Glucocorticoid Receptor Transcriptional Activation via the BRG1- Dependent Recruitment of TOP2 and Ku70/86

BRG1, the central ATPase of the human SWI/SNF complex, is critical for biological functions, including nuclear receptor (NR)-regulated transcription. Analysis of BRG1mutants demonstrated that functional motifs outside the ATPase domain are impor-tant for transcriptional activity. In the course of experiments examining protein interactions mediated through these domains, Ku70 (XRCC6) was found to associate with a BRG1 fragment encompassing the conserved helicase-SANT-associated (HSA) and BRK domains of BRG1. Subsequent transcriptional activation assays and chromatin immunoprecipitation studies showed that Ku70/86 and components of the topoisomerase II (TOP2)/poly(ADP ribose) polymerase 1 (PARP1) complex are necessary for NR-mediated SWI/SNF-dependent transcriptional activation from endogenous promoters. In addition to establishing Ku-BRG1 binding and TOP2/PARP1 recruitment by nuclear receptor transactivation, we demonstrate that the transient appearance of glucocorticoid receptor (GR)/BRG1-dependent, TOP2-mediated double-strand DNA breaks is required for efficient GR-stimu-lated transcription. Taken together, these results suggest that a direct interaction between Ku70/86 and BRG1 brings together SWI/SNF remodeling capabilities and TOP2 activity to enhance the transcriptional response to hormone stimulation. The winding of DNA around histones creates nucleosomes thatcompact DNA into a dense chromatin structure that limits accessibility and represses transcription. This chromatin organi-zation provides an additional level of control during certain nu-clear processes, such as transcription, replication, recombination