Reactive oxygen species (ROS)--induced genetic and epigenetic alterations in human carcinogenesis

Reactive oxygen species, nutrition, hypoxia and diseases: Problems solved?

Within the last twenty years the view on reactive oxygen species (ROS) has changed; they are no longer only considered to be harmful but also necessary for cellular communication and homeostasis in different organisms ranging from bacteria to mammals. In the latter, ROS were shown to modulate diverse physiological processes including the regulation of growth factor signaling, the hypoxic response, inflammation and the immune response. During the last 60–100 years the life style, at least in the Western world, has changed enormously. This became obvious with an increase in caloric intake, decreased energy expenditure as well as the appearance of alcoholism and smoking; These changes were shown to contribute to generation of ROS which are, at least in part, associated with the occurrence of several chronic diseases like adiposity, atherosclerosis, type II diabetes, and cancer. In this review we discuss aspects and problems on the role of intracellular ROS formation and nutrition with the link to diseases and their problematic therapeutical issues.

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Oxidative stress is linked to overnutrition, obesity and associated diseases or cancer.

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Reactive oxygen species (ROS) are crucially involved in modulation of signaling cascades.

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NOX proteins and hypoxia contribute to formation of ROS under different nutrient regimes.

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ROS are powerful post-transcriptional and epigenetic regulators.

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Treatment of obesity with antioxidants requires more, larger, and better monitored clinical trials.

Abundant Rodent Furan-Derived Urinary Metabolites Are Associated with Tobacco Smoke Exposure in Humans

Furan, a possible human carcinogen, is found in heat treated foods and tobacco smoke. Previous studies have shown that humans are capable of converting furan to its reactive metabolite, cis-2-butene-1,4-dial (BDA), and therefore may be susceptible to furan toxicity. Human risk assessment of furan exposure has been stymied because of the lack of mechanism-based exposure biomarkers. Therefore, a sensitive LC-MS/MS assay for six furan metabolites was applied to measure their levels in urine from furan-exposed rodents as well as in human urine from smokers and nonsmokers. The metabolites that result from direct reaction of BDA with lysine (BDA-N(α)-acetyllysine) and from cysteine-BDA-lysine cross-links (N-acetylcysteine-BDA-lysine, N-acetylcysteine-BDA-N(α)-acetyllysine, and their sulfoxides) were targeted in this study. Five of the six metabolites were identified in urine from rodents treated with furan by gavage. BDA-N(α)-acetyllysine, N-acetylcysteine-BDA-lysine, and its sulfoxide were detected in most human urine samples from three different groups. The levels of N-acetylcysteine-BDA-lysine sulfoxide were more than 10 times higher than that of the corresponding sulfide in many samples. The amount of this metabolite was higher in smokers relative to that in nonsmokers and was significantly reduced following smoking cessation. Our results indicate a strong relationship between BDA-derived metabolites and smoking. Future studies will determine if levels of these biomarkers are associated with adverse health effects in humans.

Promoter demethylation of nuclear factor-erythroid 2-related factor 2 gene in drug-resistant colon cancer cells

The mechanisms underlying drug resistance in colorectal cancer (CRC) treatment remain to be fully elucidated. Therefore, the present study aimed to investigate the underlying mechanism resistance to a widely used anticancer drug, 5-Fluorouracil (5-FU). Nuclear factor-erythroid 2-related factor 2 (Nrf2) is an important transcription factor involved in cellular protection. In the present study, it was hypothesized that the epigenetic modification of Nrf2 may be a potential target for 5-FU resistance in CRC treatment. Protein and messenger RNA levels of Nrf2, heme oxygenase-1 (HO-1), DNA methylases and DNA methyltransferases were determined and DNA methylation analysis for the Nrf2 promoter was performed in a human CRC control (SNU-C5) and resistant (SNU-C5R) cell line. The results demonstrated that Nrf2 expression levels, nuclear translocation and promoter binding were significantly increased in SNU-C5R cells compared with SNU-C5 cells. Elevated levels of activated Nrf2 in SNU-C5R cells resulted in the increased protein expression and activity of HO-1. In addition, increased production of reactive oxygen species (ROS) and upregulation of ten-eleven translocation (TET)1 were observed in SNU-C5R cells compared with SNU-C5 cells. Furthermore, methylation analysis revealed Nrf2 promoter cytosine-phosphate-guanine island hypomethylation in 5-FU-treated cells. In conclusion, the results indicated that 5-FU-induced ROS production resulted in the upregulation of TET1 expression and function. In addition, these results indicated that TET-dependent demethylation of the Nrf2 promoter upregulated Nrf2 and HO-1 expression, which induced cellular protection mechanisms, ultimately leading to drug resistance.

DNA replication stress as a hallmark of cancer

Human cancers share properties referred to as hallmarks, among which sustained proliferation, escape from apoptosis, and genomic instability are the most pervasive. The sustained proliferation hallmark can be explained by mutations in oncogenes and tumor suppressors that regulate cell growth, whereas the escape from apoptosis hallmark can be explained by mutations in the TP53, ATM, or MDM2 genes. A model to explain the presence of the three hallmarks listed above, as well as the patterns of genomic instability observed in human cancers, proposes that the genes driving cell proliferation induce DNA replication stress, which, in turn, generates genomic instability and selects for escape from apoptosis. Here, we review the data that support this model, as well as the mechanisms by which oncogenes induce replication stress. Further, we argue that DNA replication stress should be considered as a hallmark of cancer because it likely drives cancer development and is very prevalent.

Oxidative stress levels are correlated with P15 and P16 gene promoter methylation in myelodysplastic syndrome patients

Oxidative stress and abnormal DNA methylation have been implicated in some types of cancer, namely in myelodysplastic syndromes (MDS). Since both mechanisms are observed in MDS patients, we analyzed the correlation of intracellular levels of peroxides, superoxide anion, and glutathione (GSH), as well as ratios of peroxides/GSH and superoxide/GSH, with the methylation status of P15 and P16 gene promoters in bone marrow leukocytes from MDS patients. Compared to controls, these patients had lower GSH content, higher peroxide levels, peroxides/GSH and superoxide/GSH ratios, as well as higher methylation frequency of P15 and P16 gene promoters. Moreover, patients with methylated P15 gene had higher oxidative stress levels than patients without methylation (peroxides: 460 ± 42 MIF vs 229 ± 25 MIF, p = 0.001; superoxide: 383 ± 48 MIF vs 243 ± 17 MIF, p = 0.022; peroxides/GSH: 2.50 ± 0.08 vs 1.04 ± 0.34, p < 0.001; superoxide/GSH: 1.76 ± 0.21 vs 1.31 ± 0.10, p = 0.007). Patients with methylated P16 and at least one methylated gene had higher peroxide levels as well as peroxides/GSH ratio than patients without methylation. Interestingly, oxidative stress levels allow the discrimination of patients without methylation from ones with methylated P15, methylated P16, or at least one methylated (P15 or P16) promoter. Taken together, these findings support the hypothesis that oxidative stress is correlated with P15 and P16 hypermethylation.

Oxidative stress and epigenetic modifications in the pathogenesis of diabetic retinopathy

Diabetic retinopathy remains the major cause of blindness among working age adults. Although a number of metabolic abnormalities have been associated with its development, due to complex nature of this multi-factorial disease, a link between any specific abnormality and diabetic retinopathy remains largely speculative. Diabetes increases oxidative stress in the retina and its capillary cells, and overwhelming evidence suggests a bidirectional relationship between oxidative stress and other major metabolic abnormalities implicated in the development of diabetic retinopathy. Due to increased production of cytosolic reactive oxygen species, mitochondrial membranes are damaged and their membrane potentials are impaired, and complex III of the electron transport system is compromised. Suboptimal enzymatic and nonenzymatic antioxidant defense system further aids in the accumulation of free radicals. As the duration of the disease progresses, mitochondrial DNA (mtDNA) is damaged and the DNA repair system is compromised, and due to impaired transcription of mtDNA-encoded proteins, the integrity of the electron transport system is encumbered. Due to decreased mtDNA biogenesis and impaired transcription, superoxide accumulation is further increased, and the vicious cycle of free radicals continues to self-propagate. Diabetic milieu also alters enzymes responsible for DNA and histone modifications, and various genes important for mitochondrial homeostasis, including mitochondrial biosynthesis, damage and antioxidant defense, undergo epigenetic modifications. Although antioxidant administration in animal models has yielded encouraging results in preventing diabetic retinopathy, controlled longitudinal human studies remain to be conducted. Furthermore, the role of epigenetic in mitochondrial homeostasis suggests that regulation of such modifications also has potential to inhibit/retard the development of diabetic retinopathy.

Idh1 protects murine hepatocytes from endotoxin-induced oxidative stress by regulating the intracellular NADP(+)/NADPH ratio

Isocitrate dehydrogenase-1 (Idh1) is an important metabolic enzyme that produces NADPH by converting isocitrate to α-ketoglutarate. Idh1 is known to reduce reactive oxygen species (ROS) induced in cells by treatment with lipopolysaccharide (LPS) in vitro. Here, we used Idh1-deficient knockout (Idh1 KO) mice to investigate the role of Idh1 in antioxidant defense in vivo. Idh1 KO mice showed heightened susceptibility to death induced by LPS and exhibited increased serum levels of inflammatory cytokines such as tumor necrosis factor-α and interleukin-6. The serum of LPS-injected Idh1 KO mice also contained elevated levels of AST, a marker of inflammatory liver damage. Furthermore, after LPS injection, livers of Idh1 KO mice showed histological evidence of elevated oxidative DNA damage compared with livers of wild-type (WT) mice. Idh1 KO livers showed a faster and more pronounced oxidative stress than WT livers. In line with that, Idh1 KO hepatocytes showed higher ROS levels and an increase in the NADP(+)/NADPH ratio when compared with hepatocytes isolated from WT mice. These results suggest that Idh1 has a physiological function in protecting cells from oxidative stress by regulating the intracellular NADP(+)/NADPH ratio. Our findings suggest that stimulation of Idh1 activity may be an effective therapeutic strategy for reducing oxidative stress during inflammatory responses, including the early stages of septic shock.

Oxidative stress responses and NRF2 in human leukaemia

Oxidative stress as a result of elevated levels of reactive oxygen species (ROS) has been observed in almost all cancers, including leukaemia, where they contribute to disease development and progression. However, cancer cells also express increased levels of antioxidant proteins which detoxify ROS. This includes glutathione, the major antioxidant in human cells, which has recently been identified to have dysregulated metabolism in human leukaemia. This suggests that critical balance of intracellular ROS levels is required for cancer cell function, growth, and survival. Nuclear factor (erythroid-derived 2)-like 2 (NRF2) transcription factor plays a dual role in cancer. Primarily, NRF2 is a transcription factor functioning to protect nonmalignant cells from malignant transformation and oxidative stress through transcriptional activation of detoxifying and antioxidant enzymes. However, once malignant transformation has occurred within a cell, NRF2 functions to protect the tumour from oxidative stress and chemotherapy-induced cytotoxicity. Moreover, inhibition of the NRF2 oxidative stress pathway in leukaemia cells renders them more sensitive to cytotoxic chemotherapy. Our improved understanding of NRF2 biology in human leukaemia may permit mechanisms by which we could potentially improve future cancer therapies. This review highlights the mechanisms by which leukaemic cells exploit the NRF2/ROS response to promote their growth and survival.

Augmenting effects of gestational arsenite exposure of C3H mice on the hepatic tumors of the F₂ male offspring via the F₁ male offspring

Gestational exposure can affect the F2 generation through exposure of F1 germline cells. Previous studies reported that arsenite exposure of only F0 females during their pregnancy increases hepatic tumors in the F1 males in C3H mice, whose males are predisposed spontaneously to develop hepatic tumors later in life. The present study addressed the effects of gestational arsenite exposure on tumorigenesis of the F2 males in C3H mice. Expression analysis of several genes in the normal livers at 53 and 80 weeks of age clearly showed significant changes in the F2 males obtained by crossing gestational arsenite-exposed F1 (arsenite-F1) males and females compared to the control F2 males. Some of the changes were shown to occur in a late-onset manner. Then the tumor incidence was assessed at 75-82 weeks of age in the F2 males obtained by reciprocal crossing between the control and arsenite-F1 males and females. The results demonstrated that the F2 males born to arsenite-F1 males developed tumors at a significantly higher rate than the F2 males born to the control F1 males, irrespective of exposure of F1 females. Gene expressions of hepatocellular carcinoma markers β-catenin (CTNNB1) and interleukin-1 receptor antagonist in the tumors were significantly upregulated in the F2 males born to arsenite-F1 males compared to those born to the control F1 males. These results show that arsenite exposure of only F0 pregnant mice causes late-onset changes and augments tumors in the livers of the F2 males by affecting the F1 male offspring.

Risk of cancer in patients with iron deficiency anemia: a nationwide population-based study

Objective

This study evaluated the risk of cancer among patients with iron deficiency anemia (IDA) by using a nationwide population-based data set.

Method

Patients newly diagnosed with IDA and without antecedent cancer between 2000 and 2010 were recruited from the Taiwan National Health Insurance Research Database. The standardized incidence ratios (SIRs) of cancer types among patients with IDA were calculated.

Results

Patients with IDA exhibited an increased overall cancer risk (SIR: 2.15). Subgroup analysis showed that patients of both sexes and in all age groups had an increased SIR. After we excluded patients diagnosed with cancer within the first and first 5 years of IDA diagnosis, the SIRs remained significantly elevated at 1.43 and 1.30, respectively. In addition, the risks of pancreatic (SIR: 2.31), kidney (SIR: 2.23), liver (SIR: 1.94), and bladder cancers (SIR: 1.74) remained significantly increased after exclusion of patients diagnosed with cancer within 5 years after IDA diagnosis.

Conclusion

The overall cancer risk was significantly elevated among patients with IDA. After we excluded patients diagnosed with IDA and cancer within 1 and 5 years, the SIRs remained significantly elevated compared with those of the general population. The increased risk of cancer was not confined to gastrointestinal cancer when the SIRs of pancreatic, kidney, liver, and bladder cancers significantly increased after exclusion of patients diagnosed with IDA and cancer within the first 5 years. This finding may be caused by immune activities altered by IDA. Further study is necessary to determine the association between IDA and cancer risk.

An Overview of Ultraviolet B Radiation-Induced Skin Cancer Chemoprevention by Silibinin

Skin cancer incidences are rising worldwide, and one of the major causative factors is excessive exposure to solar ultraviolet radiation (UVR). Annually, ~5 million skin cancer patients are treated in United States, mostly with nonmelanoma skin cancer (NMSC), which is also frequent in other Western countries. As sunscreens do not provide adequate protection against deleterious effects of UVR, additional and alternative chemoprevention strategies are urgently needed to reduce skin cancer burden. Over the last couple of decades, extensive research has been conducted to understand the molecular basis of skin carcinogenesis, and to identifying novel agents which could be useful in the chemoprevention of skin cancer. In this regard, several natural non-toxic compounds have shown promising efficacy in preventing skin carcinogenesis at initiation, promotion and progression stages, and are considered important in better management of skin cancer. Consistent with this, we and others have studied and established the notable efficacy of natural flavonolignan silibinin against UVB-induced skin carcinogenesis. Extensive pre-clinical animal and cell culture studies report strong anti-inflammatory, anti-oxidant, DNA damage repair, immune-modulatory and anti-proliferative properties of silibinin. Molecular studies have identified that silibinin targets pleotropic signaling pathways including mitogenic, cell cycle, apoptosis, autophagy, p53, NF-κB, etc. Overall, the skin cancer chemopreventive potential of silibinin is well supported by comprehensive mechanistic studies, suggesting its greater use against UV-induced cellular damages and photocarcinogenesis.

ARHI overexpression induces epithelial ovarian cancer cell apoptosis and excessive autophagy

OBJECTIVE

ARHI is a maternally imprinted tumor suppressor gene that is responsible for initiating programmed cell death and inhibiting cancer cell growth. However, the influence of ARHI on epithelial ovarian cancer cell death and the underlying mechanisms behind how ARHI regulates cancer cells still require further studies.

METHODS

Epithelial ovarian cancer cells TOV112D and ES-2 were used in this in vitro study. Cell proliferation, apoptosis, and autophagy activities were compared in TOV112D and ES-2 cells transfected with ARHI vectors or control vectors. Bcl-2 siRNA was transfected into TOV112D cells to investigate the roles of Bcl-2 played in regulating apoptosis and autophagy.

RESULTS

ARHI expression was reduced in TOV112D and ES-2 cells compared with normal epithelial ovarian cells (NOE095 and HOSEpiC). Overexpressed ARHI inhibited cancer cell proliferation, whereas induced forced cell apoptosis and excessive formation of autophagosomes inhibited promoted cell death. Furthermore, we found that Bcl-2 expression moderately declined in response to ARHI overexpressing in ES-2 and TOV112D cells; meanwhile, more apoptotic cells and higher LC3 level presented after silence of Bcl-2 in TOV112D cells. Reduced Bcl-2-Beclin 1 complex were observed in ARHI overexpressing cells. Moreover, modulation of ARHI to Bcl-2 expression could be ascribed partially to the activation of PI3k/AKT pathway. The addition of LY294002 enabled to suppress Bcl-2 expression and cell proliferation.

CONCLUSIONS

The silence of ARHI expression in vitro seems to accelerate the malignant transformation of healthy ovarian cells by restraining apoptosis and autophagy. The overexpressed ARHI in TOV112D cancer cells suppresses the activation of PI3K/AKT and reduces the expression of Bcl-2, leading to enhanced cell apoptosis and autophagic cancer cell death.

Inhibition of oxidative metabolism leads to p53 genetic inactivation and transformation in neural stem cells

Alterations of mitochondrial metabolism and genomic instability have been implicated in tumorigenesis in multiple tissues. High-grade glioma (HGG), one of the most lethal human neoplasms, displays genetic modifications of Krebs cycle components as well as electron transport chain (ETC) alterations. Furthermore, the p53 tumor suppressor, which has emerged as a key regulator of mitochondrial respiration at the expense of glycolysis, is genetically inactivated in a large proportion of HGG cases. Therefore, it is becoming evident that genetic modifications can affect cell metabolism in HGG; however, it is currently unclear whether mitochondrial metabolism alterations could vice versa promote genomic instability as a mechanism for neoplastic transformation. Here, we show that, in neural progenitor/stem cells (NPCs), which can act as HGG cell of origin, inhibition of mitochondrial metabolism leads to p53 genetic inactivation. Impairment of respiration via inhibition of complex I or decreased mitochondrial DNA copy number leads to p53 genetic loss and a glycolytic switch. p53 genetic inactivation in ETC-impaired neural stem cells is caused by increased reactive oxygen species and associated oxidative DNA damage. ETC-impaired cells display a marked growth advantage in the presence or absence of oncogenic RAS, and form undifferentiated tumors when transplanted into the mouse brain. Finally, p53 mutations correlated with alterations in ETC subunit composition and activity in primary glioma-initiating neural stem cells. Together, these findings provide previously unidentified insights into the relationship between mitochondria, genomic stability, and tumor suppressive control, with implications for our understanding of brain cancer pathogenesis.

Peroxiredoxin 1 promotes tumorigenesis through regulating the activity of mTOR/p70S6K pathway in esophageal squamous cell carcinoma

The biological function of Peroxiredoxin 1 (Prdx1) in cancer is still ambiguous, and its mechanism has not been elucidated so far. Previous studies have shown that Prdx1 functions as tumor suppressor in several types of cancers, but other studies have indicated that it is overexpressed in some types of human cancers, and inhibition of Prdx1 by shRNA contributes to radiosensitivity and chemosensitivity. In this study, a suppression subtractive hybridization cDNA library between esophageal squamous cell carcinoma (ESCC) cell line EC9706 and noncancerous esophageal epithelial cell line Het-1A was constructed, and 11 tumorigenesis-associated genes including Prdx1 were isolated. In addition, we further confirmed that Prdx1 was overexpressed in ESCC cells at the level of protein compared with Het-1A (P < 0.05). Inhibition of Prdx1 by shRNA lentivirus decreased cell proliferation and invasion, and induced cell apoptosis, but did not affect cell cycle distribution of EC9706 cells (P > 0.05). Importantly, the total proteins of mTOR and p70S6K, as well as the activity of mTOR/p70S6K signaling pathway, were decreased in Prdx1-depletion EC9706 cells. Furthermore, the activity of mTOR/p70S6K signaling pathway was increased in Prdx1-overexpressing Het-1A cells. These findings mentioned above demonstrate that Prdx1 may be involved in tumorigenesis through regulation of mTOR/p70S6K pathway in ESCC.

Epigenetic regulation in the inner ear and its potential roles in development, protection, and regeneration

The burgeoning field of epigenetics is beginning to make a significant impact on our understanding of tissue development, maintenance, and function. Epigenetic mechanisms regulate the structure and activity of the genome in response to intracellular and environmental cues that direct cell-type specific gene networks. The inner ear is comprised of highly specialized cell types with identical genomes that originate from a single totipotent zygote. During inner ear development specific combinations of transcription factors and epigenetic modifiers must function in a coordinated manner to establish and maintain cellular identity. These epigenetic regulatory mechanisms contribute to the maintenance of distinct chromatin states and cell-type specific gene expression patterns. In this review, we highlight emerging paradigms for epigenetic modifications related to inner ear development, and how epigenetics may have a significant role in hearing loss, protection, and regeneration.

Understanding cancer development processes after HZE-particle exposure: roles of ROS, DNA damage repair and inflammation

During space travel astronauts are exposed to a variety of radiations, including galactic cosmic rays composed of high-energy protons and high-energy charged (HZE) nuclei, and solar particle events containing low- to medium-energy protons. Risks from these exposures include carcinogenesis, central nervous system damage and degenerative tissue effects. Currently, career radiation limits are based on estimates of fatal cancer risks calculated using a model that incorporates human epidemiological data from exposed populations, estimates of relative biological effectiveness and dose-response data from relevant mammalian experimental models. A major goal of space radiation risk assessment is to link mechanistic data from biological studies at NASA Space Radiation Laboratory and other particle accelerators with risk models. Early phenotypes of HZE exposure, such as the induction of reactive oxygen species, DNA damage signaling and inflammation, are sensitive to HZE damage complexity. This review summarizes our current understanding of critical areas within the DNA damage and oxidative stress arena and provides insight into their mechanistic interdependence and their usefulness in accurately modeling cancer and other risks in astronauts exposed to space radiation. Our ultimate goals are to examine potential links and crosstalk between early response modules activated by charged particle exposure, to identify critical areas that require further research and to use these data to reduced uncertainties in modeling cancer risk for astronauts. A clearer understanding of the links between early mechanistic aspects of high-LET response and later surrogate cancer end points could reveal key nodes that can be therapeutically targeted to mitigate the health effects from charged particle exposures.

Effects of melatonin on the proliferation and apoptosis of sheep granulosa cells under thermal stress

The cross-talk between oocyte and somatic cells plays a crucial role in the regulation of follicular development and oocyte maturation. As a result, granulosa cell apoptosis causes follicular atresia. In this study, sheep granulosa cells were cultured under thermal stress to induce apoptosis, and melatonin (MT) was examined to evaluate its potential effects on heat-induced granulosa cell injury. The results demonstrated that the Colony Forming Efficiency (CFE) of granulosa cells was significantly decreased (heat 19.70% ± 1.29% vs. control 26.96% ± 1.81%, p < 0.05) and the apoptosis rate was significantly increased (heat 56.16% ± 13.95%vs. control 22.80% ± 12.16%, p < 0.05) in granulosa cells with thermal stress compared with the control group. Melatonin (10⁻⁷ M) remarkably reduced the negative effects caused by thermal stress in the granulosa cells. This reduction was indicated by the improved CFE and decreased apoptotic rate of these cells. The beneficial effects of melatonin on thermal stressed granulosa cells were not inhibited by its membrane receptor antagonist luzindole. A mechanistic exploration indicated that melatonin (10⁻⁷ M) down-regulated p53 and up-regulated Bcl-2 and LHR gene expression of granulosa cells under thermal stress. This study provides evidence for the molecular mechanisms of the protective effects of melatonin on granulosa cells during thermal stress.

DNA methyltransferases 3a and 3b are differentially expressed in the early stages of a rat liver carcinogenesis model

Carcinogenesis is driven by the accumulation of mutations and abnormal DNA methylation patterns, particularly the hypermethylation of tumor‑suppressor genes. Changes in genomic DNA methylation patterns are established by the DNA methyltransferases (DNMTs) family: DNMT1, DNMT3a and DNMT3b. The DNMTs are known to be overexpressed in tumors. However, when the DNMTs expression profile is altered in earlier stages of carcinogenesis remains to be elucidated. The resistant hepatocyte model (RHM) allows the analysis of the hepatocellular carcinoma (HCC) from the formation of altered cell foci to the appearance of tumors in rats. To investigate the DNMTs expression in this model, we first observed that timp3, rassf1a and p16 genes became methylated during cancer development by methylation‑specific PCR (MSP) and the bisulphate sequencing PCR (BSP) of timp3. The differential expression at the RNA and protein level of the three DNMTs was also assessed. dnmt1 expression was higher in tumors than in normal and early cancer stages. However, no evident overexpression of the enzyme was identified by immunohistochemistry. By contrast, DNMT3a and DNMT3b were consistently subexpressed in tumors. In the present study, we report a carcinogenesis model that does not feature the overexpression of DNMT1 but exhibits a transient expression of DNMT3a and DNMT3b.

Annona muricata leaves induce G₁ cell cycle arrest and apoptosis through mitochondria-mediated pathway in human HCT-116 and HT-29 colon cancer cells

ETHNOPHARMACOLOGICAL RELEVANCE

Annona muricata known as "the cancer killer" has been widely used in the traditional medicine for the treatment of cancer and tumors. The purpose of this study is to investigate the anticancer properties of ethyl acetate extract of Annona muricata leaves (EEAM) on HT-29 and HCT-116 colon cancer cells and the underlying mechanisms.

MATERIALS AND METHODS

The effect of EEAM on the cell proliferation of HT-29 and HCT-116 cells was analyzed by the MTT (3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium) assay. High content screening system (HCS) was applied to investigate the cell membrane permeability, mitochondrial membrane potential (MMP), nuclear condensation and cytochrome c translocation from mitochondria to cytosol. Reactive oxygen species (ROS) formation, lactate dehydrogenase (LDH) release and activation of caspase-3/7, -8 and -9 were measured while treatment. Flow cytometric analysis was used to determine the cell cycle distribution and phosphatidylserine externalization. The protein expression of Bax and Bcl-2 was determined using immunofluorescence analysis. In addition, the potential of EEAM to suppress the migration and invasion of colon cancer cells was also examined.

RESULTS

EEAM exerted significant cytotoxic effects on HCT-116 and HT-29 cells as determined by MTT and LDH assays. After 24 h treatment, EEAM exhibited the IC₅₀ value of 11.43 ± 1.87 µg/ml and 8.98 ± 1.24 µg/ml against HT-29 and HCT-116 cells, respectively. Flow cytometric analysis demonstrated the cell cycle arrest at G1 phase and phosphatidylserine externalization confirming the induction of apoptosis. EEAM treatment caused excessive accumulation of ROS followed by disruption of MMP, cytochrome c leakage and activation of the initiator and executioner caspases in both colon cancer cells. Immunofluorescence analysis depicted the up-regulation of Bax and down-regulation of Bcl-2 proteins while treated with EEAM. Furthermore, EEAM conspicuously blocked the migration and invasion of HT-29 and HCT-116 cells.

CONCLUSIONS

These findings provide a scientific basis for the use of A. muricata leaves in the treatment of cancer, although further in vivo studies are still required.

Viral carcinogenesis: factors inducing DNA damage and virus integration

Viruses are the causative agents of 10%-15% of human cancers worldwide. The most common outcome for virus-induced reprogramming is genomic instability, including accumulation of mutations, aberrations and DNA damage. Although each virus has its own specific mechanism for promoting carcinogenesis, the majority of DNA oncogenic viruses encode oncogenes that transform infected cells, frequently by targeting p53 and pRB. In addition, integration of viral DNA into the human genome can also play an important role in promoting tumor development for several viruses, including HBV and HPV. Because viral integration requires the breakage of both the viral and the host DNA, the integration rate is believed to be linked to the levels of DNA damage. DNA damage can be caused by both endogenous and exogenous factors, including inflammation induced by either the virus itself or by co-infections with other agents, environmental agents and other factors. Typically, cancer develops years to decades following the initial infection. A better understanding of virus-mediated carcinogenesis, the networking of pathways involved in transformation and the relevant risk factors, particularly in those cases where tumorigenesis proceeds by way of virus integration, will help to suggest prophylactic and therapeutic strategies to reduce the risk of virus-mediated cancer.

Detoxifying effect of fermented black ginseng on H2O2-induced oxidative stress in HepG2 cells

Fermented black ginseng (FBG) is prepared by repeated steaming and drying processes with fresh ginseng followed by fermentation with Saccharomyces cerevisiae. It has recently been shown to have several bioactivities. FBG contains crude saponin (1,440 µg/ml), ginsenoside Rg2 (2.86 µg/ml), ginsenoside Rg3 (24.52 µg/ml), ginsenoside Rh1 (12.64 µg/ml), ginsenoside Rh2 (0.63 µg/ml) and ginsenoside Rf (1.32 µg/ml). The present study investigated the antioxidant defense properties of FBG against hydrogen peroxide (H2O2)-mediated oxidative stress in HepG2 human hepatocellular carcinoma cells. The increased production of reactive oxygen species (ROS) induced by H2O2 was attenuated in a dose-dependent manner when the cells were pre-treated with FBG (10-50 µg/ml). FBG induced both the expression and activity of antioxidant enzymes, such as superoxide dismutase, catalase and glutathione peroxidase in the H2O2-treated HepG2 cells. The inhibitory effects of FBG on the phosphorylation of upstream mitogen-activated protein kinases (MAPKs), such as c-Jun N-terminal kinase, extracellular signal-regulated kinase and p38 were also observed. Overall, our results demonstrate that FBG protects HepG2 cells from oxidative stress through the induction of antioxidant enzyme activity and the inhibition of MAPK pathways.

Piperlongumine treatment inactivates peroxiredoxin 4, exacerbates endoplasmic reticulum stress, and preferentially kills high-grade glioma cells

BACKGROUNDS

Piperlongumine, a natural plant product, kills multiple cancer types with little effect on normal cells. Piperlongumine raises intracellular levels of reactive oxygen species (ROS), a phenomenon that may underlie the cancer-cell killing. Although these findings suggest that piperlongumine could be useful for treating cancers, the mechanism by which the drug selectively kills cancer cells remains unknown.

METHODS

We treated multiple high-grade glioma (HGG) sphere cultures with piperlongumine and assessed its effects on ROS and cell-growth levels as well as changes in downstream signaling. We also examined the levels of putative piperlongumine targets and their roles in HGG cell growth.

RESULTS

Piperlongumine treatment increased ROS levels and preferentially killed HGG cells with little effect in normal brain cells. Piperlongumine reportedly increases ROS levels after interactions with several redox regulators. We found that HGG cells expressed higher levels of the putative piperlongumine targets than did normal neural stem cells (NSCs). Furthermore, piperlongumine treatment in HGG cells, but not in normal NSCs, increased oxidative inactivation of peroxiredoxin 4 (PRDX4), an ROS-reducing enzyme that is overexpressed in HGGs and facilitates proper protein folding in the endoplasmic reticulum (ER). Moreover, piperlongumine exacerbated intracellular ER stress, an effect that was mimicked by suppressing PRDX4 expression.

CONCLUSIONS

Our results reveal that the mechanism by which piperlongumine preferentially kills HGG cells involves PRDX4 inactivation, thereby inducing ER stress. Therefore, piperlongumine treatment could be considered as a novel therapeutic option for HGG treatment.

Long-term effects of varying consumption of ω3 fatty acids in ear, nose and throat cancer patients: assessment 1 year after radiotherapy

A prospective 1-year follow-up study in ear, nose, and throat (ENT) cancer patients was carried out one year after radiotherapy to assess the effect of varying consumption of ω3 fatty acid according to whether they consumed more or less than the 50th percentile of ω3 fatty acids. Clinical, analytical, inflammatory (CRP and IL-6), and oxidative variables (TAC, GPx, GST, and SOD) were evaluated. The study comprised 31 patients (87.1% men), with a mean age of 61.3 ± 9.1 years. Hematological variables showed significant differences in the patients with a lower consumption of ω3 fatty acids. A lower mortality and longer survival were found in the group with ω3 fatty acid consumption ≥50th percentile but the differences were not significant. No significant difference was reached in toxicity, inflammation, and oxidative stress markers. The group with ω3 fatty acid consumption <50th percentile significantly experienced more hematological and immune changes.

Epigenetic therapy as a novel approach in hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is the most common type of liver malignancy and one with high fatality. Its 5-year survival rate remains low and thus, there is a need for improvement of current treatment strategies as well as development of novel targeted methodologies in order to optimize existing therapeutic protocols. To this end, only recently, it was discovered that its pathophysiology also involves epigenetic alterations in DNA methylation, histone modifications and/or non-coding microRNA patterns. Unlike genetic events, epigenetic alterations are reversible and thus potentially considered to be an alternative option in cancer treatment protocols. In this review, we describe the general characteristics and resulted major alterations of the epigenetic machinery as well as current state of progress of epigenetic therapy (via different single or combinatorial experimental approaches) in HCC.

Effects of Tapinanthus globiferus and Zanthoxylum zanthoxyloides extracts on human leukocytes in vitro

Objective:

This study aimed at investigating the genotoxicity and cytotoxicity effect of Tapinanthus globiferus and Zanthoxylum zanthoxyloides to human leukocytes. In addition, the reductive potential and the chemical composition of the two plant extracts were also determined.

Materials and Methods:

Human leukocytes were obtained from healthy volunteer donors. The genotoxicity and cytotoxicity of T. globiferus and Z. zanthoxyloides were assessed using the comet assay and trypan blue exclusion, respectively. The antioxidant activity of the plant extracts was evaluated by the reducing power assay. Furthermore, high-performance liquid chromatography-diode array detector was used to characterize and quantify the constituents of these plants.

Results:

T. globiferus (10-150 µg/mL) was neither genotoxic nor cytotoxic at the concentrations tested, suggesting that it can be consumed safely at relatively high concentrations. However, Z. zanthoxyloides showed cytoxicity and genotoxicity to human leukocytes at the highest concentration tested (150 µg/mL). In addition, the total reducing power of T. globiferus was found higher than Z. zanthoxyloides in potassium ferricyanide reduction. Both plants extract contained flavonoids (rutin and quercetin) and phenolic acids (chlorogenic and caffeic).

Conclusion:

The results obtained support the fact that some caution should be paid regarding the dosage and the frequency of use of Z. zanthoxyloides extract.

In vitro cytotoxic and anticlastogenic activities of saxifragifolin B and cyclamin isolated from Cyclamen persicum and Cyclamen libanoticum

CONTEXT

The genus Cyclamen L. (Primulaceae) is rich in saponins known to have interesting biological activities.

OBJECTIVE

To isolate saxifragifolin B and cyclamin, two triterpene saponins, from Cyclamen libanoticum Hildebr and Cyclamen persicum Mill, and to assess their cytotoxic, clastogenic/aneugenic, and anticlastogenic effects, as well as antioxidant potential.

MATERIALS AND METHODS

Saxifragifolin B and cyclamin were tested for their cytotoxicity against SK-BR-3, HT-29, HepG2/3A, NCI-H1299, BXPC-3, 22RV1, and normal DMEM cell lines using WST-1 assay. Their clastogenic/aneugenic activities and anticlastogenic effects against the anticancer drug mitomycin C were assessed by the in vitro micronucleus assay in CHO cells. Their antioxidant capacities were determined using Fe(2+)-chelating and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging assays.

RESULTS

Both saponins were described for the first time in Cyclamen libanoticum. They showed strong cytotoxic activities against the tested cancer cell lines. Saxifragifolin B was found to be 56- and 37-times more active than mitomycin C against breast adenocarcinoma (SK-BR-3) and lung carcinoma (NCI-H1299), respectively. Also, saxifragifolin B did not induce micronuclei formation and prevented cells from mitomycin C clastogenic effect. Cyclamin induced a significant increase of micronucleated cells after metabolic activation with S9 mix, and did not possess any anticlastogenic activity. Both molecules exhibited low antioxidant activities as compared to reference compounds.

DISCUSSION AND CONCLUSIONS

This study showed the remarkable cytotoxic activity of saxifragifolin B, especially against breast adenocarcinoma and lung carcinoma and its chemoprotective activity against mitomycin C. Thus, saxifragifolin B could be suggested as a potential cytotoxic drug with a preventive effect against possible exposures to genotoxic agents.

ETV6/RUNX1 induces reactive oxygen species and drives the accumulation of DNA damage in B cells

The t(12;21)(p13;q22) chromosomal translocation is the most frequent translocation in childhood B cell precursor-acute lymphoblastic leukemia and results in the expression of an ETV6/RUNX1 fusion protein. The frequency of ETV6/RUNX1 fusions in newborns clearly exceeds the leukemia rate revealing that additional events occur in ETV6/RUNX1-positive cells for leukemic transformation. Hitherto, the mechanisms triggering these second hits remain largely elusive. Thus, we generated a novel ETV6/RUNX1 transgenic mouse model where the expression of the fusion protein is restricted to CD19(+) B cells. These animals harbor regular B cell development and lack gross abnormalities. We established stable pro-B cell lines carrying the ETV6/RUNX1 transgene that allowed us to investigate whether ETV6/RUNX1 itself favors the acquisition of second hits. Remarkably, these pro-B cell lines as well as primary bone marrow cells derived from ETV6/RUNX1 transgenic animals display elevated levels of reactive oxygen species (ROS) as tested with ETV6/RUNX1 transgenic dihydroethidium staining. In line, intracellular phospho-histone H2AX flow cytometry and comet assay revealed increased DNA damage indicating that ETV6/RUNX1 expression enhances ROS. On the basis of our data, we propose the following model: the expression of ETV6/RUNX1 creates a preleukemic clone and leads to increased ROS levels. These elevated ROS favor the accumulation of secondary hits by increasing genetic instability and double-strand breaks, thus allowing preleukemic clones to develop into fully transformed leukemic cells.

Enterococcus faecalis Infection and Reactive Oxygen Species Down-Regulates the miR-17-92 Cluster in Gastric Adenocarcinoma Cell Culture

Chronic inflammation due to bacterial overgrowth of the stomach predisposes to the development of gastric cancer and is also associated with high levels of reactive oxygen species (ROS). In recent years increasing attention has been drawn to microRNAs (miRNAs) due to their role in the pathogenesis of many human diseases including gastric cancer. Here we studied the impact of infection by the gram-positive bacteria Enterococcus faecalis (E. faecalis) on global miRNA expression as well as the effect of ROS on selected miRNAs. Human gastric adenocarcinoma cell line MKN74 was infected with living E. faecalis for 24 h or for 5 days or with E. faecalis lysate for 5 days. The miRNA expression was examined by microarray analysis using Affymetrix GeneChip miRNA Arrays. To test the effect of ROS, MKN74 cells were treated with 100 mM tert-Butyl hydroperoxide (TBHP). Following 5 days of E. faecalis infection we found 91 differentially expressed miRNAs in response to living bacteria and 2 miRNAs responded to E. faecalis lysate. We verified the down-regulation of the miR-17-92 and miR-106-363 clusters and of other miRNAs involved in the oxidative stress-response by qRT-PCR. We conclude that only infection by living E. faecalis bacteria caused a significant global response in miRNA expression in the MKN74 cell culture. E. faecalis infection as well as ROS stimulation down-regulated the expression of the miR-17-92 cluster. We believe that these changes could reflect a general response of gastric epithelial cells to bacterial infections.

The ROS-sensitive microRNA-9/9* controls the expression of mitochondrial tRNA-modifying enzymes and is involved in the molecular mechanism of MELAS syndrome

Mitochondrial dysfunction activates mitochondria-to-nucleus signaling pathways whose components are mostly unknown. Identification of these components is important to understand the molecular mechanisms underlying mitochondrial diseases and to discover putative therapeutic targets. MELAS syndrome is a rare neurodegenerative disease caused by mutations in mitochondrial (mt) DNA affecting mt-tRNA(Leu(UUR)). Patient and cybrid cells exhibit elevated oxidative stress. Moreover, mutant mt-tRNAs(Leu(UUR)) lack the taurine-containing modification normally present at the wobble uridine (U34) of wild-type mt-tRNA(Leu(UUR)), which is considered an etiology of MELAS. However, the molecular mechanism is still unclear. We found that MELAS cybrids exhibit a significant decrease in the steady-state levels of several mt-tRNA-modification enzymes, which is not due to transcriptional regulation. We demonstrated that oxidative stress mediates an NFkB-dependent induction of microRNA-9/9*, which acts as a post-transcriptional negative regulator of the mt-tRNA-modification enzymes GTPBP3, MTO1 and TRMU. Down-regulation of these enzymes by microRNA-9/9* affects the U34 modification status of non-mutant tRNAs and contributes to the MELAS phenotype. Anti-microRNA-9 treatments of MELAS cybrids reverse the phenotype, whereas miR-9 transfection of wild-type cells mimics the effects of siRNA-mediated down-regulation of GTPBP3, MTO1 and TRMU. Our data represent the first evidence that an mt-DNA disease can directly affect microRNA expression. Moreover, we demonstrate that the modification status of mt-tRNAs is dynamic and that cells respond to stress by modulating the expression of mt-tRNA-modifying enzymes. microRNA-9/9* is a crucial player in mitochondria-to-nucleus signaling as it regulates expression of nuclear genes in response to changes in the functional state of mitochondria.

Increased oxidative damage associated with unfavorable cytogenetic subgroups in chronic lymphocytic leukemia

Oxidative stress contributes to genomic instability in chronic lymphocytic leukemia (CLL), but its relationship with the acquisition of specific chromosomal abnormalities is unknown. We recruited 55 untreated CLL patients and assessed 8-oxo-2'-deoxyguanosine (8-oxo-dG), glutathione, and malondialdehyde (MDA) levels, and we compared them among the cytogenetic subgroups established using fluorescence in situ hybridization (FISH). Significant increases in 8-oxo-dG and/or MDA were observed in patients with unfavorable cytogenetic aberrations (17p and 11q deletions) compared to the 13q deletion group. TP53 deletion patients exhibited a diminished DNA repair efficiency. Finally, cases with normal FISH also showed enhanced 8-oxo-dG, which could result in adverse outcomes.

An investigation into the serum thioredoxin, superoxide dismutase, malondialdehyde, and advanced oxidation protein products in patients with breast cancer

BACKGROUND

Reactive oxygen species (free radicals) play an important role in carcinogenesis. Extensive antioxidant defense mechanisms counteract free radicals in mammalian cells. Oxidative stress is a disturbance in the balance between the production of free radicals and antioxidant defenses. There is direct evidence that oxidative stress and lipid peroxidation (LPO) are linked to the etiology of breast cancer. The increasing global incidence of breast cancer emphasizes the need to understand the various mechanisms involved in breast tumorigenesis. The present study was undertaken to investigate the oxidative stress and antioxidant status in the blood samples of patients with breast cancer.

METHODS

The present study was based on 23 women who were surgically treated at Gazi University, Faculty of Medicine, Department of General Surgery. The malondialdehyde (MDA) levels as an index of LPO along with the examination of superoxide dismutase (SOD) activities and advanced oxidation protein product (AOPP) and thioredoxin (Trx) levels were determined in the blood samples of 23 patients with breast cancer and 13 healthy controls.

RESULTS

MDA, AOPP, and Trx levels and SOD activities were significantly higher in patients with breast cancer than the controls.

CONCLUSIONS

The results showed that oxidative stress may be related to breast cancer and especially some molecules, such as Trx and AOPP, may be useful biomarkers in breast cancer diagnosis and treatment. More detailed knowledge related to the pathophysiology of these molecules could provide valuable information on the origin and development of malignant tumors, such as breast cancer.

Causes and Consequences of Age-Related Changes in DNA Methylation: A Role for ROS?

Recent genome-wide analysis of C-phosphate-G (CpG) sites has shown that the DNA methylome changes with increasing age, giving rise to genome-wide hypomethylation with site‑specific incidences of hypermethylation. This notion has received a lot of attention, as it potentially explains why aged organisms generally have a higher risk of age-related diseases. However, very little is known about the mechanisms that could cause the occurrence of these changes. Moreover, there does not appear to be a clear link between popular theories of aging and alterations in the methylome. Some of the most fruitful of these theories attribute an important role to reactive oxygen species, which seem to be responsible for an increase in oxidative damage to macromolecules, such as DNA, during the lifetime of an organism. In this review, the connection between changes in DNA methylation and these reactive oxygen species is discussed, as well as the effect of these changes on health. Deeper insights into the nature, causes and consequences of the aging methylome might provide a deeper understanding of the molecular mechanisms of aging and eventually contribute to the development of new diagnostic and therapeutic tools.

Oxidatively generated base damage to cellular DNA by hydroxyl radical and one-electron oxidants: similarities and differences

Hydroxyl radical (OH) and one-electron oxidants that may be endogenously formed through oxidative metabolism, phagocytosis, inflammation and pathological conditions constitute the main sources of oxidatively generated damage to cellular DNA. It is worth mentioning that exposure of cells to exogenous physical agents (UV light, high intensity UV laser, ionizing radiation) and chemicals may also induce oxidatively generated damage to DNA. Emphasis is placed in this short review article on the mechanistic aspects of OH and one-electron oxidant-mediated formation of single and more complex damage (tandem lesions, intra- and interstrand cross-links, DNA-protein cross-links) in cellular DNA arising from one radical hit. This concerns DNA modifications that have been accurately measured using suitable analytical methods such as high performance liquid chromatography coupled with electrospray ionization tandem mass spectrometry. Evidence is provided that OH and one-electron oxidants after generating neutral radicals and base radical cations respectively may partly induce common degradation pathways. In addition, selective oxidative reactions giving rise to specific degradation products of OH and one-electron oxidation reactions that can be used as representative biomarkers of these oxidants have been identified.

Updates of reactive oxygen species in melanoma etiology and progression

Reactive oxygen species (ROS) play crucial roles in all aspects of melanoma development, however, the source of ROS is not well defined. In this review we summarize recent advancement in this rapidly developing field. The cellular ROS pool in melanocytes can be derived from mitochondria, melanosomes, NADPH oxidase (NOX) family enzymes, and uncoupling of nitric oxide synthase (NOS). Current evidence suggests that Nox1, Nox4 and Nox5 are expressed in melanocytic lineage. While there is no difference in Nox1 expression levels in primary and metastatic melanoma tissues, Nox4 expression is significantly higher in a subset of metastatic melanoma tumors as compared to the primary tumors; suggesting distinct and specific signals and effects for NOX family enzymes in melanoma. Targeting these NOX enzymes using specific NOX inhibitors may be effective for a subset of certain tumors. ROS also play important roles in BRAF inhibitor induced drug resistance; hence identification and blockade of the source of this ROS may be an effective way to enhance efficacy and overcome resistance. Furthermore, ROS from different sources may interact with each other and interact with reactive nitrogen species (RNS) and drive the melanomagenesis process at all stages of disease. Further understanding ROS and RNS in melanoma etiology and progression is necessary for developing new prevention and therapeutic approaches.

Epigenetic modification of Nrf2 in 5-fluorouracil-resistant colon cancer cells: involvement of TET-dependent DNA demethylation

5-Fluorouracil (5-FU) is a widely used anticancer drug for the treatment of colorectal cancer (CRC). However, resistance to 5-FU often prevents the success of chemotherapy. Nuclear factor-erythroid 2-related factor 2 (Nrf2) is a transcriptional regulator and a possible target to overcome 5-FU resistance. The present study examined epigenetic changes associated with Nrf2 induction in a human CRC cell line (SNUC5) resistant to 5-FU (SNUC5/5-FUR). Nrf2 expression, nuclear translocation, and binding to promoter were higher in SNUC5/5-FUR cells than in SNUC5 cells. The activated Nrf2 in SNUC5/5-FUR cells led to an increase in the protein expression and activity of heme oxygenase-1 (HO-1), an Nrf2-regulated gene. SNUC5/5-FUR cells produced a larger amount of reactive oxygen species (ROS) than SNUC5 cells. The siRNA- or shRNA-mediated knockdown of Nrf2 or HO-1 significantly suppressed cancer cell viability and tumor growth in vitro and in vivo, resulting in enhanced 5-FU sensitivity. Methylation-specific (MS) or real-time quantitative MS-PCR data showed hypomethylation of the Nrf2 promoter CpG islands in SNUC5/5-FUR cells compared with SNUC5 cells. Expression of the DNA demethylase ten-eleven translocation (TET) was upregulated in SNUC5/5-FUR cells. ROS generated by 5-FU upregulated TET1 expression and function, whereas antioxidant had the opposite effect. These results suggested that the mechanism underlying the acquisition of 5-FU resistance in CRC involves the upregulation of Nrf2 and HO-1 expression via epigenetic modifications of DNA demethylation.

Sensing cellular states--signaling to chromatin pathways targeting Polycomb and Trithorax group function

Cells respond to extra- and intra-cellular signals by dynamically changing their gene expression patterns. After termination of the original signal, new expression patterns are maintained by epigenetic DNA and histone modifications. This represents a powerful mechanism that enables long-term phenotypic adaptation to transient signals. Adaptation of epigenetic landscapes is important for mediating cellular differentiation during development and allows adjustment to altered environmental conditions throughout life. Work over the last decade has begun to elucidate the way that extra- and intra-cellular signals lead to changes in gene expression patterns by directly modulating the function of chromatin-associated proteins. Here, we review key signaling-to-chromatin pathways that are specifically thought to target Polycomb and Trithorax group complexes, a classic example of epigenetically acting gene silencers and activators important in development, stem cell differentiation and cancer. We discuss the influence that signals triggered by kinase cascades, metabolic fluctuations and cell-cycle dynamics have on the function of these protein complexes. Further investigation into these pathways will be important for understanding the mechanisms that maintain epigenetic stability and those that promote epigenetic plasticity.

Genotoxic and epigenetic mechanisms in arsenic carcinogenicity

Arsenic is a human carcinogen with weak mutagenic properties that induces tumors through mechanisms not yet completely understood. People worldwide are exposed to arsenic-contaminated drinking water, and epidemiological studies showed a high percentage of lung, bladder, liver, and kidney cancer in these populations. Several mechanisms by which arsenical compounds induce tumorigenesis were proposed including genotoxic damage and chromosomal abnormalities. Over the past decade, a growing body of evidence indicated that epigenetic modifications have a role in arsenic-inducing adverse effects on human health. The main epigenetic mechanisms are DNA methylation in gene promoter regions that regulate gene expression, histone tail modifications that regulate the accessibility of transcriptional machinery to genes, and microRNA activity (noncoding RNA able to modulate mRNA translation). The "double capacity" of arsenic to induce mutations and epimutations could be the main cause of arsenic-induced carcinogenesis. The aim of this review is to better clarify the mechanisms of the initiation and/or the promotion of arsenic-induced carcinogenesis in order to understand the best way to perform an early diagnosis and a prompt prevention that is the key point for protecting arsenic-exposed population. Studies on arsenic-exposed population should be designed in order to examine more comprehensively the presence and consequences of these genetic/epigenetic alterations.

Cytotoxic response in human lung epithelial cells and ion characteristics of urban-air particles from Torino, a northern Italian city

Recently, much attention has been devoted to urban air pollution because epidemiological studies have reported health impacts related to particulate matter (PM). PM10 and PM2.5 were collected during different seasons in Torino, a northern Italian city, and were characterised by inorganic chemical species (secondary particulates and bio-available iron). The biological effects of aqueous and organic solvent PM extracts on human epithelial lung A549 were evaluated, and the effects on cell proliferation and lactate dehydrogenase (LDH) release were assayed. The average PM10 concentration during the sampling period was 47.9 ± 18.0 μg/m(3); the secondary particles accounted for 49 % ± 9 % of the PM10 total mass, and the bio-available iron concentration was 0.067 ± 0.045 μg/m(3). The PM2.5/PM10 ratio in Torino ranged from 0.47 to 0.90 and was higher in cold months than in warm months. The PM10 and PM2.5 extracts inhibited cell proliferation and induced LDH release in a dose-dependent manner with a seasonal trend. The PM10 extract had a stronger effect on LDH release, whereas the PM2.5 extract more strongly inhibited cell proliferation. No significant differences were observed in the effects induced by the two extracts, and no significant correlations were found between the biological effects and the PM components evaluated in this study, thus emphasising the importance of the entire mixture in inducing a cytotoxic response.

Different roles of hepatic hypothermic ischemia and ischemic preconditioning in chemically induced hepatocarcinogenesis in rats

BACKGROUND

Hepatic ischemia-reperfusion (IR) injury, an unfavorable complication of hepatectomy, could be prevented by hypothermic ischemia and ischemic preconditioning (IPC). However, the effects of these two approaches on hepatocarcinogenesis have not been examined. The aim of the study was to investigate roles of hypothermic ischemia and IPC in a chemically induced rat liver tumor model.

METHODS

Twenty-four Sprague-Dawley rats were treated with diethylnitrosamine and phenobarbital to induce hepatocellular carcinoma. Rats underwent hepatic ischemic injury, hypothermic ischemia, and IPC. Twenty-eight-wk-old rats were sacrificed to evaluate the morbidity and growth of liver tumor. Cytokines were measured at the protein and messenger RNA level.

RESULTS

IR injury significantly promoted liver tumor development. Intriguingly, hypothermic ischemia, but not IPC, delayed liver carcinogenesis, although both of them suppressed the hepatic IR injury. IPC-treated rats showed elevated interleukin (IL)-6 concentration in the serum and messenger RNA expression in liver. In addition, higher levels of IL-6 activated signal transducer and activator of transcription 3 in the liver of IPC-treated rats. The hepatic expression of target genes of signal transducer and activator of transcription 3 signaling, cyclin D1, c-myc, c-fos, and c-jun, all of which might participate in tumor progression, increased in IPC group, compared with that of IR group.

CONCLUSIONS

These data indicated hypothermic ischemia could ameliorate both IR injury and liver tumor development. However, IPC, another effective method to prevent hepatic IR injury, might exacerbate liver tumor growth. The elevated level of IL-6 was one of the reasons for the different effects of hypothermic ischemia and IPC on hepatocarcinogenesis in rats.

Biomarkers of sensitivity to potent and selective antitumor 2-(4-amino-3-methylphenyl)-5-fluorobenzothiazole (5F203) in ovarian cancer

2-(4-Amino-3-methylphenyl)-5-fluorobenzothiazole (5F203, NSC 703786) lysylamide belongs to a novel mechanistic class of antitumor agents. It elicits activity against ovarian, breast, kidney and colorectal cancer models. In sensitive breast cancer cells, 5F203 activates aryl hydrocarbon receptor (AhR) signaling. Herein, we evaluate the role of AhR in 5F203 activity in two ovarian cancer cell lines: IGROV-1 (sensitive to 5F203), SKOV-3 (resistant to this agent). In addition, cancer cells have been isolated from ascites fluid of ovarian cancer patients; sensitivity to 5F203 and concurrent AhR signal transduction has been examined in ascites-isolated ovarian cancer patients' cells. 5F203 induced enhanced CYP1A1 expression, AhR translocation and ROS formation in IGROV-1 cells and ascites-isolated ovarian cancer cells that were sensitive to 5F203. In IGROV-1 cells 5F203-induced ROS formation was accompanied by JNK, ERK and P38MAPK phosphorylation, DNA damage and cell cycle arrest prior to apoptosis. In contrast, 5F203 failed to induce CYP1A1 expression, AhR translocation or oxidative stress in 5F203-resistant SKOV-3 cells, or in ovarian cancer ascites cells inherently resistant to this agent. We propose that AhR may represent a new molecular target in the treatment of ovarian tumors and 5F203 may exemplify a potential novel treatment. Furthermore, putative biomarkers of sensitivity to this agent have been identified.