Patterns of c-fos and c-jun proto-oncogene expression, apoptosis, and proliferation in rat pleural mesothelial cells exposed to erionite or asbestos fibers

Our plain-English summary of Patterns of c-fos and c-jun proto-oncogene expression, apoptosis, and proliferation in rat pleural mesothelial cells exposed to erionite or asbestos fibers, by C.R. Timblin, G.D. Guthrie, Y.W. Janssen, et al (Toxicology and Applied Pharmacology, 1998).

The study

• Authors: C.R. Timblin, G.D. Guthrie, Y.W. Janssen, E.S. Walsh, P. Vacek, B.T. Mossman
• Journal: Toxicology and Applied Pharmacology
• Published: 1998;151(1):88-97
• Cited by: 29 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Erionite, a naturally occurring fibrous zeolite, is associated with the development of nonmalignant and malignant lung diseases and is more carcinogenic than asbestos fibers in man and rodent inhalation models of disease. To investigate the possible molecular mechanisms of erionite-induced toxicity and carcinogenesis and whether cationic content of erionite fibers was important, we examined c-fos and c-jun mRNA levels, activator protein-1 (AP-1) binding to DNA, and changes in cell proliferation and apoptosis in rat pleural mesothelial (RPM) cells exposed to different cation-substituted erionite fibers or crocidolite asbestos at various concentrations (1, 5, or 10 microg/cm2 dish) at time periods from 8 to 48 h after addition of minerals. c-fos mRNA levels in cells exposed to equal weight concentrations of various erionites and crocidolite fibers were increased comparably. When compared to other fibers, Na-erionite caused significantly increased levels of c-jun mRNA at lower mass concentrations (1 and 5 microg/cm2) than crocidolite asbestos, but comparable AP-1 binding to DNA. In comparison to untreated controls, numbers of RPM cells incorporating 5'-bromodeoxyuridine (BrdU) were increased dramatically after exposure to asbestos or Na-erionite at 5 and 10 microg/cm2. Significant dose-dependent increases in apoptosis were observed with asbestos at all time points, whereas erionites failed to induce apoptosis at 8 or 24 h, with minimal induction at higher concentrations than asbestos at 48 h. These data suggest that erionite increases the balance between cell proliferation (and/or abnormal DNA repair) and apoptosis, a normal mechanism of elimination of transformed or proliferating cells.

Copyright 1998 Academic Press.

In plain English

In this laboratory experiment, the authors exposed cultured rat pleural mesothelial cells to crocidolite asbestos or to erionite, a fibrous zeolite mineral. The erionite was treated to carry sodium, potassium, calcium or iron (Na-, K-, Ca- and Fe-erionite). Doses were 1, 5 or 10 micrograms per square centimetre of dish (µg/cm²), for 8 to 48 hours. After 8 hours, Fe-, Na- and Ca-erionite raised c-fos messenger RNA levels; Na-erionite's rise was comparable to crocidolite's. Na-erionite raised c-jun messenger RNA at 1 and 5 µg/cm², crocidolite at 10. At 48 hours, microscope counts showed more programmed cell death (apoptosis) with crocidolite at 5 µg/cm², but with Na-, Ca- and K-erionite only at 10. Flow cytometry found no significant increase in apoptosis with Na-erionite at 8, 24 or 48 hours, even at 10 µg/cm². Crocidolite and Na-erionite at 5 µg/cm² increased the number of cells labelled by BrdU, a marker of DNA synthesis or altered DNA repair. The authors concluded that the balance between apoptosis and cell proliferation may be critical, offering a possible explanation for erionite's greater tumor-causing effect than crocidolite after inhalation.

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: Laboratory (in vitro) cell culture experiment comparing cation-substituted erionite preparations with crocidolite asbestos
• Who was studied: Rat pleural mesothelial (RPM) cells isolated from the parietal pleura of Fisher 344 rats, grown in culture
• Exposure: NIEHS reference crocidolite asbestos, and erionite from East Gate, Nevada that was cation-exchanged to Na-, K-, Ca- and Fe-erionite. Doses were 1, 5 or 10 micrograms per square centimetre of dish, for 8, 24 or 48 hours. Riebeckite (a nonfibrous analogue of crocidolite) and glass beads were used as comparison particles in some assays.
• Main results:
  • After 8 hours, the MTS assay showed no significant change in viability of cells exposed to any of the erionites or to asbestos at up to 10 micrograms per square centimetre
  • After 8 hours, Fe-, Na- and Ca-erionite caused statistically significant dose-dependent increases in c-fos mRNA levels compared with untreated controls
  • c-fos mRNA increases in cells exposed to Na-erionite were comparable to those in crocidolite-exposed cells
  • After 8 hours, c-jun mRNA was significantly higher than in untreated controls in cells exposed to Na-erionite at 1 or 5 micrograms per square centimetre
  • Crocidolite significantly increased c-jun mRNA at 10 micrograms per square centimetre
  • Fe-erionite and K-erionite caused no significant increase in c-jun mRNA
  • AP-1 DNA binding increased after 24 hours of exposure to 5 micrograms per square centimetre of crocidolite or erionite. Glass beads, the negative particle control, caused no change.
  • At 48 hours, counted on cells in the dish, the number of apoptotic cells increased significantly with crocidolite at 5 micrograms per square centimetre compared with untreated controls
  • At 48 hours, by the DAPI-based count, Na-, Ca- and K-erionite raised apoptotic cell counts in a dose-dependent way, but only at the high concentration of 10 micrograms per square centimetre
  • Riebeckite and Fe-erionite at 5 and 10 micrograms per square centimetre caused no statistically significant increase in the percentage of apoptotic cells
  • Flow cytometry at 8 and 24 hours showed significant increases in apoptotic cells with crocidolite at 5 and 10 micrograms per square centimetre, and no changes with Na-erionite
  • By flow cytometry at 48 hours, Na-erionite did not significantly increase apoptosis, unlike crocidolite at 5 micrograms per square centimetre, even at 10 micrograms per square centimetre
  • At 48 hours, with BrdU (a marker of DNA synthesis) added for the last 16 hours, crocidolite at 5 micrograms per square centimetre produced a striking increase in BrdU-positive cells compared with untreated controls
  • Na-erionite at 5 micrograms per square centimetre also significantly increased BrdU-positive cells
  • Riebeckite had no effect on BrdU uptake
  • Only Ca-erionite at 10 micrograms per square centimetre decreased cell numbers after 48 hours
  • The crocidolite preparation had two to eight times more fibers per unit weight than the erionites, and a greater proportion of erionite fibers were shorter than crocidolite fibers
• The authors' conclusion: The authors concluded that the balance between apoptosis and cell proliferation may be critical in mineral-induced responses. They wrote that this offers a possible mechanistic explanation for the greater tumorigenicity of erionite compared with crocidolite asbestos after inhalation.
• Limitations the authors state:
  • DNA synthesis was measured with a 16-hour BrdU labeling period. This may not reflect changes in cell proliferation or altered DNA repair over longer periods such as 72 hours.
  • The K-exchanged erionite had a different framework composition from the other samples. The authors said the aliquots may have differed or the analyses may have contained some error.
  • No wet chemical analysis was obtained for the Fe-exchanged erionite
  • Fibers were compared on an equal-weight basis, but numbers of fibers per unit mass may differ greatly between fiber types

Topics

Medical terms in this study, explained in our Lexicon: Apoptosis, Mesothelial Cells, erionite, Zeolite, Carcinogenic, Carcinogenesis, Cation, Crocidolite.

Related studies

• Persistent induction of c-fos and c-jun expression by asbestos — N.H. Heintz, Y.M. Janssen, et al. (1993)
• Novel cell imaging techniques show induction of apoptosis and proliferation in mesothelial cells by asbestos — J.L. Goldberg, C.L. Zanella, et al. (1997)
• Induction of c-fos and c-jun proto-oncogenes in target cells of the lung and pleura by carcinogenic fibers — Y.M. Janssen, N.H. Heintz, et al. (1994)
• Increased expression of epidermal growth factor receptor in rat pleural mesothelial cells correlates with carcinogenicity of mineral fibres — S.P. Faux, C.E. Houghton, et al. (2000)
• Effect of simian virus large T antigen expression on cell cycle control and apoptosis in rat pleural mesothelial cells exposed to DNA damaging agents — V. Levresse, S. Moritz, et al. (1998)
• Asbestos-induced phosphorylation of epidermal growth factor receptor is linked to c-fos and apoptosis — C.L. Zanella, C.R. Timblin, et al. (1999)

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