Inactivation of ataxia telangiectasia mutated gene can increase intracellular reactive oxygen species levels and alter radiation-induced cell death pathways in human glioma cells

Genome-Wide Screening in Human Embryonic Stem Cells Highlights the Hippo Signaling Pathway as Granting Synthetic Viability in ATM Deficiency

ATM depletion is associated with the multisystemic neurodegenerative syndrome ataxia-telangiectasia (A-T). The exact linkage between neurodegeneration and ATM deficiency has not been established yet, and no treatment is currently available. In this study, we aimed to identify synthetic viable genes in ATM deficiency to highlight potential targets for the treatment of neurodegeneration in A-T. We inhibited ATM kinase activity using the background of a genome-wide haploid pluripotent CRISPR/Cas9 loss-of-function library and examined which mutations confer a growth advantage on ATM-deficient cells specifically. Pathway enrichment analysis of the results revealed the Hippo signaling pathway as a major negative regulator of cellular growth upon ATM inhibition. Indeed, genetic perturbation of the Hippo pathway genes SAV1 and NF2, as well as chemical inhibition of this pathway, specifically promoted the growth of ATM-knockout cells. This effect was demonstrated in both human embryonic stem cells and neural progenitor cells. Therefore, we suggest the Hippo pathway as a candidate target for the treatment of the devastating cerebellar atrophy associated with A-T. In addition to the Hippo pathway, our work points out additional genes, such as the apoptotic regulator BAG6, as synthetic viable with ATM-deficiency. These genes may help to develop drugs for the treatment of A-T patients as well as to define biomarkers for resistance to ATM inhibition-based chemotherapies and to gain new insights into the ATM genetic network.

The DNA Double-Strand Break Repair in Glioma: Molecular Players and Therapeutic Strategies

Gliomas are the most frequent type of tumor in the central nervous system, which exhibit properties that make their treatment difficult, such as cellular infiltration, heterogeneity, and the presence of stem-like cells responsible for tumor recurrence. The response of this type of tumor to chemoradiotherapy is poor, possibly due to a higher repair activity of the genetic material, among other causes. The DNA double-strand breaks are an important type of lesion to the genetic material, which have the potential to trigger processes of cell death or cause gene aberrations that could promote tumorigenesis. This review describes how the different cellular elements regulate the formation of DNA double-strand breaks and their repair in gliomas, discussing the therapeutic potential of the induction of this type of lesion and the suppression of its repair as a control mechanism of brain tumorigenesis.

The therapeutic effect in gliomas of nanobubbles carrying siRNA combined with ultrasound-targeted destruction

Background

Nanobubbles (NBs) combined with ultrasound-targeted destruction (UTD) have become promising potential carriers for drug or siRNA delivery. Due to their nano-size, NBs could penetrate tumor blood vessels and accumulate in intercellular spaces so that "sonoporation" induced by UTD would act directly on the tumor cells to increase cell membrane permeability.

Methods

Based on the successful the fabrication of NBs, we synthesized NBs carrying siRNA (NBs-siRNA) by using a biotin-streptavidin system. We then utilized ultrasound irradiation (UI)-targeted NBs-siRNA to improve siRNA transfection and achieve the inhibition of glioma growth.

Results

NBs as carriers combined with UI effectively enhanced siRNA transfection and the effect of silencing targeted genes in vitro. Additionally, a better therapeutic effect was shown in the NBs-siRNA with UI group in vivo compared with that of microbubbles (MBs) with UI or NBs-siRNA without UI.

Conclusion

These results indicated that NBs combined with UTD might be an ideal delivery vector for siRNA to achieve the noninvasive treatment of glioma.

Human iPSC-Derived Cerebellar Neurons from a Patient with Ataxia-Telangiectasia Reveal Disrupted Gene Regulatory Networks

Ataxia-telangiectasia (A-T) is a rare genetic disorder caused by loss of function of the ataxia-telangiectasia-mutated kinase and is characterized by a predisposition to cancer, pulmonary disease, immune deficiency and progressive degeneration of the cerebellum. As animal models do not faithfully recapitulate the neurological aspects, it remains unclear whether cerebellar degeneration is a neurodevelopmental or neurodegenerative phenotype. To address the necessity for a human model, we first assessed a previously published protocol for the ability to generate cerebellar neuronal cells, finding it gave rise to a population of precursors highly enriched for markers of the early hindbrain such as EN1 and GBX2, and later more mature cerebellar markers including PTF1α, MATH1, HOXB4, ZIC3, PAX6, and TUJ1. RNA sequencing was used to classify differentiated cerebellar neurons generated from integration-free A-T and control induced pluripotent stem cells. Comparison of RNA sequencing data with datasets from the Allen Brain Atlas reveals in vitro-derived cerebellar neurons are transcriptionally similar to discrete regions of the human cerebellum, and most closely resemble the cerebellum at 22 weeks post-conception. We show that patient-derived cerebellar neurons exhibit disrupted gene regulatory networks associated with synaptic vesicle dynamics and oxidative stress, offering the first molecular insights into early cerebellar pathogenesis of ataxia-telangiectasia.

Silencing of ATM expression by siRNA technique contributes to glioma stem cell radiosensitivity in vitro and in vivo

Evidence has shown that both high expression of the ataxia-telangiectasia mutated (ATM) gene and glioma stem cells (GSCs) are responsible for radioresistance in glioma. Thus, we hypothesized that brain tumor radiosensitivity may be enhanced via silencing of the ATM gene in GSCs. In the present study we successfully induced GSCs from two cell lines and used CD133 and nestin to identify GSCs. A lentivirus was used to deliver siRNA-ATMPuro (A group) to GSCs prior to radiation, while siRNA-HKPuro (N group) and GSCs (C group) were used as negative and blank controls, respectively. RT-qPCR and western blotting were performed to verify the efficiency of the siRNA-ATM technique. The expression of the ATM gene and ATM protein were significantly downregulated post-transfection. Cell Counting Kit-8 (CCK-8) and colony formation assays revealed that the A group demonstrated weak cell proliferation and lower survival fractions post-irradiation compared to the C/N groups. Flow cytometry was used to examine the percentage of cell apoptosis and G2 phase arrest, which were both higher in the A group than in the C/N groups. We found that the comet tail percentage evaluated by comet assay was higher in the A group than in the C/N groups. After radiation treatment, three radiosensitive genes [p53, proliferating cell nuclear antigen (PCNA), survivin] exhibited a decreasing tendency as determined by RT-qPCR. Mice underwent subcutaneous implantation, followed by radiation, and the resulting necrosis and hemorrhage were more obvious in the A group than in the N groups. In conclusion, silencing of ATM via the siRNA technique improved radiosensitivity of GSCs both in vitro and in vivo.

The Paradoxical Effects of Different Hepatitis C Viral Loads on Host DNA Damage and Repair Abilities

Hepatitis C virus (HCV)-induced hepatic stress is associated with increased oxidative DNA damage and has been implicated in hepatic inflammation. However, HCV infection and replication are uneven and vary among individual hepatocytes. To investigate the effect of the viral load on host DNA damage, we used an Enhanced Yellow Fluorescent Protein gene (EYFP)-tagged HCV virus to distinguish between HCV intracellular high viral load (HVL) cells and low viral load (LVL) cells. The cell sorting efficiency was confirmed by the high expression of the HCV polyprotein. We found DNA damage γ-H2AX foci in the HVL population. Comet assays demonstrated that HVL was related to the extent of the DNA strand breaks. Surprisingly, the DNA qPCR arrays and western blotting showed that the damage-related genes GPX2, MRE11, phospho-ATM, and OGG1 were significantly up-regulated in LVL cells but inversely down-regulated or consistently expressed in HVL cells. The colony survival assay to examine the repair abilities of these cells in response to irradiation showed that the LVL cells were more resistant to irradiation and had an increased ability to repair radiation-induced damage. This study found that intracellular viral loads drove cellular DNA damage levels but suppressed damage-related gene expression. However, the increase in damage-related gene expression in the LVL cells may be affected by ROS from the HVL cells. These findings provide new insights into the distinct DNA damage and repair responses resulting from different viral loads in HCV-infected cells.

Silencing of ataxia-telangiectasia mutated by siRNA enhances the in vitro and in vivo radiosensitivity of glioma

It is reported that high expression of the ataxia-telangiectasia mutated (ATM) gene is linked with radioresistance in glioma. We hypothesized that the radiosensitivity of this brain tumor is enhanced by silencing of the ATM gene. We transfected the glioma cell line U251 with the siRNA-ATMpuro (group A) lentivirus or the siRNA-HKpuro (group N, negative control) lentivirus before irradiation. RT-qPCR and western blotting were performed to verify the efficiency of siRNA‑mediated ATM silencing. Expression levels of the ATM gene and protein were obviously downregulated after transfection. Moreover, the expression of the p53, PCNA and survivin genes, which are related to radiosensitivity, was also decreased. CCK-8 and colony formation assays showed lower cell proliferation and survival in group A than in groups N and C (control group that was not transfected with any siRNA). The level of double-stranded DNA breaks was also greater in group A, as determined by the comet tail assay. Flow cytometry showed a higher rate of cell apoptosis and a higher number of cells in the G2 phase in group A. Furthermore, caspase-3, caspase-8 and caspase-9 activity was also higher in group A. In vivo analysis in mouse models created by implantation of the transfected cell lines showed that the amount of necrosis and hemorrhage was higher in group A than that in the control groups. In conclusion, silencing of ATM via the siRNA technique could improve the in vitro and in vivo radiosensitivity of glioma cells.

Impact of single-nucleotide polymorphisms on radiation pneumonitis in cancer patients

Radiation pneumonitis (RP) is one of the most important dose-limiting toxicities in the radiotherapy of thoracic tumors, which reduces the rate of local tumor control and overall survival and severely affects the patients' quality of life. Single-nucleotide polymorphisms (SNPs) have recently attracted increasing attention as biomarkers for predicting the development of RP. SNPs in inflammation-related, DNA repair-related, stress response-related and angiogenesis-related genes were proved to be associated with RP, with different underlying mechanisms. Radiogenomics focuses on the differences in radiosensitivity caused by gene sequence variation, which may prove helpful in investigating the abovementioned associations. In this review, we aimed to investigate the associations between RP and SNPs reported in recent studies and highlight the main content and prospects of radiogenomics.

Extremely low-frequency electromagnetic fields cause G1 phase arrest through the activation of the ATM-Chk2-p21 pathway

In daily life, humans are exposed to the extremely low-frequency electromagnetic fields (ELF-EMFs) generated by electric appliances, and public concern is increasing regarding the biological effects of such exposure. Numerous studies have yielded inconsistent results regarding the biological effects of ELF-EMF exposure. Here we show that ELF-EMFs activate the ATM-Chk2-p21 pathway in HaCaT cells, inhibiting cell proliferation. To present well-founded results, we comprehensively evaluated the biological effects of ELF-EMFs at the transcriptional, protein, and cellular levels. Human HaCaT cells from an immortalized epidermal keratinocyte cell line were exposed to a 1.5 mT, 60 Hz ELF-EMF for 144 h. The ELF-EMF could cause G1 arrest and decrease colony formation. Protein expression experiments revealed that ELF-EMFs induced the activation of the ATM/Chk2 signaling cascades. In addition, the p21 protein, a regulator of cell cycle progression at G1 and G2/M, exhibited a higher level of expression in exposed HaCaT cells compared with the expression of sham-exposed cells. The ELF-EMF-induced G1 arrest was diminished when the CHK2 gene expression (which encodes checkpoint kinase 2; Chk2) was suppressed by specific small interfering RNA (siRNA). These findings indicate that ELF-EMFs activate the ATM-Chk2-p21 pathway in HaCaT cells, resulting in cell cycle arrest at the G1 phase. Based on the precise control of the ELF-EMF exposure and rigorous sham-exposure experiments, all transcriptional, protein, and cellular level experiments consistently supported the conclusion. This is the first study to confirm that a specific pathway is triggered by ELF-EMF exposure.

Breast cancer stem cell-like cells are more sensitive to ionizing radiation than non-stem cells: role of ATM

There are contradictory observations about the different radiosensitivities of cancer stem cells and cancer non-stem cells. To resolve these contradictory observations, we studied radiosensitivities by employing breast cancer stem cell (CSC)-like MDA-MB231 and MDA-MB453 cells as well as their corresponding non-stem cells. CSC-like cells proliferate without differentiating and have characteristics of tumor-initiating cells [1]. These cells were exposed to γ-rays (1.25–8.75 Gy) and survival curves were determined by colony formation. A final slope, D₀, of the survival curve for each cell line was determined to measure radiosensitivity. The D₀ of CSC-like and non-stem MDA-MB-453 cells were 1.16 Gy and 1.55 Gy, respectively. Similar results were observed in MDA-MB-231 cells (0.94 Gy vs. 1.56 Gy). After determination of radiosensitivity, we investigated intrinsic cellular determinants which influence radiosensitivity including cell cycle distribution, free-radical scavengers and DNA repair. We observed that even though cell cycle status and antioxidant content may contribute to differential radiosensitivity, differential DNA repair capacity may be a greater determinant of radiosensitivity. Unlike non-stem cells, CSC-like cells have little/no sublethal damage repair, a low intracellular level of ataxia telangiectasia mutated (ATM) and delay of γ-H2AX foci removal (DNA strand break repair). These results suggest that low DNA repair capacity is responsible for the high radiosensitivity of these CSC-like cells.

ATM polymorphisms predict severe radiation pneumonitis in patients with non-small cell lung cancer treated with definitive radiation therapy

PURPOSE

The ataxia telangiectasia mutated (ATM) gene mediates detection and repair of DNA damage. We investigated associations between ATM polymorphisms and severe radiation-induced pneumonitis (RP).

METHODS AND MATERIALS

We genotyped 3 potentially functional single nucleotide polymorphisms (SNPs) of ATM (rs1801516 [D1853N/5557G>A], rs189037 [-111G>A] and rs228590) in 362 patients with non-small cell lung cancer (NSCLC), who received definitive (chemo)radiation therapy. The cumulative severe RP probabilities by genotypes were evaluated using the Kaplan-Meier analysis. The associations between severe RP risk and genotypes were assessed by both logistic regression analysis and Cox proportional hazard model with time to event considered.

RESULTS

Of 362 patients (72.4% of non-Hispanic whites), 56 (15.5%) experienced grade ≥3 RP. Patients carrying ATM rs189037 AG/GG or rs228590 TT/CT genotypes or rs189037G/rs228590T/rs1801516G (G-T-G) haplotype had a lower risk of severe RP (rs189037: GG/AG vs AA, adjusted hazard ratio [HR] = 0.49, 95% confidence interval [CI], 0.29-0.83, P=.009; rs228590: TT/CT vs CC, HR=0.57, 95% CI, 0.33-0.97, P=.036; haplotype: G-T-G vs A-C-G, HR=0.52, 95% CI, 0.35-0.79, P=.002). Such positive findings remained in non-Hispanic whites.

CONCLUSIONS

ATM polymorphisms may serve as biomarkers for susceptibility to severe RP in non-Hispanic whites. Large prospective studies are required to confirm our findings.

The role of XPC: implications in cancer and oxidative DNA damage

The accumulation of DNA damage is a slow but hazardous phenomenon that may lead to cell death, accelerated aging features and cancer. One of the most versatile and important defense mechanisms against the accumulation of DNA damage is nucleotide excision repair (NER), in which the Xeroderma pigmentosum group C (XPC) protein plays a prominent role. NER can be divided into global genome repair (GG-NER) and transcription coupled repair (TC-NER). XPC is a key factor in GG-NER where it functions in DNA damage recognition and after which the repair machinery is recruited to eliminate the DNA damage. Defective XPC functioning has been shown to result in a cancer prone phenotype, in human as well as in mice. Mutation accumulation in XPC deficient mice is accelerated and increased, resulting in an increased tumor incidence. More recently XPC has also been linked to functions outside of NER since XPC deficient mice show a divergent tumor spectrum compared to other NER deficient mouse models. Multiple in vivo and in vitro experiments indicate that XPC appears to be involved in the initiation of several DNA damage-induced cellular responses. XPC seems to function in the removal of oxidative DNA damage, redox homeostasis and cell cycle control. We hypothesize that this combination of increased oxidative DNA damage sensitivity, disturbed redox homeostasis together with inefficient cell cycle control mechanisms are causes of the observed increased cancer susceptibility in oxygen exposed tissues. Such a phenotype is absent in other NER-deficient mice, including Xpa.