Oxidant-mediated increases in redox factor-1 nuclear protein and activator protein-1 DNA binding in asbestos-treated macrophages

Our plain-English summary of Oxidant-mediated increases in redox factor-1 nuclear protein and activator protein-1 DNA binding in asbestos-treated macrophages, by D.M. Flaherty, M.M. Monick, A.B. Carter, et al (The Journal of Immunology, 2002).

The study

• Authors: D.M. Flaherty, M.M. Monick, A.B. Carter, M.W. Peterson, G.W. Hunninghake
• Journal: The Journal of Immunology
• Published: 2002;168(11):5675-81
• Cited by: 33 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Alveolar macrophages have been implicated in the pathogenesis of a number of acute and chronic lung disorders. We have previously shown that normal human alveolar macrophages exhibit decreased DNA binding activity of the transcription factor, AP-1, compared with monocytes. Furthermore, this decrease in AP-1 DNA binding appears to be due to a decrease in the redox active protein, redox factor (Ref)-1. Ref-1 is an important redox regulator of a number of transcription factors, including NF-kappaB and AP-1. In this study we evaluated the role of asbestos, a prototypic model of chronic fibrotic lung disease, in Ref-1 expression and activity. We found that incubation with low concentrations of crocidolite asbestos (0.5-1.25 microg/cm(2)) resulted in an increase in nuclear Ref-1 protein after 5 min, with a persistent elevation in protein up to 24 h. Additionally, an increase in nuclear Ref-1 could be induced by treating the cells with an oxidant-generating stimulus (iron loading plus PMA) and inhibited by diphenyleneiodonium chloride, an inhibitor of NADPH oxidase. The asbestos-induced accumulation of nuclear Ref-1 was associated with an increase in AP-1 DNA binding activity. These findings suggest that an exposure associated with fibrotic lung disease, i.e., asbestos, modulates accumulation of nuclear Ref-1 in macrophages, and that this effect is mediated by an oxidant stimulus.

In plain English

This was a laboratory study of cells in dishes, not a study of people's health. The authors exposed macrophages, a type of scavenger cell, to crocidolite asbestos. Some cells came from lung washings of healthy nonsmoking volunteers. Others came from RAW 264.7, a mouse cell line of peritoneal (abdominal) macrophages. The authors measured a protein called Ref-1 in the cell nucleus and the DNA binding of a gene-control factor, AP-1. Crocidolite raised nuclear Ref-1 in both cell types. In the mouse cells the rise appeared within 5 minutes while total cell Ref-1 stayed constant. Asbestos raised oxidant levels in the mouse cells at 30 and 60 minutes. Iron loading plus a chemical called PMA, which makes cells produce oxidants, also raised nuclear Ref-1. A blocker of the oxidant-making enzyme NADPH oxidase reduced the asbestos-induced rises in nuclear Ref-1 and AP-1 binding. Asbestos increased AP-1 binding in human macrophages treated for 24 hours. The authors concluded that crocidolite can increase nuclear Ref-1 in macrophages by a mechanism involving oxidant production. They postulated a possible role in lung fibrosis, which they did not test.

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) experiments on cultured macrophages
• Who was studied: Alveolar macrophages obtained by bronchoalveolar lavage from normal, lifetime-nonsmoking volunteers at the University of Iowa (number of volunteers not stated), and the RAW 264.7 murine macrophage cell line, which the authors describe as a murine peritoneal macrophage cell line
• Exposure: National Institute of Environmental Health Sciences long crocidolite asbestos (geometric mean length 7.1 micrometers), at low concentrations of 0.5 to 1.25 micrograms per square centimeter (0.5 micrograms per square centimeter in most experiments), for times from 5 minutes to 24 hours
• Main results:
  • Crocidolite increased nuclear Ref-1 compared with controls in RAW cells and in human alveolar macrophages
  • In RAW cells, nuclear Ref-1 rose above control levels within 5 minutes of asbestos treatment while total cellular Ref-1 stayed constant; the authors interpreted this as Ref-1 moving into the nucleus
  • In RAW cells, iron loading plus PMA (an oxidant-generating treatment) increased nuclear Ref-1 compared with controls and with PMA alone, reported as statistically significant at the 0.05 level; iron loading alone also gave a significant increase
  • Crocidolite significantly increased reactive oxygen species in RAW cells at 30 and 60 minutes
  • In RAW cells, pretreatment with DPI, an NADPH oxidase inhibitor, blocked the asbestos-induced rise in nuclear Ref-1
  • Human alveolar macrophages treated with asbestos for 24 hours showed increased AP-1 DNA binding compared with controls. In RAW cells, the asbestos-induced increase in AP-1 binding was diminished by DPI (reported at the 0.01 level)
  • In RAW cells given iron and PMA, AP-1 DNA binding rose markedly in cells carrying normal Ref-1. This response was abolished in cells carrying a Ref-1 that lacked its redox function
• The authors' conclusion: The authors concluded that crocidolite asbestos can increase nuclear Ref-1 protein in human alveolar and murine peritoneal macrophages through a mechanism involving production of reactive oxygen species that is inhibited by blocking NADPH oxidase

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, Alveolar Macrophage, Crocidolite.

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)
• The gamma-glutamylcysteine synthetase and glutathione regulate asbestos-induced expression of activator protein-1 family members and activity — A. Shukla, T. Flanders, et al. (2004)
• Cu,Zn-Superoxide Dismutase-Mediated Redox Regulation of Jumonji Domain Containing 3 Modulates Macrophage Polarization and Pulmonary Fibrosis — C. He, J.L. Larson-Casey, et al. (2016)
• 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)
• 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)
• Role of transcription factor NF-kappaB in asbestos-induced TNFalpha response from macrophages — N. Cheng, X. Shi, et al. (1999)

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