DNA double-strand breaks: signaling, repair and the cancer connection

Association between selenium, cadmium, and arsenic levels and genetic polymorphisms in DNA repair genes (XRCC5, XRCC6) in gastric cancerous and non-cancerous tissue

Gastric cancer is one of the most prevalent cancers in northern Iran. The DNA repair genes X-ray repair cross-complementing (XRCC) group 5, XRCC6, which are important members of non-homologous end-joining repair system, play an important role in repairing the DNA double-strand breaks. Chronic exposure to heavy metals has long been recognized as being capable of augmenting gastric cancer incidence among exposed human populations. Since trace elements could directly or indirectly damage DNA, and polymorphism in DNA DSBs-repair genes can alter the capacity of system repair, we assumed that XRCC5 VNTR and XRCC6-61C >G polymorphism also impress the DSBs-repair system ability and contribute to gastric cancer. Therefore, the objective of this research was to evaluate the tissue accumulation of Selenium (Se), Cadmium (Cd) and Arsenic (As), and XRCC5 VNTR, XRCC6-61C >G polymorphisms in cancerous and non-cancerous tissues in Golestan province. The study population included 46 gastric cancer patients and 43 cancer-free controls. Two polymorphisms of XRCC5, XRCC6 were genotyped using polymerase chain reaction (PCR) or polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP) method. Further employed was atomic absorption spectroscopy so as to determine the levels of Se, Cd and As. Finally, the data were analyzed by SPSS (version 16) statistical software. The Se level was significantly higher in tumors as compared to non-tumor tissues, but there was no significant correlation between As and Cd in cancerous and noncancerous tissues. Allele frequencies of the selected genes were not statistically different between groups regarding XRCC6 (-61C>G). XRCC5 0R/0R, 0R/1R, 1R/1R, and 0R/2R genotypes were more common in cancerous group. High levels of Se in cancerous tissues vs. non-cancerous tissues may be one of the carcinogenic factors; in Golestan province, unlike other regions of Iran and the world, the level of Se is high, hence the higher risks of gastric cancer.

A new method for constructing tumor specific gene co-expression networks based on samples with tumor purity heterogeneity

Motivation

Tumor tissue samples often contain an unknown fraction of stromal cells. This problem is widely known as tumor purity heterogeneity (TPH) was recently recognized as a severe issue in omics studies. Specifically, if TPH is ignored when inferring co-expression networks, edges are likely to be estimated among genes with mean shift between non-tumor- and tumor cells rather than among gene pairs interacting with each other in tumor cells. To address this issue, we propose Tumor Specific Net (TSNet), a new method which constructs tumor-cell specific gene/protein co-expression networks based on gene/protein expression profiles of tumor tissues. TSNet treats the observed expression profile as a mixture of expressions from different cell types and explicitly models tumor purity percentage in each tumor sample.

Results

Using extensive synthetic data experiments, we demonstrate that TSNet outperforms a standard graphical model which does not account for TPH. We then apply TSNet to estimate tumor specific gene co-expression networks based on TCGA ovarian cancer RNAseq data. We identify novel co-expression modules and hub structure specific to tumor cells.

Availability and implementation

R codes can be found at https://github.com/petraf01/TSNet.

Supplementary information

Supplementary data are available at Bioinformatics online.

Induction of apoptosis and modulation of homologous recombination DNA repair pathway in prostate cancer cells by the combination of AZD2461 and valproic acid

Cancer therapies using defects in homologous recombination (HR) DNA repair pathway of tumor cells are not yet approved to be applicable in patients with malignancies other than BRCA1/2-mutated tumors. This study was designed to determine the efficacy of combination therapy of a histone deacetylase inhibitor, valproic acid (VPA) and a novel PARP inhibitor AZD2461 in both PC-3 (PTEN-mutated) and DU145 (PTEN-unmutated) prostate cancer cell lines. The Trypan blue dye exclusion assay and the tetrazolium-based colorimetric (MTT) assay were performed to measure the cytotoxicity while combination effects were assessed based on Chou-Talalay's principles. Flow-cytometric assay determined the type of cell death. The real-time PCR analysis was used to evaluate the alterations in mRNA levels of HR-related genes while their protein levels were measured using the ELISA method. γ-H2AX levels were determined as a marker of DNA damage. We observed a synergistic relationship between VPA and AZD2461 in all affected fractions of PC-3 cells (CI<0.9), but not in DU145 cells (CI>1.1). Annexin-V staining analysis revealed a significant induction of apoptosis when PC-3 cells were treated with VPA+AZD2461 (p<0.05). Both mRNA and protein levels of Rad51 and Mre11 were significantly decreased in PC-3 cells co-treated with VPA+AZD2461 while enhanced H2AX phosphorylation was found in PC-3 cells after 12 and 24 hours of co-treatment (p<0.05). Our findings established a preclinical rationale for selective targeting of HR repair pathways by a combination of VPA and AZD2461 as a mechanism for reducing the HR pathway sufficiency in PTEN-mutated prostate cancer cells.

Overcoming radioresistance in WiDr cells with heavy ion irradiation and radiosensitization by 2-deoxyglucose with photon irradiation

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2-DG acts as a radiosensitizer to photons depending on the time of its application.

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There is no sensitization to ¹²C irradiation by 2-DG.

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¹²C combination therapy still has the higher dose effectiveness.

Background and purpose

Radiosensitizers and heavy ion irradiation could improve therapy for female patients with malignant tumors located in the pelvic region through dose reduction. Aim of the study was to investigate the radiosensitizing potential of 2-deoxy-d-glucose (2-DG) in combination with carbon ion-irradiation (¹²C) in representative cell lines of cancer in the female pelvic region.

Materials and methods

The human cervix carcinoma cell line CaSki and the colorectal carcinoma cell line WiDr were used. 2-DG was employed in two different settings, pretreatment and treatment simultaneous to irradiation. Clonogenic survival, α and β values for application of the linear quadratic model and relative biological effectiveness (RBE) were determined. ANOVA tests were used for statistical group comparison. Isobolograms were generated for curve comparisons.

Results

The comparison of monotherapy with ¹²C versus photons yielded RBE values of 2.4 for CaSki and 3.5 for WiDr along with a significant increase of α values in the ¹²C setting. 2-DG monotherapy reduced the colony formation of both cell lines. Radiosensitization was found in WiDr for the combination of photon irradiation with synchronous application of 2-DG. The same setup for ¹²C showed no radiosensitization, but rather an additive effect. In all settings with CaSki, the combination of irradiation and 2-DG exhibited additive properties.

Conclusion

The combination of 2-DG and photon therapy, as well as irradiation with carbon ions can overcome radioresistance of tumor cells such as WiDr.

Maintenance BEZ235 Treatment Prolongs the Therapeutic Effect of the Combination of BEZ235 and Radiotherapy for Colorectal Cancer

Our previous study demonstrated that administration of NVP-BEZ235 (BEZ235), a dual PI3K/mTOR inhibitor, before radiotherapy (RT) enhanced the radiotherapeutic effect in colorectal cancer (CRC) cells both in vitro and in vivo. Here, we evaluated whether maintenance BEZ235 treatment, after combinatorial BEZ235 + RT therapy, prolonged the antitumor effect in CRC. K-RAS mutant CRC cells (HCT116 and SW480), wild-type CRC cells (HT29), and HCT116 xenograft tumors were separated into the following six study groups: (1) untreated (control); (2) RT alone; (3) BEZ235 alone; (4) RT + BEZ235; (5) maintenance BEZ235 following RT + BEZ235 (RT + BEZ235 + mBEZ235); and (6) maintenance BEZ235 following BEZ235 (BEZ235 + mBEZ235). RT + BEZ235 + mBEZ235 treatment significantly inhibited cell viability and increased apoptosis in three CRC cell lines compared to the other five treatments in vitro. In the HCT116 xenograft tumor model, RT + BEZ235 + mBEZ235 treatment significantly reduced the tumor size when compared to the other five treatments. Furthermore, the expression of mTOR signaling molecules (p-rpS6 and p-eIF4E), DNA double-strand break (DSB) repair-related molecules (p-ATM and p-DNA-PKcs), and angiogenesis-related molecules (VEGF-A and HIF-1α) was significantly downregulated after RT + BEZ235 + mBEZ235 treatment both in vitro and in vivo when compared to the RT + BEZ235, RT, BEZ235, BEZ235 + mBEZ235, and control treatments. Cleaved caspase-3, cleaved poly (ADP-ribose) polymerase (PARP), 53BP1, and γ-H2AX expression in the HCT116 xenograft tissue and three CRC cell lines were significantly upregulated after RT + BEZ235 + mBEZ235 treatment. Maintenance BEZ235 treatment in CRC cells prolonged the inhibition of cell viability, enhancement of apoptosis, attenuation of mTOR signaling, impairment of the DNA-DSB repair mechanism, and downregulation of angiogenesis that occurred due to concurrent BEZ235 and RT treatment.

The CTIP-mediated repair of TNF-α-induced DNA double-strand break was impaired by miR-130b in cervical cancer cell

Chemotherapeutic drugs that induce DNA damage have the potential to kill cancer cells, but DNA repair protects cells from damage‐induced cell death. Thus, eliminating DNA repair is a potential approach to overcome cell drug resistance. In this study, we observed that the gene expression of C‐terminal binding protein interacting protein (CTIP) was promoted by TNF‐α stimulation and prevented TNF‐α‐induced double‐strand breaks (DSBs) in the genomes of cervical cancer cells. The putative miR‐130b targeted site within 3′ untranslated region (UTR) of CTIP mRNA was identified through in silico analysis and confirmed based on experimental data. By targeting the CTIP gene, miR‐130b caused the accumulation of DSBs and accelerated cell apoptosis in combination with poly ADP ribose polymerase (PARP) inhibitors. Additionally, overexpression of the CTIP gene elevated cancer cell viability by promoting proliferation while miR‐130b antagonized CTIP‐stimulated cell reproduction. Consequently, miR‐130b destruction of DNA repair should be employed as a strategy to treat cervical cancer.

Significance of the study

Cervical cancer threatens the health of women all over the world. In this study, we observed that miR‐130b was able to cause the accumulation of DNA double‐strand breaks through suppressing the gene expression of C‐terminal binding protein interacting protein and to accelerate cell apoptosis by preventing DNA damage repairs in cervical cancer cells. As far as we know, the impact of miR‐130b on the DNA double‐strand break repair and on the cell apoptosis induced by the destruction of DNA repair in cervical cancer cells was firstly documented. It is reasonable to believe that miR‐130b destruction of DNA repair may be employed as a strategy to treat cervical cancer in the future.

Chromosomal radiosensitivity of triple negative breast cancer patients

Purpose: Based on clinical and molecular data, breast cancer is a heterogeneous disease. Breast cancers that have no expression of estrogen receptor (ER), progesterone receptor (PR) and human epidermal growth factor receptor 2 (HER2) are defined as triple negative breast cancers (TNBCs); luminal cancers have different expressions of ER, PR and/or HER2. TNBCs are frequently linked with advanced disease, poor prognosis and occurrence in young African women, and about 15% of the cases are associated with germline BRCA1/2 mutations. Since radiotherapy is utilized as a principle treatment in the management of TNBC, we aimed to investigate the chromosomal instability and radiosensitivity of lymphocytes in TNBC patients compared to luminal breast cancer patients and healthy controls using the micronucleus (MN) assay. The effect of mutations in breast cancer susceptibility genes on chromosomal radiosensitivity was also evaluated.Methods: Chromosomal radiosensitivity was evaluated in the G0 (83 patients and 90 controls) and S/G2 (34 patients and 17 controls) phase of the cell cycle by exposing blood samples from all patients and controls to 2 and 4 Gy ionizing radiation (IR).Results: In the G0 MN assay, the combined cohort of all breast cancer, TNBC and luminal patients' exhibit significantly elevated spontaneous MN values compared to controls indicating chromosomal instability. Chromosomal radiosensitivity is also significantly elevated in the combined cohort of all breast cancer patients compared to controls. The TNBC patients, however, do not exhibit enhanced chromosomal radiosensitivity. Similarly, in the S/G2 phase, 76% of TNBC patients do not show enhanced chromosomal radiosensitivity compared to the controls. In both the G0 and S/G2 phase, luminal breast cancer patients demonstrate a shift toward chromosomal radiosensitivity compared to TNBC patients and controls.Conclusions: The observations of the MN assay suggest increased chromosomal instability and chromosomal radiosensitivity in South African breast cancer patients. However, in TNBC patients, the irradiated MN values are not elevated. Our results suggest that the healthy lymphocytes in TNBC patients could handle higher doses of IR.

Cadmium disrupts the DNA damage response by destabilizing RNF168

Cadmium (Cd) is a dispensable element for the human body and is usually considered a carcinogen. Occupational and environmental Cd exposure leads to sustained cellular proliferation in some tissues and tumorigenesis via an unclear mechanism. Here, we evaluated the role of Cd in the DNA damage response (DDR). We found that Cd exposure causes extensive DNA double-strand breaks (DSBs) and prevents accumulation of ubiquitination signals at these sites of DNA damage. Cd treatment compromises 53BP1 and BRCA1 recruitment to DSBs induced by itself or DNA damaging agents and partially inactivates the G2/M checkpoint. Mechanistically, Cd directly binds to the E3 ubiquitin ligase RNF168, induces the ubiquitin-proteasome pathway that mediates RNF168 degradation and suppresses RNF168 ubiquitin-ligase activity in vitro. Our study raises the possibility that Cd may target RNF168 to disrupt proper DSB signaling in cultured cells. This pathway may represent a novel mechanism for carcinogenesis induced by Cd.

Nymphaea lotus Linn. (Nymphaeaceae) Alleviates Sexual Disability in L-NAME Hypertensive Male Rats

Hypertension (HT) is a risk factor for erectile dysfunction (ED). This study aimed to evaluate the suppressive effect of Nymphaea lotus (N. lotus) on erectile dysfunction induced by NO deficiency in rat. 40 male rats equally divided into 4 groups received an oral treatment with 10 mg/kg/day of L-NAME, a NO blocker, during 4 weeks. Control group composed of 10 male rats received only distilled water (10 mL/kg). Thereafter oral treatments with N. lotus (75 and 200 mg/kg/day) and losartan (10 mg/kg/day) started and continued concomitantly with L-NAME in 3 groups for 4 additional weeks. Normal and negative controls received only distilled water. Sexual behaviour, orientation activities, anxiety, and penile histomorphology were evaluated at the end of treatment. L-NAME administration elevated significantly the blood pressure in male rats and decreased the copulatory rate by enhancing intromission latency and decreasing the numbers of intromission and ejaculation. However, the sexual motivation remains unaltered by chronic NO blockage suggesting that L-NAME induces penile dysfunction mainly by peripheral mechanisms. L-NAME chronic intake also induced anxiety, 4 weeks of N. lotus cotreatment prevented inhibitory effects of L-NAME on male sexual behaviour by shortening mainly ejaculation latency and postejaculatory interval while losartan does not. Losartan proved to be a more effective drug to decrease the blood pressure compared to the plant extract. Effectively, Nymphea lotus was able to reverse totally at 75 mg/kg the increment of hemodynamic parameters and the histological damage and exhibit anxiolytic-like effects in hypertensive male rats. Nymphaea lotus uses NO pathway to facilitate sexual responses at central and peripheral levels and can have a double medicinal use, against anxiety and erectile dysfunction.

Inflammation-induced DNA damage, mutations and cancer

The relationships between inflammation and cancer are varied and complex. An important connection linking inflammation to cancer development is DNA damage. During inflammation reactive oxygen and nitrogen species (RONS) are created to combat pathogens and to stimulate tissue repair and regeneration, but these chemicals can also damage DNA, which in turn can promote mutations that initiate and promote cancer. DNA repair pathways are essential for preventing DNA damage from causing mutations and cytotoxicity, but RONS can interfere with repair mechanisms, reducing their efficacy. Further, cellular responses to DNA damage, such as damage signaling and cytotoxicity, can promote inflammation, creating a positive feedback loop. Despite coordination of DNA repair and oxidative stress responses, there are nevertheless examples whereby inflammation has been shown to promote mutagenesis, tissue damage, and ultimately carcinogenesis. Here, we discuss the DNA damage-mediated associations between inflammation, mutagenesis and cancer.

ZYH005, a novel DNA intercalator, overcomes all-trans retinoic acid resistance in acute promyelocytic leukemia

Despite All-trans retinoic acid (ATRA) has transformed acute promyelocytic leukemia (APL) from the most fatal to the most curable hematological cancer, there remains a clinical challenge that many high-risk APL patients who fail to achieve a complete molecular remission or relapse and become resistant to ATRA. Herein, we report that 5-(4-methoxyphenethyl)-[1, 3] dioxolo [4, 5-j] phenanthridin-6(5H)-one (ZYH005) exhibits specific anticancer effects on APL and ATRA-resistant APL in vitro and vivo, while shows negligible cytotoxic effect on non-cancerous cell lines and peripheral blood mononuclear cells from healthy donors. Using single-molecule magnetic tweezers and molecule docking, we demonstrate that ZYH005 is a DNA intercalator. Further mechanistic studies show that ZYH005 triggers DNA damage, and caspase-dependent degradation of the PML-RARa fusion protein. As a result, APL and ATRA-resistant APL cells underwent apoptosis upon ZYH005 treatment and this apoptosis-inducing effect is even stronger than that of arsenic trioxide and anticancer agents including 5-fluorouracil, cisplatin and doxorubicin. Moreover, ZYH005 represses leukemia development in vivo and prolongs the survival of both APL and ATRA-resistant APL mice. To our knowledge, ZYH005 is the first synthetic phenanthridinone derivative, which functions as a DNA intercalator and can serve as a potential candidate drug for APL, particularly for ATRA-resistant APL.

Pyridoxine/pyridoxamine 5'-phosphate oxidase (Sgll/PNPO) is important for DNA integrity and glucose homeostasis maintenance in Drosophila

Pyridoxine/pyridoxamine 5'-phosphate oxidase (PNPO) and pyridoxal kinase (PDXK) cooperate to produce pyridoxal 5'-phosphate (PLP), the active form of vitamin B6. PDXK phosphorylates pyridoxine, pyridoxamine, and pyridoxal by producing PNP, PMP, and PLP, whereas PNPO oxidizes PNP, PMP, into PLP. We previously demonstrated that PDXK depletion in Drosophila and human cells impacts on glucose metabolism and DNA integrity. Here we characterized sgll, the Drosophila ortholog of PNPO gene, showing that its silencing by RNA interference elicits chromosome aberrations (CABs) in brains and induces diabetic hallmarks such as hyperglycemia and small body size. We showed that in sgll^RNAi neuroblasts CABs are largely produced by the genotoxic effect of the advanced glycation end products triggered by high glucose. As in sgll^RNAi cells, part of PLP is still produced by PDXK activity, these data suggest that PLP dosage need to be tightly regulated to guarantee glucose homeostasis and DNA integrity.

DNA polymerase beta participates in DNA End-joining

DNA double strand breaks (DSBs) are one of the most deleterious lesions and if left unrepaired, they lead to cell death, genomic instability and carcinogenesis. Cells combat DSBs by two pathways: homologous recombination (HR) and non-homologous end-joining (NHEJ), wherein the two DNA ends are re-joined. Recently a back-up NHEJ pathway has been reported and is referred to as alternative NHEJ (aNHEJ), which joins ends but results in deletions and insertions. NHEJ requires processing enzymes including nucleases and polymerases, although the roles of these enzymes are poorly understood. Emerging evidence indicates that X family DNA polymerases lambda (Pol λ) and mu (Pol μ) promote DNA end-joining. Here, we show that DNA polymerase beta (Pol β), another member of the X family of DNA polymerases, plays a role in aNHEJ. In the absence of DNA Pol β, fewer small deletions are observed. In addition, depletion of Pol β results in cellular sensitivity to bleomycin and DNA protein kinase catalytic subunit inhibitors due to defective repair of DSBs. In summary, our results indicate that Pol β in functions in aNHEJ and provide mechanistic insight into its role in this process.

Ginsenoside Rg1 impairs homologous recombination repair by targeting CtBP-interacting protein and sensitizes hepatoblastoma cells to DNA damage

The ginsenoside Rg1, the primary pharmacologically active ingredient of the traditional Chinese herb ginseng, is widely used in the clinical treatment of diseases of the immune and nervous systems. Recent studies have shown that it also has an antitumor effect. In this study, we explored the effects of Rg1 on hepatoblastoma (HB) and its underlying mechanisms. We demonstrated that Rg1 significantly inhibited HB cell growth both in vivo and in vitro. Mechanistic studies revealed that Rg1 impaired homologous recombination and triggered double-strand breaks in HB cells by directly targeting CtBP-interacting protein (CtIP), a key double-strand break repair factor, which is highly expressed in HB tissues. Moreover, we also demonstrated that Rg1 sensitized HB cells to DNA-damaging agents both in vitro and in vivo. In conclusion, our data not only demonstrate the potential clinical application of Rg1 as a novel chemotherapeutic candidate but also offer a mechanism-based therapeutic option by which DNA-damaging agents can be used in combination with Rg1 to target HB.

Early Passage Mesenchymal Stem Cells Display Decreased Radiosensitivity and Increased DNA Repair Activity

Cell therapies using human mesenchymal stem cells (MSCs) have received much attention in the past decade. In pursuit of the therapeutic potential of MSCs, cell expansion is required to generate a great number of cells with desired phenotype and functionality. Long‐term expansion in vitro, however, can lead to altered functions. To explore the changes in DNA damage responses (DDR) in MSCs expanded, DDR pathways following irradiation were characterized in early‐ and late‐passage bone marrow MSCs. Seventy‐two hours after irradiation, the percentage of sub‐G1 cells in early‐passage MSCs did not change significantly. Reduced TUNEL staining was observed in early‐passage MSCs compared to late‐passage MSCs 4 h after irradiation. Comet assay also revealed that early‐passage MSCs were more resistant to irradiation or DNA damages induced by genotoxic agents than late‐passage MSCs. ATM phosphorylation and γ‐H2AX and phospho‐p53 increased in early‐passage MSCs while decreased in late‐passage MSCs. Through inhibition by KU55933, DDR pathway in early‐passage MSCs was shown to be ATM‐dependent. Higher levels of poly (ADP‐ribose) polymerase‐1 (PARP‐1) and PAR synthesis were observed in early‐passage MSCs than in late‐passage MSCs. Knockdown of PARP‐1 in early‐passage MSCs resulted in sensitization to irradiation‐induced apoptosis. Overexpression of PARP‐1 in late passage MSCs could render irradiation resistance. Lower activity of DDR in late‐passage MSCs was associated with rapid proteasomal degradation of PARP‐1. In conclusion, early‐passage MSCs are more irradiation‐resistant and have increased DDR activity involving PARP‐1, ATM and their downstream signals. Stem Cells Translational Medicine2017;6:1504–1514

DNA Double Strand Breaks Repair Inhibitors: Relevance as Potential New Anticancer Therapeutics

DNA double-strand breaks are considered one of the most lethal forms of DNA damage. Many effective anticancer therapeutic approaches used chemical and physical methods to generate DNA double-strand breaks in the cancer cells. They include: IR and drugs which mimetic its action, topoisomerase poisons, some alkylating agents or drugs which affected DNA replication process. On the other hand, cancer cells are mostly characterized by highly effective systems of DNA damage repair. There are two main DNA repair pathways used to fix double-strand breaks: NHEJ and HRR. Their activity leads to a decreased effect of chemotherapy. Targeting directly or indirectly the DNA double-strand breaks response by inhibitors seems to be an exciting option for anticancer therapy and is a part of novel trends that arise after the clinical success of PARP inhibitors. These trends will provide great opportunities for the development of DNA repair inhibitors as new potential anticancer drugs. The main objective of this article is to address these new promising advances.

TICRR Contributes to Tumorigenesis Through Accelerating DNA Replication in Cancers

DNA replication is precisely regulated in cells and its dysregulation can trigger tumorigenesis. Here we identified that the TOPBP1 interacting checkpoint and replication regulator (TICRR) mRNA level was universally and highly expressed in 15 solid cancer types. Depletion of TICRR significantly inhibited tumor cell growth, colony formation and migration in vitro, and strikingly inhibited tumor growth in the xenograft model. We reveal that knockdown of TICRR inhibited not only the initiation but also the fork progression of DNA replication. Suppression of DNA synthesis by TICRR silencing caused DNA damage accumulation, subsequently activated the ATM/CHK2 dependent p53 signaling, and finally induced cell cycle arrest and apoptosis at least in p53-wild cancer cells. Further, we show that a higher TICRR level was associated with poorer overall survival (OS) and disease free survival (DFS) in multiple cancer types. In conclusion, our study shows that TICRR is involved in tumorigenesis by regulating DNA replication, acting as a common biomarker for cancer prognosis and could be a promising target for drug-development and cancer treatment.

M2I-1 disrupts the in vivo interaction between CDC20 and MAD2 and increases the sensitivities of cancer cell lines to anti-mitotic drugs via MCL-1s

Background

Drugs such as taxanes, epothilones, and vinca alkaloids are widely used in the treatment of breast, ovarian, and lung cancers but come with major side effects such as neuropathy and loss of neutrophils and as single agents have a lack of efficacy. M2I-1 (MAD2 inhibitor-1) has been shown to disrupt the CDC20-MAD2 interaction, and consequently, the assembly of the mitotic checkpoint complex (MCC).

Results

We report here that M2I-1 can significantly increase the sensitivity of several cancer cell lines to anti-mitotic drugs, with cell death occurring after a prolonged mitotic arrest. In the presence of nocodazole or taxol combined with M2I-1 cell death is triggered by the premature degradation of Cyclin B1, the perturbation of the microtubule network, and an increase in the level of the pro-apoptotic protein MCL-1s combined with a marginal increase in the level of NOXA. The elevated level of MCL-1s and the marginally increased NOXA antagonized the increased level of MCL-1, a pro-survival protein of the Bcl-2 family.

Conclusion

Our results provide some important molecular mechanisms for understanding the relationship between the mitotic checkpoint and programmed cell death and demonstrate that M2I-1 exhibits antitumor activity in the presence of current anti-mitotic drugs such as taxol and nocodazole and has the potential to be developed as an anticancer agent.

DNA lesions correlate with lymphocyte function after selective internal radiotherapy

In patients with non-resectable hepatic malignancies selective internal radiotherapy (SIRT) with yttrium-90 is an effective therapy. However, previous data indicate that SIRT leads to impaired immune function. The aim of the current study was to determine the extent of DNA lesions in peripheral blood mononuclear cells of SIRT patients and to correlate these lesions with cellular immune responses. In ten patients γH2AX and 53BP1 foci were determined. These foci are markers of DNA double-strand breaks (DSBs) and occur consecutively. In parallel, lymphocyte proliferation was assessed after stimulation with the T cell mitogen phytohemagglutinin. Analyses of vital cells were performed prior to and 1 h and 1 week after SIRT. 1 h and 1 week after SIRT numbers of γH2AX and of 53BP1 foci were more than threefold larger than before (p < 0.01). Already at baseline, foci were more abundant than published in healthy controls. Lymphocyte proliferation at baseline was below the normal range and further decreased after SIRT. Prior to therapy, there was an inverse correlation between lymphocyte proliferation and the quotient 53BP1/γH2AX; which could be considered as a measure of the course of DNA DSB repair (r = - 0.94, p < 0.0001). Proliferative responses were inversely correlated with 53BP1 foci prior to therapy and γH2AX and 53BP1 foci 1 h after therapy (r < - 0.65, p < 0.05). In conclusion, DNA foci in SIRT patients were correlated with impaired in vitro immune function. Unrepaired DNA DSBs or cell cycle arrest due to repair may cause this impairment.

Is Chickpea a Potential Substitute for Soybean? Phenolic Bioactives and Potential Health Benefits

Legume seeds are rich sources of protein, fiber, and minerals. In addition, their phenolic compounds as secondary metabolites render health benefits beyond basic nutrition. Lowering apolipoprotein B secretion from HepG2 cells and decreasing the level of low-density lipoprotein (LDL)-cholesterol oxidation are mechanisms related to the prevention of cardiovascular diseases (CVD). Likewise, low-level chronic inflammation and related disorders of the immune system are clinical predictors of cardiovascular pathology. Furthermore, DNA-damage signaling and repair are crucial pathways to the etiology of human cancers. Along CVD and cancer, the prevalence of obesity and diabetes is constantly increasing. Screening the ability of polyphenols in inactivating digestive enzymes is a good option in pre-clinical studies. In addition, in vivo studies support the role of polyphenols in the prevention and/or management of diabetes and obesity. Soybean, a well-recognized source of phenolic isoflavones, exerts health benefits by decreasing oxidative stress and inflammation related to the above-mentioned chronic ailments. Similar to soybeans, chickpeas are good sources of nutrients and phenolic compounds, especially isoflavones. This review summarizes the potential of chickpea as a substitute for soybean in terms of health beneficial outcomes. Therefore, this contribution may guide the industry in manufacturing functional foods and/or ingredients by using an undervalued feedstock.

qDSB-Seq is a general method for genome-wide quantification of DNA double-strand breaks using sequencing

DNA double-strand breaks (DSBs) are among the most lethal types of DNA damage and frequently cause genome instability. Sequencing-based methods for mapping DSBs have been developed but they allow measurement only of relative frequencies of DSBs between loci, which limits our understanding of the physiological relevance of detected DSBs. Here we propose quantitative DSB sequencing (qDSB-Seq), a method providing both DSB frequencies per cell and their precise genomic coordinates. We induce spike-in DSBs by a site-specific endonuclease and use them to quantify detected DSBs (labeled, e.g., using i-BLESS). Utilizing qDSB-Seq, we determine numbers of DSBs induced by a radiomimetic drug and replication stress, and reveal two orders of magnitude differences in DSB frequencies. We also measure absolute frequencies of Top1-dependent DSBs at natural replication fork barriers. qDSB-Seq is compatible with various DSB labeling methods in different organisms and allows accurate comparisons of absolute DSB frequencies across samples.

Design and synthesis a mitochondria-targeted dihydronicotinamide as radioprotector

Radiation-induced damage to the mitochondrial macromolecules and electron transfer chain (ETC), causing the generation of primary and secondary reactive oxygen (ROS) species. The continuous ROS production after radiation will trigger cell oxidative stress and ROS-mediated nucleus apoptosis and autophagy signaling pathways. Scavenging radiation-induced ROS effectively can help mitochondria to maintain their physiological function and relief cells from oxidative stress. Nicotinamide is a critical endogenous antioxidant helping to neutralize ROS in vivo. In this study, we designed and synthetized a novel mitochondrial-targeted dihydronicotinamide (Mito-N) with the help of mitochondrial membrane potential to enter the mitochondria and scavenge ROS. According to experiment results, Mito-N significantly increased cell viability by 30.75% by neutralizing the accumulated ROS and resisting DNA strands breaks after irradiation. Furthermore, the mice survival rate also improved with the treatment of Mito-N, by effectively ameliorating the hematopoietic system infliction under lethal dose irradiation.

Release of paused RNA polymerase II at specific loci favors DNA double-strand-break formation and promotes cancer translocations

It is not clear how spontaneous DNA double-strand breaks (DSBs) form and are processed in normal cells, and whether they predispose to cancer-associated translocations. We show that DSBs in normal mammary cells form upon release of paused RNA polymerase II (Pol II) at promoters, 5' splice sites and active enhancers, and are processed by end-joining in the absence of a canonical DNA-damage response. Logistic and causal-association models showed that Pol II pausing at long genes is the main predictor and determinant of DSBs. Damaged introns with paused Pol II-pS5, TOP2B and XRCC4 are enriched in translocation breakpoints, and map at topologically associating domain boundary-flanking regions showing high interaction frequencies with distal loci. Thus, in unperturbed growth conditions, release of paused Pol II at specific loci and chromatin territories favors DSB formation, leading to chromosomal translocations.

The DNA Damaging Revolution: PARP Inhibitors and Beyond

Cancer-specific DNA repair defects are abundant in malignant tissue and present an opportunity to capitalize on these aberrations for therapeutic benefit. Early preclinical data demonstrated the concept of synthetic lethality between BRCA genetic defects and pharmacologic PARP inhibition, suggesting that there may be monotherapy activity with this class of agents and supporting the early trial testing of this molecularly driven approach. Although the first foray into the clinic for PARP inhibitors was in combination with DNA-damaging cytotoxic agents, clinical development was limited by the more-than-additive toxicity, in particular dose-limiting myelosuppression. As more tolerable single agents, PARP inhibitors are now approved for the treatment of ovarian cancer in different settings and BRCA-mutant breast cancers. Beyond PARP inhibitors, there is now a large armamentarium of potent and relatively selective inhibitors in clinical trial testing against key targets involved in the DNA damage response (DDR), including ATR, ATM, CHK1/2, WEE1, and DNA-PK. These agents are being developed for patients with molecularly selected tumors and in rational combinations with other molecularly targeted agents and immune checkpoint inhibitors. We detail the clinical progress made in the development of PARP inhibitors, review rational combinations, and discuss the development of emerging inhibitors against novel DDR targets, including DNA repair proteins, DNA damage signaling, and DNA metabolism.

Genetic polymorphisms in DNA repair genes and their association with cervical cancer

Background and objective: Carcinoma of cervix is the second most common cancer among women worldwide. The DNA repair network plays an important role in the maintenance of genetic stability, protection against DNA damage and carcinogenesis. Alterations in repair genes XRCC1, XRCC2 and XRCC3 and been reported in certain cancers. We hypothesised an association between XRCC1+399A/G, XRCC2+31467G/A and XRCC3+18067C/T polymorphisms and the risk of cervical cancer. Subjects and methods: This study included 525 subjects (265 controls and 260 cervical cancer cases). Genotypes were determined by polymerase chain reaction-restriction fragment length polymorphism (PCR-RFLP). Results: Women with GA and AA genotypes of XRCC1+399A/G showed 2.4-3.8 fold higher risk of cervical cancer (P = 0.001). The +399A* allele was significantly linked with cervical cancer (P = 0.002). However, XRCC2+31479G/A and XRCC3+18067C/T polymorphisms did not show any statistically significant associations. Conclusion: The XRCC1+399A/G SNP is linked with cervical cancer. We suggest that this variant can be utilized as a prognostic marker for determination of cervical cancer susceptibility.

BCL10 in cell survival after DNA damage

The complex defense mechanism of the DNA damage response (DDR) developed by cells during long-term evolution is an important mechanism for maintaining the stability of the genome. Defects in the DDR pathway can lead to the occurrence of various diseases, including tumor development. Most cancer treatments cause DNA damage and apoptosis. However, cancer cells have the natural ability to repair this damage and inhibit apoptosis, ultimately leading to the development of drug resistance. Therefore, investigating the mechanism of DNA damage may contribute markedly to the future treatment of cancer. The CARMA-BCL10-MALT1 (CBM) complex formed by B cell lymphoma/leukemia 10 (BCL10) regulates apoptosis by activating NF-κB signaling. BCL10 is involved in the formation of complexes that antagonize apoptosis and contribute to cell survival after DNA damage, with cytoplasmic BCL10 entering the nucleus to promote DNA damage repair, including histone ubiquitination and the recruitment of homologous recombination (HR) repair factors. This article reviews the role of BCL10 in cell survival following DNA damage.

Quantifying length-dependent DNA end-binding by nucleoproteins

The ends of nucleic acids oligomers alter the statistics of interior nonspecific ligand binding and act as binding sites with altered properties. While the former aspect of "end effects" has received much theoretical attention in the literature, the physical nature of end-binding, and hence its potential impact on a wide range of studies with oligomers, remains poorly known. Here, we report for the first time end-binding to DNA using a model helix-turn-helix motif, the DNA-binding domain of ETV6, as a function of DNA sequence length. Spectral analysis of ETV6 intrinsic tryptophan fluorescence by singular value decomposition showed that end-binding to nonspecific fragments was negligible at >0.2 kbp and accumulated to 8% of total binding to 23-bp oligomers. The affinity for end-binding was insensitive to salt but tracked the affinity of interior binding, suggesting translocation from interior sites rather than free solution as its mechanism. As the presence of a cognate site in the 23-bp oligomer suppressed end-binding, neglect of end-binding to the short cognate DNA does not introduce significant error. However, the same applies to nonspecific DNA only if longer fragments (>0.2 kbp) are used.

Interplay between DNA Polymerases and DNA Ligases: Influence on Substrate Channeling and the Fidelity of DNA Ligation

DNA ligases are a highly conserved group of nucleic acid enzymes that play an essential role in DNA repair, replication, and recombination. This review focuses on functional interaction between DNA polymerases and DNA ligases in the repair of single- and double-strand DNA breaks, and discusses the notion that the substrate channeling during DNA polymerase-mediated nucleotide insertion coupled to DNA ligation could be a mechanism to minimize the release of potentially mutagenic repair intermediates. Evidence suggesting that DNA ligases are essential for cell viability includes the fact that defects or insufficiency in DNA ligase are casually linked to genome instability. In the future, it may be possible to develop small molecule inhibitors of mammalian DNA ligases and/or their functional protein partners that potentiate the effects of chemotherapeutic compounds and improve cancer treatment outcomes.

Mechanistic modelling supports entwined rather than exclusively competitive DNA double-strand break repair pathway

Following radiation induced DNA damage, several repair pathways are activated to help preserve genome integrity. Double Strand Breaks (DSBs), which are highly toxic, have specified repair pathways to address them. The main repair pathways used to resolve DSBs are Non-Homologous End Joining (NHEJ) and Homologous Recombination (HR). Cell cycle phase determines the availability of HR, but the repair choice between pathways in the G2 phases where both HR and NHEJ can operate is not clearly understood. This study compares several in silico models of repair choice to experimental data published in the literature, each model representing a different possible scenario describing how repair choice takes place. Competitive only scenarios, where initial protein recruitment determines repair choice, are unable to fit the literature data. In contrast, the scenario which uses a more entwined relationship between NHEJ and HR, incorporating protein co-localisation and RNF138-dependent removal of the Ku/DNA-PK complex, is better able to predict levels of repair similar to the experimental data. Furthermore, this study concludes that co-localisation of the Mre11-Rad50-Nbs1 (MRN) complexes, with initial NHEJ proteins must be modeled to accurately depict repair choice.

Clinical application of ceramide in cancer treatment

Development of innovative strategies for cancer treatment is a pressing public health issue. Despite recent advances, the mechanisms of cancer progression and the resistance to cancer treatment have not been fully elucidated. Sphingolipids, including ceramide and sphingoshin-1-phosphate, are bioactive mediators that regulate cancer cell death and survival through the dynamic balance of what has been termed the 'sphingolipid rheostat'. Specifically, ceramide, which acts as the central hub of sphingolipid metabolism, is generated via three major pathways by many stressors, including anti-cancer treatments, environmental stresses, and cytokines. We have previously shown in breast cancer patients that elevated ceramide correlated with less aggressive cancer phenotypes, leading to a prognostic impact. Recent studies showed that ceramide have the possibility of becoming the reinforcing agent of cancer treatment as well as other roles such as nanoparticles and diagnostic biomarker. We review ceramide as one of the key molecules to investigate in overcoming resistance to current drug therapies and in becoming one of the newest cancer treatments.

Should we ban total phenolics and antioxidant screening methods? The link between antioxidant potential and activation of NF-κB using phenolic compounds from grape by-products

Free radical imbalance is associated with several chronic diseases. However, recent controversies have put in check the validity of colorimetric methods to screen the functionality of polyphenols. Therefore, in this study two antioxidant methods, based on chemical reactions, were tested for their ability in anticipating the reduction of the activation of NF-κB using LPS-activated RAW 264.7 macrophages, selected as a biological model. Grape processing by-products from winemaking showed higher total phenolic content (TPC), antioxidant capacity towards peroxyl radical (31.1%) as well as reducing power (39.5%) than those of grape juice by-products. The same trend was observed when these samples were tested against LPS-activated RAW 264.7 macrophages by reducing the activation NF-κB. Feedstocks containing higher TPC and corresponding ORAC and FRAP results translated to higher reduction in the activation of NF-κB (36.5%). Therefore, this contribution demonstrates that colorimetric methods are still important screening tools owing their simplicity and widespread application.

A Structural Perspective on the Regulation of Human Single-Stranded DNA Binding Protein 1 (hSSB1, OBFC2B) Function in DNA Repair

Single-stranded DNA binding (SSB) proteins are essential to protect singe-stranded DNA (ssDNA) that exists as a result of several important DNA repair pathways in living cells. In humans, besides the well-characterised Replication Protein A (RPA) we have described another SSB termed human SSB1 (hSSB1, OBFC2B) and have shown that this protein is an important player in the maintenance of the genome. In this review we define the structural and biophysical details of how hSSB1 interacts with both DNA and other essential proteins. While the presence of the oligonucleotide/oligosaccharide (OB) domain ensures ssDNA binding by hSSB1, it has also been shown to self-oligomerise as well as interact with and being modified by several proteins highlighting the versatility that hSSB1 displays in the context of DNA repair. A detailed structural understanding of these processes will likely lead to the designs of tailored hSSB1 inhibitors as anti-cancer drugs in the near future.

Highly interacting regions of the human genome are enriched with enhancers and bound by DNA repair proteins

In specific cases, chromatin clearly forms long-range loops that place distant regulatory elements in close proximity to transcription start sites, but we have limited understanding of many loops identified by Chromosome Conformation Capture (such as Hi-C) analyses. In efforts to elucidate their characteristics and functions, we have identified highly interacting regions (HIRs) using intra-chromosomal Hi-C datasets with a new computational method based on looking at the eigenvector that corresponds to the smallest eigenvalue (here unity). Analysis of these regions using ENCODE data shows that they are in general enriched in bound factors involved in DNA damage repair and have actively transcribed genes. However, both highly transcribed regions as well as transcriptionally inactive regions can form HIRs. The results also indicate that enhancers and super-enhancers in particular form long-range interactions within the same chromosome. The accumulation of DNA repair factors in most identified HIRs suggests that protection from DNA damage in these regions is essential for avoidance of detrimental rearrangements.

Inhibition of BET Proteins and Histone Deacetylase (HDACs): Crossing Roads in Cancer Therapy

Histone DeACetylases (HDACs) are enzymes that remove acetyl groups from histones and other proteins, regulating the expression of target genes. Pharmacological inhibition of these enzymes re-shapes chromatin acetylation status, confusing boundaries between transcriptionally active and quiescent chromatin. This results in reinducing expression of silent genes while repressing highly transcribed genes. Bromodomain and Extraterminal domain (BET) proteins are readers of acetylated chromatin status and accumulate on transcriptionally active regulatory elements where they serve as scaffold for the building of transcription-promoting complexes. The expression of many well-known oncogenes relies on BET proteins function, indicating BET inhibition as a strategy to counteract their activity. BETi and HDACi share many common targets and affect similar cellular processes to the point that combined inhibition of both these classes of proteins is regarded as a strategy to improve the effectiveness of these drugs in cancer. In this work, we aim to discuss the molecular basis of the interplay between HDAC and BET proteins, pointing at chromatin acetylation as a crucial node of their functional interaction. We will also describe the state of the art of their dual inhibition in cancer therapy. Finally, starting from their mechanism of action we will provide a speculative perspective on how these drugs may be employed in combination with standard therapies to improve effectiveness and/or overcome resistance.

Expression of the DNA-dependent protein kinase catalytic subunit is associated with the radiosensitivity of human thyroid cancer cell lines

The prognosis and treatment of thyroid cancer depends on the type and stage of the disease. Radiosensitivity differs among cancer cells owing to their varying capacity for repair after irradiation. Radioactive iodine can be used to destroy thyroid cancer cells. However, patient prognosis and improvement after irradiation varies. Therefore, predictive measures are important for avoiding unnecessary exposure to radiation. We describe a new method for predicting the effects of radiation in individual cases of thyroid cancer based on the DNA-dependent protein kinase (DNA-PK) activity level in cancer cells. The radiation sensitivity, DNA-PK activity, and cellular levels of DNA-PK complex subunits in five human thyroid cancer cell lines were analyzed in vitro. A positive correlation was observed between the D10 value (radiation dose that led to 10% survival) of cells and DNA-PK activity. This correlation was not observed after treatment with NU7441, a DNA-PK-specific inhibitor. A significant correlation was also observed between DNA-PK activity and expression levels of the DNA-PK catalytic subunit (DNA-PKcs). Cells expressing low DNA-PKcs levels were radiation-sensitive, and cells expressing high DNA-PKcs levels were radiation-resistant. Our results indicate that radiosensitivity depends on the expression level of DNA-PKcs in thyroid cancer cell lines. Thus, the DNA-PKcs expression level is a potential predictive marker of the success of radiation therapy for thyroid tumors.

In vitro and in vivo genotoxicity of oxygenated polycyclic aromatic hydrocarbons

Oxygenated polycyclic aromatic hydrocarbons (oxy-PAHs) are a group of environmental pollutants found in complex mixtures together with PAHs. In contrast to the extensively studied PAHs, which have been established to have mutagenic and carcinogenic properties, much less is known about the effects of oxy-PAHs. The present work aimed to investigate the genotoxic potency of a set of environmentally relevant oxy-PAHs along with environmental soil samples in human bronchial epithelial cells (HBEC). We found that all oxy-PAHs tested induced DNA strand breaks in a dose-dependent manner and some of the oxy-PAHs further induced micronuclei formation. Our results showed weak effects in response to the oxy-PAH containing subfraction of the soil sample. The genotoxic potency was confirmed in both HBEC and HepG2 cells following exposure to oxy-PAHs by an increased level of phospho-Chk1, a biomarker used to estimate the carcinogenic potency of PAHs in vitro. We further exposed zebrafish embryos to single oxy-PAHs or a binary mixture with PAH benzo[a]pyrene (B[a]P) and found the mixture to induce comparable or greater effects on the induction of DNA strand breaks compared to the sum of that induced by B[a]P and oxy-PAHs alone. In conclusion, oxy-PAHs were found to elicit genotoxic effects at similar or higher levels to that of B[a]P which indicates that oxy-PAHs may contribute significantly to the total carcinogenic potency of environmental PAH mixtures. This emphasizes further investigations of these compounds as well as the need to include oxy-PAHs in environmental monitoring programs in order to improve health risk assessment.

Long noncoding RNAs: p53's secret weapon in the fight against cancer?

p53 regulates the expression of hundreds of genes. Recent surprising observations indicate that no single protein-coding gene controls the tumor suppressor effects of p53. This raises the possibility that a subset of these genes, regulated by a p53-induced long noncoding RNA (lncRNA), could control p53’s tumor suppressor function. We propose molecular mechanisms through which lncRNAs could regulate this subset of genes and hypothesize an exciting, direct role of lncRNAs in p53’s genome stability maintenance function. Exploring these mechanisms could reveal lncRNAs as indispensable mediators of p53 and lay the foundation for understanding how other transcription factors could act via lncRNAs.

Transcription factors regulate hundreds of genes, a subset of which could mediate its effects in a given context. This Unsolved Mystery article explores mechanisms by which long noncoding RNAs might regulate such a subset downstream of p53, a well-studied transcription factor and major tumor suppressor.

Chronic low dose exposure of hospital workers to ionizing radiation leads to increased micronuclei frequency and reduced antioxidants in their peripheral blood lymphocytes

Purpose: The regular low dose occupational exposure to ionizing radiation may induce deleterious health effects, which may be of particular interest to medical radiation workers who daily handle X-ray machines. Human peripheral blood lymphocytes are able to retain the signature of radiation-induced DNA damage, therefore, the present study was undertaken to investigate the DNA damage and antioxidants status in hospital workers occupationally exposed to low doses of X-rays. Materials and methods: The peripheral blood lymphocytes of the occupationally exposed and control groups matched for age, gender, tobacco usage, and alcohol consumption were cultured and micronuclei frequency was determined. Activities of antioxidant enzymes and lipid peroxidation were also estimated in their plasma. Results: The micronuclei frequency in the occupationally exposed group (n = 33), increased significantly (p < .0001) followed by reduced glutathione-s-transferase (p < .01) and catalase (p < .001) activities, and increased lipid peroxidation (p < .05) when compared to the control group (n = 33). Occupational exposure resulted in an effective dose ranging between 3.14 to 144.5 mSv (40.88 ± 39.86mSv) depending on the employment duration of 3-29 years (10.33 ± 7.05 years). A correlation between the micronuclei frequency (p < .05) and catalase activity (p < .05) existed in the occupationally exposed individuals depending on the smoking habit, age, duration of employment, cumulative exposure dose and number of patients handled per day. Conclusions: We have observed that protracted low dose exposure to ionizing radiation is an inevitable occupational hazard leading to persistence of oxidative stress and increased genomic instability in the radiological technicians depending on the time spent with X-rays, cumulative dose received and the number of patients handled daily raising the risk of cancer development.

Protein stability of p53 targets determines their temporal expression dynamics in response to p53 pulsing

Oscillations in p53 expression are critical for regulating the cellular response to DNA damage. Hanson et al. show that the relationship between p53 pulse frequency and target mRNA and protein decay rates regulates stress response pathway dynamics and function.

In response to DNA damage, the transcription factor p53 accumulates in a series of pulses. While p53 dynamics play a critical role in regulating stress responses, how p53 pulsing affects target protein expression is not well understood. Recently, we showed that p53 pulses generate diversity in target mRNA expression dynamics; however, given that mRNA and protein expression are not necessarily well correlated, it remains to be determined how p53 pulses impact target protein expression. Using computational and experimental approaches, we show that target protein decay rates filter p53 pulses: Distinct target protein expression dynamics are generated depending on the relationship between p53 pulse frequency and target mRNA and protein stability. Furthermore, by mutating the targets MDM2 and PUMA to alter their stabilities, we show that downstream pathways are sensitive to target protein decay rates. This study delineates the mechanisms by which p53 dynamics play a crucial role in orchestrating the timing of events in the DNA damage response network.

Transcriptomic Analysis of Planarians under Simulated Microgravity or 8 g Demonstrates That Alteration of Gravity Induces Genomic and Cellular Alterations That Could Facilitate Tumoral Transformation

The possibility of humans to live outside of Earth on another planet has attracted the attention of numerous scientists around the world. One of the greatest difficulties is that humans cannot live in an extra-Earth environment without proper equipment. In addition, the consequences of chronic gravity alterations in human body are not known. Here, we used planarians as a model system to test how gravity fluctuations could affect complex organisms. Planarians are an ideal system, since they can regenerate any missing part and they are continuously renewing their tissues. We performed a transcriptomic analysis of animals submitted to simulated microgravity (Random Positioning Machine, RPM) (s-µg) and hypergravity (8 g), and we observed that the transcriptional levels of several genes are affected. Surprisingly, we found the major differences in the s-µg group. The results obtained in the transcriptomic analysis were validated, demonstrating that our transcriptomic data is reliable. We also found that, in a sensitive environment, as under Hippo signaling silencing, gravity fluctuations potentiate the increase in cell proliferation. Our data revealed that changes in gravity severely affect genetic transcription and that these alterations potentiate molecular disorders that could promote the development of multiple diseases such as cancer.

Polymorphism of DNA Repair Genes via Homologous Recombination (HR) in Ovarian Cancer

Ovarian cancer is one of the most common types of cancer in women. The repair system via homologous recombination repairs double-strand breaks (DSB) of DNA, which are the most mortal for cell, out of all DNA damages. The genes, which encode the double-strand break repairing proteins, are highly polymorphic and, taking into account the significance of the repaired defects for cancer development, it seems important to learn the role of the polymorphisms in ovarian cancer development. The aim of the study was to determine the relationship between DNA repair genes via homologous recombination (HR) and modulation of the risk of ovarian cancer. The following polymorphisms were analysed: XRCC3-Thr241Met (rs861539), XRCC2--41657C/T (rs718282), XRCC2-Arg188His (rs3218536), BRCA1-Q356R (rs1799950) and RAD51-135 G/C (rs1801320). The study group included 600 patients with ovarian cancer and 600 healthy controls. The PCR-RFLP (PCR-based restriction fragment length polymorphism) technique was applied for polymorphism analysis. Allele XRCC3-241Met (OR 0.85, 95%CI 0.72-0.99, p < 0.045), XRCC2-41657 T (OR 1.67, 95% CI 1.42-1.96, p < .0001), BRCA1-356R (OR 1.61; % CI 1.37-1.90, p < .0001) and RAD51-135C (OR 5.16; 95% CI 4.29-6.20, p < .0001) strongly correlated with the neoplastic disease. No relationship was observed between the studied polymorphisms and the cancer progression stage according to FIGO classification. The results indicate that polymorphisms of DNA repair genes via homologous recombination may be associated with the incidence of ovarian cancer. Further research on larger groups is warranted to determine the influence of above-mentioned genetic variants on ovarian cancer risk.

From Whole-Brain Radiotherapy to Immunotherapy: A Multidisciplinary Approach for Patients with Brain Metastases from NSCLC

Non-small cell lung cancer patients with brain metastases have a multitude of treatment options, but there is currently no international and multidisciplinary consensus concerning their optimal treatment. Local therapies have the principal role, especially in symptomatic patients. Advances in surgery and radiation therapy manage considerable local control. Systemic treatments have shown effect in clinical trials and in real life clinical settings; yet, at present, this is restricted to patients with asymptomatic or stable intracranial lesions. Targeted agents can have a benefit only in patients with EGFR mutations or ALK rearrangement. Immunotherapy has shown impressive results in patients with PD-L1 expression in tumor cells. Its effects can be further enhanced by a synergy with radiotherapy, possibly by increasing the percentage of responders. The present review summarizes the need for more effective systemic treatments, so that the increased intracranial control achieved by local treatments can be translated in an increase in overall survival.