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Characterization of FOXA1 mutations in breast cancer (ATAC-seq KnockIn)

ABSTRACT: Invasive Lobular Carcinoma (ILC) is the second most frequent breast cancer (BCa) type and encompasses 10-15% of BCa cases. FOXA1 specific mutations are enriched in this subtype of BCa, however their role in breast cancer pathogenesis is still ill-defined. FOXA1, together with estrogen receptor (ER), is a key transcription factor for the correct activation of estrogen-dependent gene expression and, consequently, for mammary gland development and BCa identity. FOXA1 has the capability to bind to and de-compact heterochromatin to render it accessible for other nuclear proteins, such as ER, and allow activation of their transcriptional programs upon estrogen stimulation. In this project, we aim to elucidate the role of FOXA1 missense mutations in altering its binding to DNA, chromatin accessibility, ER-dependent transcription and their implication in limiting the sensitivity to standard-of-care anti-hormonal therapy, commonly used in ER-positive BCa patients. To this end, we have generated BCa cell lines expressing these FOXA1 mutations and we will employ ATAC-Seq, RIME assays, ChIP-Seq and RNA-Seq to ascertain their effect on DNA accessibility, DNA binding capability, as well as binding of transcriptional coregulators, such as ER, to chromatin. We will extend our analyses to our internal BCa patient datasets with detailed clinical annotation to study the correlation between presence of FOXA1 mutations and response to anti-hormonal therapy of ER-positive BCa patients. The results of this project will allow to understand how the different mutations in the Forkhead domain can alter FOXA1 and ER function, transcriptional regulation and response to anti-hormonal therapy in ER-positive BCa patients.

ORGANISM(S): Homo sapiens

PROVIDER: GSE161766 | GEO | 2020/11/19

REPOSITORIES: GEO

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Project description: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) highly enriched in ER+ endocrine-resistant (EndoR) cells. We identified Secretome14, a CGS subset encoding ER-dependent cancer secretory proteins, strongly predicts poor outcomes of ER+ BC and is elevated in ER+ metastases vs. primary tumors, irrespective to the ESR1 mutations. Parental (P) ER+ BC cells and their endocrine-resistant (EndoR) derivatives, and ER+ BC cells expressing doxycycline (Dox)-inducible ectopic FOXA1 were used in this study. Differential gene expression analysis was performed in EndoR vs. P cells and P cells +Dox vs. -Dox. We found that the FOXA1-CGS was highly enriched in the altered transcriptomes of two ER+ BC cell models (ZR75-1 and T47D) expressing ectopic H-FOXA1. The enriched hallmark gene sets, shared by the H-FOXA1 cell models, include “inflammatory response”, “complement”, and “interferon gamma response” for the H-FOXA1-induced, and “estrogen response early” and “estrogen response late” for the H-FOXA1-repressed genes. These findings point to the common transcriptional profile exhibiting an immune- over estrogen-responsive signature induced by H-FOXA1. In addition, we found that both the tamoxifen-resistant (TamR) and estrogen deprivation-resistant (EDR) derivatives of the 600MPE P cells were enriched for the H-FOXA1-induced CGS and FOXA1/ER-activated Secretome14. 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 BC.

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Characterization of FOXA1 mutations in breast cancer (ATAC-seq KnockIn)

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