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
Hemizygous deletion of 17p13, which harbors the TP53 gene, has been identified in >10% of newly diagnosed multiple myeloma (MM) patients and is associated with poor prognosis. To date, there is no conclusive evidence that TP53 is the critical gene. Furthermore, the functional effect of TP53 haploinsufficiency is not well characterized. By utilizing human myeloma cell lines, we showed that TP53 hemizygous loss was associated with decreased basal expression level with a partially or severely inactivated p53 response upon genotoxic and non-genotoxic stress. The pathway deficiency was manifested as defective p53 transcriptional activities, together with significant resistance to apoptosis. In some cases with p53 WT/- and no p53 protein expression, the remaining allele was silenced by promoter hypermethylation. We also developed a p53 target gene signature to summarize the complexity of the p53 pathway abnormalities in MM and showed that it is strongly associated with genomic complexity and patient survival. In conclusion, this study identified TP53 as the critical gene located in 17p13, and revealed its haploinsufficiency properties in MM. Furthermore, we have elucidated that multiple mechanisms can deregulate the p53 functions and that this has important prognostic impact in MM.
