Cell Signaling in Mesothelial Cells by Asbestos: Evidence for the Involvement of Oxidative Stress in the Regulation of the Epidermal Growth Factor Receptor

Our plain-English summary of Cell Signaling in Mesothelial Cells by Asbestos: Evidence for the Involvement of Oxidative Stress in the Regulation of the Epidermal Growth Factor Receptor, by S.P. Faux, C.E. Houghton (Inhalation Toxicology, 2000).

The study

• Authors: S.P. Faux, C.E. Houghton
• Journal: Inhalation Toxicology
• Published: 2000;12 Suppl 3:327-36
• Cited by: 4 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Asbestos has been shown to stimulate the mitogen-activated protein kinase signaling cascade after autophosphoryiation of the epidermal growth factor recptor (EGF-R), an event important in regulating the response of cells to extracellular signals. In studies reported here, we have examined whether mineral fibers with known carcinogenicity can be discriminated from nonpathogenic fibers by their ability to upregulate expression of EGF-R protein in mesothelial cells. Crocidolite and erionite, two fibrous preparations known to induce mesothelioma, increased expression of EGF-R protein in a time- and dose-dependent manner, whereas milled (nonfibrous) crocidolite and chrysotile asbestos, two preparations with much less or no ability to induce mesothelioma, did not. Intense patterns of EGF-R protein expression were linked to mesothelial cells phagocytosing long fibers as observed by phase-contrast microscopy. To determine the importance of EGF-R expression in these cells, we assessed downstream signaling events in rat pleural mesothelial (RPM) cells by looking at the induction of activator protein-1 (AP-I), a transcription factor that controls the transition to S phase in the cell cycle, leading to cell proliferation. Crocidolite induced AP-I in RPM cells in a dose-dependent manner, and this induction of AP-I in RPM cells was inhibited by coincubation with tyrphostin AG 1478, a potent inhibitor of the EGF-R. To examine the mechanism of induction of EGF-R in RPM cells by asbestos, RPM cells were treated with crocidolite in the presence and absence of the antioxidant N-acetylcysteine (NAC). Reduced glutathione (GSH) was examined as a marker of oxidative stress and the expression of EGF-R protein was measured. Crocidolite asbestos caused a dose-dependent depletion of GSH in RPM cells, and the presence of NAC ameliorated the expression of EGF-R protein by crocidolite. Our data suggest that carcinogenic fibers induce EGF-R via a mechanism involving oxidative stress initiating cell signaling cascades in mesothelial cells leading to cell proliferation and carcinogenesis.

In plain English

This was a laboratory study of cells grown in culture, not a study of people. The authors exposed pleural mesothelial cells from male Fischer 344 rats to crocidolite asbestos, chrysotile asbestos, milled (non-fibrous) crocidolite and erionite. They measured a growth factor receptor protein called EGF-R. The authors described crocidolite and erionite as fibers known to induce mesothelioma, and both increased EGF-R staining. Averaged over 10 random microscope fields, intense staining was seen in 45.46% of crocidolite-treated cells and 40% of erionite-treated cells. It was seen in 0% of sham-treated, milled crocidolite-treated and chrysotile-treated cells. Cells trying to engulf long crocidolite fibers stained strongly, and cells exposed to shorter fibers did not. Crocidolite lowered glutathione, a marker of oxidative stress. Pretreatment with the antioxidant N-acetylcysteine restored glutathione and reduced EGF-R expression. A drug that blocks EGF-R significantly reduced crocidolite's activation of AP-1, a factor linked to cell proliferation. The authors concluded that a fiber's ability to raise EGF-R correlated with its carcinogenicity.

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
• Who was studied: Pleural mesothelial cells isolated from male Fischer 344 rats and grown in culture for four passages; the number of animals is not given
• Exposure: UICC reference crocidolite, chrysotile B and milled crocidolite asbestos, plus erionite from Rome, Oregon. Fibers were added at 2.5 and 5.0 micrograms per square centimetre. Some cells were also pretreated with N-acetylcysteine (5 mM for 18 h), cycloheximide, or the EGF-R inhibitor tyrphostin AG 1478.
• Main results:
  • Crocidolite and erionite increased EGF-R protein expression in the rat pleural mesothelial cells over sham controls.
  • Milled (non-fibrous) crocidolite and chrysotile did not increase EGF-R protein expression over the sham control.
  • Intense EGF-R staining was seen in 45.46 plus or minus 4.54% of crocidolite-treated cells (mean plus or minus SD of 10 random fields), compared with 0 for sham, milled crocidolite and chrysotile.
  • Intense EGF-R staining was seen in 40 plus or minus 7.62% of erionite-treated cells (mean plus or minus SD of 10 random fields).
  • Cells attempting to engulf long crocidolite fibers showed increased EGF-R staining and took on a spindle (fusiform) shape.
  • Cells exposed to a number of shorter fibers stayed polygonal and showed no increase in EGF-R protein.
  • Crocidolite depleted reduced glutathione (a marker of oxidative stress) in the cells. Pretreatment with N-acetylcysteine replaced it in a dose-dependent fashion.
  • N-acetylcysteine pretreatment reduced crocidolite-induced EGF-R protein expression.
  • The protein-synthesis inhibitor cycloheximide abolished EGF-R protein expression caused by asbestos. The authors took this as evidence that new protein was being made.
  • Pretreatment with the EGF-R inhibitor tyrphostin AG 1478 significantly reduced crocidolite-induced increases in AP-1 DNA binding (p less than 0.05).
• The authors' conclusion: The authors concluded that the ability of mineral fibers to upregulate the expression and activation of EGF-R in rat pleural mesothelial cells correlated with their carcinogenicity. They also concluded that this regulation is under the control of oxidative stress. They suggested that chronic EGF-R expression and the resulting cell proliferation could act as a tumor-promoting event.

Topics

Medical terms in this study, explained in our Lexicon: Mesothelial Cells, Oxidative Stress, Mineral Fiber, Crocidolite, erionite, Mesothelioma, Chrysotile, Glutathione (GSH).

Related studies

• 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)
• Increased epidermal growth factor-receptor protein in a human mesothelial cell line in response to long asbestos fibers — J.C. Pache, Y.M. Janssen, et al. (1998)
• Cyclooxygenase-2, epidermal growth factor receptor, and aromatase signaling in inflammation and mesothelioma — B. Nuvoli, R. Galati (2013)
• Epidermal growth factor receptor mutations in 510 Finnish non--small-cell lung cancer patients — S. Mäki-Nevala, M. Rönty, et al. (2014)
• Role of iron in inactivation of epidermal growth factor receptor after asbestos treatment of human lung and pleural target cells — A. Baldys, A.E. Aust (2005)
• Malignant pleural mesothelioma and epidermal growth factor receptor (EGF-R). Relationship of EGF-R with histology and survival using fixed paraffin embedded tissue and the F4, monoclonal antibody — H. Dazzi, P.S. Hasleton, et al. (1990)

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