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Role of direct interaction in BRCA1 inhibition of estrogen receptor activity
1Department of Radiation Oncology, Long Island Jewish Medical Center, The Long Island Campus for the Albert Einstein College of Medicine, 270-05 76th Avenue, New Hyde Park, New York, NY 11040, USA.
Abstract:
The BRCA1 gene was previously found to inhibit the transcriptional activity of the estrogen receptor [ER-alpha] in human breast and prostate cancer cell lines. In this study, we found that breast cancer-associated mutations of BRCA1 abolish or reduce its ability to inhibit ER-alpha activity and that domains within the amino- and carboxyl-termini of the BRCA1 protein are required for the inhibition. BRCA1 inhibition of ER-alpha activity was demonstrated under conditions in which a BRCA1 transgene was transiently or stably over-expressed in cell lines with endogenous wild-type BRCA1 and in a breast cancer cell line that lacks endogenous functional BRCA1 (HCC1937). In addition, BRCA1 blocked the expression of two endogenous estrogen-regulated gene products in human breast cancer cells: pS2 and cathepsin D. The BRCA1 protein was found to associate with ER-alpha in vivo and to bind to ER-alpha in vitro, by an estrogen-independent interaction that mapped to the amino-terminal region of BRCA1 (ca. amino acid 1-300) and the conserved carboxyl-terminal activation function [AF-2] domain of ER-alpha. Furthermore, several truncated BRCA1 proteins containing the amino-terminal ER-alpha binding region blocked the ability of the full-length BRCA1 protein to inhibit ER-alpha activity. Our findings suggest that the amino-terminus of BRCA1 interacts with ER-alpha, while the carboxyl-terminus of BRCA1 may function as a transcriptional repression domain. Oncogene (2001) 20, 77 - 87.
Insights
Breast cancer-associated BRCA1 mutations impair its ability to inhibit estrogen receptor alpha (ER-alpha) activity. The BRCA1 protein interacts with ER-alpha, suggesting a role in regulating estrogen-responsive genes.
Area of Science:
- Molecular Biology
- Genetics
- Cancer Research
Background:
- The BRCA1 gene is known to inhibit estrogen receptor alpha (ER-alpha) transcriptional activity in cancer cell lines.
- BRCA1 mutations are linked to breast and prostate cancer development.
Purpose of the Study:
- To investigate how breast cancer-associated BRCA1 mutations affect its inhibitory function on ER-alpha.
- To identify the domains of BRCA1 involved in ER-alpha inhibition and interaction.
Main Methods:
- Overexpression of BRCA1 transgenes in various human breast and prostate cancer cell lines.
- In vivo and in vitro binding assays to assess BRCA1-ER-alpha interaction.
- Analysis of estrogen-regulated gene products (pS2 and cathepsin D) expression.
Main Results:
- Breast cancer-associated BRCA1 mutations significantly reduce or abolish ER-alpha inhibition.
- Specific domains in the amino- and carboxyl-termini of BRCA1 are crucial for ER-alpha inhibition.
- BRCA1 directly associates with ER-alpha through an estrogen-independent interaction involving BRCA1's N-terminus and ER-alpha's AF-2 domain.
- BRCA1 blocks the expression of endogenous estrogen-regulated genes pS2 and cathepsin D.
Conclusions:
- The N-terminus of BRCA1 mediates interaction with ER-alpha, while the C-terminus may act as a transcriptional repression domain.
- BRCA1's ability to inhibit ER-alpha activity is compromised by cancer-associated mutations, potentially contributing to tumorigenesis.