Mis-splicing of mitotic regulators sensitizes SF3B1-mutated human HSCs to CHK1 inhibition [scRNA-seq]

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. Single cell RNA sequencing was performed on SF3B1 K700E mutant HSPCs and AAVS1 gene edited controls. Gene edited BFP+CD34+ HSPCs were flow-sorted 72 hours after gene editing.