P53 mediates amosite asbestos-induced alveolar epithelial cell mitochondria-regulated apoptosis

Our plain-English summary of P53 mediates amosite asbestos-induced alveolar epithelial cell mitochondria-regulated apoptosis, by V. Panduri, S. Surapureddi, S. Soberanes, et al (American Journal of Respiratory Cell and Molecular Biology, 2006).

The study

• Authors: V. Panduri, S. Surapureddi, S. Soberanes, S.A. Weitzman, N. Chandel, D.W. Kamp
• Journal: American Journal of Respiratory Cell and Molecular Biology
• Published: 2006;34(4):443-52
• Cited by: 51 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Asbestos causes pulmonary toxicity in part by generating reactive oxygen species that cause DNA damage. We previously showed that the mitochondria-regulated (intrinsic) death pathway mediates alveolar epithelial cell (AEC) DNA damage and apoptosis. Because p53 regulates the DNA damage response in part by inducing intrinsic cell death, we determined whether p53-dependent transcriptional activity mediates asbestos-induced AEC mitochondrial dysfunction and apoptosis. We show that inhibitors of p53-dependent transcriptional activation (pifithrin and type 16-E6 protein) block asbestos-induced AEC mitochondrial membrane potential change (DeltaPsim), caspase 9 activation, and apoptosis. We demonstrate that asbestos activates p53 promoter activity, mRNA levels, protein expression, and Bax and p53 mitochondrial translocation. Further, pifithrin, E6, phytic acid, or rho(0)-A549 cells (cells incapable of mitochondrial reactive oxygen species production) block asbestos-induced p53 activation. Finally, we show that asbestos augments p53 expression in cells at the bronchoalveolar duct junctions of rat lungs and that phytic acid prevents this. These data suggest that p53-dependent transcription pathways mediate asbestos-induced AEC mitochondria-regulated apoptosis. This suggests an important interactive effect between p53 and the mitochondria in the pathogenesis of asbestos-induced pulmonary toxicity that may have broader implications for our understanding of pulmonary fibrosis and lung cancer.

In plain English

This laboratory study tested whether p53-dependent transcription mediates amosite asbestos-induced alveolar epithelial cell (AEC) mitochondria-regulated apoptosis. The authors used A549 cells (human malignant cells with some alveolar type II, AT2, features and wild-type p53), A549 cells transfected with a plasmid expressing human papillomavirus type 16 E6 protein or empty vector, rho-zero A549 cells unable to produce mitochondrial reactive oxygen species, primary rat AT2 cells, and archived rat lungs from an earlier asbestosis model (5 mg amosite instilled intratracheally). In A549 cells pifithrin blocked asbestos-induced mitochondrial membrane potential change and apoptosis; in rat AT2 cells it reduced apoptosis and caspase 9 activation (TUNEL: control 2.6 ± 0.6%, asbestos 39.9 ± 2.0%, pifithrin plus asbestos 18.0 ± 1.9% positive cells). Asbestos raised p53 promoter activity to 160 ± 10, 172 ± 6 and 190 ± 5 percent of control at 1, 4 and 24 h; phytic acid and deferoxamine nearly abolished this at all three times, while sodium benzoate did so at 4 and 24 h (135 ± 22 percent at 1 h, not marked significant). The increase was reduced in rho-zero cells and, at 4 h, undetectable in E6 cells. Mitochondria-targeted Bax and p53 in A549 cells rose 4.0- and 2.3-fold. In rat lungs, asbestos increased p53 staining at bronchoalveolar duct junctions; phytic acid reduced it.

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: experimental in vitro cell-culture study (human A549 cell lines, transfected and rho-zero variants, primary rat alveolar type II cells) with immunohistochemistry on archived rat lung tissue from a previous animal model
• Who was studied: Human A549 cells (malignant, AT2-like, wild-type p53), A549-E6 and A549-vector cells, rho-zero A549 cells, primary rat AT2 cells obtained by elastase digestion, and archived paraffin-embedded lungs from a previously described rat model of asbestosis
• Exposure: Amosite asbestos (UICC reference standard fibers), 25 micrograms per square centimetre (0 to 50 in dose-response work) for 1 to 24 h in cells, with doxorubicin 500 ng/ml as positive control and pifithrin, phytic acid, deferoxamine or sodium benzoate as inhibitors; in rats, a single intratracheal instillation of 5 mg amosite
• Main results:
  • In primary rat AT2 cells, pifithrin reduced asbestos-induced apoptosis and caspase 9 activation (TUNEL at 24 h: control 2.6 plus or minus 0.6%, asbestos 39.9 plus or minus 2.0%, pifithrin plus asbestos 18.0 plus or minus 1.9%; caspase 9: asbestos 200 plus or minus 30% of control, pifithrin plus asbestos 130 plus or minus 20%; n = 6 per group)
  • In A549 cells, pifithrin blocked asbestos-induced mitochondrial membrane potential change and apoptosis (TUNEL)
  • A549 empty-vector cells showed dose-dependent mitochondrial dysfunction and apoptosis with asbestos, while A549-E6 cells (functionally inactive p53) were nearly completely protected
  • p53 promoter activity in asbestos-exposed A549 cells was 160 plus or minus 10, 172 plus or minus 6 and 190 plus or minus 5 percent of control at 1, 4 and 24 h; with phytic acid 120 plus or minus 8, 100 plus or minus 1 and 125 plus or minus 5; with deferoxamine 105 plus or minus 2, 100 plus or minus 1 and 105 plus or minus 1; with sodium benzoate 135 plus or minus 22 (not marked significant versus asbestos), 100 plus or minus 1 and 109 plus or minus 4 (n = 6)
  • The authors described the inhibition by these agents as nearly complete at 1, 4 and 24 h
  • At 4 h, asbestos-induced p53 promoter activity was 346 plus or minus 58% of control in A549 cells versus 102 plus or minus 3% in A549-E6 cells (p less than 0.05; n = 6), that is, the asbestos-induced increase was not detectable in E6 cells
  • p53 promoter activity after asbestos was significantly lower in rho-zero A549 cells, which cannot produce mitochondrial reactive oxygen species
  • Asbestos increased A549 p53 mRNA more than 2.5-fold at 24 h, and pifithrin abolished this
  • A549 p53 protein rose 2.5-fold versus control at 4 h (p less than 0.05) and remained raised at 24 h (3-fold); pifithrin, HPV-E6 and phytic acid blocked the increase
  • Asbestos increased mitochondria-targeted Bax 4.0-fold and mitochondrial p53 2.3-fold compared with controls in A549 cells; pifithrin blocked both translocations
  • In rat lungs, asbestos increased p53 immunostaining in cells at the bronchoalveolar duct region compared with saline-treated controls, and phytic acid reduced this staining
• The authors' conclusion: The authors concluded that p53-dependent transcription pathways mediate asbestos-induced AEC mitochondria-regulated apoptosis, and suggested an interactive effect between p53 and the mitochondria in asbestos-induced pulmonary toxicity
• Limitations the authors state:
  • The authors noted the reliance on pharmacologic inhibitors, and that pifithrin is not entirely specific, also inhibiting heat shock and glucocorticoid signaling
  • Pharmacologic inhibitors might act by blocking asbestos uptake into alveolar epithelial cells rather than only by their intended target
  • In the rat lung tissue, the cells staining for p53 were not formally identified

Topics

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

Medical terms in this study, explained in our Lexicon: Amosite, Apoptosis, Reactive Oxygen Species (ROS), Translocation, A549 Cells, Pulmonary Fibrosis, Lung Cancer.

Related studies

• Asbestos causes apoptosis in alveolar epithelial cells: role of iron-induced free radicals — A. Aljandali, H. Pollack, et al. (2001)
• Mitochondria-targeted Ogg1 and aconitase-2 prevent oxidant-induced mitochondrial DNA damage in alveolar epithelial cells — S.J. Kim, P. Cheresh, et al. (2014)
• 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)
• The c-Jun N-terminal kinase signaling pathway mediates chrysotile asbestos-induced alveolar epithelial cell apoptosis — P. Li, T. Liu, et al. (2015)
• Asbestos-induced alveolar epithelial cell apoptosis. The role of endoplasmic reticulum stress response — D.W. Kamp, G. Liu, et al. (2013)
• Cigarette smoke augments asbestos-induced alveolar epithelial cell injury: role of free radicals — D.W. Kamp, M.J. Greenberger, et al. (1998)

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