A protein kinase Cdelta-dependent protein kinase D pathway modulates ERK1/2 and JNK1/2 phosphorylation and Bim-associated apoptosis by asbestos

Our plain-English summary of A protein kinase Cdelta-dependent protein kinase D pathway modulates ERK1/2 and JNK1/2 phosphorylation and Bim-associated apoptosis by asbestos, by S.A. Buder-Hoffmann, A. Shukla, T.F. Barrett, et al (The American Journal of Pathology, 2009).

The study

• Authors: S.A. Buder-Hoffmann, A. Shukla, T.F. Barrett, M.B. MacPherson, K.M. Lounsbury, B.T. Mossman
• Journal: The American Journal of Pathology
• Published: 2009;174(2):449-59
• Cited by: 26 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Inhalation of asbestos and oxidant-generating pollutants causes injury and compensatory proliferation of lung epithelium, but the signaling mechanisms that lead to these responses are unclear. We hypothesized that a protein kinase (PK)Cdelta-dependent PKD pathway was able to regulate downstream mitogen-activated protein kinases, affecting pro- and anti-apoptotic responses to asbestos. Elevated levels of phosphorylated PKD (p-PKD) were observed in distal bronchiolar epithelial cells of mice inhaling asbestos. In contrast, PKCdelta-/- mice showed significantly lower levels of p-PKD in lung homogenates and in situ after asbestos inhalation. In a murine lung epithelial cell line, asbestos caused significant increases in the phosphorylation of PKCdelta-dependent PKD, ERK1/2, and JNK1/2/c-Jun that occurred with decreases in the BH3-only pro-apoptotic protein, Bim. Silencing of PKCdelta, PKD, and use of small molecule inhibitors linked the ERK1/2 pathway to the prevention of Bim-associated apoptosis as well as the JNK1/2/c-Jun pathway to the induction of apoptosis. Our studies are the first to show that asbestos induces PKD phosphorylation in lung epithelial cells both in vivo and in vitro. PKCdelta-dependent PKD phosphorylation by asbestos is causally linked to a cellular pathway that involves the phosphorylation of both ERK1/2 and JNK1/2, which play opposing roles in the apoptotic response induced by asbestos.

In plain English

This was a laboratory study in mice and in mouse lung cells. It looked at chemical signals inside the cells lining the lungs after asbestos exposure. Normal mice and mice lacking an enzyme called PKC-delta breathed either clean air or chrysotile asbestos (7 milligrams per cubic meter of air, 6 hours a day, 5 days a week) for 9 or 40 days. In normal mice, an activated form of a second enzyme, PKD, increased in cells lining the small airways. Mice lacking PKC-delta did not show this increase. In a mouse lung cell line exposed to crocidolite asbestos, PKD activation peaked 3 to 10 hours after exposure and was markedly reduced when PKC-delta was silenced. Silencing PKD reduced activation of two other signaling enzymes, ERK1/2 and JNK1/2. It also increased the number of cells undergoing programmed cell death (apoptosis) at 48 hours. Blocking JNK reduced asbestos-associated apoptosis. Blocking ERK1/2 raised levels of BimEL, a form of a protein that promotes cell death. The authors concluded that PKD functions as a regulatory pathway affecting downstream signaling by asbestos.

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 (wild-type versus PKC-delta knockout mice) combined with cell culture experiments in a mouse lung epithelial cell line
• Who was studied: Wild-type and PKC-delta knockout mice (C57Bl/6 background, 8 to 12 weeks old), 4 mice per group per time point for lung immunostaining. Also a non-transformed mouse alveolar type II epithelial cell line (C10). The work was done at the University of Vermont College of Medicine.
• Exposure: Mice inhaled the NIEHS reference sample of chrysotile asbestos at 7 mg per cubic meter of air, 6 hours/day, 5 days/week, for 9 or 40 days; control mice breathed ambient (clean) air. C10 cells were exposed to NIEHS reference crocidolite asbestos. In one experiment, C10 cells were exposed to hydrogen peroxide (0.5 and 5.0 mmol/L for 30 minutes) as a soluble substitute for asbestos.
• Main results:
  • In wild-type mice inhaling chrysotile, activated (phosphorylated) PKD was found mainly in bronchiolar epithelial cells and was still increased after 40 days of exposure. PKC-delta knockout mice did not show increased phosphorylated PKD.
  • In C10 cells, asbestos-induced PKD phosphorylation peaked from 3 to 10 hours.
  • Silencing PKC-delta in C10 cells markedly reduced phosphorylated PKD compared with a scrambled control.
  • C10 cells with PKD silenced showed significantly decreased ERK1/2 and JNK1/2 phosphorylation in response to asbestos.
  • Asbestos increased c-Jun phosphorylation and c-Jun protein in C10 cells; both were decreased in cells with PKD silenced.
  • Numbers of asbestos-induced apoptotic cells were significantly increased at 48 hours in C10 cells with PKD silenced.
  • The JNK inhibitor SP600125 inhibited asbestos-associated apoptosis, most strikingly at 48 hours.
  • The NF-kappaB pathway inhibitor Bay11-7082 at 5 or 10 did not change asbestos-induced apoptosis.
  • Levels of the pro-apoptotic proteins BimL and BimEL decreased in C10 cells from 10 to 48 hours after asbestos exposure.
  • The ERK1/2 inhibitor U0126 increased BimEL at 10 and 24 hours after asbestos exposure, while the JNK inhibitor SP600125 did not alter the asbestos-associated decrease in BimEL.
  • In immunoprecipitation experiments, PKC-delta and ERK1/2 associated with PKD protein after 10 and 24 hours of asbestos exposure.
• The authors' conclusion: The authors concluded that PKC-delta-dependent PKD functions as a regulatory pathway affecting the downstream outcomes of MAPK (ERK1/2 and JNK1/2) activation by asbestos.
• Limitations the authors state:
  • In the JNK1/2 immunoprecipitation experiments, similar trends were seen, but variability between groups prevented statistically significant differences.
  • Asbestos-induced ERK1/2 phosphorylation was difficult to detect in individual cells because fibers sit unevenly on cells. Hydrogen peroxide was therefore used instead of asbestos to test whether both signals occur in the same cell.

Topics

Medical terms in this study, explained in our Lexicon: Apoptosis, Epithelium.

Related studies

• Asbestos-induced apoptosis is protein kinase C delta-dependent — A. Shukla, M. Stern, et al. (2003)
• 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)
• Enhanced apoptosis by pemetrexed and simvastatin in malignant mesothelioma and lung cancer cells by reactive oxygen species-dependent mitochondrial dysfunction and Bim induction — K.E. Hwang, Y.S. Kim, et al. (2014)
• Licochalcone A induces apoptosis in malignant pleural mesothelioma through downregulation of Sp1 and subsequent activation of mitochondria-related apoptotic pathway — K.H. Kim, G. Yoon, et al. (2015)
• Involvement of protein kinase C, phospholipase C, and protein tyrosine kinase pathways in oxygen radical generation by asbestos-stimulated alveolar macrophage — Y. Lim, S.H. Kim, et al. (1997)
• 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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