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, Jun 2009

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 γ-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. 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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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. - 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)


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Sylvie Desjardins, Joly Beauparlant, Yvan Labrie, Geneviève Ouellette, , Francine Durocher. 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, 2009, pp. 181, 9, DOI: 10.1186/1471-2407-9-181