XRCC3 depletion induces spontaneous DNA breaks and p53-dependent cell death

AR expression-independent XRCC3 mediates DNA damage-induced p53/Bax signaling pathway activation against prostate cancer

BACKGROUND

Androgen deprivation therapy (ADT) resistance is closely associated with altered AR status. Aberrant AR expression is critical for the induction of ADT resistance, necessitating the identification of an anti-PCa target independent of AR expression.

METHODS

Transcriptomic data and clinical information of PRAD were obtained from TCGA database. Genes with PCa-related and AR expression-independent were screened by bioinformatics, and characterized by PPI and GO functional enrichment analyses. Candidate genes were locked by co-expression correlation and disease-free survival (DFS) analyses. A prognostic gene set was established using LASSO Cox regression algorithm. Cox proportional risk regression was performed to identify a key prognostic gene. Expression of the target protein in PCa tissues was verified by The Human Protein Atlas database. In vitro validation of cellular function and molecular mechanism by knockdown and overexpression of the target gene.

RESULTS

Two AR expression-independent genes (SLC43A1 and XRCC3) were available for the optimal prognostic model. This gene set effectively predicted PRAD patients' DFS at 1-, 3- and 5-year, where XRCC3 and tumor (T) stage were independent risk factors. XRCC3 was higher expressed in PRAD patients with T3-T4 stages and accompanied by poorer DFS. IHC staining also validated its higher expression in high-risk PCa tissues. In vitro experiments demonstrated that silencing XRCC3 significantly inhibited 22Rv1 and DU145 cell proliferation, migration and invasion, while promoted apoptosis. Further, silencing XRCC3 promoted DNA damage-induced p53/Bax signaling pathway activation, which was absent with overexpression.

CONCLUSION

Silencing XRCC3 exerts anti-PCa effects by promoting DNA damage-induced p53/Bax signaling pathway activation in an AR expression-independent manner.

BER genes expression in oral and pre-oral cancer: Combinatorial approach to propose potential biomarker

OBJECTIVE

DNA repair genes and their variants have been found to alter the risk of oral cancer.

METHOD

The level of expression of XRCC3, NBS1, and OGG1 genes among 20 cases of oral cancer, 6 pre-oral cancer, and 50 healthy control subjects was measured with RT-PCR. All the subjects were also genotyped for XRCC3 rs861539 C>T, NBS1 rs1805794 C>G, and OGG1 rs1052133 C>G polymorphisms by the PCR-RFLP method; their genotypes were correlated with their level of expression. Further, a localized fold structure analysis of the mRNA sequence surrounding the studied SNPs was performed with RNAfold.

RESULTS

Results showed increased expression of XRCC3, NBS1, and OGG1 transcripts among oral cancer (4.49 fold, 3.45 fold, and 3.27 fold) as well as pre-oral cancer (3.04 fold, 5.32 fold, and 1.74 fold) as compared to control subjects. The transcript level of OGG1 was found to be significantly increased (6.68 fold, p-value 0.009) with the GG genotype compared to the CC genotype. The C>T polymorphism of XRCC3 and the C>G polymorphism of OGG1 result in an apparent change in its mRNA secondary structure. Folding energy with the C allele for XRCC3 C>T polymorphism was lower than that of the T allele (MFE C vs T: -50.20 kcal/mol vs -48.70 kcal/mol). In the case of OGG1 C>G polymorphism MFE for the C allele was higher (-23.30 kcal/mole) than with the G allele (-24.80 kcal/mol).

CONCLUSION

Our results showed elevated levels of XRCC3, NBS1, and OGG1 both in oral cancer and pre-oral cancer conditions, which indicates their role as prospective biomarkers of oral cancer and pre-cancerous lesions. SNPs in these genes alter their level of expression, possibly by altering the secondary structure of their transcript. However, due to the small sample size our study can only provide a suggestive conclusion and warned future study with large sample size to verify our findings.

POGZ promotes homology-directed DNA repair in an HP1-dependent manner

The heterochromatin protein HP1 plays a central role in the maintenance of genome stability but little is known about how HP1 is controlled. Here, we show that the zinc finger protein POGZ promotes the presence of HP1 at DNA double-strand breaks (DSBs) in human cells. POGZ depletion delays the resolution of DSBs and sensitizes cells to different DNA-damaging agents, including cisplatin and talazoparib. Mechanistically, POGZ promotes homology-directed DNA repair by retaining the BRCA1/BARD1 complex at DSBs in an HP1-dependent manner. In vivo CRISPR inactivation of Pogz is embryonically lethal. Pogz haploinsufficiency (Pogz+ /delta) results in developmental delay, impaired intellectual abilities, hyperactive behaviour and a compromised humoral immune response in mice, recapitulating the main clinical features of the White Sutton syndrome (WHSUS). Pogz+ /delta mice are further radiosensitive and accumulate DSBs in diverse tissues, including the spleen and brain. Altogether, our findings identify POGZ as an important player in homology-directed DNA repair both in vitro and in vivo.

pATM and γH2AX are effective radiation biomarkers in assessing the radiosensitivity of 12C6+ in human tumor cells

Background

Tumour radiosensitivity would be particularly useful in optimizing the radiation dose during radiotherapy. The aim of the current study was to evaluate the potential value of phosphorylated H2AX (γH2AX) and ATM (pATM) in assessing ¹²C⁶⁺ radiosensitivity of tumour cells.

Methods

Human cervical carcinoma HeLa cells, hepatoma HepG2 cells, and mucoepidermoid carcinoma MEC-1 cells were irradiated with different doses of ¹²C⁶⁺. The survival fraction was assayed with clonogenic survival method and the foci of γH2AX and pATM was visualized using immunocytochemical methods. Flow cytometry was used to assay γH2AX, pATM and the cell cycle.

Results

The survival fraction decreased immediately in dose-dependent manner, but in turn, significantly increased during 24 h after ¹²C⁶⁺ irradiation. Both γH2AX and pATM foci accumulated linearly with doses and with a maximum induction at 0.5 h for γH2AX and 0.5 or 4 h for pATM, respectively, and a fraction foci kept for 24 h. The expression of γH2AX and pATM was in relation to cell cycle. The G0/G1 phase cells had the highest expression of γH2AX after 0.5 h irradiation and then decreased to a lower level at 24 h after irradiation. An obvious increase of pATM in G2/M phase was shown after 24 h of 2 and 4 Gy irradiation. The significant G2/M phase arrest was shown. There was a close relationship between the clonogenic survival and γH2AX and pATM expression both in timing and dose in response to ¹²C⁶⁺.

Conclusions

The rate of γH2AX and pATM formation and loss may be an important factor in the response of cells to ¹²C⁶⁺. pATM and γH2AX are effective radiation biomarkers in assessing the radiosensitivity of ¹²C⁶⁺ in human tumor cells.

XRCC3 is a promising target to improve the radiotherapy effect of esophageal squamous cell carcinoma

Radiotherapy is widely applied for treatment of esophageal squamous cell carcinoma (ESCC). The Rad51-related protein XRCC3 plays roles in the recombinational repair of DNA double-strand breaks to maintain chromosome stability and repair DNA damage. The present study aimed to investigate the effect of XRCC3 on the radiotherapy response of ESCC and the underlying mechanisms of the roles of XRCC3 in ESCC radiosensitivity. XRCC3 expression in ESCC cells and tissues was higher than that in normal esophageal epithelial cells and corresponding adjacent noncancerous esophageal tissue. High XRCC3 expression was positively correlated with resistance to chemoradiotherapy in ESCC and an independent predictor for short disease-specific survival of ESCC patients. Furthermore, the therapeutic efficacy of radiotherapy in vitro and in vivo was substantially increased by knockdown of XRCC3 in ESCC cells. Ectopic overexpression of XRCC3 in both XRCC3-silenced ESCC cells dramatically enhanced ESCC cells' resistance to radiotherapy. Moreover, radiation resistance conferred by XRCC3 was attributed to enhancement of homologous recombination, maintenance of telomere stability, and a reduction of ESCC cell death by radiation-induced apoptosis and mitotic catastrophe. Our data suggest that XRCC3 protects ESCC cells from ionizing radiation-induced death by promoting DNA damage repair and/or enhancing telomere stability. XRCC3 may be a novel radiosensitivity predictor and promising therapeutic target for ESCC.

Induction of H2AX phosphorylation in tumor cells by gossypol acetic acid is mediated by phosphatidylinositol 3-kinase (PI3K) family

BACKGROUND

H2AX is phosphorylated (γH2AX) by members of the phosphatidylinositol 3-kinase (PI3K) family, including Ataxia telangiectasia-mutated (ATM), ATM- and Rad3-related (ATR) and DNA-PK in response to DNA damage. Our study shows that gossypol acetic acid (GAA) alone can induce γH2AX in Human mucoepidermoid carcinoma cell line (MEC-1) in vitro. Thus, we further examined the possible mechanisms of GAA to induce γH2AX in tumor cells.

MATERIALS AND METHODS

The PI3K inhibitors caffeine and wortmannin were used in an effort to identify the kinase(s) responsible for GAA -induced γH2AX in MEC-1 cells. DNA dependent protein kinase (DNA-PK) - proficient and -deficient cells, human glioma cell lines M059K and M059J, were also used to evaluate the kinases responsible for GAA induced H2AX phosphorylation. γH2AX expression was detected by immunofluorescent microscopy. Flow cytometry assay was used to assay γH2AX and cell cycle.

RESULTS

GAA induced H2AX phosphorylation in a cell cycle-dependent manner and a significant G0/G1 phase arrest in MEC-1 cells was shown. Caffeine and wortmannin significantly inhibited GAA-induced H2AX phosphorylation in MEC-1 cells. GAA induced H2AX phosphorylation in M059K, but not in M059J. Taken together, these data suggested that GAA treatment alone could induce H2AX phosphorylation in a cell cycle dependent manner in MEC-1 and M059K, but not in M059J cells. A significant G0/G1 phase arrest was shown in MEC-1.

CONCLUSIONS

The member of PI3K family, DNA-PK, ATM and ATR are involved in the H2AX phosphorylation of MEC-1 cells.

XRCC3 and RAD51 expression are associated with clinical factors in breast cancer

AIMS

XRCC3 and RAD51 are two important members in homologous recombination repair pathway. This study was performed to detect the expressions of these two molecules in breast cancer and explore their correlations with clinicopathological factors.

METHODS AND RESULTS

Immunohistochemistry was used to detect protein expressions of XRCC3 and RAD51 in 248 cases of breast cancer tissue and 78 cases of adjacent non-cancerous tissue. Data showed that expressions for both XRCC3 and RAD51 were significantly increased in breast cancer. High XRCC3 expression was associated with large tumor size and positive PR and HER2 status, while high RAD51 expression was associated with axillary lymph node metastasis and positive PR and HER2 status. The result of multivariate analysis demonstrated that HER2, PR and RAD51 were significantly association with XRCC3. And besides XRCC3, axillary lymph node metastasis and PR were significantly correlated with RAD51.

CONCLUSIONS

XRCC3 and RAD51 were significantly associated with clinicopathological factors and they might play important roles in the development and progress of breast cancer.

Effects of the novel DNA dependent protein kinase inhibitor, IC486241, on the DNA damage response to doxorubicin and cisplatin in breast cancer cells

The purpose of this study was to determine the degree to which the novel DNA-PKcs inhibitor, IC486241 (ICC), synergizes the cytotoxicity of DNA damaging agents in 3 genetically diverse breast cancer cell lines. The sulforhodamine B (SRB) assay was employed as a primary screening method to determine the in-vitro cytotoxicity and the degree of synergy of ICC in combination with the topoisomerase II inhibitor, doxorubicin, or the DNA cross linking agent, cisplatin. Molecular mechanisms underlying drug toxicity were probed using immunostaining and flow cytometry, as well as, the alkaline comet assay to detect DNA damage. In this study, improved cytotoxicity and significant synergy were observed with both anticancer agents in the presence of nontoxic concentrations of ICC. Moreover, ICC decreased doxorubicin-induced DNA-PKcs autophosphorylation on Ser2056 and increased doxorubicin-induced DNA fragmentation. In conclusion, the novel DNA-PKcs inhibitor, ICC, synergistically sensitized 3 breast cancer cell lines to doxorubicin and cisplatin. Enhanced efficacy of doxorubicin was achieved by inhibiting non-homologous end joining resulting in increased accumulation of DNA damage.

Dual inhibition of the homologous recombinational repair and the nonhomologous end-joining repair pathways in chronic lymphocytic leukemia therapy

Resistance to chlorambucil in chronic lymphocytic leukemia (CLL) has been associated with increased DNA repair. Specifically, inhibition of either c-abl, which modulates Rad51 directed homologous recombination or DNA-PK dependent nonhomologous end joining has been shown to sensitize primary CLL lymphocytes to chlorambucil. Here we report that inhibition of c-abl can result in a compensatory increase in DNA-PK and thus inhibition of both c-abl and DNA-PK optimally sensitizes CLL lymphocytes to chlorambucil. In this paper we report a drug-induced compensatory change between two DNA repair pathways with potential therapeutic implications in CLL therapy.

The effect of a DNA repair gene on cellular invasiveness: XRCC3 over-expression in breast cancer cells

Over-expression of DNA repair genes has been associated with resistance to radiation and DNA-damage induced by chemotherapeutic agents such as cisplatin. More recently, based on the analysis of genome expression profiling, it was proposed that over-expression of DNA repair genes enhances the invasive behaviour of tumour cells. In this study we present experimental evidence utilizing functional assays to test this hypothesis. We assessed the effect of the DNA repair proteins known as X-ray complementing protein 3 (XRCC3) and RAD51, to the invasive behavior of the MCF-7 luminal epithelial-like and BT20 basal-like triple negative human breast cancer cell lines. We report that stable or transient over-expression of XRCC3 but not RAD51 increased invasiveness in both cell lines in vitro. Moreover, XRCC3 over-expressing MCF-7 cells also showed a higher tumorigenesis in vivo and this phenotype was associated with increased activity of the metalloproteinase MMP-9 and the expression of known modulators of cell-cell adhesion and metastasis such as CD44, ID-1, DDR1 and TFF1. Our results suggest that in addition to its' role in facilitating repair of DNA damage, XRCC3 affects invasiveness of breast cancer cell lines and the expression of genes associated with cell adhesion and invasion.

The level of oxidative stress and the expression of genes involved in DNA-damage signaling pathways in depressive patients with colorectal carcinoma

OBJECTIVES

This study investigated the connection among the oxidative stress, depression and expression of specific genes involved in DNA-damage signaling pathways in patients with colorectal carcinoma (CRC).

METHODS

A unique Dukes'C subset of patients with newly diagnosed colorectal adenocarcinoma were assessed using the Hamilton Depression Rating Scale (HAMD), Zung Self-rating Depression Scale (SDS), Zung Self-rating Anxiety Scale (SAS), Symptom Checklist 90 (SCL-90) and other multiple-item questionnaires. Oxidative-stress-related parameters in sera and the expression of genes were monitored during a pretreatment period.

RESULTS

Eighty-two eligibility cases were divided into 2 groups based on an HAMD score cutoff of 20: the mean score was 28.29 in Group A (depression, n=52) and 16.50 in Group B (nondepression, n=30). The serum total antioxidant capacity, catalase, and superoxide dismutase concentrations were lower in Group A, whereas those of nitric oxide and malondialdehyde were higher in Group A. Importantly, the 8-hydroxy-deoxyguanosine level was higher in Group A than in Group B (P<.05). Microarray analysis revealed that the expressions of p34, PA26, and ABL were higher in Group A, whereas those of HRAD51, CR6, and XRCC3 were higher in Group B.

CONCLUSION

Oxidative stress is capable of causing neuronal toxicity via lipid peroxidation, DNA damage, and abnormalities of gene expression, and therefore is a possible pathogenic mechanism underlying depression in patients with CRC.

Dasatinib sensitizes primary chronic lymphocytic leukaemia lymphocytes to chlorambucil and fludarabine in vitro

The dual c-abl/Src kinase inhibitor, dasatinib, utilized to treat chronic myeloid leukaemia (CML) when used at clinically attainable sublethal concentrations, synergistically sensitized primary chronic lymphocytic leukaemia (CLL) lymphocytes to chlorambucil and fludarabine. In contrast, dasatinib alone demonstrated toxicity to CLL lymphocytes at concentrations that are generally not clinically attainable. Dasatinib resistance and poorer dasatinib-mediated sensitization to chlorambucil and fludarabine was associated with higher expression of c-abl protein levels. In contrast, chlorambucil and fludarabine resistance correlated with basal p53 protein levels. Moreover, Western blot analysis after in vitro treatment of primary CLL lymphocytes with dasatinib, chlorambucil and/or fludarabine, showed that dasatinib: (i) inhibited c-abl function (e.g. downregulation of c-abl protein levels and decreased the phosphorylation of a c-abl downstream target, Dok2), (ii) decreased chlorambucil/fludarabine induced accumulation of p53 protein levels, (iii) altered the response to chlorambucil/fludarabine induced DNA-damage as evidenced by an increase in chlorambucil/fludarabine-induced H2AX phosphorylation, and (iv) accentuated the c-abl downregulation induced by chlorambucil/fludarabine. Our results suggest that dasatinib in combination with chlorambucil or fludarabine may improve the therapy of CLL.