Discovery of a Glucocorticoid Receptor (GR) Activity Signature Using Selective GR Antagonism in ER-Negative Breast Cancer

Abstract

Although high glucocorticoid receptor (GR) expression in early-stage estrogen receptor (ER)-negative breast cancer is associated with shortened relapse-free survival (RFS), how associated GR transcriptional activity contributes to aggressive breast cancer behavior is not well understood. Using potent GR antagonists and primary tumor gene expression data, we sought to identify a tumor-relevant gene signature based on GR activity that would be more predictive than GR expression alone. Global gene expression and GR ChIP-sequencing were performed to identify GR-regulated genes inhibited by two chemically distinct GR antagonists, mifepristone and CORT108297. Differentially expressed genes from MDA-MB-231 cells were cross-evaluated with significantly expressed genes in GR-high versus GR-low ER-negative primary breast cancers. The resulting subset of GR-targeted genes was analyzed in two independent ER-negative breast cancer cohorts to derive and then validate the GR activity signature (GRsig). Gene expression pathway analysis of glucocorticoid-regulated genes (inhibited by GR antagonism) revealed cell survival and invasion functions. GR ChIP-seq analysis demonstrated that GR antagonists decreased GR chromatin association for a subset of genes. A GRsig that comprised = 74 GR activation-associated genes (also reversed by GR antagonists) was derived from an adjuvant chemotherapy-treated Discovery cohort and found to predict probability of relapse in a separate Validation cohort (HR = 1.9; = 0.012). The GRsig discovered herein identifies high-risk ER-negative/GR-positive breast cancers most likely to relapse despite administration of adjuvant chemotherapy. Because GR antagonism can reverse expression of these genes, we propose that addition of a GR antagonist to chemotherapy may improve outcome for these high-risk patients. .

Contribution of Immune Cells to Glucocorticoid Receptor Expression in Breast Cancer

“…Our analysis showed that high GR expression was associated with better outcomes in TNBC in METABRIC but not validated in TCGA where only a trend towards improved survival was seen with no statistical significance. Our findings in TNBC subtype did not replicate results from previous publications probably due to the different data cohort (TCGA and METABRIC) and methodology for ER-positivity used here [ 10 , 13 , 20 ]. As published by Conzen et al in Cancer Research , 8 Gene Expression Omnibus (GEO) studies were combined and expression of ESR1 was used to categorize samples into specific subtypes with 1378 patients (1024 ESR1 positive and 354 ESR1 negative) [ 10 ].…”

“…Our study shows that GR-high breast cancer has better survival compared to GR-low breast cancer, particularly in ER-positive/HER2-negative breast cancer. This is consistent with previous retrospective studies showing that GR expression in ER-positive breast cancer is associated with better outcomes [ 10 , 13 , 20 ]. On the contrary, previous studies have shown that GR expression in ER-negative breast cancer was associated with worse RFS.…”

“…Although the role of GR activation in chemoresistance and enhanced aggressive phenotype have been studied both in vitro [ 13 ] and in vivo [ 13 ], both models lack immune cells. It is well known that TNBC have more immune cell infiltration than ER-positive tumors [ 14 ].…”

Editorial: Hormone Receptors and Breast Cancer

“…TNBCs are a group of heterogeneous BCs and represent a challenge for therapy. On the other hand, other steroid receptors, such as vitamin D receptor (10), glucocorticoid and androgen receptors (11, 12), as well as tyrosine kinase receptors, including IGF-1 and insulin receptors (13–15), can be also expressed in breast cells, and their roles and significance in cancer cell growth might deserve further investigation.…”

Flightless-I mediates the repression of estrogen receptor α target gene expression by the glucocorticoid receptor in MCF-7 cells

“…Studies have demonstrated that GR and ERα alter each other's regulatory and phenotypic roles. For instance, GR expression is associated with more favorable clinical outcomes in breast cancer [30][31][32][33]. Previous studies have documented the repressive actions of GR on specific ERα transcriptional responses [15].…”