An extracellular signal-regulated kinase 2 survival pathway mediates resistance of human mesothelioma cells to asbestos-induced injury

Our plain-English summary of An extracellular signal-regulated kinase 2 survival pathway mediates resistance of human mesothelioma cells to asbestos-induced injury, by A. Shukla, T.F. Barrett, M.B. MacPherson, et al (American Journal of Respiratory Cell and Molecular Biology, 2011).

The study

• Authors: A. Shukla, T.F. Barrett, M.B. MacPherson, J.M. Hillegass, N.K. Fukagawa, W.A. Swain, K.J. O'Byrne, J.R. Testa, H.I. Pass, S.P. Faux, B.T. Mossman
• Journal: American Journal of Respiratory Cell and Molecular Biology
• Published: 2011;45(5):906-14
• Cited by: 14 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

We hypothesized that normal human mesothelial cells acquire resistance to asbestos-induced toxicity via induction of one or more epidermal growth factor receptor (EGFR)-linked survival pathways (phosphoinositol-3-kinase/AKT/mammalian target of rapamycin and extracellular signal-regulated kinase [ERK] 1/2) during simian virus 40 (SV40) transformation and carcinogenesis. Both isolated HKNM-2 mesothelial cells and a telomerase-immortalized mesothelial line (LP9/TERT-1) were more sensitive to crocidolite asbestos toxicity than an SV40 Tag-immortalized mesothelial line (MET5A) and malignant mesothelioma cell lines (HMESO and PPM Mill). Whereas increases in phosphorylation of AKT (pAKT) were observed in MET5A cells in response to asbestos, LP9/TERT-1 cells exhibited dose-related decreases in pAKT levels. Pretreatment with an EGFR phosphorylation or mitogen-activated protein kinase kinase 1/2 inhibitor abrogated asbestos-induced phosphorylated ERK (pERK) 1/2 levels in both LP9/TERT-1 and MET5A cells as well as increases in pAKT levels in MET5A cells. Transient transfection of small interfering RNAs targeting ERK1, ERK2, or AKT revealed that ERK1/2 pathways were involved in cell death by asbestos in both cell lines. Asbestos-resistant HMESO or PPM Mill cells with high endogenous levels of ERKs or AKT did not show dose-responsive increases in pERK1/ERK1, pERK2/ERK2, or pAKT/AKT levels by asbestos. However, small hairpin ERK2 stable cell lines created from both malignant mesothelioma lines were more sensitive to asbestos toxicity than shERK1 and shControl lines, and exhibited unique, tumor-specific changes in endogenous cell death-related gene expression. Our results suggest that EGFR phosphorylation is causally linked to pERK and pAKT activation by asbestos in normal and SV40 Tag-immortalized human mesothelial cells. They also indicate that ERK2 plays a role in modulating asbestos toxicity by regulating genes critical to cell injury and survival that are differentially expressed in human mesotheliomas.

In plain English

This was a laboratory study of human cells, not of people. The authors exposed five kinds of cells to crocidolite asbestos over a range of concentrations. These were normal pleural mesothelial cells taken at autopsy (HKNM-2), a telomerase-immortalized mesothelial line (LP9/TERT-1), a line immortalized with the SV40 virus T antigen (MET5A), and two malignant mesothelioma lines, HMESO (epithelioid) and PPM Mill (sarcomatoid). The normal cells and LP9 cells showed dose-related damage. At the highest concentrations, release of a cell-damage marker (LDH) rose more than fourfold in these cells, against less than twofold in MET5A cells. PPM Mill cells showed no injury at any of the concentrations tested on them over 24 hours. In LP9 and MET5A cells, asbestos raised activation of the ERK1/2 survival signal, and drugs blocking EGFR or MEK1/2 prevented this. In the two mesothelioma lines, asbestos did not significantly raise ERK or AKT activation. However, versions of these lines with ERK2 silenced were the most sensitive to asbestos. Comparing these different cell types, the authors concluded that their results suggest resistance to asbestos toxicity increases as mesothelial cells become tumor-forming.

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) experiment on human mesothelial and malignant mesothelioma cell lines, using toxicity assays, Western blots, chemical inhibitors, RNA interference (gene silencing) and gene-expression microarrays
• Who was studied: No human subjects. Five kinds of human cells: normal pleural mesothelial cells isolated at autopsy (HKNM-2), a telomerase-immortalized peritoneal mesothelial line (LP9/TERT-1), an SV40 Tag-immortalized mesothelial line (MET5A), an epithelioid malignant mesothelioma line (HMESO) and a sarcomatoid malignant mesothelioma line (PPM Mill)
• Exposure: Crocidolite asbestos (National Institute of Environmental Health Sciences reference sample) added to cell cultures over a range of concentrations. The scanned text prints these as 5 to 25 "mg/cm2 dish", but the unit may have been altered by scanning. Exposure lasted from 4 to 24 hours depending on the experiment.
• Main results:
  • In the normal HKNM-2 and LP9 cells, LDH release (a marker of cell damage) rose more than fourfold at the highest asbestos concentrations. The scanned text prints these as 20–25 "mg asbestos/cm2 dish", and the unit may have been damaged by scanning. In SV40-immortalized MET5A cells, the rise was less than twofold.
  • In HMESO mesothelioma cells, LDH release did not increase significantly.
  • PPM Mill mesothelioma cells showed no injury (no change in appearance, no increased LDH release, no decrease in viability) at the asbestos concentrations tested, in experiments run over 24 hours. The highest concentration is printed in the scanned text as 20 "mg asbestos/cm2 dish", and the unit may have been damaged by scanning.
  • Asbestos caused dose-related decreases in activated AKT (pAKT/AKT) in LP9 cells.
  • Asbestos increased activated AKT (pAKT/AKT) in MET5A cells.
  • Asbestos-induced increases in activated ERK1/2 in LP9 and MET5A cells were blocked by the MEK1/2 inhibitor U0126. They were also blocked by the EGFR inhibitor AG1478.
  • In the two mesothelioma lines, asbestos did not significantly increase activated ERK1, ERK2 or AKT, either at 8 hours or at 24 hours.
  • In LP9 and MET5A cells, silencing ERK1 or ERK2 further reduced cell survival after asbestos, compared with control-treated cells.
  • In both mesothelioma lines (HMESO and PPM Mill), cells with ERK2 silenced were the most sensitive to asbestos (P < 0.05).
  • Silencing ERK2 in HMESO cells increased expression of eight cell death-related genes (more than threefold) and decreased expression of three (P < 0.05).
  • Silencing ERK2 in PPM Mill cells increased expression of seven genes and decreased expression of eight (P < 0.05).
• The authors' conclusion: Based on comparisons among different cell types (normal, immortalized and mesothelioma lines), the authors concluded that their results suggest resistance to asbestos toxicity increases as human mesothelial cells become tumorigenic. They did not follow the same cells through this change.
• Limitations the authors state:
  • The authors stated it is difficult to tell whether the asbestos concentrations used in cell cultures are comparable to exposures in the body that lead to tumors.
  • The chemical inhibitors used may not act only on their intended targets.
  • EGFR activation is probably not the only route by which asbestos activates ERK in mesothelial cells.
  • Too few normal HKNM-2 cells were available for the Western blot experiments, so LP9 cells were used instead.

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: Mesothelioma, Mesothelial Cells, EGFR, SV40, Carcinogenesis, Crocidolite, Malignant Mesothelioma.

Related studies

• 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)
• 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)
• 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)
• Role of extracellular signal-regulated protein kinases in apoptosis by asbestos and H2O2 — L.A. Jiménez, C. Zanella, et al. (1997)
• Extracellular signal-regulated kinase 5 and cyclic AMP response element binding protein are novel pathways inhibited by vandetanib (ZD6474) and doxorubicin in mesotheliomas — M. Sayan, A. Shukla, et al. (2014)
• 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)

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