GSE175418
ER reprogramming promotes a select pro-metastatic secretome in high FOXA1-expressing ER-positive endocrine-resistant and metastatic breast cancer [ChIP-seq]
Aberrant activation of the forkhead protein FOXA1 is observed in advanced hormone-related cancers. However, to date, key mediators of high FOXA1 signaling remain elusive. We demonstrate that ectopic high FOXA1 (H-FOXA1) expression promotes estrogen receptor-positive (ER+) breast cancer (BC) metastasis in a xenograft mouse model. Mechanistically, H-FOXA1 reprograms ER-chromatin binding to elicit a core gene signature (CGS) and an ER-dependent secretome highly enriched in ER+ endocrine-resistant (EndoR) cells. ER+ BC MCF7-parental (P) cells treated with estrogen deprivation or estrogen, and with doxycycline (Dox)-inducible FOXA1 overexpression were used in this study. We found that a majority of the lost or retained ER binding induced by H-FOXA1 overlapped with the ER binding sites in P cells induced by estrogen vs. tamoxifen treatment. The lost ER binding sites were also significantly enriched for the ER binding under E2 vs. ED, which corresponds to 11% of the total E2-stimulated ER binding, suggesting that H-FOXA1 induces a loss of selective E2-stimulated ER binding sites. In addition, we found that the proportion of H-FOXA1-induced ER-loss regions were significantly enriched for the unique ER binding sites in P vs. tamoxifen-resistant (TamR) cells, yet no enrichment of the ER-gain regions was observed in the unique ER binding in TamR vs. P cells. Our findings uncover H-FOXA1-induced ER reprogramming driving EndoR and metastasis, possibly via a H-FOXA1/ER-dependent secretome that warrants further studies to clarify its involvement in disease progression of ER+ metastatic breast cancer. Overall design: Examination of ER-chromatin binding in MCF7-P cells upon ectopic FOXA1 overexpression and in MCF7-P cells upon estrogen-deprivation vs. estrogen treatment.