ABSTRACT
ETV6 (or TEL), a transcriptional repressor belonging to the ETS family, is frequently involved in chromosomal translocations linked with human cancers. It displays a DNA-binding mode distinct from other ETS proteins due to the presence of a self-associating PNT domain. In this study, we used NMR spectroscopy to dissect the structural and dynamic bases for the autoinhibition of ETV6 DNA binding by sequences C-terminal to its ETS domain. The C-terminal inhibitory domain (CID) contains two helices, H4 and H5, which sterically block the DNA-binding interface of the ETS domain. Importantly, these appended helices are only marginally stable as revealed by amide hydrogen exchange and (15)N relaxation measurements. The CID is thus poised to undergo a facile conformational change as required for DNA binding. The CID also dampens millisecond timescale motions of the ETS domain hypothesized to be critical for the recognition of specific ETS target sequences. This work illustrates the use of appended sequences on conserved structural domains to generate biological diversity and complements previous studies of the allosteric mechanism of ETS1 autoinhibition to reveal both common and divergent features underlying the regulation of DNA binding by ETS transcription factors.
Subject(s)
Proto-Oncogene Proteins c-ets/chemistry , Proto-Oncogene Proteins c-ets/metabolism , Repressor Proteins/chemistry , Repressor Proteins/metabolism , Animals , Binding Sites , DNA/metabolism , Humans , Mice , Models, Molecular , Molecular Dynamics Simulation , Nuclear Magnetic Resonance, Biomolecular , Protein Conformation , Protein Structure, Tertiary , ETS Translocation Variant 6 ProteinABSTRACT
The transcriptional programs regulated through the activity of the androgen receptor (AR) modulate normal prostate development and the maintenance of prostatic functions at maturity. AR signaling also controls key survival and growth functions operative in prostate cancer. Inhibiting the AR program remains the key target in the treatment of advanced prostate cancer, and suppressing AR also holds great potential for preventing the development or progression of early stage prostate cancer. In this review, we detail molecular mechanisms of AR activity, cellular components contributing to the maintenance of AR signaling despite AR-ligand suppression, and discuss treatment strategies designed to target components of resistance to AR-directed therapeutics.
Subject(s)
Androgens/metabolism , Neoplasms, Hormone-Dependent/metabolism , Prostatic Neoplasms/metabolism , Androgen Receptor Antagonists/pharmacology , Androgen Receptor Antagonists/therapeutic use , Androgens/biosynthesis , Androgens/physiology , Animals , Antineoplastic Agents/pharmacology , Antineoplastic Agents/therapeutic use , Gene Expression Regulation, Neoplastic , Humans , Male , Neoplasms, Hormone-Dependent/pathology , Neoplasms, Hormone-Dependent/therapy , Orchiectomy , Prostatic Neoplasms/pathology , Prostatic Neoplasms/therapy , Protein Isoforms/genetics , Receptors, Androgen/genetics , Receptors, Androgen/metabolism , Receptors, Androgen/physiology , Signal TransductionABSTRACT
The ETS protein TEL, a transcriptional repressor, contains a PNT domain that, as an isolated fragment in vitro, self-associates to form a head-to-tail polymer. How such polymerization might affect the DNA-binding properties of full-length TEL is unclear. Here we report that monomeric TEL binds to a consensus ETS site with unusually low affinity (K(d) = 2.8 x 10(-8) M). A deletion analysis demonstrated that the low affinity was caused by a C-terminal inhibitory domain (CID) that attenuates DNA binding by approximately 10-fold. An NMR spectroscopically derived structure of a TEL fragment, deposited in the Protein Data Bank, revealed that the CID consists of two alpha-helices, one of which appears to block the DNA binding surface of the TEL ETS domain. Based on this structure, we substituted two conserved glutamic acids (Glu-431 and Glu-434) with alanines and found that this activated DNA binding and enhanced trypsin sensitivity in the CID. We propose that TEL displays a conformational equilibrium between inhibited and activated states and that electrostatic interactions involving these negatively charged residues play a role in stabilizing the inhibited conformation. Using a TEL dimer as a model polymer, we show that self-association facilitates cooperative binding to DNA. Cooperativity was observed on DNA duplexes containing tandem consensus ETS sites at variable spacing and orientations, suggesting flexibility in the region of TEL linking its self-associating PNT domain and DNA-binding ETS domain. We speculate that TEL compensates for the low affinity, which is caused by autoinhibition, by binding to DNA as a cooperative polymer.
