Asbestos causes translocation of p65 protein and increases NF-kappa B DNA binding activity in rat lung epithelial and pleural mesothelial cells

Our plain-English summary of Asbestos causes translocation of p65 protein and increases NF-kappa B DNA binding activity in rat lung epithelial and pleural mesothelial cells, by Y.M. Janssen, K.E. Driscoll, B. Howard, et al (The American Journal of Pathology, 1997).

The study

• Authors: Y.M. Janssen, K.E. Driscoll, B. Howard, T.R. Quinlan, M. Treadwell, A. Barchowsky, B.T. Mossman
• Journal: The American Journal of Pathology
• Published: 1997;151(2):389-401
• Cited by: 72 articles, as counted by NIH iCite
• Read it: PubMed · Free full text

Abstract

The mechanisms of cell signaling and altered gene expression by asbestos, a potent inflammatory, fibrogenic, and carcinogenic agent, are unclear. Activation of the transcription factor, nuclear factor (NF)-kappa B, is critical in up-regulating the expression of many genes linked to inflammation and proliferation. Inhalation models of crocidolite- and chrysotile-induced inflammation and asbestosis were used to study the localization of p65, a protein subunit of the NF-kappa B transcription factor, in sham control rats and those exposed to asbestos. In addition, we investigated, using electrophoretic mobility shift analysis, whether in vitro exposure of rat lung epithelial cells and rat pleural mesothelial cells to asbestos increased binding of nuclear proteins, including p65, to the NF-kappa B DNA response element. Furthermore, translocation of p65 into the nucleus was determined by confocal microscopy. In comparison with sham animals, striking increases in p65 immunofluorescence were observed in airway epithelial cells of rats at 5 days after inhalation of asbestos. These increases were diminished by 20 days, the time period necessary for development of fibrotic lesions. In contrast, although inter-animal variability was observed, immunoreactivity for p65 was more dramatic in the interstitial compartment of asbestos-exposed rat lungs at both 5 and 20 days. Changes in p65 expression in pleural mesothelial cells exposed to asbestos in inhalation experiments were unremarkable. Exposure to asbestos also caused significant increases in nuclear protein complexes that bind the NF-kappa B consensus DNA sequence in both rat lung epithelial and rat pleural mesothelial cells. Using confocal microscopy, we observed partial nuclear translocation of p65 in rat pleural mesothelial cells exposed to asbestos. This partial response contrasted with the effects of lipopolysaccharide, which caused rapid and complete translocation of p65 from cytoplasm to nucleus. Our studies are the first to show the presence of the NF-kappa B system in lung tissue and evidence of activation in vitro and in vivo after exposure to a potent inflammatory, fibrinogenic, and carcinogenic environmental agent.

In plain English

This was a laboratory study in rats and rat cells. The authors examined NF-kappa B, a protein switch that turns on genes linked to inflammation and cell growth, by tracking one of its parts, a protein called p65. Male Fischer 344 rats breathed chrysotile asbestos, crocidolite asbestos, or clean air for 6 hours a day, 5 days a week, for 5 or 20 days, with 3 to 4 rats per group. After 5 days, rats that inhaled asbestos showed more pronounced p65 staining in the cells lining the airways than sham rats. By 20 days, that staining was comparable to the sham rats. Focal increases appeared in the lung interstitium (the tissue between the air sacs) at both times. The pleural mesothelium showed no clear increase. In cultured rat lung epithelial and pleural mesothelial cells, crocidolite increased NF-kappa B binding to DNA. In the mesothelial cells, non-fibrous riebeckite and glass beads did not significantly increase it. About 50% of crocidolite-exposed mesothelial cells showed p65 in the cell nucleus. This compared with about 1 to 3% of untreated or glass-exposed cells, and 90% of cells given the bacterial toxin LPS. The authors suggested this activation may contribute to chronic lung inflammation.

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 in rats combined with in vitro (cell culture) experiments
• Who was studied: Male Fischer 344 rats (3 to 4 per group per time point), plus cultured rat lung epithelial cells (RLE-6TN line) and rat pleural mesothelial (RPM) cells isolated from Fischer 344 rats
• Exposure: Rats inhaled chrysotile or crocidolite asbestos (average daily chamber concentrations 8.25 plus or minus 0.23 and 7.20 plus or minus 0.27 mg/m3, respectively) or clean air for 6 hours/day, 5 days/week, for 5 or 20 days. Cultured cells were exposed to crocidolite asbestos and compared with non-fibrous riebeckite, glass beads, and LPS as a positive control.
• Main results:
  • In rats inhaling asbestos for 5 days, p65 staining increased more in bronchial epithelial cells than in sham rats
  • At 20 days, p65 staining in bronchiolar epithelium was comparable between sham rats and rats exposed to chrysotile or crocidolite
  • Focal increases in p65 in the lung interstitium were seen in rats exposed to either fiber type at 5 and 20 days
  • No clear increase in p65 was seen in the pleural mesothelium of rats after inhaling asbestos
  • In crocidolite-exposed rat lungs at 20 days, p65 staining occurred in regions where no asbestos fibers could be detected
  • In both cultured rat lung epithelial and pleural mesothelial cells, crocidolite asbestos increased binding of nuclear proteins to the NF-kappa B DNA sequence
  • In rat lung epithelial cells, binding of the p65/p50 complex rose with increasing asbestos dose (significant linear trend, P less than 0.05)
  • In rat pleural mesothelial cells, non-fibrous riebeckite caused only insignificant increases in NF-kappa B binding, and glass beads did not alter it
  • In pleural mesothelial cells, about 1 to 3% of untreated or glass-exposed cells showed p65 in the nucleus, versus about 50% of crocidolite-exposed cells
  • LPS led to 90% of pleural mesothelial cells showing p65 in the nucleus. By comparison, asbestos produced only partial translocation, with p65 in both cytoplasm and nucleus.
• The authors' conclusion: The authors suggested that sustained activation of NF-kappa B by asbestos, and switching on of genes that depend on it, may contribute to the chronic inflammatory process in the lungs of experimental animals and of workers after occupational asbestos exposure
• Limitations the authors state:
  • The authors noted variability between animals in p65 staining in the interstitial compartment

Topics

Medical terms in this study, explained in our Lexicon: Translocation, Mesothelial Cells, Fibrogenic, Carcinogenic, Inflammation, Crocidolite, Chrysotile, Interstitial.

Related studies

• Asbestos induces nuclear factor kappa B (NF-kappa B) DNA-binding activity and NF-kappa B-dependent gene expression in tracheal epithelial cells — Y.M. Janssen, A. Barchowsky, et al. (1995)
• Crocidolite activates NF-kappa B and MIP-2 gene expression in rat alveolar epithelial cells. Role of mitochondrial-derived oxidants — K.E. Driscoll, J.M. Carter, et al. (1998)
• Possible role of lipid peroxidation in the induction of NF-kappa B and AP-1 in RFL-6 cells by crocidolite asbestos: evidence following protection by vitamin E — S.P. Faux, P.J. Howden (1997)
• Patterns of 8-hydroxydeoxyguanosine formation in DNA and indications of oxidative stress in rat and human pleural mesothelial cells after exposure to crocidolite asbestos — H. Fung, Y.W. Kow, et al. (1997)
• Patterns of c-fos and c-jun proto-oncogene expression, apoptosis, and proliferation in rat pleural mesothelial cells exposed to erionite or asbestos fibers — C.R. Timblin, G.D. Guthrie, et al. (1998)
• Expression and activity of urokinase and its receptor in endothelial and pulmonary epithelial cells exposed to asbestos — A. Barchowsky, R.R. Roussel, et al. (1998)

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