Asbestos-induced apoptosis is protein kinase C delta-dependent

Our plain-English summary of Asbestos-induced apoptosis is protein kinase C delta-dependent, by A. Shukla, M. Stern, K.M. Lounsbury, et al (American Journal of Respiratory Cell and Molecular Biology, 2003).

The study

• Authors: A. Shukla, M. Stern, K.M. Lounsbury, T. Flanders, B.T. Mossman
• Journal: American Journal of Respiratory Cell and Molecular Biology
• Published: 2003;29(2):198-205
• Cited by: 51 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Alveolar epithelial and mesothelial cells undergo apoptosis in response to asbestos, a phenomenon that may be important in injury and/or initiation of compensatory proliferation. Here, we report a functional role of protein kinase (PKC)delta in apoptosis by crocidolite asbestos. We first show that asbestos increases the kinase activity of PKC delta in alveolar type II epithelial cells (C10 line) and causes its translocation to mitochondria, events associated with caspase-9 cleavage and apoptosis as detected by the Apostain technique. Pretreatment of C10 cells with rottlerin (Rot), a PKC delta-selective inhibitor, before addition of asbestos prevented cleavage of caspase-9 and blocked the appearance of apoptotic cells. Asbestos-induced apoptosis also was inhibited in cells stably expressing a dominant-negative kinase-deficient mutant of PKC delta (dnPKC delta), but not dnPKC alpha. Activities of PKC alpha and PKC zeta increased after exposure to asbestos, but neither isoform migrated to mitochondria. A general inhibitor of PKCs, bisindolylmaleimide I, had no effect on asbestos-induced apoptosis. Hydrogen peroxide (H2O2) induced activation of PKCs delta, alpha, zeta, and theta, translocation of PKC delta to mitochondria, and caspase-9 cleavage. However, H2O2-induced apoptosis was not inhibited by cell lines stably expressing either dnPKC delta or dnPKC alpha, suggesting that activation of PKC delta has a distinct role in the development of asbestos-induced apoptosis.

In plain English

This was a laboratory study of a mouse lung cell line (C10, alveolar type II epithelial cells) grown in culture. No people or live animals were studied. The authors exposed the cells to crocidolite asbestos at 5 micrograms per square centimeter, and to hydrogen peroxide for comparison. They examined an enzyme family called protein kinase C (PKC) and its link to apoptosis, a form of programmed cell death. Asbestos increased the activity of PKC alpha, delta and zeta, but only PKC delta moved to the mitochondria, as early as 4 hours after exposure. Rottlerin, a PKC delta-selective inhibitor, completely blocked cleavage of caspase-9, a step in cell death, and blocked asbestos-induced apoptosis in a dose-dependent way. A general PKC inhibitor, bisindolylmaleimide I, did not block it. Cells carrying an inactive form of PKC delta, but not of PKC alpha, showed significantly less asbestos-induced apoptosis. Neither altered cell line reduced apoptosis caused by hydrogen peroxide. The authors concluded that increased PKC delta activity was causally associated with asbestos-induced apoptosis in these lung epithelial 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 (in vitro) cell-culture experiment using chemical inhibitors and genetically altered (dominant-negative) cell lines, with sham-treated controls
• Who was studied: C10, a contact-inhibited, nontransformed mouse (murine) alveolar type II lung epithelial cell line grown in culture
• Exposure: Crocidolite asbestos (NIEHS reference sample) at 5 micrograms per square centimeter, mostly for up to 24 hours. Hydrogen peroxide (300 micromolar) was used as an oxidative-stress comparison and the phorbol ester PDBu (100 ng/ml) as a PKC-stimulating comparison.
• Main results:
  • In asbestos-exposed C10 cells, the activities of PKC alpha, delta and zeta increased over time. The activity of PKC theta was not affected by asbestos (isoform names taken from the PubMed abstract because the article text lost the Greek letters).
  • In asbestos-exposed cells, PKC delta increased in the mitochondrial fraction as early as 4 hours after the fibers were added. The other isoforms examined were present in mitochondria but did not increase.
  • Pretreatment with rottlerin (15 micromolar) completely abolished caspase-9 cleavage in control cells and in cells exposed to asbestos for 8 and 16 hours.
  • At 24 hours, rottlerin completely abolished asbestos-induced apoptosis, while the general PKC inhibitor bisindolylmaleimide I did not inhibit it.
  • Rottlerin given at 5, 10 and 15 micromolar reduced asbestos-induced apoptosis in a dose-dependent way.
  • C10 cells expressing a dominant-negative (kinase-deficient) PKC delta showed significantly less asbestos-induced apoptosis than empty-vector cells, without toxicity to control cells.
  • C10 cells expressing a dominant-negative PKC alpha showed no change in asbestos-induced apoptosis.
  • Apoptosis in untreated cells was 2 to 4 percent and was unaffected by the empty vector alone.
  • In the dominant-negative PKC delta cell line, asbestos caused no movement of PKC delta to mitochondria and no cytotoxicity.
  • Hydrogen peroxide-induced apoptosis was not inhibited in either dominant-negative cell line (data not shown).
• The authors' conclusion: The authors concluded that asbestos increased PKC delta activity and that this was causally associated with apoptosis in pulmonary epithelial cells. In contrast, hydrogen peroxide caused apoptosis that did not depend on PKC delta. They presented the sequence of events as a hypothetical model.
• Limitations the authors state:
  • The authors noted that chemical inhibitors may affect other kinases. This is why they also used dominant-negative mutant cell lines.
  • The effect of rottlerin on hydrogen peroxide-induced caspase-9 cleavage was not explored because the two together were more toxic to the cells.

Topics

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

Related studies

• A protein kinase Cdelta-dependent protein kinase D pathway modulates ERK1/2 and JNK1/2 phosphorylation and Bim-associated apoptosis by asbestos — S.A. Buder-Hoffmann, A. Shukla, et al. (2009)
• Role of extracellular signal-regulated protein kinases in apoptosis by asbestos and H2O2 — L.A. Jiménez, C. Zanella, et al. (1997)
• Fibroblast growth factor-10 prevents asbestos-induced alveolar epithelial cell apoptosis by a mitogen-activated protein kinase-dependent mechanism — D. Upadhyay, V. Panduri, et al. (2005)
• Asbestos-induced peribronchiolar cell proliferation and cytokine production are attenuated in lungs of protein kinase C-delta knockout mice — A. Shukla, K.M. Lounsbury, et al. (2007)
• P53 mediates amosite asbestos-induced alveolar epithelial cell mitochondria-regulated apoptosis — V. Panduri, S. Surapureddi, et al. (2006)
• Activation of protein kinase C by crocidolite asbestos in hamster tracheal epithelial cells — M. Perderiset, J.P. Marsh, et al. (1991)

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