ABSTRACT
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.
Subject(s)
Cell Transformation, Neoplastic/genetics , Core Binding Factor Alpha 3 Subunit/physiology , Gene Expression Regulation, Neoplastic , Lymphoma, Extranodal NK-T-Cell/genetics , Nose Neoplasms/genetics , Proto-Oncogene Proteins c-myc/physiology , Transcription, Genetic/genetics , Apoptosis , Azepines/pharmacology , Binding Sites , Cell Division , Cell Line, Tumor , Core Binding Factor Alpha 3 Subunit/antagonists & inhibitors , Core Binding Factor Alpha 3 Subunit/genetics , Enhancer Elements, Genetic , Genes, Reporter , Genetic Vectors , Humans , Lymphoma, Extranodal NK-T-Cell/etiology , Lymphoma, Extranodal NK-T-Cell/metabolism , Lymphoma, Extranodal NK-T-Cell/pathology , Molecular Targeted Therapy , Nose Neoplasms/etiology , Nose Neoplasms/metabolism , Nose Neoplasms/pathology , Protein Interaction Mapping , Proto-Oncogene Proteins c-myc/antagonists & inhibitors , RNA Interference , RNA, Small Interfering/genetics , Recombinant Fusion Proteins/metabolism , Triazoles/pharmacology , Up-RegulationABSTRACT
RUNX1/AML1 is among the most commonly mutated genes in human leukemia. Haploinsufficiency of RUNX1 causes familial platelet disorder with predisposition to myeloid malignancies (FPD/MM). However, the molecular mechanism of FPD/MM remains unknown. Here we show that murine Runx1(+/-) hematopoietic cells are hypersensitive to granulocyte colony-stimulating factor (G-CSF), leading to enhanced expansion and mobilization of stem/progenitor cells and myeloid differentiation block. Upon G-CSF stimulation, Runx1(+/-) cells exhibited a more pronounced phosphorylation of STAT3 as compared with Runx1(+/+) cells, which may be due to reduced expression of Pias3, a key negative regulator of STAT3 signaling, and reduced physical sequestration of STAT3 by RUNX1. Most importantly, blood cells from a FPD patient with RUNX1 mutation exhibited similar G-CSF hypersensitivity. Taken together, Runx1 haploinsufficiency appears to predispose FPD patients to MM by expanding the pool of stem/progenitor cells and blocking myeloid differentiation in response to G-CSF.
