Persistent localization of activated extracellular signal-regulated kinases (ERK1/2) is epithelial cell-specific in an inhalation model of asbestosis

Our plain-English summary of Persistent localization of activated extracellular signal-regulated kinases (ERK1/2) is epithelial cell-specific in an inhalation model of asbestosis, by A.B. Cummins, C. Palmer, B.T. Mossman, et al (The American Journal of Pathology, 2003).

The study

• Authors: A.B. Cummins, C. Palmer, B.T. Mossman, D.J. Taatjes
• Journal: The American Journal of Pathology
• Published: 2003;162(3):713-20
• Cited by: 32 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Asbestos fibers up-regulate the extracellular signal-regulated kinase (ERK1/2) pathway in mesothelial and pulmonary epithelial cells in vitro, but the cell-type expression patterns and intracellular localization of activated, ie, phosphorylated, ERK in the lung after inhalation of asbestos are unclear. C57/BL6 mice were exposed to 7-mg/m(3) air of crocidolite asbestos for 5 and 30 days, the times required for the development of epithelial cell hyperplasia and fibrotic lesions, respectively. Exposure to asbestos caused striking increases in both unphosphorylated and phosphorylated ERK (p-ERK), which were most marked at 30 days and co-localized in bronchiolar and alveolar epithelial cells using an antibody to cytokeratin. Alveolar macrophages, detected with an anti-macrophage antibody, did not express p-ERK. p-ERK was localized at the apical cell surface of bronchiolar and alveolar type II epithelial cells exposed to asbestos fibers, and was most marked in areas of epithelial hyperplasia in association with fibrotic lesions. Because translocation of p-ERK to the nucleus is associated with activation of early response genes and transcription factors, laser scanning cytometry was used to determine the kinetics of activation and nuclear translocation of p-ERK in an alveolar type II epithelial cell line in vitro after exposure to asbestos or the ERK stimuli, epidermal growth factor, or H(2)O(2). Results showed that cytoplasmic to nuclear translocation of p-ERK occurred in a protracted manner in cells exposed to asbestos. The immunolocalization of p-ERK at the membrane surface, a site of initial exposure to asbestos fibers, and the chronic activation of p-ERK in epithelial cells at sites of fibrogenesis are consistent with the concept that epithelial cell signaling through the ERK pathway contributes to remodeling of the lung during the development of pulmonary fibrosis.

In plain English

This short communication reported a laboratory study in mice and in cultured mouse lung cells, not a study of people. Groups of 5 or 6 mice per time point breathed either ordinary air or crocidolite asbestos (7 mg/m3 air) for 6 hours a day, and their lungs were examined after 5 and 30 days. The authors stained lung tissue for a signaling protein called ERK and its activated form (p-ERK). At 5 days, levels looked comparable in air-exposed and asbestos-exposed mice. At 30 days, when inflammation and fibrosis were present, both forms were increased in asbestos-exposed mice. Activated ERK was found in epithelial (lining) cells, especially at the airway-facing surface of small-airway cells and within fibrotic lesions. It was not found in macrophages. In cultured mouse lung epithelial cells, activated ERK did not move into the cell nucleus until 4 hours after asbestos was added. With the growth factor EGF, this movement peaked by 30 minutes. The authors concluded that ERK activation in epithelial cells persists during the development of asbestosis.

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 inhalation experiment in mice with microscopy of lung tissue, plus a cell-culture (in vitro) experiment; published as a short communication
• Who was studied: C57/BL6 mice aged 8 to 12 weeks, 5 or 6 per group per time point, exposed to air or asbestos. A non-cancerous mouse alveolar type II epithelial cell line (C10) was also studied. The work was done at the University of Vermont College of Medicine; the study dates are not given.
• Exposure: Mice inhaled the NIEHS reference sample of crocidolite asbestos at 7 mg/m3 air for 6 hours per day and were killed at 5 and 30 days; controls breathed ambient air. Cultured C10 cells were exposed to crocidolite asbestos fibers, epidermal growth factor (EGF) or hydrogen peroxide (H2O2).
• Main results:
  • At 5 days, expression of non-activated and activated ERK appeared comparable in air-exposed (sham) and asbestos-exposed mice
  • At 30 days, when inflammation and fibrosis occurred in the lungs, both forms of ERK were increased in asbestos-exposed mice
  • In asbestos-exposed mice, activated ERK was especially concentrated on the apical (airway-facing) surface of distal bronchiolar epithelial cells
  • In asbestos-exposed lungs, activated ERK staining did not overlap with the macrophage marker, but it did co-localize with the epithelial cell marker cytokeratin
  • Activated-ERK-positive epithelial cells were seen within asbestos-associated fibrotic lesions at 30 days
  • In cultured C10 cells exposed to asbestos, activated ERK did not move into the nucleus until 4 hours after fibers were added, compared with untreated control cells, and this persisted in a small fraction of cells at 24 hours
  • H2O2 gave a similar pattern in C10 cells, but a smaller proportion of cells showed increased nuclear-to-cytoplasmic ratios of activated ERK than with asbestos
  • In EGF-treated C10 cells, nuclear movement of activated ERK was faster: maximal by 30 minutes and decreased by 4 hours
• The authors' conclusion: The authors concluded that increased ERK and ERK activation were epithelial cell-specific in this mouse model of asbestos-induced fibrosis, and that ERK activation in epithelial cells persists during the development of asbestosis
• Limitations the authors state:
  • Asbestos fibers are difficult to see in lung cells in the inhalation model, so fiber contact with stained cells could not be directly shown in the mice
  • The cell-culture concentrations were chosen because they strongly increase activated ERK, and it is not clear what level of nuclear activated ERK is needed for a biological effect

Topics

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

Medical terms in this study, explained in our Lexicon: Crocidolite, Alveolar Macrophage, Macrophage, Translocation, Pulmonary Fibrosis.

Related studies

• The duration of nuclear extracellular signal-regulated kinase 1 and 2 signaling during cell cycle reentry distinguishes proliferation from apoptosis in response to asbestos — Z. Yuan, D.J. Taatjes, et al. (2004)
• Asbestos inhalation induces tyrosine nitration associated with extracellular signal-regulated kinase 1/2 activation in the rat lung — A. Iwagaki, N. Choe, et al. (2003)
• Different accumulation of activated extracellular signal-regulated kinases (ERK 1/2) and role in cell-cycle alterations by epidermal growth factor, hydrogen peroxide, or asbestos in pulmonary epithelial cells — S. Buder-Hoffmann, C. Palmer, et al. (2001)
• Asbestos-mediated CREB phosphorylation is regulated by protein kinase A and extracellular signal-regulated kinases 1/2 — C.A. Barlow, T.F. Barrett, et al. (2007)
• Increased phosphorylated extracellular signal-regulated kinase immunoreactivity associated with proliferative and morphologic lung alterations after chrysotile asbestos inhalation in mice — R.F. Robledo, S.A. Buder-Hoffmann, et al. (2000)
• Role of extracellular signal-regulated protein kinases in apoptosis by asbestos and H2O2 — L.A. Jiménez, C. Zanella, et al. (1997)

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