RAD50

Gene Summary

Gene:RAD50; RAD50 double strand break repair protein
Aliases: NBSLD, RAD502, hRad50
Location:5q31.1
Summary:The protein encoded by this gene is highly similar to Saccharomyces cerevisiae Rad50, a protein involved in DNA double-strand break repair. This protein forms a complex with MRE11 and NBS1. The protein complex binds to DNA and displays numerous enzymatic activities that are required for nonhomologous joining of DNA ends. This protein, cooperating with its partners, is important for DNA double-strand break repair, cell cycle checkpoint activation, telomere maintenance, and meiotic recombination. Knockout studies of the mouse homolog suggest this gene is essential for cell growth and viability. Mutations in this gene are the cause of Nijmegen breakage syndrome-like disorder.[provided by RefSeq, Apr 2010]
Databases:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:DNA repair protein RAD50
Source:NCBIAccessed: 16 March, 2017

Ontology:

What does this gene/protein do?
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Pathways:What pathways are this gene/protein implicaed in?
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Cancer Overview

Research Indicators

Publications Per Year (1992-2017)
Graph generated 16 March 2017 using data from PubMed using criteria.

Literature Analysis

Mouse over the terms for more detail; many indicate links which you can click for dedicated pages about the topic.

  • Cancer Gene Expression Regulation
  • Breast Cancer
  • Chromosome 5
  • Sensitivity and Specificity
  • Ovarian Cancer
  • DNA Repair Enzymes
  • Cell Cycle Proteins
  • Protein-Serine-Threonine Kinases
  • Transcription
  • Smoking
  • Nuclear Proteins
  • Rabbits
  • Microsatellite Repeats
  • alpha Karyopherins
  • RecQ Helicases
  • DNA Repair
  • Xenograft Models
  • Double-Stranded DNA Breaks
  • Transcription Factors
  • Telomeric Repeat Binding Protein 2
  • Xeroderma Pigmentosum
  • Risk Factors
  • DNA-Binding Proteins
  • Taiwan
  • Sequence Homology
  • Colorectal Cancer
  • Mutation
  • Tumor Suppressor Proteins
  • Immunohistochemistry
  • Genetic Recombination
  • United Kingdom
  • Ataxia Telangiectasia Mutated Proteins
  • Telomere
  • Ultraviolet Rays
  • Ubiquitin-Protein Ligases
  • DNA Damage
  • Nervous System Diseases
  • Trihexosylceramides
  • Genetic Predisposition
  • T-Lymphocytes
  • Transfection
Tag cloud generated 16 March, 2017 using data from PubMed, MeSH and CancerIndex

Specific Cancers (3)

Data table showing topics related to specific cancers and associated disorders. Scope includes mutations and abnormal protein expression.

Note: list is not exhaustive. Number of papers are based on searches of PubMed (click on topic title for arbitrary criteria used).

Latest Publications: RAD50 (cancer-related)

Kostianets O, Shyyan M, Antoniuk SV, et al.
Panel of SEREX-defined antigens for breast cancer autoantibodies profile detection.
Biomarkers. 2017; 22(2):149-156 [PubMed] Related Publications
CONTENT: Identification of panel of SEREX-defined antigens for breast cancer autoantibodies profile detection.
OBJECTIVE: To create panel of antigens that can differentiate breast cancer patients and healthy individuals.
METHODS: SEREX (serological analysis of cDNA expression libraries) method, ELISA (enzyme-linked immunosorbent assay), qPCR (quantitative polymerase chain reaction).
RESULTS: In large-scale screening of 16 SEREX-antigens by sera of breast cancer patients and healthy donors, a combination of six antigens (RAD50, PARD3, SPP1, SAP30BP, NY-BR-62 and NY-CO-58) was identified, which can differentiate breast cancer patients and healthy donors with 70% sensitivity and 91% specificity. Elevated mRNA expression of SPP1 gene was revealed in breast tumors (2-7-fold) that correlated with SPP1 antigen immunoreactivity in autologous patients' sera.
CONCLUSIONS: The new panel of six SEREX-antigens was proposed, which enables creation of serological assay for breast cancer diagnostics and/or prognosis.

Kleibl Z, Kristensen VN
Women at high risk of breast cancer: Molecular characteristics, clinical presentation and management.
Breast. 2016; 28:136-44 [PubMed] Related Publications
The presence of breast cancer in any first-degree female relative in general nearly doubles the risk for a proband and the risk gradually increases with the number of affected relatives. Current advances in molecular oncology and oncogenetics may enable the identification of high-risk individuals with breast-cancer predisposition. The best-known forms of hereditary breast cancer (HBC) are caused by mutations in the high-penetrance genes BRCA1 and BRCA2. Other genes, including PTEN, TP53, STK11/LKB1, CDH1, PALB2, CHEK2, ATM, MRE11, RAD50, NBS1, BRIP1, FANCA, FANCC, FANCM, RAD51, RAD51B, RAD51C, RAD51D, and XRCC2 have been described as high- or moderate-penetrance breast cancer-susceptibility genes. The majority of breast cancer-susceptibility genes code for tumor suppressor proteins that are involved in critical processes of DNA repair pathways. This is of particular importance for those women who, due to their increased risk of breast cancer, may be subjected to more frequent screening but due to their repair deficiency might be at the risk of developing radiation-induced malignancies. It has been proven that cancers arising from the most frequent BRCA1 gene mutation carriers differ significantly from the sporadic disease of age-matched controls in their histopathological appearances and molecular characteristics. The increased depth of mutation detection brought by next-generation sequencing and a better understanding of the mechanisms through which these mutations cause the disease will bring novel insights in terms of oncological prevention, diagnostics, and therapeutic options for HBC patients.

Frimer M, Levano KS, Rodriguez-Gabin A, et al.
Germline mutations of the DNA repair pathways in uterine serous carcinoma.
Gynecol Oncol. 2016; 141(1):101-7 [PubMed] Related Publications
OBJECTIVE: Treatment options are limited for patients with uterine serous carcinoma (USC). Knowledge of USC's somatic mutation landscape is rapidly increasing, but its role in hereditary cancers remains unclear. We aim to evaluate the frequency and characteristics of germline mutations in genes commonly implicated in carcinogenesis, including those within homologous recombination (HR) and mismatch repair (MMR) pathways in patients with pure USC.
METHODS: By using targeted capture exome sequencing, 43 genes were analyzed in a cohort of 7 consecutive patients with paired tumor and non-tumor USC samples in our institutional tumor repository. Mutations predicted to have damaging effects on protein function are validated by Sanger Sequencing.
RESULTS: We found 21 germline mutations in 11 genes in our USC cohort. Five patients harbored 7 germline mutations (33.3%) within genes involved in the HR pathway, RAD51D being the most common. Four patients had 9 (42.8%) germline mutations in hereditary colon cancer genes, most commonly MLH. All patients (42.7%) who are platinum-sensitive had HR germline mutations (RAD50, NBN, ATM). Patients with HER2 overexpression (2/7, 28.6%) had germline HR mutations and were platinum-sensitive. Three patients in our cohort reported a personal history of breast cancer, one with HR germline mutation, and 2 in patients with germline mutations in HCC genes. In addition, 5 out of 7 patients had germline mutations in genes associated with growth factor signaling pathway.
CONCLUSIONS: A significant proportion of our cohort harbor germline mutations in DNA repair genes. This may be associated with the high rate of breast cancer in our patients and their family, and suggests a targeted cohort for genetic counseling. If validated in a larger cohort, our findings may allow clinicians to expand therapeutic options to include targeted therapies and inclusion of USC patient in preventative and genetic counseling.

Zhang M, Liu G, Xue F, et al.
Copy number deletion of RAD50 as predictive marker of BRCAness and PARP inhibitor response in BRCA wild type ovarian cancer.
Gynecol Oncol. 2016; 141(1):57-64 [PubMed] Article available free on PMC after 01/04/2017 Related Publications
OBJECTIVE: To identify novel prognostic and therapeutic markers for PARP inhibitors in BRCA wild type ovarian cancer (OvCa).
METHODS: BRCAness status was defined by analyzing whole-exome deep sequencing data from 220 BRCAwt OvCa cases in TCGA. Thirty-three DNA-repair genes were screened in an integrated manner for BRCA-independent mechanism of BRCAness using multiple-dimensional genomic data. Publicly available databases and siRNA knock-down were used for external validation and evaluation of drug response in OvCa cell lines.
RESULTS: In 220 BRCAwt OvCa patients, tumors exhibiting the BRCAness signature have enhanced OS (HR [95% CI]=0.33 [0.15-0.69], P=0.004) and PFS (HR [95% CI]=0.51 [0.24-1.08], P=0.077), strongly suggesting a BRCA-independent mechanism of drug sensitivity in those patients. Systematic screening of driving molecular events of BRCAness revealed that RAD50 deletion is a marker of BRCAness. The RAD50 deletion occurred in 18% of BRCAwt OvCa patients. RAD50 deletion led to its decreased mRNA expression in tumors (fold change=0.63, P=3.56×10(-13)). In BRCAwt patients, RAD50 deletion was associated with significantly better OS (HR [95% CI]=0.44 [0.25-0.78], P=0.005) and PFS (HR [95% CI]=0.60 [0.37-0.99], P=0.044), adjusted by age and stage. Knockdown of RAD50 expression augmented OvCa cell's responses to cisplatin and olaparib. Among 19 OvCa cell lines, the RAD50 copy number deletion is significantly associated with better responses to two structurally distinct PARPis (i.e. olaparib and rucaparib).
CONCLUSION: Our study identified the copy number deletion of RAD50 as a candidate marker for survival and response to PARPis in BRCAwt OvCa tumors.

Chang L, Huang J, Wang K, et al.
Targeting Rad50 sensitizes human nasopharyngeal carcinoma cells to radiotherapy.
BMC Cancer. 2016; 16:190 [PubMed] Article available free on PMC after 01/04/2017 Related Publications
BACKGROUND: The Mre11-Rad50-Nbs1 (MRN) complex is well known for its crucial role in initiating DNA double strand breaks (DSBs) repair pathways to resistant irradiation (IR) injury and thus facilitating radioresistance which severely reduces radiocurability of nasopharyngeal cancer (NPC). Targeting native cellular MRN function would sensitize NPC cells to IR.
METHODS: A recombinant adenovirus containing a mutant Rad50 gene (Ad-RAD50) expressing Rad50 zinc hook domain but lacking the ATPase domain and the Mre11 interaction domain was constructed to disrupt native cellular MRN functions. The effects of Ad-RAD50 on the MRN functions were assessed in NPC cells lines using western blot, co-immunoprecipitation and confocal microscopy analyses. The increased radiosensitivity of transient Ad-RAD50 to IR was examined in NPC cells, including MTT assay, colony formation. The molecular mechanisms of radiosensitization were confirmed by neutral comet assay and western bolts. Nude mice subcutaneous injection, tumor growth curve and TUNEL assay were used to evaluate tumor regression and apoptosis in vivo.
RESULTS: Rad50 is remarkably upregulated in NPC cells after IR, implying the critical role of Rad50 in MRN functions. The transient expression of this mutant Rad50 decreased the levels of native cellular Rad50, Mre11 and Nbs1, weakened the interactions among these proteins, abrogated the G2/M arrest induced by DSBs and reduced the DNA repair ability in NPC cells. A combination of IR and mutant RAD50 therapy produced significant tumor cytotoxicity in vitro, with a corresponding increase in DNA damage, prevented proliferation and cell viability. Furthermore, Ad-RAD50 sensitized NPC cells to IR by causing dramatic tumor regression and inducing apoptosis in vivo.
CONCLUSION: Our findings define a novel therapeutic approach to NPC radiosensitization via targeted native cellular Rad50 disruption.

Lin PH, Kuo WH, Huang AC, et al.
Multiple gene sequencing for risk assessment in patients with early-onset or familial breast cancer.
Oncotarget. 2016; 7(7):8310-20 [PubMed] Article available free on PMC after 01/04/2017 Related Publications
Since BRCA mutations are only responsible for 10-20% of cases of breast cancer in patients with early-onset or a family history and since next-generation sequencing technology allows the simultaneous sequencing of a large number of target genes, testing for multiple cancer-predisposing genes is now being considered, but its significance in clinical practice remains unclear. We then developed a sequencing panel containing 68 genes that had cancer risk association for patients with early-onset or familial breast cancer. A total of 133 patients were enrolled and 30 (22.6%) were found to carry germline deleterious mutations, 9 in BRCA1, 11 in BRCA2, 2 in RAD50, 2 in TP53 and one each in ATM, BRIP1, FANCI, MSH2, MUTYH, and RAD51C. Triple-negative breast cancer (TNBC) was associated with the highest mutation rate (45.5%, p = 0.025). Seven of the 9 BRCA1 mutations and the single FANCI mutation were in the TNBC group; 9 of the 11 BRCA2, 1 of the 2 RAD50 as well as BRIP1, MSH2, MUTYH, and RAD51C mutations were in the hormone receptor (HR)(+)Her2(-) group, and the other RAD50, ATM, and TP53 mutations were in the HR(+)Her2(+) group. Mutation carriers were considered as high-risk to develop malignancy and advised to receive cancer screening. Screening protocols of non-BRCA genes were based on their biologic functions; for example, patients carrying RAD51C mutation received a screening protocol similar to that for BRCA, since BRCA and RAD51C are both involved in homologous recombination. In conclusion, we consider that multiple gene sequencing in cancer risk assessment is clinically valuable.

Li J, Meeks H, Feng BJ, et al.
Targeted massively parallel sequencing of a panel of putative breast cancer susceptibility genes in a large cohort of multiple-case breast and ovarian cancer families.
J Med Genet. 2016; 53(1):34-42 [PubMed] Article available free on PMC after 01/04/2017 Related Publications
INTRODUCTION: Gene panel testing for breast cancer susceptibility has become relatively cheap and accessible. However, the breast cancer risks associated with mutations in many genes included in these panels are unknown.
METHODS: We performed custom-designed targeted sequencing covering the coding exons of 17 known and putative breast cancer susceptibility genes in 660 non-BRCA1/2 women with familial breast cancer. Putative deleterious mutations were genotyped in relevant family members to assess co-segregation of each variant with disease. We used maximum likelihood models to estimate the breast cancer risks associated with mutations in each of the genes.
RESULTS: We found 31 putative deleterious mutations in 7 known breast cancer susceptibility genes (TP53, PALB2, ATM, CHEK2, CDH1, PTEN and STK11) in 45 cases, and 22 potential deleterious mutations in 31 cases in 8 other genes (BARD1, BRIP1, MRE11, NBN, RAD50, RAD51C, RAD51D and CDK4). The relevant variants were then genotyped in 558 family members. Assuming a constant relative risk of breast cancer across age groups, only variants in CDH1, CHEK2, PALB2 and TP53 showed evidence of a significantly increased risk of breast cancer, with some supportive evidence that mutations in ATM confer moderate risk.
CONCLUSIONS: Panel testing for these breast cancer families provided additional relevant clinical information for <2% of families. We demonstrated that segregation analysis has some potential to help estimate the breast cancer risks associated with mutations in breast cancer susceptibility genes, but very large case-control sequencing studies and/or larger family-based studies will be needed to define the risks more accurately.

Beumer JH, Fu KY, Anyang BN, et al.
Functional analyses of ATM, ATR and Fanconi anemia proteins in lung carcinoma : ATM, ATR and FA in lung carcinoma.
BMC Cancer. 2015; 15:649 [PubMed] Article available free on PMC after 01/04/2017 Related Publications
BACKGROUND: ATM and ATR are kinases implicated in a myriad of DNA-damage responses. ATM kinase inhibition radiosensitizes cells and selectively kills cells with Fanconi anemia (FA) gene mutations. ATR kinase inhibition sensitizes cells to agents that induce replication stress and selectively kills cells with ATM and TP53 mutations. ATM mutations and FANCF promoter-methylation are reported in lung carcinomas.
METHODS: We undertook functional analyses of ATM, ATR, Chk1 and FA proteins in lung cancer cell lines. We included Calu6 that is reported to be FANCL-deficient. In addition, the cancer genome atlas (TCGA) database was interrogated for alterations in: 1) ATM, MRE11A, RAD50 and NBN; 2) ATR, ATRIP and TOPBP1; and 3) 15 FA genes.
RESULTS: No defects in ATM, ATR or Chk1 kinase activation, or FANCD2 monoubiquitination were identified in the lung cancer cell lines examined, including Calu6, and major alterations in these pathways were not identified in the TCGA database. Cell lines were radiosensitized by ATM kinase inhibitor KU60019, but no cell killing by ATM kinase inhibitor alone was observed. While no synergy between gemcitabine or carboplatin and ATR kinase inhibitor ETP-46464 was observed, synergy between gemcitabine and Chk1 kinase inhibitor UCN-01 was observed in 54 T, 201 T and H460, and synergy between carboplatin and Chk1 kinase inhibitor was identified in 201 T and 239 T. No interactions between ATM, ATR and FA activation were observed by either ATM or ATR kinase inhibition in the lung cancer cell lines.
CONCLUSIONS: Analyses of ATM serine 1981 and Chk1 serine 345 phosphorylation, and FANCD2 monoubiquitination revealed that ATM and ATR kinase activation and FA pathway signaling are intact in the lung cancer cell lines examined. As such, these posttranslational modifications may have utility as biomarkers for the integrity of DNA damage signaling pathways in lung cancer. Different sensitization profiles between gemcitabine and carboplatin and ATR kinase inhibitor ETP-46464 and Chk1 kinase inhibitor UCN-01 were observed and this should be considered in the rationale for Phase I clinical trial design with ATR kinase inhibitors.

Day FR, Hinds DA, Tung JY, et al.
Causal mechanisms and balancing selection inferred from genetic associations with polycystic ovary syndrome.
Nat Commun. 2015; 6:8464 [PubMed] Article available free on PMC after 01/04/2017 Related Publications
Polycystic ovary syndrome (PCOS) is the most common reproductive disorder in women, yet there is little consensus regarding its aetiology. Here we perform a genome-wide association study of PCOS in up to 5,184 self-reported cases of White European ancestry and 82,759 controls, with follow-up in a further ∼2,000 clinically validated cases and ∼100,000 controls. We identify six signals for PCOS at genome-wide statistical significance (P<5 × 10(-8)), in/near genes ERBB4/HER4, YAP1, THADA, FSHB, RAD50 and KRR1. Variants in/near three of the four epidermal growth factor receptor genes (ERBB2/HER2, ERBB3/HER3 and ERBB4/HER4) are associated with PCOS at or near genome-wide significance. Mendelian randomization analyses indicate causal roles in PCOS aetiology for higher BMI (P=2.5 × 10(-9)), higher insulin resistance (P=6 × 10(-4)) and lower serum sex hormone binding globulin concentrations (P=5 × 10(-4)). Furthermore, genetic susceptibility to later menopause is associated with higher PCOS risk (P=1.6 × 10(-8)) and PCOS-susceptibility alleles are associated with higher serum anti-Müllerian hormone concentrations in girls (P=8.9 × 10(-5)). This large-scale study implicates an aetiological role of the epidermal growth factor receptors, infers causal mechanisms relevant to clinical management and prevention, and suggests balancing selection mechanisms involved in PCOS risk.

Panero J, Stella F, Schutz N, et al.
Differential Expression of Non-Shelterin Genes Associated with High Telomerase Levels and Telomere Shortening in Plasma Cell Disorders.
PLoS One. 2015; 10(9):e0137972 [PubMed] Article available free on PMC after 01/04/2017 Related Publications
Telomerase, shelterin proteins and various interacting factors, named non-shelterin proteins, are involved in the regulation of telomere length (TL). Altered expression of any of these telomere-associated genes can lead to telomere dysfunction, causing genomic instability and disease development. In this study, we investigated the expression profile of a set of non-shelterin genes involved in essential processes such as replication (RPA1), DNA damage repair pathways (MRE11-RAD50-NBS1) and stabilization of telomerase complex (DKC1), in 35 patients with monoclonal gammopathy of undetermined significance (MGUS) and 40 cases with multiple myeloma (MM). Results were correlated with hTERT expression, TL and clinical parameters. Overall, a significant increase in DKC1, RAD50, MRE11, NBS1 and RPA1 expression along with an upregulation of hTERT in MM compared with MGUS was observed (p≤0.032). Interestingly, in both entities high mRNA levels of non-shelterin genes were associated with short TLs and increased hTERT expression. Significant differences were observed for DKC1 in MM (p ≤0.026), suggesting an important role for this gene in the maintenance of short telomeres by telomerase in myeloma plasma cells. With regard to clinical associations, we observed a significant increase in DKC1, RAD50, MRE11 and RPA1 expression in MM cases with high bone marrow infiltration (p≤0.03) and a tendency towards cases with advanced ISS stage, providing the first evidence of non-shelterin genes associated to risk factors in MM. Taken together, our findings bring new insights into the intricate mechanisms by which telomere-associated proteins collaborate in the maintenance of plasma cells immortalization and suggest a role for the upregulation of these genes in the progression of the disease.

Aloraifi F, McCartan D, McDevitt T, et al.
Protein-truncating variants in moderate-risk breast cancer susceptibility genes: a meta-analysis of high-risk case-control screening studies.
Cancer Genet. 2015; 208(9):455-63 [PubMed] Related Publications
Several "moderate-risk breast cancer susceptibility genes" have been conclusively identified. Pathogenic mutations in these genes are thought to cause a two to fivefold increased risk of breast cancer. In light of the current development and use of multigene panel testing, the authors wanted to systematically obtain robust estimates of the cancer risk associated with loss-of-function mutations within these genes. An electronic search was conducted to identify studies that sequenced the full coding regions of ATM, CHEK2, BRIP1, PALB2, NBS1, and RAD50 in a general and gene-targeted approach. Inclusion was restricted to studies that sequenced the germline DNA in both high-risk cases and geographically matched controls. A meta-analysis was then performed on protein-truncating variants (PTVs) identified in the studies for an association with breast cancer risk. A total of 10,209 publications were identified, of which 64 studies comprising a total of 25,418 cases and 52,322 controls in the 6 interrogated genes were eligible under our selection criteria. The pooled odds ratios for PTVs in the susceptibility genes were at least >2.6. Additionally, mutations in these genes have shown geographic and ethnic variation. This comprehensive study emphasizes the fact that caution should be taken when identifying certain genes as moderate susceptibility with the lack of sufficient data, especially with regard to the NBS1, RAD50, and BRIP1 genes. Further data from case-control sequencing studies, and especially family studies, are warranted.

Rajkumar T, Meenakumari B, Mani S, et al.
Targeted Resequencing of 30 Genes Improves the Detection of Deleterious Mutations in South Indian Women with Breast and/or Ovarian Cancers.
Asian Pac J Cancer Prev. 2015; 16(13):5211-7 [PubMed] Related Publications
BACKGROUND: We earlier used PCR-dHPLC for mutation analysis of BRCA1 and BRCA2. In this article we report application of targeted resequencing of 30 genes involved in hereditary cancers.
MATERIALS AND METHODS: A total of 91 patient samples were analysed using a panel of 30 genes in the Illumina HiScan SQ system. CLCBio was used for mapping reads to the reference sequences as well as for quality-based variant detection. All the deleterious mutations were then reconfirmed using Sanger sequencing. Kaplan Meier analysis was conducted to assess the effect of deleterious mutations on disease free and overall survival.
RESULTS: Seventy four of the 91 samples had been run earlier using the PCR-dHPLC and no deleterious mutations had been detected while 17 samples were tested for the first time. A total of 24 deleterious mutations were detected, 11 in BRCA1, 4 in BRCA2, 5 in p53, one each in RAD50, RAD52, ATM and TP53BP1. Some 19 deleterious mutations were seen in patients who had been tested earlier with PCR-dHPLC [19/74] and 5/17 in the samples tested for the first time, Together with our earlier detected 21 deleterious mutations in BRCA1 and BRCA2, we now had 45 mutations in 44 patients. BRCA1c.68_69delAG;p.Glu23ValfsX16 mutation was the most common, seen in 10/44 patients. Kaplan Meier survival analysis did not show any difference in disease free and overall survival in the patients with and without deleterious mutations.
CONCLUSIONS: The NGS platform is more sensitive and cost effective in detecting mutations in genes involved in hereditary breast and/or ovarian cancers.

Aloraifi F, McDevitt T, Martiniano R, et al.
Detection of novel germline mutations for breast cancer in non-BRCA1/2 families.
FEBS J. 2015; 282(17):3424-37 [PubMed] Related Publications
The identification of the breast cancer susceptibility genes BRCA1 and BRCA2 enhanced clinicians' ability to select high-risk individuals for aggressive surveillance and prevention, and led to the development of targeted therapies. However, BRCA1/2 mutations account for only 25% of familial breast cancer cases. To systematically identify rare, probably pathogenic variants in familial cases of breast cancer without BRCA1/2 mutations, we developed a list of 312 genes, and performed targeted DNA enrichment coupled to multiplex next-generation sequencing on 104 'BRCAx' patients and 101 geographically matched controls in Ireland. As expected, this strategy allowed us to identify mutations in several well-known high-susceptibility and moderate-susceptibility genes, including ATM (~ 5%), RAD50 (~ 3%), CHEK2 (~ 2%), TP53 (~ 1%), PALB2 (~ 1%), and MRE11A (~ 1%). However, we also identified novel pathogenic variants in 30 other genes, which, when taken together, potentially explain the etiology of the missing heritability in up to 35% of BRCAx patients. These included novel potential pathogenic mutations in MAP3K1, CASP8, RAD51B, ZNF217, CDKN2B-AS1, and ERBB2, including a splice site mutation, which we predict would generate a constitutively active HER2 protein. Taken together, this work extends our understanding of the genetics of familial breast cancer, and supports the need to implement hereditary multigene panel testing to more appropriately orientate clinical management.

Dickreuter E, Eke I, Krause M, et al.
Targeting of β1 integrins impairs DNA repair for radiosensitization of head and neck cancer cells.
Oncogene. 2016; 35(11):1353-62 [PubMed] Related Publications
β1 Integrin-mediated cell-extracellular matrix interactions allow cancer cell survival and confer therapy resistance. It was shown that inhibition of β1 integrins sensitizes cells to radiotherapy. Here, we examined the impact of β1 integrin targeting on the repair of radiation-induced DNA double-strand breaks (DSBs). β1 Integrin inhibition was accomplished using the monoclonal antibody AIIB2 and experiments were performed in three-dimensional cell cultures and tumor xenografts of human head and neck squamous cell carcinoma (HNSCC) cell lines. AIIB2, X-ray irradiation, small interfering RNA-mediated knockdown and Olaparib treatment were performed and residual DSB number, protein and gene expression, non-homologous end joining (NHEJ) activity as well as clonogenic survival were determined. β1 Integrin targeting impaired repair of radiogenic DSB (γH2AX/53BP1, pDNA-PKcs T2609 foci) in vitro and in vivo and reduced the protein expression of Ku70, Rad50 and Nbs1. Further, we identified Ku70, Ku80 and DNA-PKcs but not poly(ADP-ribose) polymerase (PARP)-1 to reside in the β1 integrin pathway. Intriguingly, combined inhibition of β1 integrin and PARP using Olaparib was significantly more effective than either treatment alone in non-irradiated and irradiated HNSCC cells. Here, we support β1 integrins as potential cancer targets and highlight a regulatory role for β1 integrins in the repair of radiogenic DNA damage via classical NHEJ. Further, the data suggest combined targeting of β1 integrin and PARP as promising approach for radiosensitization of HNSCC.

Gurung RL, Lim SN, Low GK, Hande MP
MST-312 Alters Telomere Dynamics, Gene Expression Profiles and Growth in Human Breast Cancer Cells.
J Nutrigenet Nutrigenomics. 2014; 7(4-6):283-98 [PubMed] Related Publications
BACKGROUND: Targeting telomerase is a potential cancer management strategy given that it allows unlimited cellular replication in the majority of cancers. Dysfunctional telomeres are recognized as double-strand breaks. However, the status of DNA repair response pathways following telomerase inhibition is not well understood in human breast cancer cells. Here, we evaluated the effects of MST-312, a chemically modified derivative from tea catechin, epigallocatechin gallate, on telomere dynamics and DNA damage gene expression in breast cancer cells.
METHODOLOGY: Breast cancer cells MCF-7 and MDA-MB-231 were treated with MST-312, and telomere-telomerase homeostasis, induced DNA damage and gene expression profiling were analyzed.
RESULTS: MST-312 decreased telomerase activity and induced telomere dysfunction and growth arrest in breast cancer cells with more profound effects in MDA-MB-231 than in MCF-7 cells. Consistent with these data, the telomere-protective protein TRF2 was downregulated in MDA-MB-231 cells. MST-312 induced DNA damage at telomeres accompanied by reduced expression of DNA damage-related genes ATM and RAD50. Co-treatment with MST-312 and the poly(ADP-ribose) polymerase 1 (PARP-1) inhibitor PJ-34 further enhanced growth reduction as compared to single treatment with MST-312 or PJ-34.
CONCLUSIONS: Our work demonstrates potential importance for the establishment of antitelomerase cancer therapy using MST-312 along with PARP-1 inhibition in breast cancer therapy.

Zhang D, Tang B, Xie X, et al.
The interplay between DNA repair and autophagy in cancer therapy.
Cancer Biol Ther. 2015; 16(7):1005-13 [PubMed] Article available free on PMC after 01/04/2017 Related Publications
DNA is the prime target of anticancer treatments. DNA damage triggers a series of signaling cascades promoting cellular survival, including DNA repair, cell cycle arrest, and autophagy. The elevated basal and/or stressful levels of both DNA repair and autophagy observed in tumor cells, in contrast to normal cells, have been identified as the most important drug-responsive programs that impact the outcome of anticancer therapy. The exact relationship between DNA repair and autophagy in cancer cells remains unclear. On one hand, autophagy has been shown to regulate some of the DNA repair proteins after DNA damage by maintaining the balance between their synthesis, stabilization, and degradation. One the other hand, some evidence has demonstrated that some DNA repair molecular have a crucial role in the initiation of autophagy. In this review, we mainly discuss the interplay between DNA repair and autophagy in anticancer therapy and expect to enlighten some effective strategies for cancer treatment.

Amemiya Y, Bacopulos S, Al-Shawarby M, et al.
A Comparative Analysis of Breast and Ovarian Cancer-related Gene Mutations in Canadian and Saudi Arabian Patients with Breast Cancer.
Anticancer Res. 2015; 35(5):2601-10 [PubMed] Related Publications
Previous reports have indicated that patients with breast cancer who are from the Eastern Province of Saudi Arabia have a different gene expression profile from that known for their age-matched North American population. In the present study, breast tumor samples from Canadian and Saudi Arabian patients were screened for known and unknown mutations within BRCA1 and BRCA2 as well as 21 additional genes, including, ATM, BARD1, CDH1, P53, EPCAM, MSH6, and RAD50, which have been implicated in breast and ovarian cancer predisposition. A total of 129 non-synonymous mutations were identified by Ion Torrent amplicon sequencing. Forty-one mutations in 18 genes were unique to the Canadian population and 59 mutations in 20 genes were unique to the Saudi Arabian population. A total of 55/129 unique mutations in 22 genes were not previously reported in the database. Twenty-nine mutations in 16 genes were common to both populations; one of these mutations was not previously reported in the database. The most frequently mutated gene in both populations was the BRCA2 gene, followed by BRCA1 and TP53. Unique to this work is the identification of mutations frequently found in the Saudi Arabian population that are rare in the Canadian population. This work will allow direction of genetic analysis resources toward the clinical needs of each particular population.

Kuo YC, Wu HT, Hung JJ, et al.
Nijmegen breakage syndrome protein 1 (NBS1) modulates hypoxia inducible factor-1α (HIF-1α) stability and promotes in vitro migration and invasion under ionizing radiation.
Int J Biochem Cell Biol. 2015; 64:229-38 [PubMed] Related Publications
Hypoxia-inducible factor (HIF) is a heterodimer transcription factor complex that monitors the cellular response to the oxygen levels in cells. Hypoxia-inducible factor-1α (HIF-1α) has been shown to be stabilized by ionizing radiation (IR) and its stabilization promotes tumor progression and metastasis. Nijmegen breakage syndrome protein 1 (NBS1), a component of the MRE11-RAD50-NBS1 complex, plays an important role in the cellular response to DNA damage but its overexpression contributes to transformation and has been found to correlate with metastasis. However, whether NBS1 participates in IR-induced metastasis needs to be further determined. The aim of this study is to investigate whether radiation-induced HIF-1α stabilization is regulated by NBS1 and thereby promotes tumor cell migration/invasion. Here, we show that both NBS1 and HIF-1α expression are up-regulated after exposure to IR, and NBS1 increases HIF-1α expression at the protein level. In addition, IR treatment promotes the epithelial-mesenchymal transition (EMT) and in vitro cell migration and invasion activity, which could be abolished by suppression of NBS1. Furthermore, NBS1 directly interacts with HIF-1α and reduces the ubiquitination of HIF-1α⋅ Co-expression of HIF-1α and NBS1 in primary tumors of patients with lung adenocarcinoma correlates with a worse prognosis. These results provide a new function of NBS1 in stabilizing HIF-1α under IR, which leads to enhanced cancer cell migration and invasion.

Sheikh A, Hussain SA, Ghori Q, et al.
The spectrum of genetic mutations in breast cancer.
Asian Pac J Cancer Prev. 2015; 16(6):2177-85 [PubMed] Related Publications
Breast cancer is the most common malignancy in women around the world. About one in 12 women in the West develop breast cancer at some point in life. It is estimated that 5%-10% of all breast cancer cases in women are linked to hereditary susceptibility due to mutations in autosomal dominant genes. The two key players associated with high breast cancer risk are mutations in BRCA 1 and BRCA 2. Another highly important mutation can occur in TP53 resulting in a triple negative breast cancer. However, the great majority of breast cancer cases are not related to a mutated gene of high penetrance, but to genes of low penetrance such as CHEK2, CDH1, NBS1, RAD50, BRIP1 and PALB2, which are frequently mutated in the general population. In this review, we discuss the entire spectrum of mutations which are associated with breast cancer.

Rondeau S, Vacher S, De Koning L, et al.
ATM has a major role in the double-strand break repair pathway dysregulation in sporadic breast carcinomas and is an independent prognostic marker at both mRNA and protein levels.
Br J Cancer. 2015; 112(6):1059-66 [PubMed] Article available free on PMC after 01/04/2017 Related Publications
BACKGROUND: Ataxia telangiectasia mutated (ATM) is a kinase that has a central role in the maintenance of genomic integrity by activating cell cycle checkpoints and promoting repair of DNA double-strand breaks (DSB). In breast cancer, a low level of ATM was correlated with poor outcome; however, the molecular mechanism of this downregulation is still unclear.
METHODS: We used qRT-PCR assay to quantify mRNA levels of ATM gene in 454 breast tumours from patients with known clinical/pathological status and outcome; reverse phase protein arrays (RPPA) were used to assess the levels of ATM and 14 proteins in 233 breast tumours.
RESULTS: ATM mRNA was associated with poor metastasis-free survival (MFS) (P=0.00012) on univariate analysis. ATM mRNA and protein levels were positively correlated (P=0.00040). A low level of ATM protein was correlated with poorer MFS (P=0.000025). ATM expression at mRNA or protein levels are independent prognostic factors on multivariate analysis (P=0.00046 and P=0.00037, respectively). The ATM protein level was positively correlated with the levels of six proteins of the DSB repair pathway: H2AX (P<0.0000001), XRCC5 (P<0.0000001), NBN (P<0.0000001), Mre11 (P=0.0000029), Rad50 (P=0.0064), and TP53BP1 (P=0.026), but not with proteins involved in other pathways that are altered in cancer. Low expression of ATM protein was significantly associated with high miR-203 expression (P=0.011).
CONCLUSION: We confirmed that ATM expression is an independent prognostic marker at both RNA and protein levels. We showed that alteration of ATM is involved in dysregulation of the DSB repair pathway. Finally, miR-203 may be responsible for downregulation of ATM in breast cancers.

Kim DH, Oh SY, Kim SY, et al.
DNA ligase4 as a prognostic marker in nasopharyngeal cancer patients treated with radiotherapy.
Asian Pac J Cancer Prev. 2014; 15(24):10985-9 [PubMed] Related Publications
BACKGROUND: The capability for DNA double-strand breaks (DSBs) repair is crucial for inherent radiosensitivity of tumor and normal cells. We have investigated the clinicopathologic significance of DNA repair gene expression in nasopharyngeal (NP) carcinoma.
MATERIALS AND METHODS: A total of 65 NP cancer patients who received radiotherapy were included. The immunopositivity to Ku 70, DNA-PKcs, MRN, RAD50, XRCC4, and LIG4 were examined in all tumor tissues.
RESULTS: The patients comprised 42 males and 23 females, with a median age of 56 years (range, 18-84). The expression levels of RAD50 (0,+1,+2,+3) were 27.7%, 32.3%, 21.5%, and 18.5%. LIG4 (±) were 43.1% and 56.9% respectively. The 5-year OS rate of patients with LIG4 (±) were 90% and 67.9%, respectively (p=0.035). The 5-year TTP rate of patients with LIG4 (±) were 75.9%, 55.5%, respectively (P=0.039).
CONCLUSIONS: Our results suggest the possibility of predicting the radiosensitivity of NP cancer by performing immunohistochemical analysis of LIG4.

Dai X, Fagerholm R, Khan S, et al.
INPP4B and RAD50 have an interactive effect on survival after breast cancer.
Breast Cancer Res Treat. 2015; 149(2):363-71 [PubMed] Related Publications
Genes sharing similar genomic landscape have the potential to interactively orchestrate certain clinicopathological features of a disease. Deletion of the RAD50 gene is a common event particularly in basal-like breast cancer, and often occurs together with deletions of BRCA1, RB1, TP53, PTEN, and INPP4B. In this study, we investigate whether these co-deleted genes have interactive effects on survival in breast cancer. Using publicly available TCGA data, we employed Cox's proportional hazards models to test whether genomic deletions of these genes, or reduced protein or transcript levels associate with breast cancer patient survival in an interactive manner. Further validation was obtained at the transcriptional level by including 1,596 additional cases from 13 publicly available gene expression data sets from the KM-plotter database. Our results indicate that RAD50 and INPP4B associate interactively with breast cancer survival at the transcriptional, translational, and genomic levels in the TCGA data set (p (interaction) < 0.05). While neither of the genes was independently prognostic on its own, low INPP4B levels in combination with above median RAD50 abundance associated with increased hazard, both at the mRNA (HR 2.39, 95 % CI 1.20-4.76) and protein (HR 2.92, 95 % CI 1.42-6.00) levels, whereas concomitant deletion or low expression of both genes associated with unexpectedly improved survival. A similar pattern was observed in the KM-plotter data set (p (interaction) = 0.0067). We find that RAD50 and INPP4B expression levels have a synergistic influence on breast cancer survival, possibly through their effects on treatment response.

Berlin A, Lalonde E, Sykes J, et al.
NBN gain is predictive for adverse outcome following image-guided radiotherapy for localized prostate cancer.
Oncotarget. 2014; 5(22):11081-90 [PubMed] Article available free on PMC after 01/04/2017 Related Publications
Despite the use of clinical prognostic factors (PSA, T-category and Gleason score), 20-60% of localized prostate cancers (PCa) fail primary local treatment. Herein, we determined the prognostic importance of main sensors of the DNA damage response (DDR): MRE11A, RAD50, NBN, ATM, ATR and PRKDC. We studied copy number alterations in DDR genes in localized PCa treated with image-guided radiotherapy (IGRT; n=139) versus radical prostatectomy (RadP; n=154). In both cohorts, NBN gains were the most frequent genomic alteration (14.4 and 11% of cases, respectively), and were associated with overall tumour genomic instability (p<0.0001). NBN gains were the only significant predictor of 5yrs biochemical relapse-free rate (bRFR) following IGRT (46% versus 77%; p=0.00067). On multivariate analysis, NBN gain remained a significant independent predictor of bRFR after adjusting for known clinical prognostic variables (HR=3.28, 95% CI 1.56-6.89, Wald p-value=0.0017). No DDR-sensing gene was prognostic in the RadP cohort. In vitro studies correlated NBN gene overexpression with PCa cells radioresistance. In conclusion, NBN gain predicts for decreased bRFR in IGRT, but not in RadP patients. If validated independently, Nibrin gains may be the first PCa predictive biomarker to facilitate local treatment decisions using precision medicine approaches with surgery or radiotherapy.

Chevrier S, Boidot R
gDNA enrichment by a transposase-based technology for NGS analysis of the whole sequence of BRCA1, BRCA2, and 9 genes involved in DNA damage repair.
J Vis Exp. 2014; (92):e51902 [PubMed] Article available free on PMC after 01/04/2017 Related Publications
The widespread use of Next Generation Sequencing has opened up new avenues for cancer research and diagnosis. NGS will bring huge amounts of new data on cancer, and especially cancer genetics. Current knowledge and future discoveries will make it necessary to study a huge number of genes that could be involved in a genetic predisposition to cancer. In this regard, we developed a Nextera design to study 11 complete genes involved in DNA damage repair. This protocol was developed to safely study 11 genes (ATM, BARD1, BRCA1, BRCA2, BRIP1, CHEK2, PALB2, RAD50, RAD51C, RAD80, and TP53) from promoter to 3'-UTR in 24 patients simultaneously. This protocol, based on transposase technology and gDNA enrichment, gives a great advantage in terms of time for the genetic diagnosis thanks to sample multiplexing. This protocol can be safely used with blood gDNA.

Li H, Chen X, Yu Y, et al.
Metformin inhibits the growth of nasopharyngeal carcinoma cells and sensitizes the cells to radiation via inhibition of the DNA damage repair pathway.
Oncol Rep. 2014; 32(6):2596-604 [PubMed] Related Publications
Nasopharyngeal carcinoma (NPC) is a leading cause of cancer-related mortality. Radiotherapy is one of the primary modalities for NPC treatment. However, in patients in the late stages of the disease, the local control rate and overall survival rate remain low. Therefore, it is urgent to identify new targets that can improve the outcome of radiotherapy in this neoplasm. In the present study, we investigated the effects of metformin on the radiosensitivity of NPC cells and explored the potential mechanisms. The radiosensitizing effects of metformin on NPC cells were measured by colony formation assay. Cell apoptosis was assessed by Hoechst 33342 staining analysis. DNA damage was detected by monitoring γ-H2AX foci with immunofluorescence. The changes in apotosis-related and DNA damage repair-related proteins were detected by western blotting. Our study demonstrated that metformin significantly reduced the cell viability, enhanced radiosensitivity and potentiated radiation-induced caspase-9/-3 cleavage in the NPC cells. In addition, metformin plus radiation significantly upregulated the expression of p-ATM, p-ATR, γ-H2AX and downregulated the expression of ATM, ATR, p95/NBS1, Rad50, DNA-PK, Ku70 and Ku80. Therefore, our results suggest that metformin possesses a strong radiosensitizing potential in NPC cells. This radiosensitizing effect was associated with inhibition of DNA double-strand break repair processes through HR repair and the NHEJ repair signaling pathway, thereby enhancing radiation-induced cell apoptosis. These findings imply that metformin is a potent radiation-sensitizing agent and may be a promising candidate for clinical evaluation as part of a combined regimen for the treatment of nasopharyngeal carcinoma.

Fan X, Wang YY, Zhang CB, et al.
Expression of RINT1 predicts seizure occurrence and outcomes in patients with low-grade gliomas.
J Cancer Res Clin Oncol. 2015; 141(4):729-34 [PubMed] Related Publications
PURPOSE: Most patients with low-grade gliomas (LGGs) experience epileptic seizures as an initial symptom. However, the mechanism of LGG-related epilepsy is poorly understood. Genetic changes in brain tumors influence epileptic seizures, but few biomarkers have been associated with LGG-related seizures. We investigated the association between LGG-related epilepsy and tumor-specific molecular changes.
METHODS: Clinical characteristics, RNA sequence data, and case follow-up data were reviewed for 76 patients with histologically confirmed LGG. Gene expression (n = 21,469) was compared between patients with preoperative epileptic seizures and those without preoperative epileptic seizures. The Engel classification was used at 6 months after surgery to evaluate the prognostic role of genes that passed the screen.
RESULTS: Expression of RAD50 interactor 1 (RINT1) significantly differed between LGG patients with and without preoperative epileptic seizures (p = 0.003). This result was validated by applying the same analysis to RNA sequence data from The Cancer Genome Atlas (p = 0.048). Patients with high RINT1 expression were at increased risk of LGG-related seizures compared to those with low expression (p = 0.044). RINT1 was also identified as a predictor of seizure outcomes in patients with LGG at 6 months after tumor resection (p = 0.022).
CONCLUSIONS: Our results suggest that high RINT1 expression may represent a risk factor for LGG-related seizures and may be associated with seizure outcomes.

Peng G, Woodman SE, Mills GB
RADical response puts an exceptional responder in CHKmate: a synthetic lethal curative response to DNA-damaging chemotherapy?
Cancer Discov. 2014; 4(9):988-90 [PubMed] Article available free on PMC after 01/04/2017 Related Publications
SUMMARY: In this issue of Cancer Discovery, AI-Ahmadie and colleagues identify a somatic mutation in the RAD50 gene as a likely contributing factor to an unusual curative response to systemic combination therapy employing the DNA-damaging agent irinotecan and a checkpoint kinase 1 inhibitor in a patient with recurrent, metastatic small-cell cancer. This study highlights the importance of in-depth analysis of exceptional responders to chemotherapy and targeted therapy in early-phase clinical trials and opens new avenues for developing cancer genome-based combination therapy to improve the efficacy of traditional chemotherapy through synthetically lethal interactions.

Al-Ahmadie H, Iyer G, Hohl M, et al.
Synthetic lethality in ATM-deficient RAD50-mutant tumors underlies outlier response to cancer therapy.
Cancer Discov. 2014; 4(9):1014-21 [PubMed] Article available free on PMC after 01/04/2017 Related Publications
UNLABELLED: Metastatic solid tumors are almost invariably fatal. Patients with disseminated small-cell cancers have a particularly unfavorable prognosis, with most succumbing to their disease within two years. Here, we report on the genetic and functional analysis of an outlier curative response of a patient with metastatic small-cell cancer to combined checkpoint kinase 1 (CHK1) inhibition and DNA-damaging chemotherapy. Whole-genome sequencing revealed a clonal hemizygous mutation in the Mre11 complex gene RAD50 that attenuated ATM signaling which in the context of CHK1 inhibition contributed, via synthetic lethality, to extreme sensitivity to irinotecan. As Mre11 mutations occur in a diversity of human tumors, the results suggest a tumor-specific combination therapy strategy in which checkpoint inhibition in combination with DNA-damaging chemotherapy is synthetically lethal in tumor cells but not normal cells with somatic mutations that impair Mre11 complex function.
SIGNIFICANCE: Strategies to effect deep and lasting responses to cancer therapy in patients with metastatic disease have remained difficult to attain, especially in early-phase clinical trials. Here, we present an in-depth genomic and functional genetic analysis identifying RAD50 hypomorphism as a contributing factor to a curative response to systemic combination therapy in a patient with recurrent, metastatic small-cell cancer.

Koppensteiner R, Samartzis EP, Noske A, et al.
Effect of MRE11 loss on PARP-inhibitor sensitivity in endometrial cancer in vitro.
PLoS One. 2014; 9(6):e100041 [PubMed] Article available free on PMC after 01/04/2017 Related Publications
AIM OF THE STUDY: To evaluate the frequency of MRE11/RAD50/NBS1 (MRN)-complex loss of protein expression in endometrial cancers (EC) and to determine whether loss of MRE11 renders the cancer cells sensitive to Poly(ADP-ribose) polymerase (PARP)-inhibitory treatment.
METHODS: MRN expression was examined in 521 samples of endometrial carcinomas and in 10 cancer cell lines. A putative mutation hotspot in the form of an intronic poly(T) allele in MRE11 was sequenced in selected cases (n = 26). Sensitivity to the PARP-inhibitor, BMN673 was tested in colony formation assays before and after MRE11 silencing using siRNA. Homologous recombination (HR) DNA repair was evaluated by RAD51-foci formation assay upon irradiation and drug treatment.
RESULTS: Loss of MRE11 protein was found in 30.7% of EC tumours and significantly associated with loss of RAD50, NBS1 and mismatch repair protein expression. One endometrial cell line showed a markedly reduced MRE11 expression due to a homozygous poly(T) mutation of MRE11, thereby exhibiting an increased sensitivity to BMN673. MRE11 depletion sensitizes MRE11 expressing EC cell lines to the treatment with BMN673. The increased sensitivity to PARP-inhibition correlates with reduced RAD51 foci formation upon ionizing radiation in MRE11-depleted cells.
CONCLUSION: Loss of the MRE11 protein predicts sensitivity to PARP-inhibitor sensitivity in vitro, defining it as an additional synthetic lethal gene with PARP. The high incidence of MRE11 loss in ECs can be potentially exploited for PARP-inhibitor therapy. Furthermore, MRE11 protein expression using immunohistochemistry could be investigated as a predictive biomarker for PARP-inhibitor treatment.

Damiola F, Pertesi M, Oliver J, et al.
Rare key functional domain missense substitutions in MRE11A, RAD50, and NBN contribute to breast cancer susceptibility: results from a Breast Cancer Family Registry case-control mutation-screening study.
Breast Cancer Res. 2014; 16(3):R58 [PubMed] Article available free on PMC after 01/04/2017 Related Publications
INTRODUCTION: The MRE11A-RAD50-Nibrin (MRN) complex plays several critical roles related to repair of DNA double-strand breaks. Inherited mutations in the three components predispose to genetic instability disorders and the MRN genes have been implicated in breast cancer susceptibility, but the underlying data are not entirely convincing. Here, we address two related questions: (1) are some rare MRN variants intermediate-risk breast cancer susceptibility alleles, and if so (2) do the MRN genes follow a BRCA1/BRCA2 pattern wherein most susceptibility alleles are protein-truncating variants, or do they follow an ATM/CHEK2 pattern wherein half or more of the susceptibility alleles are missense substitutions?
METHODS: Using high-resolution melt curve analysis followed by Sanger sequencing, we mutation screened the coding exons and proximal splice junction regions of the MRN genes in 1,313 early-onset breast cancer cases and 1,123 population controls. Rare variants in the three genes were pooled using bioinformatics methods similar to those previously applied to ATM, BRCA1, BRCA2, and CHEK2, and then assessed by logistic regression.
RESULTS: Re-analysis of our ATM, BRCA1, and BRCA2 mutation screening data revealed that these genes do not harbor pathogenic alleles (other than modest-risk SNPs) with minor allele frequencies>0.1% in Caucasian Americans, African Americans, or East Asians. Limiting our MRN analyses to variants with allele frequencies of <0.1% and combining protein-truncating variants, likely spliceogenic variants, and key functional domain rare missense substitutions, we found significant evidence that the MRN genes are indeed intermediate-risk breast cancer susceptibility genes (odds ratio (OR)=2.88, P=0.0090). Key domain missense substitutions were more frequent than the truncating variants (24 versus 12 observations) and conferred a slightly higher OR (3.07 versus 2.61) with a lower P value (0.029 versus 0.14).
CONCLUSIONS: These data establish that MRE11A, RAD50, and NBN are intermediate-risk breast cancer susceptibility genes. Like ATM and CHEK2, their spectrum of pathogenic variants includes a relatively high proportion of missense substitutions. However, the data neither establish whether variants in each of the three genes are best evaluated under the same analysis model nor achieve clinically actionable classification of individual variants observed in this study.

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