Transactivation of the estrogen receptor promoter by BRCA1

William B. Archey,Bradley A. Arrick

doi:10.1186/s12935-017-0401-2

William B. Archey, Bradley A. Arrick

Open Access

https://doi.org/10.1186/s12935-017-0401-2

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Abstract

BackgroundAbsence of the estrogen receptor-α (ER) is perhaps the most distinctive pathological feature of breast cancers arising in women who inherit a mutation in BRCA1. Two hypotheses, not necessarily mutually exclusive, exist in the literature that describe mechanisms of ER transcriptional repression in breast cancer. One hypothesis suggests that methylation of cytosine–guanine dinucleotides (CpGs) primarily mediates repression, while the other maintains that transcriptional control is mediated by certain positive and negative promoter elements.MethodsTo determine if wild type BRCA1 could induce activity of the ER promoter, we performed a series of transient transfections with ER promoter segments linked to a luciferase reporter. The effect of BRCA1 on endogenous ER expression was evaluated by RNA analysis.ResultsFollowing cotransfection with a BRCA1 expression plasmid, we observed that ER promoter-driven luciferase activity was significantly increased in both MCF10A and IMEC cells (p < 0.005 and 0.0005 respectively, two-tailed t test). Specifically, the full length ER promoter construct showed approximately 5.6-fold (MCF10A) and tenfold (IMEC) increases in luciferase activity following BRCA1 transfection, compared with transfection with an empty expression plasmid (i.e. lacking BRCA1 sequence). We localized the ER promoter segment responsible for transactivation by BRCA1 to a 109 bp region containing an AP2γ homologous site.ConclusionsThe work described here, along with previously published work, indicates that activity of certain transcriptional regulatory elements and CpG methylation both represent important mechanisms by which the ER gene is typically inactive in breast cancers associated with BRCA1 mutations. The absence of ER in these breast cancers has significant implications for pathogenesis, prevention, and treatment.

Highlights

Absence of the estrogen receptor-α (ER) is perhaps the most distinctive pathological feature of breast cancers arising in women who inherit a mutation in BRCA1
We have reported that cytosine–guanine dinucleotides (CpGs) methylation of the ER gene is more extensive in ER-negative BRCA1-linked breast cancers compared with ER-negative breast cancers not linked to germline mutations in BRCA1 [10]
To focus our examination of transactivation of the ER promoter by BRCA1 in a cell type relevant to its role as a tumor suppressor gene in breast cancer, we performed all experiments with two human nontumorigenic mammary epithelial cell lines

Summary

Introduction

Absence of the estrogen receptor-α (ER) is perhaps the most distinctive pathological feature of breast cancers arising in women who inherit a mutation in BRCA1. Hayashi et al [12] have provided the clearest evidence that the upstream P0 promoter is utilized in ER-positive breast cancers They have described a transcriptional enhancer element in close proximity to this promoter that significantly augments transcription from P0-based promoter constructs in MCF-7 cells [16]. A negative cis element, located ~3.2 kb upstream of P1, was identified via a strategy of transfecting cells with decoy fragments of dsDNA corresponding to segments of promoter sequence. Using this approach, Penolazzi et al [17] reported that introduction of multiple copies of decoy dsDNA corresponding to a putative 102 bp negative element into MCF-7 or MDA-231 cells increased or reactivated ER expression, respectively. The most upstream positive enhancer element, termed ER-EH0 was mapped to a 35 bp segment beginning at −3744, relative to P1

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