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Abstract Breast cancer is the most frequently diagnosed cancer in women worldwide. Oestrogen Receptor-α (ERα), is expressed in two thirds of human breast cancers, and the majority of patients are sensitive to endocrine therapy, i. e. anti-oestrogens or aromatase inhibitors that aim to block oestrogen signalling. In addition to ERα, the other members of the steroid receptor family (androgen, AR; progesterone, PR; glucocorticoid, GR; mineralocorticoid receptors, MR) also appear to play an important role in tumour development and recurrence, but the role of this signalling in cancer progression has not been fully characterised. Therefore, this study aims to address the role of the steroid receptor family members in breast cancer and to assess the effect of downstream signalling upon prognosis. Investigation of receptor signalling cross-talk using reporter, proliferation and migration assays, demonstrated that ERα and the other steroid receptors inhibit each other’s activity in endocrine responsive breast cancer cell lines, MCF7 and T47D. Furthermore, treatment with antioestrogen reversed the suppressive effects of ER𝛼;;; on the activity of the androgen, glucocorticoid progesterone receptors. To characterize receptor crosstalk on a global scale, RNA-seq and ChIP-seq datasets were analysed. Analysis of the ChIP-seq data demonstrated that the PR, GR and AR reprogramming of ERα results in the loss of ERα canonical binding sites and the gain of novel response elements/binding sites. Motif enrichment analysis of the novel ERα binding sites suggested that the altered binding in response to AR, GR and PR signalling, promotes the recruitment of ERα to androgen, glucocorticoid and progesterone response elements, respectively. Gene ontology analysis also revealed that this change in ERα binding sites is correlated with alterations in genes linked to cell proliferation and growth. Moreover, transcriptome studies showed that cotreatment of cells with estradiol and glucocorticoid or mineralocorticoid resulted in the upregulation of apoptotic signalling pathways. These findings may provide an explanation for the observed downregulation of GR and MR expression in ERα positive breast cancer. Patient datasets were used to investigate the prognostic significance of the steroid receptor target genes of interest, more specifically, those deregulated as a result of cross-talk. Considering overall survival and disease specific survival, univariate and multivariate Cox models with Lasso Regression were used to identify prognostic gene signatures using RNAₛeq datasets. Kaplan-Meier (KM) and ROC analyses were applied to evaluate risk models. Established genetic markers associated with MR, AR, GR and PR was used to stratify BC patients into low and high risk groups. Patients survival was found to be positively correlated with these signatures, demonstrates that these gene sets have prognostic value. Further studies are required to validate these preliminary results to understand the role of steroid receptor crosstalk in breast cancer formation, progression, and survival. Citation Format: Aygun Azadova, Greg Brooke, Antonio Marco. Steroid receptor cross-talk in breast cancer abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 2 (Late-Breaking, Clinical Trial, and Invited Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (7Suppl): Abstract nr LB335.
Azadova et al. (Fri,) studied this question.