and Mutations Exert Divergent Effects on DNA Repair and Sensitivity of Leukemia Cells to PARP Inhibitors.

Somatic variants in and are founding mutations in hematological malignancies that affect the epigenetic regulation of DNA methylation. Mutations in both genes often co-occur with activating mutations in genes encoding oncogenic tyrosine kinases such as , and , or with mutations affecting related signaling pathways such as and . Here, we show that and mutations exert divergent roles in regulating DNA repair activities in leukemia cells expressing these oncogenes. Malignant TET2-deficient cells displayed downregulation of BRCA1 and LIG4, resulting in reduced activity of BRCA1/2-mediated homologous recombination (HR) and DNA-PK-mediated non-homologous end-joining (D-NHEJ), respectively. TET2-deficient cells relied on PARP1-mediated alternative NHEJ (Alt-NHEJ) for protection from the toxic effects of spontaneous and drug-induced DNA double-strand breaks. Conversely, DNMT3A-deficient cells favored HR/D-NHEJ owing to downregulation of PARP1 and reduction of Alt-NHEJ. Consequently, malignant TET2-deficient cells were sensitive to PARP inhibitor (PARPi) treatment and , whereas DNMT3A-deficient cells were resistant. Disruption of TET2 dioxygenase activity or TET2-Wilms' tumor 1 (WT1)-binding ability was responsible for DNA repair defects and sensitivity to PARPi associated with TET2 deficiency. Moreover, mutation or deletion of mimicked the effect of mutation on DSB repair activity and sensitivity to PARPi. Collectively, these findings reveal that and mutations may serve as biomarkers of synthetic lethality triggered by PARPi, which should be explored therapeutically. SIGNIFICANCE: and mutations affect distinct DNA repair mechanisms and govern the differential sensitivities of oncogenic tyrosine kinase-positive malignant hematopoietic cells to PARP inhibitors.