散发性乳腺和卵巢肿瘤中的启动子高甲基化与BRCA1失活

Promoter hypermethylation and BRCA1 inactivation in sporadic breast and ovarian tumors.

作者信息

Esteller M, Silva J M, Dominguez G, Bonilla F, Matias-Guiu X, Lerma E, Bussaglia E, Prat J, Harkes I C, Repasky E A, Gabrielson E, Schutte M, Baylin S B, Herman J G

机构信息

The Johns Hopkins Oncology Center, Baltimore, MD 21231, USA.

出版信息

J Natl Cancer Inst. 2000 Apr 5;92(7):564-9. doi: 10.1093/jnci/92.7.564.

DOI:10.1093/jnci/92.7.564

PMID:10749912

Abstract

BACKGROUND

Inherited mutations in the BRCA1 gene may be responsible for almost half of inherited breast carcinomas. However, somatic (acquired) mutations in BRCA1 have not been reported, despite frequent loss of heterozygosity (LOH or loss of one copy of the gene) at the BRCA1 locus and loss of BRCA1 protein in tumors. To address whether BRCA1 may be inactivated by pathways other than mutations in sporadic tumors, we analyzed the role of hypermethylation of the gene's promoter region.

METHODS

Methylation patterns in the BRCA1 promoter were assessed in breast cancer cell lines, xenografts, and 215 primary breast and ovarian carcinomas by methylation-specific polymerase chain reaction (PCR). BRCA1 RNA expression was determined in cell lines and seven xenografts by reverse transcription-PCR. P values are two-sided.

RESULTS

The BRCA1 promoter was found to be unmethylated in all normal tissues and cancer cell lines tested. However, BRCA1 promoter hypermethylation was present in two breast cancer xenografts, both of which had loss of the BRCA1 transcript. BRCA1 promoter hypermethylation was present in 11 (13%) of 84 unselected primary breast carcinomas. BRCA1 methylation was strikingly associated with the medullary (67% methylated; P =.0002 versus ductal) and mucinous (55% methylated; P =.0033 versus ductal) subtypes, which are overrepresented in BRCA1 families. In a second series of 66 ductal breast tumors informative for LOH, nine (20%) of 45 tumors with LOH had BRCA1 hypermethylation, while one (5%) of 21 without LOH was methylated (P =.15). In ovarian neoplasms, BRCA1 methylation was found only in tumors with LOH, four (31%) of 13 versus none of 18 without LOH (P =.02). The BRCA1 promoter was unmethylated in other tumor types.

CONCLUSION

Silencing of the BRCA1 gene by promoter hypermethylation occurs in primary breast and ovarian carcinomas, especially in the presence of LOH and in specific histopathologic subgroups. These findings support a role for this tumor suppressor gene in sporadic breast and ovarian tumorigenesis.

摘要

背景

BRCA1基因的遗传性突变可能是近半数遗传性乳腺癌的病因。然而，尽管BRCA1基因座频繁出现杂合性缺失（LOH，即基因的一个拷贝丢失）且肿瘤中BRCA1蛋白缺失，但尚未有关于BRCA1基因体细胞（获得性）突变的报道。为了探究在散发性肿瘤中BRCA1是否可能通过除突变以外的途径失活，我们分析了该基因启动子区域高甲基化的作用。

方法

通过甲基化特异性聚合酶链反应（PCR）评估乳腺癌细胞系、异种移植瘤以及215例原发性乳腺癌和卵巢癌中BRCA1启动子的甲基化模式。通过逆转录PCR测定细胞系和7个异种移植瘤中的BRCA1 RNA表达。P值为双侧。

结果

在所检测的所有正常组织和癌细胞系中，BRCA1启动子均未发生甲基化。然而，在两个乳腺癌异种移植瘤中存在BRCA1启动子高甲基化，二者均缺失BRCA1转录本。在84例未经选择的原发性乳腺癌中，11例（13%）存在BRCA1启动子高甲基化。BRCA1甲基化与髓样（67%甲基化；与导管样相比，P = 0.0002）和黏液样（55%甲基化；与导管样相比，P = 0.0033）亚型显著相关，这两种亚型在BRCA1家族中占比过高。在第二组66例可提供LOH信息的导管性乳腺癌肿瘤中，45例存在LOH的肿瘤中有9例（20%）发生BRCA1高甲基化，而21例无LOH的肿瘤中有1例（5%）发生甲基化（P = 0.15）。在卵巢肿瘤中，仅在存在LOH的肿瘤中发现BRCA1甲基化，13例中有4例（31%），而18例无LOH的肿瘤中均未发现（P = 0.02）。在其他肿瘤类型中，BRCA1启动子未发生甲基化。