Gene Summary

Gene:PRKDC; protein kinase, DNA-activated, catalytic polypeptide
Aliases: HYRC, p350, DNAPK, DNPK1, HYRC1, IMD26, XRCC7, DNA-PKcs
Summary:This gene encodes the catalytic subunit of the DNA-dependent protein kinase (DNA-PK). It functions with the Ku70/Ku80 heterodimer protein in DNA double strand break repair and recombination. The protein encoded is a member of the PI3/PI4-kinase family.[provided by RefSeq, Jul 2010]
Databases:VEGA, OMIM, HGNC, Ensembl, GeneCard, Gene
Protein:DNA-dependent protein kinase catalytic subunit
Source:NCBIAccessed: 15 March, 2017


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 15 March 2017 using data from PubMed using criteria.

Literature Analysis

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Tag cloud generated 15 March, 2017 using data from PubMed, MeSH and CancerIndex

Specific Cancers (6)

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: PRKDC (cancer-related)

Sanie-Jahromi F, Saadat I, Saadat M
Effects of extremely low frequency electromagnetic field and cisplatin on mRNA levels of some DNA repair genes.
Life Sci. 2016; 166:41-45 [PubMed] Related Publications
AIMS: It has been shown that exposure to extremely-low frequency (˂300Hz) oscillating electromagnetic field (EMF) can affect gene expression. The effects of different exposure patterns of 50-Hz EMF and co-treatment of EMF plus cisplatin (CDDP) on mRNA levels of seven genes involved in DNA repair pathways (GADD45A, XRCC1, XRCC4, Ku70, Ku80, DNA-PKcs and LIG4) were evaluated.
MAIN METHODS: Two 50-Hz EMF intensities (0.25 and 0.50mT), three exposure patterns (5min field-on/5min field-off, 15min field-on/15min field-off, 30min field-on continuously) and two cell lines (MCF-7 and SH-SY5Y) were used. The mRNA levels were measured using quantitative real-time PCR.
KEY FINDINGS: The examined genes had tendency to be down-regulated in MCF-7 cells treated with EMF. In the pattern of 15min field-on/15min field-off of the 0.50mT EMF, no increase in mRNA levels were observed, but the mRNA levels of GADD45A, XRCC1, XRCC4, Ku80, Ku70, and LIG4 were down-regulated. A significant elevation in IC50 of CDDP was observed when MCF-7 and SH-SY5Y cells were co-treated with CDDP+EMF in comparison with the cells treated with CDDP alone. GADD45A mRNA levels in MCF-7 and SH-SY5Y cells co-treated with CDDP+EMF were increased and at the same time the mRNA levels of XRCC4, Ku80, Ku70 and DNA-PKcs were down-regulated.
SIGNIFICANCE: Present study provides evidence that co-treatment of CDDP+EMF can enhance down-regulation of the genes involved in non-homologous end-joining pathway. It might be suggested that co-treatment of CDDP+EMF could be more promising for sensitizing cancer cells to DNA double strand breaks.

Shin K, Kim KH, Yoon MS, et al.
Expression of Interactive Genes Associated with Apoptosis and Their Prognostic Value for Ovarian Serous Adenocarcinoma.
Adv Clin Exp Med. 2016 May-Jun; 25(3):513-21 [PubMed] Related Publications
BACKGROUND: Malignant ovarian tumor is one of the leading causes of worldwide cancer death. It is usually characterized by insidious onset and late diagnosis because of the absence of symptoms, allowing ovarian cancer cases to progress rapidly and become unresectable. The tumor suppressor, p53, plays an important role in regulating cell cycles and apoptosis. p53 is regulated by several molecules, and it interacts with other apoptotic proteins.
OBJECTIVES: To compare the prognosis of ovarian serous carcinoma and evaluate the expression of DNA-PKcs, Akt3, GSK-3β, and p53 in cancerous cells.
MATERIAL AND METHODS: DNA-PKcs, Akt3, GSK-3β, and p53 expression levels were scored using immunohistochemistry staining of tissue samples from 132 women with ovarian serous adenocarcinoma. Expression was confirmed by real-time RT-PCR. Analyses were stratified by age, tumor grades, cancer stages and serum CA 125 levels.
RESULTS: Significant differences in DNA-PKcs, Akt3, and p53 expression were observed between participants with different stages and tumor grades of ovarian serous adenocarcinoma. DNA-PKcs and p53 expression increased along with increasing tumor grade. Meanwhile, DNA-PKcs, Akt3, and p53 expression increased along with increasing cancer stage, and with a decrease in 5-year overall survival rate.
CONCLUSIONS: This study shows that elevated expression of DNA-PKcs, Akt3, and p53 in ovarian serous adenocarcinoma tissues are an indication of more advanced disease and worse prognosis.

Li K, Li X, Tian J, et al.
Downregulation of DNA-PKcs suppresses P-gp expression via inhibition of the Akt/NF-κB pathway in CD133-positive osteosarcoma MG-63 cells.
Oncol Rep. 2016; 36(4):1973-80 [PubMed] Related Publications
The development of chemoresistance is closely linked to the plateau of the survival rate in osteosarcoma (OS) patients. CD133-positive (CD133+) OS cells are known as cancer stem cells (CSCs) in OS and exhibit the characteristic of chemoresistance. In this study, CD133+ and CD133‑negative (CD133‑) MG‑63 cells were isolated by magnetic activated cell sorting (MACS). We verified that CD133+ MG‑63 cells were more resistant to cisplatin (CDDP) than CD133‑ MG‑63 cells. DNA‑dependent protein kinase catalytic subunit (DNA‑PKcs) and P‑glycoprotein (P‑gp) were expressed at higher levels in the CD133+ MG‑63 cells compared with those levels in the CD133‑ MG‑63 cells, whereas downregulation of DNA‑PKcs by small interfering RNA (siRNA) decreased chemoresistance to CDDP and P‑gp expression at the mRNA and protein levels in these cells. This indicated that DNA‑PKcs was correlated with P‑gp expression in the CD133+ MG‑63 cells. The Akt/NF‑κB pathway was hyperactivated in the CD133+ MG‑63 cells, whereas inhibition of the Akt/NF‑κB pathway downregulated P‑gp expression. In addition, downregulation of DNA‑PKcs suppressed the activity of the Akt/NF‑κB pathway. These results revealed that downregulation of DNA‑PKcs could decrease P‑gp expression via suppression of the Akt/NF‑κB pathway in CD133+ MG‑63 cells. Therefore, inhibition of DNA‑PKcs decreases P‑gp expression and sensitizes OS CSCs to chemotherapeutic agents in vitro, which needs to be further validated in vivo.

Sunada S, Kanai H, Lee Y, et al.
Nontoxic concentration of DNA-PK inhibitor NU7441 radio-sensitizes lung tumor cells with little effect on double strand break repair.
Cancer Sci. 2016; 107(9):1250-5 [PubMed] Free Access to Full Article Related Publications
High-linear energy transfer (LET) heavy ions have been increasingly employed as a useful alternative to conventional photon radiotherapy. As recent studies suggested that high LET radiation mainly affects the nonhomologous end-joining (NHEJ) pathway of DNA double strand break (DSB) repair, we further investigated this concept by evaluating the combined effect of an NHEJ inhibitor (NU7441) at a non-toxic concentration and carbon ions. NU7441-treated non-small cell lung cancer (NSCLC) A549 and H1299 cells were irradiated with X-rays and carbon ions (290 MeV/n, 50 keV/μm). Cell survival was measured by clonogenic assay. DNA DSB repair, cell cycle distribution, DNA fragmentation and cellular senescence induction were studied using a flow cytometer. Senescence-associated protein p21 was detected by western blotting. In the present study, 0.3 μM of NU7441, nontoxic to both normal and tumor cells, caused a significant radio-sensitization in tumor cells exposed to X-rays and carbon ions. This concentration did not seem to cause inhibition of DNA DSB repair but induced a significant G2/M arrest, which was particularly emphasized in p53-null H1299 cells treated with NU7441 and carbon ions. In addition, the combined treatment induced more DNA fragmentation and a higher degree of senescence in H1299 cells than in A549 cells, indicating that DNA-PK inhibitor contributes to various modes of cell death in a p53-dependent manner. In summary, NSCLC cells irradiated with carbon ions were radio-sensitized by a low concentration of DNA-PK inhibitor NU7441 through a strong G2/M cell cycle arrest. Our findings may contribute to further effective radiotherapy using heavy ions.

Zeng Q, Wang Z, Liu C, et al.
Knockdown of NFBD1/MDC1 enhances chemosensitivity to cisplatin or 5-fluorouracil in nasopharyngeal carcinoma CNE1 cells.
Mol Cell Biochem. 2016; 418(1-2):137-46 [PubMed] Related Publications
Nasopharyngeal carcinoma (NPC) is a rare but highly invasive cancer that is prevalent among people of southern Chinese ancestry in southern China and Southeast Asia. Radiotherapy and cisplatin (CDDP)-based chemotherapy are the main treatment options. Unfortunately, disease response to concurrent chemoradiotherapy varies among patients with NPC, and many cases are resistant to CDDP and radiotherapy. NFBD1 functions in cell cycle checkpoint activation and DNA repair following DNA damage. In this study, we identified the NFBD1 as a tractable molecular target to chemosensitize NPC cells. NFBD1 expression in NPC CNE1 cell lines was depleted using lentivirus-mediated short hairpin RNA, and the elevated sensitivity of these NFBD1-inhibited NPC cells to therapeutic reagent CDDP and 5-fluorouracil (5-FU) was evaluated using MTS assays. Flow cytometry analysis also showed that NFBD1 knockdown led to an obvious induction of apoptosis in CDDP- or 5-FU-treated CNE1 cells. Furthermore, we implicated the involvement of NFBD1 in Rad51 and DNA-PKcs foci formation following CDDP or 5-FU chemotherapy. In conclusion, NFBD1 knockdown improves the chemosensitivity of NPC cells by inhibiting cell growth and promoting apoptosis through the impairment of DNA damage repair, suggesting NFBD1 as a novel therapeutic target for NPC.

Gravina GL, Festuccia C, Popov VM, et al.
c-Myc Sustains Transformed Phenotype and Promotes Radioresistance of Embryonal Rhabdomyosarcoma Cell Lines.
Radiat Res. 2016; 185(4):411-22 [PubMed] Related Publications
We have previously reported that the MEK/ERK pathway sustains in vitro and in vivo transformed phenotype and radioresistance of embryonal rhabdomyosarcoma (ERMS) cell lines. Furthermore, we found that aberrant MEK/ERK signaling activation promotes c-Myc oncoprotein accumulation. In this study, the role of c-Myc in sustaining the ERMS transformed and radioresistant phenotype is characterized. RD and TE671 cell lines conditionally expressing MadMyc chimera protein, c-Myc-dominant negative and shRNA directed to c-Myc were used. Targeting c-Myc counteracted in vitro ERMS adherence and in suspension, growth motility and the expression of pro-angiogenic factors. c-Myc depletion decreased MMP-9, MMP-2, u-PA gelatinolytic activity, neural cell adhesion molecule sialylation status, HIF-1α, VEGF and increased TSP-1 protein expression levels. Rapid but not sustained targeting c-Myc radiosensitized ERMS cells by radiation-induced apoptosis, DNA damage and impairing the expression of DNA repair proteins RAD51 and DNA-PKcs, thereby silencing affected ERMS radioresistance. c-Myc sustains ERMS transformed phenotype and radioresistance by protecting cancer cells from radiation-induced apoptosis and DNA damage, while promoting radiation-induced DNA repair. This data suggest that c-Myc targeting can be tested as a promising treatment in cancer therapy.

Sun S, Cheng S, Zhu Y, et al.
Identification of PRKDC (Protein Kinase, DNA-Activated, Catalytic Polypeptide) as an essential gene for colorectal cancer (CRCs) cells.
Gene. 2016; 584(1):90-6 [PubMed] Related Publications
Oncogene and non-oncogene addictions describe the phenomenon that tumor cells become reliant on certain genes for maintenance of malignancy. Reversal of these mutations profoundly affects tumor growth and survival, providing a fundamental rationale for development of targeted cancer therapy. However, inadequate knowledge on cancer signaling networks and lack of potential drug targets limited its clinical application. A screen was conducted using a custom small interfering RNA (siRNA) library in colorectal cancer (CRC). Transient knockdown followed by cell proliferation assays were performed to validate the essentiality of PRKDC (Protein Kinase, DNA-Activated, Catalytic Polypeptide) in CRC. Western blot analysis was performed to examine the mechanism by which PRKDC confers selective survival advantage in CRC cells. Inducible knockdown and overexpression cell lines were introduced into nude mice to assess PRKDC dependency of CRC cells in vivo. PRKDC expression level in patient samples and overall survival of patients with low or high PRKDC expression were analyzed. Transient knockdown of PRKDC reduced cell proliferation/survival in HCT116 and DLD1, but not FHC cells. PRKDC down-regulation induced apoptosis partially through inhibiting AKT activation, and sensitized HCT116 cells to chemotherapeutic agents interfering with DNA replication. Inducible knockdown of PRKDC inhibited tumor growth in vivo. PRKDC was up-regulated in cancerous tissues compared with normal tissues. Patients with high PRKDC expression showed poorer overall survival. PRKDC is an essential gene required for CRC cell proliferation/survival, which may represent as a potential prognostic biomarker and an ideal therapeutic target for CRC.

Williams MT, Yousafzai YM, Elder A, et al.
The ability to cross the blood-cerebrospinal fluid barrier is a generic property of acute lymphoblastic leukemia blasts.
Blood. 2016; 127(16):1998-2006 [PubMed] Related Publications
Prevention of central nervous system (CNS) relapse is critical for cure of childhood B-cell precursor acute lymphoblastic leukemia (BCP-ALL). Despite this, mechanisms of CNS infiltration are poorly understood, and the timing, frequency, and properties of BCP-ALL blasts entering the CNS compartment are unknown. We investigated the CNS-engrafting potential of BCP-ALL cells xenotransplanted into immunodeficient NOD.Cg- ITALIC! Prkdc (ITALIC! scid) ITALIC! Il2rg (ITALIC! tm1Wjl)/SzJ mice. CNS engraftment was seen in 23 of 29 diagnostic samples (79%): 2 of 2 from patients with overt CNS disease and 21 of 27 from patients thought to be CNS negative by diagnostic lumbar puncture. Histologic findings mimic human pathology and demonstrate that leukemic cells transit the blood-cerebrospinal fluid barrier situated close to the dural sinuses, the site of recently discovered CNS lymphatics. Retrieval of blasts from the CNS showed no evidence for chemokine receptor-mediated selective trafficking. The high frequency of infiltration and lack of selective trafficking led us to postulate that CNS tropism is a generic property of leukemic cells. To test this, we performed serial dilution experiments which showed CNS engraftment in 5 of 6 mice after transplant of as few as 10 leukemic cells. Clonal tracking techniques confirmed the polyclonal nature of CNS-infiltrating cells, with multiple clones engrafting in both the CNS and periphery. Overall, these findings suggest that subclinical seeding of the CNS is likely to be present in most BCP-ALL patients at original diagnosis, and efforts to prevent CNS relapse should concentrate on effective eradication of disease from this site rather than targeting entry mechanisms.

Chang HY, Chang TC, Huang WY, et al.
RON Nuclear Translocation under Hypoxia Potentiates Chemoresistance to DNA Double-Strand Break-Inducing Anticancer Drugs.
Mol Cancer Ther. 2016; 15(2):276-86 [PubMed] Related Publications
Tumor hypoxia is associated with radioresistance, chemoresistance, and metastasis, which eventually lead to cancer progression and a poor patient prognosis. RON [also known as macrophage-stimulating protein receptor (MST1R)] belongs to the c-MET [also known as hepatocyte growth factor receptor (HGFR)] receptor tyrosine kinase (RTK) superfamily. To identify the interaction partners of RON nuclear translocation in response to hypoxia, the nuclear extract of TSGH8301 bladder cancer cells was immunoprecipitated for tandem mass profiling analysis. Nuclear RON interacted with adenosine triphosphate (ATP)-dependent DNA helicase 2 (Ku70) and DNA-dependent protein kinase catalytic subunit (DNA-PKcs) to activate nonhomologous end joining (NHEJ) DNA repair. The interaction was time dependent, extending 3 to 24 hours posthypoxia or until the components had been exposed to the chemotherapeutic drugs doxorubicin and epirubicin. Stable knockdown experiments in vitro suggest the importance of RON for the chemoresistance of cancer cells under hypoxia. In addition, the tyrosine kinase domain of nuclear RON is crucial for interaction with Ku70 under hypoxia. J82 cells transfected with RON showed a survival advantage in the presence of epirubicin and hypoxia. This suggests that nuclear RON activates NHEJ repair by interacting with Ku70/DNA-PKcs and inhibiting RON activity to increase cancer cell chemosensitivity. Mol Cancer Ther; 15(2); 276-86. ©2016 AACR.

Dolman ME, van der Ploeg I, Koster J, et al.
DNA-Dependent Protein Kinase As Molecular Target for Radiosensitization of Neuroblastoma Cells.
PLoS One. 2015; 10(12):e0145744 [PubMed] Free Access to Full Article Related Publications
Tumor cells might resist therapy with ionizing radiation (IR) by non-homologous end-joining (NHEJ) of IR-induced double-strand breaks. One of the key players in NHEJ is DNA-dependent protein kinase (DNA-PK). The catalytic subunit of DNA-PK, i.e. DNA-PKcs, can be inhibited with the small-molecule inhibitor NU7026. In the current study, the in vitro potential of NU7026 to radiosensitize neuroblastoma cells was investigated. DNA-PKcs is encoded by the PRKDC (protein kinase, DNA-activated, catalytic polypeptide) gene. We showed that PRKDC levels were enhanced in neuroblastoma patients and correlated with a more advanced tumor stage and poor prognosis, making DNA-PKcs an interesting target for radiosensitization of neuroblastoma tumors. Optimal dose finding for combination treatment with NU7026 and IR was performed using NGP cells. One hour pre-treatment with 10 μM NU7026 synergistically sensitized NGP cells to 0.63 Gy IR. Radiosensitizing effects of NU7026 increased in time, with maximum effects observed from 96 h after IR-exposure on. Combined treatment of NGP cells with 10 μM NU7026 and 0.63 Gy IR resulted in apoptosis, while no apoptotic response was observed for either of the therapies alone. Inhibition of IR-induced DNA-PK activation by NU7026 confirmed the capability of NGP cells to, at least partially, resist IR by NHEJ. NU7026 also synergistically radiosensitized other neuroblastoma cell lines, while no synergistic effect was observed for low DNA-PKcs-expressing non-cancerous fibroblasts. Results obtained for NU7026 were confirmed by PRKDC knockdown in NGP cells. Taken together, the current study shows that DNA-PKcs is a promising target for neuroblastoma radiosensitization.

Wang W, Long L, Wang L, et al.
Knockdown of Cathepsin L promotes radiosensitivity of glioma stem cells both in vivo and in vitro.
Cancer Lett. 2016; 371(2):274-84 [PubMed] Related Publications
The presence of glioma stem cells (GSCs) in tumor is relevant for glioma treatment resistance. This study assessed whether knockdown of Cathepsin L can influence GSC growth, tumor radiosensitivity, and clinical outcome. Protein levels of Cathepsin L and stem cell markers (CD133 and Nestin) were analyzed in samples from 90 gliomas of different WHO grades and 6 normal brain tissues by immunohistochemistry. Two glioma stem cell lines with overexpressed Cathepsin L were stably transfected with Cathepsin L short hairpin RNA expression vectors. The effects of Cathepsin L inhibition on radiosensitivity, self-renewal, stemness, DNA damage, and apoptosis were evaluated. In addition, an intracranial animal model and subcutaneous tumor xenografts in nude mice were used to assess tumor response to Cathepsin L inhibition in vivo. Our results proved that expressions of Cathepsin L and CD133, but not of Nestin, correlated with malignant grades of glioma tissues. GSCs with high Cathepsin L and CD133 co-expression were extraordinarily radioresistant. Cathepsin L inhibition with radiotherapy significantly reduced GSC growth, promoted apoptosis, and improved radiosensitivity. Knockdown of Cathepsin L resulted in a dramatic reduction of CD133 expression, as well as the decreased phosphorylation of DNA repair checkpoint proteins (ATM and DNA-PKcs). Furthermore, combination of Cathepsin L inhibition and radiotherapy potently blocked tumor growth and decreased blood vessel formation in vivo. Taken together, these findings suggest Cathepsin L as a promising therapeutic target for clinical therapy in GBM patients.

Tamura R, Yoshihara K, Yamawaki K, et al.
Novel kinase fusion transcripts found in endometrial cancer.
Sci Rep. 2015; 5:18657 [PubMed] Free Access to Full Article Related Publications
Recent advances in RNA-sequencing technology have enabled the discovery of gene fusion transcripts in the transcriptome of cancer cells. However, it remains difficult to differentiate the therapeutically targetable fusions from passenger events. We have analyzed RNA-sequencing data and DNA copy number data from 25 endometrial cancer cell lines to identify potential therapeutically targetable fusion transcripts, and have identified 124 high-confidence fusion transcripts, of which 69% are associated with gene amplifications. As targetable fusion candidates, we focused on three in-frame kinase fusion transcripts that retain a kinase domain (CPQ-PRKDC, CAPZA2-MET, and VGLL4-PRKG1). We detected only CPQ-PRKDC fusion transcript in three of 122 primary endometrial cancer tissues. Cell proliferation of the fusion-positive cell line was inhibited by knocking down the expression of wild-type PRKDC but not by blocking the CPQ-PRKDC fusion transcript expression. Quantitative real-time RT-PCR demonstrated that the expression of the CPQ-PRKDC fusion transcript was significantly lower than that of wild-type PRKDC, corresponding to a low transcript allele fraction of this fusion, based on RNA-sequencing read counts. In endometrial cancers, the CPQ-PRKDC fusion transcript may be a passenger aberration related to gene amplification. Our findings suggest that transcript allele fraction is a useful predictor to find bona-fide therapeutic-targetable fusion transcripts.

Middleton FK, Patterson MJ, Elstob CJ, et al.
Common cancer-associated imbalances in the DNA damage response confer sensitivity to single agent ATR inhibition.
Oncotarget. 2015; 6(32):32396-409 [PubMed] Free Access to Full Article Related Publications
ATR is an attractive target in cancer therapy because it signals replication stress and DNA lesions for repair and to S/G2 checkpoints. Cancer-specific defects in the DNA damage response (DDR) may render cancer cells vulnerable to ATR inhibition alone. We determined the cytotoxicity of the ATR inhibitor VE-821 in isogenically matched cells with DDR imbalance. Cell cycle arrest, DNA damage accumulation and repair were determined following VE-821 exposure.Defects in homologous recombination repair (HRR: ATM, BRCA2 and XRCC3) and base excision repair (BER: XRCC1) conferred sensitivity to VE-821. Surprisingly, the loss of different components of the trimeric non-homologous end-joining (NHEJ) protein DNA-PK had opposing effects. Loss of the DNA-binding component, Ku80, caused hypersensitivity to VE-821, but loss of its partner catalytic subunit, DNA-PKcs, did not. Unexpectedly, VE-821 was particularly cytotoxic to human and hamster cells expressing high levels of DNA-PKcs. High DNA-PKcs was associated with replicative stress and activation of the DDR. VE-821 suppressed HRR, determined by RAD51 focus formation, to a greater extent in cells with high DNA-PKcs.Defects in HRR and BER and high DNA-PKcs expression, that are common in cancer, confer sensitivity to ATR inhibitor monotherapy and may be developed as predictive biomarkers for personalised medicine.

Zhou C, Tang H, Yu J, et al.
Blood-based DNA methylation of DNA repair genes in the non-homologous end-joining (NEHJ) pathway in patient with glioma.
Int J Clin Exp Pathol. 2015; 8(8):9463-7 [PubMed] Free Access to Full Article Related Publications
UNLABELLED: To investigate the blood-based DNA methylation of repair genes including LIG4, XRCC4, XRCC5, XRCC6 and XRCC7 that involved in non-homologous end-joining (NEHJ) DNA repair pathway in patients with glioma. Blood samples were obtained from 114 glioma patients, 96 normal controls, and 81 glioma patients after radiotherapy and chemotherapy. Blood-based DNA methylation of the five NHEJ repair genes was assayed by methylation-specific polymerase chain reaction (MSP). The DNA methylation level of XRCC5 and XRCC7 in glioma group are significantly higher than those of normal group (P<0.001). Moreover, radiotherapy treatment significantly increased methylation level of XRCC5 and XRCC7 compared to glioma group. No significant difference for the methylation of the other three genes, LIG4, XRCC4 and XRCC6 were detected among three groups.
IN CONCLUSION: our findings indicate that DNA methylation modification plays an important role to regulate the gene expression of XRCC5 and XRCC7, from the results that the gene methylation level of the glioma group is higher than that of the normal group. Increased methylation of XRCC5 and XRCC7 in blood samples of glioma patients and patients with radiotherapy and chemotherapy suggests that blood-based methylation level of XRCC5 and XRCC7 could be a potential indicator for evaluating of the effect of radiotherapy and chemotherapy for glioma patient.

Hausmann C, Temme A, Cordes N, Eke I
ILKAP, ILK and PINCH1 control cell survival of p53-wildtype glioblastoma cells after irradiation.
Oncotarget. 2015; 6(33):34592-605 [PubMed] Free Access to Full Article Related Publications
The prognosis is generally poor for patients suffering from glioblastoma multiforme (GBM) due to radiation and drug resistance. Prosurvival signaling originating from focal adhesion hubs essentially contributes to therapy resistance and tumor aggressiveness. As the underlying molecular mechanisms remain largely elusive, we addressed whether targeting of the focal adhesion proteins particularly interesting new cysteine-histidine-rich 1 (PINCH1), integrin-linked kinase (ILK) and ILK associated phosphatase (ILKAP) modulates GBM cell radioresistance. Intriguingly, PINCH1, ILK and ILKAP depletion sensitized p53-wildtype, but not p53-mutant, GBM cells to radiotherapy. Concomitantly, these cells showed inactivated Glycogen synthase kinase-3β (GSK3β) and reduced proliferation. For PINCH1 and ILKAP knockdown, elevated levels of radiation-induced γH2AX/53BP1-positive foci, as a marker for DNA double strand breaks, were observed. Mechanistically, we identified radiation-induced phosphorylation of DNA protein kinase (DNAPK), an important DNA repair protein, to be dependent on ILKAP. This interaction was fundamental to radiation survival of p53-wildtype GBM cells. Conclusively, our data suggest an essential role of PINCH1, ILK and ILKAP for the radioresistance of p53-wildtype GBM cells and provide evidence for DNAPK functioning as a central mediator of ILKAP signaling. Strategies for targeting focal adhesion proteins in combination with radiotherapy might be a promising approach for patients with GBM.

Alsubhi N, Middleton F, Abdel-Fatah TM, et al.
Chk1 phosphorylated at serine345 is a predictor of early local recurrence and radio-resistance in breast cancer.
Mol Oncol. 2016; 10(2):213-23 [PubMed] Related Publications
Radiation-induced DNA damage activates the DNA damage response (DDR). DDR up-regulation may predict radio-resistance and increase the risk of early local recurrence despite radiotherapy in early stage breast cancers. In 1755 early stage breast cancers, DDR signalling [ATM, ATR, total Ckh1, Chk1 phosphorylated at serine(345) (pChk1), Chk2, p53], base excision repair [PARP1, POLβ, XRCC1, FEN1, SMUG1], non-homologous end joining (Ku70/Ku80, DNA-PKcs) and homologous recombination [RAD51, BRCA1, γH2AX, BLM, WRN, RECQL5, PTEN] protein expression was correlated to time to early local recurrence. Pre-clinically, radio-sensitization by inhibition of Chk1 activation by ATR inhibitor (VE-821) and inhibition of Chk1 (V158411) were investigated in MDA-MB-231 (p53 mutant) and MCF-7 (p53 wild-type) breast cancer cells. In the whole cohort, 208/1755 patients (11.9%) developed local recurrence of which 126 (61%) developed local recurrence within 5 years of initiation of primary therapy. Of the 20 markers tested, only pChk1 and p53 significantly associated with early local recurrence (p value = 0.015 and 0.010, respectively). When analysed together, high cytoplasmic pChk1-nuclear pChk1 (p = 0.039), high cytoplasmic pChk1-p53 (p = 0.004) and high nuclear pChk1-p53 (p = 0.029) co-expression remain significantly linked to early local recurrence. In multivariate analysis, cytoplasmic pChk1 level independently predicted early local recurrence (p = 0.025). In patients who received adjuvant local radiotherapy (n = 949), p53 (p = 0.014) and high cytoplasmic pChk1-p53 (p = 0.017) remain associated with early local recurrence. Pre-clinically, radio-sensitisation by VE-821 or V158411 was observed in both MCF-7 and MDA-MB-231 cells and was more pronounced in MCF-7 cells. We conclude that pChk1 is a predictive biomarker of radiotherapy resistance and early local recurrence.

Hu S, Fu S, Xu X, et al.
The mechanism of radiosensitization by YM155, a novel small molecule inhibitor of survivin expression, is associated with DNA damage repair.
Cell Physiol Biochem. 2015; 37(3):1219-30 [PubMed] Related Publications
BACKGROUND/AIMS: Survivin, a member of the inhibitor of apoptosis protein family, is an attractive target for cancer therapy. We investigated the effects of YM155, a small molecule inhibitor of survivin expression, on the radiosensitivity of human non-small cell lung cancer (NSCLC) cell lines and elucidated a relationship between the cellular localization of survivin and DNA double-strand break repair.
METHODS: The cellular distribution of survivin was determined by Western blotting of subcellular fractions and by immunofluorescent staining in A549 NSCLC cells. Radiation-induced DNA damage was evaluated based on histone H2AX phosphorylation and foci formation. The relationship between the cellular localization of survivin and DNA double-strand break repair was analyzed by Western blotting and co-immunoprecipitations.
RESULTS: YM155 down-regulated survivin expression in NSCLC cells in a concentration- and time-dependent manner. An in vitro clonogenic survival assay revealed that YM155 increased the sensitivity of NSCLC cells to radiation. After irradiation, we observed a rapid accumulation of survivin in the nucleus. An immunofluorescent analysis of histone x03B3;-H2AX demonstrated that the inhibition of survivin expression by YM155 resulted in impaired DNA double-strand break repair. Co-immunoprecipitation assays using nuclear extracts revealed an interaction between survivin, Ku70, x03B3;-H2AX, and DNA-PKcs. Furthermore, S2056 autophosphorylation of DNA-PKcs was reduced in survivin-depleted cells.
CONCLUSIONS: These results suggested that YM155 sensitized NSCLC cells to radiation, at least in part by inhibiting DNA repair and enhancing apoptosis via the down-regulation of survivin expression. YM155 pretreatment inhibited DNA-PKcs autophosphorylation at S2056. Nuclear survivin was involved in DNA double-strand break repair via interactions with members of the DNA double-strand break repair machinery.

Wu L, Zhang J, Wu H, Han E
DNA-PKcs interference sensitizes colorectal cancer cells to a mTOR kinase inhibitor WAY-600.
Biochem Biophys Res Commun. 2015; 466(3):547-53 [PubMed] Related Publications
Colorectal cancer (CRC) is one leading contributor of cancer-related mortalities. Mammalian target of rapamycin (mTOR), existing in two complexes (mTORC1/2), is a valuable target for possible CRC interference. In the current study, we showed that WAY-600, a potent mTOR inhibitor, only exerted moderate activity against primary and HT-29 CRC cells. We proposed that DNA-dependent protein kinase catalytic subunit (DNA-PKcs) could be the major resistance factor of WAY-600 in CRC cells. DNA-PKcs inhibitors, including NU7026 and NU7441, dramatically enhanced WAY-600-induced cytotoxic and pro-apoptotic effect against the CRC cells. Further, WAY-600-exerted cytotoxicity was significantly increased in DNA-PKcs-silenced (by targeted siRNA/shRNA) CRC cells, but was attenuated with DNA-PKcs overexpression. Our evidence suggested that DNA-PKcs Thr-2609 phosphorylation might be critical for WAY-600's resistance. Mutation of this site through introducing a dominant negative DNA-PKcs (T2609A) dramatically potentiated WAY-600's sensitivity in HT-29 cells. Meanwhile, overexpression of protein phosphatase 5 (PP5) dephosphorylated DNA-PKcs at Thr-2609, and significantly increased WAY-600's sensitivity in HT-29 cells. In vivo, WAY-600-induced anti-HT-29 xenograft growth activity was significantly potentiated with NU7026 co-administration. These results suggest that DNA-PKcs could be the major resistance factor of WAY-600 in CRC cells.

Somers J, Wilson LA, Kilday JP, et al.
A common polymorphism in the 5' UTR of ERCC5 creates an upstream ORF that confers resistance to platinum-based chemotherapy.
Genes Dev. 2015; 29(18):1891-6 [PubMed] Free Access to Full Article Related Publications
We show that a common polymorphic variant in the ERCC5 5' untranslated region (UTR) generates an upstream ORF (uORF) that affects both the background expression of this protein and its ability to be synthesized following exposure to agents that cause bulky adduct DNA damage. Individuals that harbor uORF1 have a marked resistance to platinum-based agents, illustrated by the significantly reduced progression-free survival of pediatric ependymoma patients treated with such compounds. Importantly, inhibition of DNA-PKcs restores sensitivity to platinum-based compounds by preventing uORF1-dependent ERCC5 expression. Our data support a model in which a heritable 5' noncoding mRNA element influences individuals' responses to platinum-based chemotherapy.

Bouley J, Saad L, Grall R, et al.
A new phosphorylated form of Ku70 identified in resistant leukemic cells confers fast but unfaithful DNA repair in cancer cell lines.
Oncotarget. 2015; 6(29):27980-8000 [PubMed] Free Access to Full Article Related Publications
Ku70-dependent canonical nonhomologous end-joining (c-NHEJ) DNA repair system is fundamental to the genome maintenance and B-cell lineage. c-NHEJ is upregulated and error-prone in incurable forms of chronic lymphocytic leukemia which also displays telomere dysfunction, multiple chromosomal aberrations and the resistance to DNA damage-induced apoptosis. We identify in these cells a novel DNA damage inducible form of phospho-Ku70. In vitro in different cancer cell lines, Ku70 phosphorylation occurs in a heterodimer Ku70/Ku80 complex within minutes of genotoxic stress, necessitating its interaction with DNA damage-induced kinase pS2056-DNA-PKcs and/or pS1981-ATM. The mutagenic effects of phospho-Ku70 are documented by a defective S/G2 checkpoint, accelerated disappearance of γ-H2AX foci and kinetics of DNA repair resulting in an increased level of genotoxic stress-induced chromosomal aberrations. Together, these data unveil an involvement of phospho-Ku70 in fast but inaccurate DNA repair; a new paradigm linked to both the deregulation of c-NHEJ and the resistance of malignant cells.

Zou K, Liu C, Zhang Z, Zou L
The effect of elemene on lung adenocarcinoma A549 cell radiosensitivity and elucidation of its mechanism.
Clinics (Sao Paulo). 2015; 70(8):556-62 [PubMed] Free Access to Full Article Related Publications
OBJECTIVE: To investigate the effect of elemene on the radiosensitivity of A549 cells and its possible molecular mechanism.
METHODS: Apoptosis of A549 cells was detected by flow cytometry and fluorescence microscopy. The effect of double-strand break (DSB) damage repair in A549 cells was evaluated using the neutral comet assay. Protein expression levels were detected using western blotting, and the correlation between protein levels was analyzed.
RESULTS: Elemene exhibited a radiosensitizing effect on A549 cells. The level of apoptosis induced by elemene combined with radiation was significantly greater (p<0.01) than that elicited by either radiation or elemene alone. Following radiation and subsequent repair for 24 h, the tail intensity of A549 cells treated with a combination of elemene and radiation was greater than that of cells treated with either elemene or radiation alone (p<0.01). This result indicates that elemene inhibits cellular DSB repair. Both elemene combined with radiation and radiation alone decreased the protein expression of DNA-PKcs and Bcl-2 compared to elemene alone (p<0.01), while p53 protein expression was increased (p<0.01). A negative correlation was observed between DNA-PKcs and p53 expression (r=-0.569, p=0.040), while a positive correlation was found between DNA-PKcs and Bcl-2 expression (r=0.755, p=0.012).
CONCLUSIONS: Elemene exhibits a radiosensitizing effect on A549 cells, and its underlying molecular mechanism of action may be related to the downregulation of DNA-PKcs gene expression.

Wagner W, Ciszewski WM, Kania KD
L- and D-lactate enhance DNA repair and modulate the resistance of cervical carcinoma cells to anticancer drugs via histone deacetylase inhibition and hydroxycarboxylic acid receptor 1 activation.
Cell Commun Signal. 2015; 13:36 [PubMed] Free Access to Full Article Related Publications
BACKGROUND: The consideration of lactate as an active metabolite is a newly emerging and attractive concept. Recently, lactate has been reported to regulate gene transcription via the inhibition of histone deacetylases (HDACs) and survival of cancer cells via hydroxycarboxylic acid receptor 1 (HCAR1). This study examined the role of L- and D-lactate in the DNA damage response in cervical cancer cells.
METHODS: Three cervical cancer cell lines were examined: HeLa, Ca Ski and C33A. The inhibitory activity of lactate on HDACs was analysed using Western blot and biochemical methods. The lactate-mediated stimulation of DNA repair and cellular resistance to neocarzinostatin, doxorubicin and cisplatin were studied using γ-H2AX, comet and clonogenic assays. HCAR1 and DNA repair gene expression was quantified by real-time PCR. DNA-PKcs activity and HCAR1 protein expression were evaluated via immunocytochemistry and Western blot, respectively. HCAR1 activation was investigated by measuring intracellular cAMP accumulation and Erk phosphorylation. HCAR1 expression was silenced using shRNA.
RESULTS: L- and D-lactate inhibited HDACs, induced histone H3 and H4 hyperacetylation, and decreased chromatin compactness in HeLa cells. Treating cells with lactate increased LIG4, NBS1, and APTX expression by nearly 2-fold and enhanced DNA-PKcs activity. Based on γ-H2AX and comet assays, incubation of cells in lactate-containing medium increased the DNA repair rate. Furthermore, clonogenic assays demonstrated that lactate mediates cellular resistance to clinically used chemotherapeutics. Western blot and immunocytochemistry showed that all studied cell lines express HCAR1 on the cellular surface. Inhibiting HCAR1 function via pertussis toxin pretreatment partially abolished the effects of lactate on DNA repair. Down-regulating HCAR1 decreased the efficiency of DNA repair, abolished the cellular response to L-lactate and decreased the effect of D-lactate. Moreover, HCAR1 shRNA-expressing cells produced significantly lower mRNA levels of monocarboxylate transporter 4. Finally, the enhancement of DNA repair and cell survival by lactate was suppressed by pharmacologically inhibiting monocarboxylate transporters using the inhibitor α-cyano-4-hydroxycinnamic acid (α-CHCA).
CONCLUSIONS: Our data indicate that L- and D-lactate present in the uterine cervix may participate in the modulation of cellular DNA damage repair processes and in the resistance of cervical carcinoma cells to anticancer therapy.

Toulany M, Rodemann HP
Phosphatidylinositol 3-kinase/Akt signaling as a key mediator of tumor cell responsiveness to radiation.
Semin Cancer Biol. 2015; 35:180-90 [PubMed] Related Publications
The phosphatidylinositol 3-kinase (PI3K)/Akt pathway is a key cascade downstream of several protein kinases, especially membrane-bound receptor tyrosine kinases, including epidermal growth factor receptor (EGFR) family members. Hyperactivation of the PI3K/Akt pathway is correlated with tumor development, progression, poor prognosis, and resistance to cancer therapies, such as radiotherapy, in human solid tumors. Akt/PKB (Protein Kinase B) members are the major kinases that act downstream of PI3K, and these are involved in a variety of cellular functions, including growth, proliferation, glucose metabolism, invasion, metastasis, angiogenesis, and survival. Accumulating evidence indicates that activated Akt is one of the major predictive markers for solid tumor responsiveness to chemo/radiotherapy. DNA double-strand breaks (DNA-DSB), are the prime cause of cell death induced by ionizing radiation. Preclinical in vitro and in vivo studies have shown that constitutive activation of Akt and stress-induced activation of the PI3K/Akt pathway accelerate the repair of DNA-DSB and, consequently, lead to therapy resistance. Analyzing dysregulations of Akt, such as point mutations, gene amplification or overexpression, which results in the constitutive activation of Akt, might be of special importance in the context of radiotherapy outcomes. Such studies, as well as studies of the mechanism(s) by which activated Akt1 regulates repair of DNA-DSB, might help to identify combinations using the appropriate molecular targeting strategies with conventional radiotherapy to overcome radioresistance in solid tumors. In this review, we discuss the dysregulation of the components of upstream regulators of Akt as well as specific modifications of Akt isoforms that enhance Akt activity. Likewise, the mechanisms by which Akt interferes with repair of DNA after exposure to ionizing radiation, will be reviewed. Finally, the current status of Akt targeting in combination with radiotherapy will be discussed.

Goodwin JF, Kothari V, Drake JM, et al.
DNA-PKcs-Mediated Transcriptional Regulation Drives Prostate Cancer Progression and Metastasis.
Cancer Cell. 2015; 28(1):97-113 [PubMed] Free Access to Full Article Related Publications
Emerging evidence demonstrates that the DNA repair kinase DNA-PKcs exerts divergent roles in transcriptional regulation of unsolved consequence. Here, in vitro and in vivo interrogation demonstrate that DNA-PKcs functions as a selective modulator of transcriptional networks that induce cell migration, invasion, and metastasis. Accordingly, suppression of DNA-PKcs inhibits tumor metastases. Clinical assessment revealed that DNA-PKcs is significantly elevated in advanced disease and independently predicts for metastases, recurrence, and reduced overall survival. Further investigation demonstrated that DNA-PKcs in advanced tumors is highly activated, independent of DNA damage indicators. Combined, these findings reveal unexpected DNA-PKcs functions, identify DNA-PKcs as a potent driver of tumor progression and metastases, and nominate DNA-PKcs as a therapeutic target for advanced malignancies.

Yang HL, Qiao DD, Li K, et al.
Association of genetic polymorphisms in PRKDC and XRCC4 with risk of ESCC in a high-incidence region of North China.
Tumori. 2016 Mar-Apr; 102(2):131-4 [PubMed] Related Publications
BACKGROUND: The nonhomologous end-joining (NHEJ) pathway is the main mechanism repairing DNA double-strand breaks (DSBs) in human cells. This research was designed to study the association between selected variants in NHEJ members and esophageal squamous cell carcinoma (ESCC).
METHODS: Two single nucleotide polymorphisms (SNPs), PRKDC (rs7003908) and X-ray repair cross complementing group 4 (XRCC4; rs1805377), were genotyped in a total of 189 patients with ESCC and 189 unrelated control individuals in a high-risk area for ESCC in North China, and the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method was applied.
RESULTS: A significantly different distribution was found in the frequency of PRKDC (rs7003908) genotype between the ESCC group and controls. Individuals homozygous for the C allele had a significant (3.185-fold) increased risk of ESCC. As for XRCC4 (rs1805377) polymorphism, no difference was found in distribution between the ESCC and control groups.
CONCLUSIONS: Our results suggest that variation in DNA repair genes may be associated with risk of ESCC.

Li X, Tian J, Bo Q, et al.
Targeting DNA-PKcs increased anticancer drug sensitivity by suppressing DNA damage repair in osteosarcoma cell line MG63.
Tumour Biol. 2015; 36(12):9365-72 [PubMed] Related Publications
Many chemotherapy drugs exert anticancer effects through causing DNA damage, such as DNA topoisomerase inhibitor and platinum-containing drugs. DNA damage repair is an important mechanism of drug resistance which is responsible for metastasis and recurrence after chemotherapy. DNA-dependent protein kinase (DNA-PK) plays an important role in non-homology end joining (NHEJ) pathway. In this study, we aimed to determine whether DNA-PK catalytic subunit (DNA-PKcs) is expressed in osteosarcoma MG63 cell line and involved in drug resistance induced by DNA repair. We found that DNA-PKcs was expressed in osteosarcoma cell line MG63. The pDNA-PKcs(T2609) was more expressed in cells treated with cisplatin (DDP) and etoposide (VP16). Down-regulation of DNA-PKcs produced higher sensitivity of MG63 cells to DDP or VP16 through increasing apoptosis and causing cell cycle arrest in the G1 phase. Our study supported that DNA-PKcs was involved in drug-induced DNA damage repair and related to chemosensitivity of osteosarcoma MG63 cells.

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.

Burdine LJ, Burdine MS, Moreland L, et al.
Proteomic Identification of DNA-PK Involvement within the RET Signaling Pathway.
PLoS One. 2015; 10(6):e0127943 [PubMed] Free Access to Full Article Related Publications
Constitutive activation of the Rearranged during Transfection (RET) proto-oncogene leads to the development of MEN2A medullary thyroid cancer (MTC). The relatively clear genotype/phenotype relationship seen with RET mutations and the development of MEN2A is unusual in the fact that a single gene activity can drive the progression towards metastatic disease. Despite knowing the oncogene responsible for MEN2A, MTC, like most tumors of neural crest origin, remains largely resistant to chemotherapy. Constitutive activation of RET in a SK-N-MC cell line model reduces cell sensitivity to chemotherapy. In an attempt to identify components of the machinery responsible for the observed RET induced chemoresistance, we performed a proteomic screen of histones and associated proteins in cells with a constitutively active RET signaling pathway. The proteomic approach identified DNA-PKcs, a DNA damage response protein, as a target of the RET signaling pathway. Active DNA-PKcs, which is phosphorylated at site serine 2056 and localized to chromatin, was elevated within our model. Treatment with the RET inhibitor RPI-1 significantly reduced s2056 phosphorylation in RET cells as well as in a human medullary thyroid cancer cell line. Additionally, inhibition of DNA-PKcs activity diminished the chemoresistance observed in both cell lines. Importantly, we show that activated DNA-PKcs is elevated in medullary thyroid tumor samples and that expression correlates with expression of RET in thyroid tumors. These results highlight one mechanism by which RET signaling likely primes cells for rapid response to DNA damage and suggests DNA-PKcs as an additional target in MTC.

Xu L, Tang H, El-Naggar AK, et al.
Genetic variants in DNA double-strand break repair genes and risk of salivary gland carcinoma: a case-control study.
PLoS One. 2015; 10(6):e0128753 [PubMed] Free Access to Full Article Related Publications
DNA double strand break (DSB) repair is the primary defense mechanism against ionizing radiation-induced DNA damage. Ionizing radiation is the only established risk factor for salivary gland carcinoma (SGC). We hypothesized that genetic variants in DSB repair genes contribute to individual variation in susceptibility to SGC. To test this hypothesis, we conducted a case-control study in which we analyzed 415 single nucleotide polymorphisms (SNPs) in 45 DSB repair genes in 352 SGC cases and 598 controls. Multivariate logistic regression analysis was performed to calculate odds ratios (ORs) and 95% confidence intervals (CIs). Rs3748522 in RAD52 and rs13180356 in XRCC4 were significantly associated with SGC after Bonferroni adjustment; ORs (95% CIs) for the variant alleles of these SNPs were 1.71 (1.40-2.09, P = 1.70 × 10(-7)) and 0.58 (0.45-0.74, P = 2.00 × 10(-5)) respectively. The genetic effects were modulated by histological subtype. The association of RAD52-rs3748522 with SGC was strongest for mucoepidermoid carcinoma (OR = 2.21, 95% CI: 1.55-3.15, P = 1.25 × 10(-5), n = 74), and the association of XRCC4-rs13180356 with SGC was strongest for adenoid cystic carcinoma (OR = 0.60, 95% CI: 0.42-0.87, P = 6.91 × 10(-3), n = 123). Gene-level association analysis revealed one gene, PRKDC, with a marginally significant association with SGC risk in non-Hispanic whites. To our knowledge, this study is the first to comprehensively evaluate the genetic effect of DSB repair genes on SGC risk. Our results indicate that genetic variants in the DSB repair pathways contribute to inter-individual differences in susceptibility to SGC and show that the impact of genetic variants differs by histological subtype. Independent studies are warranted to confirm these findings.

Chatterjee P, Choudhary GS, Alswillah T, et al.
The TMPRSS2-ERG Gene Fusion Blocks XRCC4-Mediated Nonhomologous End-Joining Repair and Radiosensitizes Prostate Cancer Cells to PARP Inhibition.
Mol Cancer Ther. 2015; 14(8):1896-906 [PubMed] Free Access to Full Article Related Publications
Exposure to genotoxic agents, such as ionizing radiation (IR), produces DNA damage, leading to DNA double-strand breaks (DSB); IR toxicity is augmented when the DNA repair is impaired. We reported that radiosensitization by a PARP inhibitor (PARPi) was highly prominent in prostate cancer cells expressing the TMPRSS2-ERG gene fusion protein. Here, we show that TMPRSS2-ERG blocks nonhomologous end-joining (NHEJ) DNA repair by inhibiting DNA-PKcs. VCaP cells, which harbor TMPRSS2-ERG and PC3 cells that stably express it, displayed γH2AX and 53BP1 foci constitutively, indicating persistent DNA damage that was absent if TMPRSS2-ERG was depleted by siRNA in VCaP cells. The extent of DNA damage was enhanced and associated with TMPRSS2-ERG's ability to inhibit DNA-PKcs function, as indicated by its own phosphorylation (Thr2609, Ser2056) and that of its substrate, Ser1778-53BP1. DNA-PKcs deficiency caused by TMPRSS2-ERG destabilized critical NHEJ components on chromatin. Thus, XRCC4 was not recruited to chromatin, with retention of other NHEJ core factors being reduced. DNA-PKcs autophosphorylation was restored to the level of parental cells when TMPRSS2-ERG was depleted by siRNA. Following IR, TMPRSS2-ERG-expressing PC3 cells had elevated Rad51 foci and homologous recombination (HR) activity, indicating that HR compensated for defective NHEJ in these cells, hence addressing why TMPRSS2-ERG alone did not lead to radiosensitization. However, the presence of TMPRSS2-ERG, by inhibiting NHEJ DNA repair, enhanced PARPi-mediated radiosensitization. IR in combination with PARPi resulted in enhanced DNA damage in TMPRSS2-ERG-expressing cells. Therefore, by inhibiting NHEJ, TMPRSS2-ERG provides a synthetic lethal interaction with PARPi in prostate cancer patients expressing TMPRSS2-ERG.

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