The long-term objective of this proposal is to elucidate the mechanism by which BRCA1 suppresses development of breast and ovarian cancers in women. Despite the wealth of evidence that implicates BRCA1 in DNA damage response, it remains unclear as to why loss of BRCA1 function predominantly increases cancer risks in estrogen-responsive tissues. Recent published work and our own preliminary data lead us to the hypothesis that BRCA1 may negatively regulate the tissue-specific expression of aromatase, a rate-limiting enzyme in estrogen biosynthesis and a key player in breast cancer development. Loss of BRCA1 function in ovary and adipose stromal cells in breast tissue may lead to elevated levels of both circulating and local estrogen, thus increasing cancer risks in the major estrogen-responsive tissues. This hypothesis could explain the tissue and gender-specific phenomena of BRCA1. Furthermore, our model predicts that depletion of BRCA1 in ovary or stromal cells in breast tissue may contribute to tumor development in an endocrine or paracrine manner, even when the tumorigenic epithelial cells themselves still retain the functional alleles of BRCA1. This could at least partially explain why somatic mutations of BRCA1 are rarely found in sporadic breast and ovarian cancer. To test this hypothesis, we will study the effect of BRCA1 on aromatase expression by ectopically expression and siRNA knockdown of BRCA1 in tissue culture cells. We will also elucidate the mechanism by which BRCA1 is recruited to the tissue-specific promoter of the aromatase gene. Furthermore, we will investigate the impact of BRCA1 on transcription initiation at the aromatase promoter. Finally we will use mouse models to determine the effect of Brcal on aromatase expression in vivo, circulating estrogen levels, and estrogen-dependent growth in reproductive tissues. The potential link between BRCA1 and aromatase expression represents a conceptual advance in understanding the tumor suppressor function of BRCA1. Given that aromatase inhibitors have become one of the most effective drugs in breast cancer treatment, the proposed work promises to provide novel targets for diagnostic and therapeutic purposes.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA118578-05
Application #
7667685
Study Section
Integrative and Clinical Endocrinology and Reproduction Study Section (ICER)
Program Officer
Woodhouse, Elizabeth
Project Start
2006-08-01
Project End
2011-07-31
Budget Start
2009-08-01
Budget End
2010-07-31
Support Year
5
Fiscal Year
2009
Total Cost
$245,846
Indirect Cost
Name
University of Texas Health Science Center San Antonio
Department
Other Basic Sciences
Type
Schools of Medicine
DUNS #
800772162
City
San Antonio
State
TX
Country
United States
Zip Code
78229
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Ghosh, Sagar; Gu, Fei; Wang, Chou-Miin et al. (2014) Genome-wide DNA methylation profiling reveals parity-associated hypermethylation of FOXA1. Breast Cancer Res Treat 147:653-9
Lu, Yunzhe; Li, Jiezhi; Cheng, Dongmei et al. (2012) The F-box protein FBXO44 mediates BRCA1 ubiquitination and degradation. J Biol Chem 287:41014-22
Chiang, Huai-Chin; Nair, Sreejith J; Yeh, I-Tien et al. (2012) Association of radiotherapy with preferential depletion of luminal epithelial cells in a BRCA1 mutation carrier. Exp Hematol Oncol 1:31
Ghosh, Sagar; Kang, Tao; Wang, Howard et al. (2011) Mechanical phenotype is important for stromal aromatase expression. Steroids 76:797-801
Lu, Yunzhe; Kang, Tao; Hu, Yanfen (2011) BRCA1/BARD1 complex interacts with steroidogenic factor 1--A potential mechanism for regulation of aromatase expression by BRCA1. J Steroid Biochem Mol Biol 123:71-8
Ghosh, Sagar; Dean, Angela; Walter, Marc et al. (2010) Cell density-dependent transcriptional activation of endocrine-related genes in human adipose tissue-derived stem cells. Exp Cell Res 316:2087-98
Ghosh, Sagar; Hu, Yanfen; Li, Rong (2010) Cell density is a critical determinant of aromatase expression in adipose stromal cells. J Steroid Biochem Mol Biol 118:231-6
Hu, Yanfen (2009) BRCA1, hormone, and tissue-specific tumor suppression. Int J Biol Sci 5:20-7
Ghosh, Sagar; Choudary, Ahsan; Ghosh, Sangeeta et al. (2009) IKKbeta mediates cell shape-induced aromatase expression and estrogen biosynthesis in adipose stromal cells. Mol Endocrinol 23:662-70

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