title: Reduced BRCA1 transcript levels in freshly isolated blood leukocytes from BRCA1 mutation carriers is mutation specific.
abstract: BRCA1 mutation carriers face a high lifetime risk of developing both breast and ovarian cancer. Haploinsufficiency is thought to predispose these women to cancer by reducing the pool of available BRCA1 transcript and protein, thereby compromising BRCA1 function. Whether or not cancer-free BRCA1 mutation carriers have lower messenger (m)RNA transcript levels in peripheral blood leukocytes has not been evaluated. The primary aim of this study was to characterize an association between BRCA1 mutation status and BRCA1 mRNA leukocyte expression levels among healthy women with a BRCA1 mutation.
  
  
  
  RNA was extracted from freshly isolated peripheral blood leukocytes of 58 cancer-free, female participants (22 BRCA1 mutation carriers and 36 non-carriers). The expression levels of 236 cancer-associated genes, including BRCA1, were quantified using the Human Cancer Reference gene panel from the Nanostring Technologies nCounter Analysis System.
  
  
  
  Multivariate modeling demonstrated that carrying a BRCA1 mutation was the most significant predictor of BRCA1 mRNA levels. BRCA1 mRNA levels were significantly lower in BRCA1 mutation carriers compared to non-carriers (146.7 counts vs. 175.1 counts; P = 0.002). Samples with BRCA1 mutations within exon 11 had lower BRCA1 mRNA levels than samples with mutations within the 5' and 3' regions of the BRCA1 gene (122.1 counts vs. 138.9 and 168.6 counts, respectively; P = 0.003). Unsupervised hierarchical clustering of gene expression profiles from freshly isolated blood leukocytes revealed that BRCA1 mutation carriers cluster more closely with other BRCA1 mutation carriers than with BRCA1 wild-type samples. Moreover, a set of 17 genes (including BRCA1) previously shown to be involved in carcinogenesis, were differentially expressed between BRCA1 mutation carriers and non-carriers.
  
  
  
  Overall, these findings support the concept of BRCA1 haploinsufficiency wherein a specific mutation results in dosage-dependent alteration of BRCA1 at the transcriptional level. This study is the first to show a decrease in BRCA1 mRNA expression in freshly isolated blood leukocytes from healthy, unaffected BRCA1 mutation carriers.
authors.affiliation: Women's College Research Institute, Women's College Hospital, 76 Grenville Street, 6th Floor, Toronto, ON, Canada.|Faculty of Medicine and Dentistry, University of Alberta, 2J2.00 WC Mackenzie Health Sciences Centre, Edmonton, AB, Canada.
authors.forename: Rania
authors.initials: R
authors.lastname: Chehade
authors.affiliation: Women's College Research Institute, Women's College Hospital, 76 Grenville Street, 6th Floor, Toronto, ON, Canada.|Department of Nutritional Sciences, University of Toronto, FitzGerald Building, 150 College Street, Room 316, Toronto, ON, Canada.
authors.forename: Rachael
authors.initials: R
authors.lastname: Pettapiece-Phillips
authors.affiliation: Princess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada.|Department of Pharmacology and Toxicology, University of Toronto, Toronto, ON, Canada.
authors.forename: Leonardo
authors.initials: L
authors.lastname: Salmena
authors.affiliation: Princess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada.
authors.forename: Max
authors.initials: M
authors.lastname: Kotlyar
authors.affiliation: Princess Margaret Cancer Centre, University Health Network, Toronto, ON, Canada.|Department of Medical Biophysics and Computer Science, University of Toronto, Toronto, ON, Canada.
authors.forename: Igor
authors.initials: I
authors.lastname: Jurisica
authors.affiliation: Women's College Research Institute, Women's College Hospital, 76 Grenville Street, 6th Floor, Toronto, ON, Canada.|Department of Nutritional Sciences, University of Toronto, FitzGerald Building, 150 College Street, Room 316, Toronto, ON, Canada.|Dalla Lana School of Public Health, University of Toronto, 155 College Street Health Science Building, 6th Floor, Toronto, ON, Canada.
authors.forename: Steven A
authors.initials: SA
authors.lastname: Narod
authors.affiliation: Women's College Research Institute, Women's College Hospital, 76 Grenville Street, 6th Floor, Toronto, ON, Canada.|Dalla Lana School of Public Health, University of Toronto, 155 College Street Health Science Building, 6th Floor, Toronto, ON, Canada.
authors.forename: Mohammad R
authors.initials: MR
authors.lastname: Akbari
authors.affiliation: Women's College Research Institute, Women's College Hospital, 76 Grenville Street, 6th Floor, Toronto, ON, Canada. joanne.kotsopoulos@wchospital.ca.|Department of Nutritional Sciences, University of Toronto, FitzGerald Building, 150 College Street, Room 316, Toronto, ON, Canada. joanne.kotsopoulos@wchospital.ca.|Dalla Lana School of Public Health, University of Toronto, 155 College Street Health Science Building, 6th Floor, Toronto, ON, Canada. joanne.kotsopoulos@wchospital.ca.
authors.forename: Joanne
authors.initials: J
authors.lastname: Kotsopoulos
mesh_terms: D000293:Adolescent; D000328:Adult; D016000:Cluster Analysis; D005260:Female; D018628:Gene Dosage; D020869:Gene Expression Profiling; D019398:Genes, BRCA1; D057895:Haploinsufficiency; D064368:Healthy Volunteers; D006579:Heterozygote; D006801:Humans; D007962:Leukocytes / Q000378:metabolism*; D008875:Middle Aged; D009154:Mutation; D059365:Nonsense Mediated mRNA Decay; D012333:RNA, Messenger / Q000235:genetics; D014158:Transcription, Genetic; D059467:Transcriptome; D055815:Young Adult
chemical_list: D012333:RNA, Messenger
keywords: BRCA1; Haploinsufficiency; Hereditary breast and ovarian cancer; mRNA expression