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
BMC Cancer
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
Sylvie Desjardins 0
Joly Charles Beauparlant 0
Yvan Labrie 0
Genevive Ouellette 0
INHERIT BRCAs 0
Francine Durocher 0
0 Address: Cancer Genomics Laboratory, Oncology and Molecular Endocrinology Research Centre, Centre Hospitalier Universitaire de Quebec and Laval University , Quebec , Canada
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 nonBRCA1 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 -H2AX, was observed in one breast cancer case and one healthy control. A promoter variant c.-242110delAGTA 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. Conclusion: 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.
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Background
Pathogenic mutations in BRCA1, BRCA2, TP53, ATM,
CHEK2, BRIP1 and PALB2 have been associated with an
increased breast cancer risk and, together, are found in less
than 25% of breast cancer families showing a clear pattern
of inheritance (high-risk families) [1]. It is thus clear that
other susceptibility alleles remain to be identified to
explain the increased risk in the remnant high-risk
families. As the number and characteristics of such alleles are
undetermined, a focussed candidate gene approach based
on genes closely interacting with the known susceptibility
genes such as BRCA1 and BRCA2, the two major
susceptibility genes identified yet, constitutes a study design of
choice to identify rare-moderate-penetrance susceptibility
alleles.
In the cell, nibrin, encoded by the NBN gene (also known
as NBS1), participates in pathways of double strand
breaks (DSB)-induced DNA repair and, together with its
partners MRE11A and RAD50, is required for activation of
these pathways in response to DNA damages [2]. In fact,
nibrin is at the crossroad of several pathways implicating
genes already associated with breast cancer susceptibility
and/or chromosomal instability disorders [2,3].
Individuals homozygous for hypomorphic mutations in NBN
suffer from the Nijmegen Breakage Syndrome (NBS), an
autosomal recessive chromosomal instability disorder
characterized by microcephaly, growth retardation,
immunodeficiency and hyper-radiosensitivity [4].
Cancers, in particular haematological malignancies, are
common adverse events in patients with NBS, as almost 40%
of them develop a malignancy before the age of 21 years,
and this correlates with a marked impairment in DSB
repair observed in cells from these patients [5].
Some studies have associated an heterozygous NBN status
with numerous types of cancers, including breast cancer
[6-10], suggesting that being a carrier of a deleterious
mutation in NBN may confer an increased risk of
approximately 2 to 3-fold [6]. This was also supported by the
observation that relatives of NBS patients display a higher
than expected rate of cancers [4,11]. However, other
studies failed to find an association with an increased risk of
cancer [12,13].
In support of a role of NBN in tumor formation, evidence
from mouse models demonstrated that Nbn
heterozygosity predisposes cells to malignancies, as they display a
wide variety of tumors: liver, mammary gland, prostate,
lung as well as lymphomas [14]. Indeed, cells from these
mice displayed an elevated frequency of chromosomal
aberrations. These observations were correla (...truncated)