The ubiquitin-proteasome system (UPS) plays an integral role in controlling protein turnover to modulate cellular processes such as growth, proliferation, differentiation, and apoptosis. This occurs through multiple mechanisms that rely on the regulation of numerous transcription factors such as steroid hormone nuclear receptors. The glucocorticoid receptor (GR) is a member of this receptor family and its activation promotes nuclear translocation and downstream transcriptional activity through the recruitment of co-regulatory complexes. Our goal is to understand the mechanisms by which the proteasome regulates glucocorticoid receptor-mediated gene transcription. To explore the effects of proteasome inhibition upon GR-mediated transcription, we used ChIP-Seq and microarray studies using breast cancer cells to examine GR binding and gene expression profiles after treatment with dexamethasone (dex) or dex in combination with a proteasome inhibitor, MG132 (dex + mg), for 1 hour and 18 hours. More than 14000 and 5000 GR-binding sites were apparent after both treatments in the 1 hour and 18 hour samples, respectively. GR binding sites seen during 1 hour of treatment can be mapped to more than 9000 genes while the binding sites in the 18 hour treatment samples mapped to over 5000 genes. In addition, over 55% of binding sites in all treatment groups are within 50 kilobases of annotated transcription start sites. To verify these putative interactions, we assayed the transcript levels of genes at both time periods and examined the levels of bound GR throughout the gene. The results reveal a differential regulation of genes that can be divided into three classes: dex-responsive, dex + mg-responsive, or dually responsive. Further analyses will reveal if there are clearly defined chromatin states that demarcate each class. These data provide insights into the intricate mechanisms of proteasome-mediated GR regulation and highlight proteasomal-regulated genes involved in numerous diseases and developmental disorders.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr 3928. doi:1538-7445.AM2012-3928