Role of transcription factor NF-kappaB in asbestos-induced TNFalpha response from macrophages

Our plain-English summary of Role of transcription factor NF-kappaB in asbestos-induced TNFalpha response from macrophages, by N. Cheng, X. Shi, J. Ye, et al (Experimental and Molecular Pathology, 1999).

The study

• Authors: N. Cheng, X. Shi, J. Ye, V. Castranova, F. Chen, S.S. Leonard, V. Vallyathan, Y. Rojanasakul
• Journal: Experimental and Molecular Pathology
• Published: 1999;66(3):201-10
• Cited by: 19 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Asbestos exposure in humans is associated with inflammatory, fibrotic, and malignant diseases in the lung. Increasing evidence supports the hypothesis that the production of proinflammatory cytokines such as tumor necrosis factor-alpha (TNFalpha) is an important mediator of the pathologic responses of asbestosis. In this study, we examine the role of nuclear transcription factor-kappaB (NF-kappaB) and free oxygen radicals in asbestos-induced TNFalpha gene and protein expression in lung macrophages. Exposure of the cells to crocidolite asbestos caused a parallel increase in TNFalpha production and NF-kappaB activation, as analyzed by enzyme-linked immunosorbent assay and electrophoretic mobility shift assay. Inhibition of NF-kappaB by SN50, an inhibitor of NF-kappaB nuclear translocation, or by sequence-specific oligonucleotides directed against the NF-kappaB binding site of TNFalpha promoter attenuated the asbestos effect on TNFalpha production. Gene transfection assays using an expression plasmid containing a luciferase reporter gene and a TNFalpha-derived NF-kappaB gene promoter further indicated the dependence of NF-kappaB activation on asbestos-induced gene expression. The effects of asbestos on NF-kappaB and TNFalpha activation were inhibited by oxygen radical scavengers and were enhanced by antioxidant enzyme inhibitors. These results indicate that asbestos-induced TNFalpha gene expression is mediated through a process that involves NF-kappaB activation and free radical reactions.

Copyright 1999 Academic Press.

In plain English

This was a laboratory study in cells, not a study of people or of disease rates. The authors exposed macrophages, a type of immune cell, to crocidolite asbestos. Some cells came from the lungs of male Sprague–Dawley rats and some were a macrophage cell line called RAW 264.7. They measured TNF-alpha, an inflammation-related protein, and the activity of NF-kappaB, a protein that switches genes on. In rat lung macrophages, crocidolite raised TNF-alpha production, and the rise grew with dose and time. Titanium dioxide, used as a comparison dust, had no such effect. Crocidolite also increased NF-kappaB activity with dose. Blocking NF-kappaB, either with a peptide called SN50 or with a matching DNA fragment, reduced the TNF-alpha response. A control DNA fragment had no effect. Substances that remove free radicals or bind metals lowered both responses, and blocking one antioxidant enzyme increased TNF-alpha. The authors concluded that crocidolite activates TNF-alpha production in macrophages and that NF-kappaB activation through metal-mediated free radical reactions is an important step.

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) experiment on cultured cells. It used protein measurement (ELISA), DNA-binding assays (EMSA) and reporter-gene (luciferase) transfection assays.
• Who was studied: Alveolar macrophages collected by lung lavage from male Sprague–Dawley rats, and the macrophage cell line RAW 264.7. The gene transfection experiments used only RAW 264.7 cells, because the rat lung macrophages could not be transfected.
• Exposure: Crocidolite asbestos obtained from NIOSH, originally from a mine in South Africa. Concentrations were printed as 25–100 mg/ml, with 50 mg/ml typical and described as subcytotoxic; the unit symbol appears damaged (see text problems). Exposures lasted up to 24 hours. Titanium dioxide served as a nonfibrogenic control dust.
• Main results:
  • In rat alveolar macrophages and RAW 264.7 cells, crocidolite increased TNF-alpha production in a dose- and time-dependent manner. The response leveled off at about 8 hours, at a concentration printed as approximately 50 mg/ml.
  • Titanium dioxide, the control dust, did not stimulate TNF-alpha secretion.
  • At the optimal stimulating condition, the authors reported that asbestos did not cause a significant toxic effect on the cells compared with controls. The trypan blue figures were 7 plus or minus 3% for treated cells versus 5 plus or minus 4% for controls, with 4 replicates.
  • In rat alveolar macrophages, the NF-kappaB inhibitor SN50 completely inhibited crocidolite-induced TNF-alpha production.
  • A DNA fragment matching the NF-kappaB binding site of the TNF-alpha gene inhibited TNF-alpha production, while the nonspecific control fragment (C-ON) had no effect.
  • In rat alveolar macrophages exposed to crocidolite for 6 hours, NF-kappaB binding activity rose with dose.
  • In transfected RAW 264.7 cells, crocidolite caused a dose-dependent increase in TNF-alpha promoter (reporter gene) activity, which SN50 inhibited.
  • In RAW 264.7 cells pretreated with sodium formate (a free radical scavenger) or deferoxamine (a metal chelator), NF-kappaB activity fell with dose, and TNF-alpha production fell in parallel.
  • Mercaptosuccinate, an inhibitor of glutathione peroxidase, increased TNF-alpha secretion. Diethyldithiocarbamic acid, an inhibitor of superoxide dismutase, decreased it.
• The authors' conclusion: The authors concluded that crocidolite asbestos can activate TNF-alpha production in macrophages and that NF-kappaB inhibitors and free radical scavengers can inhibit this activation. They further concluded that NF-kappaB activation through metal-mediated free radical reactions is an important step in asbestos-induced TNF-alpha production.

Topics

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

Medical terms in this study, explained in our Lexicon: Macrophage, Asbestos Exposure, Cytokine, Tumor Necrosis Factor-alpha (TNF-α), Crocidolite, Translocation.

Related studies

• Iron and reactive oxygen species in the asbestos-induced tumor necrosis factor-alpha response from alveolar macrophages — P.P. Simeonova, M.I. Luster (1995)
• Activated TNF-alpha/NF-kappaB signaling via down-regulation of Fas-associated factor 1 in asbestos-induced mesotheliomas from Arf knockout mice — D.A. Altomare, C.W. Menges, et al. (2009)
• Alveolar macrophage cytokine and growth factor production in a rat model of crocidolite-induced pulmonary inflammation and fibrosis — K.E. Driscoll, J.K. Maurer, et al. (1995)
• TNF-alpha inhibits asbestos-induced cytotoxicity via a NF-kappaB-dependent pathway, a possible mechanism for asbestos-induced oncogenesis — H. Yang, M. Bocchetta, et al. (2006)
• Lung mesothelial cell and fibroblast responses to pleural and alveolar macrophage supernatants and to lavage fluids from crocidolite-exposed rats — I.Y. Adamson, H. Prieditis, et al. (1997)
• Differential proliferation of rat lung fibroblasts induced by the platelet-derived growth factor-AA, -AB, and -BB isoforms secreted by rat alveolar macrophages — J.C. Bonner, A.R. Osornio-Vargas, et al. (1991)

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