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FOXC1 is involved in ER? silencing by counteracting GATA3 binding and is implicated in endocrine resistance.

ABSTRACT: Estrogen receptor-? (ER?) mediates the essential biological function of estrogen in breast development and tumorigenesis. Multiple mechanisms, including pioneer factors, coregulators and epigenetic modifications have been identified as regulators of ER? signaling in breast cancer. However, previous studies of ER? regulation have focused on luminal and HER2-positive subtypes rather than basal-like breast cancer (BLBC), in which ER? is underexpressed. In addition, mechanisms that account for the decrease or loss of ER expression in recurrent tumors after endocrine therapy remain elusive. Here, we demonstrate a novel FOXC1-driven mechanism that suppresses ER? expression in breast cancer. We find that FOXC1 competes with GATA-binding protein 3 (GATA3) for the same binding regions in the cis-regulatory elements upstream of the ER? gene and thereby downregulates ER? expression and consequently its transcriptional activity. The forkhead domain of FOXC1 is essential for the competition with GATA3 for DNA binding. Counteracting the action of GATA3 at the ER? promoter region, overexpression of FOXC1 hinders recruitment of RNA polymerase II and increases histone H3K9 trimethylation at ER? promoters. Importantly, ectopic FOXC1 expression in luminal breast cancer cells reduces sensitivity to estrogen and tamoxifen. Furthermore, in breast cancer patients with ER-positive primary tumors who received adjuvant tamoxifen treatment, FOXC1 expression is associated with decreased or undetectable ER expression in recurrent tumors. Our findings highlight a clinically relevant mechanism that contributes to the low or absent ER? expression in BLBC. This study suggests a new paradigm to study ER? regulation during breast cancer progression and indicates a role of FOXC1 in the modulation of cellular response to endocrine treatment.

SUBMITTER: Yu-Rice Y

PROVIDER: S-EPMC5287293 | biostudies-literature | 2016 Oct

REPOSITORIES: biostudies-literature

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FOXC1 is involved in ERα silencing by counteracting GATA3 binding and is implicated in endocrine resistance.

Yu-Rice Y Y Jin Y Y Han B B Qu Y Y Johnson J J Watanabe T T Cheng L L Deng N N Tanaka H H Gao B B Liu Z Z Sun Z Z Bose S S Giuliano A E AE Cui X X

Oncogene 20160404 41

Estrogen receptor-α (ERα) mediates the essential biological function of estrogen in breast development and tumorigenesis. Multiple mechanisms, including pioneer factors, coregulators and epigenetic modifications have been identified as regulators of ERα signaling in breast cancer. However, previous studies of ERα regulation have focused on luminal and HER2-positive subtypes rather than basal-like breast cancer (BLBC), in which ERα is underexpressed. In addition, mechanisms that account for the d ...[more]

PMID: 27041579

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Project description:Estrogen Receptor (ESR1) drives growth in the majority of human breast cancers by binding to regulatory elements and inducing transcription events that promote tumor growth. Differences in enhancer occupancy by ESR1, contribute to the diverse expression profiles and clinical outcome observed in breast cancer patients. GATA3 is an ESR1 co-operating transcription factor mutated in breast tumors, however its genomic properties are not fully defined. In order to investigate the composition of enhancers involved in estrogen-induced transcription and the potential role of GATA3, we performed extensive ChIP-sequencing in unstimulated breast cancer cells and following estrogen treatment. We find that GATA3 is pivotal in mediating enhancer accessibility at regulatory regions involved in ESR1-mediated transcription. GATA3 silencing resulted in a global redistribution of co-factors and active histone marks prior to estrogen stimulation. These global genomic changes altered the ESR1 binding profile that subsequently occurred following estrogen, with events exhibiting both loss and gain in binding affinity, implying a GATA3 mediated re-distribution of ESR1 binding. The GATA3-mediated re-distributed ESR1 profile correlated with changes in gene expression, suggestive of its functionality. Chromatin loops at the TFF locus involving ESR1 bound enhancers occurred independently of ESR1 when GATA3 was silenced, indicating that GATA3, when present on the chromatin, may serve as a licensing factor for estrogen- ESR1 mediated interactions between cis-regulatory elements. Together these experiments suggest that GATA3 directly impacts ESR1 enhancer accessibility and may potentially explain the contribution of mutant-GATA3 in the heterogeneity of ESR1+ breast cancer. MCF7 cells were transfected with siRNA and cultured in hormone deprived conditions for a further 3 days. Cells were subsequently treated with 100nM estrogen (E2) or control (Veh) for 6 hrs. We performed two independent biological experiments each using three different siRNAs against GATA3 individually (six siGATA3 replicates in total). For siControl we used RNA from five biological replicates.

Project description:BackgroundEstrogen receptor (ER) positive breast cancer is often effectively treated with drugs that inhibit ER signaling, i.e., tamoxifen (TAM) and aromatase inhibitors (AIs). However, 30% of ER+ breast cancer patients develop resistance to therapy leading to tumour recurrence. Changes in the methylation profile have been implicated as one of the mechanisms through which therapy resistance develops. Therefore, we aimed to identify methylation loci associated with endocrine therapy resistance.MethodsWe used genome-wide DNA methylation profiles of primary ER+/HER2- tumours from The Cancer Genome Atlas in combination with curated data on survival and treatment to predict development of endocrine resistance. Association of individual DNA methylation markers with survival was assessed using Cox proportional hazards models in a cohort of ER+/HER2- tumours (N =?552) and two sub-cohorts corresponding to the endocrine treatment (AI or TAM) that patients received (N =?210 and N =?172, respectively). We also identified multivariable methylation signatures associated with survival using Cox proportional hazards models with elastic net regularization. Individual markers and multivariable signatures were compared with DNA methylation profiles generated in a time course experiment using the T47D ER+ breast cancer cell line treated with tamoxifen or deprived from estrogen.ResultsWe identified 134, 5 and 1 CpGs for which DNA methylation is significantly associated with survival in the ER+/HER2-, TAM and AI cohorts respectively. Multi-locus signatures consisted of 203, 36 and 178 CpGs and showed a large overlap with the corresponding single-locus signatures. The methylation signatures were associated with survival independently of tumour stage, age, AI treatment, and luminal status. The single-locus signature for the TAM cohort was conserved among the loci that were differentially methylated in endocrine-resistant T47D cells. Similarly, multi-locus signatures for the ER+/HER2- and AI cohorts were conserved in endocrine-resistant T47D cells. Also at the gene set level, several sets related to endocrine therapy and resistance were enriched in both survival and T47D signatures.ConclusionsWe identified individual and multivariable DNA methylation markers associated with therapy resistance independently of luminal status. Our results suggest that these markers identified from primary tumours prior to endocrine treatment are associated with development of endocrine resistance.

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FOXC1 is involved in ER? silencing by counteracting GATA3 binding and is implicated in endocrine resistance.

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FOXC1 is involved in ERα silencing by counteracting GATA3 binding and is implicated in endocrine resistance.

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