Contact sensitizer nickel sulfate activates the transcription factors NF-kB and AP-1 and increases the expression of nitric oxide synthase in a skin dendritic cell line

MicroRNA-Gene Interactions Impacted by Toxic Metal(oid)s during EMT and Carcinogenesis

Chronic environmental exposure to toxic metal(loid)s significantly contributes to human cancer development and progression. It is estimated that approximately 90% of cancer deaths are a result of metastasis of malignant cells, which is initiated by epithelial-mesenchymal transition (EMT) during early carcinogenesis. EMT is regulated by many families of genes and microRNAs (miRNAs) that control signaling pathways for cell survival, death, and/or differentiation. Recent mechanistic studies have shown that toxic metal(loid)s alter the expression of miRNAs responsible for regulating the expression of genes involved in EMT. Altered miRNA expressions have the potential to be biomarkers for predicting survival and responses to treatment in cancers. Significantly, miRNAs can be developed as therapeutic targets for cancer patients in the clinic. In this mini review, we summarize key findings from recent studies that highlight chemical-miRNA-gene interactions leading to the perturbation of EMT after exposure to toxic metal(loid)s including arsenic, cadmium, nickel, and chromium.

Association of cerebral spinal fluid copper imbalance in amyotrophic lateral sclerosis

A plethora of environmental risk factors has been persistently implicated in the pathogenesis of amyotrophic lateral sclerosis (ALS), including metal/metalloids. This study aimed to examine potential associations between cerebral spinal fluid (CSF) metal/metalloids and ALS risks. CSF concentrations of copper (Cu), nickel (Ni), mercury (Hg), arsenic (As), manganese (Mn), and iron (Fe) in ALS (spinal- and bulbar-onset) patients and controls were measured using inductively coupled plasma mass spectrometry (ICP-MS). Results from this study revealed marked differences between control, spinal-onset, and bulbar-onset groups. We report that Cu levels were lower in the ALS and spinal-onset groups compared to the control group. Ni level were higher in the spinal-onset group compared to the control and bulbar-onset groups. In addition, associations between CSF metal/metalloid levels with disease severity, sex, and serum triglycerides were also examined to broach the potential relevance of neurotoxic metal/metalloids in ALS disease heterogeneity.

ALS risk factors: Industrial airborne chemical releases

Most amyotrophic lateral sclerosis (ALS) cases are sporadic (∼90%) and environmental exposures are implicated in their etiology. Large industrial facilities are permitted the airborne release of certain chemicals with hazardous properties and report the amounts to the US Environmental Protection Agency (EPA) as part of its Toxics Release Inventory (TRI) monitoring program. The objective of this project was to identify industrial chemicals released into the air that may be associated with ALS etiology. We geospatially estimated residential exposure to contaminants using a de-identified medical claims database, the SYMPHONY Integrated Dataverse®, with ∼26,000 nationally distributed ALS patients, and non-ALS controls matched for age and gender. We mapped TRI data on industrial releases of 523 airborne contaminants to estimate local residential exposure and used a dynamic categorization algorithm to solve the problem of zero-inflation in the dataset. In an independent validation study, we used residential histories to estimate exposure in each year prior to diagnosis. Air releases with positive associations in both the SYMPHONY analysis and the spatio-temporal validation study included styrene (false discovery rate (FDR) 5.4e-5), chromium (FDR 2.4e-4), nickel (FDR 1.6e-3), and dichloromethane (FDR 4.8e-4). Using a large de-identified healthcare claims dataset, we identified geospatial environmental contaminants associated with ALS. The analytic pipeline used may be applied to other diseases and identify novel targets for exposure mitigation. Our results support the future evaluation of these environmental chemicals as potential etiologic contributors to sporadic ALS risk.

Induction of NUPR1 and AP‑1 contributes to the carcinogenic potential of nickel

Nickel (Ni) is carcinogenic to humans, and causes cancers of the lung, nasal cavity, and paranasal sinuses. The primary mechanisms of Ni‑mediated carcinogenesis involve the epigenetic reprogramming of cells and the ability for Ni to mimic hypoxia. However, the exact mechanisms of carcinogenesis related to Ni are obscure. Nuclear protein 1 (NUPR1) is a stress‑response gene overexpressed in cancers, and is capable of conferring chemotherapeutic resistance. Likewise, activator protein 1 (AP‑1) is highly responsive to environmental signals, and has been associated with cancer development. In this study, NUPR1 was found to be rapidly and highly induced in human bronchial epithelial (BEAS‑2B) cells exposed to Ni, and was overexpressed in Ni‑transformed BEAS‑2B cells. Similarly, AP‑1 subunits, JUN and FOS, were induced in BEAS‑2B cells following Ni exposure. Knockdown of JUN or FOS was found to significantly suppress NUPR1 induction following Ni exposure, demonstrating their importance in NUPR1 transactivation. Reactive oxygen species (ROS) are known to induce AP‑1, and Ni has been shown to produce ROS. Treatment of BEAS‑2B cells with antioxidants was unable to prevent NUPR1 induction by Ni, suggesting that NUPR1 induction by Ni relies on mechanisms other than oxidative stress. To determine how NUPR1 is transcriptionally regulated following Ni exposure, the NUPR1 promoter was cloned and inserted into a luciferase gene reporter vector. Multiple JUN binding sites reside within the NUPR1 promoter, and upon deleting a JUN binding site in the upstream most region within the NUPR1 promoter using site‑directed mutagenesis, NUPR1 promoter activity was significantly reduced. This suggests that AP‑1 transcriptionally regulates NUPR1. Moreover, knockdown of NUPR1 significantly reduced colony formation and anchorage‑independent growth in Ni‑transformed BEAS‑2B cells. Therefore, these results collectively demonstrate a novel mechanism of NUPR1 induction following Ni exposure, and provide a molecular basis by which NUPR1 may contribute to lung carcinogenesis.

Time-course analysis of the effect of embedded metal on skeletal muscle gene expression

As a consequence of military operations, many veterans suffer from penetrating wounds and long-term retention of military-grade heavy metal fragments. Fragments vary in size and location, and complete surgical removal may not be feasible or beneficial in all cases. Increasing evidence suggests retention of heavy metal fragments may have serious biological implications, including increased risks for malignant transformation. Previous studies assessed the tumorigenic effects of metal alloys in rats, demonstrating combinations of metals are sufficient to induce tumor formation after prolonged retention in skeletal muscle tissue. In this study, we analyzed transcriptional changes in skeletal muscle tissue in response to eight different military-relevant pure metals over 12 mo. We found that most transcriptional changes occur at 1 and 3 mo after metal pellets are embedded in skeletal muscle and these effects resolve at 6 and 12 mo. We also report significant immunogenic effects of nickel and cobalt and suppressive effects of lead and depleted uranium on gene expression. Overall, skeletal muscle exhibits a remarkable capacity to adapt to and recover from internalized metal fragments; however, the cellular response to chronic exposure may be restricted to the metal-tissue interface. These data suggest that unless affected regions are specifically captured by biopsy, it would be difficult to reliably detect changes in muscle gene expression that would be indicative of long-term adverse health outcomes.

Migratory dendritic cells in skin-draining lymph nodes have nickel-binding capabilities

Nickel (Ni) is the most frequent metal allergen and induces Th1-dependent type-IV allergies. In local skin, epidermal Langerhans cells (LCs) and/or dermal dendritic cells (DCs) uptake antigens and migrate to draining lymph nodes (LNs). However, the subsets of antigen-presenting cells that contribute to Ni presentation have not yet been identified. In this study, we analyzed the Ni-binding capabilities of murine DCs using fluorescent metal indicator Newport Green. Elicitation of Ni allergy was assessed after intradermal (i.d.) injection of Ni-treated DCs into ear pinnae of Ni-sensitized mice. The Ni-binding capabilities of MHC class II^hi CD11c^int migratory DCs were significantly stronger than those of MHC class II^int CD11c^hi resident DCs and CD11c^int PDCA1⁺ MHC class II^int B220⁺ plasmacytoid DCs. Migratory DCs in skin-draining and mandibular LNs showed significantly stronger Ni-binding capabilities than those in mesenteric and medial iliac LNs. An i.d. injection of IL-1β induced the activation of LCs and dermal DCs with strong Ni-binding capabilities. Ni-binding LCs were detected in draining LNs after i.d. challenge with IL-1β and Ni. Moreover, an i.d. injection of Ni-treated DCs purified from skin-draining LNs elicited Ni-allergic inflammation. These results demonstrated that migratory DCs in skin-draining LNs have strong Ni-binding capabilities and elicit Ni allergy.

Nuclear factor erythroid 2 - related factor 2 and its relationship with cellular response in nickel exposure: a systems biology analysis

Background

Nickel and nickel-containing compounds (NCC) are known human carcinogens. However, the precise molecular mechanisms of nickel-induced malignant transformation remain unknown. Proposed mechanisms suggest that nickel and NCC may participate in the dual activation/inactivation of enzymatic pathways involved in cell defenses against oxidative damage, where Nuclear factor-erythroid 2 related factor 2 (Nrf2) plays a central role.

Methods

For assessing the potential role of proteins involved in the Nrf2-mediated response to nickel and NCC exposure, we designed an interactome network using the STITCH search engine version 5.0 and the STRING software 10.0. The major NCC-protein interactome (NCPI) generated was analyzed using the MCODE plugin, version 1.5.1 for the detection of interaction modules or subnetworks. Main centralities of the NCPI were determined with the CentiScape 2.2 plugin of Cytoscape 3.4.0 and main biological processes associated with each cluster were assessed using the BiNGO plugin of Cytoscape 3.4.0.

Results

Water-soluble NiSO₄ and insoluble Ni₃S₂ were the most connected to proteins involved in the NCPI network. Nfr2 was detected as one of the most relevant proteins in the network, participating in several multifunctional protein complexes in clusters 1, 2, 3 and 5. Ontological analysis of cluster 3 revealed several processes related to unfolded protein response (UPR) and response to endoplasmic reticulum (ER) stress.

Conclusions

Cellular response to NCC exposure was very comparable, particularly concerning oxidative stress response, inflammation, cell cycle/proliferation, and apoptosis. In this cellular response, Nfr2 was highly centralized and participated in several multifunctional protein complexes, including several related to ER-stress. These results add evidence on the possible Ni²⁺ induced – ER stress mainly associated with insoluble NCC. In this scenario, we also show how protein degradation mediated by ubiquitination seems to play key roles in cellular responses to Ni.

Electrophilic nitro-fatty acids suppress allergic contact dermatitis in mice

BACKGROUND

Reactions between nitric oxide (NO), nitrite (NO2-), and unsaturated fatty acids give rise to electrophilic nitro-fatty acids (NO₂ -FAs), such as nitro oleic acid (OA-NO₂ ) and nitro linoleic acid (LNO₂ ). Endogenous electrophilic fatty acids (EFAs) mediate anti-inflammatory responses by modulating metabolic and inflammatory signal transduction reactions. Hence, there is considerable interest in employing NO₂ -FAs and other EFAs for the prevention and treatment of inflammatory disorders. Thus, we sought to determine whether OA-NO₂ , an exemplary nitro-fatty acid, has the capacity to inhibit cutaneous inflammation.

METHODS

We evaluated the effect of OA-NO₂ on allergic contact dermatitis (ACD) using an established model of contact hypersensitivity in C57Bl/6 mice utilizing 2,4-dinitrofluorobenzene as the hapten.

RESULTS

We found that subcutaneous (SC) OA-NO₂ injections administered 18 h prior to sensitization and elicitation suppresses ACD in both preventative and therapeutic models. In vivo SC OA-NO₂ significantly inhibits pathways that lead to inflammatory cell infiltration and the production of inflammatory cytokines in the skin. Moreover, OA-NO₂ is capable of enhancing regulatory T-cell activity. Thus, OA-NO₂ treatment results in anti-inflammatory effects capable of inhibiting ACD by inducing immunosuppressive responses.

CONCLUSION

Overall, these results support the development of OA-NO₂ as a promising therapeutic for ACD and provides new insights into the role of electrophilic fatty acids in the control of cutaneous immune responses potentially relevant to a broad range of allergic and inflammatory skin diseases.

Mechanism of Action of the Novel Nickel(II) Complex in Simultaneous Reactivation of the Apoptotic Signaling Networks Against Human Colon Cancer Cells

The aim of this study was to evaluate the cytotoxic potential of a novel nickel(II) complex (NTC) against WiDr and HT-29 human colon cancer cells by determining the IC50 using the standard MTT assay. The NTC displayed a strong suppressive effect on colon cancer cells with an IC50 value of 6.07 ± 0.22 μM and 6.26 ± 0.13 μM against WiDr and HT-29 respectively, after 24 h of treatment. Substantial reduction in the mitochondrial membrane potential and increase in the release of cytochrome c from the mitochondria directed the induction of the intrinsic apoptosis pathway by the NTC. Activation of this pathway was further evidenced by significant activation of caspase 3/7 and 9. The NTC was also shown to activate the extrinsic pathway of apoptosis via activation of caspase-8 which is linked to the suppression of NF-κB translocation to the nucleus. Cell cycle arrest in the G1 phase was confirmed by flow cytometry and up-regulation of glutathione reductase expression was quantified by qPCR. Results of the current work indicates that NTC possess a potent cancer cell abolishing activity by simultaneous induction of intrinsic and extrinsic pathways of apoptosis in colon cancer cell lines.

Nickel ion inhibits nuclear factor-kappa B activity in human oral squamous cell carcinoma

Background

The spontaneous IL-8 secretion observed in OSCC is partially dependent on the disregulated activity of transcription factor NF-κB. Nickel compounds are well established human carcinogens, however, little is known about the influence of nickel on the spontaneous secretion of IL-8 in oral squamous cell carcinoma (OSCC) cells. The aim of the present study was to investigate whether Ni²⁺ ions can influence on IL-8 secretion by OSCC.

Methods and Results

The IL-8 secretion was measured by ELISA. The expression of IL-8 mRNA was examined by real-time PCR. The NF-κB activity was measured by luciferase assay. The phosphorylation status and nuclear localization of NF-κB subunits were examined by Western blotting or Transfactor kit and immunofluorescence staining, respectively. The interaction of NF-κB p50 subunit and Ni²⁺ ions was examined by Ni²⁺-column pull down assay. The site-directed mutagenesis was used to generate a series of p50 mutants. Scratch motility assay was used to monitor the cell mobility. Our results demonstrated that, on the contrary to our expectations, Ni²⁺ ions inhibited the spontaneous secretion of IL-8. As IL-8 reduction was observed in a transcriptional level, we performed the luciferase assay and the data indicated that Ni²⁺ ions reduced the NF-κB activity. Measurement of p50 subunit in the nucleus and the immunofluorescence staining revealed that the inhibitory effect of Ni²⁺ ions was attributed to the prevention of p50 subunit accumulation to the nucleus. By Ni²⁺-column pull down assay, Ni²⁺ ions were shown to interact directly with His cluster in the N-terminus of p50 subunit. The inhibitory effect of Ni²⁺ ions was reverted in the transfectant expressing the His cluster-deleted p50 mutant. Moreover, Ni²⁺ ions inhibited the OSCC mobility in a dose dependent fashion.

Conclusions

Taken together, inhibition of NF-κB activity by Ni²⁺ ion might be a novel therapeutic strategy for the treatment of oral cancer.

Dual effect of nickel on L-arginine/nitric oxide system in RAW 264.7 macrophages

The immunogenic mechanisms of the potent contact allergen nickel are not completely clear. Nitric oxide (NO) serves as a fundamental signalling and effector molecule in the immune system, but little is known about its possible role in immune reactions elicited by nickel. We investigated the effects of nickel on the L-arginine/inducible NO synthase (iNOS) system in a murine macrophage cell line, RAW 264.7. Both LPS-stimulated and non-stimulated RAW 264.7 cells were incubated in the presence of 0-100 μM nickel sulphate for 24 h. Subsequently, NO production, iNOS protein expression, L-arginine uptake and gene expression of iNOS and cationic amino acid transporter systems (CAT) were measured. We found that 100 μM NiSO4 increased LPS-induced nitrite production as well as the formation of [(3)H]-L-citrulline from [(3)H]-L-arginine in the RAW 264.7 cells. Correspondingly, the expression of iNOS gene and protein was also remarkably enhanced. Nevertheless, nickel had an inhibitory effect on L-arginine transport which disappeared gradually upon LPS-stimulation in parallel with an increase in NO output. LPS was found to significantly amplify CAT-3 as well as CAT-2 mRNA expression, mirroring the increase in L-arginine transport. In the range of 1-10 μM, NiSO4 did not have any additional effect on CAT mRNA expression, but at 100 μM it was able to enhance CAT-1 and CAT-3 mRNA expression upon LPS stimulation. Our data indicate that nickel interferes with macrophages' L-arginine/NOS system on multiple levels. Considering the potent biological effects of NO, these influences may contribute to nickel toxicity.

Gene expression profiles in peripheral blood mononuclear cells of Chinese nickel refinery workers with high exposures to nickel and control subjects

BACKGROUND

Occupational exposure to nickel (Ni) is associated with an increased risk of lung and nasal cancers. Ni compounds exhibit weak mutagenic activity, alter the cell's epigenetic homeostasis, and activate signaling pathways. However, changes in gene expression associated with Ni exposure have only been investigated in vitro. This study was conducted in a Chinese population to determine whether occupational exposure to Ni was associated with differential gene expression profiles in the peripheral blood mononuclear cells (PBMC) of Ni-refinery workers when compared with referents.

METHODS

Eight Ni-refinery workers and ten referents were selected. PBMC RNA was extracted and gene expression profiling was conducted using Affymetrix exon arrays. Differentially expressed genes (DEG) between both groups were identified in a global analysis.

RESULTS

There were a total of 2,756 DEGs in the Ni-refinery workers relative to the referents [false discovery rate (FDR) adjusted P < 0.05] with 770 upregulated genes and 1,986 downregulated genes. DNA repair and epigenetic genes were significantly overrepresented (P < 0.0002) among the DEGs. Of 31 DNA repair genes, 29 were repressed in the Ni-refinery workers and 2 were overexpressed. Of the 16 epigenetic genes, 12 were repressed in the Ni-refinery workers and 4 were overexpressed.

CONCLUSIONS

The results of this study indicate that occupational exposure to Ni is associated with alterations in gene expression profiles in PBMCs of subjects.

IMPACT

Gene expression may be useful in identifying patterns of deregulation that precede clinical identification of Ni-induced cancers.

Zinc, cadmium and nickel increase the activation of NF-κB and the release of cytokines from THP-1 monocytic cells

The sustained activation of the transcription factor nuclear factor κB (NF-κB) by metal-activated signalling pathways can lead to chronic inflammatory processes and related diseases, including carcinogenesis. The aim of the present work was to clarify the effect of zinc, nickel and cadmium on NF-κB activation in the THP-1 human monocytic leukemia cell line. The production of the NF-κB downstream pro-inflammatory mediators tumor necrosis factor (TNF)-α and interleukin (IL)-1β, IL-6 and IL-8 was also evaluated due to their important roles in the pathogenesis of chronic inflammatory and autoimmune diseases and, ultimately, in the development of cancer. The results obtained demonstrated that zinc, nickel and cadmium significantly activate NF-κB, and the release of the chemokine IL-8. Cadmium also induced the release of TNF-α and IL-6 in THP-1 monocytic cells, which may indicate some potential to induce deleterious effects through this pathway.

Nickel-induced down-regulation of ΔNp63 and its role in the proliferation of keratinocytes

Epidemiological, animal, and cell studies have demonstrated that nickel compounds are human carcinogens. The mechanisms of their carcinogenic actions remain to be investigated. p63, a close homologue of the p53 tumor suppressor protein, has been linked to cell fate determination and/or maintenance of self-renewing populations in several epithelial tissues, including skin, mammary gland, and prostate. ΔNp63, a dominant negative isoform of p63, is amplified in a variety of epithelial tumors including squamous cell carcinomas and carcinomas of the prostate and mammary glands. The present study shows that nickel suppressed ΔNp63 expression in a short-time treatment (up to 48 h). Nickel treatment caused activation of NF-κB. Blockage of NF-κB partially reversed nickel-induced ΔNp63 suppression. Nickel decreased interferon regulatory factor (IRF) 3 and IRF7, IKKε, and Sp100. Over-expression of IRF3 increased ΔNp63 expression suppressed by nickel. Nickel was able to activate p21, and its activation was offset by the over-expression of ΔNp63. In turn, elevated p63 expression counteracted the ability of nickel to restrict cell growth. The present study demonstrated that nickel decreased interferon regulatory proteins IRF3 and IRF7, and activated NF-κB, resulting in ΔNp63 suppression and then p21 up-regulation. ΔNp63 plays an important role in nickel-induced cell proliferation.

Signal transduction profile of chemical sensitisers in dendritic cells: an endpoint to be included in a cell-based in vitro alternative approach to hazard identification?

The development of non-animal testing methods for the assessment of skin sensitisation potential is an urgent challenge within the framework of existing and forthcoming legislation. Efforts have been made to replace current animal tests, but so far no alternative methods have been developed. It is widely recognised that alternatives to animal testing cannot be accomplished with a single approach, but rather will require the integration of results obtained from different in vitro and in silico assays. The argument subjacent to the development of in vitro dendritic cell (DC)-based assays is that sensitiser-induced changes in the DC phenotype can be differentiated from those induced by irritants. This assumption is derived from the unique capacity of DC to convert environmental signals encountered at the skin into a receptor expression pattern (MHC class II molecules, co-stimulatory molecules, chemokine receptors) and a soluble mediator release profile that will stimulate T lymphocytes. Since signal transduction cascades precede changes in surface marker expression and cytokine/chemokine secretion, these phenotypic modifications are a consequence of a signal transduction profile that is specifically triggered by sensitisers and not by irritants. A limited number of studies have addressed this subject and the present review attempts to summarise and highlight all of the signalling pathways modulated by skin sensitisers and irritants. Furthermore, we conclude this review by focusing on the most promising strategies suitable for inclusion into a cell-based in vitro alternative approach to hazard identification.

Effects and mechanisms of aloperine on 2, 4-dinitrofluorobenzene-induced allergic contact dermatitis in BALB/c mice

Allergic contact dermatitis is a prototypic T-cell-mediated cutaneous inflammatory response. Multiple cell types, inflammatory mediators and cytokines are involved in the regulation of immunologic and inflammatory processes in allergic contact dermatitis. Aloperine is an isolated alkaloid found in the plant of Sophora alopecuroides L. It has been clinically proved effective in China for a long time for skin inflammatory diseases such as allergic contact dermatitis. However, the mechanism of aloperine on allergic contact dermatitis is largely unknown. Therefore, the aim of this study was to investigate the effect of aloperine on 2, 4-dinitrofluorobenzene (DNFB)-induced allergic contact dermatitis in BALB/c mice and the possible underlying mechanisms. The results showed that topical application of DNFB on the ear provoked typical allergic contact dermatitis with ear swelling and ear erythema in BALB/c mice. Treatments with 1% aloperine suppressed DNFB-induced increase in ear thickness and ear erythema. Moreover, 1% aloperine treatment significantly decreased the up-regulated mRNA and protein levels of tumor necrosis factor-alpha (TNF-alpha), interleukin-1beta (IL-1beta) and interleukin-6 (IL-6) induced by DNFB in ear biopsy homogenates. Our findings suggest that aloperine greatly improves the DNFB-induced allergic contact dermatitis in mice. The therapeutic mechanism might be related to the reduction of TNF-alpha, IL-1beta and IL-6 production induced by DNFB.

Effects of nickel on cyclin expression, cell cycle progression and cell proliferation in human pulmonary cells

Frequent exposure to nickel compounds has been considered as one of the potential causes of human lung cancer. However, the molecular mechanism of nickel-induced lung carcinogenesis remains obscure. In the current study, slight S-phase increase, significant G(2)/M cell cycle arrest, and proliferation blockage were observed in human bronchial epithelial cells (Beas-2B) upon nickel exposure. Moreover, the induction of cyclin D1 and cyclin E by nickel was shown for the first time in human pulmonary cells, which may be involved in nickel-triggered G(1)/S transition and cell transformation. In addition, we verified that hypoxia-inducible factor-1alpha, an important transcription factor of nickel response, was not required for the cyclin D1 or cyclin E induction. The role of p53 in nickel-induced G(2)/M arrest was excluded, respecting that its protein level, ser(15) phosphorylation, and transcriptional activity were not changed in nickel response. Further study revealed that cyclin A was not activated in nickel response, and cyclin B1, which not only promotes G(2)/M transition but also prevents M-phase exit of cells if not degraded in time, was up-regulated by nickel through a manner independent of hypoxia-inducible factor. More importantly, our results verified that overexpressed cyclin B1, veiling the effect of cyclin D1 or cyclin E, mediated nickel-caused M-phase blockage and cell growth inhibition, which may render pulmonary cells more sensitive to DNA damage and facilitates cancer initiation. These results will not only deepen our understanding of the molecular mechanism involved in nickel carcinogenecity, but also lead to the further study on chemoprevention of nickel-associated human cancer.

The influence of Ni(II) on surface antigen expression in murine macrophages

Biomedical alloys may release nickel ions during corrosion phenomena and, in addition to their interaction with oral tissues, these ions may also influence characteristic properties of the immune system cells. The aim of this study was to evaluate the effect of nickel chloride on the expression of functionally distinct surface antigens in murine RAW macrophages. The expression of the surface antigens CD14, CD40, MHC class I, MHC class II, CD80, CD86, CD54 was analyzed by flow cytometry. The bacterial endotoxin lipopolysaccharide (LPS) was used as a positive control to induce antigen expression. Cells were stimulated with NiCl(2) (0.1 and 0.5mm) in the presence and absence of LPS (0.1 or 25 microg/ml). After exposure periods of 6, 24 and 48 h, LPS caused a time- and dose-dependent increase in the expression of all surface antigens. CD14 expression was up-regulated by 0.1 microg/ml LPS by about 10-fold after 24h and 100-fold after 48 h. After 48 h, NiCl(2) alone up-regulated the expression of all surface antigens between 2- and 4-fold, while in cells stimulated by LPS, 0.1mm NiCl(2) was effective only on CD14, CD40 and MHC class I. Moreover, 0.5mm NiCl(2) even inhibited the LPS-induced expression of all surface antigens, except for CD54, which was still significantly up-regulated. These results show that nickel chloride is able to induce an up-regulation of surface antigen expression, but a high concentration may impair essential functions of macrophages stimulated by LPS.

Soluble and insoluble nickel compounds exert a differential inhibitory effect on cell growth through IKKalpha-dependent cyclin D1 down-regulation

It is well-known that insoluble nickel compounds possess much more potent carcinogenic activities as compared with soluble nickel compounds. Although it is assumed that the different entry and clearance rate are responsible for the difference, the mechanisms underlying the different carcinogenic activities are still not well understood yet. In the present study, we found that exposure to soluble, but not insoluble nickel compounds, caused a significant inhibition of cell growth and G1/G0 cell cycle arrest, which was concomitant with a marked down-regulation of cylin D1, an essential nuclear protein for controlling G1/S transition, while both soluble and insoluble nickel compounds showed similar effects on NFkappaB activation, HIF-1alpha protein accumulation and TNF-alpha transcription and CAP43 protein expression at same doses range. The down-regulation of cyclin D1 is due to protein degradation rather than inhibition of transcription, because the nickel compounds treatment did not change cyclin D1 mRNA level, while MG132, the proteasome inhibitor, can rescue the degradation of cyclin D1 caused by soluble nickel compound. Moreover, the soluble nickel-induced cyclin D1 degradation is dependent on its Thr286 residue and requires IKKalpha, but not HIF-1alpha, which are both reported to be involved in cyclin D1 down-regulation. Taken together, we demonstrate that soluble, but not insoluble nickel compound, is able to cause cyclin D1 degradation and a cell growth arrest in an IKKalpha-dependent manner. Given the role of cyclin D1 and cell proliferation in carcinogenesis, we anticipate that the different effects of soluble and insoluble nickel compounds on cyclin D1 degradation and cell growth arrest may at least partially account for their different carcinogenic activities.

Effect of Skin Sensitizers on Inducible Nitric Oxide Synthase Expression and Nitric Oxide Production in Skin Dendritic Cells: Role of Different Immunosuppressive Drugs

Nitric oxide (NO) is involved in the pathogenesis of acute and chronic inflammatory conditions, namely in allergic contact dermatitis (ACD). However, the mechanism by which NO acts in ACD remains elusive. The present study focuses on the effects of different contact sensitizers (2,4-dinitrofluorbenzene, 1,4-phenylenediamine, nickel sulfate), the inactive analogue of DNFB, 2,4-dichloronitrobenzene, and two irritants (sodium dodecyl sulphate and benzalkonium chloride) on the expression of the inducible isoform of nitric oxide synthase (iNOS) and NO production in skin dendritic cells. It was also studied the role of different immunosuppressive drugs on iNOS expression and NO production. Only nickel sulfate increased the expression of iNOS and NO production being these effects inhibited by dexamathasone. In contrast, cyclosporin A and sirolimus, two other immunosuppressive drugs tested, did not affect iNOS expression triggered by nickel.

The role of a nuclear protein, histone H1, on signalling pathways for the maturation of dendritic cells

We have demonstrated previously that liver allograft tolerance is associated with the immunosuppressive activity of anti-histone H1 autoreactive antibodies induced in the serum of liver transplantation. Furthermore, we and others have shown that nuclear proteins such as histone H1 and high mobility group box 1 play an important role in maturation of dendritic cells (DCs), although the precise mechanisms are still unknown. In the present study, we focus upon the significance of histone H1 on DCs in terms of the intracellular signalling pathway of DCs. Our immunostaining and immunoblot studies demonstrated that histone H1 was detected in cytoplasm and culture supernatants upon the activation of DCs. Histone H1 blockage by anti-histone H1 antibody down-regulated the intracellular activation of mitogen-activated protein kinases (MAPKs) (p38) and IkappaBalpha of DCs, and inhibited DC activity in the proliferation of CD4+ T cells. On the other hand, the addition of histone H1 without endotoxin stimulation up-regulated major histocompatibility complex class II, the CD80 and CD86 surface markers of DCs and the activation of MAPKs (p38 and extracellular-regulated kinase 1/2) and IkappaBalpha. These results suggest that the translocation of histone H1 from nuclei to cytoplasm and the release of their own histone H1 are necessary for the maturation of DCs and the activation for T lymphocytes.

Carcinogenic effect of nickel compounds

Nickel is a widely distributed metal that is industrially applied in many forms. Accumulated epidemiological evidence confirms that exposures to nickel compounds are associated with increased nasal and lung cancer incidence, both in mostly occupational exposures. Although the molecular mechanisms by which nickel compounds cause cancer are still under intense investigation, the carcinogenic actions of nickel compounds are thought to involve oxidative stress, genomic DNA damage, epigenetic effects, and the regulation of gene expression by activation of certain transcription factors related to corresponding signal transduction pathways. The present review summarizes our current knowledge on the molecular mechanisms of nickel carcinogenesis, with special emphasis on the role of nickel induced reactive oxygen species (ROS) and signal transduction pathways.

Ni(II) activates the Nrf2 signaling pathway in human monocytic cells

Nickel is a component of biomedical alloys that is released during corrosion and causes inflammation in tissues by as yet unknown mechanisms. Recent data show that Ni(II) at concentrations of 10-50 microM amplifies lipopolysaccharide-triggered, NFkappaB-mediated cytokine secretion from monocytes. In the current study, we tested the hypothesis that Ni(II) amplifies cytokine secretion by activating the Nrf2 antioxidant pathway rather than by enhancing activity of the NFkappaB signaling pathway. Human THP1 monocytes were exposed to Ni(II) concentrations of 10-30 microM for 6-72 h, then immunoblots of whole-cell lysates or cytosolic and nuclear proteins were used to detect changes in Nrf2 or NFkappaB signaling. Our results show that Ni(II) increased (by 1-2 fold) whole-cell Nrf2 levels and nuclear translocation of Nrf2, and amplified lipopolysaccharide (LPS)-induction of Nrf2 (by 3-5 fold), but had no detectable effect on the initial activation or nuclear translocation of NFkappaB. Because Nrf2 target gene products are known regulators of NFkappaB nuclear activity, our results suggest that Ni(II) may affect cytokine secretion indirectly via modulation of the Nrf2 pathway.

Release of IL-1beta via IL-1beta-converting enzyme in a skin dendritic cell line exposed to 2,4-dinitrofluorobenzene

We used a mouse fetal skin dendritic cell line (FSDC) to study the effect of the strong allergen 2,4-dinitrofluorobenzene (DNFB) on interleukin (IL)-1beta release and IL-1beta receptor immunoreactivity. Stimulation with DNFB (30 minutes) increased IL-1 release without changing the mRNA levels of the protein. Furthermore, DNFB increased transiently the interleukin-1beta-converting enzyme (ICE) activity, as measured with its fluorogenic substrate Z-Tyr-Val-Ala-Asp-AFC. The ICE inhibitor Z-YVAD-FMK prevented the release of IL-1beta evoked by DNFB. Incubation of the cells with DNFB (30 minutes) strongly increased IL-1beta receptor immunoreactivity. The rapid effect of DNFB on the release of mature IL-1beta, without inducing an increase of IL-1beta mRNA in FSDC, suggests a posttranslational modification of pro-IL-1beta by ICE activity.

Role of oxidative stress in ERK and p38 MAPK activation induced by the chemical sensitizer DNFB in a fetal skin dendritic cell line

The intracellular mechanisms involved in the early phase of dendritic cell (DC) activation upon contact with chemical sensitizers are not well known. The strong skin sensitizer 2,4-dinitrofluorobenzene (DNFB) was shown to induce the activation of mitogen-activated protein kinases (MAPK) in DC. In the present study, we investigated a putative role for oxidative stress in DNFB-induced MAPK activation and upregulation of the costimulatory molecule CD40. In a DC line generated from fetal mouse skin, DNFB induced a significant increase in protein oxidation, measured by the formation of carbonyl groups, while it had almost no effect on lipid peroxidation. The antioxidants glutathione and vitamin E, which inhibit protein and lipid oxidation, respectively, were used to assess the role of oxidative stress in DNFB-induced MAPK activation. Glutathione, but not vitamin E, inhibited DNFB-induced p38 MAPK and ERK1/2 phosphorylation, whereas none of the antioxidants interfered significantly with the DNFB-induced upregulation of CD40 protein levels. Taken together, these results indicate that DNFB activates p38 MAPK and ERK1/2 via production of reactive oxygen species, and that protein oxidation plays an important role in MAPK activation.

Contact sensitizers downregulate the expression of the chemokine receptors CCR6 and CXCR4 in a skin dendritic cell line

Chemokines are involved in the control of dendritic cell (DC) trafficking, which is critical for the immune response, namely in allergic contact dermatitis (ACD). In this work, we investigated by flow cytometry the effect of the contact sensitizers 2,4-dinitrofluorobenzene (DNFB), 1,4-phenylenediamine (PPD) and nickel sulfate (NiSO(4)), on the surface expression of the chemokine receptors CCR6 and CXCR4 in DC. As an experimental model of a DC we used a fetal skin-derived dendritic cell line (FSDC), which has morphological, phenotypical and functional characteristics of skin DC. Our results show that all the skin sensitizers studied decreased the membrane expression of the chemokine receptors CCR6 and CXCR4. In contrast, 2,4-dichloronitrobenzene (DCNB), the inactive analogue of DNFB without contact sensitizing properties, was without effect on the surface expression of these receptors. Lipopolysaccharide (LPS), which induces the maturation of DC, also reduced surface CCR6 and CXCR4 expression.

The effects of anti-histone H1 antibody on immune cells responsible for rejection reaction

We previously demonstrated the immunosuppressive activity of anti-histone H1 autoreactive antibodies (Ab) transiently induced in serum of a rat tolerogenic orthotopic liver transplantation (OLT) model. In the present study, we investigated the effects of anti-histone H1 Ab on dendritic cells (DCs), T-cells, lymphokine-activated killer (LAK) cells, and human natural killer (NK) cells. The effects of anti-histone H1 Ab on Concanavalin A (ConA) blast, on rat DC cytokine profiles and phenotypes, and on T-cells, LAK cells, and human NK cells were examined by flow cytometry and RT-PCR. The cytotoxicity of LAK and NK cells pretreated with anti-histone H1 Ab was assayed. The addition of anti-histone H1 Ab to ConA blast inhibited the proliferation of 5-(6)-carboxy-fluorescein succinimidyl ester (CFSE)-labeled lymphocytes without toxicity but increased the population of CD4+CD25+ T-cells. DCs treated with anti-histone H1 Ab expressed lower levels of CD80/CD86, IL-1beta, and IL-6. The addition of anti-histone H1 Ab to LAK culture decreased the percentages of NKR-P1 populations and down-regulated levels of inducible nitric oxide synthase (iNOS), IL-2, and INF-gamma in RT-PCR. The cytotoxicity of LAK and NK cells was lower when pretreated with anti-histone H1 Ab than when pretreated with control IgG. We found that the blockade of histone H1 modulated DCs toward tolerogenic status, decreased the cytotoxicity of LAK and NK cells, and induced CD4+CD25+ T-cells. These results suggest that the use of anti-histone H1 Abs might be a useful strategy for the development of a form of immunosuppression.

Melanoma and the Problem of Malignancy

Of the overt biological properties exhibited by malignant cells two appear to command particular attention; these are (1) the transmigratory ability which empowers these cells to invade surrounding tissues and results in their metastatic and destructive potential, and (2) their ability to evade detection by the immune system of the host. Both of these characteristics may well involve several disparate mechanisms. However, it may be that there are some metabolic features that are common to malignant neoplasms which could go some way to explaining one of these behavioural anomalies. It is proposed that abnormalities of oxidative metabolism of cancer cells, resulting in the generation of reactive oxygen species, are responsible for the inhibition of the functions of vicinal antigen-presenting cells and, thus, the failure of the immune system to recognize tumour-specific antigens likely to be expressed by malignant cells as part of their transmigratory capability.