Approximately 70% of invasive breast cancer expresses estrogen receptor-alpha (ER). Our lab and others have found that 50-60% of early-stage ER+ breast cancers also express glucocorticoid receptor (GR), and that high GR expression provides favorable prognostic information in early-stage breast cancer independently of PR expression. Specifically, in an analysis of primary tumor GR expression in ER+ invasive breast tumors from over 1000 ER+ early-stage patients with >20 year clinical follow-up, we discovered that high tumor GR mRNA expression (and by implication, high GR activity) was associated with a significantly lower risk of relapse. More recently, we found that in ER+ breast cancer cell line models, GR activation remodels chromatin so that ER- chromatin association and ER-target gene expression are significantly altered. Based on these data, we hypothesize that ER and GR can provide coordinated regulation of good prognosis, anti-proliferative and pro- differentiation genes. We propose to determine the molecular mechanisms underlying GR-mediated modulation of both wild-type and mutant ER transcriptional activity, and to define the specific patterns of ER/GR-mediated gene expression in breast cancer.
In Aim 1, we will characterize how GR ligand binding domain activation [by either dexamethasone (dex) or novel selective GR modulators (SGRMs)] affects ER activity, consequent ER-mediated gene expression, and ultimately ER-associated tumor cell proliferation.
In Aim 2, we will investigate GR and ER chromatin and co-regulator association in the presence of dex in comparison to the novel SGRMs. This will allow us to better understand the requirements of chromatin conformation and GR/ER co-regulator assembly in modifying ER+ breast cancer's proliferative gene expression. Finally, in Aim 3, we will use in vivo ER+ breast cancer patient-derived xenograft models, mutant ER-expressing cell lines, and tamoxifen-resistant ER+ models to define SGRM anti-tumor activity with the aim of defining clinical contexts in which GR modulators are most likely to be effective. Together, these experiments will both increase our understanding of GR/ER crosstalk in breast cancer (and possibly other hormone-sensitive cancers e.g. endometrial) and are expected to lead to new GR-targeted therapies that harness our discovery of anti-proliferative activity following GR modulation in ER+/GR+ breast cancer.
One of the most pressing problems in breast cancer treatment is to devise new therapies for estrogen receptor-expressing tumors that do not respond adequately to anti-estrogen therapies. For these tumors, our laboratory discovered that a related hormone receptor, the glucocorticoid or stress hormone receptor, can also be targeted to help reduce tumor growth driven by estrogen. In this project we will perform experiments to understand the mechanisms whereby these two hormone receptors act in breast cancer, with the overall goal of developing new, effective and relatively non-toxic treatments for breast cancer.
