Involvement of histone hypoacetylation in Ni2+-induced bcl- 2 down-regulation and human hepatoma cell apoptosis

Epigenetic Regulation in Chromium-, Nickel- and Cadmium-Induced Carcinogenesis

Environmental and occupational exposure to heavy metals, such as hexavalent chromium, nickel, and cadmium, are major health concerns worldwide. Some heavy metals are well-documented human carcinogens. Multiple mechanisms, including DNA damage, dysregulated gene expression, and aberrant cancer-related signaling, have been shown to contribute to metal-induced carcinogenesis. However, the molecular mechanisms accounting for heavy metal-induced carcinogenesis and angiogenesis are still not fully understood. In recent years, an increasing number of studies have indicated that in addition to genotoxicity and genetic mutations, epigenetic mechanisms play critical roles in metal-induced cancers. Epigenetics refers to the reversible modification of genomes without changing DNA sequences; epigenetic modifications generally involve DNA methylation, histone modification, chromatin remodeling, and non-coding RNAs. Epigenetic regulation is essential for maintaining normal gene expression patterns; the disruption of epigenetic modifications may lead to altered cellular function and even malignant transformation. Therefore, aberrant epigenetic modifications are widely involved in metal-induced cancer formation, development, and angiogenesis. Notably, the role of epigenetic mechanisms in heavy metal-induced carcinogenesis and angiogenesis remains largely unknown, and further studies are urgently required. In this review, we highlight the current advances in understanding the roles of epigenetic mechanisms in heavy metal-induced carcinogenesis, cancer progression, and angiogenesis.

Nickel nanoparticles induce epithelial-mesenchymal transition in human bronchial epithelial cells via the HIF-1α/HDAC3 pathway

We and others have previously demonstrated that exposure to nickel nanoparticles (Nano-Ni) caused fibrogenic and carcinogenic effects; however, the underlying mechanisms are still not fully understood. This study aimed to investigate the effects of Nano-Ni on epithelial-mesenchymal transition (EMT) in human bronchial epithelial cells (BEAS-2B) and its underlying mechanisms since EMT is involved in both cancer pathogenesis and tissue fibrosis. Our results showed that exposure to Nano-Ni, compared to the control Nano-TiO2, caused a remarkable decrease in the expression of E-cadherin and an increase in the expression of vimentin and α-SMA, indicating an inducible role of Nano-Ni in EMT development in human bronchial epithelial cells. HIF-1α nuclear accumulation, HDAC3 upregulation, and decreased histone acetylation were also observed in the cells exposed to Nano-Ni, but not in those exposed to Nano-TiO2. Pretreatment of the cells with a specific HIF-1α inhibitor, CAY10585, or HIF-1α-specific siRNA transfection prior to Nano-Ni exposure resulted in the restoration of E-cadherin and abolished Nano-Ni-induced upregulation of vimentin and α-SMA, suggesting a crucial role of HIF-1α in Nano-Ni-induced EMT development. CAY10585 pretreatment also attenuated the HDAC3 upregulation and increased histone acetylation. Inhibition of HDAC3 with specific siRNA significantly restrained Nano-Ni-induced reduction in histone acetylation and restored EMT-related protein expression to near control levels. In summary, our findings suggest that exposure to Nano-Ni promotes the development of EMT in human bronchial epithelial cells by decreasing histone acetylation through HIF-1α-mediated HDAC3 upregulation. Our findings may provide information for further understanding of the molecular mechanisms of Nano-Ni-induced fibrosis and carcinogenesis.

Pathogenic Mechanisms and Therapeutic Implication in Nickel-Induced Cell Damage

Background:

Nickel (Ni) is mostly applied in a number of industrial areas such as printing inks, welding, alloys, electronics and electrical professions. Occupational or environmental exposure to nickel may lead to cancer, allergy reaction, nephrotoxicity, hepatotoxicity, neurotoxicity, as well as cell damage, apoptosis and oxidative stress.

Methods:

In here, we focused on published studies about cell death, carcinogenicity, allergy reactions and neurotoxicity, and promising agents for the prevention and treatment of the toxicity by Ni.

Results:

Our review showed that in the last few years, more researches have focused on reactive oxygen species formation, oxidative stress, DNA damages, apoptosis, interaction with involving receptors in allergy and mitochondrial damages in neuron induced by Ni.

Conclusion:

The collected data in this paper provide useful information about the main toxicities induced by Ni, also, their fundamental mechanisms, and how to discover new ameliorative agents for prevention and treatment by reviewing agents with protective and therapeutic consequences on Ni induced toxicity.

Nickel: Human Health and Environmental Toxicology

Nickel is a transition element extensively distributed in the environment, air, water, and soil. It may derive from natural sources and anthropogenic activity. Although nickel is ubiquitous in the environment, its functional role as a trace element for animals and human beings has not been yet recognized. Environmental pollution from nickel may be due to industry, the use of liquid and solid fuels, as well as municipal and industrial waste. Nickel contact can cause a variety of side effects on human health, such as allergy, cardiovascular and kidney diseases, lung fibrosis, lung and nasal cancer. Although the molecular mechanisms of nickel-induced toxicity are not yet clear, mitochondrial dysfunctions and oxidative stress are thought to have a primary and crucial role in the toxicity of this metal. Recently, researchers, trying to characterize the capability of nickel to induce cancer, have found out that epigenetic alterations induced by nickel exposure can perturb the genome. The purpose of this review is to describe the chemical features of nickel in human beings and the mechanisms of its toxicity. Furthermore, the attention is focused on strategies to remove nickel from the environment, such as phytoremediation and phytomining.

Concise Review of Nickel Human Health Toxicology and Ecotoxicology

Nickel (Ni) metal and Ni compounds are widely used in applications like stainless steel, alloys, and batteries. Nickel is a naturally occurring element in water, soil, air, and living organisms, and is essential to microorganisms and plants. Thus, human and environmental nickel exposures are ubiquitous. Production and use of nickel and its compounds can, however, result in additional exposures to humans and the environment. Notable human health toxicity effects identified from human and/or animal studies include respiratory cancer, non-cancer toxicity effects following inhalation, dermatitis, and reproductive effects. These effects have thresholds, with indirect genotoxic and epigenetic events underlying the threshold mode of action for nickel carcinogenicity. Differences in human toxicity potencies/potentials of different nickel chemical forms are correlated with the bioavailability of the Ni2+ ion at target sites. Likewise, Ni2+ has been demonstrated to be the toxic chemical species in the environment, and models have been developed that account for the influence of abiotic factors on the bioavailability and toxicity of Ni2+ in different habitats. Emerging issues regarding the toxicity of nickel nanoforms and metal mixtures are briefly discussed. This review is unique in its covering of both human and environmental nickel toxicity data.

Nickel(II)-induced nasal epithelial toxicity and oxidative mitochondrial damage

In probing the underlying mechanisms of nickel(II)-induced cytotoxicity on nasal epithelium, we investigated the effects of nickel(II) acetate on nasal epithelial RPMI-2650 cells. Nickel(II) elicited apoptosis, as signified by pyknotic and fragmented nuclei, increased caspase-3/7 activity, and an increase in annexin V binding, hypodiploid DNA, and Bax/Bcl-2 protein ratio. Nickel(II)-induced G2/M arrest was associated with up-regulation of p21(WAF1/CIP1) expression, decrease in phosphorylation at Thr(161) of Cdc2, and down-regulation of cyclin B1. Associated with these responses, ROS generation and mitochondrial depolarization increased in a nickel(II) concentration-dependent fashion. Pretreatment with N-acetylcysteine (NAC) attenuated these changes. p53 reporter gene assay and analyses of p53, Puma, Bax, and Bcl-2 protein levels indicated that NAC inhibited nickel(II)-induced activation of p53-mediated mitochondrial apoptotic pathway. Collectively, our study provides evidences that nickel(II) may induce oxidative damage on nasal epithelium in which antioxidant NAC protects cells against nickel(II)-induced apoptosis through the prevention of oxidative stress-mediated mitochondrial damage.

Research Advances on Pathways of Nickel-Induced Apoptosis

High concentrations of nickel (Ni) are harmful to humans and animals. Ni targets a number of organs and produces multiple toxic effects. Apoptosis is important in Ni-induced toxicity of the kidneys, liver, nerves, and immune system. Apoptotic pathways mediated by reactive oxygen species (ROS), mitochondria, endoplasmic reticulum (ER), Fas, and c-Myc participate in Ni-induced cell apoptosis. However, the exact mechanism of apoptosis caused by Ni is still unclear. Understanding the mechanism of Ni-induced apoptosis may help in designing measures to prevent Ni toxicity.

Prevention of cytotoxicity of nickel by quercetin: the role of reactive oxygen species and histone acetylation

Excessive exposure to nickel may cause health effects on the blood, lung, nose, kidney, reproductive system, skin and the unborn child. In the present study, we found that Ni²⁺ exposure led to a time- and dose-dependent proliferation arrest and death in human leukemia HL-60 cells. In the presence of 1 mM Ni²⁺, reactive oxygen species (ROS) generation (indicated by the level of malondialdehyde) increased to 323% and histone acetylation decreased to 32%. Interestingly, quercetin (QU) dose dependently prevented Ni²⁺-induced cell proliferation arrest and death from 0 to 80 μM but showed similar activity of scavenging ROS at the concentrations of 20, 40 and 80 µM. When the effect of QU on histone acetylation was studied, QU significantly prevented Ni²⁺-induced histone hypoacetylation at 40 or 80 µM. Moreover, increase in histone acetylation by trichostatin A could also significantly enhance the protection effect of QU at 10 or 20 µM but not at higher concentrations. Thus, our results further confirmed the critical role of ROS and histone hypoacetylation in the cytotoxicity of Ni²⁺ exposure and proved that QU is a potentially useful native dietary compound to efficiently prevent Ni²⁺-caused cytotoxicity through both diminishing ROS generation and increasing histone acetylation.

Nickel (II)-induced cytotoxicity and apoptosis in human proximal tubule cells through a ROS- and mitochondria-mediated pathway

Nickel compounds are known to be toxic and carcinogenic in kidney and lung. In this present study, we investigated the roles of reactive oxygen species (ROS) and mitochondria in nickel (II) acetate-induced cytotoxicity and apoptosis in the HK-2 human renal cell line. The results showed that the cytotoxic effects of nickel (II) involved significant cell death and DNA damage. Nickel (II) increased the generation of ROS and induced a noticeable reduction of mitochondrial membrane potential (MMP). Analysis of the sub-G1 phase showed a significant increase in apoptosis in HK-2 cells after nickel (II) treatment. Pretreatment with N-acetylcysteine (NAC) not only inhibited nickel (II)-induced cell death and DNA damage, but also significantly prevented nickel (II)-induced loss of MMP and apoptosis. Cell apoptosis triggered by nickel (II) was characterized by the reduced protein expression of Bcl-2 and Bcl-xL and the induced the protein expression of Bad, Bcl-Xs, Bax, cytochrome c and caspases 9, 3 and 6. The regulation of the expression of Bcl-2-family proteins, the release of cytochrome c and the activation of caspases 9, 3 and 6 were inhibited in the presence of NAC. These results suggest that nickel (II) induces cytotoxicity and apoptosis in HK-2 cells via ROS generation and that the mitochondria-mediated apoptotic signaling pathway may be involved in the positive regulation of nickel (II)-induced renal cytotoxicity.

Measuring and modeling of binary mixture effects of pharmaceuticals and nickel on cell viability/cytotoxicity in the human hepatoma derived cell line HepG2

The interaction of drugs and non-therapeutic xenobiotics constitutes a central role in human health risk assessment. Still, available data are rare. Two different models have been established to predict mixture toxicity from single dose data, namely, the concentration addition (CA) and independent action (IA) model. However, chemicals can also act synergistic or antagonistic or in dose level deviation, or in a dose ratio dependent deviation. In the present study we used the MIXTOX model (EU project ENV4-CT97-0507), which incorporates these algorithms, to assess effects of the binary mixtures in the human hepatoma cell line HepG2. These cells possess a liver-like enzyme pattern and a variety of xenobiotic-metabolizing enzymes (phases I and II). We tested binary mixtures of the metal nickel, the anti-inflammatory drug diclofenac, and the antibiotic agent irgasan and compared the experimental data to the mathematical models. Cell viability was determined by three different methods the MTT-, AlamarBlue(R) and NRU assay. The compounds were tested separately and in combinations. We could show that the metal nickel is the dominant component in the mixture, affecting an antagonism at low-dose levels and a synergism at high-dose levels in combination with diclofenac or irgasan, when using the NRU and the AlamarBlue assay. The dose-response surface of irgasan and diclofenac indicated a concentration addition. The experimental data could be described by the algorithms with a regression of up to 90%, revealing the HepG2 cell line and the MIXTOX model as valuable tool for risk assessment of binary mixtures for cytotoxic endpoints. However the model failed to predict a specific mode of action, the CYP1A1 enzyme activity.

Nickel(II)-induced oxidative stress, apoptosis, G2/M arrest, and genotoxicity in normal rat kidney cells

In order to elucidate the effects of nickel (Ni) on oxidative stress, apoptosis, and genotoxicity in renal cells, the levels of intracellular oxidants, lipid peroxidation, apoptotic proteins, and DNA damage were measured in normal rat kidney (NRK) cells after nickel chloride (NiCl(2)) treatment. NiCl(2) appeared to increase the formation of the fluorescent oxidized compound (dichlorofluorescein, DCF) and levels of thiobarbituric acid-reactive substances (TBARS). In flow cytometric analysis, a rise in cell proportion in sub-G1 phase occurred in a concentration-dependent manner. After Ni treatment, there was reduced expression of Bcl-2 and Bcl-xL proteins, while induced Bad and Bax proteins expression was higher. Single-strand DNA breakage induced by Ni in NRK cells was determined by comet assay. Significant increase DNA damage score (arbitrary units) was noted in a concentration-related manner after treatment with Ni. Induction of intracellular oxidants by Ni was accompanied by an increasing frequency of DNA strand breakage. Our data indicate that Ni-induced oxidative stress and genotoxicity in NRK cells may involve reactive oxygen intermediates, and that Bcl family-mediated signaling pathway may be involved in positive regulation of Ni-induced renal cytotoxicity.

Epigenetics: origins and implications for cancer epidemiology

This paper provides information on the evolution of the 'epigenetics' concept since Aristotle and draws attention to the importance of epigenetic implications for cancer epidemiology in the years to come. Clearly, to understand origins of the concept of epigenetics, it is worthwhile to consider historical arguments associated with evolution. Equally clearly, in the last half of the 20th century, great advances in the understanding of epigenetics and, more specifically, great advances in the understanding of epigenetics in cancer have been made. However, reaping the full benefits of epigenetics lies beyond the predominant experimental studies of today. In general, epigenetics opens many doors in the field of cancer, but it also adds another level of complex, inter-related, and multi-dimensional information to research, and to its interpretation. Overall, future cancer studies should consider, or at least be sensitive to, epigenetic effects and mechanisms. Moving the focus beyond 'pristine' inheritance via DNA alone, cancer epidemiology investigating epigenetic exposures such as environmental factors (exposure to heavy metals, air pollution, arsenic and other toxins), dietary patterns (starvation, famine, contamination), and lifestyle habits (smoking, level of physical activity, and BMI) in populations has the prospect to significantly benefit future cancer prevention and treatment schemes.

Environmental toxicity, oxidative stress and apoptosis: ménage à trois

Apoptosis is an evolutionary conserved homeostatic process involved in distinct physiological processes including organ and tissue morphogenesis, development and senescence. Its deregulation is also known to participate in the etiology of several human diseases including cancer, neurodegenerative and autoimmune disorders. Environmental stressors (cytotoxic agents, pollutants or toxicants) are well known to induce apoptotic cell death and to contribute to a variety of pathological conditions. Oxidative stress seems to be the central element in the regulation of the apoptotic pathways triggered by environmental stressors. In this work, we review the established mechanisms by which oxidative stress and environmental stressors regulate the apoptotic machinery with the aim to underscore the relevance of apoptosis as a component in environmental toxicity and human disease progression.

Uptake of nickel from 316L stainless steel into contacting osteoblastic cells and metal ion interference with BMP-2-induced alkaline phosphatase

Bone cells contacting nickel (Ni)-containing implant materials may be affected by Ni species via disturbed signaling pathways involved in bone cell development. Here we analyze effects of the Ni-containing steel 316L and major metal constituents thereof on bone morphogenetic protein-2 (BMP-2)-induced alkaline phosphatase (ALP) of MC3T3-E1 cells. While cells grew normally on 316L, cellular Ni content increased 10-fold vs. control within 4 days. With respect to the major components of 316L, Ni2+ (3-50 microM) was most inhibitory to BMP-2-induced ALP, whereas even 50 microM Fe3+, Cr3+, Mo5+, or Mn2+ had no such effect. In line with this, BMP-2-induced ALP was significantly reduced in cells on 316L. This effect was not prevented by the metal ion chelator diethylenetriaminepentaacetic acid (DTPA). Instead, DTPA abolished the stimulatory effect of BMP-2 on ALP, pointing to chelatable metal ions involved. Zn2+, as one possible candidate, antagonized the Ni2+ inhibition of BMP-2-induced ALP in both MC3T3-E1 and human bone marrow stromal cells. Results show that cells contacting 316L steel are exposed to increased concentrations of Ni which suffice to impair BMP-2-induced ALP activity. Zn2+, as a competitor of this inhibition, may help to restore normal osteoblastic function and bone development under these conditions.

Overexpression of myocyte enhancer factor 2 and histone hyperacetylation in hepatocellular carcinoma

PURPOSE

It has been indicated that activated hepatic stellate cells (HSCs) play key roles on the pathogenesis of hepatocellular carcinoma (HCC). The purpose of the study was to investigate the potential mechanism in it.

METHODS

Activation of HSCs, the expression of myocyte enhancer factor 2 (MEF2), class II histone deacetylases (II HDACs) and histone acetylation were analyzed in specimens of primary HCCs, cirrhotic and normal livers. Activated HSCs were identified using anti-a-smooth muscle actin (a-SMA) by Immunohistochemistry (IHC). The levels of expression of MEF2A, MEF2C and II HDACs mRNA and protein were measured by real time quantitative PCR and western blot (WB). Histone acetylation was assessed using anti-acetyl-histone H3, -H4 by WB and IHC. A P value < 0.05 was considered statistically significant.

RESULTS

A-SMA positive activated HSCs were more prominent in HCCs and cirrhotic livers than in normal livers, accompanied by marked expression of MEF2A and MEF2C. The expression of MEF2A, MEF2C and II HDACs, both mRNA and protein, were much more enhanced in HCCs than those in cirrhotic and normal livers (P < 0.05). Histone H3 and H4 were hyperacetylated in HCCs compared with those in cirrhotic and normal livers (P < 0.05). The correlation coefficients between the expression of MEF2 and II HDACs, acetyl-histones were all beyond 0.5.

CONCLUSIONS

These data showed a potential molecular mechanism that activated HSCs participate in the pathogenesis of HCCs by overexpression of MEF2 and its consequent impact on histone hyperacetylation. Further investigations aimed at interfering MEF2 expression are needed.

Curcumin-induced histone hypoacetylation enhances caspase-3-dependent glioma cell death and neurogenesis of neural progenitor cells

Acetylation of histones and nonhistone proteins is an important post-translational modification involved in the regulation of gene expression in mammalian cells. Dysfunction of histone acetyltransferase (HAT) is often associated with the manifestation of several diseases. In this report, HATs are new targets for the development of therapeutics. Our studies first proved that curcumin induces histone hypoacetylation in brain cancer cells and finally induces apoptotic cell death through a (PARP)- and caspase 3-mediated manner. In addition, curcumin induces recontrolling of neural stem cell fates. It induces effective neurogenesis, synaptogenesis, and migration of neural progenitor cells in vitro in brain-derived adult neural stem cells. We also confirmed the neurogenic effect of curcumin in our in vivo experiments. Curcumin actively suppressed differentiation in astrocytes while promoting differentiation into the neurons associated with decrease of histone H3 and H4 acetylation. We suggest that histone hypoacetylation plays an important role in determine stem cell fate through controlling the simultaneous expression of many genes. Thus, the present finding that curcumin, a nontoxic dietary compound, is a histone acetyltransferase inhibitor would supply a new window to understand further the molecular mechanism of histone acetylase inhibitors (HAI) in cancer and neural stem cells and provide a new target molecule for treating central nervous system disorders.

Curcumin-induced histone hypoacetylation: The role of reactive oxygen species

Curcumin (Cur), a well-known dietary pigment derived from Curcuma longa, is a promising anticancer drug, but its in vivo target molecules remain to be clarified. Here we report that exposure of human hepatoma cells to Cur led to a significant decrease of histone acetylation. Histone acetyltransferase (HAT) and histone deacetylase (HDAC) are the enzymes controlling the state of histone acetylation in vivo. Cur treatment resulted in a comparable inhibition of histone acetylation in the absence or presence of trichostatin A (the specific HDAC inhibitor), and showed no effect on the in vitro activity of HDAC. In contrast, the domain negative of p300 (a most potent HAT protein) could block the inhibition of Cur on histone acetylation; and the Cur treatment significantly inhibited the HAT activity both in vivo and in vitro. Thus, it is HAT, but not HDAC that is involved in Cur-induced histone hypoacetylation. At the same time, exposure of cells to low or high concentrations of Cur diminished or enhanced the ROS generation, respectively. And the promotion of ROS was obviously involved in Cur-induced histone hypoacetylation, since Cur-caused histone acetylation and HAT activity decrease could be markedly diminished by the antioxidant enzymes, superoxide dismutase (SOD), catalase (CAT) or their combination, but not by their heat-inactivated forms. The data presented here prove that HAT is one of the in vivo target molecules of Cur; through inhibiting its activity, Cur induces histone hypoacetylation in vivo, where the ROS generation plays an important role. Considering the critical roles of histone acetylation in eukaryotic gene transcription and the involvement of histone hypoacetylation in the lose of cell viability caused by high concentrations of Cur, these results open a new door for us to further understand the molecular mechanism involved in the in vivo function of Cur.

Histone hypoacetylation is involved in 1,10-phenanthroline?Cu2+-induced human hepatoma cell apoptosis

The 1,10-orthophenanthroline (OP)-Cu(2+) combination, one generally used reactive oxygen species (ROS) generation system, is known to induce cell apoptosis, but the mechanism of ROS generation in this process remains unclear. Here we found that in the presence of 5 microM Cu(2+), OP inhibited histone acetyltransferase (HAT) activity, resulting in decreased acetylation in both histone H3 and H4. This inhibition of histone acetylation and HAT activity was significantly attenuated by preventing or scavenging ROS generation with the Cu(2+) chelator of bathocuproine disulfonate, or the antioxidants of N-acetyl-cysteine and mannitol, respectively, indicating the involvement of ROS generation in OP-Cu(2+) -induced histone hypoacetylation. At the same time, this ROS generation is found to be involved in OP-Cu(2+) -induced apoptosis in human hepatoma Hep3B cells. The important role of histone hypoacetylation in the induction of apoptosis was also proven by the marked diminution of apoptosis by 100 nM trichostatin A, a specific inhibitor of histone deacetylase, or the overexpression of p300, an HAT protein. Collectively, these observations suggest that histone hypoacetylation represents one unrevealed mechanism involved in the in vivo function of OP-Cu(2+) -generated ROS, at least in their induction of cell apoptosis.