Related Experiment Video

Updated: Mar 23, 2026

Silencing of BRCA2 to Identify Novel BRCA2-regulated Biological Functions in Cultured Human Cells

Silencing of BRCA2 to Identify Novel BRCA2-regulated Biological Functions in Cultured Human Cells

Published on: August 12, 2015

BRCA1 positively regulates FOXO3 expression by restricting FOXO3 gene methylation and epigenetic silencing through

C Gong^1,2, S Yao¹, A R Gomes¹

¹Department of Surgery and Cancer, Imperial College London, London, UK.

|April 5, 2016

Abstract:

BRCA1 mutation or depletion correlates with basal-like phenotype and poor prognosis in breast cancer but the underlying reason remains elusive. RNA and protein analysis of a panel of breast cancer cell lines revealed that BRCA1 deficiency is associated with downregulation of the expression of the pleiotropic tumour suppressor FOXO3. Knockdown of BRCA1 by small interfering RNA (siRNA) resulted in downregulation of FOXO3 expression in the BRCA1-competent MCF-7, whereas expression of BRCA1 restored FOXO3 expression in BRCA1-defective HCC70 and MDA-MB-468 cells, suggesting a role of BRCA1 in the control of FOXO3 expression. Treatment of HCC70 and MDA-MB-468 cells with either the DNA methylation inhibitor 5-aza-2'-deoxycitydine, the N-methyltransferase enhancer of zeste homologue 2 (EZH2) inhibitor GSK126 or EZH2 siRNA induced FOXO3 mRNA and protein expression, but had no effect on the BRCA1-competent MCF-7 cells. Chromatin immunoprecipitation (ChIP) analysis demonstrated that BRCA1, EZH2, DNMT1/3a/b and histone H3 lysine 27 trimethylation (H3K27me3) are recruited to the endogenous FOXO3 promoter, further advocating that these proteins interact to modulate FOXO3 methylation and expression. In addition, ChIP results also revealed that BRCA1 depletion promoted the recruitment of the DNA methyltransferases DNMT1/3a/3b and the enrichment of the EZH2-mediated transcriptional repressive epigenetic marks H3K27me3 on the FOXO3 promoter. Methylated DNA immunoprecipitation assays also confirmed increased CpG methylation of the FOXO3 gene on BRCA1 depletion. Analysis of the global gene methylation profiles of a cohort of 33 familial breast tumours revealed that FOXO3 promoter methylation is significantly associated with BRCA1 mutation. Furthermore, immunohistochemistry further suggested that FOXO3 expression was significantly associated with BRCA1 status in EZH2-positive breast cancer. Consistently, high FOXO3 and EZH2 mRNA levels were significantly associated with good and poor prognosis in breast cancer, respectively. Together, these data suggest that BRCA1 can prevent and reverse FOXO3 suppression via inhibiting EZH2 and, consequently, its ability to recruit the transcriptional repressive H3K27me3 histone marks and the DNA methylases DNMT1/3a/3b, to induce DNA methylation and gene silencing on the FOXO3 promoter.

Insights

BRCA1 deficiency silences the tumor suppressor FOXO3 by promoting DNA methylation and epigenetic silencing. Restoring BRCA1 function reactivates FOXO3, offering a potential therapeutic target for breast cancer.

Area of Science:

Oncology
Molecular Biology
Epigenetics

Background:

BRCA1 mutations are linked to aggressive breast cancer, but the molecular mechanisms are unclear.
BRCA1 deficiency correlates with a basal-like phenotype and poor prognosis.
The tumor suppressor FOXO3's role in BRCA1-deficient breast cancer is under investigation.

Purpose of the Study:

To elucidate the relationship between BRCA1, FOXO3 expression, and epigenetic modifications in breast cancer.
To investigate the mechanism by which BRCA1 influences FOXO3 expression.
To explore the prognostic significance of FOXO3 and EZH2 in breast cancer.

Main Methods:

RNA and protein analysis in breast cancer cell lines.
Small interfering RNA (siRNA) for BRCA1 knockdown.
Treatment with DNA methylation and EZH2 inhibitors.
Chromatin immunoprecipitation (ChIP) and methylated DNA immunoprecipitation (MeDIP) assays.
Analysis of familial breast tumor methylation profiles and immunohistochemistry.

Main Results:

BRCA1 deficiency leads to downregulation of FOXO3 expression.
BRCA1 influences FOXO3 expression through epigenetic mechanisms involving EZH2 and DNA methylation.
BRCA1 depletion promotes recruitment of EZH2 and DNA methyltransferases to the FOXO3 promoter, leading to gene silencing.
FOXO3 promoter methylation is associated with BRCA1 mutation in familial breast tumors.
FOXO3 expression correlates with BRCA1 status in EZH2-positive breast cancer.

Conclusions:

BRCA1 prevents FOXO3 suppression by inhibiting EZH2-mediated epigenetic silencing.
BRCA1's role in maintaining FOXO3 expression is crucial for breast cancer prognosis.
Targeting the BRCA1-FOXO3 pathway may offer therapeutic strategies for breast cancer.

Read full analysis

More Related Videos

Utilizing Functional Genomics Screening to Identify Potentially Novel Drug Targets in Cancer Cell Spheroid Cultures

Utilizing Functional Genomics Screening to Identify Potentially Novel Drug Targets in Cancer Cell Spheroid Cultures

Published on: December 26, 2016

Author Spotlight: Exploring Salidroside's Molecular Mechanisms in Breast Cancer Treatment

Author Spotlight: Exploring Salidroside's Molecular Mechanisms in Breast Cancer Treatment

Published on: June 9, 2023

Related Concept Videos

Epigenetic Regulation

Epigenetic Regulation

Epigenetic mechanisms play an essential role in healthy development. Conversely, precisely regulated epigenetic mechanisms are disrupted in diseases like cancer.

Epigenetic Regulation

Epigenetic Regulation

Epigenetic changes alter the physical structure of the DNA without changing the genetic sequence and often regulate whether genes are turned on or off. This regulation ensures that each cell produces only proteins necessary for its function. For example, proteins that promote bone growth are not produced in muscle cells. Epigenetic mechanisms play an essential role in healthy development. Conversely, precisely regulated epigenetic mechanisms are disrupted in diseases like cancer.
X-chromosome...

Epigenetic Regulation

Epigenetic Regulation

mTOR Signaling and Cancer Progression

mTOR Signaling and Cancer Progression

The mammalian target of rapamycin or mTOR protein was discovered in 1994 due to its direct interaction with rapamycin. The protein gets its name from a yeast homolog called TOR. The mTOR protein complex in mammalian cells plays a major role in balancing anabolic processes such as the synthesis of proteins, lipids, and nucleotides and catabolic processes, such as autophagy in response to environmental cues, such as availability of nutrients and growth factors.
The mTOR pathway or the...

mTOR Signaling and Cancer Progression

mTOR Signaling and Cancer Progression

Negative Regulator Molecules

Negative Regulator Molecules

Positive regulators allow a cell to advance through cell cycle checkpoints. Negative regulators have an equally important role as they terminate a cell’s progression through the cell cycle—or pause it—until the cell meets specific criteria.

Articles linked to this work by shared authors, journal, and citation graph.

Measurement of the Ratio of Branching Fractions B(B_{c}^{+}→J/ψτ^{+}ν_{τ})/B(B_{c}^{+}→J/ψμ^{+}ν_{μ}).

Physical review letters·2026

Precision Measurement of the Muon Charge Asymmetry from W-Boson Decays in pp Collisions at sqrt[s]=13 TeV in the Forward Region.

Physical review letters·2026

Polarization Measurement of Λ_{c}^{+} and Λ[over ¯]_{c}^{-} Baryons in p-Ne Collisions at sqrt[s_{NN}]=68.6 GeV.

Physical review letters·2026

First Measurement of the Decay-Time-Integrated CP Asymmetry in B_{s}^{0}→D_{s}^{-}π^{+} Decays.

Physical review letters·2026

First Evidence of the Decay B^{+}→π^{+}e^{+}e^{-}.

Physical review letters·2026

Study of Nuclear Effects on Charm Production in Light-Ion Collisions.

Physical review letters·2026

See all related articles