Influence of XRCC4 expression in esophageal cancer cells on the response to radiotherapy

Meeting report: the 66th annual meeting of the Japanese Radiation Research Society in Tokyo, Japan, 6-8 November 2023

The 66th Annual Meeting of the Japanese Radiation Research Society took place in Tokyo, Japan, from 6 to 8 November 2023. The meeting covered a wide range of radiation research topics, including basic mechanisms involved in radiation effects, translational research, and epidemiology. Some sessions were jointly organized with the International Commission on Radiological Protection (ICRP). Here, we report on some plenary and keynote talks presented at the meeting.

X-ray cross-complementing family: the bridge linking DNA damage repair and cancer

Genomic instability is a common hallmark of human tumours. As a carrier of genetic information, DNA is constantly threatened by various damaging factors that, if not repaired in time, can affect the transmission of genetic information and lead to cellular carcinogenesis. In response to these threats, cells have evolved a range of DNA damage response mechanisms, including DNA damage repair, to maintain genomic stability. The X-ray repair cross-complementary gene family (XRCC) comprises an important class of DNA damage repair genes that encode proteins that play important roles in DNA single-strand breakage and DNA base damage repair. The dysfunction of the XRCC gene family is associated with the development of various tumours. In the context of tumours, mutations in XRCC and its aberrant expression, result in abnormal DNA damage repair, thus contributing to the malignant progression of tumour cells. In this review, we summarise the significant roles played by XRCC in diverse tumour types. In addition, we discuss the correlation between the XRCC family members and tumour therapeutic sensitivity.

Systematic analysis identifies XRCC4 as a potential immunological and prognostic biomarker associated with pan-cancer

BACKGROUND

XRCC4 is a NHEJ factor identified recently that plays a vital role in repairing DNA double-stranded breaks. Studies have reported the associations between abnormal expression of XRCC4 and tumor susceptibility and radiosensitivity, but the potential biological mechanisms by which XRCC4 exerts effects on tumorigenesis are not fully understood. This study aimed to systematically investigate the role of XRCC4 across cancer types.

METHODS

The TIMER, GTEX and Xiantao Academic database were used to interpret the expression of XRCC4. Genomic alterations and protein expression in human organic and tumor tissues were applied in cBioPortal and the Human Protein Atlas databases. Correlations between XRCC4 expression and immune and molecular subtypes were analyzed by using the TISIDB database. Protein-protein interactions, GO and KEGG enrichment were also applied for XRCC4-related genes. The TIMER and the Tumor Immune Single Cell Hub (TISCH) online databases were used to explore the relationship between XRCC4 and tumor immune microenvironment. Drug sensitivity information was acquired from the CellMiner database to analyze the effect of XRCC4 on sensitivity analysis.

RESULTS

The XRCC4 expression was significantly upregulated in 15 tumor types and downregulated in two tumor types compared with the normal tissues, most of which were validated by the results of Xiantao academic platform. XRCC4 was expressed at intermediate level in malignant cells. The XRCC4 expression was related to the molecular and immune subtypes of human cancers, and the survival outcome of 11 types of cancers, including KIRC, STAD and LIHC. The main type of frequent genetic alteration is amplification. Strong correlations were also found between XRCC4 and immune checkpoint genes in 33 human cancers. Furthermore, the abnormal expression of XRCC4 was related to immune cell infiltration and drug sensitivity. Enrichment analysis showed that XRCC4 was significantly correlated with DNA damage response.

CONCLUSIONS

This comprehensive pan-cancer analysis suggested that XRCC4 may play a vital role in the prognosis and immunotherapy response in cancer patients, and it is a promising therapy target in the future.

DNA repair pathways as a novel therapeutic strategy in esophageal cancer: A review study

Esophageal cancer (EC) is a common malignancy with a poor prognosis worldwide. There are two core pathways that repair double-strand breaks, homologous recombination (HR) and non-homologous end joining (NHEJ) and numerous proteins are recognized that affect the occurrence of HR and NHEJ. Altered DNA damage response (DDR) pathways are associated with cancer susceptibility and affect therapeutic response and resistance in cancers. DDR pathway alterations in EC are still poorly understood. Therefore, the identification of alterations in specific genes in DDR pathways may potentially result in novel treatments for resistant cancers, especially EC. In this review, we aimed to focus on different aspects of DNA damage and repair processes in EC. Also, we reviewed new therapeutic strategies via targeting DNA repair machinery components.

Prediction of Results of Radiotherapy With Ku70 Expression and an Artificial Neural Network

Background/Aim: Accurate prediction of radiotherapy results is indispensable for the individualized selection of treatment modalities of cancer. We examined the application of the artificial neural network (ANN) model in predicting radiotherapy results using clinical factors and immunohistochemical staining of Ku70 as inputs. Patients and Methods: We analyzed 79 prostate cancer patients with localized adenocarcinoma treated with radiotherapy between August 2001 and October 2010. We also analyzed 46 hypopharyngeal cancer patients with squamous cell carcinoma treated with radiotherapy between March 2002 and December 2009. The properly trained ANN analysis using a standard feedforward, back-propagation neural network was used to predict the radiotherapy treatment results. Results: The areas under the receiver-operating characteristic curve (AUC) were 0.939 for patients treated with intensity modulated radiotherapy (IMRT)+androgen deprivation therapy (ADT), 0.803 for IMRT alone, and 0.960 for 3D-conformal radiotherapy (CRT) alone in prostate cancer. Sensitivity and specificity were 85.7% and 90.4% for IMRT+ADT, 75.0% and 88.5% for IMRT alone, and 92.3% and 100% for 3D-CRT alone. The AUC was 0.901 for hypopharyngeal cancer. Sensitivity and specificity were 66.7% and 88.2%, respectively. Conclusion: We demonstrated a possibility to predict the radiotherapy treatment results in prostate and hypopharyngeal cancer using ANN in combination with Ku70 expression and clinical factors as inputs.

DNA-PK in human malignant disorders: Mechanisms and implications for pharmacological interventions

The DNA-PK holoenzyme is a fundamental element of the DNA damage response machinery (DDR), which is responsible for cellular genomic stability. Consequently, and predictably, over the last decades since its identification and characterization, numerous pre-clinical and clinical studies reported observations correlating aberrant DNA-PK status and activity with cancer onset, progression and responses to therapeutic modalities. Notably, various studies have established in recent years the role of DNA-PK outside the DDR network, corroborating its role as a pleiotropic complex involved in transcriptional programs that operate biologic processes as epithelial to mesenchymal transition (EMT), hypoxia, metabolism, nuclear receptors signaling and inflammatory responses. In particular tumor entities as prostate cancer, immense research efforts assisted mapping and describing the overall signaling networks regulated by DNA-PK that control metastasis and tumor progression. Correspondingly, DNA-PK emerges as an obvious therapeutic target in cancer and data pertaining to various pharmacological approaches have been published, largely in context of combination with DNA-damaging agents (DDAs) that act by inflicting DNA double strand breaks (DSBs). Currently, new generation inhibitors are tested in clinical trials. Several excellent reviews have been published in recent years covering the biology of DNA-PK and its role in cancer. In the current article we are aiming to systematically describe the main findings on DNA-PK signaling in major cancer types, focusing on both preclinical and clinical reports and present a detailed current status of the DNA-PK inhibitors repertoire.

TheXRCC4rs1805377 polymorphism is not associated with the risk of cancer: An updated meta-analysis

Objectives

A growing number of studies have reported that genes involved in the repair of DNA double-strand breaks might be cancer-susceptibility genes. The x-ray cross-complementing group 4 gene ( XRCC4) encodes a protein that functions in the repair of DNA double-strand breaks, and this meta-analysis aimed to investigate the relationship between the XRCC4 rs1805377 polymorphism and cancer occurrence.

Methods

We retrieved case–control studies that met the inclusion criteria from PubMed, Web of Science, Embase, and China National Knowledge Infrastructure databases. Associations between rs1805377 and cancer risk were evaluated by odds ratios (ORs) using a random effects model and 95% confidence intervals (CIs) as well as sensitivity and subgroup analyses.

Results

After inclusion criteria were met, the meta-analysis involved 24 studies that included 9,633 cancer patients and 10,544 healthy controls. No significant association was found between rs1805377 and the risk of cancer (pooled OR = 1.107; 95% CI = 0.955–1.284) in the dominant genetic model. Similarly, no significant association was observed in the subgroup analysis.

Conclusions

Through this meta-analysis, we found no association between the rs1805377 polymorphism and cancer occurrence. This may provide useful information for relevant future studies into the etiology of cancer.

Evaluation of X-Ray Repair Cross-Complementing Family Members as Potential Biomarkers for Predicting Progression and Prognosis in Hepatocellular Carcinoma

The X-ray repair cross-complementing (XRCC) gene family has been revealed to participate in the carcinogenesis and development of numerous cancers. However, the expression profiles and prognostic values of XRCCs (XRCC1-6) in hepatocellular carcinoma (HCC) have not been explored up to now. The transcriptional levels of XRCCs in primary HCC tissues were analyzed by UALCAN and GEPIA. The relationship between XRCCs expression and HCC clinical characteristics was evaluated using UALCAN. Moreover, the prognostic values of XRCCs expression and mutations in HCC patients were investigated via the GEPIA and cBioPortal, respectively. Last but not least, the functions and pathways of XRCCs in HCC were also predicted by cBioPortal and DVAID. The transcriptional levels of all XRCCs in HCC tissues were notably elevated compared with normal liver tissues. Meanwhile, upregulated XRCCs expression was positively associated with clinical stages and tumor grades of HCC patients. Survival analysis using the GEPIA database revealed that high transcription levels of XRCC2/3/4/5/6 were associated with lower overall survival (OS) and high transcription levels of XRCC1/2/3/6 were correlated with poor disease-free survival (DFS) in HCC patients. Furthermore, Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) demonstrated the possible mechanisms of XRCCs and their associated genes participating in the oncogenesis of HCC. Our findings systematically elucidate the expression profiles and distinct prognostic values of XRCCs in HCC, which might provide promising therapeutic targets and novel prognostic biomarkers for HCC patients.

Influence of XRCC4 expression by breast cancer cells on ipsilateral recurrence after breast-conserving therapy

BACKGROUND

We examined the expression of nonhomologous end-joining (NHEJ) proteins by breast cancer cells in patients with or without ipsilateral breast tumor recurrence (IBTR) after breast-conserving therapy. We also investigated whether there was a difference of NHEJ-related protein expression by tumor cells between two types of IBTR, i.e., true recurrence (TR) with regrowth from the tumor bed or development of a new primary tumor (NP).

PATIENTS AND METHODS

The original cohort comprised 560 breast cancer patients who received breast-conserving therapy between February 1995 and March 2006, including 520 patients without IBTR and 40 patients with IBTR. Propensity score matching was employed to select 40 trios (120 patients) consisting of 1 patient with IBTR and 2 patients without IBTR. Immunohistochemical examination of proteins related to NHEJ was performed in surgical specimens.

RESULTS

The 40 patients with IBTR included 22 patients who developed TR and 18 who had NP. The 15-year overall survival rate was 85.9% for patients with NP and 95.5% for those with TR, while it was 96.5% for patients without IBTR. Patients with high XRCC4 expression in tumor cells had significantly higher IBTR rates than those with low XRCC4 expression (P < 0.001). The frequency of TR was significantly higher in patients with high expression of XRCC4 than in those with low XRCC4 expression (p < 0.001). XRCC4 expression by tumor cells was not significantly related to development of NP.

CONCLUSION

IBTR due to TR may be related to low radiosensitivity of tumor cells, possibly related to high XRCC4 expression.

Silencing of XRCC4 increases radiosensitivity of triple-negative breast cancer cells

Background: Radiotherapy is an important locoregional treatment, and its effect on triple-negative breast cancer (TNBC) needs to be enhanced. The aim of the present study was to investigate the potential effects of XRCC4 on radiosensitivity of TNBC. Methods: The RNAi technique was implemented to establish the TNBC stable cell line with XRCC4 knockdown. MTT assay was used to detect the effect of XRCC4 knockdown on cell proliferation. Western blot and immunohistochemistry assays were employed to identify protein expression. Colony assay was performed to detect the effect of XRCC4 knockdown on the colony formation ability of TNBC cells with radiation treatment. Comet assay was conducted to evaluate the influence of XRCC4 silencing on DNA repair activity in ionizing radiation. In addition, we performed a survival analysis based on data in TCGA database. Results: XRCC4 knockdown by lentivirus-mediated shRNA had no significant effect on proliferation of TNBC cells. Knockdown of XRCC4 could substantially increase the sensitivity of TNBC cells to ionizing radiation. The DNA damage level was detected to be increased in the XRCC4 knockdown group, indicating there was a significant repair delay in the XRCC4-deleted cells. Clinical sample analysis exhibited that there were various XRCC4 expression in different patients with TNBC. Moreover, survival analysis showed that high expression of XRCC4 was significantly associated with poor progression-free survival after radiotherapy in TNBC patients. Conclusion: Our findings suggest that XRCC4 knockdown sensitizes TNBC cells to ionizing radiation, and could be considered as a novel predictor of radiosensitivity and a promising target for TNBC.

Caspase-mediated cleavage of X-ray repair cross-complementing group 4 promotes apoptosis by enhancing nuclear translocation of caspase-activated DNase

X-ray repair cross-complementing group 4 (XRCC4), a repair protein for DNA double-strand breaks, is cleaved by caspases during apoptosis. In this study, we examined the role of XRCC4 in apoptosis. Cell lines, derived from XRCC4-deficient M10 mouse lymphoma cells and stably expressing wild-type XRCC4 or caspase-resistant XRCC4, were established and treated with staurosporine (STS) to induce apoptosis. In STS-induced apoptosis, expression of wild-type, but not caspase-resistant, XRCC4 in XRCC4-deficient cells enhanced oligonucleosomal DNA fragmentation and the appearance of TUNEL-positive cells by promoting nuclear translocation of caspase-activated DNase (CAD), a major nuclease for oligonucleosomal DNA fragmentation. CAD activity is reportedly regulated by the ratio of two inhibitor of CAD (ICAD) splice variants, ICAD-L and ICAD-S mRNA, which, respectively, produce proteins with and without the ability to transport CAD into the nucleus. The XRCC4-dependent promotion of nuclear import of CAD in STS-treated cells was associated with reduction of ICAD-S mRNA and protein, and enhancement of phosphorylation and nuclear import of serine/arginine-rich splicing factor (SRSF) 1. These XRCC4-dependent, apoptosis-enhancing effects were canceled by depletion of SRSF1 or SR protein kinase (SRPK) 1. In addition, overexpression of SRSF1 in XRCC4-deficient cells restored the normal level of apoptosis, suggesting that SRSF1 functions downstream of XRCC4 in activating CAD. This XRCC4-dependent, SRPK1/SRSF1-mediated regulatory mechanism was conserved in apoptosis in Jurkat human leukemia cells triggered by STS, and by two widely used anti-cancer agents, Paclitaxel and Vincristine. These data imply that the level of XRCC4 expression could be used to predict the effects of apoptosis-inducing drugs in cancer treatment.

Prognostic significance of XRCC4 expression in hepatocellular carcinoma

Background

Our previous investigations have shown that the variants of X-ray repair complementing 4 (XRCC4) may be involved in hepatocellular carcinoma (hepatocarcinoma) tumorigenesis. This study aimed to investigate the possible prognostic significance of XRCC4 expression for hepatocarcinoma patients and possible value for the selection of transarterial chemoembolization (TACE) treatment.

Materials and Methods

We conducted a hospital-based retrospective analysis (including 421 hepatocarcinoma cases) to analyze the effects of XRCC4 on hepatocarcinoma prognosis and TACE. The levels of XRCC4 expression were tested using immunohistochemistry. The sensitivity of cancer cells to anti-cancer drug doxorubicin was evaluated using the half-maximal inhibitory concentration (IC50).

Results

XRCC4 expression was significantly correlated with pathological features including tumor stage, liver cirrhosis, and micro-vessel density. XRCC4 expression was an independent prognostic factor of hepatocarcinoma, and TACE treatments had no effects on prognosis of hepatocarcinoma patients with high XRCC4 expression. More intriguingly, TACE improved the prognosis of hepatocarcinoma patients with low XRCC4 expression. Functionally, XRCC4 overexpression increased while XRCC4 knockdown reduced the IC50 of cancer cells to doxorubicin.

Conclusions

These results suggest that XRCC4 may be an independent prognostic factor for hepatocarcinoma patients, and that decreasing XRCC4 expression may be beneficial for post-operative adjuvant TACE treatment in hepatocarcinoma.