Coordinated mis-splicing of TMEM14C and ABCB7 causes ring sideroblast formation in SF3B1-mutant myelodysplastic syndrome
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ABSTRACT: Purpose: Mutant SF3B1 is near universally associated with MDS-RS but the exact mechanism of how mutant-SF3B1 induces ring sideroblast formation is unclear. Methods: iPSC samples were differentiated from 5F-HPC derived from MDS-RS patient iPSCs. CD34+ progenitors were isolated using the CD34 enrichment kit (Miltenyi). CD34-CD71+GlyA- pro-erythroblasts were isolated by flow sorting on day 4. CD71+GlyA+ erythroblasts were isolated by flow sorting on day 9. Libraries with DNA fragments of ~300bp were selected using AMPure XP bead purification. Purified libraries were sequenced on an Illumina HiSeq 2000 using paired-end, 50 bp reads. Mis-splicing analysis was performed as described in Inoue et al. 2019. Results: Mis-splicing analysis reveals ~100 genes that are strongly mis-spliced (>40%) by mutant SF3B1 during erythroid differentiation. We identify that mis-splicing of TMEM14C and ABCB7 contribute to RS formation in mutant SF3B1 cells. Conclusion: Our iPS derived mutant SF3B1MDS-RS in vitro model is the first demonstration of a cell line that recapitulates mis-splicing, erythroid differentiation, and ring sideroblast formation.
Project description:SF3B1 K700E is the most frequent mutation in myelodysplastic syndrome (MDS), but the mechanisms by which it drives MDS pathogenesis remain unclear. We derived a panel of 18 genetically matched SF3B1 K700E- and SF3B1 WT-induced pluripotent stem cell (iPSC) lines from patients with MDS with ring sideroblasts (MDS-RS) harboring isolated SF3B1 K700E mutations and performed RNA and ATAC sequencing in purified CD34+/CD45+ hematopoietic stem/progenitor cells (HSPCs) derived from them. We developed a novel computational framework integrating splicing with transcript usage and gene expression analyses and derived a SF3B1 K700E splicing signature consisting of 59 splicing events linked to 34 genes, which associates with the SF3B1 mutational status of primary MDS patient cells. The chromatin landscape of SF3B1 K700E HSPCs showed increased priming toward the megakaryocyte- erythroid lineage. Transcription factor motifs enriched in chromatin regions more accessible in SF3B1 K700E cells included, unexpectedly, motifs of the TEAD family. TEAD expression and transcriptional activity were upregulated in SF3B1-mutant iPSC-HSPCs, in support of a Hippo pathway-independent role of TEAD as a potential novel transcriptional regulator of SF3B1 K700E cells. This study provides a comprehensive characterization of the transcriptional and chromatin landscape of SF3B1 K700E HSPCs and nominates novel mis-spliced genes and transcriptional programs with putative roles in MDS-RS disease biology.
Project description:Splicing factor SF3B1 mutations are frequent somatic lesions in myeloid neoplasms that transform hematopoietic stem cells (HSCs) by inducing mis-splicing of target genes. However, the molecular and functional consequences of SF3B1 mutations in human HSCs remain unclear. Here, we identify the mis-splicing program in human HSCs as a targetable vulnerability by precise gene editing of SF3B1 K700E mutations in primary CD34+ cells. Mutant SF3B1 induced pervasive mis-splicing and reduced expression of genes regulating mitosis in single cell transcriptomics, critically BUBR1 and CDC27, leading to altered differentiation and delayed G2/M progression. Mutant SF3B1 mis-splicing or reduced expression of BUBR1 and CDC27 was sufficient to delay G2/M transit, leading to activation of CHK1, sensitizing cells to CHK1 inhibition. Clinical CHK1 inhibitor prexasertib selectively targeted SF3B1-mutant HSCs and abrogated engraftment in vivo. These findings identify mis-splicing of mitotic regulators in SF3B1-mutant HSCs as a targetable vulnerability engaged by pharmacological CHK1 inhibition.
Project description:Splicing factor SF3B1 mutations are frequent somatic lesions in myeloid neoplasms that transform hematopoietic stem cells (HSCs) by inducing mis-splicing of target genes. However, the molecular and functional consequences of SF3B1 mutations in human HSCs remain unclear. Here, we identify the mis-splicing program in human HSCs as a targetable vulnerability by precise gene editing of SF3B1 K700E mutations in primary CD34+ cells. Mutant SF3B1 induced pervasive mis-splicing and reduced expression of genes regulating mitosis in single cell transcriptomics, critically BUBR1 and CDC27, leading to altered differentiation and delayed G2/M progression. Mutant SF3B1 mis-splicing or reduced expression of BUBR1 and CDC27 was sufficient to delay G2/M transit, leading to activation of CHK1, sensitizing cells to CHK1 inhibition. Clinical CHK1 inhibitor prexasertib selectively targeted SF3B1-mutant HSCs and abrogated engraftment in vivo. These findings identify mis-splicing of mitotic regulators in SF3B1-mutant HSCs as a targetable vulnerability engaged by pharmacological CHK1 inhibition.
Project description:SF3B1 knockdown in human CD34+ cells leads to increased apoptosis and cell cycle arrest of early-stage erythroid cells and generation of abnormally nucleated late-stage erythroblasts. RNA-seq analysis of SF3B1-knockdown erythroid progenitor CFU-E cells revealed altered splicing of an E3 ligase Makorin Ring Finger Protein 1 (MKRN1) and subsequent activation of p53 pathway.Decreased expression of genes involved in mitosis/cytokinesis pathway including polo-like kinase 1 (PLK1) was noted in SF3B1-knockdown polychromatic and orthochromatic erythroblasts comparing to control cells.
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.
Project description:Mutations in the RNA splicing factor gene SF3B1 are common across hematologic and solid cancers and result in widespread alterations in splicing, but therapeutic means to correct this mis-splicing do not exist. Here, we utilize synthetic introns uniquely responsive to mutant SF3B1 to identify trans factors required for aberrant mutant SF3B1 splicing activity. This revealed the G-patch domain-containing protein GPATCH8 as required for mutant SF3B1-induced splicing alterations and impaired hematopoiesis. GPATCH8 is involved in quality control of branchpoint selection, interacts with the RNA helicase DHX15, and functionally opposes SUGP1, a G-patch protein recently implicated in SF3B1-mutant diseases. Silencing of GPATCH8 corrected one-third of mutant SF3B1-dependent splicing defects and was sufficient to improve dysfunctional hematopoiesis in SF3B1-mutant mouse and primary human progenitors. These data identify GPATCH8 as a novel splicing factor required for mis-splicing by mutant SF3B1 and highlight the therapeutic impact of correcting aberrant splicing in SF3B1-mutant cancers.
Project description:This collection contains microRNA expression profiling data for samples purified from umbilical cord blood, belonging to one of the followiing populations: MEP, MEGA1, MEGA2, ERY1, ERY2, ERY3. MEP: megakaryocyte-erythrocyte precursors (defined by CD34+ CD38+ IL-3Ra- CD45RA- ); MEGA1: megakaryocyte population 1 (defined by CD34+ CD61+ CD41+ CD45- ); MEGA2: megakaryocyte population 2 (defined by CD34- CD61+ CD41+ CD45- ); ERY1: erythrocyte population 1 (defined by CD34+ CD71+ GlyA- ); ERY2: erythrocyte population 2 (defined by CD34- CD71+ GlyA- ); ERY3: erythrocyte population 3 (defined by CD34- CD71+ GlyA+ ). Keywords: microRNA, miRNA, MEP, megakaryocyte, erythrocyte, lineage specification Varied numbers of samples were analyzed per population. Each sample came from one donor. Data were normalized as described (Lu et al., Nature 435, 834-838, 2005) with modifications. Average readings from water-only labeled samples were used for probe-specific background subtraction. Linear normalization among different bead sets for the same sample was performed using readings from 2 post-control probes with equal contribution. Sample normalization was subsequently carried out assuming equal total fluorescence readings.
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.
Project description:Mutations in the RNA splicing factor SF3B1 are common across hematologic and solid cancers and result in widespread alterations in splicing but therapeutic means to correct this mis-splicing do not exist. Here we utilize synthetic introns uniquely responsive to mutant SF3B1 to identify trans factors required for aberrant mutant SF3B1 splicing activity. This revealed the G-patch domain containing protein GPATCH8 as required for mutant SF3B1-induced splicing alterations and impaired hematopoiesis. GPATCH8 is involved in quality control of branchpoint selection, interacts with the RNA helicase DHX15, and functionally opposes SUGP1, a G-patch protein recently implicated in SF3B1 mutant diseases. Silencing of GPATCH8 corrected one-third of mutant SF3B1 splicing defects and was sufficient to improve hematopoiesis in SF3B1 mutant mouse and human cells. These data identify GPATCH8 as a novel splicing factor required for mis-splicing by mutant SF3B1 and the therapeutic impact of correcting aberrant splicing in SF3B1 mutant cancers.