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      BRCA1 promoter hypermethylation in sporadic epithelial ovarian carcinoma: Association with low expression of BRCA1, improved survival and co-expression of DNA methyltransferases

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          Abstract

          The breast cancer susceptibility gene 1 ( BRCA1) inactivation in sporadic epithelial ovarian carcinoma (EOC) is common and low BRCA1 expression is associated with promoter hypermethylation. The clinical validation of BRCA1 methylation as a prognostic marker in EOC remains unresolved. The aim of the present study was to determine the aberrant promoter methylation of BRCA1 in benign and malignant ovarian tumor tissues, to establish the association with the clinicopathological significance and the prognostic value. Additionally, the contribution of DNA methyltransferase (DNMT) expression to BRCA1 promoter hypermethylation was determined. The rate of BRCA1 methylation was observed to be 35.2% (50/142) in the EOCs; however, no methylation (0/32) was observed in the benign tumors. BRCA1 methylation was significantly associated with the downregulation of BRCA1 expression (P<0.001) and the frequency of BRCA1 methylation was greater in the carcinomas of patients whose tumor was bilateral than that of patients with a unilateral carcinoma (P=0.015). BRCA1 methylation was significantly associated with the preoperative serum carbohydrate antigen-125 level (P=0.013), improved overall survival (P=0.005) and disease-free survival (P=0.007). In addition, a significant correlation was observed between the co-expression of DNMTs and the methylation status of BRCA1. Thus, the present study provided support for BRCA1 promoter hypermethylation as a prognostic marker for survival in sporadic EOC, and co-expression of DNMTs was observed to contribute to BRCA1 promoter hypermethylation.

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          Most cited references31

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          A strong candidate for the breast and ovarian cancer susceptibility gene BRCA1.

          A strong candidate for the 17q-linked BRCA1 gene, which influences susceptibility to breast and ovarian cancer, has been identified by positional cloning methods. Probable predisposing mutations have been detected in five of eight kindreds presumed to segregate BRCA1 susceptibility alleles. The mutations include an 11-base pair deletion, a 1-base pair insertion, a stop codon, a missense substitution, and an inferred regulatory mutation. The BRCA1 gene is expressed in numerous tissues, including breast and ovary, and encodes a predicted protein of 1863 amino acids. This protein contains a zinc finger domain in its amino-terminal region, but is otherwise unrelated to previously described proteins. Identification of BRCA1 should facilitate early diagnosis of breast and ovarian cancer susceptibility in some individuals as well as a better understanding of breast cancer biology.
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            The DNA methyltransferases of mammals.

            T Bestor (2000)
            The biological significance of 5-methylcytosine was in doubt for many years, but is no longer. Through targeted mutagenesis in mice it has been learnt that every protein shown by biochemical tests to be involved in the establishment, maintenance or interpretation of genomic methylation patterns is encoded by an essential gene. A human genetic disorder (ICF syndrome) has recently been shown to be caused by mutations in the DNA methyltransferase 3B (DNMT3B) gene. A second human disorder (Rett syndrome) has been found to result from mutations in the MECP2 gene, which encodes a protein that binds to methylated DNA. Global genome demethylation caused by targeted mutations in the DNA methyltransferase-1 (Dnmt1) gene has shown that cytosine methylation plays essential roles in X-inactivation, genomic imprinting and genome stabilization. The majority of genomic 5-methylcytosine is now known to enforce the transcriptional silence of the enormous burden of transposons and retroviruses that have accumulated in the mammalian genome. It has also become clear that programmed changes in methylation patterns are less important in the regulation of mammalian development than was previously believed. Although a number of outstanding questions have yet to be answered (one of these questions involves the nature of the cues that designate sites for methylation at particular stages of gametogenesis and early development), studies of DNA methyltransferases are likely to provide further insights into the biological functions of genomic methylation patterns.
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              Association between BRCA1 and BRCA2 mutations and survival in women with invasive epithelial ovarian cancer.

              Approximately 10% of women with invasive epithelial ovarian cancer (EOC) carry deleterious germline mutations in BRCA1 or BRCA2. A recent article suggested that BRCA2-related EOC was associated with an improved prognosis, but the effect of BRCA1 remains unclear. To characterize the survival of BRCA carriers with EOC compared with noncarriers and to determine whether BRCA1 and BRCA2 carriers show similar survival patterns. A pooled analysis of 26 observational studies on the survival of women with ovarian cancer, which included data from 1213 EOC cases with pathogenic germline mutations in BRCA1 (n = 909) or BRCA2 (n = 304) and from 2666 noncarriers recruited and followed up at variable times between 1987 and 2010 (the median year of diagnosis was 1998). Five-year overall mortality. The 5-year overall survival was 36% (95% CI, 34%-38%) for noncarriers, 44% (95% CI, 40%-48%) for BRCA1 carriers, and 52% (95% CI, 46%-58%) for BRCA2 carriers. After adjusting for study and year of diagnosis, BRCA1 and BRCA2 mutation carriers showed a more favorable survival than noncarriers (for BRCA1: hazard ratio [HR], 0.78; 95% CI, 0.68-0.89; P < .001; and for BRCA2: HR, 0.61; 95% CI, 0.50-0.76; P < .001). These survival differences remained after additional adjustment for stage, grade, histology, and age at diagnosis (for BRCA1: HR, 0.73; 95% CI, 0.64-0.84; P < .001; and for BRCA2: HR, 0.49; 95% CI, 0.39-0.61; P < .001). The BRCA1 HR estimate was significantly different from the HR estimated in the adjusted model (P for heterogeneity = .003). Among patients with invasive EOC, having a germline mutation in BRCA1 or BRCA2 was associated with improved 5-year overall survival. BRCA2 carriers had the best prognosis.
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                Author and article information

                Journal
                Oncol Lett
                Oncol Lett
                OL
                Oncology Letters
                D.A. Spandidos
                1792-1074
                1792-1082
                April 2014
                13 February 2014
                13 February 2014
                : 7
                : 4
                : 1088-1096
                Affiliations
                [1 ]Department of Pharmacology, School of Pharmacy, China Medical University, Shenyang, Liaoning 110001, P.R. China
                [2 ]Department of Obstetrics and Gynecology, First Affiliated Hospital, China Medical University, Shenyang, Liaoning 110001, P.R. China
                [3 ]Department of Pathology, College of Basic Medical Sciences, China Medical University, Shenyang, Liaoning 110001, P.R. China
                Author notes
                Correspondence to: Professor Minjie Wei, Department of Pharmacology, School of Pharmacy, China Medical University, 92 Bei’er Road, Shenyang, Liaoning 110001, P.R. China, E-mail: weiminjiecmu@ 123456163.com
                Article
                ol-07-04-1088
                10.3892/ol.2014.1878
                3961372
                24944674
                47ba7eaf-b815-4bc6-9498-678a1a354b21
                Copyright © 2014, Spandidos Publications

                This is an open-access article licensed under a Creative Commons Attribution-NonCommercial 3.0 Unported License. The article may be redistributed, reproduced, and reused for non-commercial purposes, provided the original source is properly cited.

                History
                : 13 June 2013
                : 02 January 2014
                Categories
                Articles

                Oncology & Radiotherapy
                ovarian cancer,breast cancer susceptibility gene 1,methylation,dna methyltransferases,immunohistochemistry

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