Gene expression dose-response changes in microarrays after exposure of human peripheral lung epithelial cells to nickel(II)

Gene-expression profiling using suppression-subtractive hybridization and cDNA microarray in rat mononuclear cells in response to welding-fume exposure

Welders with radiographic pneumoconiosis abnormalities have shown a gradual clearing of the X-ray identified effects following removal from exposure. In some cases, the pulmonary fibrosis associated with welding fumes appears in a more severe form in welders. Accordingly, for the early detection of welding-fume-exposure-induced pulmonary fibrosis, the gene expression profiles of peripheral mononuclear cells from rats exposed to welding fumes were studied using suppression-subtractive hybridization (SSH) and a cDNA microarray. As such, Sprague-Dawley rats were exposed to a stainless steel arc welding fume for 2 h/day in an inhalation chamber with a 107.59 / 2.6 mg/m3 concentration of total suspended particulate (TSP) for 30 days. Thereafter, the total RNA was extracted from the peripheral blood mononuclear cells, the cDNA synthesized from the total RNA using the SMARTTM PCR cDNA method, and SSH performed to select the welding-fume-exposure-regulated genes. The cDNAs identified by the SSH were then cloned into a plasmid miniprep, sequenced and the sequences analysed using the NCBI BLAST programme. In the SSH cloned cDNA microarray analysis, five genes were found to increase their expression by 1.9-fold or more, including Rgs 14, which plays an important function in cellular signal transduction pathways; meanwhile 36 genes remained the same and 30 genes decreased their expression by more than 59%, including genes associated with the immune response, transcription factors and tyrosine kinases. Among the 5200 genes analysed, 256 genes (5.1%) were found to increase their gene expression, while 742 genes (15%) decreased their gene expression in response to the welding-fume exposure when tested using a commercial 5.0k DNA microarray. Therefore, unlike exposure to other toxic substances, prolonged welding-fume exposure was found to substantially downregulate many genes.

CMRF: analyzing differential gene regulation in two group perturbation experiments

BACKGROUND

Microarray experiments often measure expressions of genes taken from sample tissues in the presence of external perturbations such as medication, radiation, or disease. The external perturbation can change the expressions of some genes directly or indirectly through gene interaction network. In this paper, we focus on an important class of such microarray experiments that inherently have two groups of tissue samples. When such different groups exist, the changes in expressions for some of the genes after the perturbation can be different between the two groups. It is not only important to identify the genes that respond differently across the two groups, but also to mine the reason behind this differential response. In this paper, we aim to identify the cause of this differential behavior of genes, whether because of the perturbation or due to interactions with other genes.

RESULTS

We propose a new probabilistic Bayesian method CMRF based on Markov Random Field to identify such genes. CMRF leverages the information about gene interactions as the prior of the model. We compare the accuracy of CMRF with SSEM and Student's t test and our old method SMRF on semi-synthetic dataset generated from microarray data. CMRF obtains high accuracy and outperforms all the other three methods. We also conduct a statistical significance test using a parametric noise based experiment to evaluate the accuracy of our method. In this experiment, CMRF generates significant regions of confidence for various parameter settings.

CONCLUSIONS

In this paper, we solved the problem of finding primarily differentially regulated genes in the presence of external perturbations when the data is sampled from two groups. The probabilistic Bayesian method CMRF based on Markov Random Field incorporates dependency structure of the gene networks as the prior to the model. Experimental results on synthetic and real datasets demonstrated the superiority of CMRF compared to other simple techniques.

Genome-Wide Analyses of Metal Responsive Genes in Caenorhabditis elegans

Metals are major contaminants that influence human health. Many metals have physiologic roles, but excessive levels can be harmful. Advances in technology have made toxicogenomic analyses possible to characterize the effects of metal exposure on the entire genome. Much of what is known about cellular responses to metals has come from mammalian systems; however the use of non-mammalian species is gaining wider attention. Caenorhabditis elegans is a small round worm whose genome has been fully sequenced and its development from egg to adult is well characterized. It is an attractive model for high throughput screens due to its short lifespan, ease of genetic mutability, low cost, and high homology with humans. Research performed in C. elegans has led to insights in apoptosis, gene expression, and neurodegeneration, all of which can be altered by metal exposure. Additionally, by using worms one can potentially study mechanisms that underline differential responses to metals in nematodes and humans, allowing for identification of novel pathways and therapeutic targets. In this review, toxicogenomic studies performed in C. elegans exposed to various metals will be discussed, highlighting how this non-mammalian system can be utilized to study cellular processes and pathways induced by metals. Recent work focusing on neurodegeneration in Parkinson’s disease will be discussed as an example of the usefulness of genetic screens in C. elegans and the novel findings that can be produced.

Identification of differentially expressed genes in lung tissues of nickel-exposed rats using suppression subtractive hybridization

Occupational exposure to nickel compound, such as nickel refining, electroplating, and in conjunction with other metals, is harmful to the health, causing respiratory distress, and lung and nasal cancer. In this work, the different gene expression patterns of lung tissues from nickel-exposed rats and controls were investigated. The suppression subtractive hybridization (SSH) method was used to generate two subtracted cDNA libraries with gene transcripts differentially expressed after nickel inducing. Dot-blot hybridizations were used to confirm differential ratios of expression of obtained SSH clones. Out of 768 unique SSH clones, which were chosen randomly from the two subtraction libraries (384 of each), 319 could be verified as differentially expressed. According to blast screening and functional annotation, 28% genes in nickel-induced cDNA library were related to cell differentiation, whereas 21% in driver library were related to oxygen transport. Two novel expressed sequence tags (ESTs; NCBI Accession No. FC809414 and No. FC809411) in nickel-induced cDNA library were obtained. The genes detected in the present study are probably important genes associated with nickel-induced lung cancer.

Toxicogenomics: transcription profiling for toxicology assessment

Toxicogenomics, the application of transcription profiling to toxicology, has been widely used for elucidating the molecular and cellular actions of chemicals and other environmental stressors on biological systems, predicting toxicity before any functional damages, and classification of known or new toxicants based on signatures of gene expression. The success of a toxicogenomics study depends upon close collaboration among experts in different fields, including a toxicologist or biologist, a bioinformatician, statistician, physician and, sometimes, mathematician. This review is focused on toxicogenomics studies, including transcription profiling technology, experimental design, significant gene extraction, toxicological results interpretation, potential pathway identification, database input and the applications of toxicogenomics in various fields of toxicological study.

Gene-expression profiling of human mononuclear cells from welders using cDNA microarray

A toxicogenomic chip developed to detect welding-related diseases was tested and validated for field trials. To verify the suitability of the microarray, white blood cells (WBC) or whole blood was purified and characterized from 20 subjects in the control group (average work experience of 7 yr) and 20 welders in the welding-fume exposed group (welders with an average work experience of 23 yr). Two hundred and fifty-three rat genes homologous to human genes were obtained and spotted on the chip slide. Meanwhile, a human cDNA chip spotted with 8600 human genes was also used to detect any increased or decreased levels of gene expression among the welders. After comparing the levels of gene expression between the control and welder groups using the toxicogenomic chips, 103 genes were identified as likely to be specifically changed by welding-fume exposure. Eighteen of the 253 rat genes were specifically changed in the welders, while 103 genes from the human cDNA chip were specifically changed. The genes specifically expressed by the welders were associated with inflammatory responses, toxic chemical metabolism, stress proteins, transcription factors, and signal transduction. In contrast, there was no significant change in the genes related to short-term welding-fume exposure, such as tumor necrosis factor (TNF)-alpha and interleukin. In conclusion, if further validation studies are conducted, the present toxicogenomic gene chips could be used for the effective monitoring of welding-fume-exposure-related diseases among welders.

Using mummichog (Fundulus heteroclitus) arrays to monitor the effectiveness of remediation at a superfund site in Charleston, South Carolina, U.S.A

We previously developed a cDNA array for mummichogs (Fundulus heteroclitus), an estuarine minnow, that is targeted for identifying differentially expressed genes from exposure to polycyclic aromatic hydrocarbons and several metals, including chromium. A chromium-contaminated Superfund site at Shipyard Creek in Charleston, South Carolina, USA, is undergoing remediation, providing us a unique opportunity to study the utility of arrays for monitoring the effectiveness of site remediation. Mummichogs were captured in Shipyard Creek in Charleston prior to remediation (2000) and after remediation began (2003 and 2005). Simultaneously, mummichogs were collected from a reference site at the Winyah Bay National Estuarine Research Reserve (NERR) in Georgetown, South Carolina, USA. The hepatic gene expression pattern of fish captured at Shipyard Creek in 2000 showed wide differences from the fish captured at NERR in 2000. Interestingly, as remediation progressed the gene expression pattern of mummichogs captured at Shipyard Creek became increasingly similar to those captured at NERR. The arrays acted as multidimensional biomarkers as the number of differentially expressed genes dropped from 22 in 2000 to four in 2003, and the magnitude of differential expression dropped from 3.2-fold in 2000 to no gene demonstrating a difference over 1.5-fold in 2003. Furthermore, the arrays indicated changes in the bioavailability of chromium caused by hydraulic dredging in the summer of 2005. This research is, to our knowledge, the first report using arrays as biomarkers for a weight-of-evidence hazard assessment and demonstrates that arrays can be used as multidimensional biomarkers to monitor site mitigation because the gene expression profile is associated with chromium bioavailability and body burden.

Novel Microarray-Based Method for Estimating Exposure to Ionizing Radiation

Accurate estimation of the dose of ionizing radiation to which individuals have been exposed is critical for therapeutic treatment. We investigated whether gene expression profiles could be used to evaluate the dose received, thereby serving as a biological dosimeter. We used cDNA microarrays to monitor changes in gene expression profiles induced by ionizing radiation in mouse total blood. The subsets of genes best characterizing each dose were identified by resampling the original data set and calculating the intersection of the dose signatures. This analytical strategy minimizes the impact of potential genetic/epigenetic variation between mice and overcomes the bias in gene selection inherent to microarray technology. The significance of the identified signatures was evaluated by monitoring the type I error rate by in silico negative control simulation. Based on the distribution of the mean ratios of the selected probes, we were able to identify transcription profiles giving 83% to 100% correct estimation of the dose received by test mice, demonstrating that the selected probes could be used to determine the dose of radiation to which the animals had been exposed. This method could potentially be generalized to determine the level of exposure to other toxins and could be used to develop new related clinical applications.

MIP-1β, a novel biomarker for in vitro sensitization test using human monocytic cell line

In order to seek a novel biomarker for predicting skin sensitization, changes in the gene expression profile of THP-1 cells on exposure to 2,4-dinitrochlorobenzene (DNCB), p-phenylenediamine (pPD) and nickel sulfate (Ni) were assessed using oligo-DNA microarrays. While the change in gene expression varied depending on the sensitizers, up-regulation of MIP-1 beta mRNA expression was detected in both DNCB-treated and Ni-treated THP-1 cells. This finding was validated by RT-PCR and confirmed at the protein level by ELISA. Secretion of MIP-1 beta from THP-1 was detected after 24-h treatment with sensitizers such as DNCB, Ni, 2-mercaptobenzothiazole (2-MBT) and cobalt sulfate (Co), while pPD and non-sensitizers such as sodium dodecyl sulfate (SDS) and benzalkonium chloride (BC) had no effect. The use of both MIP-1 beta production and CD86 expression as criteria reduced the number of false-negatives, and the results were in good agreement with those of in vivo assays. MIP-1 beta may be useful as a novel biomarker in in vitro sensitization assay using THP-1 cells, either alone or in combination with known markers.

Alterations in the expression of intestinal enzymes in rats exposed to nickel

The effect of feeding nickel (50 mg kg(-1) body weight) daily for 7 days was studied on the development of various brush border enzymes across the crypt-villus axis. The activities of brush border maltase (P < 0.05), lactase (P < 0.05), alkaline phosphatase (P < 0.05) and leucine amino peptidase (P < 0.05) were augmented in purified brush borders, whereas sucrase, trehlase (P < 0.01) and glutamyl transpeptidase (P < 0.05) were reduced in nickel fed animals compared with controls. Kinetic and heat inactivation studies with brush border sucrase and alkaline phosphatase confirmed these findings. Western blot analysis of alkaline phosphatase showed a strong signal for the enzyme protein but a reduced level of sucrase antigen in nickel fed rat intestine compared with the controls. These findings suggest that the expression of various brush border enzymes along the crypt-villus axis is modulated in rat intestine exposed to nickel, which may disrupt the digestive functions of the intestinal tissue.

Ni(II) affects ubiquitination of core histones H2B and H2A

The molecular mechanisms of nickel-induced malignant cell transformation include effects altering the structure and covalent modifications of core histones. Previously, we found that exposure of cells to Ni(II) resulted in truncation of histones H2A and H2B and thus elimination of some modification sites. Here, we investigated the effect of Ni(II) on one such modification, ubiquitination, of histones H2B and H2A in nuclei of cultured 1HAEo- and HPL1D human lung cells. After 1-5 days of exposure, Ni(II) up to 0.25 mM stimulated mono-ubiquitination of both histones, while at higher concentrations a suppression was found. Di-ubiquitination of H2A was not affected except for a drop after 5 days at 0.5 mM Ni(II). The decrease in mono-ubiquitination coincided with the appearance of truncated H2B that lacks the K120 ubiquitination site. However, prevention of truncation did not avert the decrease of H2B ubiquitination, indicating mechanistic independence of these effects. The changes in H2B ubiquitination did not fully coincide with concurrent changes in the nuclear levels of the ubiquitin-conjugating enzymes Rad6 and UbcH6. Overall, our results suggest that dysregulation of H2B ubiquitination is a part of Ni(II) adverse effects on gene expression and DNA repair which may assist in cell transformation.

Biological effects of metal-on-metal hip replacements

The advantages seen by patients receiving total hip arthroplasties and the implications of the release of both metal particles and soluble metal ions are discussed. This paper describes some of the early changes that have been observed in metal-on-metal hip arthroplasties, in terms of both changes in metal levels in blood and chromosome changes.

Effects of hTERT on metal ion-induced genomic instability

There is currently a great interest in delayed chromosomal and other damaging effects of low-dose exposure to a variety of pollutants which appear collectively to act through induction of stress-response pathways related to oxidative stress and ageing. These have been studied mostly in the radiation field but evidence is accumulating that the mechanisms can also be triggered by chemicals, especially heavy metals. Humans are exposed to metals, including chromium (Cr) (VI) and vanadium (V) (V), from the environment, industry and surgical implants. Thus, the impact of low-dose stress responses may be larger than expected from individual toxicity projections. In this study, a short (24 h) exposure of human fibroblasts to low doses of Cr (VI) and V (V) caused both acute chromosome damage and genomic instability in the progeny of exposed cells for at least 30 days after exposure. Acutely, Cr (VI) caused chromatid breaks without aneuploidy while V (V) caused aneuploidy without chromatid breaks. The longer-term genomic instability was similar but depended on hTERT positivity. In telomerase-negative hTERT- cells, Cr (VI) and V (V) caused a long lasting and transmissible induction of dicentric chromosomes, nucleoplasmic bridges, micronuclei and aneuploidy. There was also a long term and transmissible reduction of clonogenic survival, with an increased beta-galactosidase staining and apoptosis. This instability was not present in telomerase-positive hTERT+ cells. In contrast, in hTERT+ cells the metals caused a persistent induction of tetraploidy, which was not noted in hTERT- cells. The growth and survival of both metal-exposed hTERT+ and hTERT- cells differed if they were cultured at subconfluent levels or plated out as colonies. Genomic instability is considered to be a driving force towards cancer. This study suggests that the type of genomic instability in human cells may depend critically on whether they are telomerase-positive or -negative and that their sensitivities to metals could depend on whether they are clustered or diffuse.

Comprehensive analysis of the renal transcriptional response to acute uranyl nitrate exposure

Background

Chemical and radiological toxicities related to uranium acute exposure have been widely studied in nuclear fuel workers and military personnel. It is well known that uranyl nitrate induces acute renal failure (ARF). However, the mechanisms of this metal-induced injury are not well defined at the molecular level.

Results

Renal function and histology were assessed in mice receiving uranyl nitrate (UN(+)) and controls (UN(-)). To identify the genomic response to uranium exposure, serial analysis gene expression (SAGE) of the kidney was performed in both groups. Over 43,000 mRNA SAGE tags were sequenced. A selection of the differentially expressed transcripts was confirmed by real-time quantitative PCR and Western blotting. UN(+) animals developed renal failure and displayed the characteristic histological lesions of UN nephropathy. Of the >14,500 unique tags identified in both libraries, 224 had a modified expression level; they are known to participate in inflammation, ion transport, signal transduction, oxidative stress, apoptosis, metabolism, and catabolism. Several genes that were identified had not previously been evaluated within the context of toxic ARF such as translationally controlled tumor protein, insulin like growth factor binding protein 7 and ribosomal protein S29, all apoptosis related genes.

Conclusion

We report a comprehensive description of the UN induced modifications in gene expression levels, including the identification of genes previously unrelated to ARF. The study of these genes and the metabolisms they control should improve our understanding of toxic ARF and enlighten on the molecular targets for potential therapeutic interventions.

Metallothionein-I/II double knockout mice are no more sensitive to the carcinogenic effects of nickel subsulfide than wild-type mice

Metallothionein (MT) is a high-affinity metal-binding protein thought to mitigate the toxicity of various metals. MT may limit the toxicity of a metal by direct binding or through action as an antioxidant for metals that generate reactive oxygen species. Nickel compounds have carcinogenic potential in humans and animals, possibly by production of oxidative stress. The impact of MT deficiency on the carcinogenic effects of nickel is unknown. Thus, groups (n=25) of male MT-I/II double knockout (MT-null) or MT wild-type (WT) mice were exposed to a single treatment of nickel (0.5 or 1.0 mg Ni3S2/site, intramuscularly, [i.m.], into both hind legs), or left untreated (control) and observed over the next 104 weeks. There were no differences in the incidence of spontaneous tumors in MT-null and WT mice. Nickel induced injection site fibrosarcomas in a dose-related fashion to a similar extent in both WT and MT-null mice. Nickel-treatment had no effect on total lung tumor incidence, although some phenotypic-specific differences occurred in the proportion of benign and malignant pulmonary tumors. Overall, MT-null mice appear no more sensitive to the carcinogenic effects of nickel than WT mice. Thus, poor MT production does not appear to be a predisposing factor for nickel carcinogenesis.

Inhibition of core histones acetylation by carcinogenic nickel(II)

Nickel, a well-established human carcinogen, was shown to decrease acetylation of histones H4 and H3 in cultured cells. Such a decrease is expected to suppress gene expression. However, nickel is known to not only suppress but also enhance the expression of many genes. So, perhaps, nickel can alter histone acetylation in a more complex way? In a first step of testing this presumption, we examined acetylation status of histones H2A, H2B, H3 and H4, in human (HAE) and rat (NRK) cells exposed to nickel(II) under various conditions. In both cell lines, acetylation of all four histones was down-regulated by nickel(II) in a concentration- and time-dependent manner. Acetylation of histone H2B was suppressed to greater extent than that of the others, with histone H3 being relatively least affected. The analysis of acetylation status of each of the four lysine sites at the N-terminal tail of histone H2B revealed decreases consistent with those observed in the total acetylation patterns, with the K12 and K20 residues being markedly more affected than K5 and K15 residues. Thus, the decrease in acetylation was to some degree site specific. In NRK cells, the observed uniform down-regulation of histone acetylation was consistent with a marked suppression of global gene transcription measured as [3H]-uridine incorporation into mRNA. However, in HAE cells, global RNA expression was transiently increased (in 24 h) before dropping below control after longer exposure (3 days). In conclusion, the effects of Ni(II) on histone acetylation are inhibitory, with their extent depending on the dose and exposure time. This uniform inhibition, however, is not consistently reflected in global RNA expression that in HAE cells may include both increase and decrease of the expression, clearly indicating the involvement of factors other than histone acetylation. The observed effects may contribute to neoplastic transformation of Ni(II)-exposed cells.

Effects of nickel poisoning on expression pattern of the 72/73 and 94 kDa stress proteins in rat organs and in the COS-7, HepG2, and A549 cell lines

The present study deals with the effects of Ni on the expression level of three stress proteins, namely, the cytosolic HSP72 and HSP73, and the reticulum-associated GRP94. Experiments were carried out on "Wistar'' female rats daily injected with 4 mg NiCl2 per kg body weight for 1, 3, 5, and 10 days. Another set of experiments were carried out using cell lines, derived from the monkey kidney (COS-7), and from human tumors of the lung (A549) and liver (HepG2). Cells were cultured for 4 days in the permanent presence of 100, 200, or 400 microM NiCl2. In control rats, stress proteins pattern was found to be tissue specific: two protein bands of 96 and 94 kDa were immunodetected with the anti-GRP94 antibody in kidney and liver extracts, whereas only the 96 kDa band was present in ovary extracts. HSP73 was present in kidney, liver, and ovary whereas HSP72 was only found in kidney. In kidney of nickel-treated animals, HSP73 and the 96 kDa proteins were overexpressed whereas HSP72 was strongly down regulated. No such effect was observed in liver or ovary. Similarly, in nickel-treated cell lines, HSP72 was downregulated and GRP94 (96 kDa protein) was overexpressed. HSP73 expression appeared moderately increased in A549 cells but decreased in COS-7 cells. Because long-term caloric restriction was reported to reduce free radical generation in cells, the effect of 1 month food restriction (50%) was tested in rats as a possible way to lower oxidative damages induced by Ni. No significant effect on HSP expression was observed.

Analysis of dose-response effects on gene expression data with comparison of two microarray platforms

MOTIVATION

The problems of analyzing dose effects on gene expression are gaining attention in biomedical research. A specific challenge is to detect genes with expression levels that change according to dose levels in a non-random manner, but nonetheless may be considered as potential biomarkers.

METHOD

We are among the first to formally apply a tool that uses an isotonic (monotonic) regression approach to this area of study. We introduce a test statistic to select genes with significant dose-response expression in a monotonic fashion based on a permutation procedure. We then compare the results with those achieved from the application of a likelihood ratio-based test.

RESULTS

We apply the isotonic regression approach to a study of gene expression in the RKO colon carcinoma cell line in response to varying dosage levels of the chemotherapeutic agent 5-fluorouracil. A feature of both Affymetrix and printed 75mer oligomer cDNA arrays produced from the same samples provides an opportunity to compare the two microarray platforms.

AVAILABILITY

Statistical software S-plus Code to implement the method is available from the authors.

CONTACT

kcoombes@mdanderson.org

Altered gene expression in human hepatoma HepG2 cells exposed to low-level 2,4-dichlorophenoxyacetic acid and potassium nitrate

2,4-dichlorophenoxyacetic acid (2,4-D) and nitrate are agricultural contaminants found in rural ground water. It is not known whether levels found in groundwater pose a human or environmental health risk, nor is the mechanism of toxicity at the molecular/cellular level understood. This study focused on determining whether 2,4-D or nitrate at environmentally realistic levels elicit gene expression changes in exposed cells. cDNA microarray technology was used to determine the impact of 2,4-D and nitrate in an in vitro model of exposure. Human hepatoma HepG2 cells were incubated with 2,4-D or nitrate alone for 24 h. Cell viability (neutral red assay) and proliferation (BrdU incorporation) were assessed following exposure. Total RNA from treated and control cells were isolated, reverse transcribed and reciprocal labelled with Cy3 or Cy5 dyes, and hybridized to a human cDNA microarray. The hybridized microarray chips were scanned, quantified and analyzed to identify genes affected by 2,4-D or nitrate exposure based on a two-fold increase or decrease in gene expression and reproducibility (affected in three or more treatments). Following filtering, normalization and hierarchical clustering initial data indicate that numerous genes were found to be commonly expressed in at least three or more treatments of 2,4-D or nitrate tested. The affected genes indicate that HepG2 cells respond to environmental, low-level exposure and produce a cellular response that is associated with alterations in the expression of many genes. The affected genes were characterized as stress response, cell cycle control, immunological and DNA repair genes. These findings serve to highlight new pathway(s) in which to further probe the effects of environmental levels of 2,4-D and nitrate.

Highly efficient molecular delivery into mammalian cells using carbon nanotube spearing

Introduction of exogenous DNA into mammalian cells represents a powerful approach for manipulating signal transduction. The available techniques, however, are limited by low transduction efficiency and low cell viability after transduction. Here we report a highly efficient molecular delivery technique, named nanotube spearing, based on the penetration of nickel-embedded nanotubes into cell membranes by magnetic field driving. DNA plasmids containing the enhanced green fluorescent protein (EGFP) sequence were immobilized onto the nanotubes, and subsequently speared into targeted cells. We have achieved an unprecedented high transduction efficiency in Bal17 B-lymphoma, ex vivo B cells and primary neurons with high viability after transduction. This technique may provide a powerful tool for highly efficient gene transfer into a variety of cells, especially the hard-to-transfect cells.

Microarray analysis of altered gene expression in murine fibroblasts transformed by nickel(II) to nickel(II)-resistant malignant phenotype

B200 cells are Ni(II)-transformed mouse BALB/c-3T3 fibroblasts displaying a malignant phenotype and increased resistance to Ni(II) toxicity. In an attempt to find genes whose expression has been altered by the transformation, the Atlas Mouse Stress/Toxicology cDNA Expression Array (Clontech Laboratories, Inc., Palo Alto, CA) was used to analyze the levels of gene expression in both parental and Ni(II)-transformed cells. Comparison of the results revealed a significant up- or downregulation of the expression of 62 of the 588 genes present in the array (approximately 10.5%) in B200 cells. These genes were assigned to different functional groups, including transcription factors and oncogenes (9/14; fractions in parentheses denote the number of up-regulated versus the total number of genes assigned to this group), stress and DNA damage response genes (11/12), growth factors and hormone receptors (6/9), metabolism (7/7), cell adhesion (2/7), cell cycle (3/6), apoptosis (3/4), and cell proliferation (2/3). Among those genes, overexpression of beta-catenin and its downstream targets c-myc and cyclin D1, together with upregulated cyclin G, points at the malignant character of B200 cells. While the increased expression of glutathione (GSH) synthetase, glutathione-S-transferase A4 (GSTA4), and glutathione-S-transferase theta (GSTT), together with high level of several genes responding to oxidative stress, suggests the enforcement of antioxidant defenses in Ni-transformed cells.

Minimal influence of metallothionein over-expression on nickel carcinogenesis in mice

Metallothionein (MT) is a metal-binding protein associated with tolerance to metals and oxidative stress. Nickel is a metal carcinogen potentially acting through oxidative attack on critical biomolecules. We investigated the role of MT in nickel carcinogenesis using MT-transgenic mice that constitutively over-express MT-I in all tissues tested. Groups of 25 male MT-transgenic and wild type (C57BL/6; WT) mice received intramuscular injections of nickel subsulfide (Ni3S2) in both thighs at doses of 0 (control), 0.5, or 1.0 mg/site at 12 weeks of age and were observed for 104 weeks. Injection site tumors (ISTs; primarily fibrosarcomas) started occurring 45 weeks after nickel injection and IST incidence was similar in the WT (control - 0%, 0.5 mg/site - 20%, 1.0 mg/site - 40%) and MT-transgenic mice (control - 0%, 0.5mg/site - 28%, 1.0mg/site - 29%.). At the 0.5 mg/site dose the average time to IST in MT-transgenic mice was approximately 13 weeks shorter than in WT mice. Spontaneous lung tumors developed in 25% of control WT mice but none developed in control MT-transgenic mice. A nickel dose-related trend for increased lung tumors occurred in MT-transgenic mice but not in WT mice. Thus, the over-expression of MT did not significantly mitigate the carcinogenic response to nickel.

In vitro evaluation of matrix metalloproteinases as predictive testing for nickel, a model sensitizing agent

The identification of potential damage due to chemical exposure in the workplace is a major health and regulatory concern. Traditional tests that measure both sensitization and elicitation responses require the use of animals. An alternative to this widespread use of experimental animals could have a crucial impact on risk assessment, especially for the preliminary screening of new molecules. We developed an in vitro model for the screening of potential toxic compounds. Human keratinocytes (HaCat) were used as target cells while matrix metalloproteinases (MMP) were selected as responders because they are key enzymes involved in extracellular matrix (ECM) degradation in physiological and pathological conditions. Chemical exposure was performed using nickel sulphate as a positive tester. Nickel contact induced upregulation of MMP-2 and IL-8 mRNA production. Molecular activation occurred even at very low nickel concentrations even though no phenotypic changes were observed. MMP-9 accumulation was found in the medium of treated cells with respect to controls. These observations led to the hypothesis that even minimal exposure can accumulate transcriptional activity resulting in long-term clinical signs after contact. Our simple in vitro model can be applied as a useful preliminary complement to the animal studies to screen the effects of new potential toxic compounds.