mRNA expression patterns in different stages of asbestos-induced carcinogenesis in rats

Our plain-English summary of mRNA expression patterns in different stages of asbestos-induced carcinogenesis in rats, by H. Sandhu, W. Dehnen, M. Roller, et al (Carcinogenesis, 2000).

The study

• Authors: H. Sandhu, W. Dehnen, M. Roller, J. Abel, K. Unfried
• Journal: Carcinogenesis
• Published: 2000;21(5):1023-9
• Cited by: 50 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Human malignant mesotheliomas are induced almost exclusively by fibrous dusts. The nature of interactions between fibers and target cells, and the molecular mechanisms leading to tumorigenesis, are not yet understood. Here, the mRNA expression patterns at different stages of asbestos-induced carcinogenesis in rats were monitored by suppression subtractive hybridization (SSH) and array assay. Several genes were upregulated in pretumorous tissues from asbestos-treated rats, in asbestos-induced tumors and in cells treated with asbestos in vitro. The upregulation of the proto-oncogene c-myc, fra-1 and egfr in fiber-induced carcinogenesis was demonstrated at different stages of carcinogenesis. A possible role of Fra-1 as one of the dimeric proteins generating the AP-1 transcription factor was substantiated by its dose-dependent expression in mesothelial cells treated with asbestos in vitro. The upregulation of osteopontin (an extracellular matrix protein) and of zyxin and integrin-linked kinase (intracellular proteins associated with the focal adhesion contact), indicate that fibers may affect integrin-linked signal transduction and extracellular matrix proteins.

In plain English

This was a laboratory study in rats and rat cells, not people. The authors gave 8-week-old Wistar rats a single injection of 2 mg crocidolite asbestos into the abdominal cavity, then looked for genes whose activity changed. Tumors developed 70 to 110 weeks after treatment. Compared with control tissue, asbestos-induced tumors showed increased activity of five gene sequences, including osteopontin (opn), zyxin (zyx) and bcat. These were not induced in mesothelial cells treated with asbestos in culture. In tissue from rats killed 52 weeks after injection, before any tumors were found, c-myc, ilk and egfr were clearly increased, and c-jun and fra-1 gave stronger signals. Fra-1, c-myc, ilk and egfr were then tested in the asbestos-induced tumors and were expressed there as well. In cultured rat mesothelial cells, crocidolite increased fra-1 and c-myc, and fra-1 responded to increasing doses. The authors concluded that Fra-1, c-myc and EGFR may be involved in asbestos-induced mesothelioma development. They said they could not completely rule out that granular dusts also affect regulation of the signal-transduction genes identified.

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 (rats given asbestos by intraperitoneal injection), with gene-expression analyses of tissues and additional cell-culture experiments
• Who was studied: Wistar rats at a laboratory in Düsseldorf, Germany. Tumors came from rats killed when visibly ill (tumors appeared 70 to 110 weeks after treatment), and control rats were killed after 100 weeks. A second group was killed at 52 weeks, with pooled samples from seven treated and five control rats. The study also used a rat mesothelial cell line (44R.M.-4), primary rat pleural mesothelial cells, and a rat mesothelioma cell line (RZ 328).
• Exposure: A single intraperitoneal injection of 2 mg crocidolite asbestos from South Africa in saline. Controls received saline alone or 25 mg granular silicon carbide. In the cell experiments, crocidolite was applied at 0.01 to 10 µg/cm2 for 48 h.
• Main results:
  • Comparing asbestos-induced tumors with control tissue (suppression subtractive hybridization), five cDNA clones showed clear differences: opn, zyx, bcat and two unidentified sequences (clones 35 and 49).
  • By RT-PCR, these five sequences showed enhanced expression in tumors, and no expression was detected in control tissues.
  • In the 44R.M.-4 mesothelial cell line treated with 10 µg/cm2 crocidolite for 48 h, none of these five sequences was induced. The authors reported similar results in pretumorous tissue (data not shown).
  • In pretumorous omentum from asbestos-treated rats at 52 weeks (array assay), c-myc, ilk and egfr were clearly induced compared with non-treated tissue.
  • In the same pretumorous tissue, c-jun and fra-1 showed enhanced signal strength.
  • Because the signal difference was greater for fra-1 than for c-jun, only fra-1 was investigated further.
  • When fra-1, c-myc, ilk and egfr were examined in tumors, they were expressed in asbestos-induced tumors, and no expression was detectable in non-tumorous omenta.
  • For comparison, in tumors induced by nickel powder, egfr and ilk were expressed but fra-1 and c-myc were not. In tumors induced by benzo[a]pyrene, all of these genes were weakly detectable.
  • In cultured mesothelial cells (the cell line and primary cells) treated with 10 µg/cm2 crocidolite for 48 h, RT-PCR products of fra-1 and c-myc increased.
  • In those cell experiments, egfr and ilk were not induced.
  • In the 44R.M.-4 cell line, fra-1 expression responded to increasing crocidolite doses. No fra-1 expression was found in cells given carrier only.
• The authors' conclusion: The authors concluded that Fra-1, c-myc and EGFR may be involved in asbestos-induced mesothelioma carcinogenesis in the living animal.
• Limitations the authors state:
  • The authors could not completely rule out that granular (non-fibrous) dusts also affect the regulation of the signal-transduction genes identified in the study.
  • The authors noted that an egfr increase limited to individual cells in contact with long fibers may not be detectable when measuring mRNA from the whole cell population.

Topics

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

Medical terms in this study, explained in our Lexicon: Carcinogenesis, Malignant Mesothelioma, Tumorigenesis, EGFR, Mesothelial Cells, Osteopontin.

Related studies

• Changes in DNA 8-hydroxyguanine levels, 8-hydroxyguanine repair activity, and hOGG1 and hMTH1 mRNA expression in human lung alveolar epithelial cells induced by crocidolite asbestos — H.N. Kim, Y. Morimoto, et al. (2001)
• P53 mutations in tumours induced by intraperitoneal injection of crocidolite asbestos and benzo[a]pyrene in rats — K. Unfried, N. Kociok, et al. (1997)
• Small interfering RNAs (siRNAs) targeting TGF-beta1 mRNA suppress asbestos-induced expression of TGF-beta1 and CTGF in fibroblasts — T.C. Lai, D.A. Pociask, et al. (2009)
• SV40-induced expression of calretinin protects mesothelial cells from asbestos cytotoxicity and may be a key factor contributing to mesothelioma pathogenesis — T. Henzi, W.V. Blum, et al. (2009)
• Analysis of K-ras and p53 mutations in mesotheliomas from humans and rats exposed to asbestos — Z. Ni, Y. Liu, et al. (2000)
• Asbestos promotes morphological transformation and elevates expression of a gene family invariably induced by tumor promoters in C3H/10T1/2 cells — C.L. Parfett, R. Pilon, et al. (1996)

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