BRCA1 promoter methylation in sporadic breast cancer is associated with reduced BRCA1 copy number and chromosome 17 aneusomy.
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 receptor-negative (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-2'-deoxycytidine and trichostatin A. We identified five CpGs at positions -533, -355, -173, -21, 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.
Wei
Minjie
M
Center for Clinical Cancer Genetics, Department of Medicine, University of Chicago, Chicago, Illinois 60637-1463, USA.
Grushko
Tatyana A
TA
Dignam
James
J
Hagos
Fitsum
F
Nanda
Rita
R
Sveen
Lise
L
Xu
Jinhua
J
Fackenthal
James
J
Tretiakova
Maria
M
Das
Soma
S
Olopade
Olufunmilayo I
OI
D000782:Aneuploidy; D000964:Antimetabolites, Antineoplastic / Q000494:pharmacology; D001374:Azacitidine / Q000031:analogs & derivatives / Q000494:pharmacology; D019313:BRCA1 Protein / Q000096:biosynthesis / Q000172:deficiency / Q000235:genetics; D001940:Breast / Q000378:metabolism / Q000502:physiology / Q000648:ultrastructure; D001943:Breast Neoplasms / Q000235:genetics* / Q000378:metabolism; D045744:Cell Line, Tumor; D002886:Chromosomes, Human, Pair 17 / Q000235:genetics*; D019175:DNA Methylation / Q000187:drug effects; D000077209:Decitabine; D005260:Female; D018628:Gene Dosage; D015870:Gene Expression / Q000187:drug effects; D019398:Genes, BRCA1 / Q000502:physiology*; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D008214:Lymphocytes / Q000378:metabolism / Q000502:physiology; D008875:Middle Aged; D011401:Promoter Regions, Genetic; D012333:RNA, Messenger / Q000096:biosynthesis / Q000235:genetics
D000964:Antimetabolites, Antineoplastic; D019313:BRCA1 Protein; D006877:Hydroxamic Acids; D012333:RNA, Messenger; C012589:trichostatin A; D000077209:Decitabine; D001374:Azacitidine