Evidence for BRCA1 Haploinsufficiency in Expression Profiles from Morphologically Normal Fallopian Tube Epithelium.
Sophia George, Anca Milea, James Greenaway, Carl Virtanen, Sanjeev Shaw, Monika Sharma, Patricia Shaw. University Health Network, Toronto, Canada
Background: Histological precursors of High Grade Serous Carcinoma have been identified in fallopian tube epithelium of women at genetic high risk of ovarian/tubal/peritoneal carcinoma. One of the putative precursors, the p53 signature, is also found frequently in women at low risk. The most immediate precursor to invasive disease, serous tubal intraepithelial carcinoma (STIC) is found more frequently in mutation carriers. We have previously reported that tubal epithelium from mutation carriers (FTE-BRCA) has a differential gene expression signature during the luteal phase of the ovarian cycle. The purpose of this study is to determine whether morphologically normal FTE-BRCA has an expression profile different from non-carriers (FTE-non BRCA).
Design: Morphologically normal tubal epithelium was microdissected from snap-frozen tissues from 12 BRCA1 mutation carriers undergoing risk-reducing surgery and from 12 control samples. All samples were from pre-menopausal women, and an equal number of samples from the follicular and luteal phases were included. Following RNA extraction, reverse transcription and linear amplification, samples were hybridized to Affymetrix GeneChips. Normalized data was subjected to cluster analysis and differentially expressed genes identified using SAM and GeneSpring. Selected candidate genes were validated by real-time RT-PCR and immunohistochemistry on tissue microarrays (TMA) of normal tubes and ovarian cancers. Stained slides were scanned and digital slides (Aperio Scanner XT) analysed using automated image analysis (TMALab, Genie, Aperio, Inc).
Results: 135 genes were differentially expressed, and largely upregulated, with a greater than 2-fold difference and a p-value less than 0.05, in FTE-BRCA compared to FTE-non BRCA. The differences were present in both follicular and luteal phases. The selected target genes are involved in cell proliferation, in DNA damage and in inflammatory signaling. The differential expression of 5 targets was validated by RT-PCR and by immunohistochemistry. Levels of BRCA1 mRNA were not decreased in FTE-BRCA compared to non-BRCA.
Conclusions: We have demonstrated for the first time that FTE from BRCA1 heterozygotes differs from FTE-non BRCA in the absence of histological lesions. These differences suggest that BRCA1 haploinsufficiency exists in normal FTE-BRCA, and that normal FTE-BRCA may respond differently to the microenvironment. These changes may reflect the earliest molecular changes of serous carcinogenesis, and may be markers of increased cancer risk.
Category: Gynecologic & Obstetrics
Tuesday, March 1, 2011 11:45 AM
Platform Session: Section D, Tuesday Morning