SUMOylation regulates chromatin protein network and accessibility at glucocorticoid receptor-binding sites

Glucocorticoid receptor (GR) is an essential transcription factor (TF), controlling metabolism, development and immune responses. SUMOylation regulates chromatin occupancy and target gene expression of GR in a locus-selective manner, but the mechanism of regulation has remained elusive. Here, we show using selective isolation of chromatin-associated proteins that the protein network around chromatin-bound GR is affected by SUMOylation, with several nuclear receptor coregulators and chromatin modifiers being more avidly associated with SUMOylation-deficient than SUMOylation competent GR. This difference is reflected in our chromatin accessibility and gene expression data, showing that the SUMOylation-deficient GR is more potent in opening chromatin at glucocorticoid-regulated enhancers and inducing expression of their target loci. Our results thus show that SUMOylation determines GR specificity by regulating the chromatin protein network and accessibility at GR-driven enhancers. We speculate that a similar mechanism is utilized by many other SUMOylated TFs.