Asbestos promotes morphological transformation and elevates expression of a gene family invariably induced by tumor promoters in C3H/10T1/2 cells

Can a 12-gene expression signature predict the cell transforming potential of tumor promoting agents in Bhas 42 cells?

To date, long-term rodent carcinogenesis assays are the only assays recognized by regulators to assess non-genotoxic carcinogens, but their reliability has been questioned. In vitro cell transformation assays (CTAs) could represent an interesting alternative to animal models as it has the advantage of detecting both genotoxic and non-genotoxic transforming chemicals. Among them, Bhas 42 CTA uses a cell line that has been transfected with the oncogenic sequence v-Ha-ras. This sequence confers an "initiated" status to these cells and makes them particularly sensitive to non-genotoxic agents. In a previous work, transcriptomic analysis revealed that the treatment of Bhas 42 cells with transforming silica (nano)particles and 12-O-tetradecanoylphorbol-13-acetate (TPA) commonly modified the expression of 12 genes involved in cell proliferation and adhesion. In the present study, we assess whether this signature would be the same for four other soluble transforming agents, i.e. mezerein, methylarsonic acid, cholic acid and quercetin. The treatment of Bhas 42 cells for 48 h with mezerein modified the expression of the 12 genes of the signature according to the same profile as that of the TPA. However, methylarsonic acid and cholic acid gave an incomplete signature with changes in the expression of only 7 and 5 genes, respectively. Finally, quercetin treatment induced no change in the expression of all genes but exhibited higher cytotoxicty. These results suggest that among the transforming agents tested, some may share similar mechanisms of action leading to cell transformation while others may activate different additional pathways involved in such cellular process. More transforming and non-transforming agents and gene markers should be tested in order to try to identify a relevant gene signature to predict the transforming potential of non-genotoxic agents.

Predictive early gene signature during mouse Bhas 42 cell transformation induced by synthetic amorphous silica nanoparticles

Synthetic amorphous silica nanoparticles (SAS) are used widely in industrial applications. These nanoparticles are not classified for their carcinogenicity in humans. However, some data still demonstrate a potential carcinogenic risk of these compounds in humans. The Bhas 42 cell line was developed to screen chemicals, as tumor-initiators or -promoters according to their ability to trigger cell-to-cell transformation, in a cell transformation assay. In the present study, we performed unsupervised transcriptomic analysis after exposure of Bhas 42 cells to NM-203 SAS as well as to positive (Min-U-Sil 5® crystalline silica microparticles, and 12-O-tetradecanoylphorbol-13-acetate) and negative (diatomaceous earth) control compounds. We identified a common gene signature for 21 genes involved in the early stage of the SAS- Min-U-Sil 5®- or TPA-induced cell transformation. These genes were related to cell proliferation (over expression) and cell adhesion (under expression). Among them, 12 were selected on the basis of their potential impact on cell transformation. RT-qPCR and western blotting were used to confirm the transcriptomic data. Moreover, similar gene alterations were found when Bhas 42 cells were treated with two other transforming SAS. In conclusion, the results obtained in the current study highlight a 12-gene signature that could be considered as a potential early "bio-marker" of cell transformation induced by SAS and perhaps other chemicals.

Nonpulmonary outcomes of asbestos exposure

The adverse pulmonary effects of asbestos are well accepted in scientific circles. However, the extrapulmonary consequences of asbestos exposure are not as clearly defined. In this review the potential for asbestos to produce diseases of the peritoneum, immune, gastrointestinal (GIT), and reproductive systems are explored as evidenced in published, peer-reviewed literature. Several hundred epidemiological, in vivo, and in vitro publications analyzing the extrapulmonary effects of asbestos were used as sources to arrive at the conclusions and to establish areas needing further study. In order to be considered, each study had to monitor extrapulmonary outcomes following exposure to asbestos. The literature supports a strong association between asbestos exposure and peritoneal neoplasms. Correlations between asbestos exposure and immune-related disease are less conclusive; nevertheless, it was concluded from the combined autoimmune studies that there is a possibility for a higher-than-expected risk of systemic autoimmune disease among asbestos-exposed populations. In general, the GIT effects of asbestos exposure appear to be minimal, with the most likely outcome being development of stomach cancer. However, IARC recently concluded the evidence to support asbestos-induced stomach cancer to be "limited." The strongest evidence for reproductive disease due to asbestos is in regard to ovarian cancer. Unfortunately, effects on fertility and the developing fetus are under-studied. The possibility of other asbestos-induced health effects does exist. These include brain-related tumors, blood disorders due to the mutagenic and hemolytic properties of asbestos, and peritoneal fibrosis. It is clear from the literature that the adverse properties of asbestos are not confined to the pulmonary system.

Combined effects of tumor promoters and serum on proliferin mRNA induction: a biomarker sensitive to saccharin, 2,3,7,8-TCDD, and other compounds at minimal concentrations promoting C3H/10T1/2 cell transformation

Increases in proliferin (PLF) gene family mRNA abundance and promotional effects in cell transformation assays are paired responses that follow exposures to diverse chemical and physical agents in the C3H/10T1/2 in vitro model of multi-stage carcinogenesis. This study measured PLF mRNA abundance changes over 1 to 3 d in response to several types of promoters that were previously unassessed for this effect. Saccharin is a known promoter of cell transformation in C3H/10T1/2 cell cultures, but unlike 12-O-tetradecanoylphorbol 13-acetate (TPA) or mezerein, PLF mRNA abundance increases were inconsistently detected following simple addition of saccharin to the culture medium. Consistent effects occurred when pretreatments with promoting concentrations of saccharin or sodium saccharin (1-13 mM) were combined with subsequent additions of serum or complete medium changes. When added at or near their lowest observed effect levels (LOELs) for transformation, other promoters of 10T1/2 cells such as formaldehyde (50-100 microM), diethylstilbesterol (DES) (0.5-30 microM), and 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD) (4-40 pM) were shown to be inducers of both basal and serum-induced PLF mRNA levels. Acetaldehyde (300-900 microM) was comparable to formaldehyde as an inducer. In contrast to these various promoters, pretreatment with phenobarbital or methanol, both non-promoters in these cells, did not affect serum-induced PLF mRNA levels at concentrations up to 3 mM and 2 M, respectively. The published values for the LOELs of 17 promoters of cell transformation and the LOELs determined to date for PLF mRNA induction were highly correlated over a 1 billion - fold concentration range. The response of PLF mRNA is a short-term marker sensitive to the active concentration ranges of diverse chemical agents with promotional activity in C3H/10T1/2 cell transformation system.

Use of a cell transformation assay with established cell lines, and a metabolic cooperation assay with V79 cells for the detection of tumour promoters: a review

Extensive studies on the safety evaluation of chemicals have indicated that a considerable number of non-genotoxic chemicals are carcinogenic. Tumour promoters are likely to be among these non-genotoxic carcinogens, and their detection is considered to be an important approach to the prevention of cancer. In this review, the results are summarised for in vitro transformation assays involving established cell lines, and for an assay for inhibition of gap junctional intercellular communication for the detection of tumour promoters, which involves V79 cells. Although the number of chemicals examined is still too small to permit a full evaluation of the correlation between in vitro cell transformation and in vivo carcinogenicity, it is clear that the sensitivity of the focus formation assay is very high. In the case of the metabolic cooperation assay, the sensitivity appears to be rather poor, but the assay can be considered to be useful because of its simple procedure and its considerable database. These in vitro assays for tumour promoters are recommended as useful tools for the detection of non-genotoxic carcinogens.

Crocidolite induces cell transformation and p53 gene mutation in BALB/c-3T3 cells

Cell transformation is one of the most common assays used to study morphological changes in the multistep process of carcinogenesis. The present study was initiated to investigate the ability of crocidolite to induce cell transformation in BALB/c-3T3 cells and to analyze the relationship between p53 mutations and crocidolite-induced cell transformation, if any. Cell transformation was carried out according to standard procedures. Exponentially growing cells were exposed to different concentrations (0.2-20 microg/cm(2)) of crocidolite fibers for 72 h. Foci obtained from cell transformation were analyzed for their ability to grow in soft agar (anchorage-independence) and p53 alterations. The results of this study demonstrate that there was an increase in transformation frequency (TF) with an increase in concentration of crocidolite. Also, focal cells were able to grow on soft agar, indicating anchorage-independence. cDNA was prepared from RNA isolated from Type 3 foci and subjected to mutational analysis. Eleven exons of the p53 gene from eight transformed cell lines were analyzed for alterations using polymerase chain reaction single-strand conformation polymorphism (PCR-SSCP). Alterations were found in seven of eight cell lines, two of them were in exons 4-6, and five in exons 9-11. The alterations were randomly scattered among the crocidolite dose groups. These results suggest that crocidolite induces mutations predominantly in exons 9-11 of the p53 gene in a nondose-dependent manner.

Promotion of morphological transformation by Di-n-butyltin dichloride in C3H/10T1/2 cells: prediction by prior expression of tumour promoter-responsive genes

Previous studies in our laboratory have shown that chemical treatments may induce increases in proliferin gene family mRNA accumulation in cultured murine embryonic cells. Proliferin inductions are highly correlated with subsequent promotional outcomes during two-stage focus-formation assays in C3H/10T1/2 cell cultures. In work reported here, the strong affiliation between these two responses was further validated after treating cells with di-n-butyltin dichloride which is a polyvinyl chloride (PVC) plastic additive that often contaminates food and water. Increased proliferin expression and promotion of morphological transformation occurred at similar concentrations. Promotion of transformation was detected at di-n-butyltin dichloride concentrations of 80 nM (24 ng/ml) and above, if added to initiated cultures before confluent monolayers had formed. Proliferin induction and morphological transformation were both reduced in confluent cultures treated with di-n-butyltin dichloride, as compared to subconfluent cultures. Proliferin expression measured in near-confluent cultures was induced up to 10-fold during the 36-hr period following di-n-butyltin dichloride exposure and was accompanied by increased accumulation of transcripts from many genes regulated by oxidative stresses, growth-inducing agents, and/or other promoting agents (asbestos, superoxide radicals ). Di-n-butyltin dichloride-induced mRNA species included members of the fos and jun proto-oncogene families, c-myc, egr1, ribonucleotide reductase (R2 subunit), odc, macrophage chemotactic protein/je, hsp70, metallothionine IIA, c-sod and mn-sod. The observed patterns of RNA accumulation suggested that a small subset of mRNA species, including proliferin, exhibit regulatory behaviour as a response to dissimilar agents or conditions that promote focus-formation in C3H/10T1/2 cultures. Plausible predictions of promotional effects in two-stage morphological transformation assays can be made from gene-expression responses to test agents.