Functionally characterizing the co-regulator repertoire of the Glucocorticoid Receptor

How steroid hormone receptors (SHRs) orchestrate transcriptional activity remains to be completely understood. Upon ligand activation, SHRs translocate to the nucleus and bind to the genome together with a co-regulator repertoire, crucial to induce gene expression. However, the essentiality of specific members of the SHR complex to drive transcription following hormonal stimuli remains elusive.  Through a FACS-based genome-wide CRISPR screen, we functionally dissected the co-regulatory complex of the Glucocorticoid Receptor (GR), and identified novel proteins that are imperative to drive ligand-induced transcription. We describe a novel functional interaction between PAXIP1 and STAG2 -Cohesin II subunit- as co-regulators of GR. We show that, without altering the GR cistrome, PAXIP1 and STAG2 depletion change the GR-transcriptome, by impairing the recruitment of 3D-genome organization proteins to the GR complex. Importantly, we show that PAXIP1 is required for stability of cohesin II on the genome, its localization to GR-bound sites, and maintenance of enhancer-promoter interactions. Moreover, in lung cancer, where GR acts a tumor suppressor, PAXIP1/STAG2 loss enhances GR-mediated tumor suppressor activity by modifying local chromatin interactions. All together, we introduce PAXIP1 and STAG2 as novel co-regulators of GR, required to maintain 3D genome architecture and ensure a correct transcriptional programme following hormonal stimuli.