Related Experiment Video
Updated: Jul 10, 2026
Identifying the Effects of BRCA1 Mutations on Homologous Recombination using Cells that Express Endogenous Wild-type BRCA1
Published on: February 17, 2011
Molecular basis for estrogen receptor alpha deficiency in BRCA1-linked breast cancer
Alison M Hosey1, Julia J Gorski, Margaret M Murray
1Centre for Cancer Research and Cell Biology, Queen's University Belfast, 97 Lisburn Rd, Belfast, Northern Ireland, BT9 7BL, UK.
Background:
BRCA1-mutant breast tumors are typically estrogen receptor alpha (ER alpha) negative, whereas most sporadic tumors express wild-type BRCA1 and are ER alpha positive. We examined a possible mechanism for the observed ER alpha-negative phenotype of BRCA1-mutant tumors.
Methods:
We used a breast cancer disease-specific microarray to identify transcripts that were differentially expressed between paraffin-embedded samples of 17 BRCA1-mutant and 14 sporadic breast tumors. We measured the mRNA levels of estrogen receptor 1 (ESR1) (the gene encoding ER alpha), which was differentially expressed in the tumor samples, by quantitative polymerase chain reaction. Regulation of ESR1 mRNA and ER alpha protein expression was assessed in human breast cancer HCC1937 cells that were stably reconstituted with wild-type BRCA1 expression construct and in human breast cancer T47D and MCF-7 cells transiently transfected with BRCA1-specific short-interfering RNA (siRNA). Chromatin immunoprecipitation assays were performed to determine if BRCA1 binds the ESR1 promoter and to identify other interacting proteins. Sensitivity to the antiestrogen drug fulvestrant was examined in T47D and MCF-7 cells transfected with BRCA1-specific siRNA. All statistical tests were two-sided.
Results:
Mean ESR1 gene expression was 5.4-fold lower in BRCA1-mutant tumors than in sporadic tumors (95% confidence interval [CI] = 2.6-fold to 40.1-fold, P = .0019). The transcription factor Oct-1 recruited BRCA1 to the ESR1 promoter, and both BRCA1 and Oct-1 were required for ER alpha expression. BRCA1-depleted breast cancer cells expressing exogenous ER alpha were more sensitive to fulvestrant than BRCA1-depleted cells transfected with empty vector (T47D cells, the mean concentration of fulvestrant that inhibited the growth of 40% of the cells [IC40] for empty vector versus ER alpha: >10(-5) versus 8.0 x 10(-9) M [95% CI = 3.1 x 10(-10) to 3.2 x 10(-6) M]; MCF-7 cells, mean IC40 for empty vector versus ER alpha: >10(-5) versus 4.9 x 10(-8) M [95% CI = 2.0 x 10(-9) to 3.9 x 10(-6) M]).
Conclusions:
BRCA1 alters the response of breast cancer cells to antiestrogen therapy by directly modulating ER alpha expression.
Insights
BRCA1 mutations decrease estrogen receptor alpha (ER alpha) expression in breast tumors. BRCA1 directly regulates ER alpha, impacting breast cancer cell response to antiestrogen therapy.
Area of Science:
- Oncology
- Molecular Biology
- Genetics
Background:
- BRCA1-mutant breast tumors typically exhibit an estrogen receptor alpha (ER alpha)-negative phenotype, contrasting with ER alpha-positive sporadic tumors.
- Investigated the molecular mechanisms underlying the ER alpha-negative status in BRCA1-mutant breast cancers.
Purpose of the Study:
- To elucidate the role of BRCA1 in regulating ER alpha expression in breast cancer.
- To understand how BRCA1 influences breast cancer cell sensitivity to antiestrogen therapy.
Main Methods:
- Differential gene expression analysis using microarrays on BRCA1-mutant and sporadic breast tumors.
- Quantitative PCR to measure ESR1 (ER alpha gene) mRNA levels.
- In vitro studies using breast cancer cell lines to assess BRCA1's regulation of ESR1 and ER alpha protein, including chromatin immunoprecipitation assays and drug sensitivity testing with fulvestrant.
Main Results:
- BRCA1-mutant tumors showed a significant 5.4-fold decrease in ESR1 mRNA levels compared to sporadic tumors.
- BRCA1, recruited by transcription factor Oct-1 to the ESR1 promoter, is essential for ER alpha expression.
- BRCA1-depleted cells expressing ER alpha demonstrated increased sensitivity to the antiestrogen fulvestrant.
Conclusions:
- BRCA1 directly modulates ER alpha expression in breast cancer cells.
- This modulation by BRCA1 influences the efficacy of antiestrogen therapies in breast cancer treatment.
Related Concept Videos
01:11Pharmacogenetics of Drug Targets: β₂-Adrenergic Receptors, Apo E, Thymidylate Synthase
01:20The Retinoblastoma Gene
The first-ever tumor suppressor gene called Rb was identified in retinoblastoma - a rare eye tumor in children. In inherited forms of the disease, a child inherits one defective copy of the Rb gene, which predisposes them to retinoblastoma. However,...
01:32RNA Splicing