Electrostatic repulsion causes anticooperative DNA binding between tumor suppressor ETS transcription factors and JUN-FOS at composite DNA sites

Abstract

Many transcription factors regulate gene expression in a combinatorial fashion often by binding in close proximity on composite cis-regulatory DNA elements. Here we investigate the molecular basis by which ETS transcription factors bind with AP1 transcription factors JUN-FOS at composite DNA-binding sites. The ability to bind to DNA with JUN-FOS correlates with the phenotype of these proteins in prostate cancer: the oncogenic ERG and ETV1/4/5 subfamilies co-occupy ETS-AP1 sites with JUN-FOS in vitro, whereas JUN-FOS robustly inhibits DNA binding by the tumor suppressors EHF and SPDEF. EHF binds to ETS-AP1 DNA with tighter affinity than ERG in the absence of JUN-FOS, which may enable EHF to compete with ERG and JUN-FOS for binding to ETS-AP1 sites. Genome-wide mapping of EHF and ERG binding sites in a prostate epithelial cell line reveal that EHF is preferentially excluded from closely spaced ETS-AP1 DNA sequences. Structural modeling and mutational analyses indicate that adjacent positively-charged surfaces from EHF and JUN-FOS disfavor simultaneous DNA binding due to electrostatic repulsion. The conservation of positively charged residues on the JUN-FOS interface identified ELF1 as an additional ETS factor that exhibits anticooperative DNA binding, and we present evidence that ELF1 is frequently downregulated in prostate cancer. In summary, the divergence of electrostatic features of ETS factors at their JUN-FOS interface enables distinct binding events at ETS-AP1 DNA sequences. We propose that this mechanism can drive unique targeting of ETS transcription factors, thereby facilitating distinct transcriptional programs.