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
Runt-related transcription factor 3 (RUNX3) is a well-documented tumour suppressor that is frequently inactivated in gastric cancer. Here, we define a novel mechanism by which RUNX3 exerts its tumour suppressor activity involving the TEAD-YAP complex, a potent positive regulator of proliferative genes. We report that the TEAD-YAP complex is not only frequently hyperactivated in liver and breast cancer, but also confers a strong oncogenic activity in gastric epithelial cells. The increased expression of TEAD-YAP in tumour tissues significantly correlates with poorer overall survival of gastric cancer patients. Strikingly, RUNX3 physically interacts with the N-terminal region of TEAD through its Runt domain. This interaction markedly reduces the DNA-binding ability of TEAD that attenuates the downstream signalling of TEAD-YAP complex. Mutation of RUNX3 at Arginine 122 to Cysteine, which was previously identified in gastric cancer, impairs the interaction between RUNX3 and TEAD. Our data reveal that RUNX3 acts as a tumour suppressor by negatively regulating the TEAD-YAP oncogenic complex in gastric carcinogenesis.
