The RUNX genes encode transcription factors involved in development and human disease. RUNX1 and RUNX3 are frequently associated with leukemias, yet the basis for their involvement in leukemogenesis is not fully understood. Here, we show that Runx1;Runx3 double-knockout (DKO) mice exhibited lethal phenotypes due to bone marrow failure and myeloproliferative disorder. These contradictory clinical manifestations are reminiscent of human inherited bone marrow failure syndromes such as Fanconi anemia (FA), caused by defective DNA repair. Indeed, Runx1;Runx3 DKO cells showed mitomycin C hypersensitivity, due to impairment of monoubiquitinated-FANCD2 recruitment to DNA damage foci, although FANCD2 monoubiquitination in the FA pathway was unaffected. RUNX1 and RUNX3 interact with FANCD2 independently of CBFβ, suggesting a nontranscriptional role for RUNX in DNA repair. These findings suggest that RUNX dysfunction causes DNA repair defect, besides transcriptional misregulation, and promotes the development of leukemias and other cancers.
RUNX3, runt-domain transcription factor, is a master regulator of gene expression in major developmental pathways. It acts as a tumor suppressor in many cancers but is oncogenic in certain tumors. We observed upregulation of RUNX3 mRNA and protein expression in nasal-type extranodal natural killer (NK)/T-cell lymphoma (NKTL) patient samples and NKTL cell lines compared to normal NK cells. RUNX3 silenced NKTL cells showed increased apoptosis and reduced cell proliferation. Potential binding sites for MYC were identified in the RUNX3 enhancer region. Chromatin immunoprecipitation–quantitative PCR revealed binding activity between MYC and RUNX3. Co-transfection of the MYC expression vector with RUNX3 enhancer reporter plasmid resulted in activation of RUNX3 enhancer indicating that MYC positively regulates RUNX3 transcription in NKTL cell lines. Treatment with a small-molecule MYC inhibitor (JQ1) caused significant downregulation of MYC and RUNX3, leading to apoptosis in NKTL cells. The growth inhibition resulting from depletion of MYC by JQ1 was rescued by ectopic MYC expression. In summary, our study identified RUNX3 overexpression in NKTL with functional oncogenic properties. We further delineate that MYC may be an important upstream driver of RUNX3 upregulation and since MYC is upregulated in NKTL, further study on the employment of MYC inhibition as a therapeutic strategy is warranted.
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