RUNX1 Is Regulated by Androgen Receptor to Promote Cancer Stem Markers and Chemotherapy Resistance in Triple Negative Breast Cancer.

Triple negative breast cancer (TNBC) is an aggressive breast cancer subtype for which no effective targeted therapies are available. Growing evidence suggests that chemotherapy-resistant cancer cells with stem-like properties (CSC) may repopulate the tumor. The androgen receptor (AR) is expressed in up to 50% of TNBCs, and AR inhibition decreases CSC and tumor initiation. Runt-related transcription factor 1 (RUNX1) correlates with poor prognosis in TNBC and is regulated by the AR in prostate cancer. Our group has shown that RUNX1 promotes TNBC cell migration and regulates tumor gene expression. We hypothesized that RUNX1 is regulated by the AR and that both may work together in TNBC CSC to promote disease recurrence following chemotherapy. Chromatin immunoprecipitation sequencing (ChIP-seq) experiments in MDA-MB-453 revealed AR binding to RUNX1 regulatory regions. RUNX1 expression is upregulated by dihydrotestosterone (DHT) in MDA-MB-453 and in an AR+-TNBC HCI-009 patient-derived xenograft (PDX) tumors (p < 0.05). RUNX1 is increased in a CSC-like experimental model in MDA-MB-453 and SUM-159PT cells (p < 0.05). Inhibition of RUNX1 transcriptional activity reduced the expression of CSC markers. Interestingly, RUNX1 inhibition reduced cell viability and enhanced paclitaxel and enzalutamide sensitivity. Targeting RUNX1 may be an attractive strategy to potentiate the anti-tumor effects of AR inhibition, specifically in the slow-growing CSC-like populations that resist chemotherapy which lead to metastatic disease.

Progesterone increases tissue factor gene expression, procoagulant activity, and invasion in the breast cancer cell line ZR-75-1.

Progesterone in hormonal preparations increases the incidence of breast cancer. Tissue factor (TF), the initiator of the extrinsic coagulation pathway, is associated with metastasis in a wide variety of cancers. We demonstrate herein that TF mRNA and protein are up-regulated by progesterone in the breast cancer cell line ZR-75. Epidermal growth factor, also associated with increased breast cancer risk, did not regulate TF. The increase in TF is both rapid and transient; increasing after 6 h, reaching a maximum at 24 h, before decreasing to basal levels at 72 h. Sucrose gradient experiments demonstrated that TF is located in the heavy fraction of the plasma membrane, although caveolin-1 is not expressed in ZR-75. To understand the physiological implications of an increase in TF, we performed coagulation and invasion assays. An increase in TF corresponded to an increase in procoagulant activity. Furthermore, progesterone increased the invasion of ZR-75 cells through a matrigel, an effect that was blocked by an antibody against TF. Because TF expression is associated with an enhanced risk of metastasis, we postulate that the progesterone-dependent up-regulation of TF provides a survival advantage to burgeoning breast cancer cells and may contribute to the increased risk of cancer associated with combined hormone replacement therapy.