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DNA methylation profiles of primary ovarian cancers

ABSTRACT: Targeted approaches have revealed frequent epigenetic alterations in ovarian cancer, but the scope and relation of these changes to histologic subtype of disease is unclear. Genome-wide methylation and expression data for 14 clear cell carcinoma (CCC), 32 non-CCC, and 4 corresponding normal cell lines were generated to determine how methylation profiles differ between cells of different histological derivations of ovarian cancer. Consensus clustering showed that CCC is epigenetically distinct. Inverse relationships between expression and methylation in CCC were identified, suggesting functional regulation by methylation, and included 22 hypomethylated (UM) genes and 276 hypermethylated (HM) genes. Categorical and pathway analyses indicated that the CCC-specific UM genes were involved in response to stress and many contain hepatocyte nuclear factor (HNF) 1 binding sites, while the CCC-specific HM genes included members of the estrogen receptor alpha (ERalpha) network and genes involved in tumor development. We independently validated the methylation status of 17 of these pathway-specific genes, and confirmed increased expression of HNF1 network genes and repression of ERalpha pathway genes in CCC cell lines and primary cancer tissues relative to non-CCC specimens. Treatment of three CCC cell lines with the demethylating agent Decitabine significantly induced expression for all five genes analyzed. Coordinate changes in pathway expression were confirmed using two primary ovarian cancer datasets (p<0.0001 for both). Our results suggest that methylation regulates specific pathways and biological functions in CCC, with hypomethylation influencing the characteristic biology of the disease while hypermethylation contributes to the carcinogenic process.

ORGANISM(S): Homo sapiens

PROVIDER: GSE51820 | GEO | 2014/12/31

SECONDARY ACCESSION(S): PRJNA225585

REPOSITORIES: GEO

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Project description:The etiology of ovarian cancer is poorly understood, mainly due to the lack of an appropriate experimental model for studying the onset and progression of this disease. We have created a mouse model termed ERalpha d/d in which a conditional deletion of estrogen receptor alpha (ERalpha) gene occurred in the anterior pituitary, but ERalpha expression remained intact in the hypothalamus and the ovary. The loss of negative-feedback regulation by estrogen (E) at the level of the pituitary led to elevated production of luteinizing hormone (LH) by this tissue. Hyperstimulation of ovarian cells by LH resulted in increased steroidogenesis, leading to high circulating levels of progesterone, testosterone and E. The ERalpha d/d mice exhibited formation of palpable ovarian epithelial tumors starting at 5 months of age, and by 12 months, most mice carrying these tumors died. Besides proliferating epithelial cells, these tumors also contained an expanded population of stromal cells, which express P450 aromatase suggesting that these cells acquired the ability to synthesize E. In ERalpha d/d mice, in response to the E produced by the stromal cells, the ERalpha signaling is accentuated in the ovarian epithelial cells, triggering increased ERalpha-dependent gene expression, abnormal cell proliferation, and tumorigenesis. The ERalpha d/d animal model of ovarian epithelial tumorigenesis will serve as a powerful tool for exploring the involvement of E-dependent signaling pathways in the etiology of ovarian cancer. To identify aberrantly regulated genes in epithelial ovarian tumors, we performed gene expression profling of ovarian tumor tissue isolated from ERaplha d/d mice and normal ovary tissue isolated from ERaplha f/f control mice. The ERalpha d/d mouse model was created via conditional deletion of ERalpha by employing the Cre-LoxP strategy. Transgenic mice expressing Cre recombinase under the control of progesterone receptor (PR) promoter, termed PR-cre mice, were crossed with mice harboring the M-bM-^@M-^XfloxedM-bM-^@M-^Y ERalpha gene (ERalpha f/f) to create the ERalpah d/d mice in which the ERalpha gene is deleted in cells expressing PR. Ovarian tumor tissue was isolated from ERalpha d/d mice and normal ovary tissue was isolated from ERalpha f/f mice at 5 months and 10 months of age. Tissues were snap frozen and total RNA was isolated. Total RNA was pooled from 3 mice for each sample subjected to microarray analysis.

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DNA methylation profiles of primary ovarian cancers

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