Project description:Patients with primary refractory acute myeloid leukemia (AML) have a dismal long-term prognosis. Elucidating the resistance mechanisms to induction chemotherapy could help identify strategies to improve AML patient outcomes. Herein, we retrospectively analyzed the multi-omics data of more than 1,500 AML cases and found that patients with spliceosome mutations had a higher risk of developing refractory disease. RNA splicing analysis revealed that the mis-spliced genes in refractory patients converged on translation-associated pathways, promoted mainly by U2AF1 mutations. Integrative analyses of binding and splicing in AML cell lines substantiated that the splicing perturbations of mRNA translation genes originated from both the loss and gain of mutant U2AF1 binding. In particular, the U2AF1-S34F and U2AF1-Q157R mutants orchestrated the inclusion of exon 11 (encoding a premature termination codon) in the eukaryotic translation initiation factor 4A2 (EIF4A2). This aberrant inclusion led to reduced eIF4A2 protein expression via nonsense-mediated mRNA decay. Consequently, U2AF1 mutations caused a net decrease in global mRNA translation that induced the integrated stress response (ISR) in AML cells, which was confirmed by single-cell RNA-seq. The induction of ISR enhanced the ability of AML cells to respond and adapt to stress, contributing to chemoresistance. A pharmacologic inhibitor of ISR, ISRIB, sensitized U2AF1 mutant cells to chemotherapy. These findings highlight a resistance mechanism by which U2AF1 mutations drive chemoresistance and provide a therapeutic approach for AML through targeting the ISR pathway.
Project description:Whole-exome sequencing studies have identified common mutations affecting genes encoding components of the RNA splicing machinery in hematological malignancies. Here, we sought to determine how mutations affecting the 3' splice site recognition factor U2AF1 altered its normal role in RNA splicing. We find that U2AF1 mutations influence the similarity of splicing programs in leukemias, but do not give rise to widespread splicing failure. U2AF1 mutations cause differential splicing of hundreds of genes, affecting biological pathways implicated in myeloid disease such as DNA methylation (DNMT3B), X chromosome inactivation (H2AFY), the DNA damage response (ATR, FANCA), and apoptosis (CASP8). We show that U2AF1 mutations alter the preferred 3' splice site motif in vivo, in cell culture, and in vitro. Mutations affecting the first and second zinc fingers give rise to different alterations in splice site preference and largely distinct downstream splicing programs. These allele-specific effects are consistent with a computationally predicted model of U2AF1 in complex with RNA. Our findings suggest that U2AF1 mutations contribute to pathogenesis by causing quantitative changes in splicing that affect diverse cellular pathways, and give insight into the normal function of U2AF1’s zinc finger domains. mRNA profiles of K562 cells expressing U2AF1 WT, mutants and knockdown of U2AF1 generated by deep sequencing.
Project description:The mechanisms by which mutations of the splicing factor gene U2AF1 contribute to lung adenocarcinoma pathogenesis are not well understood. Here, we used prime editing to modify the endogenous U2AF1 gene in lung adenocarcinoma cells and assessed the resulting impact on alternative splicing. One specific KRAS mutation, G12S, leads to skipping of KRAS exon 2 and generation of a non-functional KRAS transcript. However, expression of the U2AF1 S34F mutant reverts this exon skipping and restores KRAS function, leading to an enrichment of U2AF1 S34F mutations in KRAS G12S-mutant lung adenocarcinomas. A comprehensive analysis of splicing factor/oncogene mutation co-occurrence in cancer genomes also revealed significant co-enrichment of KRAS Q61R and U2AF1 I24T mutations. Experimentally, KRAS Q61R mutation leads to KRAS exon 3 skipping, which in turn can be rescued by the expression of U2AF1 I24T. Our findings provide evidence that splicing factor mutations can rescue splicing defects caused by oncogenic mutations in a dynamic process of cascading selection.
Project description:The mechanisms by which mutations of the splicing factor gene U2AF1 contribute to lung adenocarcinoma pathogenesis are not well understood. Here, we used prime editing to modify the endogenous U2AF1 gene in lung adenocarcinoma cells and assessed the resulting impact on alternative splicing. One specific KRAS mutation, G12S, leads to skipping of KRAS exon 2 and generation of a non-functional KRAS transcript. However, expression of the U2AF1 S34F mutant reverts this exon skipping and restores KRAS function, leading to an enrichment of U2AF1 S34F mutations in KRAS G12S-mutant lung adenocarcinomas. A comprehensive analysis of splicing factor/oncogene mutation co-occurrence in cancer genomes also revealed significant co-enrichment of KRAS Q61R and U2AF1 I24T mutations. Experimentally, KRAS Q61R mutation leads to KRAS exon 3 skipping, which in turn can be rescued by the expression of U2AF1 I24T. Our findings provide evidence that splicing factor mutations can rescue splicing defects caused by oncogenic mutations in a dynamic process of cascading selection.
Project description:Whole-exome sequencing studies have identified common mutations affecting genes encoding components of the RNA splicing machinery in hematological malignancies. Here, we sought to determine how mutations affecting the 3' splice site recognition factor U2AF1 altered its normal role in RNA splicing. We find that U2AF1 mutations influence the similarity of splicing programs in leukemias, but do not give rise to widespread splicing failure. U2AF1 mutations cause differential splicing of hundreds of genes, affecting biological pathways implicated in myeloid disease such as DNA methylation (DNMT3B), X chromosome inactivation (H2AFY), the DNA damage response (ATR, FANCA), and apoptosis (CASP8). We show that U2AF1 mutations alter the preferred 3' splice site motif in vivo, in cell culture, and in vitro. Mutations affecting the first and second zinc fingers give rise to different alterations in splice site preference and largely distinct downstream splicing programs. These allele-specific effects are consistent with a computationally predicted model of U2AF1 in complex with RNA. Our findings suggest that U2AF1 mutations contribute to pathogenesis by causing quantitative changes in splicing that affect diverse cellular pathways, and give insight into the normal function of U2AF1’s zinc finger domains.
Project description:U2AF1 is a core component of spliceosome and controls cell-fate specific alternative splicing. U2AF1 mutations have been frequently identified in myelodysplastic syndromes (MDS) and acute myeloid leukemia (AML) patients, and mutations in U2AF1 are associated with poor prognosis in hematopoietic malignant diseases. To investigate the effects of U2af1 S34F in hematopoietic cells, we performed global gene expression profiling by RNA sequencing on U2af1-WT and U2af1 S34F 32D cells. We find that U2AF1 S34F causes increased reactive oxygen species (ROS) production. In hematopoietic cell line, a defect in mitochondrial function and DNA damage response deficiency are found in U2AF1 S34F expressing 32D cells.
Project description:Splicing factor mutations are common among cancers, recently emerging as drivers of myeloid malignancies. U2AF1 carries hotspot mutations in its RNA binding motifs; yet how they affect splicing and promote cancer remains unclear. The U2AF1/U2AF2 heterodimer is critical for 3’ splice site (3’SS) definition. To specifically unmask changes in U2AF1 function in vivo, we developed a crosslinking and immunoprecipitation procedure detecting contacts between U2AF1 and the 3’SS AG at single-nucleotide resolution (fractionated eCLIP-seq or freCLIP-seq). Our data reveal that U2AF1 S34F and Q157R mutants establish new 3’SS contacts at -3 and +1 nucleotides, respectively. These effects compromise U2AF2-RNA interactions, resulting predominantly in intron retention and exon exclusion. Integrating RNA binding (eCLIP-seq and freCLIP-seq), splicing (RNA-seq) and turnover (TimeLapse-seq or TL-seq) data, we predicted that U2AF1 mutations directly affect stress granule components. Remarkably, U2AF1-mutant cell lines and patient-derived MDS/AML blasts displayed a heightened stress granule response, pointing to a novel role for biomolecular condensates in adaptive oncogenic strategies. Keywords: splicing, RNA binding, U2AF1, U2AF2, S34F, Q157R, hotspot mutations, 3'SS, 3' splice site, myeloid malignancies, eCLIP, freCLIP, RNA-seq, RNA turnover, TimeLapse-seq, TL-seq, RNA granules, stress granules, stress response, biomolecular condensates, MDS, AML
Project description:Studies of AML patient samples have shown that specific combinations of AML disease alleles confer an adverse outcome, however, in vivo models do not exist for the majority of common, poor-prognosis genotypes. Here we show that TET2/FLT3 mutations can cooperate to induce AML in vivo using a genetically engineered mouse model, and that this model has a defined stem-cell population with a characteristic transcriptional and epigenetic profile. TET2 and FLT3 mutations cooperate to induce site-specific changes in DNA methylation and gene expression, including at loci that regulate hematopoietic differentiation. We demonstrate that re-expression of genes that are silenced in TET2/FLT3-mutant AML restores normal differentiation, demonstrating that the epigenetic program of TET2/FLT3-mutant AML cells can be reversed in vitro and in vivo. Using ERRBS, we profiled genome-wide DNA methylation patterns of the hematopoietic stem cells (LSK) population in Wide-type, Flt3-IDT, Tet2-/-, and Tet2-/-Flt3-IDT mice, each in triplicates