Abstract
Aim: The present study aimed at investigating whether X-ray repair cross complementing protein 3 (XRCC3) genotype may serve as a useful marker for detecting leiomyoma and predicting risk. Materials and Methods: A total of 640 women (166 patients with leiomyoma and 474 healthy controls) were examined for their XRCC3 rs1799794, rs45603942, rs861530, rs3212057, rs1799796, rs861539, rs28903081 genotype. The distributions of genotypic and allelic frequencies between the two groups were compared. Results: The results showed that the CT and TT genotypes of XRCC3 rs861539 were associated with increased leiomyoma risk (odds ratio=2.19, 95% confidence interval=1.23-3.90; odds ratio=3.72, 95% confidence interval=1.23-11.26, respectively). On allelic frequency analysis, we found a significant difference in the distribution of the T allelic frequency of the XRCC3 rs861539 (p=5.88×10−5). None of the other six single nucleotide polymorphisms were associated with altered leiomyoma susceptibility. Conclusion: The T allele (CT and TT genotypes) of XRCC3 rs861539 contributes to increased risk of leiomyoma among Taiwanese women and may serve as a early detection and predictive marker.
Worldwide, uterine leiomyoma is the most commonly diagnosed benign uterine neoplasm, and almost one fourth of women were affected by leiomyoma during their lifetime (1). Early during the 1970s, uterine leiomyoma was found to be monoclonal, and its tumorigenesis may be derived from growth and proliferation of a single smooth muscle cell (2). Uterine leiomyoma is estimated to be present in 30-70% of clinically reproductive women, and has become a common health threat (3-5). Statistically, it was estimated that about seven out of every ten Caucasian women and eight out of every ten African American women eventually develop uterine leiomyoma (3). In addition, some factors such as ethnicity, nulliparity, obesity, diet and age, especially those of early menarche, were revealed to be predisposing factors for uterine leiomyoma (6). Although clear heredity or genetic involvement has not yet been well-described for uterine leiomyoma, it has been shown that individual differences in susceptibility may be inherited in genes encoding DNA repair proteins, which may be closely associated with personal uterine leiomyoma risk (7). Furthermore, Hakverdi and colleagues found novel chromosomal aberrations in the tissues from patients with uterine leiomyoma (8).
The X-ray repair cross-complementing group 3 (XRCC3) gene located on human chromosomes 14q32.3, encodes for the DNA repair protein XRCC3. In 1998, XRCC3 was shown to play a role in homologous recombination (HR) to repair double-strand breaks via interacting with RAD51 recombinase (RAD51) (9). In 2002, XRCC3-mutant cells were found to have increased gene conversion tract lengths, increased frequencies of discontinuous tracts, and frequent local rearrangements. The results indicated that XRCC3 is involved not only in HR initiation, but also in formation and stabilizing of HR intermediates (10). In recent years, mounting evidence has shown the association between the genotypes of XRCC3, such as the rs861539 C/T (also named Thr241Met, T241M, C18067T and C722T) single nucleotide polymorphism (SNP) and risk of cancer, including of the lung (11-13), oral cavity (14), stomach (15), bladder (16), breast (17, 18), colorectum (19) and nasopharynx (20). In addition, variants of this polymorphism may affect the function of XRCC3, with decreased DNA repair capacity and elevated level of bulky DNA adducts in leukocytes of healthy individuals (11). Thus, the rs861539 polymorphism and others of XRCC3 may also contribute to the pathogenesis and development of uterine leiomyoma.
In the present study, we aimed to examine the contribution of XRCC3 genotype to uterine leiomyoma risk. The distributions of the genotypic and allelic frequencies for XRCC3 at promoter A-315G (rs1799794), promoter C-280T (rs45603942), intron5 (rs861530), exon6 (rs3212057), intron7 (rs1799796), exon8 (rs861539) and exon10 (rs28903081) were examined among women with and without uterine leiomyoma in Taiwan.
Materials and Methods
Investigated population. Six hundred and forty pre-menopausal women with and without uterine leiomyoma were recruited in this study. Among them, 166 were surgically- and histologically-diagnosed with leiomyoma. The other 474 women were confirmed as not having leiomyoma after detailed ultrasonography. Patients with previous malignancy, metastasized cancer from other or unknown origin, and any genetic or familial diseases were excluded. The clinical characteristics of patients, including histological details, were all graded and defined by expert surgeons. All participants voluntarily completed a self-administered questionnaire and provided their peripheral blood samples. Approval from the Institutional Review Board and written-informed consent was obtained from all participants. We also sincerely followed the principles outlined in the Declaration of Helsinki for human investigations. The demographic information for the leiomyoma cases and healthy controls are listed in Table I.
Genotyping conditions. Genomic DNA was extracted from peripheral blood leucocytes using the QIAamp Blood Mini Kit (Blossom, Taipei, Taiwan). In this study, a total of seven polymorphic sites were analyzed in both the control and case groups. Briefly, all of the seven polymorphic sites were genotyped by means of a polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Each PCR reaction consisted of an initial cycle at 94°C for 5 min; 40 cycles at 94°C for 30 s, 55°C for 30 s, and 72°C for 30 s; and a final extension at 72°C for 10 min. After the PCR process, the SNP-containing DNA amplicons were subjected to individual overnight digestion by the restriction endonucleases listed in Table II for genotyping of each SNP. Following digestion, each sample was immediately analyzed by 3% agarose gel electrophoresis. Details such as the primer sequences, and enzymatic digestion conditions for genotyping of each SNP are summarized in Table II.
Statistical analyses. To ensure that the controls used were representative of the general population and to exclude the possibility of genotyping error, the deviation of the genotype frequencies of XRCC3 SNPs in the controls from those expected under the Hardy–Weinberg equilibrium was assessed using the goodness-of-fit test. Pearson's chi-square test was used to compare the distribution of the XRCC3 genotypes between leiomyoma cases and healthy controls. Student's t-test was used to compare the difference between case and control groups by age. The leiomyoma risk associated with the genotypes was estimated as odds ratio (OR) with 95% confidence intervals (CIs) using unconditional logistic regression. Data were recognized as significant when the statistical p-value outcome was less than 0.05.
Results
The frequency distributions of demographic characteristics for the 166 patients with leiomyoma and 474 non-leiomyoma controls are summarized in Table I. There was no difference in the distributions of age, height and weight between the patient and control groups (Table I). Overall, women in the control group had significantly more children than those in the patient group (p=0.0003) (Table I).
The distributions of the XRCC3 genotypic frequencies for rs1799794, rs45603942, rs861530, rs3212057, rs1799796, rs861539 and rs28903081 among the patients with leiomyoma and controls are presented and analyzed in Table III. The data show that the genotypes of XRCC3 rs861539 were differently distributed between leiomyoma and non-leiomyoma groups (p=0.0018) (Table III). XRCC3 rs861539 heterozygous variant CT and homozygous variant TT genotypes were significantly associated with higher risk of leiomyoma (p=0.0018) compared with the wild-type CC genotype (Table III). The distributions of the XRCC3 genotypes of rs1799794, rs45603942, rs861530 and rs1799796 were not different among the patients and controls (Table III). In this study, we found that our Taiwanese population had only one genotype at XRCC3 rs3212057 (GG) and rs28903081 (GG) (Table III).
We also examined the distributions of the XRCC3 allelic frequencies for rs1799794, rs45603942, rs861530, rs1799796 and rs861539 among the controls and the patients, and the results are presented in Table IV. Consistent with the findings that the CT and TT genotypes of XRCC3 rs861539 were associated with an increased risk of leiomyoma (Table III), the T allele was found at a significantly higher percentage (10.8%) among the patients than the controls (4.6%) (p=5.88×10−5) (Table IV). For the other polymorphic sites of XRCC3 examined, the distributions of the allelic frequencies were not different between the control and patient groups (Table IV).
Discussion
Uterine leiomyomas are the most common female genital tumors (21, 22). In Taiwan, the prevalence of uterine leiomyoma has been increasing in recent years. However, despite its high incidence, its etiology and pathogenesis remain obscure. Clinically, uterine leiomyoma has many features similar to those of solid tumors. Loss of maintenance of genome integrity is closely associated with tumorigenesis, and cancer may occur more frequently among those who carry inherited defects in their DNA repair genes such as XRCC3. XRCC3 protein has been reported to play a role in DNA repair (23), and mutations of XRCC3 gene have been related to severe chromosomal instability (10). From the viewpoint of proteomics, the altered quality (activity) and quantity (expression level) of XRCC3 protein have been reported to be associated with a more aggressive tumor phenotype, higher recurrence rate, and poorer prognosis of several types of cancers, such as of the breast and colorectum, and in non-small cell lung cancer (24-26).
We surveyed the MEDLINE database, finding no literature investigating the association of XRCC3 genotypes with leiomyoma susceptibility. In this case–control study in Taiwan, we are the first to examine seven polymorphic genotypes of XRCC3, and their contribution to determine individual susceptibility to leiomyoma. We found that XRCC3 rs861539 variant CT and TT genotypes were associated with an increased leiomyoma risk (Tables III and IV). There was also a significant trend that carrying two variant T alleles was associated with higher risk than carrying one (OR=3.72 vs. 2.19, p=0.0018) or none (Table III). The T allele can serve as a biomarker for early detection of and predictive for leiomyoma.
Regarding factors, we found that age, height and weight were not risk factors for leiomyoma in Taiwan (Table I). In 2001, it was reported that individuals carrying a T allele at XRCC3 rs861539 have a significantly higher level of bulky DNA adducts in their lymphocyte DNA than those carrying the C allele (11, 27). Although we did not measure the levels of bulky DNA adducts in white blood cells in our study, our findings support previous data showing that people with XRCC3 rs861539 CT and TT genotypes had a more instable genome than those with wild-type CC genotype, leading to a higher risk for leiomyoma (14, 20).
Elevated lifetime estrogen exposure is a major risk factor for breast cancer and estrogen-induced reactive oxygen species (ROS) and ROS-mediated signaling pathways contribute to breast cancer development. ROS was found to activate mitogenic growth factor signaling pathway in primarily cultured human leiomyoma smooth muscle cells (28). At the same time, ROS may cause DNA double-strand breaks which should be removed by XRCC3 and other DNA repair proteins. The etiology of leiomyoma is complex, and one possible mechanism is that women exposed to estrogen for longer due to their earlier menarche or later menopause may be at higher risk of leiomyoma as a result of exposure to ROS for a longer period during their lifetime. Therefore, age- and hormone-related factors are risk factors for leiomyoma (4, 5). Regarding genetic factors of leiomyoma, women with variant genotypes at XRCC3 rs861539 may be at even higher risk since their genomes are more unstable than those with wild-type genotype. In the future, it is very important to investigate the gene interaction with other factors to reveal the etiology of leiomyoma.
In conclusion, our findings suggest for the first time that the T allele of XRCC3 rs861539 may be associated with higher risk of leiomyoma, and can serve as a marker for early detection and prediction of leiomyoma.
Acknowledgements
We appreciate Chia-En Miao, Lin-Lin Hou, Tzu-Chia Wang, Yun-Ru Syu for their excellent technical assistance. This study was supported by research grants from Taichung Armed Forces General Hospital (104-A11, 104-A13, 104-A23) and Taiwan Ministry of Health and Welfare Clinical Trial and Research Center of Excellence (MOHW104-TDU-B-212-113002). The authors declare no conflict of interest.
Footnotes
↵* These Authors contributed equally to this study.
- Received May 11, 2015.
- Revision received June 16, 2015.
- Accepted June 18, 2015.
- Copyright© 2015 International Institute of Anticancer Research (Dr. John G. Delinassios), All rights reserved