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DNA is the hereditary material in humans and almost all other organisms. It is essential for maintaining accurate transmission of genetic information. In the life cycle, DNA replication, cell division, or genome damage, including that caused by endogenous and exogenous agents, may cause DNA aberrations. Of all forms of DNA damage, DNA double-strand breaks (DSBs) are the most serious. If the repair function is defective, DNA damage may cause gene mutation, genome instability, and cell chromosome loss, which in turn can even lead to tumorigenesis. DNA damage can be repaired through multiple mechanisms. Homologous recombination (HR) and non-homologous end joining (NHEJ) are the two main repair mechanisms for DNA DSBs. Increasing amounts of evidence reveal that protein modifications play an essential role in DNA damage repair. Protein deubiquitination is a vital post-translational modification which removes ubiquitin molecules or polyubiquitinated chains from substrates in order to reverse the ubiquitination reaction. This review discusses the role of deubiquitinating enzymes (DUBs) in repairing DNA DSBs. Exploring the molecular mechanisms of DUB regulation in DSB repair will provide new insights to combat human diseases and develop novel therapeutic approaches.
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Objective:To clarify the role of classic Wnt signaling pathway in the radioresistance of esophageal cancer cells (ECC), and investigate the underlying mechanism, aiming to identify critical molecular targets for clinically enhancing the radiosensitivity of esophageal cancer.Methods:The radiosensitivity of four types of ECCs (EC9706, ECA109, KYSE70 and KYSE150) were assessed by colony formation assay. Western blot and RT-PCR were used to detect the activation of classical Wnt signaling pathway after irradiation. Classic Wnt signaling pathway activator (AZD2858) and inhibitor (XAV-939) were utilized to comprehensively evaluate the effect of classic Wnt signaling pathway on the radiosensitivity of ECCs. Cellular immunofluorescence staining was performed to detect the production and repair of DNA double-strand breaks (DSB), as well as the foci formation of DSB repair proteins after irradiation.Results:The results of colony formation assay showed that the radiosensitivity of four types of ECCs from high to low was EC9706, ECA109, KYSE70 and KYSE150. In KYSE150, a radioresistant cell type, the level of nuclear β-catenin and the transcription of c-Myc gene were significantly increased after irradiation (both P<0.05). However, in EC9706, a radiosensitive cell type, the level of nuclear β-catenin and c-Myc gene transcription were not affected by irradiation (both P>0.05). Moreover, EC9706 cells showed enhanced radioresistance in the presence of AZD2858( P<0.05), whereas XAV-939 treatment decreased the radioresistance in KYSE150 cells ( P<0.05). AZD2858 accelerated the DSB repair in EC9706 cells ( P<0.05), whereas XAV-939 delayed the DSB repair in KYSE150 cells ( P<0.05). Furthermore, the results of immunofluorescence staining showed that XAV-939 reduced the DSB repair capacity by inhibiting homologous recombination repair-related proteins (BRCA1 and RAD51) rather than non-homologous end junction repair-related proteins (Ku80 and XRCC4). Conclusions:The classic Wnt signaling pathway participates in the regulation of radiosensitivity in ECCs by regulating the homologous recombination repair of DSB after irradiation. Inhibition of the classic Wnt signaling pathway can counteract the radioresistance of ECCs and enhance the killing effect of irradiation on ECCs.
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Applying poly(ADP-ribose) polymerase inhibitors (PARPi) to the treatment of cancers with homologous recombination deficiency (HRDness) has been a great advance in the field of molecular therapeutics. However, in the clinic patients lacking the specific mutations or developing reverse mutations in the process of PARPi treatment may not benefit from PARPi monotherapy. Therefore, targeting homologous recombination (HR) repair with molecularly targeted agents is becoming an attractive research focus and is raising the concept of "chemical HRDness". HR repair is an evolutionarily conserved and extensively regulated process that employs sister chromatids as the template to repair DNA double-strand breaks with high fidelity. In addition to directly targeting HR components, modulation of regulatory pathways controlling HR repair is effective in achieving the "HRDness" phenotype; this includes modulation of the cell cycle checkpoint regulatory pathway, the phosphatidylinositol 3-kinase (PI3K) signaling pathway, the chromatin remodeling pathway, etc. Targeting HR repair can not only result in "synthetic lethality" when combined with PARPi, but also sensitizes cancers to traditional radio/chemotherapy and novel immunotherapy. In this review we describe the HR repair pathway and its regulatory pathways, summarize the preclinical and clinical outcomes of targeting HR repair, discuss the remaining problems in this field and provide a prospective on its application in tumor therapy.
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The small ubiquitin-like modified protein (SUMO) is a protein structurally similar to ubiquitin which is involved in post-translational modification of proteins. SUMOylation refers to the process that SUMO molecule covalently binding to the specific lysine site of target proteins through maturation, activation, binding and ligation by ubiquitin-like specific protease 1 (Ulp1), E1 activating enzyme, E2 binding enzyme, and E3 ligase. SUMOylation alters the activity of target proteins, which is involved in the regulation of various cellular functions such as transcriptional regulation, regulation of embryonic development, cellular stress, maintenance of chromatin structure and genomic stability. In recent years, it has been found that SUMOylation modification is also widely involved in DNA damage repair, especially DNA double-strand breaks (DSBs), which are the most serious types of DNA damage. SUMOylation is involved in almost all processes of DSBs repair, so its role in DNA damage repair has become a research hotspot. In this paper, the research progress of the regulation of SUMOylation in DSBs repair was reviewed.
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Aim To explore the relationship between Mre11/Rad50/Nbs1 ( MRN ) complex focus formation and DNA double-strand breaks( DSBs) caused by cinob-ufagin in human hepatocellular carcinoma HepG2 cells. Methods The Na+,K+-ATPaseα1 subunit expression level in liver cancer tissues was detected by immunohis-tochemistry. After HepG2 cells were treated with 5μmol·L-1 cinobufagin for 6, 12 and 24 h, the drug-in-duced DSBs were assessed by single cell gel electro-phroesis ( SCGE ) , the gene transcription and protein levels of Mrel1, Nbs1, Rad50 and p53 were evaluated by Real time-PCR and Western blot. The cell cycle in parallel was analyzed by flow cytometry. Results The Na+, K+-ATPase α1 subunit expression level in liver cancer tissues was significantly increased compared with the tissue adjacent to carcinoma ( P <0. 05 ) . The 5μmol · L-1 cinobufagin could induce the DSBs in a time-dependent manner (P <0. 05), and it could up-regulate the gene expression levels of Mre11, Nbs1, Rad50 and p53 in HepG2 cells ( P<0. 05 ) . The pro-portions of HepG2 cells in S phase were ( 21. 32 ± 4. 21) % in the control group, and (33. 25 ± 5. 72) %, (56. 72 ± 6. 29) % and (67. 32 ± 9. 42) % in HepG2 cells treated with 5 μmol · L-1 cinobufagin for 6, 12 and 24 h, respectively. The proportions of cells in S phase in cinobufagin groups were significantly increased compared with the control group ( P<0. 05 ) . Conclu-sion Cinobufagin could induce the cell cycle arrest in liver cancer HepG2 cells by activation of Mre11/Rad50/Nbs1 Complex.
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Hormesis is an adaptive response to a variety of oxidative stresses that renders cells resistant to harmful doses of stressing agents. Caffeic acid (CaA) is an important antioxidant that has protective effects against DNA damage caused by reactive oxygen species (ROS). However, whether CaA-induced protection is a hormetic effect remains unknown, as is the molecular mechanism that is involved. We found that a low concentration (10 μM) of CaA increased human liver L-02 cell viability, attenuated hydrogen peroxide (H2O2)-mediated decreases in cell viability, and decreased the extent of H2O2-induced DNA double-strand breaks (DSBs). In L-02 cells exposed to H2O2, CaA treatment reduced ROS levels, which might have played a protective role. CaA also activated the extracellular signal-regulated kinase (ERK) signal pathway in a time-dependent manner. Inhibition of ERK by its inhibitor U0126 or by its specific small interfering RNA (siRNA) blocked the CaA-induced improvement in cell viability and the protective effects against H2O2-mediated DNA damage. This study adds to the understanding of the antioxidant effects of CaA by identifying a novel molecular mechanism of enhanced cell viability and protection against DNA damage.
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Humans , Antioxidants/pharmacology , Caffeic Acids/pharmacology , Cell Survival/drug effects , DNA Damage/drug effects , Extracellular Signal-Regulated MAP Kinases/drug effects , Reactive Oxygen Species/analysis , Analysis of Variance , Blotting, Western , Cells, Cultured , Cell Line/drug effects , Extracellular Signal-Regulated MAP Kinases/antagonists & inhibitors , Liver , Oxidative Stress/drug effects , Reproducibility of Results , Time FactorsABSTRACT
Whether nucleic acids that circulate in blood have any patho-physiological functions in the host have not been explored. We report here that far from being inert molecules, circulating nucleic acids have significant biological activities of their own that are deleterious to healthy cells of the body. Fragmented DNA and chromatin (DNAfs and Cfs) isolated from blood of cancer patients and healthy volunteers are readily taken up by a variety of cells in culture to be localized in their nuclei within a few minutes. The intra-nuclear DNAfs and Cfs associate themselves with host cell chromosomes to evoke a cellular DNAdamage- repair-response (DDR) followed by their incorporation into the host cell genomes. Whole genome sequencing detected the presence of tens of thousands of human sequence reads in the recipient mouse cells. Genomic incorporation of DNAfs and Cfs leads to dsDNA breaks and activation of apoptotic pathways in the treated cells. When injected intravenously into Balb/C mice, DNAfs and Cfs undergo genomic integration into cells of their vital organs resulting in activation of DDR and apoptotic proteins in the recipient cells. Cfs have significantly greater activity than DNAfs with respect to all parameters examined, while both DNAfs and Cfs isolated from cancer patients are more active than those from normal volunteers. All the above pathological actions of DNAfs and Cfs described above can be abrogated by concurrent treatment with DNase I and/or anti-histone antibody complexed nanoparticles both in vitro and in vivo. Taken together, our results suggest that circulating DNAfs and Cfs are physiological, continuously arising, endogenous DNA damaging agents with implications for ageing and a multitude of human pathologies including initiation of cancer.
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AIM:To discover the effect of MCPH1 on the DNA damage induced by ionizing radiation in esoph-ageal cancer cells.METHODS:ECA109 cancer cells were radiated at dose of 8 Gy.The nuclear foci of relevant factors were detected 1 h after irradiation in the ECA109 cells after silence of MDC1 gene.A cell line was established that was sta-ble low expression of MCPH1.The nuclear foci induced by ionizing radiation after silence of MCPH1 were determined.RE-SULTS:The MCPH1 gene silenced ECA109 cell line was successfully constructed.A strong relationship between MDC1, MCPH1 andγ-H2AX was observed 1 h after 8 Gy irradiation.Silence of MDC1 did not affect the nuclear foci formation ofγ-H2AX and MCPH1.The nuclear foci of MDC1 but notγ-H2AX significantly reduced after silencing of MCPH1.CON-CLUSION:MCPH1 is located in the downstream of H2AX and upstream formation of MDC1, and regulates the nuclear fo-ci formation of MDC1 during DNA damage response.
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DNA damage response (DDR) in different cell cycle starus of human peripheral blood lymphocytes (PBLs) and the role of H2AX in DDR were investigated.The PBLs were stimulated into cell cycle with phytohemagglutinin (PHA).The apoptotic ratio and the phosphorylation H2AX (S139)were flow cytometrically measured in resting and proliferating PBLs after treatment with camptothecin (CPT) or X-ray.The expressions of γH2AX,Bcl-2,caspase-3 and caspase-9 were detected by Western blotting.DDR in 293T cells was detected after H2AX was silenced by RNAi method.Our results showed that DNA double strand breaks (DSBs) were both induced in quiescent and proliferating PBLs after CPT or X-ray treatment.The phosphorylation of H2AX and apoptosis were more sensitive in proliferating PBLs compared with quiescent lymphocytes (P＜0.05).The expression levels of anti-apoptotic proteins Bcl-2 were reduced and cleaved caspase-3 and caspase-9 were increased.No significant changes were observed in CPT-induced apoptosis in 293T cells between H2AX knocking down group and controls.It was concluded that proliferating PBLs were more vulnerable to DNA damage compared to non-stimulated lymphocytes and had higher apoptosis rates.γH2AX may only serve as a marker of DNA damage but exert no effect on apoptosis regulation.
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The present study investigated the enhanced radiosensitivity of U-251 cells induced by sodium butyrate (NaB) and its possible mechanisms.Increased radiosensitivity of U251 cells was examined by clonogenic cell survival assays.The expression of Ku70 mRNA and protein was detected by using RT-PCR and Western blotting respectively.γ-H2AX foci were measured at different time points after ionizing irradiation alone or combined with NaB treatment.The results showed that cell survival rate was significantly reduced,both D0 and Dq values were decreased (D0:1.43 Gy vs.1.76 Gy; Dq:1.22 Gy vs.2.05 Gy) after the combined treatment as compared with irradiation alone,and sensitivity enhancing ratio (SER) reached 1.23.The average number ofγ-H2AX foci per cell receiving the combined treatment was significantly increased at different time points,and the expression levels of Ku70mRNA and protein were suppressed by NaB in a dose-dependent manner.It was concluded that enhanced radiosensitivity induced by NaB involves an inhibited expression of Ku70 and an increase in γ-H2AX foci,which suggests decreased ability in DSB repair.
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Hepatitis B virus (HBV)-induced hepatocellular carcinoma (HCC) is one of the most frequently occurring cancers. Hepadnaviral DNA integrations are considered to be essential agents which can promote the process of the hepatocarcinogenesis. More and more researches were designed to find the relationship of the two. In this study, we investigated whether HBV DNA integration occurred at sites of DNA double-strand breaks (DSBs), one of the most detrimental DNA damage. An 18-bp I-SceI homing endonuclease recognition site was introduced into the DNA of HepG2 cell line by stable DNA transfection, then cells were incubated in patients' serum with high HBV DNA copies and at the same time, DSBs were induced by transient expression of I-SceI after transfection of an I-SceI expression vector. By using nest PCR, the viral DNA was detected at the sites of the break. It appeared that integration occurred between part of HBV x gene and the I-Scel induced breaks. The results suggested that DSBs, as the DNA damages, may serve as potential targets for bepadnaviral DNA insertion and the integrants would lead to widespread host genome changes necessarily. It provided a new site to investigate the integration.
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DNA double-strand breaks (DSBs) are a serious threat to the cell, for if not or miss-repaired, they can lead to chromosomal aberration, mutation and cancer. DSBs in human cells are repaired via non-homologous DNA end joining (NHEJ) and homologous recombination repair pathways. In the former process, the structure of DNA termini plays an important role, as does the genetic constitution of the cells, through being different in normal and pathological cells. In order to investigate the dependence of NHEJ on DSB structure in normal and cancer cells, we used linearized plasmids with various, complementary or non-complementary, single-stranded or blunt DNA termini, as well as whole-cell extract isolated from normal human lymphocytes, chronic myeloid leukemia K562 cells and lung cancer A549 cells. We observed a pronounced variability in the efficacy of NHEJ reaction depending on the type of ends. Plasmids with complementary and blunt termini were more efficiently repaired than the substrate with 3' protruding single-strand ends. The hierarchy of the effectiveness of NHEJ was on average, from the most effective to the least, A549/ normal lymphocytes/ K562. Our results suggest that the genetic constitution of the cells together with the substrate terminal structure may contribute to the efficacy of the NHEJ reaction. This should be taken into account on considering its applicability in cancer chemo-or radiotherapy by pharmacologically modulating NHEJ cellular responses.
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Objective To investigate ff the γ-H12AX foci is a precise index for the DSB formation and repair in mature neurons of brain in vivo after clinically relevant doses irradiation. Methods For the DSB formation experiment, the mature neurons in the neocortex of brain tissue of C57BL/6 mice were analyzed at 10 rain after whole-body irradiation with 0.1, 0.5 and 1.0 Gy. For the DSB repair kinetics experiment, the mature neurons in the neocortex of brain tissue of repair-proficient (C57BL/6 mice) and repair-deficient mouse strains (BALB/c, A-T and SCID mice) were analyzed at 0.5, 2.5, 5, 24 and 48 h after whole-body irradiation with 2 Gy. The mature neurons in the neocortex of brain tissue of sham-irradiated mice of each strain served as controls. γ-H2AX immunohistochemistry and γ-H2AX and NeuN double immunofluorescence analysis was used to measure DSBs formation and repair in the mature neurons in the neocortex of brain tissue of the different mouse strains. Results For the DSB formation experiment, γ-H2AX foci levels with a clear linear dose correlation and very low backgrounds in the nuclei in the neocortex of brain tissue were observed. Scoring the loss of γ-H12AX foci allowed us to verify the different, genetically determined DSB repair deficiencies, including the minor impairment of BALB/c mice. Repair-proficient C57BL/6 mice exhibited the fastest decrease in foei number with time, and displayed low levels of residual damage at 24 h and 48 h post-irradiation. In contrast, SCID mice showed highly increased γ-H2AX foci levels at all repair times (0.5 h to 48 h) while A-T mice exhibited a lesser defect which was most significant at later repair times (≥ 5 h). Radiosensitive BALB/c mice exhibited slighdy elevated foei numbers compared with C57BI./6 mice at 5 h and 24 h but not at 48 h post-irradiation. Conclusion Quantifying the γ-H2AX loci in normal tissue represents a sensitive tool for the detection of induction and repair of radiation-induced DSBs at clinically relevant doses in vivo.
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DNA double-strand breaks (DSBs) occur commonly in the all living and in cycling cells. They constitute one of the most severe form of DNA damage, because they affect both strand of DNA. DSBs result in cell death or a genetic alterations including deletion, loss of heterozygosity, translocation, and chromosome loss. DSBs arise from endogenous sources like metabolic products and reactive oxygen, and also exogenous factors like ionizing radiation. Defective DNA DSBs can lead to toxicity and large scale sequence rearrangement that can cause cancer and promote premature aging. There are two major pathways for their repair: homologous recombination(HR) and non-homologous end-joining(NHEJ). The HR pathway is a known "error-free" repair mechanism, in which a homologous sister chromatid serves as a template. NHEJ, on the other hand, is a "error-prone" pathway, in which the two termini of the broken DNA molecule are used to form compatible ends that are directly ligated. This review aims to provide a fundamental understanding of how HR and NHEJ pathways operate, cause genome instability, and what kind of genes during the pathways are associated with head and neck cancer.
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Humans , Aging, Premature , Cell Death , Chromatids , DNA , DNA Damage , Genomic Instability , Hand , Head , Head and Neck Neoplasms , Loss of Heterozygosity , Oxygen , Radiation, Ionizing , SiblingsABSTRACT
DNA double-strand breaks (DSBs) occur commonly in the all living and in cycling cells. They constitute one of the most severe form of DNA damage, because they affect both strand of DNA. DSBs result in cell death or a genetic alterations including deletion, loss of heterozygosity, translocation, and chromosome loss. DSBs arise from endogenous sources like metabolic products and reactive oxygen, and also exogenous factors like ionizing radiation. Defective DNA DSBs can lead to toxicity and large scale sequence rearrangement that can cause cancer and promote premature aging. There are two major pathways for their repair: homologous recombination(HR) and non-homologous end-joining(NHEJ). The HR pathway is a known "error-free" repair mechanism, in which a homologous sister chromatid serves as a template. NHEJ, on the other hand, is a "error-prone" pathway, in which the two termini of the broken DNA molecule are used to form compatible ends that are directly ligated. This review aims to provide a fundamental understanding of how HR and NHEJ pathways operate, cause genome instability, and what kind of genes during the pathways are associated with head and neck cancer.
Subject(s)
Humans , Aging, Premature , Cell Death , Chromatids , DNA , DNA Damage , Genomic Instability , Hand , Head , Head and Neck Neoplasms , Loss of Heterozygosity , Oxygen , Radiation, Ionizing , SiblingsABSTRACT
Epigenetic changes are important etiological factors of human tumor. The integrity of the genome is frequently challenged by the damage of DNA. However, the highly condensed structure of chromatin imposes significant obstacles on the repair processes. Eukaryotes have developed intricate mechanisms to overcome this repressive barrier imposed by chromatin. Covalent histone modifications and ATP-dependent chromatin remodeling play important roles in the process of DNA repair. Recent advances of the epigenetic regulations in the repair process were summarized. New findings in the cellular responses to DNA double strand breaks and how histone modifications and chromatin remodeling contributes to DNA double strand break repair were introduced. Future challenges in this field are also discussed.
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Objective To analyze the dose rate effect and potentially lethal damage repair in DNA double strand break repair deficient murine cells (SCID) irradiated by ? ray. Methods The wild type(CB.17+/+) and SCID cells were exposed to ? ray at high and low dose rates. The high dose rate exposure was fractionated into two equal doses at 24?h intervals. The survival rates of irradiated cells were calculated by clony forming analysis. Results When ? ray was given to wild type(CB.17+/+) cells in two fractions at 24?h intervals, the survival rate was significantly higher than that when the same total dose was given singly. In contrast, there was no difference in the survival rates between the single and fractionated exposure in SCID cells. SCID cells were more sensitive than CB.17+/+ cells to both low and high dose rates ? ray exposure for cell killing. The survival rate by low dose rate exposure was significantly higher than that by high dose rate exposure, not only in CB.17+/+ cells but also in SCID cells. Conclusions SCID cells are deficient in repairing ? ray induced double strand breaks. There is dose rate effect in both SCID and CB.17+/+ cells.
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The evaluation of radiation-induced DNA double strand breaks(DSB) was made following irradiation of human lymphocytes, murille lymphocytes and EL-4 leukemia cells over a wide dose range of 60Co g-rays. In lipopolysacchande(LPS) or phytohemagglutinin(PHA)-stimulated murine lymphocytes, the slopes of the strand scission factor(SSF) revealed that lymphocytes with LPS increased DNA DSB formation by a factor of 1.432 (p<0.005). Furthermore, strand break production was relatively inefficient in the T lymphocytes compared to the B lymphocytes. And EL-4 leukemia cells were found to form significantly more DNA DSB to a greater extent than normal lymphocytes (p<0.705). The in vitro studies of the intrinsic radiosensitivity between human lymphocytes and murine lymphocytes showed similar phasic kinetics. However, murine lymphocytes were lower in DNA DSB formation and higher in the relative radiation dose of 10 percent DNA strand breaks at 3.5 hours following g-irradiation than human lymphocytes. Though it is difficult to interpret these results, these differences may be result from environmental and genetic factors. From our data, if complementary explanations for this difference will be proposed, the differences in the dose-effect relationship for the induction of DSB between humans and mice must be related to interspecies variations in the physiological condition of the peripheral blood in vitro and not to differences in the intrinsic radiation sensitivity of the lymphocytes. These results can be estimated on the basis of dose-effect correlation enabling the interpretation of clinical response and the radiobiological parameters of cytometrical assessment.