DNA methylation profiling of asbestos-treated MeT5A cell line reveals novel pathways implicated in asbestos response

Our plain-English summary of DNA methylation profiling of asbestos-treated MeT5A cell line reveals novel pathways implicated in asbestos response, by E. Casalone, A. Allione, C. Viberti, et al (Archives of Toxicology, 2018).

The study

• Authors: E. Casalone, A. Allione, C. Viberti, B. Pardini, S. Guarrera, M. Betti, I. Dianzani, E. Aldieri, G. Matullo
• Journal: Archives of Toxicology
• Published: 2018;92(5):1785-1795
• Cited by: 13 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Occupational and environmental asbestos exposure is the main determinant of malignant pleural mesothelioma (MPM), however, the mechanisms by which its fibres contribute to cell toxicity and transformation are not completely clear. Aberrant DNA methylation is a common event in cancer but epigenetic modifications involved specifically in MPM carcinogenesis need to be better clarified. To investigate asbestos-induced DNA methylation and gene expression changes, we treated Met5A mesothelial cells with different concentrations of crocidolite and chrysotile asbestos (0.5 ÷ 5.0 µg/cm2, 72 h incubation). Overall, we observed 243 and 302 differentially methylated CpGs (≥ 10%) between the asbestos dose at 5 µg/cm2 and untreated control, in chrysotile and crocidolite treatment, respectively. To examine the dose-response effect, Spearman's correlation test was performed and significant CpGs located in genes involved in migration/cell adhesion processes were identified in both treatments. Moreover, we found that both crocidolite and chrysotile exposure induced a significant up-regulation of CA9 and SRGN (log2 fold change > 1.5), previously reported as associated with a more aggressive MPM phenotype. However, we found no correlation between methylation and gene expression changes, except for a moderate significant inverse correlation at the promoter region of DKK1 (Spearman rho = - 1, P value = 0.02) after chrysotile exposure. These results describe for the first time the relationship between DNA methylation modifications and asbestos exposure. Our findings provide a basis to further explore and validate asbestos-induced DNA methylation changes, that could influence MPM carcinogenesis and possibly identifying new chemopreventive target.

In plain English

This was a laboratory experiment on cells, not a study of people. The authors exposed MeT5A cells, a commercial SV-40 transformed human non-malignant mesothelial cell line, to crocidolite or chrysotile asbestos fibres and measured DNA methylation and gene activity. Fibres were given at 0.5, 1.0, 2.5 and 5.0 µg/cm2 for 72 hours, with untreated cells as controls. At the highest dose, 243 CpG sites changed methylation by at least 10% with chrysotile and 302 with crocidolite. The authors described the changes overall as slight. Methylation at some sites tracked dose: rising at 4 and falling at 6 with chrysotile, rising at 11 and falling at 7 with crocidolite. The two fibre types mostly affected different sites. Nine genes changed activity with both fibres, including CA9 and SRGN, which increased. Methylation and gene activity were linked at only one site, in the DKK1 gene after chrysotile (Spearman rho minus 1, P value 0.02). The authors concluded that the two fibres produced different methylation patterns, pointing to genes involved in cell migration and adhesion. They noted these cells may not reflect normal mesothelial cells or conditions in the body.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: In vitro laboratory experiment on a human mesothelial cell line, with genome-wide DNA methylation and gene expression arrays
• Who was studied: MeT5A cells, a commercial SV-40 transformed human non-malignant mesothelial cell line (ATCC CRL-9444); no human subjects
• Exposure: UICC crocidolite or chrysotile asbestos fibres at 0.5, 1.0, 2.5 and 5.0 µg/cm2 for 72 hours, compared with untreated cells
• Main results:
  • Chrysotile: 243 CpG sites were differentially methylated (change of at least 10%) between the 5 µg/cm2 dose and untreated control. Only 5 of them changed by more than 20%.
  • Chrysotile dose-response: 4 CpG sites (in TNR, PAX2, CRYL1) showed a significant positive correlation with dose. 6 CpGs (in LHX8, LRRC66, LMOD2, TMEM132D, BCAS3) showed a significant negative correlation.
  • Crocidolite: 302 differentially methylated sites were found in 214 genes.
  • Crocidolite dose-response: 11 CpGs showed a positive correlation with dose (Spearman rho = 1, P value = 0.02), including sites in LAMC1, LAMB4 and NRXN2. 7 probes showed a negative correlation (Spearman rho = −1, P value = 0.02).
  • The two fibre types mostly changed methylation at different sites. 26 CpG sites were modified by both, 15 of them in the same direction.
  • The authors described the methylation changes in both crocidolite- and chrysotile-treated cells as slight.
  • Gene expression at the 5 µg/cm2 dose versus untreated cells changed significantly for 1788 transcripts with chrysotile and 3994 transcripts with crocidolite (P value < 0.02).
  • Nine genes changed expression with both fibres. KCTD12, PRAGMIN, HNRNPU, TMEM106A and ZNF483 decreased. NEU1, SNORD3A, SRGN and CA9 increased, with CA9 and SRGN at a log2 fold change greater than 1.5.
  • Methylation correlated with gene expression at only one CpG, at the transcriptional start site of DKK1, after chrysotile (P value = 0.02, Spearman rho = −1). No significant relationship was seen in crocidolite-treated cells.
  • Real-time PCR testing of DKK1, CA9 and SRGN confirmed the microarray results.
• The authors' conclusion: The authors concluded that crocidolite and chrysotile induced different patterns of methylation changes. They suggested a network of genes involved in cell migration and cell adhesion, to be investigated further in other experimental settings.
• Limitations the authors state:
  • A cell line was used because sufficient primary human mesothelial cells were difficult to obtain.
  • In vitro experiments cannot precisely reflect conditions in the body, such as interactions with inflammatory cells and extracellular matrix.
  • MeT5A cells are SV40-immortalized, and SV40 infection is known to reduce the sensitivity of mesothelial cells to asbestos toxicity, which may affect the changes seen.

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile, Crocidolite.

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Pleural Mesothelioma, Carcinogenesis, Mesothelial Cells, Crocidolite, Chrysotile, Dose-response relationship.

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