ABSTRACT
Perturbation in iron homeostasis is a hallmark of some hematologic diseases. Abnormal sideroblasts with accumulation of iron in the mitochondria are named ring sideroblasts (RS). RS is a cardinal feature of refractory anemia with RS (RARS) and RARS with marked thrombocytosis (RARS/-T). Mutations in SF3B1, a member of the RNA splicing machinery are frequent in RARS/-T and defects of this gene were linked to RS formation. Here we showcase the differences in iron architecture of SF3B1-mutant and wild-type (WT) RARS/-T and provide new mechanistic insights by which SF3B1 mutations lead to differences in iron. We found higher iron levels in SF3B1 mutant vs WT RARS/-T by transmission electron microscopy/spectroscopy/flow cytometry. SF3B1 mutations led to increased iron without changing the valence as shown by the presence of Fe(2+) in mutant and WT. Reactive oxygen species and DNA damage were not increased in SF3B1-mutant patients. RNA-sequencing and Reverse transcriptase PCR showed higher expression of a specific isoform of SLC25A37 in SF3B1-mutant patients, a crucial importer of Fe(2+) into the mitochondria. Our studies suggest that SF3B1 mutations contribute to cellular iron overload in RARS/-T by deregulating SLC25A37.
Subject(s)
Cation Transport Proteins/genetics , Introns , Iron/metabolism , Mitochondrial Proteins/genetics , Mutation , Myelodysplastic Syndromes/metabolism , Phosphoproteins/genetics , RNA Splicing , Ribonucleoprotein, U2 Small Nuclear/genetics , Case-Control Studies , DNA Damage , Flow Cytometry , Humans , Mitochondria/metabolism , Myelodysplastic Syndromes/genetics , RNA Splicing Factors , Reactive Oxygen Species/metabolism , Reverse Transcriptase Polymerase Chain Reaction , Sequence Analysis, DNAABSTRACT
We hypothesized that specific molecular mutations are important biomarkers for response to DNA methyltransferase inhibitors (DNMT inhibitors) and may have prognostic value in patients with myelodysplastic syndromes (MDS). Mutational analysis was performed in 92 patients with MDS and related disorders who received 5-azacytidine (n=55), decitabine (n=26) or both (n=11). Mutational status was correlated with overall response rate (ORR), progression-free survival (PFS) and overall survival (OS) by univariate and multivariate analysis. Risk stratification models were created. TET2, DNMT3A, IDH1/IDH2, ASXL1, CBL, RAS and SF3B1 mutations were found in 18, 9, 8, 26, 3, 2 and 13% of patients, respectively. In multivariate analysis, TET2(MUT) and/or DNMT3A(MUT) (P=0.03), platelets > or = 100 × 10(9)/l (P=0.007) and WBC<3.0 × 10(9)/l (P=0.03) were independent predictors of better response. TET2(MUT) and/or DNMT3A(MUT) (P=0.04) status was also independently prognostic for improved PFS, as were good or intermediate cytogenetic risk (P<0.0001), age<60 (P=0.0001), treatment with both 5-azacytidine and decitabine (P=0.02) and hemoglobin > or = 10 g/dl (P=0.01). Better OS was associated with ASXL1(WT) (P=0.008) and SF3B1(MUT) (P=0.01), and, similar to PFS, cytogenetic risk (P=0.0002), age (P=0.02) and hemoglobin (P=0.04). These data support the role of molecular mutations as predictive biomarkers for response and survival in MDS patients treated with DNMT inhibitors.
