ABSTRACT
Analysis of 4,405 variants in 89,050 European subjects from 41 case-control studies identified three independent association signals for estrogen-receptor-positive tumors at 11q13. The strongest signal maps to a transcriptional enhancer element in which the G allele of the best candidate causative variant rs554219 increases risk of breast cancer, reduces both binding of ELK4 transcription factor and luciferase activity in reporter assays, and may be associated with low cyclin D1 protein levels in tumors. Another candidate variant, rs78540526, lies in the same enhancer element. Risk association signal 2, rs75915166, creates a GATA3 binding site within a silencer element. Chromatin conformation studies demonstrate that these enhancer and silencer elements interact with each other and with their likely target gene, CCND1.
Subject(s)
Breast Neoplasms/genetics , Chromosomes, Human, Pair 11/genetics , Cyclin D1/genetics , Enhancer Elements, Genetic/genetics , Polymorphism, Single Nucleotide/genetics , Binding Sites , Case-Control Studies , Cell Line, Tumor , Chromatin/chemistry , Chromatin/genetics , Chromatin Immunoprecipitation , Cyclin D1/metabolism , Electrophoretic Mobility Shift Assay , Female , GATA3 Transcription Factor/antagonists & inhibitors , GATA3 Transcription Factor/genetics , GATA3 Transcription Factor/metabolism , Gene Expression Regulation, Neoplastic , Humans , Luciferases/metabolism , Promoter Regions, Genetic/genetics , RNA, Messenger/genetics , RNA, Small Interfering/genetics , Real-Time Polymerase Chain Reaction , Reverse Transcriptase Polymerase Chain Reaction , Silencer Elements, Transcriptional/genetics , ets-Domain Protein Elk-4/antagonists & inhibitors , ets-Domain Protein Elk-4/genetics , ets-Domain Protein Elk-4/metabolismABSTRACT
Glioma is the most common adult primary brain tumor. Its most malignant form, glioblastoma multiforme (GBM), is almost invariably fatal, due in part to the intrinsic resistance of GBM to radiation- and chemotherapy-induced apoptosis. We analyzed B-cell leukemia-2 (Bcl-2) anti-apoptotic proteins in GBM and found myeloid cell leukemia-1 (Mcl-1) to be the highest expressed in the majority of malignant gliomas. Mcl-1 was functionally important, as neutralization of Mcl-1 induced apoptosis and increased chemotherapy-induced apoptosis. To determine how Mcl-1 was regulated in glioma, we analyzed the promoter and identified a novel functional single nucleotide polymorphism in an uncharacterized E26 transformation-specific (ETS) binding site. We identified the ETS transcription factor ELK4 as a critical regulator of Mcl-1 in glioma, since ELK4 downregulation was shown to reduce Mcl-1 and increase sensitivity to apoptosis. Importantly the presence of the single nucleotide polymorphism, which ablated ELK4 binding in gliomas, was associated with lower Mcl-1 levels and a greater dependence on Bcl-xL. Furthermore, in vivo, ELK4 downregulation reduced tumor formation in glioblastoma xenograft models. The critical role of ELK4 in Mcl-1 expression and protection from apoptosis in glioma defines ELK4 as a novel potential therapeutic target for GBM.
