNA synthesis, accelerated replication forks, and single-stranded DNA exposure upon differentiation. Importantly, histone deacetylase inhibition using vorinostat restored Rloop formation,slowed down DNA replication forks and improved SF3B1-mutated erythroblast differentiation. In conclusion, loss of R-loops with associated DNA replication stress is a hallmark of SF3B1-mutated MDS ineffective erythropoiesis, which could be used as a new therapeutic target.

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