GRP78, HSP72/73, and cJun stress protein levels in lung epithelial cells exposed to asbestos, cadmium, or H2O2

Our plain-English summary of GRP78, HSP72/73, and cJun stress protein levels in lung epithelial cells exposed to asbestos, cadmium, or H2O2, by C.R. Timblin, Y.M. Janssen, J.L. Goldberg, et al (Free Radical Biology & Medicine, 1998).

The study

• Authors: C.R. Timblin, Y.M. Janssen, J.L. Goldberg, B.T. Mossman
• Journal: Free Radical Biology & Medicine
• Published: 1998;24(4):632-42
• Cited by: 49 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Occupational exposure to crocidolite asbestos is associated with the development of nonmalignant and malignant pulmonary disease. Considerable evidence indicates that the mechanisms of asbestos-induced toxicity involve the production of active oxygen species (AOS). Production of AOS in excess of cellular defenses creates an environment of oxidative stress and stimulates the expression of a number of different genes whose products may be involved in mediating responses from oxidant injury. To further investigate the mechanisms of asbestos-induced pathogenicity, we have examined by Western blot analyses the induction of the stress response proteins GRP78 and HSP72/73 in rat lung epithelial cells (RLE) exposed to crocidolite asbestos. In comparative studies, we also examined GRP78, HSP72/73, and cJun expression in RLE cells exposed to equitoxic concentrations of cadmium chloride (CdCl2) and hydrogen peroxide (H2O2). Our results demonstrate that asbestos and H2O2 do not alter GRP78 or HSP72/73 protein levels in RLE cells, but do increase levels of cJun protein. Increases by asbestos and H2O2 were not accompanied by alterations in cellular glutathione levels in this cell type, but asbestos caused elevations in protein levels of manganese-containing superoxide dismutase (MnSOD), an indirect indicator of oxidant stress. In contrast, exposure of cells to CdCl2 led to no changes in MnSOD protein levels, but increases in GRP78, HSP72/73, and cJun proteins as well as significant increases in oxidized and reduced thiol pools. Results suggest that environmental agents causing oxidative injury to lung epithelium elicit different patterns of stress responses.

In plain English

This was a laboratory study of rat lung cells grown in dishes. The cells came from a rat lung cell line called RLE, which grows indefinitely. The authors exposed the cells to crocidolite asbestos and, for comparison, to cadmium chloride or hydrogen peroxide. They first measured how many cells died at different doses, then chose roughly equally toxic doses of each agent. They measured stress-response proteins (GRP78, HSP72/73 and cJun), an antioxidant enzyme (MnSOD) and glutathione. Crocidolite did not change GRP78 or HSP72/73 levels. Levels of cJun and MnSOD both rose at 24 and 48 hours, and glutathione did not change. Hydrogen peroxide also left GRP78 and HSP72/73 unchanged. It raised cJun at 4 hours, raised MnSOD, and raised glutathione at 24 hours. Cadmium chloride raised GRP78, HSP72/73 and cJun, did not change MnSOD, and significantly increased glutathione. The authors concluded that the three agents produce different patterns of stress protein expression in lung epithelial cells. The study used cells in culture, not people or live animals.

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) cell culture experiment
• Who was studied: RLE cells, a spontaneously immortalized rat type II alveolar epithelial cell line, used between passages 31 and 41; experiments performed in duplicate
• Exposure: NIEHS reference crocidolite asbestos at concentrations printed as 1, 5 and 10 mg/cm2 of dish area. For comparison, cadmium chloride at concentrations printed as 1, 5 and 10 mM and hydrogen peroxide at 100, 200 and 500 mM. Later experiments used approximately equitoxic doses: asbestos at 5 and 10 mg/cm2, cadmium chloride at 10 mM and hydrogen peroxide at 200 mM. Units are as printed and may have lost a micro symbol.
• Main results:
  • Asbestos at 1 mg/cm2 had no effect on cell viability. At 10 mg/cm2, viability was significantly decreased at all time points (8, 24 and 48 h).
  • In cells exposed to crocidolite asbestos, levels of GRP78 and HSP72/73 proteins were not altered.
  • In cells exposed to 5 and 10 mg/cm2 asbestos, increases in cJun protein were apparent at 24 and 48 h.
  • MnSOD protein increased at 24 and 48 h in cells exposed to asbestos (5 and 10 mg/cm2) and to hydrogen peroxide (200 mM).
  • In cells exposed to cadmium chloride (10 mM), MnSOD levels were unaltered at 24 and 48 h.
  • In cells exposed to asbestos, no changes were detected in reduced (GSH) or oxidized (GSSG) glutathione.
  • Hydrogen peroxide for 24 h increased GSH levels.
  • Cadmium chloride produced significant increases in GSH at 24 and 48 h.
  • Cadmium chloride (10 mM) markedly increased GRP78 protein after 48 h.
  • Cadmium chloride increased HSP72/73 protein from as early as 8 h through 48 h.
  • cJun protein in hydrogen peroxide-exposed cells returned to control levels by 24 h, but remained elevated at 48 h in cadmium chloride-exposed cells.
• The authors' conclusion: The authors concluded that crocidolite asbestos, cadmium chloride and hydrogen peroxide, all agents that induce oxidant stress, produce different patterns of stress protein expression in lung epithelial cells.

Topics

Medical terms in this study, explained in our Lexicon: Occupational Exposure, Crocidolite, Oxidative Stress, Glutathione (GSH), Superoxide, Epithelium.

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