Role of H2AX in DNA damage response and human cancers

Overexpression of METTL3 in lung cancer cells inhibits radiation-induced bystander effect

BACKGROUND

Radiation-induced bystander effects (RIBE) increase the complexity of radiation therapy (RT). m6A modification is implicated in ionizing radiation damage. This study aims to investigate the RIBE and the mechanism after promoting m6A modification.

METHODS

Lung adenocarcinoma cells were treated to simulate a hypoxic and 0.5 Gy RT environment. The expression levels of METTL3, METTL14, and YTDHF2 were quantified by RT-qPCR. Paracellular clonogenicity and the expression of 53BP1 and γ-H2AX were assessed by immunofluorescence. The proliferative rate was evaluated by CCK-8. Probes were employed to measure ROS levels. Micronucleus formation was evaluated microscopically. m6A-mRNA/lncRNA microarrays, MERIP-PCR, RT-qPCR, and ELISA were utilized to assess m6A modification levels and the expression of inflammatory factors.

RESULTS

m6A modification levels were significantly diminished under hypoxic, low-dose irradiation conditions. The overexpression of METTL3 in irradiated cancer cells resulted in increased clonogenicity and proliferation of paracellular cells, suppressed the rate of micronucleus formation, and reduced DNA damage by modulating the inflammatory response. m6A-mRNA/lncRNA microarray analyses revealed a higher correlation of inflammatory molecules NF-κB and TRAF6. Further analysis demonstrated that the m6A modification levels of inflammation-related factors such as IL-6, TLR4, NF-κB2, and TRAF6 were significantly up-regulated, while their mRNA expression levels were notably decreased. Additionally, the expression of IL-10 and TGF-β was significantly reduced, with no significant changes observed in IL-1 expression.

CONCLUSION

The overexpression of METTL3 facilitated m6A modification and mitigated the inflammatory response, thereby promoting paracellular cloning and proliferation, inhibiting micronucleus formation, alleviating DNA damage, and achieving the objective of suppression of RIBE.

Cellular stress and epigenetic regulation in adult stem cells

Stem cells are a unique class of cells that possess the ability to differentiate and self-renew, enabling them to repair and replenish tissues. To protect and maintain the potential of stem cells, the cells and the environment surrounding these cells (stem cell niche) are highly responsive and tightly regulated. However, various stresses can affect the stem cells and their niches. These stresses are both systemic and cellular and can arise from intrinsic or extrinsic factors which would have strong implications on overall aging and certain disease states. Therefore, understanding the breadth of drivers, namely epigenetic alterations, involved in cellular stress is important for the development of interventions aimed at maintaining healthy stem cells and tissue homeostasis. In this review, we summarize published findings of epigenetic responses to replicative, oxidative, mechanical, and inflammatory stress on various types of adult stem cells.

Self-assembling peptides induced by eyes absent enzyme to boost the efficacy of doxorubicin therapy in drug-resistant breast cancer cells

Enzyme-induced self-assembly (EISA) is a recently developed nanotechnology technique in which small molecules are induced by cellular enzymes self-assembling into nanostructures inside cancer cells. This technique can boost the efficacy of chemotherapy drugs by avoiding drug efflux, inhibiting the cells' DNA repair mechanisms, and targeting the mitochondria. In this work, we study the self-assembly of a short peptide and its fluorescence analogue induced by Eyes absent (EYA) tyrosine phosphatases to boost the efficacy of doxorubicin (DOX) therapy in drug-resistant types of breast cancer cells, MDA-MB-231 and MCF-7. The peptides Fmoc-FF-YP and NBD-FF-YP were synthesized with the solid-phase peptide synthesis (SPPS) method and analyzed with HPLC and MALDI-TOF. Dynamic light scattering was used to determine the size distribution of peptides exposed to the EYA enzyme in vitro. The presence of EYA enzymes in breast cancer cells was confirmed using the western blotting assay. The intracellular location of the peptide self-assembly was studied by imaging fluorescence NBD-tagged peptides. The efficacy of the peptide alone and with DOX was determined against MCF-7 and MDA-MB-231 using MTT and LIVE-DEAD assays. Nucleus and cytoplasm F-actin (Phalloidin) staining was used to determine cell morphology changes in response to the combination therapy of peptides/DOX. At an optimal concentration, the peptides are not toxic to the cells; however, they boost the efficacy of DOX against drug-resistant breast cancer cells. We used state-of-the-art computer-aided techniques to predict the molecular structure of peptides and their interactions with EYA. This study demonstrates an approach for incorporating non-cytotoxic components into DOX combination therapy, thereby avoiding increased systemic burden or adverse effects.

Pathogenic effects of Leu200Pro and Arg387His VRK1 protein variants on phosphorylation targets and H4K16 acetylation in distal hereditary motor neuropathy

Rare recessive variants in the human VRK1 gene are associated with several motor neuron diseases (MND), such as amyotrophic lateral sclerosis, spinal muscular atrophy, or distal hereditary motor neuropathies (dHMN). A case with dHMN carrying two novel VRK1 gene variants, expressing Leu200Pro (L200P) and Arg387His (R387H) variant proteins, identified that these protein variants are functionally different. The Leu200Pro variant shares with several variants in the catalytic domain the loss of the kinase activity on different substrates, such as histones, p53, or coilin. However, the distal Arg387His variant and the distal Trp375* (W375X) chinese variant, both located at the end of the low complexity C-terminal region and proximal to the termination codon, retain their catalytic activity on some substrates, and mechanistically their functional impairment is different. The L200P variant, as well as most VRK1 pathogenic variants, impairs the phosphorylation of BAF and histone H4K16 acetylation, which are required for DNA attachment to the nuclear envelope and chromatin accessibility to DNA repair mechanisms, respectively. The R387H variant impairs phosphorylation of H2AX, an early step in different types of DNA damage responses. The functional variability of VRK1 protein variants and their different combinations are a likely contributor to the clinical phenotypic heterogeneity of motor neuron and neurological diseases associated with rare VRK1 pathogenic variants. KEY MESSAGES: VRK1 variants implicated in motor neuron diseases are functionally different. The L200P variant is kinase inactive, and the R387H variant is partially active. VRK1 variants alter H4K16 acetylation and loss of coilin and BAF phosphorylation. VRK1 variants alter Cajal bodies and DNA damage responses. VRK1 variant combination determines the neurological phenotype heterogeneity.

Enterohemorrhagic Escherichia coli effector EspF triggers oxidative DNA lesions in intestinal epithelial cells

Attaching/effacing (A/E) pathogens induce DNA damage and colorectal cancer by injecting effector proteins into host cells via the type III secretion system (T3SS). EspF is one of the T3SS-dependent effector proteins exclusive to A/E pathogens, which include enterohemorrhagic Escherichia coli. The role of EspF in the induction of double-strand breaks (DSBs) and the phosphorylation of the repair protein SMC1 has been demonstrated previously. However, the process of damage accumulation and DSB formation has remained enigmatic, and the damage response is not well understood. Here, we first showed a compensatory increase in the mismatch repair proteins MutS homolog 2 (MSH2) and MSH6, as well as poly(ADP-ribose) polymerase 1, followed by a dramatic decrease, threatening cell survival in the presence of EspF. Flow cytometry revealed that EspF arrested the cell cycle at the G2/M phase to facilitate DNA repair. Subsequently, 8-oxoguanine (8-oxoG) lesions, a marker of oxidative damage, were assayed by ELISA and immunofluorescence, which revealed the accumulation of 8-oxoG from the cytosol to the nucleus. Furthermore, the status of single-stranded DNA (ssDNA) and DSBs was confirmed. We observed that EspF accelerated the course of DNA lesions, including 8-oxoG and unrepaired ssDNA, which were converted into DSBs; this was accompanied by the phosphorylation of replication protein A 32 in repair-defective cells. Collectively, these findings reveal that EspF triggers various types of oxidative DNA lesions with impairment of the DNA damage response and may result in genomic instability and cell death, offering novel insight into the tumorigenic potential of EspF.IMPORTANCEOxidative DNA lesions play causative roles in colitis-associated colon cancer. Accumulating evidence shows strong links between attaching/effacing (A/E) pathogens and colorectal cancer (CRC). EspF is one of many effector proteins exclusive to A/E pathogens with defined roles in the induction of oxidative stress, double-strand breaks (DSBs), and repair dysregulation. Here, we found that EspF promotes reactive oxygen species generation and 8-oxoguanine (8-oxoG) lesions when the repair system is activated, contributing to sustained cell survival. However, infected cells exposed to EspF presented 8-oxoG, which results in DSBs and ssDNA accumulation when the cell cycle is arrested at the G2/M phase and the repair system is defective or saturated by DNA lesions. In addition, we found that EspF could intensify the accumulation of nuclear DNA lesions through oxidative and replication stress. Overall, our work highlights the involvement of EspF in DNA lesions and DNA damage response, providing a novel avenue by which A/E pathogens may contribute to CRC.

DNA damage signalling histone H2AX is required for tumour growth

Cancer most frequently develops in self-renewal tissues that are the target of genetic alterations due to mutagens or intrinsic DNA replication errors. Histone γH2AX has a critical role in the cellular DNA repair pathway cascade and contributes to genomic stability. However, the role of γH2AX in the ontology of cancer is unclear. We have investigated this issue in the epidermis, a self-renewal epithelium continuously exposed to genetic hazard and replication stress. Silencing H2AX caused cell cycle hyperactivation, impaired DNA repair and epidermal hyperplasia in the skin. However, mutagen-induced carcinogenesis was strikingly reduced in the absence of H2AX. KO tumours appeared significantly later than controls and were fewer, smaller and more benign. The stem cell marker Δp63 drastically diminished in the KO epidermis. We conclude that H2AX is required for tissue-making during both homoeostasis and tumourigenesis, possibly by contributing to the control and repair of stem cells. Therefore, although H2AX is thought to act as a tumour suppressor and our results show that it contributes to homeostasis, they also indicate that it is required for the development of cancer.

Contribution of histone variants to aneuploidy: a cancer perspective

Histone variants, which generally differ in few amino acid residues, can replace core histones (H1, H2A, H2B, and H3) to confer specific structural and functional features to regulate cellular functions. In addition to their role in DNA packaging, histones modulate key processes such as gene expression regulation and chromosome segregation, which are frequently dysregulated in cancer cells. During the years, histones variants have gained significant attention as gatekeepers of chromosome stability, raising interest in understanding how structural and functional alterations can contribute to tumourigenesis. Beside the well-established role of the histone H3 variant CENP-A in centromere specification and maintenance, a growing body of literature has described mutations, aberrant expression patterns and post-translational modifications of a variety of histone variants in several cancers, also coining the term "oncohistones." At the molecular level, mechanistic studies have been dissecting the biological mechanisms behind histones and missegregation events, with the potential to uncover novel clinically-relevant targets. In this review, we focus on the current understanding and highlight knowledge gaps of the contribution of histone variants to aneuploidy, and we have compiled a database (HistoPloidyDB) of histone gene alterations linked to aneuploidy in cancers of the The Cancer Genome Atlas project.

1,2,4-trihydroxybenzene induces stress granule formation and causes DNA damage in human keratinocytes

Household chemical products are typically evaluated for toxicity through ingestion and inhalation, with limited information on skin absorption. Furthermore, current research focuses on the long-term toxic effects of harmful substances contained in these household chemical products, however not much is known about their acute toxic effects. In this study, the effects of 1,2,4-trihydroxybenzene (THB) in human keratinocytes by examining its effects on stress granule (SG) formation, a marker of acute stress response, and DNA double strand breaks caused by repeated exposure. THB effectively induced SG formation via endoplasmic reticulum stress-mediated eIF2α phosphorylation in keratinocytes. Furthermore, repeated exposure to THB causes apoptotic cell death due to DNA double strand breaks. Collectively, THB exposure leads to skin toxicity, suggesting precautions for the use of THB-containing household chemical products.

In Vitro High-Throughput Genotoxicity Testing Using γH2AX Biomarker, Microscopy and Reproducible Automatic Image Analysis in ImageJ—A Pilot Study with Valinomycin

(1) Background: The detection of DNA double-strand breaks in vitro using the phosphorylated histone biomarker (γH2AX) is an increasingly popular method of measuring in vitro genotoxicity, as it is sensitive, specific and suitable for high-throughput analysis. The γH2AX response is either detected by flow cytometry or microscopy, the latter being more accessible. However, authors sparsely publish details, data, and workflows from overall fluorescence intensity quantification, which hinders the reproducibility. (2) Methods: We used valinomycin as a model genotoxin, two cell lines (HeLa and CHO-K1) and a commercial kit for γH2AX immunofluorescence detection. Bioimage analysis was performed using the open-source software ImageJ. Mean fluorescent values were measured using segmented nuclei from the DAPI channel and the results were expressed as the area-scaled relative fold change in γH2AX fluorescence over the control. Cytotoxicity is expressed as the relative area of the nuclei. We present the workflows, data, and scripts on GitHub. (3) Results: The outputs obtained by an introduced method are in accordance with expected results, i.e., valinomycin was genotoxic and cytotoxic to both cell lines used after 24 h of incubation. (4) Conclusions: The overall fluorescence intensity of γH2AX obtained from bioimage analysis appears to be a promising alternative to flow cytometry. Workflow, data, and script sharing are crucial for further improvement of the bioimage analysis methods.

Nano-sized polystyrene plastic particles affect many cancer-related biological processes even in the next generations; zebrafish modeling

With the ever-increasing plastic pollution, the nano-sized plastic particles that are constantly released from the main materials have a greater potential threat. Studies continue on how to eliminate plastic waste, which has become a global problem, from nature. We are aware that complete elimination is not easy at all, but it is not known clearly that even if it is successful, its effects on organisms will also disappear completely. In this study, zebrafish injected with 20 nm-sized polystyrene particles (PS) only during the embryonic period were grown in an environment without plastic exposure. The effects of PS on their offspring embryo/larvae were examined at morphological, molecular and metabolomic levels. Results showed that parental PNP exposure caused significant malformations, decreased survival rate, increased heart rate and blood flow rate, as well as decreased eye size, height and locomotor activity, which were attributed to growth retardation in the offspring. According to the results of whole-mount immunofluorescence larval staining, cell death and reactive oxygen species were significantly increased, while lipid accumulation was decreased in new generation larvae from zebrafish injected with PNP. In order to elucidate the mechanisms underlying these morphological, physiological and molecular damages, the metabolome analyses were performed by evaluating the Q-TOF MS/MS spectra with chemometric analyses in the offspring larvae. According to the metabolomics results, 28 annotated metabolomes suggested by the OPLS-DA analysis that may vary significantly through a variable in projection scores were detected. In addition, it was detected that the significantly increased histopathological findings and immunopositivity of JNK, H2A.X, PI3 and NOP10 in new generation larvae. In conclusion, it has been shown that exposure to PS, even only during the embryonic period, may affect many cancer-related biological processes in the next generation.

Long non-coding RNA NR2F2-AS1: its expanding oncogenic roles in tumor progression

Long non-coding RNA (LncRNA) is a new type of non-coding RNA whose transcription is more than 200 nucleotides in length and can be up to 100 kb. The crucial regulatory function of lncRNAs in different cellular processes is now notable in many human diseases, especially in different steps of tumorigenesis, making them clinically significant. This research tried to collect all evidence obtained so far regarding Nuclear Receptor subfamily 2 group F member 2 Antisense RNA 1 (NR2F2-AS1) to explore its role in carcinogenesis and molecular mechanism in several cancers. Collecting evidence value an oncogenic role for NR2F2-AS1, whose dysregulation changes the status for cancerous cells to gain the supremacy toward cellular proliferation, dissemination, and ultimately migration. The NR2F2-AS1 acts as competitive endogenous RNA (ceRNA) and contains several microRNA response elements (MREs) for different microRNAs involved in various pathways such as PI3K/AKT, Wnt/β-catenin, and TGF-β. This clinically makes NR2F2-AS1 a remarkable lncRNA which contributes to cancer progression and invasion and perhaps could be a candidate as a prognostic marker or even a therapeutic target.

The genotoxic potential of mixed nitrosamines in drinking water involves oxidative stress and Nrf2 activation

Nitrosamine by-products in drinking water are designated as probable human carcinogens by the IARC, but the health effects of simultaneous exposure to multiple nitrosamines in drinking water remain unknown. Genotoxicity assays were used to assess the effects of both individual and mixed nitrosamines in finished drinking water produced by a large water treatment plant in Shanghai, China. Cytotoxicity and genotoxicity were measured at 1, 10-, 100- and 1000-fold actual concentrations by the Ames test, Comet assay, γ-H2AX assay, and the cytokinesis-block micronuclei assay; oxidative stress and the Nrf2 pathway were also assessed. Nitrosamines detected in drinking water included NDMA (36.45 ng/L), NDPA (44.68 ng/L), and NEMA (37.27 ng/L). Treatment with a mixture of the three nitrosamines at 1000-fold actual drinking-water concentration induced a doubling of revertants in Salmonella typhimurium strain TA100, DNA and chromosome damage in HepG2 cells, while 1-1000-fold concentrations of compounds applied singly lacked these effects. Treatment with 100- and 1000-fold concentrations increased ROS, GSH, and MDA and decreased SOD activity. Thus, nitrosamine mixtures showed greater genotoxic potential than that of the individual compounds. N-Acetylcysteine protected against the nitrosamine-induced chromosome damage, and Nrf2 pathway activation suggested that oxidative stress played pivotal roles in the genotoxic property of the nitrosamine mixtures.

Effects of deltamethrin and thiacloprid on cell viability, colony formation and DNA double-strand breaks in human bronchial epithelial cells

Deltamethrin (DEL) and thiacloprid (THIA) are commonly used insecticides applied either separately or as a mixture. We aimed to investigate the effects of DEL and THIA on cell viability, proliferation and DNA damage in human bronchial epithelial cells (BEAS-2B) because their effects in lung cells are not known. Our results indicate that all concentrations of DEL and THIA statistically decreased colony formation, plating efficiency and survival fraction in a concentration-dependent manner in BEAS-2B cells expect the lowest concentration for 24 h. MTT assay showed that treatment of DEL + THIA increased the cytotoxicity at higher concentrations. DEL + THIA significantly induced the foci formation of phosphorylated H2AX protein and p53 binding protein 1 at the highest concentration (44 μM DEL+666 μM THIA) for 120 h. Because gH2AX foci number was still higher in the recovery group given an additional 24 h after 120 h, the recovery period was not sufficient for DNA double-strand breaks repair.

A high-throughput drug combination screen identifies an anti-glioma synergism between TH588 and PI3K inhibitors

Background

Glioblastoma multiforme (GBM) is the most common and lethal type of primary brain tumor. More than half of GBMs contain mutation(s) of PTEN/PI3K/AKT, making inhibitors targeting the PI3K pathway very attractive for clinical investigation. However, so far, PI3K/AKT/mTOR inhibitors have not achieved satisfactory therapeutic effects in clinical trials of GBM. In this study, we aimed to develop a high-throughput screening method for high-throughput identification of potential targeted agents that synergize with PI3K inhibitors in GBM.

Methods

A Sensitivity Index (SI)-based drug combination screening method was established to evaluate the interactions between BKM120, a pan-PI3K inhibitor, and compounds from a library of 606 target-selective inhibitors. Proliferation, colony and 3D spheroid formation assays, western blotting, comet assay, γ-H2AX staining were used to evaluate the anti-glioma effects of the top-ranked candidates. The drug combination effects were analyzed by the Chou-Talalay method.

Results

Six compounds were successfully identified from the drug screen, including three previously reported compounds that cause synergistic antitumor effects with PI3K/mTOR inhibitors. TH588, an putative MTH1 inhibitor exhibited significant synergy with BKM120 in suppressing the proliferation, colony formation and 3D spheroid formation of GBM cells. Further investigation revealed that both DNA damage and apoptosis were markedly enhanced upon combination treatment with TH588 and BKM120. Finally, activation of PI3K or overexpression of AKT compromised the anti-glioma efficacy of TH588.

Conclusions

The screening method developed in this study demonstrated its usefulness in the rapid identification of synergistic drug combinations of PI3K inhibitors and targeted agents.

Genomic instability and cancer: lessons from Drosophila

Cancer is a genetic disease that involves the gradual accumulation of mutations. Human tumours are genetically unstable. However, the current knowledge about the origins and implications of genomic instability in this disease is limited. Understanding the biology of cancer requires the use of animal models. Here, we review relevant studies addressing the implications of genomic instability in cancer by using the fruit fly, Drosophila melanogaster, as a model system. We discuss how this invertebrate has helped us to expand the current knowledge about the mechanisms involved in genomic instability and how this hallmark of cancer influences disease progression.

The CD26/DPP4-inhibitor vildagliptin suppresses lung cancer growth via macrophage-mediated NK cell activity

CD26/dipeptidyl peptidase 4 (DPP4) is a transmembrane protein which is expressed by various malignant cells. We found that the expression of CD26/DPP4 was significantly higher in lung adenocarcinoma samples in our own patient cohort compared to normal lung tissue. We therefore hypothesize that the inhibition of CD26/DPP4 can potentially suppress lung cancer growth. The CD26/DPP4 inhibitor vildagliptin was employed on Lewis Lung Carcinoma (LLC) cell line and a human lung adenocarcinoma (H460) cell line. Two weeks after subcutaneous injection of tumor cells into C57BL/6 and CD1/nude mice, the size of LLC and H460 tumors was significantly reduced by vildagliptin. Immunohistochemically, the number of macrophages (F4/80+) and NK cells (NKp46+) was significantly increased in vildagliptin-treated tumor samples. Mechanistically, we found in vitro that lung cancer cell lines expressed increased levels of surfactant protein upon vildagliptin treatment thereby promoting the pro-inflammatory activity of macrophages. By the depletion of macrophages with clodronate and by using NK cell deficient (IL-15-/-) mice, tumors reversed to the size of controls, suggesting that indeed macrophages and NK cells were responsible for the observed tumor-suppressing effect upon vildagliptin treatment. FACS analysis showed tumor-infiltrating NK cells to express tumor necrosis-related apoptosis-inducing ligand (TRAIL) which induced the intra-cellular stress marker γH2AX. Accordingly, we found upregulated γH2AX in vildagliptin-treated tumors and TRAIL-treated cell lines. Moreover, the effect of vildagliptin-mediated enhanced NK cell cytotoxicity could be reversed by antagonizing the TRAIL receptor. Our data provide evidence that the CD26/DPP4-inhibitor vildagliptin reduces lung cancer growth. We could demonstrate that this effect is exerted by surfactant-activated macrophages and NK cells that act against the tumor via TRAIL-mediated cytotoxicity.

Comparative Transcriptomics Unravels Prodigiosin's Potential Cancer-Specific Activity Between Human Small Airway Epithelial Cells and Lung Adenocarcinoma Cells

Objective: Non-Small Cell Lung Cancer (NSCLC) is extremely lethal upon metastasis and requires safe and effective systemic therapies to improve a patient's prognosis. Prodigiosin (PG) appears to selectively and effectively target cancer but not healthy cells. However, PG's cancer-specific activity has remained elusive until recently. Methods: PG's cancer-specific performance was compared to Docetaxel (DTX), Paclitaxel (PTX), and Doxorubicin (DOX) against human lung adenocarcinoma (A549) and human small airway epithelial cells (HSAEC). Combination of PG with DTX, PTX, or DOX in a 1:1 ED50 ratio was also evaluated. MTT assay was used to determine the post-treatment cell viability. RNA-sequencing was used for comparative transcriptomics analysis between A549 and HSAEC treated with 1.0 μM PG for 24 h. Results: PG reduced A549 cell viability by four-folds greater than HSAEC. In comparison to DTX, PTX and DOX, PG was ~1.7 times more toxic toward A549, and 2.5 times more protective toward HSAEC. Combination of PG in a 1:1 ED50 ratio with DTX, PTX, or DOX failed to exhibit synergistic toxicity toward A549 or protection toward HSAEC. In A549, genes associated in DNA replication were downregulated, while genes directly or indirectly associated in lipid and cholesterol biogenesis were upregulated. In HSAEC, co-upregulation of oncogenic and tumor-suppressive genes was observed. Conclusion: An overactive lipid and cholesterol biogenesis could have caused A549's autophagy, while a balancing-act between genes of oncogenic and tumor-suppressive nature could have conferred HSAEC heightened survival. Overall, PG appears to be a smart chemotherapeutic agent that may be both safe and effective for NSCLC patients.

Genetic variants in ATM, H2AFX and MRE11 genes and susceptibility to breast cancer in the polish population

Background

DNA damage repair is a complex process, which can trigger the development of cancer if disturbed. In this study, we hypothesize a role of variants in the ATM, H2AFX and MRE11 genes in determining breast cancer (BC) susceptibility.

Methods

We examined the whole sequence of the ATM kinase domain and estimated the frequency of founder mutations in the ATM gene (c.5932G > T, c.6095G > A, and c.7630-2A > C) and single nucleotide polymorphisms (SNPs) in H2AFX (rs643788, rs8551, rs7759, and rs2509049) and MRE11 (rs1061956 and rs2155209) among 315 breast cancer patients and 515 controls. The analysis was performed using high-resolution melting for new variants and the polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method for recurrent ATM mutations. H2AFX and MRE11 polymorphisms were analyzed using TaqMan assays. The cumulative genetic risk scores (CGRS) were calculated using unweighted and weighted approaches.

Results

We identified four mutations (c.6067G > A, c.8314G > A, c.8187A > T, and c.6095G > A) in the ATM gene in three BC cases and two control subjects. We observed a statistically significant association of H2AFX variants with BC. Risk alleles (the G of rs7759 and the T of rs8551 and rs2509049) were observed more frequently in BC cases compared to the control group, with P values, odds ratios (OR) and 95% confidence intervals (CIs) of 0.0018, 1.47 (1.19 to 1.82); 0.018, 1.33 (1.09 to 1.64); and 0.024, 1.3 (1.06 to 1.59), respectively. Haplotype-based tests identified a significant association of the H2AFX CACT haplotype with BC (P <  0.0001, OR = 27.29, 95% CI 3.56 to 209.5). The risk of BC increased with the growing number of risk alleles. The OR (95% CI) for carriers of ≥ four risk alleles was 1.71 (1.11 to 2.62) for the CGRS.

Conclusions

This study confirms that H2AFX variants are associated with an increased risk of BC. The above-reported sequence variants of MRE11 genes may not constitute a risk factor of breast cancer in the Polish population. The contribution of mutations detected in the ATM gene to the development of breast cancer needs further detailed study.

Doxorubicin kinetics and effects on lung cancer cell lines using in vitro Raman micro-spectroscopy: binding signatures, drug resistance and DNA repair

Raman micro-spectroscopy is a non-invasive analytical tool, whose potential in cellular analysis and monitoring drug mechanisms of action has already been demonstrated, and which can potentially be used in pre-clinical and clinical applications for the prediction of chemotherapeutic efficacy. To further investigate such potential clinical application, it is important to demonstrate its capability to differentiate drug mechanisms of action and cellular resistances. Using the example of Doxorubicin (DOX), in this study, it was used to probe the cellular uptake, signatures of chemical binding and subsequent cellular responses, of the chemotherapeutic drug in two lung cancer cell lines, A549 and Calu-1. Multivariate statistical analysis was used to elucidate the spectroscopic signatures associated with DOX uptake and subcellular interaction. Biomarkers related to DNA damage and repair, and mechanisms leading to apoptosis were also measured and correlated to Raman spectral profiles. Results confirm the potential of Raman spectroscopic profiling to elucidate both drug kinetics and pharmacodynamics and differentiate cellular drug resistance associated with different subcellular accumulation rates and subsequent cellular response to DNA damage, pointing towards a better understanding of drug resistance for personalised targeted treatment.

miR-638 suppresses DNA damage repair by targeting SMC1A expression in terminally differentiated cells

The reduction of DNA damage repair capacity in terminally differentiated cells may be involved in sensitivity to cancer chemotherapy drugs; however, the underlying molecular mechanism is still not fully understood. Herein, we evaluated the role of miR-638 in the regulation of DNA damage repair in terminally differentiated cells. Our results show that miR-638 expression was up-regulated during cellular terminal differentiation and involved in mediating DNA damage repair processes. Results from a luciferase reporting experiment show that structural maintenance of chromosomes (SMC)1A was a potential target of miR-638; this was verified by western blot assays during cell differentiation and DNA damage induction. Overexpression of miR-638 enhanced the sensitivity of cancer cells to cisplatin, thus reducing cell viability in response to chemotherapy drug treatment. Furthermore, miR-638 overexpression affected DNA damage repair processes by interfering with the recruitment of the DNA damage repair-related protein, γH2AX, to DNA break sites. These findings indicate that miR-638 might act as a sensitizer in cancer chemotherapy and accompany chemotherapy drugs to enhance chemotherapeutic efficacy and to improve the chance of recovery from cancer.

Oridonin induces apoptosis in human oral cancer cells via phosphorylation of histone H2AX

Oridonin, a natural diterpenoid purified from Rabdosia rubescens, has displayed beneficial biological activities, including anti-proliferation and anti-angiogenesis effects, in various types of cancers. However, the anti-cancer potential of oridonin and its mechanism in oral cancer have never previously been studied. In this study, we assessed the role of oridonin as an inducer of apoptosis in HSC-3 and HSC-4 human oral cancer cells. Our results showed that oridonin reduces the viability of human oral cancer cells and significantly increases the expression of γH2AX, a well-known marker of DNA damage. 4',6-Diamidino-2-phenylindole (DAPI) staining and western blotting showed that oridonin causes nuclear condensation and fragmentation, and induces cleavage of poly(ADP-ribose) polymerase (PARP). Moreover, oridonin-induced γH2AX accumulation was partially abrogated by Z-VAD, a pan-caspase inhibitor. Taken together, our results suggest that oridonin can effectively induce apoptosis by augmenting the expression of γH2AX in response to DNA damage and might be a promising anti-cancer drug candidate for the treatment of oral cancer.

Sunitinib induces genomic instability of renal carcinoma cells through affecting the interaction of LC3-II and PARP-1

Deficiency of autophagy has been linked to increase in nuclear instability, but the role of autophagy in regulating the formation and elimination of micronuclei, a diagnostic marker for genomic instability, is limited in mammalian cells. Utilizing immunostaining and subcellular fractionation, we found that either LC3-II or the phosphorylated Ulk1 localized in nuclei, and immunoprecipitation results showed that both LC3 and Unc-51-like kinase 1 (Ulk1) interacted with γ-H2AX, a marker for the DNA double-strand breaks (DSB). Sunitinib, a multi-targeted receptor tyrosine kinase inhibitor, was found to enhance the autophagic flux concurring with increase in the frequency of micronuclei accrued upon inhibition of autophagy, and similar results were also obtained in the rasfonin-treated cells. Moreover, the punctate LC3 staining colocalized with micronuclei. Unexpectedly, deprivation of SQSTM1/p62 alone accumulated micronuclei, which was not further increased upon challenge with ST. Rad51 is a protein central to repairing DSB by homologous recombination and treatment with ST or rasfonin decreased its expression. In several cell lines, p62 appeared in the immunoprecipites of Rad51, whereas LC3, Ulk1 and p62 interacted with PARP-1, another protein involved in DNA repair and genomic stability. In addition, knockdown of either Rad51 or PARP-1 completely inhibited the ST-induced autophagic flux. Taken together, the data presented here demonstrated that both LC3-II and the phosphorylated Ulk1 localized in nuclei and interacted with the proteins essential for nuclear stability, thereby revealing a more intimate relationship between autophagy and genomic stability.

Resveratrol-3-O-glucuronide and resveratrol-4'-O-glucuronide reduce DNA strand breakage but not apoptosis in Jurkat T cells treated with camptothecin

Resveratrol has been reported to inhibit or induce DNA damage, depending upon the type of cell and the experimental conditions. Dietary resveratrol is present in the body predominantly as metabolites and limited data is available concerning the activities of these metabolic products. In the present study, physiologically obtainable levels of the resveratrol metabolites resveratrol-3-O-glucuronide, resveratrol-4'-O-glucuronide and resveratrol-3-O-sulfate were evaluated for their ability to protect Jurkat T cells against DNA damage induced by the topoisomerase I inhibitors camptothecin and topotecan. The cells were pretreated for 24 h with 10 µM resveratrol aglycone or each resveratrol metabolite prior to the induction of DNA damage with camptothecin or topotecan. In separate experiments, the cells were co-treated with resveratrol or its metabolites, and a topoisomerase I inhibitor. The detection of histone 2AX phosphorylation and terminal deoxynucleotidyl transferase dUTP nick end-labeling (TUNEL) were used to determine DNA damage, and apoptosis was measured using an antibody against cleaved poly ADP-ribose polymerase. It was identified that pretreatment of the cells with resveratrol-3-O-glucuronide and resveratrol-4'-O-glucuronide reduced the mean fluorescence intensity of staining for DNA strand breaks following treatment with camptothecin, while the percentage of cells undergoing apoptosis was unchanged. However, pretreatment of the cells with resveratrol aglycone increased the DNA damage and apoptosis induced by the drugs. These results suggest that the glucuronide metabolites of resveratrol partially protected the cells from DNA damage, but did not influence the induction of cell death by camptothecin and topotecan. These data suggest that resveratrol aglycone treatment may be beneficial for treating types of cancer that have direct contact with resveratrol prior to its metabolism, including gastrointestinal cancers, which are routinely treated with topoisomerase I inhibitors.

Validation of a flow cytometry-based detection of γ-H2AX, to measure DNA damage for clinical applications

BACKGROUND

The nucleosomal histone protein H2AX is specifically phosphorylated (γ-H2AX) adjacent to DNA double-strand breaks (DSBs) and is used for quantifying DSBs. Many chemotherapies and ionizing radiation (IR) used in cancer treatment result in DSBs. Therefore, γ-H2AX has a significant potential as a biomarker in evaluating patient sensitivity and responsiveness to IR and chemotherapy.

METHODS

Here, we report a flow cytometry-based quantification of γ-H2AX (FCM-γ-H2AX assay) customized for clinical practice.

RESULTS

We validated that our method is able to detect DNA damage in peripheral blood mononuclear cells (PBMCs) treated with DSB inducing agents. The method also detected the DNA repair deficiency in PBMCs treated with DNA repair inhibitors, as well as the deficiency in DNA repair signaling in PBMCs from two ataxia telangiectasia patients.

CONCLUSIONS

The FCM-γ-H2AX assay has sufficient analytical sensitivity and precision to measure levels of DNA damage and DNA repair for clinical purposes. © 2016 International Clinical Cytometry Society.

Protein expression changes induced in a malignant melanoma cell line by the curcumin analogue compound D6

Background

We have previously demonstrated that the hydroxylated biphenyl compound D6 (3E,3′E)-4,4′-(5,5′,6,6′-tetramethoxy-[1,1′-biphenyl]-3,3′-diyl)bis(but-3-en-2-one), a structural analogue of curcumin, exerts a strong antitumor activity on melanoma cells both in vitro and in vivo. Although the mechanism of action of D6 is yet to be clarified, this compound is thought to inhibit cancer cell growth by arresting the cell cycle in G2/M phase, and to induce apoptosis through the mitochondrial intrinsic pathway. To investigate the changes in protein expression induced by exposure of melanoma cells to D6, a differential proteomic study was carried out on D6-treated and untreated primary melanoma LB24Dagi cells.

Methods

Proteins were fractionated by SDS-PAGE and subjected to in gel digestion. The peptide mixtures were analyzed by liquid chromatography coupled with tandem mass spectrometry. Proteins were identified and quantified using database search and spectral counting. Proteomic data were finally uploaded into the Ingenuity Pathway Analysis software to find significantly modulated networks and pathways.

Results

Analysis of the differentially expressed protein profiles revealed the activation of a strong cellular stress response, with overexpression of several HSPs and stimulation of ubiquitin-proteasome pathways. These were accompanied by a decrease of protein synthesis, evidenced by downregulation of proteins involved in mRNA processing and translation. These findings are consistent with our previous results on gene expression profiling in melanoma cells treated with D6.

Conclusions

Our findings confirm that the curcumin analogue D6 triggers a strong stress response in melanoma cells, turning down majority of cell functions and finally driving cells to apoptosis.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-016-2362-6) contains supplementary material, which is available to authorized users.

Evaluation of chemical phototoxicity, focusing on phosphorylated histone H2AX

Histone H2AX is a minor component of nuclear histone H2A. The phosphorylation of histone H2AX at Ser 139, termed γ-H2AX, was originally identified as an early event after the direct formation of DNA double-strand breaks (DSBs) by ionizing radiation. Now, the generation of γ-H2AX is also considered to occur in association with secondarily formed DSBs by cellular processing such as DNA replication and repair at the site of the initial damage, including DNA adducts, crosslinks, and UV-induced photolesions. Therefore, γ-H2AX is currently attracting attention as a new biomarker for detecting various genotoxic insults. We have determined the toxic impact of various environmental stresses such as chemicals, light and/or their coexposure using γ-H2AX, and found that the γ-H2AX assay exhibited high sensitivity and a low false-positive rate as a detection system of genotoxic potential. In this review, we introduced our recent findings concerning the evaluation of chemical phototoxicity, focusing on γ-H2AX.

Down-regulation of G9a triggers DNA damage response and inhibits colorectal cancer cells proliferation

G9a, a histone methyltransferase, is aberrantly expressed in some human tumor types. By comparing 182 paired colorectal cancer and peritumoral tissues, we found that G9a was highly expressed in colorectal cancer (CRC). Overexpression of G9a promoted CRC cells proliferation and colony formation, whereas knockdown of G9a inhibited CRC cells proliferation. Depletion of G9a increased the rate of chromosome aberration, induced DNA double strand breaks and CRC cells senescence. G9a inhibition synergistically increased γH2AX expression induced by topoisomerase I inhibitors and ultimately led to CRC cell death. The findings that down-regulation of G9a triggers DNA damage response and inhibits colorectal cancer cells proliferation may define G9a as potential oncotarget in CRC.

Elevated DNA damage response in pancreatic cancer

Pancreatic cancer is one of the most aggressive and intractable human malignant tumors and a leading cause of cancer-related death across the world, with incidence equaling mortality. Because of the extremely high malignance, this disease is usually diagnosed at its advanced stage and recurs even after surgical excision. Pancreatic adenocarcinoma is generally thought to arise from pathological changes of pancreatic duct, and the pancreatic ductal adenocarcinoma accounts for more than 90 % of malignant neoplasms of the pancreas. To date, scientists have revealed several risk factors for pancreatic cancer, including smoking, family history, and aging. However, the underlying molecular mechanism remains unclear. Meanwhile, more mutations of DNA damage response factors have been identified in familial pancreatic cancers, implying a potential link between DNA damage and pancreatic cancer. DNA damage is a recurring phenomenon in our bodies which could be induced by exogenous agents and endogenous metabolism. Accumulated DNA lesions cause genomic instability which eventually results in tumorigenesis. In this study, we showed obvious DNA damages existed in human pancreatic cancer, which activated DNA damage response and the DNA repair pathway including ataxia-telangiectasia mutated, DNA-PK, CHK1, and CHK2. The persistent DNA damage in pancreatic tissue may be the source for its tumorigenesis.

γ-H2AX as a biomarker for DNA double-strand breaks in ecotoxicology

The visualisation of DNA damage response proteins enables the indirect measurement of DNA damage. Soon after the occurrence of a DNA double-strand break (DSB), the formation of γ-H2AX histone variants is to be expected. This review is focused on the potential use of the γ-H2AX foci assay in assessing the genotoxicity of environmental contaminants including cytostatic pharmaceuticals, since standard methods may not be sensitive enough to detect the damaging effect of low environmental concentrations of such drugs. These compounds are constantly released into the environment, potentially representing a threat to water quality, aquatic organisms, and, ultimately, human health. Our review of the literature revealed that this method could be used in the biomonitoring and risk assessment of aquatic systems affected by wastewater from the production, usage, and disposal of cytostatic pharmaceuticals.

Microbial pathogens trigger host DNA double-strand breaks whose abundance is reduced by plant defense responses

Immune responses and DNA damage repair are two fundamental processes that have been characterized extensively, but the links between them remain largely unknown. We report that multiple bacterial, fungal and oomycete plant pathogen species induce double-strand breaks (DSBs) in host plant DNA. DNA damage detected by histone γ-H2AX abundance or DNA comet assays arose hours before the disease-associated necrosis caused by virulent Pseudomonas syringae pv. tomato. Necrosis-inducing paraquat did not cause detectable DSBs at similar stages after application. Non-pathogenic E. coli and Pseudomonas fluorescens bacteria also did not induce DSBs. Elevation of reactive oxygen species (ROS) is common during plant immune responses, ROS are known DNA damaging agents, and the infection-induced host ROS burst has been implicated as a cause of host DNA damage in animal studies. However, we found that DSB formation in Arabidopsis in response to P. syringae infection still occurs in the absence of the infection-associated oxidative burst mediated by AtrbohD and AtrbohF. Plant MAMP receptor stimulation or application of defense-activating salicylic acid or jasmonic acid failed to induce a detectable level of DSBs in the absence of introduced pathogens, further suggesting that pathogen activities beyond host defense activation cause infection-induced DNA damage. The abundance of infection-induced DSBs was reduced by salicylic acid and NPR1-mediated defenses, and by certain R gene-mediated defenses. Infection-induced formation of γ-H2AX still occurred in Arabidopsis atr/atm double mutants, suggesting the presence of an alternative mediator of pathogen-induced H2AX phosphorylation. In summary, pathogenic microorganisms can induce plant DNA damage. Plant defense mechanisms help to suppress rather than promote this damage, thereby contributing to the maintenance of genome integrity in somatic tissues.

Multicellular organisms are continuously exposed to microbes and have developed sophisticated defense mechanisms to counter attack by microbial pathogens. Organisms also encounter many types of DNA damage and have evolved multiple mechanisms to maintain their genomic integrity. Even though these two fundamental responses have been characterized extensively, the relationship between them remains largely unclear. Our study demonstrates that microbial plant pathogens with diverse life styles, including bacteria, oomycete and fungal pathogens, induce double-strand breaks (DSBs) in the genomes of infected host plant cells. DSB induction is apparently a common feature during plant-pathogen interactions. DSBs are the most deleterious form of DNA damage and can lead to chromosomal aberrations and gene mutations. In response to pathogen infection, plant immune responses are activated and contribute to suppressing pathogen-induced DSBs, thereby maintaining better genome integrity and stability. The findings identify important ways that the plant immune and DNA damage repair responses are interconnected. Awareness of the above phenomena may foster future development of disease management approaches that improve crop productivity under biotic stress.

Kaposi's sarcoma-associated herpesvirus induces the ATM and H2AX DNA damage response early during de novo infection of primary endothelial cells, which play roles in latency establishment

The DNA damage response (DDR) that evolved to repair host cell DNA damage also recognizes viral DNA entering the nucleus during infections. Here, we investigated the modulation of DDR signaling during de novo infection of primary endothelial cells by Kaposi's sarcoma-associated herpesvirus (KSHV). Phosphorylation of representative DDR-associated proteins, such as ataxia telangiectasia mutated (ATM) and H2AX, was induced as early as 30 min (0.5 h) postinfection and persisted during in vitro KSHV latency. Phosphorylated H2AX (γH2AX) colocalized at 30 min (0.5 h) with the KSHV genome entering the nuclei. Total H2AX protein levels also increased, and the increase was attributed to a decrease in degradative H2AX Lys48-linked polyubiquitination with a concomitant increase in Lys63-linked polyubiquitination that was shown to increase protein stability. ATM and H2AX phosphorylation and γH2AX nuclear foci were also induced by UV-inactivated KSHV, which ceased at later times of infection. Inhibition of ATM kinase activity by KU-55933 and H2AX knockdown by small interfering RNA significantly reduced the expression of the KSHV latency-associated nuclear antigen 1 (LANA-1; ORF73) and LANA-1 nuclear puncta. Knockdown of H2AX also resulted in a >80% reduction in the nuclear KSHV DNA copy numbers. Similar results were also observed in ATM-negative cells, although comparable levels of viral DNA entered ATM-negative and ATM-positive cell nuclei. In contrast, knockdown of CHK1 and CHK2 did not affect ORF73 expression. Collectively, these results demonstrate that KSHV induces ATM and H2AX, a selective arm of the DDR, for the establishment and maintenance of its latency during de novo infection of primary endothelial cells.

IMPORTANCE

Eukaryotic cells mount a DNA damage response (DDR) to sense and repair different types of cellular DNA damage. In addition, DDR also recognizes exogenous genetic material, such as the viral DNA genome entering the nucleus during infections. The present study was undertaken to determine whether de novo Kaposi's sarcoma-associated herpesvirus (KSHV) infection modulates DDR. Our results demonstrate that early during de novo infection of primary endothelial cells, KSHV induces a selective arm of DDR signaling, such as the ATM kinase and its downstream target, H2AX, which are essential for KSHV's latent gene expression and the establishment of latency. These studies suggest that targeting ATM and H2AX could serve as an attractive strategy to block the establishment of KSHV latent infection and the associated malignancies.

Selective anticancer copper(ii)-mixed ligand complexes: targeting of ROS and proteasomes

The ternary copper(ii) complexes 1–4 exhibited anticancer selectivity, as evidenced by MTT assay, % apoptosis, cell cycle arrest, ROS induction and DNA DSBs. Proteasome of cancer cells are also inhibited.

Dissimilar effects of β-lapachone- and hydroxyurea-induced DNA replication stress in root meristem cells of Allium cepa

Two anticancer drugs, β-lapachone (β-lap, a naphthoquinone) and hydroxyurea (HU, an inhibitor of ribonucleotide reductase), differently affect nuclear morphology and cell cycle control mechanisms in root meristem cells of Allium cepa. The 18 h treatment with 100 μM β-lap results in a lowered number of M-phase cells, increased occurrence of mitotic abnormalities, including over-condensation of chromosomes, their enhanced stickiness, formation of anaphase bridges, micronucleation and reduced mitotic spindles. Following prolonged incubations using high doses of β-lap, cell nuclei reveal dark-red fluorescence evenly distributed in chromatin surrounding the unstained regions of nucleoli. Both drugs generate H2O2 and induce DNA double strand breaks, which is correlated with γ-phoshorylation of H2AX histones. However, the extent of H2AX phosphorylation (including the frequency of γ-H2AX foci and the relative number cells creating phospho-H2AX domains) is considerably reduced in root meristem cells treated jointly with the β-lap/HU mixture. Furthermore, various effects of caffeine (an inhibitor of ATM/ATR cell cycle checkpoint kinases) on β-lap- and HU-induced γ-phoshorylation of H2AX histones and the protective activity of HU against β-lap suggest that their genotoxic activities are largely dissimilar. β-Lap treatment results in the induction of apoptosis-like programmed cell death, while HU treatment leads to cell adaptation to replication stress and promotion of abnormal nuclear divisions with biphasic interphase/mitotic states of chromatin condensation.

Non-apoptotic function of caspases in a cellular model of hydrogen peroxide-associated colitis

Oxidative stress, caused by reactive oxygen species (ROS), is a major contributor to inflammatory bowel disease (IBD)-associated neoplasia. We mimicked ROS exposure of the epithelium in IBD using non-tumour human colonic epithelial cells (HCEC) and hydrogen peroxide (H2 O2 ). A population of HCEC survived H2 O2 -induced oxidative stress via JNK-dependent cell cycle arrests. Caspases, p21(WAF1) and γ-H2AX were identified as JNK-regulated proteins. Up-regulation of caspases was linked to cell survival and not, as expected, to apoptosis. Inhibition using the pan-caspase inhibitor Z-VAD-FMK caused up-regulation of γ-H2AX, a DNA-damage sensor, indicating its negative regulation via caspases. Cell cycle analysis revealed an accumulation of HCEC in the G1 -phase as first response to oxidative stress and increased S-phase population and then apoptosis as second response following caspase inhibition. Thus, caspases execute a non-apoptotic function by promoting cells through G1 - and S-phase by overriding the G1 /S- and intra-S checkpoints despite DNA-damage. This led to the accumulation of cells in the G2 /M-phase and decreased apoptosis. Caspases mediate survival of oxidatively damaged HCEC via γ-H2AX suppression, although its direct proteolytic inactivation was excluded. Conversely, we found that oxidative stress led to caspase-dependent proteolytic degradation of the DNA-damage checkpoint protein ATM that is upstream of γ-H2AX. As a consequence, undetected DNA-damage and increased proliferation were found in repeatedly H2 O2 -exposed HCEC. Such features have been associated with neoplastic transformation and appear here to be mediated by a non-apoptotic function of caspases. Overexpression of upstream p-JNK in active ulcerative colitis also suggests a potential importance of this pathway in vivo.

A computational platform for robotized fluorescence microscopy (II): DNA damage, replication, checkpoint activation, and cell cycle progression by high-content high-resolution multiparameter image-cytometry

Dissection of complex molecular-networks in rare cell populations is limited by current technologies that do not allow simultaneous quantification, high-resolution localization, and statistically robust analysis of multiple parameters. We have developed a novel computational platform (Automated Microscopy for Image CytOmetry, A.M.I.CO) for quantitative image-analysis of data from confocal or widefield robotized microscopes. We have applied this image-cytometry technology to the study of checkpoint activation in response to spontaneous DNA damage in nontransformed mammary cells. Cell-cycle profile and active DNA-replication were correlated to (i) Ki67, to monitor proliferation; (ii) phosphorylated histone H2AX (γH2AX) and 53BP1, as markers of DNA-damage response (DDR); and (iii) p53 and p21, as checkpoint-activation markers. Our data suggest the existence of cell-cycle modulated mechanisms involving different functions of γH2AX and 53BP1 in DDR, and of p53 and p21 in checkpoint activation and quiescence regulation during the cell-cycle. Quantitative analysis, event selection, and physical relocalization have been then employed to correlate protein expression at the population level with interactions between molecules, measured with Proximity Ligation Analysis, with unprecedented statistical relevance.

Biological effects of low-dose radiation from computed tomography scanning

PURPOSE

With the widespread use of computed tomography (CT), the risks of low-dose radiation from CT have been increasingly highlighted. This study aims to illustrate the CT-induced biological effects and analyze the potential beneficial or harmful outcomes so as to provide radiologists with reasonable advice on CT usage.

MATERIALS AND METHODS

The related literature was analyzed according to the topics of stochastic effect, hereditary effect, deterministic effect, accumulative injuries, hormesis and adaptive response; population epidemiology data were also analyzed.

RESULTS

CT accounts for 9% of X-ray examinations and approximately 40-67% of medical-related radiation, the dose is within the range of low-dose radiation (LDR). Two opposite viewpoints exist nowadays regarding the biological effects of CT scanning: They are either harmful or harmless. Approximately 0.6% and 1.5% of the cumulative cancer risk could be attributed to diagnostic X-rays in the UK and Germany, respectively. The probability of CT scans induced-cancer is about 0.7% and CT angiography's risk is around 0.13%. It is estimated that approximately 29,000 cancers could be related to CT scans in the USA every year. Meanwhile, another investigation of 25,104 patients who underwent 45,632 CT scans in 4 years showed that the majority of CT-induced cancers were accidents rather than certainties of frequent CT scans.

CONCLUSION

Although the LDR effects of CT are still controversial, the current problems include the high frequency-use and abuse of CT scans, the increase of radiation dose and accumulative dose in high-accuracy CT, and the poor understanding of carcinogenic risks. The underlying biological basis needs further exploring and the ratio of risks and benefits should be considered.

FOXM1 (Forkhead box M1) in tumorigenesis: overexpression in human cancer, implication in tumorigenesis, oncogenic functions, tumor-suppressive properties, and target of anticancer therapy

FOXM1 (Forkhead box M1) is a typical proliferation-associated transcription factor and is also intimately involved in tumorigenesis. FOXM1 stimulates cell proliferation and cell cycle progression by promoting the entry into S-phase and M-phase. Additionally, FOXM1 is required for proper execution of mitosis. In accordance with its role in stimulation of cell proliferation, FOXM1 exhibits a proliferation-specific expression pattern and its expression is regulated by proliferation and anti-proliferation signals as well as by proto-oncoproteins and tumor suppressors. Since these factors are often mutated, overexpressed, or lost in human cancer, the normal control of the foxm1 expression by them provides the basis for deregulated FOXM1 expression in tumors. Accordingly, FOXM1 is overexpressed in many types of human cancer. FOXM1 is intimately involved in tumorigenesis, because it contributes to oncogenic transformation and participates in tumor initiation, growth, and progression, including positive effects on angiogenesis, migration, invasion, epithelial-mesenchymal transition, metastasis, recruitment of tumor-associated macrophages, tumor-associated lung inflammation, self-renewal capacity of cancer cells, prevention of premature cellular senescence, and chemotherapeutic drug resistance. However, in the context of urethane-induced lung tumorigenesis, FOXM1 has an unexpected tumor suppressor role in endothelial cells because it limits pulmonary inflammation and canonical Wnt signaling in epithelial lung cells, thereby restricting carcinogenesis. Accordingly, FOXM1 plays a role in homologous recombination repair of DNA double-strand breaks and maintenance of genomic stability, that is, prevention of polyploidy and aneuploidy. The implication of FOXM1 in tumorigenesis makes it an attractive target for anticancer therapy, and several antitumor drugs have been reported to decrease FOXM1 expression.

Compromised hematopoiesis and increased DNA damage following non-lethal ionizing radiation of a human hematopoietic system reconstituted in immunodeficient mice

PURPOSE

Precise understanding of radiation effects is critical to development of new modalities for the prevention and treatment of radiation-induced damage. In this study, we evaluated the effects of non-lethal doses of X-ray irradiation on human hematopoietic stem and progenitor cells (HSPC) reconstituted in NOD/Shi-scid, IL2Rγ(null) (NOG) immunodeficient mice.

MATERIALS AND METHODS

We transplanted cord blood CD34(+) HSPC into NOG mice irradiated with 2.0 Gy via tail veins. At the 12th week after transplantation, the NOG mice were irradiated with 0, 0.5, 1.0, 2.0, or 4.0 Gy, and the radiation effects on human HSPC in vivo were evaluated.

RESULTS

Although a majority of the mice irradiated with 2.0 Gy or more died in 12 weeks after irradiation, the mice that were exposed to 0.5 or 1.0 Gy of irradiation survived and were subjected to analysis. The chimerism of human CD45(+) hematopoietic cells in peripheral blood and bone marrow (BM) of the recipient mice was reduced in an X-ray dose-dependent manner after irradiation. Percentages of human CD34(+) HSPC as well as human (CD34+CD38-) HSC in BM similarly declined. (CD34+CD38-) HSC purified from the humanized mice at the 12th week after irradiation showed significantly increased numbers of phosphorylated H2AX (γH2AX) foci, a marker of DNA breaks, in an X-ray dose- dependent manner. Expression of p16INK4A, a hallmark of aging of HSC, was also detected only in HSPC from irradiated mice.

CONCLUSIONS

With further refinement, the humanized mouse model might be effectively used to study the biological effects of non-lethal radiation in vivo.

Splicing switch of an epigenetic regulator by RNA helicases promotes tumor-cell invasiveness

Both epigenetic and splicing regulation contribute to tumor progression, but the potential links between these two levels of gene-expression regulation in pathogenesis are not well understood. Here, we report that the mouse and human RNA helicases Ddx17 and Ddx5 contribute to tumor-cell invasiveness by regulating alternative splicing of several DNA- and chromatin-binding factors, including the macroH2A1 histone. We show that macroH2A1 splicing isoforms differentially regulate the transcription of a set of genes involved in redox metabolism. In particular, the SOD3 gene that encodes the extracellular superoxide dismutase and plays a part in cell migration is regulated in an opposite manner by macroH2A1 splicing isoforms. These findings reveal a new regulatory pathway in which splicing factors control the expression of histone variant isoforms that in turn drive a transcription program to switch tumor cells to an invasive phenotype.

γH2AX as a novel endpoint to detect DNA damage: applications for the assessment of the in vitro genotoxicity of cigarette smoke

Histone H2AX is rapidly phosphorylated to become γH2AX after exposure to DNA-damaging agents that cause double-strand DNA breaks (DSBs). γH2AX can be detected and quantified by numerous methods, giving a direct correlation with the number of DSBs. This relationship has made γH2AX an increasingly utilised endpoint in multiple scientific fields since its discovery in 1998. Applications include its use in pre-clinical drug assessment, as a biomarker of DNA damage and in in vitro mechanistic studies. Here, we review current in vitro regulatory and non-regulatory genotoxicity assays proposing the γH2AX assay as a potential complement to the current test battery. Additionally, we evaluate the use of the γH2AX assay to measure DSBs in vitro in tobacco product testing.

Unstabilized DNA breaks in HTLV-1 Tax expressing cells correlate with functional targeting of Ku80, not PKcs, XRCC4, or H2AX

BACKGROUND

Expression of the human T-cell leukemia virus type 1 (HTLV-1) Tax oncoprotein rapidily induces a significant increase of micronuclei (MN) and unstabilized DNA breaks in cells. Unstabilized DNA breaks can have free 3'-OH ends accessible to in situ addition of digoxygenin (DIG)-labeled dUTP using terminal deoxynucleotidyl transferase. In the present work, we used a GFP-Tax (green fluorescent protein) plasmid, which produces a functionally active GFP-tagged Tax protein, to detect the cellular target(s) for Tax which might mechanistically explain the clastogenic phenomenon. We examined the induction of MN and unstabilized DNA breaks in wild type cells and cells individually knocked out for Ku80, PKcs, XRCC4, and H2AX proteins. We also assessed in the same cells, the signal strengths produced by DIG-dUTP incorporation at the unstable DNA breaks in the presence and absence of Tax.

RESULTS

Cells mutated for PKcs, XRCC4 and H2AX showed increased frequency of MN and unstabilized DNA breaks in response to the expression of Tax, while cells genetically mutated for Ku80 were refractory to Tax's induction of these cytogenetic effects. Moreover, by measuring the size of DIG-dUTP incorporation signal, which indicates the extent of unstable DNA ends, we found that Tax induces larger signals than those in control cells. However, in xrs-6 cells deficient for Ku80, this Tax effect was not seen.

CONCLUSIONS

The data here demonstrate that clastogenic DNA damage in Tax expressing cells is explained by Tax targeting of Ku80, but not PKcs, XRCC4 or H2AX, which are all proteins directly or indirectly related to the non-homologous end-joining (NHEJ) repair system. Of note, the Ku80 protein plays an important role at the initial stage of the NHEJ repair system, protecting and stabilizing DNA-breaks. Accordingly, HTLV-1 Tax is shown to interfere with a normal cellular protective mechanism for stabilizing DNA breaks. These DNA breaks, unprotected by Ku80, are unstable and are subject to erosion or end-to-end fusion, ultimately leading to additional chromosomal aberrations.

Chromatin specialization in bivalve molluscs: a leap forward for the evaluation of Okadaic Acid genotoxicity in the marine environment

Marine biotoxins synthesized by Harmful Algal Blooms (HABs) represent one of the most important sources of contamination in marine environments as well as a serious threat to fisheries and aquaculture-based industries in coastal areas. Among these biotoxins Okadaic Acid (OA) is of critical interest as it represents the most predominant Diarrhetic Shellfish Poisoning biotoxin in the European coasts. Furthermore, OA is a potent tumor promoter with aneugenic and clastogenic effects on the hereditary material, most notably DNA breaks and alterations in DNA repair mechanisms. Therefore, a great effort has been devoted to the biomonitoring of OA in the marine environment during the last two decades, mainly based on physicochemical and physiological parameters using mussels as sentinel organisms. However, the molecular genotoxic effects of this biotoxin make chromatin structure a good candidate for an alternative strategy for toxicity assessment with faster and more sensitive evaluation. To date, the development of chromatin-based studies to this purpose has been hampered by the complete lack of information on chromatin of invertebrate marine organisms, especially in bivalve molluscs. Our preliminary results have revealed the presence of histone variants involved in DNA repair and chromatin specialization in mussels and clams. In this work we use this information to put forward a proposal focused on the development of chromatin-based tests for OA genotoxicity in the marine environment. The implementation of such tests in natural populations has the potential to provide an important leap in the biomonitoring of this biotoxin. The outcome of such monitoring may have critical implications for the evaluation of DNA damage in these marine organisms. They will provide as well important tools for the optimization of their harvesting and for the elaboration of additional tests designed to evaluate the safety of their consumption and potential implications for consumer's health.

Regulation of ATM/DNA-PKcs Phosphorylation by BRCA1-Associated BAAT1

BRCA1 has been implicated in the DNA damage pathway and regulation of genome stability, however, it does not contain intrinsic catalytic activity to repair the DNA lesions. Thus, a potential activity of BRCA1 is to assemble proteins that sense DNA damage and to transduce checkpoint signals to downstream. We have recently isolated a protein termed BAAT1, which binds to BRCA1, ATM, DNA-PKcs, and SMC1. Phosphorylation of ATM/DNA-PKcs is greatly reduced in BAAT1-knockdown cells, suggesting that sensing of DNA lesions mediated by BRCA1/BAAT1 is critical for activation of these kinases.

Histone modifiers in cancer: friends or foes?

Covalent modifications of histones can regulate all DNA-dependent processes. In the last few years, it has become more and more evident that histone modifications are key players in the regulation of chromatin states and dynamics as well as in gene expression. Therefore, histone modifications and the enzymatic machineries that set them are crucial regulators that can control cellular proliferation, differentiation, plasticity, and malignancy processes. This review discusses the biology and biochemistry of covalent histone posttranslational modifications (PTMs) and evaluates the dual role of their modifiers in cancer: as oncogenes that can initiate and amplify tumorigenesis or as tumor suppressors.