BRCA1 Promoter Methylation in Sporadic Breast Cancer Is Associated with Reduced BRCA1 Copy Number and Chromosome 17 Aneusomy

Abstract

To explore the molecular mechanisms for the similarities between inherited and noninherited forms of breast cancer, we tested the hypothesis that inactivation of BRCA1 by promoter hypermethylation is associated with reduced gene copy number and chromosome 17 aneusomy as observed in tumors from BRCA1 mutation carriers. Using a combination of methylation-specific PCR analysis and fluorescence in situ hybridization, we observed varying degrees of promoter methylation in 39 of 131 (29.8%) primary tumors. Despite significant tumor heterogeneity, mean copy numbers of BRCA1 and CEP17 per cell were lower in methylated cases compared with unmethylated cases [1.78 versus 2.30 (P = 0.001) and 1.85 versus 2.29 (P = 0.005), respectively]. Methylation was more frequently observed in younger women (P = 0.05) with high-grade (P = 0.001), estrogen receptornegative (P = 0.04), and progesterone receptor-negative (P = 0.01) tumors. Moreover, methylation was associated with reduced or absent BRCA1 transcripts, which was reversible in the heavily BRCA1-methylated cell line UACC3199 following treatment with 5-aza-2V-deoxycytidine and trichostatin A. We identified five CpGs at positions À533, À355, À173, À21, and +44 as critical in the reexpression of BRCA1. We conclude that BRCA1 methylation contributes to a subset of sporadic breast cancers with the resulting molecular and clinicopathologic phenotype similar to that of hereditary BRCA1-associated breast cancers. Our data support a model of carcinogenesis in which BRCA1 promoter methylation may serve as a ''first hit,'' much like an inherited germ line mutation, and promote tumor progression down a restricted set of molecular pathways. (Cancer Res 2005; 65(23): 10692-9)

Distinct genomic aberration patterns are found in familial breast cancer associated with different immunohistochemical subtypes

“…All BRCAX cancers were studied previously for hypermethylation of the BRCA1 gene promoter and loss of heterozygosity; interestingly, the BRCAX samples that had basal-like phenotype showed biallelic inactivation of the BRCA1 gene (Honrado et al, 2007). This model of carcinogenesis in the BRCAX tumors is in agreement with the low level of BRCA1 mRNA expression reported in basal-like cancers (Staff et al, 2003;Wei et al, 2005;. On the other hand, the ERBB2 subtype comprised only of BRCAX tumors (four cases, B14%) (Table 1).…”

Single CpG hypermethylation, allele methylation errors, and decreased expression of multiple tumor suppressor genes in normal body cells of mutation‐negative early‐onset and high‐risk breast cancer patients

“…Promoter hypermethylation of TS genes can serve as the first and/or the second hit in Knudson's model of tumor development. Approximately 20% of sporadic, in particular triple‐negative breast cancers33, 34 and a subset of ovarian cancers35 display BRCA1 promoter hypermethylation. It seems plausible to assume that the few hypermethylated alleles that were observed in some BC and control samples represent stochastic or environmentally induced somatic epimutations.…”

Estrogen receptor α, BRCA1, and FANCF promoter methylation occur in distinct subsets of sporadic breast cancers

“…It has been reported that BRCA1-associated breast cancers, which predominantly occur in premenopausal women, are more frequently of the ER-negative phenotype [7]. We previously demonstrated that inactivation of BRCA1 by promoter methylation is associated with reduced transcripts, decreased gene copy number and chromosome 17 aneusomy, as observed in tumors from BRCA1 mutation carriers [8]. Furthermore, an increasing number of studies have provided evidence linking disruption of Fanconi anemia/BRCA cascade in sporadic cancers [9].…”

“…Methylation specific PCR of BRCA1 was done using primer sequences reported previously for the methylated reaction [15] and unmethylated reaction [8]. FANCF methylation was analyzed as previously described [11].…”

“…The methylation status of individual CpG sites was determined by comparison with the sequence from known ER sequences. The number of methylated CpGs at each specific site was divided by the number of clones analyzed (n = 10), to yield a value that represents the percentage of methylation for each site as previously described [8].…”