Introducing a novel allele for the polymorphism of variable number of tandem repeats in the promoter region of XRCC5

Genetic association of XRCC5 gene polymorphisms with breast cancer among Jordanian women

Purpose

Breast cancer (BC) is a complex disease that is governed by several different environmental and inherited factors. There are many genes have been linked with BC development by screening specific genetic variants within these genes. In this study, we aim to investigate the correlation between Variable Number Tandem Repeat (VNTR) in XRCC5 gene and BC.

Materials and methods

Polymerase Chain Reaction (PCR) and Gel electrophoresis were used to genotype the XRCC5 gene polymorphism in 200 cases with breast cancer and 200 healthy individuals. All participants were Jordanian women from Arab descents. Clinical and pathological characteristics for BC patients were summarized and categorized according to their medical records.

Results

In this study, we found a strong correlation between the VNTR polymorphism in the XRCC5 gene and BC risk (P-value<0.0001). Remarkably, three different genotypes (2R\2R, 3R\2R and 3R\3R) showed significant association with BC (P-value<0.0001). This study also reported a significant difference in the distribution of allele frequencies between BC patients and healthy individuals (3R; P-value<0.0001 and 2R; P-value<0.001). However, we propose that VNTR of XRCC5 gene did not interfere with BC prognosis.

Conclusion

We speculate that the VNTR of XRCC5 gene may influence BC development. More investigations are needed in this regard to clarify the underlying role of the XRCC5 genetic variant in tumorgenesis including BC development.

Differences of Variable Number Tandem Repeats in XRCC5 Promoter Are Associated with Increased or Decreased Risk of Breast Cancer in BRCA Gene Mutation Carriers

Ku80 is a subunit of the Ku heterodimer that binds to DNA double-strand break ends as part of the non-homologous end joining (NHEJ) pathway. Ku80 is also involved in homologous recombination (HR) via its interaction with BRCA1. Ku80 is encoded by the XRCC5 gene that contains a variable number tandem repeat (VNTR) insertion in its promoter region. Different VNTR genotypes can alter XRCC5 expression and affect Ku80 production, thereby affecting NHEJ and HR pathways. VNTR polymorphism is associated with multiple types of sporadic cancer. In this study, we investigated its potential association with familial breast cancer at the germline level. Using PCR, PAGE, Sanger sequencing, and statistical analyses, we compared VNTR genotypes in the XRCC5 promoter between healthy individuals and three types of familial breast cancer cases: mutated BRCA1 (BRCA1⁺), mutated BRCA2 (BRCA2⁺), and wild-type BRCA1/BRCA2 (BRCAx). We observed significant differences of VNTR genotypes between control and BRCA1⁺ group (P < 0.0001) and BRCA2⁺ group (P = 0.0042) but not BRCAx group (P = 0.2185), and the differences were significant between control and cancer-affected BRCA1⁺ cases (P < 0.0001) and BRCA2⁺ cases (P = 0.0092) but not cancer-affected BRCAx cases (P = 0.4251). Further analysis indicated that 2R/2R (OR = 1.94, 95%CI = 1.26–2.95, P = 0.0096) and 2R/1R (OR = 1.58, 95%CI = 1.11–2.26, P = 0.0388) were associated with increased risk but 1R/1R (OR = 0.55, 95%CI = 0.35–0.84, P = 0.0196) and 1R/0R (OR = 0, 95%CI = 0–0.29, P = 0.0012) were associated with decreased risk in cancer-affected BRCA1⁺ group; 2R/1R (OR = 1.94, 95%CI = 1.14–3.32, P = 0.0242) was associated with increased risk in cancer-affected BRCA2⁺ group. No correlation was observed for the altered risk between cancer-affected or -unaffected carriers and between different age of cancer diagnosis in cancer-affected carriers. The frequently observed VNTR association with in BRCA1⁺ and BRCA2⁺ breast cancer group indicates that VNTR polymorphism in the XRCC5 promoter is associated with altered risk of breast cancer in BRCA1⁺ and BRCA2⁺ carriers.

Susceptibility to gastric cancer and polymorphisms of insertion/deletion at the intron 3 of the XRCC4 and VNTR at the promoter region of the XRCC5

The genes encoding X-ray repair cross-complementing group 4 (XRCC4; OMIM: 194363) and 5 (XRCC5; OMIM: 194364) are involved in repair of DNA double-strand breaks. To investigating the associations between polymorphisms of Insertion/Deletion (I/D, rs28360071) in the intron 3 of the XRCC4 and VNTR in the promoter region of the XRCC5 and risk of gastric cancer, the present study was carried out. We included 159 (56 females, 103 males) with gastric cancer and 242 (75 females, 167 males) healthy blood donors frequency matched for age and gender. Using PCR-based methods, the genotypes of the study polymorphisms were determined. The alleles of VNTR XRCC5 polymorphism divided into two groups: L (0 and 1 repeats) and H (2 and 3 repeats) alleles. For the I/D XRCC4 polymorphism, after stratification of the subjects according to their family history (FH) of cancer, either the ID (OR = 3.19, 95%CI: 1.35-7.50, P = 0.008) or the DD genotypes (OR = 4.62, 95%CI: 1.63-13.0, P = 0.004) among positive FH persons, increased the risk of gastric cancer compared with the reference group (persons who have negative FH and II genotype). For the VNTR XRCC5 polymorphism, the LH + HH genotypes among positive FH persons, increased the risk of gastric cancer compared with the reference group (persons who have negative FH and LL genotype) (OR = 2.88, 95%CI: 1.34-6.18, P = 0.006). Sensitivity analysis showed that the above mentioned associations were not occurred due to the maldistribution of the genotypes among missing data. The present study suggests that both polymorphisms of the XRCC4 and XRCC5 might be risk factors for gastric cancer development especially among persons with positive FH.

Impact of sodium arsenite on chromosomal aberrations with respect to polymorphisms of detoxification and DNA repair genes

Arsenic compounds can increase production of reactive oxygen species. Reactive oxygen species can induce double-strand breaks in DNA, which is a cause of chromosome aberrations (CAs). This study was conducted to determine the association between arsenic exposure and polymorphisms of genes involved in detoxification (glutathione S-transferase T1 [GSTT1], glutathione S-transferase M1 [GSTM1], glutathione S-transferase O2 [GSTO2], catalase [CAT], and NAD(P)H quinone oxidoreductase1 [NQO1]) as well as nonhomologous end joining DNA repair genes (XRCC4, XRCC5, and XRCC6) with induction of chromosomal aberrations. The participants consisted of 123 healthy males who were genotyped using polymerase chain reaction-based methods. Primary cultures of whole blood were treated with sodium arsenite (NaAsO(2); iAs(III); at final concentration 1 µmol/L), mitomycin C (at final concentration 60 ηg/mL; as positive control), or untreated. For each culture, mitotic index (MI), chromatid breaks (CBs), CAs, and total percentage of aberrant cells were determined. The levels of CB and percentage of aberrant cells were significantly higher in the TT genotype of CAT (C-262T polymorphism) than the CC genotype. The CB value in samples with GSTM1 active genotype was significantly higher than the null genotype. The MI in samples with TT genotype of NQO1 (C609T polymorphism) was significantly higher than MI in samples having CC and CT genotypes. There was no association between MI, CB, CA, and percentage of aberrant cells and polymorphisms of XRCC4, XRCC5, and XRCC6.

Association of XRCC5 VNTR polymorphism with the development of chronic myeloid leukemia

Double-strand breaks (DSBs) inducing agents influence the fidelity of DNA repair in both normal cells and leukemic cells, causing major genomic instability. In eukaryotic cells, non-homologous end joining pathway (NHEJ) is the major mechanism for DSB repair. Human X-ray repair cross-complementing 5 (XRCC5) gene encodes for the protein KU86, an important component of NHEJ pathway. Variable number of tandem repeats (VNTR) polymorphism (rs 6147172) in the promoter region of XRCC5 gene was shown to have effect on gene expression and was found to be associated with the development of several cancers. We analyzed VNTR polymorphism of XRCC5 gene in 461 chronic myeloid leukemia (CML) cases and 408 controls by polymerase chain reaction. Our results showed that frequency of 0R/0R genotype was significantly elevated in CML cases compared to that of controls (p = 0.05). Significant difference in the genotype distribution was observed between cases and controls (p = 0.02). The risk of CML development was found to be elevated for individuals carrying lower repeats (1R p = 0.03; 0R p = 0.007). Elevated 0R/0R genotype frequency was found to be significantly associated with early age at onset (≤ 30 years) and slightly elevated in chronic phase and poor hematologic response to imatinib mesylate. The influence of zero repeat on enhanced expression of XRCC5 might confer risk to error-prone repair leading to genomic instability and CML. Hence, the VNTR polymorphism in the promoter region of XRCC5 gene could serve as an important prognostic marker in CML development.

The novel allele (3R) of the VNTR polymorphism in the XRCC5 promoter region dramatically decreases the gene expression

Polymorphism of variable number of tandem repeats (VNTR) in the promoter region of X-ray repair cross-complementing 5 (MIM: 194364, XRCC5; rs6147172) was reported. The aim of the present study is to evaluate the influence of this polymorphism on XRCC5 mRNA levels. Genotypes of XRCC5 VNTR were determined by high resolution of melting analysis (HRMA). The quantitative XRCC5 mRNA expression (compared to ß-actin expression) among 0R/1R, 1R/2R, and 1R/3R genotypes was investigated. There was a negative correlation between the overall number of tandem repeats and XRCC5 expression (r=-0.965, df=7, P<0.001). The mRNA level of XRCC5 decreased as function of number of tandem repeats. The 3R allele of the VNTR polymorphism in the XRCC5 promoter region dramatically decreases the gene expression.