Role of extracellular signal-regulated protein kinases in apoptosis by asbestos and H2O2

Our plain-English summary of Role of extracellular signal-regulated protein kinases in apoptosis by asbestos and H2O2, by L.A. Jiménez, C. Zanella, H. Fung, et al (The American Journal of Physiology, 1997).

The study

• Authors: L.A. Jiménez, C. Zanella, H. Fung, Y.M. Janssen, P. Vacek, C. Charland, J. Goldberg, B.T. Mossman
• Journal: The American Journal of Physiology
• Published: 1997;273(5):L1029-35
• Cited by: 108 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Stimulation of cell signaling cascades by oxidants may be important in the pathogenesis of pulmonary and pleural diseases. Here, we demonstrate in rat pleural mesothelial cells that apoptotic concentrations of crocidolite asbestos and H2O2 induce phosphorylation and activation of extracellular signal-regulated protein kinases (ERK). Activation of c-jun-NH2-terminal protein kinases (JNK)/stress-activated protein kinases was also observed in response to H2O2. In contrast, asbestos caused more protracted activation of ERK without JNK activation. Both H2O2- and asbestos-induced activation of ERK was abolished by catalase. Moreover, chelation of surface iron from crocidolite fibers or addition of N-acetyl-L-cysteine prevented ERK activation and apoptosis by crocidolite, indicating an oxidative mechanism of cell signaling. The MEK1 inhibitor PD-98059 abrogated asbestos-induced apoptosis, confirming a causal relationship between ERK activation and apoptosis. These results suggest that distinct cell-signaling cascades may be important in phenotypic responses elicited by oxidant stresses.

In plain English

This was a laboratory study of cells grown in dishes, not a study of people. The authors exposed rat pleural mesothelial cells, taken from the chest lining of Fischer 344 rats, to crocidolite asbestos (5 to 10 µg/cm2 of dish) or to hydrogen peroxide (H2O2, 100 to 300 µM). They measured two signaling enzymes, ERK and JNK, and apoptosis, a form of programmed cell death. H2O2 raised ERK2 activity about 30-fold at 300 µM at early times, falling to 10-fold over 4 hours. It also activated JNK1, with a peak 13-fold increase at 1 hour. Crocidolite activated ERK2 at every time point up to 72 hours but caused no statistically significant JNK1 increase. Catalase, removing iron from the fibers, and the antioxidant N-acetyl-L-cysteine (NAC) each reduced crocidolite-induced ERK activation. By flow cytometry, about 8% of crocidolite-exposed cells were apoptotic, against 0.66% of untreated cells, and NAC reduced this. An ERK-pathway blocker, PD-98059, reduced asbestos-induced apoptosis. The authors concluded that the ERK pathway is causally associated with apoptosis by asbestos in these cells.

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 cell-culture (in vitro) experiment
• Who was studied: Rat pleural mesothelial (RPM) cells isolated from the parietal pleura of Fischer 344 rats, used between passages 1 and 12; University of Vermont
• Exposure: Crocidolite asbestos (NIEHS reference sample) at 5 to 10 µg/cm2 of dish area, and hydrogen peroxide (H2O2) at 100, 200 or 300 µM. Some experiments added catalase, N-acetyl-L-cysteine, iron chelators or the MEK1 inhibitor PD-98059.
• Main results:
  • In cells given 300 µM H2O2, ERK2 activity rose about 30-fold above control at early time points and fell to a 10-fold increase over a 4-hour period.
  • In cells exposed to crocidolite (5 µg/cm2), ERK2 activation was seen at each time point up to 72 hours.
  • In cells given 300 µM H2O2, JNK1 activity peaked at 1 hour, 13-fold above untreated controls.
  • Crocidolite (5 µg/cm2) did not cause statistically significant increases in JNK1 activation at any time point examined.
  • Catalase reduced ERK2 activation by crocidolite. Inactivated catalase and BSA did not have this effect.
  • Removing iron from crocidolite fibers with desferrioxamine and Ferrozine before use reduced ERK activity compared with unchelated fibers. Desferrioxamine added to the medium did not block ERK activation.
  • Pretreating cells with NAC for 18 hours inhibited ERK2 activation by crocidolite.
  • By flow cytometry, about 8% of crocidolite-exposed cells were apoptotic at 24 hours, compared with 0.66% of untreated controls. By DAPI staining, crocidolite gave a threefold increase. NAC pretreatment significantly reduced apoptosis by both methods.
  • The MEK1 inhibitor PD-98059 reduced crocidolite-induced ERK2 activation and crocidolite-induced apoptosis, the latter measured by DAPI staining.
• The authors' conclusion: The authors concluded that their results with PD-98059 substantiate that the ERK pathway is causally associated with apoptosis by asbestos. They also suggested that distinct cell-signaling cascades may be important in cell responses to oxidant stresses.
• Limitations the authors state:
  • Flow cytometry undercounted apoptosis in asbestos-exposed groups (8% versus 15% by DAPI), because cells stuck to long fibers did not pass through the filter.
  • In the crocidolite JNK experiment, some time points were assayed on different dates, which may account for higher control activity at later time points.
  • The authors stated that the specific reactive oxygen species responsible for the signaling events remain unidentified.

Topics

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

Medical terms in this study, explained in our Lexicon: Apoptosis, Mesothelial Cells, Crocidolite.

Related studies

• 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)
• 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)
• Persistent localization of activated extracellular signal-regulated kinases (ERK1/2) is epithelial cell-specific in an inhalation model of asbestosis — A.B. Cummins, C. Palmer, et al. (2003)
• Apoptosis induced by crocidolite asbestos in human lung epithelial cells involves inactivation of Akt and MAPK pathways — A. Baldys, P. Pande, et al. (2007)
• An extracellular signal-regulated kinase 2 survival pathway mediates resistance of human mesothelioma cells to asbestos-induced injury — A. Shukla, T.F. Barrett, et al. (2011)

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