Asbestos-mediated CREB phosphorylation is regulated by protein kinase A and extracellular signal-regulated kinases 1/2

Our plain-English summary of Asbestos-mediated CREB phosphorylation is regulated by protein kinase A and extracellular signal-regulated kinases 1/2, by C.A. Barlow, T.F. Barrett, A. Shukla, et al (American Journal of Physiology. Lung Cellular and Molecular Physiology, 2007).

The study

• Authors: C.A. Barlow, T.F. Barrett, A. Shukla, B.T. Mossman, K.M. Lounsbury
• Journal: American Journal of Physiology. Lung Cellular and Molecular Physiology
• Published: 2007;292(6):L1361-9
• Cited by: 27 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Asbestos is a ubiquitous, naturally occurring fiber that has been linked to the development of malignant and fibrotic lung diseases. Asbestos exposure leads to apoptosis, followed by compensatory proliferation, yet many of the signaling cascades coupled to these outcomes are unclear. Because CREs (Ca(2+)/cAMP-response elements) are found in the promoters of many genes important for regulation of proliferation and apoptosis, CREB (CRE binding protein) is likely to play an important role in the development of asbestos-mediated lung injury. To explore this possibility, we tested the hypotheses that asbestos exposure leads to CREB phosphorylation in lung epithelial cells and that protein kinase A (PKA) and extracellular signal-regulated kinases 1/2 (ERK1/2) are central regulators of the CREB pathway. Persistent CREB phosphorylation was observed in lung sections from mice following inhalation of crocidolite asbestos. Exposure of C10 lung epithelial cells to crocidolite asbestos led to rapid CREB phosphorylation and apoptosis that was decreased by the inhibition of PKA or ERK1/2 using the specific inhibitors H89 and U0126, respectively. Furthermore, crocidolite asbestos selectively induced a sustained increase in MAP kinase phosphatase-1 mRNA and protein. Silencing CREB protein dramatically reduced asbestos-mediated ERK1/2 phosphorylation, yet significantly increased the number of cells undergoing asbestos-induced apoptosis. These data reveal a novel and selective role for CREB in asbestos-mediated signaling through pathways regulated by PKA and ERK1/2, further providing evidence that CREB is an important regulator of apoptosis in asbestos-induced responses of lung epithelial cells.

In plain English

This laboratory study in mice and mouse lung cells examined how crocidolite asbestos activates CREB. CREB is a protein that helps control genes involved in cell growth and cell death. Mice breathed crocidolite asbestos at 7 mg/m3 of air, 6 hours a day, 5 days a week, for 4 or 30 days. In their lungs, activated CREB was markedly raised, mainly in cells lining the small airways (bronchioles). At 30 days it was especially prominent in areas developing fibrotic lesions. In cultured C10 mouse lung cells, crocidolite significantly raised CREB activation at 2, 4, 8 and 24 hours. Chrysotile did not produce a significant increase, though there was a trend at later times. Drugs blocking two signaling enzymes, PKA and ERK1/2, reduced CREB activation. They also lowered the share of asbestos-exposed cells dying from 22.08% to 12.97% and 14.24%, respectively. By contrast, removing CREB itself raised cell death after asbestos, from 15.40% to 28.40%. The authors concluded that cross talk between PKA, ERK1/2 and CREB is likely to play an important role in fibrosis from asbestos-related lung injury.

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 study: animal inhalation experiment in mice plus cell-culture (in vitro) experiments
• Who was studied: C57Bl/6 mice aged 8 to 12 weeks (number of mice not stated) at the University of Vermont, and C10 cells, a non-transformed mouse alveolar type II lung epithelial cell line. Cell experiments were performed in triplicate.
• Exposure: Mice: ambient air or crocidolite asbestos at 7 mg/m3 air, 6 h/day, 5 days/wk, for 4 or 30 days. The authors state this concentration is similar to past workplace levels before occupational safety standards. Cells: crocidolite or chrysotile asbestos (NIEHS reference samples) at 5 per square centimeter of dish surface; the unit is printed as '5 g/cm2', apparently with the micro sign lost. Glass beads were the nontoxic control particle. Some cells also received the inhibitors H89 (PKA), U0126 (ERK1/2 pathway) or AG-1478 (EGFR), or CREB-silencing siRNA.
• Main results:
  • In mice inhaling crocidolite, nuclear phospho-CREB (activated CREB) was dramatically elevated, primarily in bronchiolar epithelial cells, at 4 and 30 days. At 30 days it was particularly prominent in areas developing peribronchiolar fibrotic lesions.
  • In C10 cells, crocidolite asbestos caused a significant increase in CREB phosphorylation after 2, 4, 8 and 24 hours of exposure.
  • In C10 cells, chrysotile asbestos did not induce a significant increase in CREB phosphorylation, although the authors described a definite trend toward an increase at later time points. Glass beads did not stimulate CREB phosphorylation (data not shown).
  • In crocidolite-exposed C10 cells, the PKA inhibitor H89 substantially reduced CREB phosphorylation. The ERK1/2-pathway inhibitor U0126 decreased it. The EGFR inhibitor AG-1478 inhibited it only at early time points.
  • In crocidolite-exposed C10 cells, apoptosis was 22.08% (plus or minus 3.80) in vehicle-control cells. It was 12.97% (plus or minus 2.97) with H89 and 14.24% (plus or minus 3.45) with U0126. The difference was reported as statistically significant at a P value of 0.001; the comparison sign is lost in the text. There were three experiments.
  • In C10 cells, crocidolite significantly increased mkp-1 mRNA at 2, 4 and 8 hours and increased MKP-1 protein. It had no effect on MKP-3.
  • Silencing CREB in C10 cells reduced crocidolite-induced ERK1/2 phosphorylation but did not affect mkp-1 induction.
  • Among asbestos-exposed C10 cells, apoptosis was 15.40% (plus or minus 1.78) in control-siRNA cells and 28.40% (plus or minus 4.15) in CREB-silenced cells. The difference was reported as significant at a P value of 0.001; the comparison sign is lost in the text.
• The authors' conclusion: The authors concluded that crocidolite asbestos leads to rapid and prolonged CREB phosphorylation in lung epithelial cells in vivo and in vitro. They further concluded that cross talk between PKA, ERK1/2 and CREB is likely to play an important role in the development of fibrosis related to asbestos-mediated lung injury.
• Limitations the authors state:
  • The authors stated that it is difficult to determine how the asbestos concentrations used in cell culture relate to human exposures over time.
  • The authors noted that CREB knockdown increased asbestos-induced apoptosis, whereas their PKA and ERK1/2 inhibitor studies and an earlier oxidant study showed reduced apoptosis. They offered possible explanations for this discrepancy.

Topics

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

Medical terms in this study, explained in our Lexicon: Asbestos Exposure, Apoptosis, Crocidolite.

Related studies

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• 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)
• 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)
• 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)
• 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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