Agonist-specific Protein Interactomes of Glucocorticoid and Androgen Receptor as Revealed by Proximity Mapping.

Glucocorticoid receptor (GR) and androgen receptor (AR) are steroid-inducible transcription factors (TFs). The GR and the AR are central regulators of various metabolic, homeostatic and differentiation processes and hence important therapeutic targets, especially in inflammation and prostate cancer, respectively. Hormone binding to these steroid receptors (SRs) leads to DNA binding and activation or repression of their target genes with the aid of interacting proteins, coregulators. However, protein interactomes of these important drug targets have remained poorly defined. We used proximity-dependent biotin identification to map the protein interaction landscapes of GR and AR in the presence and absence of their cognate agonist (dexamethasone, 5α-dihydrotestosterone) and antagonist (RU486, enzalutamide) in intact human cells. We reproducibly identified more than 30 proteins that interacted with the GR in an agonist-specific manner and whose interactions were significantly influenced by the DNA-binding function of the receptor. Interestingly, the agonist-dependent interactome of the GR overlapped considerably with that of the AR. In addition to known coactivators, corepressors and components of BAF (SWI/SNF) chromatin-remodeling complex, we identified a number of proteins, including lysine methyltransferases and demethylases that have not been previously linked to glucocorticoid or androgen signaling. A substantial number of these novel agonist-dependent GR/AR-interacting proteins, e.g. BCOR, IRF2BP2, RCOR1, and TLE3, have previously been implicated in transcription repression. This together with our data on the effect of BCOR, IRF2BP2, and RCOR1 on GR target gene expression suggests multifaceted functions and roles for SR coregulators. These first high confidence SR interactomes will aid in therapeutic targeting of the GR and the AR.