|Year : 2021 | Volume
| Issue : 4 | Page : 1031-1038
Nonhomologous end joining repair pathway molecules as predictive biomarkers for patients with oral squamous cell carcinoma
Jigna S Joshi1, Hemangini H Vora2, Nandita R Ghosh3, Rajen N Tankshali4, Dhaval H Jetly5, Trupti I Trivedi6
1 Stem Cell Biology Lab, Department of Cancer Biology, The Gujarat Cancer & Research Institute, Ahmedabad, Gujarat, India
2 Immunohematology Lab, Department of Cancer Biology, The Gujarat Cancer & Research Institute, Ahmedabad, Gujarat, India
3 Tumor Biology Lab, Department of Cancer Biology, The Gujarat Cancer & Research Institute, Ahmedabad, Gujarat, India
4 Department of Surgical Oncology, Gujarat Cancer & Research Institute, Ahmedabad, Gujarat, India
5 Department of Onco-Pathology, Gujarat Cancer & Research Institute, Ahmedabad, Gujarat, India
6 Clinical Carcinogenesis Lab, Department of Cancer Biology, The Gujarat Cancer & Research Institute, Ahmedabad, Gujarat, India
|Date of Submission||12-Sep-2019|
|Date of Decision||14-Oct-2019|
|Date of Acceptance||19-Dec-2019|
|Date of Web Publication||18-Aug-2021|
Trupti I Trivedi
Clinical Carcinogenesis Lab, Department of Cancer Biology, The Gujarat Cancer & Research Institute, Ahmedabad - 380 016, Gujarat
Source of Support: None, Conflict of Interest: None
Purpose: Nonhomologous end-joining (NHEJ) is critical for the repair of either pathologic double-strand breaks (DSBs) and/or for the repair of physiologic DSBs created during radiotherapy to kill the tumor cell. Therefore, patients with higher expression of NHEJ repair proteins might develop resistance to ionizing radiation, allowing the disease to recur. As cancer of the oral cavity is a serious health problem globally, the present study aimed to examine the expression of Ku70/80, X-ray repair cross-complementing protein 4 (XRCC4) and DNA ligase IV-core molecules of the NHEJ pathway in patients with oral cancer.
Materials and Methods: Protein expression of Ku70/80, XRCC4, and DNA ligase IV were studied by Immunohistochemistry and mRNA expression of Ku70 and Ku80 were studied using reverse transcription polymerase chain reaction. Data were analyzed statistically using SPSS.
Results: A univariate survival analysis revealed an association of Ku70 mRNA with shorter overall survival (OS). While protein expression of XRCC4 showed an association with reduced relapse-free survival and shorter OS. Multivariate survival analysis demonstrated that XRCC4 and DNA ligase IV are independent prognosticators for predicting adverse disease outcomes.
Conclusion: Strong expression of repair proteins – XRCC4 and DNA ligase IV is associated with unfavorable disease outcome in patients with oral squamous cell carcinoma.
Keywords: DNA ligase IV, Ku70/80, multivariate survival, oral squamous cell carcinoma, X-ray repair cross-complementing protein 4
|How to cite this article:|
Joshi JS, Vora HH, Ghosh NR, Tankshali RN, Jetly DH, Trivedi TI. Nonhomologous end joining repair pathway molecules as predictive biomarkers for patients with oral squamous cell carcinoma. J Can Res Ther 2021;17:1031-8
|How to cite this URL:|
Joshi JS, Vora HH, Ghosh NR, Tankshali RN, Jetly DH, Trivedi TI. Nonhomologous end joining repair pathway molecules as predictive biomarkers for patients with oral squamous cell carcinoma. J Can Res Ther [serial online] 2021 [cited 2021 Dec 4];17:1031-8. Available from: https://www.cancerjournal.net/text.asp?2021/17/4/1031/324036
| > Introduction|| |
Oral squamous cell carcinoma (OSCC) has a miserable prognosis with an estimated incidence of half a million cases diagnosed per year worldwide. Among them, half of the patients suffer from tumor-related complications because of the heterogeneity and complex behavioral pattern of this malignancy. The 5-year survival rate remains poor at about 15%–50% in spite of the recent advances in diagnostic and therapeutic modalities for the past 30 years.,,, Therefore, earlier detection of oral cancer is becoming ever more important to develop the methods for monitoring disease progression, to increase individual therapeutic efficacy and to offer the best chance of long-term survival. Although in India, an increased incidence of OSCC is owing to the increased prevalence of daily life habits such as chewing betel quid, tobacco, and areca nut, the effect of alcohol cannot be neglected. This tobacco and alcohol consumption may lead to frequent DNA lesions and may damage the genetic codes. Several mutagens found in the tobacco reduces the antioxidant level and induces the oxidative stress, leading to the development of double-strand breaks (DSBs). If such genetic damages are left unrepaired, it may initiate dysregulation in cell cycle and autonomous growth leading to malignant transformation of a particular cell. The repair of such DSBs is critical for maintaining genome stability. Notably, defects in the repair of DSBs cause the accumulation of genomic rearrangements that promote tumorigenesis. For the repair of such DSBs, two distinct pathways are found to be in action that is: homologous recombination (HR) and nonhomologous end-joining (NHEJ) among which NHEJ pathway could be a chief DSB repair pathway in human somatic cells. The repair of DSBs by NHEJ occurs in organisms ranging from bacteria to mammals, indicating that this type of repair has been conserved during evolution. This appears to reflect the major contribution of NHEJ to cell survival following exposure to agents that cause DSBs. In NHEJ pathway, Ku heterodimer which is composed of 69 and 83-kD polypeptides binds to the broken ends of DNA within seconds of their formation and then recruits the other downstream repair factors of the pathway, followed by the last step of rejoining through the recruitment of X-ray repair cross-complementing protein 4 (XRCC4) and DNA ligase IV to the DSBs.,, XRCC4 interacts strongly with DNA ligase IV through a tandem BRCA1 carboxyl-terminal domain in a coiled-coil region, resulting in a formation of a highly stable complex., If, any mutation takes place in this complex will result in an imbalance of DSB repair activity., The final step of ligation in the NHEJ pathway of broken DNA ends is carried out by the (ATP) adenosine triphosphate dependent DNA ligase IV which is a ubiquitous phase.,,, The DNA ligase IV is found important in the maintenance of genomic stability. Further, it is expected that cells defective in DSB repair will have more sensitivity towards chemotherapeutic agents. So, the study of DNA ligase has remained an attractive therapeutic target in cancers.,, Based on this information, the current study aimed to evaluate the protein expression of core molecules of the NHEJ pathway that are Ku70/80, XRCC4, and DNA ligase IV and its effect on the disease outcome in patients with OSCC.
| > Materials and Methods|| |
Patient selection and follow-up details
Formalin-fixed and paraffin-embedded (FFPE) tissue specimens from 100 patients with primary OSCC who underwent surgery were obtained from the histopathology department of the institute [Figure 1]. Informed consent was obtained from all individual participants included in the study. The detailed clinical data was obtained from the patients' case files maintained at the medical record department of the institute [Table 1]. For overall survival (OS) and relapse-free survival (RFS) analysis, patients were followed for a minimum period of 24 months or until death. Patients enrolled in survival analysis are depicted in [Figure 2]. This study has been approved by the institutional review committee for the dissertation/thesis/publication/conference presentation and the institutional ethics committee.
|Figure 1: (Original) Schematic diagram of patients enrolled in the study|
Click here to view
|Table 1: Clinicopathological characteristics of the oral squamous cell carcinoma patients|
Click here to view
|Figure 2: (Original) Schematic diagram of patients enrolled in the study for survival analysis (a) patients enrolled in protein expression analysis and (b) patients enrolled in mRNA expression analysis|
Click here to view
RNA extraction and reverse transcription polymerase chain reaction
Out of a total of 100 patients enrolled in the present study, total RNA was extracted from a total of 66 snap-frozen OSCC tumor tissues using RNA iso-plus (Takara) solution. After measuring the yield of total extracted RNA, 1 μg of total RNA was reverse transcribed using iScript cDNA synthesis kit (Bio-Rad, California, US). The primer sequences for Ku70 were F: 5'-GATGCCTCCAAGGCTATGTTTGA-3', R: 5'-TTCTCGGTACCATAGAACACCACAG-3'. Ku80 were F: 5'-ACGATTTGGTACAGATGGCACT-3', R: 5'-GCTCCTTGAAGACGCACAGTTT-3' and for glyceraldehyde-3-phosphate dehydrogenase (GAPDH) were F: 5'-CGGAGTCAACGGATTTGGTCGTAT-3', R: 5'-AGCCTTCTCCATGGTGGTGAAGAC-3'. Following first-strand cDNA synthesis, an aliquot of cDNA was subjected to 40 cycles of PCR to determine the integrity of the GAPDH mRNA using a Q5 High-fidelity DNA polymerase kit (NEB, “Ipswich”, Massachusetts, USA). The amplified DNA fragment was 149 bp, 548 bp, and 309 bp for Ku70, Ku80, and GAPDH, respectively. Samples of the amplified products were then subjected to 2% agarose gel electrophoresis, stained with EtBr and visualized under gel documentation system (Alpha imager-EP, Santa Carla, CA, USA).
Immunohistochemistry and scoring
Immunohistochemistry (IHC) was carried out on FFPE OSCC tumor tissue sections with 4 μm-thicknesses to analyze the protein expression of Ku70/80, XRCC4 and DNA ligase IV. Sections were deparaffinized and rehydrated followed by blocking of endogenous peroxidase activity using 3% H2O2. Tissue antigenicity was retrieved using 10 mM tri-sodium citrate buffer. Nonspecific conjugations were blocked using a protein block provided in rabbit-specific HRP/DAB (ABC) detection IHC kit (Abcam, Cambridge, UK). Primary antibodies (Ku70/80, Genetex, 1:200; XRCC4, Santa Cruz, 1:200; DNA ligase IV, Genetex, 1:200) diluted in tris buffered saline were then applied to the sections and incubated overnight at 4°C. Antibody binding was visualized using the 3,3-diamino-benzidine as chromogen and counterstained with Mayer's hematoxylin, dehydrated in ethanol, mounted in dibutyl phthalate xylene, coverslipped, and observed under the light microscope.
The scoring method applied was a modified H-score method. Data were divided into weak and strong expression groups by the median H-score values. Nuclear immune reactions were obtained for Ku70/80 and XRCC4, while for DNA ligase IV nuclear as well as cytoplasmic immune reactions were obtained.
Statistical analysis was performed using Statistical Package for Social Sciences version-20 (IBM, Armonk, New York, US). A two-tailed Chi-square test was used to examine the association between protein expression and clinicopathological parameters. Spearman's correlation coefficient (r) was used to calculate the correlation between the two parameters. The univariate survival was calculated using Kaplan–Meier survival function and tested for statistical significance using the log-rank statistics. For multivariate survival analysis, Cox forward stepwise regression model was used. Variables with or without prognostic potential in univariate survival analysis were included for multivariate survival analysis. P < 0.05 was taken into consideration to show statistical significance.
| > Results|| |
mRNA expression of Ku70, Ku80, and association with clinicopathological parameters
Expression of Ku70 and Ku80 mRNA was examined in a total of 66 snap-frozen OSCC tumor tissues. The expression of Ku70 and 80 mRNA was detected in all the patients [Figure 3]. Expression of Ku70 and Ku80 mRNA, however, was not significantly correlated with any of the clinicopathological parameters such as age, gender, anatomic site, tobacco habit, tumor size, tumor stage, lymph node status, tumor differentiation and presence of lymphatic permeation and vascular permeation.
|Figure 3: (Original) mRNA expression of Ku70, Ku80, and glyceraldehyde-3-phosphate dehydrogenase from the oral squamous cell carcinoma tumor samples from lanes 1-5 from left to right|
Click here to view
Protein expression of Ku70/80, X-ray repair cross-complementing protein 4, DNA ligase IV and association with clinicopathological parameters
IHC was performed to determine the protein expression of Ku70/80, XRCC4 and DNA ligase IV in a total of 100 patients with OSCC. For Ku70/80 and XRCC4, nuclear immunostaining was observed while for the DNA ligase IV, both nuclear as well as cytoplasmic immunostaining was observed [Figure 4]. For statistical evaluation, nuclear and cytoplasmic expressions were scored independently and compared separately. The positivity of Ku70/80, XRCC4 and DNA ligase IV was 99% (99/100), 100% (100/100), and 96% (96/100), respectively. Overall, expression of Ku70/80 and XRCC4 protein was higher as compared to DNA ligase IV protein expression in patients with OSCC [Figure 5]. Two-tailed Chi-square test revealed that Ku70/80 was significantly associated with patients without lymphatic permeation (P = 0.049), XRCC4 was significantly associated with tumor stage (P = 0.032) and locoregional aggressive disease (P = 0.010) while, nuclear DNA ligase IV was significantly associated with tobacco habituates (P = 0.010) [Table 2] and [Figure 6]. Intercorrelation of studied proteins has shown in [Table 3], indicating that XRCC4 protein expression was significantly positively correlated with Ku70/80 (P = 0.005) and DNA ligase IV (P = 0.005).
|Figure 4: (Original) Representative immunohistochemistry image (original ×40) of (a) nuclear expression of Ku70/80, (b) nuclear expression of X-ray repair cross-complementing protein 4, and (c) nuclear and cytoplasmic expression of DNA ligase IV protein in oral squamous cell carcinoma tumor sections|
Click here to view
|Figure 5: (Original) Protein expression analysis of Ku70/80, X-ray repair cross-complementing protein 4, nuclear DNA ligase IV and cytoplasmic DNA ligase IV|
Click here to view
|Figure 6: (Original) (a) strong expression of Ku70/80 in lymph-node negative patients, (b) strong expression of X-ray repair cross-complementing protein 4 in stage III/IV patients, (c) strong expression of X-ray repair cross-complementing protein 4 in positive lymph node patients, and (d) strong expression of nuclear DNA ligase in tobacco habituate patients|
Click here to view
|Table 2: Correlation of Ku70/80, XRCC4 and DNA ligase IV protein expression with clinicopathological parameters in oral squamous cell carcinoma patients|
Click here to view
|Table 3: Intercorrelation of Ku70/80, XRCC4 and DNA ligase IV protein expression in oral squamous cell carcinoma patients|
Click here to view
Using Kaplan–Meier univariate survival function, strong expression of Ku70 mRNA was found to be associated significantly with reduced OS (log-rank = 5.19, P = 0.023) while strong expression of XRCC4 protein was found as a significant prognosticator in developing disease relapse (log-rank = 5.744, P = 0.017) and reduced OS (log-rank = 4.291, P = 0.038) in patients with OSCC [Figure 7]. However, multivariate survival analysis of predictors using a multivariate Cox regression forward stepwise model revealed strong expression of XRCC4 as a significant independent prognosticator in predicting reduced OS (HR = 1.911, P = 0.047) [Table 4]. However, when multivariate survival analysis carried out including studied NHEJ markers along with clinicopathological parameters, weak expression of cytoplasmic expression of DNA ligase IV showed a trend towards significance as a prognosticator in predicting shorter OS (HR = 3.730, P = 0.053) in patients with OSCC [Table 4].
|Figure 7: (Original) Survival analysis in oral squamous cell carcinoma patients (a) strong Ku70 mRNA expression associated with reduced overall survival, (b) strong X-ray repair cross-complementing protein 4 protein expression associated with reduced relapse-free survival, and (c) strong X-ray repair cross-complementing protein 4 protein expression associated with reduced overall survival|
Click here to view
|Table 4: Multivariate overall survival analysis using Cox regression forward stepwise model in patients with OSCC|
Click here to view
| > Discussion|| |
Although remarkable improvement has been made over the last decades in the understanding of the pathogenesis of OSCC, patients still die within a shorter period of time even after 1st-line treatment. Critical analysis of factors involved in survival and prognosis potentially leads to a better understanding of the pathogenesis of OSCC. Therefore, identification of patient and/or tumor-specific marker associated with increased or decreased survival time is an important stratagem. Although multiple studies have been conducted concerning the prognostic importance of different variables, the picture remains incomplete and unclear.
The current study demonstrated the significance of proteins having an important role in the repair of the DNA DSB and its impact on disease outcome in patients with OSCC. When studied NHEJ molecules were correlated with clinicopathological parameters, a strong expression of Ku70/80 protein was significantly associated with the absence of lymphatic permeation. In gastric carcinoma, the higher expression of Ku70/80 protein was correlated negatively with the clinical stage. However, Alshareeda et al. in 2013 also found that Ku70/80 protein expression was associated with higher tumor grade (Grade III) and lymphovascular invasion in breast cancer indicative of its association with malignant behavior of breast cancer cells. Such discrepancy in the results could be due to the different malignancy and phenotype. Further, the strong expression of XRCC4 protein was significantly associated with advanced-stage disease and lymph node involvement indicating its association with tumor aggressiveness. About DNA ligase IV protein, a significantly high incidence of strong nuclear DNA ligase IV protein expression was observed in tobacco habituates. While, a trend was observed in males patients with cancer of the buccal mucosa, demonstrating that the expression of DSB repair molecules has been elevated as a result of the increased oxidative stress due to frequent tobacco exposure to the buccal mucosa.
Univariate survival analysis revealed that the strong expression of Ku70 mRNA was significantly associated with a shorter OS. In accordance, in colorectal cancer, higher Ku70 mRNA expression was associated with poorer prognosis in rectal and advanced colorectal cancer., However, Pavón et al. in 2008 found that in patients with locally advanced head and neck squamous cell carcinoma (HNSCC), tumors with higher Ku70 mRNA expression had a significantly increased RFS and OS. Discrepancy in the findings could be the outcome of the altered gene expression of Ku70 as a result of the several posttranscriptional modifications. However, in HNSCC, tumors expressing lower Ku80 mRNA had a reduced OS. Further, a strong expression of XRCC4 protein was significantly associated with a high incidence of disease relapse and death in OSCC patients. In hypopharyngeal cancer patients with stage I to III disease, lower expression of the XRCC4 was tended to have better locoregional control. The polymorphism in the XRCC4 gene is found to be susceptible to the development of various human cancers like urothelial bladder cancer, breast cancer, and pancreatic cancer.,, Further, Datkhile et al. in 2016 found that the polymorphism in T allele of XRCC4 (G1394T) is responsible for higher genetic susceptibility to oral cancer and oral carcinogenesis which might be used as a novel useful marker for primary prevention and intervention.
In the present study, cells expressing higher Ku70 mRNA expression found to have reduced OS. In agreement with this, in uterine cervical cancer biopsy sample and in rectal cancer, cells expressing low levels of Ku70 and Ku70/80 protein respectively, were radiosensitive and exhibited a significantly better RT outcome with improved survival., Further, silencing Ku70 by siRNA resulted in the downregulation of Ku70 which induces sensitization to etoposide, cisplatin or topotecan in the human cervical carcinoma HeLa cell line. The lower expression of Ku70 or Ku80 in preradiation biopsy samples of the tumor was correlated with better objective responses, suggesting an association of low expression of Ku protein with high radiosensitivity in hypopharyngeal carcinoma. In multivariate survival analysis including all established clinicopathological variables and studied DDR markers, cytoplasmic DNA ligase IV entered at step 3 in predicting shorter OS. While in multivariate survival analysis including studied NHEJ molecules revealed XRCC4 as an independent prognosticator in predicting shorter OS in patients with OSCC. In agreement with the present study, in human cells expressing defective DNA ligase IV, other DSBs repairing factors such as XRCC4 and XRCC4 like factor (XLF) failed to bind broken DNA molecules, indicating that participation of ligase IV is required for the substrate recognition by XRCC4 and XLF in vivo. Further, in patients with nasopharyngeal cancer, Kim et al. reported a decrease in 5 years RFS and OS rate of patients with negative DNA ligase IV expression.
Further, XRCC4 functions as a regulatory element and is required for precise end-joining of blunt DNA DSBs to stabilize DNA ligase IV, stimulate DNA ligase IV activity and directs DNA ligase IV to the site of the DNA breaks via its DNA binding capacity. Therefore, the association of strong XRCC4 and weak DNA ligase IV with reduced OS could be due to the polymorphism of XRCC4 or mutation in DNA ligase IV leading to the defective function in the repair of DNA DSBs. Although, broad analysis of certain experimental and clinical-epidemiologic results have suggested a role of receptor signaling such as estrogen receptor as a chief safeguard of genome stability and to have a strong interaction with DNA controlling and repairing pathways. Hence, in the current study, further receptor expression analysis is warranted.
| > Conclusion|| |
Collectively, in the present study, strong expression of Ku70 mRNA, XRCC4, and weak expression of cytoplasmic DNA ligase IV were significantly associated with reduced OS in OSCC patients indicating increased repair activity of DNA DSBs of the tumor cells by NHEJ pathway may lead to the progression of the disease. Further, the current study identified weak cytoplasmic DNA ligase IV as significant prognostic factors in predicting reduced RFS. While weak cytoplasmic DNA ligase IV and XRCC4 as a potential prognosticator in predicting reduced OS in patients with OSCC which might have great clinical implication in future for designing a treatment strategy.
Financial support and sponsorship
This study was financially supported by the Gujarat Cancer Society/The Gujarat Cancer and Research Institute.
Conflicts of interest
There are no conflicts of interest.
| > References|| |
Parkin DM, Bray F, Ferlay J, Pisani P. Estimating the world cancer burden: Globocan 2000. Int J Cancer 2001;94:153-6.
Haddad RI, Shin DM. Recent advances in head and neck cancer. N Engl J Med 2008;359:1143-54.
Carvalho AL, Nishimoto IN, Califano JA, Kowalski LP. Trends in incidence and prognosis for head and neck cancer in the United States: A site-specific analysis of the SEER database. Int J Cancer 2005;114:806-16.
Prince ME, Ailles LE. Cancer stem cells in head and neck squamous cell cancer. J Clin Oncol 2008;26:2871-5.
Warnakulasuriya S. Global epidemiology of oral and oropharyngeal cancer. Oral Oncol 2009;45:309-16.
McCullough MJ, Prasad G, Farah CS. Oral mucosal malignancy and potentially malignant lesions: An update on the epidemiology, risk factors, diagnosis and management. Aust Dent J 2010;55 Suppl 1:61-5.
Facompre N, Nakagawa H, Herlyn M, Basu D. Stem-like cells and therapy resistance in squamous cell carcinomas. Adv Pharmacol 2012;65:235-65.
Hoeijmakers JH. Genome maintenance mechanisms for preventing cancer. Nature 2001;411:366-74.
Pouget JP, Mather SJ. General aspects of the cellular response to low- and high-LET radiation. Eur J Nucl Med 2001;28:541-61.
Pastwa E, Błasiak J. Non-homologous DNA end joining. Acta Biochim Pol 2003;50:891-908.
Korabiowska M, König F, Schlott T, Slotty P, Romeike B, Cordon-Cardo C, et al
. Quantitative analysis of Ku70 and Ku80 mRNA gene expression in melanoma brain metastases. correlation with immunohistochemistry and in situ
hybridization. Cancer Genomics Proteomics 2004;1:225-30.
Mari PO, Florea BI, Persengiev SP, Verkaik NS, Brüggenwirth HT, Modesti M, et al
. Dynamic assembly of end-joining complexes requires interaction between Ku70/80 and XRCC4. Proc Natl Acad Sci U S A 2006;103:18597-602.
Lieber MR. The mechanism of human nonhomologous DNA end joining. J Biol Chem 2008;283:1-5.
Critchlow SE, Bowater RP, Jackson SP. Mammalian DNA double-strand break repair protein XRCC4 interacts with DNA ligase IV. Curr Biol 1997;7:588-98.
Grawunder U, Zimmer D, Fugmann S, Schwarz K, Lieber MR. DNA ligase IV is essential for V(D)J recombination and DNA double-strand break repair in human precursor lymphocytes. Mol Cell 1998;2:477-84.
Hammel M, Rey M, Yu Y, Mani RS, Classen S, Liu M, et al
. XRCC4 protein interactions with XRCC4-like factor (XLF) create an extended grooved scaffold for DNA ligation and double strand break repair. J Biol Chem 2011;286:32638-50.
Williams GJ, Hammel M, Radhakrishnan SK, Ramsden D, Lees-Miller SP, Tainer JA. Structural insights into NHEJ: Building up an integrated picture of the dynamic DSB repair super complex, one component and interaction at a time. DNA Repair (Amst) 2014;17:110-20.
Bassing CH, Alt FW. The cellular response to general and programmed DNA double strand breaks. DNA Repair (Amst) 2004;3:781-96.
Pollard JM, Gatti RA. Clinical radiation sensitivity with DNA repair disorders: An overview. Int J Radiat Oncol Biol Phys 2009;74:1323-31.
Chistiakov DA, Voronova NV, Chistiakov PA. Genetic variations in DNA repair genes, radiosensitivity to cancer and susceptibility to acute tissue reactions in radiotherapy-treated cancer patients. Acta Oncol 2008;47:809-24.
O'Driscoll M, Jeggo PA. The role of double-strand break repair – Insights from human genetics. Nat Rev Genet 2006;7:45-54.
Chen X, Zhong S, Zhu X, Dziegielewska B, Ellenberger T, Wilson GM, et al
. Rational design of human DNA ligase inhibitors that target cellular DNA replication and repair. Cancer Res 2008;68:3169-77.
Ellenberger T, Tomkinson AE. Eukaryotic DNA ligases: Structural and functional insights. Annu Rev Biochem 2008;77:313-38.
Kondo N, Takahashi A, Mori E, Ohnishi K, McKinnon PJ, Sakaki T, et al
. DNA ligase IV as a new molecular target for temozolomide. Biochem Biophys Res Commun 2009;387:656-60.
Someya M, Sakata K, Matsumoto Y, Satoh M, Narimatsu H, Hareyama M. Immunohistochemical analysis of Ku70/86 expression of breast cancer tissues. Oncol Rep 2007;18:1483-7.
Li W, Xie C, Yang Z, Chen J, Lu NH. Abnormal DNA-PKcs and Ku 70/80 expression may promote malignant pathological processes in gastric carcinoma. World J Gastroenterol 2013;19:6894-901.
Alshareeda AT, Negm OH, Albarakati N, Green AR, Nolan C, Sultana R, et al
. Clinicopathological significance of KU70/KU80, a key DNA damage repair protein in breast cancer. Breast Cancer Res Treat 2013;139:301-10.
Dave JH, Vora HH, Trivedi TI, Ghosh NR. Nibrin expression in oral squamous cell carcinoma: Association with clinicopathological parameters. J Cancer Metastasis Treat 2016;2:436-42.
Komuro Y, Watanabe T, Hosoi Y, Matsumoto Y, Nakagawa K, Tsuno N, et al
. The expression pattern of Ku correlates with tumor radiosensitivity and disease free survival in patients with rectal carcinoma. Cancer 2002;95:1199-205.
Komuro Y, Watanabe T, Hosoi Y, Matsumoto Y, Nakagawa K, Suzuki N, et al
. Prognostic significance of Ku70 protein expression in patients with advanced colorectal cancer. Hepatogastroenterology 2005;52:995-8.
Pavón MA, Parreño M, León X, Sancho FJ, Céspedes MV, Casanova I, et al
. Ku70 predicts response and primary tumor recurrence after therapy in locally advanced head and neck cancer. Int J Cancer 2008;123:1068-79.
Li GC, He F, Shao X, Urano M, Shen L, Kim D, et al
. Adenovirus-mediated heat-activated antisense Ku70 expression radiosensitizes tumor cells in vitro
and in vivo
. Cancer Res 2003;63:3268-74.
Hayashi J, Sakata KI, Someya M, Matsumoto Y, Satoh M, Nakata K, et al
. Analysis and results of Ku and XRCC4 expression in hypopharyngeal cancer tissues treated with chemoradiotherapy. Oncol Lett 2012;4:151-5.
Mittal RD, Gangwar R, Mandal RK, Srivastava P, Ahirwar DK. Gene variants of XRCC4 and XRCC3 and their association with risk for urothelial bladder cancer. Mol Biol Rep 2012;39:1667-75.
Zhou LP, Luan H, Dong XH, Jin GJ, Ma DL, Shang H. Association of functional polymorphisms of the XRCC4 gene with the risk of breast cancer: A meta-analysis. Asian Pac J Cancer Prev 2012;13:3431-6.
Ding Y, Li LN. Association between single nucleotide polymorphisms of X-ray repair cross-complementing protein 4 gene and development of pancreatic cancer. Genet Mol Res 2015;14:9626-32.
Datkhile KD, Patil MN, Khamkar TS, Vhaval RD, Durgawale PP, Chougule PG, et al. Genetic polymorphisms in DNA repair genes (hOGG1 and APE1) and their association with oral cancer susceptibility in rural Indian population: A hospital based casecontrol study. Int J Med Sci Public Health 2016;6:23-8.
Wilson CR, Davidson SE, Margison GP, Jackson SP, Hendry JH, West CM. Expression of Ku70 correlates with survival in carcinoma of the cervix. Br J Cancer 2000;83:1702-6.
Tian X, Chen G, Xing H, Weng D, Guo Y, Ma D. The relationship between the down-regulation of DNA-PKcs or Ku70 and the chemosensitization in human cervical carcinoma cell line HeLa. Oncol Rep 2007;18:927-32.
Jayaram S, Ketner G, Adachi N, Hanakahi LA. Loss of DNA ligase IV prevents recognition of DNA by double-strand break repair proteins XRCC4 and XLF. Nucleic Acids Res 2008;36:5773-86.
Kim DH, Oh SY, Kim SY, Lee S, Koh MS, Lee JH, et al
. DNA ligase4 as a prognostic marker in nasopharyngeal cancer patients treated with radiotherapy. Asian Pac J Cancer Prev 2014;15:10985-9.
Suba Z. DNA stabilization by the upregulation of estrogen signaling in BRCA gene mutation carriers. Drug Des Devel Ther 2015;9:2663-75.
[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7]
[Table 1], [Table 2], [Table 3], [Table 4]