Characterization of preneoplastic and neoplastic rat mesothelial cell lines: the involvement of TETs, DNMTs, and 5-hydroxymethylcytosine

Our plain-English summary of Characterization of preneoplastic and neoplastic rat mesothelial cell lines: the involvement of TETs, DNMTs, and 5-hydroxymethylcytosine, by D. Roulois, S. Deshayes, M.N. Guilly, et al (Oncotarget, 2016).

The study

• Authors: D. Roulois, S. Deshayes, M.N. Guilly, J.S. Nader, C. Liddell, M. Robard, P. Hulin, A. Ouacher, V. Le Martelot, J.F. Fonteneau, M. Grégoire, C. Blanquart, D.L. Pouliquen
• Journal: Oncotarget
• Published: 2016;7(23):34664-87
• Cited by: 14 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Malignant mesothelioma (MM) is one of the worst cancers in terms of clinical outcome, urging the need to establish and characterize new preclinical tools for investigation of the tumorigenic process, improvement of early diagnosis and evaluation of new therapeutic strategies. For these purposes, we characterized a collection of 27 cell lines established from F344 rats, after 136 to 415 days of induction with crocidolite asbestos administered intraperitoneally. Four mesotheliomas were distinguished from 23 preneoplastic mesothelial cell lines (PN) according to their propensity to generate tumors after orthotopic transplantation into syngeneic rats, their growth pattern, and the expression profile of three genes. PN cell lines were further discriminated into groups / subgroups according to morphology in culture and the expression profiles of 14 additional genes. This approach was completed by analysis of positive and negative immunohistochemical MM markers in the four tumors, of karyotype alterations in the most aggressive MM cell line in comparison with a PN epithelioid cell line, and of human normal mesothelial and mesothelioma cells and a tissue array. Our results showed that both the rat and human MM cell lines shared in common a dramatic decrease in the relative expression of Cdkn2a and of epigenetic regulators, in comparison with PN and normal human mesothelial cells, respectively. In particular, we identified the involvement of the relative expression of the Ten-Eleven Translocation (TET) family of dioxygenases and Dnmt3a in relation to the 5-hydroxymethylcytosine level in malignant transformation and the acquisition of metastatic potential.

In plain English

This was a laboratory study in rats and cultured cells. At 8 weeks of age, 33 F344 rats (16 males, 17 females) received an injection of 10 mg of crocidolite asbestos fibers into the abdominal cavity. Between 136 and 415 days later, the authors established 27 cell lines from these rats. They classed 23 as preneoplastic (changed, but not cancer) and 4 as mesothelioma, mainly according to whether the cells grew tumors when placed into rats of the same strain. Compared with the preneoplastic lines, the mesothelioma lines had significantly lower expression of the Cdkn2a gene and of the gene regulators Dnmt3a, Dnmt3b, TET1 and TET3. They also had lower levels of the DNA mark 5-hydroxymethylcytosine, while overall DNA methylation did not differ significantly. Human pleural mesothelioma cell lines likewise showed lower Cdkn2a, Dnmt3a and TET2 expression than normal mesothelial cells. Three of the four rat tumor lines spread to other tissues. The authors concluded that these changes were correlated with aggressive behavior.

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: Animal experiment with characterization of rat cell lines, plus comparison with human mesothelioma cell lines and a human tissue array
• Who was studied: 33 Fischer F344 rats (16 males, 17 females). From them came 23 preneoplastic mesothelial cell lines from peritoneal lavage fluid and 4 mesothelioma cell lines (M5-T1, F4-T2, F5-T1, M5-T2) from tumor implants and nodules. Also studied were human pleural mesothelioma cell lines, normal human mesothelial cells, and a human tissue array of 20 normal, 20 grade I and 16 grade II mesothelioma samples
• Exposure: A single intraperitoneal injection of 10 mg crocidolite fibers (UICC sample) in rats at 8 weeks of age; cells were collected 136 to 415 days later
• Main results:
  • Cdkn2a expression was significantly lower in the neoplastic rat cell lines than in the preneoplastic rat cell lines
  • In human cells, Cdkn2a expression was considerably lower in pleural mesothelioma cell lines than in normal mesothelial cells
  • Overall DNA (cytosine) methylation did not differ significantly between preneoplastic and neoplastic rat cell lines
  • The global level of 5-hydroxymethylcytosine was significantly lower in neoplastic than in preneoplastic rat cell lines
  • Dnmt3a expression was significantly lower in neoplastic than in preneoplastic cells, in both rat and human mesothelial cell lines; Dnmt3b was also significantly lower in the rat
  • TET gene expression decreased in both species. The decrease was significant for TET1 and TET3 in the rat, and for TET2 in human pleural mesothelioma cell lines compared with normal mesothelial cells
  • Of the four rat mesothelioma lines, the most aggressive (M5-T1) had the lowest TET3 expression: 117.5, compared with 255.5, 287.3 and 863.9 for the other three
  • Three of the four rat mesothelioma lines produced metastases after transplantation. The M5-T2 tumor did not spread and grew only on the omentum
  • In the M5-T1 cell line, the most common chromosome change was a deletion of chromosome 5, seen in 82% of metaphases
  • In the human tissue array, 5-hydroxymethylcytosine staining fell progressively from normal mesothelial cells to grade I and then grade II mesothelioma
• The authors' conclusion: The authors concluded that epigenetic alterations, namely lower TET and DNMT expression and lower 5-hydroxymethylcytosine in tumor cells, were correlated with the acquisition of an aggressive phenotype, in agreement with human mesothelioma. They also stated that the rat models resembled human mesothelioma cells.
• Limitations the authors state:
  • The human tissue microarray had too few samples to analyze grade III and IV mesothelioma

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelial Cells, Malignant Mesothelioma, Crocidolite, Mesothelioma, Epithelioid, CDKN2A, Translocation, Malignant Transformation.

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