A transcriptional repressive role for epithelial-specific ETS factor ELF3 on oestrogen receptor alpha in breast cancer cells

Oestrogen receptor-alpha (ER alpha) is a ligand-dependent transcription factor that primarily mediates oestrogen (E2)-dependent gene transcription required for mammary gland development. Coregulators critically regulate ER alpha transcription functions by directly interacting with it. In the present study, we report that ELF3, an epithelial-specific ETS transcription factor, acts as a transcriptional repressor of ER alpha. Co-immunoprecipitation (Co-IP) analysis demonstrated that ELF3 strongly binds to ER alpha in the absence of E2, but ELF3 dissociation occurs upon E2 treatment in a dose- and time-dependent manner suggesting that E2 negatively influences such interaction. Domain mapping studies further revealed that the ETS (E-twenty six) domain of ELF3 interacts with the DNA binding domain of ER alpha. Accordingly, ELF3 inhibited ER alpha's DNA binding activity by preventing receptor dimerization, partly explaining the mechanism by which ELF3 represses ER alpha transcriptional activity. Ectopic expression of ELF3 decreases ER alpha transcriptional activity as demonstrated by oestrogen response elements (ERE)-luciferase reporter assay or by endogenous ER alpha target genes. Conversely ELF3 knockdown increases ER alpha transcriptional activity. Consistent with these results, ELF3 ectopic expression decreases E2-dependent MCF7 cell proliferation whereas ELF3 knockdown increases it. We also found that E2 induces ELF3 expression in MCF7 cells suggesting a negative feedback regulation of ER alpha signalling in breast cancer cells. A small peptide sequence of ELF3 derived through functional interaction between ER alpha a and ELF3 could inhibit DNA binding activity of ER alpha and breast cancer cell growth. These findings demonstrate that ELF3 is a novel transcriptional repressor of ER alpha in breast cancer cells. Peptide interaction studies further represent a novel therapeutic option in breast cancer therapy.