The gamma-glutamylcysteine synthetase and glutathione regulate asbestos-induced expression of activator protein-1 family members and activity

Our plain-English summary of The gamma-glutamylcysteine synthetase and glutathione regulate asbestos-induced expression of activator protein-1 family members and activity, by A. Shukla, T. Flanders, K.M. Lounsbury, et al (Cancer Research, 2004).

The study

• Authors: A. Shukla, T. Flanders, K.M. Lounsbury, B.T. Mossman
• Journal: Cancer Research
• Published: 2004;64(21):7780-6
• Cited by: 20 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Asbestos fibers cause persistent increases in activator protein-1 (AP-1) family member proto-oncogenes in lung epithelial and mesothelial cells that are linked to proliferation and cell transformation. Using lung epithelial cells, the progenitor cells of lung cancers, we report that crocidolite asbestos initially depletes intracellular glutathione followed by up-regulation of both catalytic and modifier subunits of gamma-glutamylcysteine synthetase. In vivo asbestos inhalation experiments confirm increased protein levels of gamma-glutamylcysteine synthetase in mouse lungs. We also show that asbestos-induced mRNA levels of fos/jun proto-oncogenes, fra-1 transactivation, and AP-1 to DNA binding activity are glutathione-dependent. Epidermal growth factor receptor activity by asbestos is blocked by N-acetyl-l-cysteine, suggesting that it is an initial redox-activated event leading to downstream AP-1 proto-oncogene up-regulation. The overexpression of subunits of gamma-glutamylcysteine synthetase in combination completely blocked asbestos-induced up-regulation of AP-1 proto-oncogene expression. However, when overexpressed individually, the modifier subunit had more dramatic effects than the catalytic subunit. Our work shows that the glutathione-controlled redox status of the epithelial cell plays a pivotal role in asbestos-induced epidermal growth factor receptor and proto-oncogene activation as well as AP-1 activity.

In plain English

This was a laboratory study. It used a mouse lung epithelial cell line (C10) exposed to crocidolite asbestos, plus a mouse inhalation experiment with chrysotile asbestos. It examined glutathione, an antioxidant inside cells, and the AP-1 family of genes (such as c-jun, junB, c-fos and fra-1), which the authors link to cell proliferation and transformation. In the cells, crocidolite first lowered reduced glutathione from 2 to 8 hours, and levels then rose over 48 hours. Asbestos increased the mRNA levels of these genes, measured at 8 hours. Pretreating cells with substances that raise glutathione reduced this increase, while a drug that depletes glutathione made it larger. When the cells were made to produce more of both parts of the enzyme that makes glutathione, the asbestos-induced rise in these genes' mRNA was completely blocked. Asbestos also activated a growth-factor receptor (EGFR), and N-acetyl-L-cysteine reduced this. Mice that inhaled chrysotile for 9 days had higher protein levels of the enzyme's catalytic subunit in their lungs. The authors concluded that glutathione inside cells may play an essential role in protecting cells against these asbestos-induced changes.

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 experiments on a cultured mouse lung epithelial cell line, plus an animal (mouse) inhalation experiment
• Who was studied: A nontransformed mouse alveolar type II epithelial cell line (C10), and C57/BL6 mice aged 8 to 12 weeks (lungs from 4 mice per group used for protein analysis)
• Exposure: Crocidolite asbestos (NIEHS reference samples) was added to cultured cells for periods from 1 to 96 hours. Mice inhaled chrysotile asbestos (NIEHS reference standard) at 7 mg/m3 air, 6 hours/day, 5 days/week for 9 days, and were compared with mice breathing ambient air.
• Main results:
  • In C10 cells, crocidolite first decreased reduced glutathione from 2 to 8 hours, after which levels progressively increased over 48 hours.
  • In C10 cells, pretreatment with N-acetyl-L-cysteine or glutathione ester decreased asbestos-induced steady-state mRNA levels of c-jun, junB, c-fos and fra-1. Pretreatment with BSO, which depletes glutathione, increased them.
  • In C10 cells, asbestos exposure for 24 hours increased fra-1 promoter activity. N-acetyl-L-cysteine diminished this increase and BSO increased it.
  • In C10 cells, asbestos increased EGFR activity from 1 to 8 hours, and activity returned to control levels at 48 hours. N-acetyl-L-cysteine pretreatment decreased this activity, while catalase and deferoxamine had no effect.
  • In C10 cells, mRNA of both subunits of the glutathione-making enzyme rose significantly at 8 hours and stayed raised for 96 hours. In mice, 9 days of chrysotile inhalation increased protein levels of the catalytic subunit in whole lung.
  • In C10 cells, overexpressing both enzyme subunits together completely inhibited the asbestos-induced rise in proto-oncogene mRNA. Overexpressed one at a time, the modifier subunit inhibited it more than the catalytic subunit.
• The authors' conclusion: The authors concluded that intracellular glutathione may play an essential role in protecting intact cells against asbestos fiber-induced up-regulation of AP-1 proto-oncogenes and transformation.
• Limitations the authors state:
  • The cell and animal experiments used different fiber types: the crocidolite reference samples were too depleted for inhalation work, so chrysotile was used in mice.

Topics

Medical terms in this study, explained in our Lexicon: Glutathione (GSH), Mesothelial Cells, Lung Cancer, Crocidolite.

Related studies

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• Overexpression of gamma-glutamylcysteine synthetase in human malignant mesothelioma — K. Järvinen, Y. Soini, et al. (2002)
• Modulation of DNA single-strand breaks by intracellular glutathione in human lung cells exposed to asbestos fibers — A. Puhakka, T. Ollikainen, et al. (2002)
• Oxidant-mediated increases in redox factor-1 nuclear protein and activator protein-1 DNA binding in asbestos-treated macrophages — D.M. Flaherty, M.M. Monick, et al. (2002)
• Retinoid signaling and activator protein-1 expression in ferrets given beta-carotene supplements and exposed to tobacco smoke — X.D. Wang, C. Liu, et al. (1999)
• Glutathione modulates the formation of 8-hydroxydeoxyguanosine in isolated DNA and mutagenicity in Salmonella typhimurium TA100 induced by mineral fibres — P.J. Howden, S.P. Faux (1996)

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