Project description:Myelodysplastic syndromes (MDS) are clonal stem cell disorders driven by heterogeneous genetic alterations leading to variable clinical course. MDS with splicing factor SF3B1 mutations is a distinct subtype with a favorable outcome. However, selected co-mutations induce poor prognosis and how these genetic lesions cooperate in human hematopoietic stem and progenitor cells (HSPCs) during disease progression is still unclear. Here, we integrated clinical and molecular profiling of patients with SF3B1 mutations with gene editing of primary and iPSC-derived human HSPCs to show that high-risk co-mutations impart distinct effects on lineage programs of SF3B1-mutant HSPCs. Secondary RUNX1 or STAG2 mutations were clinically associated with advanced disease and reduced survival. However, RUNX1 and STAG2 mutations induced opposing regulation of myeloid transcriptional programs and differentiation in SF3B1-mutant HSPCs. Moreover, high-risk RUNX1 and STAG2, but not low-risk TET2, mutations expanded distinct SF3B1-mutant HSPC subpopulations. These findings provide evidence that progression from low- to high-risk MDS involves distinct molecular and cellular routes depending on co-mutation patterns.
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.
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.
Project description: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.
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.
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.
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.
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.
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.