Variations in the NBN/NBS1 gene and the risk of breast cancer in non-BRCA1/2 French Canadian families with high risk of breast cancer.
BACKGROUND
The Nijmegen Breakage Syndrome is a chromosomal instability disorder characterized by microcephaly, growth retardation, immunodeficiency, and increased frequency of cancers. Familial studies on relatives of these patients indicated that they also appear to be at increased risk of cancer.


METHODS
In a candidate gene study aiming at identifying genetic determinants of breast cancer susceptibility, we undertook the full sequencing of the NBN gene in our cohort of 97 high-risk non-BRCA1 and -BRCA2 breast cancer families, along with 74 healthy unrelated controls, also from the French Canadian population. In silico programs (ESEfinder, NNSplice, Splice Site Finder and MatInspector) were used to assess the putative impact of the variants identified. The effect of the promoter variant was further studied by luciferase gene reporter assay in MCF-7, HEK293, HeLa and LNCaP cell lines.


RESULTS
Twenty-four variants were identified in our case series and their frequency was further evaluated in healthy controls. The potentially deleterious p.Ile171Val variant was observed in one case only. The p.Arg215Trp variant, suggested to impair NBN binding to histone gamma-H2AX, was observed in one breast cancer case and one healthy control. A promoter variant c.-242-110delAGTA displayed a significant variation in frequency between both sample sets. Luciferase reporter gene assay of the promoter construct bearing this variant did not suggest a variation of expression in the MCF-7 breast cancer cell line, but indicated a reduction of luciferase expression in both the HEK293 and LNCaP cell lines.


CONCLUSIONS
Our analysis of NBN sequence variations indicated that potential NBN alterations are present, albeit at a low frequency, in our cohort of high-risk breast cancer cases. Further analyses will be needed to fully ascertain the exact impact of those variants on breast cancer susceptibility, in particular for variants located in NBN promoter region.
Desjardins
Sylvie
S
Cancer Genomics Laboratory, Oncology and Molecular Endocrinology Research Centre, Centre Hospitalier Universitaire de Québec and Laval University, Québec, Canada. sylvie.desjardins@crchul.ulaval.ca
Beauparlant
Joly Charles
JC
Labrie
Yvan
Y
Ouellette
Geneviève
G
Durocher
Francine
F
D017398:Alternative Splicing; D001943:Breast Neoplasms / Q000235:genetics*; D002170:Canada; D016022:Case-Control Studies; D018797:Cell Cycle Proteins / Q000235:genetics*; D045744:Cell Line, Tumor; D005260:Female; D005602:France / Q000208:ethnology; D017353:Gene Deletion; D019398:Genes, BRCA1; D024522:Genes, BRCA2; D017930:Genes, Reporter; D020022:Genetic Predisposition to Disease; D014644:Genetic Variation; D006238:Haploidy; D006367:HeLa Cells; D006801:Humans; D008156:Luciferases / Q000096:biosynthesis / Q000235:genetics; D009687:Nuclear Proteins / Q000235:genetics*; D010051:Ovarian Neoplasms / Q000235:genetics; D020641:Polymorphism, Single Nucleotide
D018797:Cell Cycle Proteins; C112156:NBN protein, human; D009687:Nuclear Proteins; D008156:Luciferases