Role of alphavbeta5 integrin receptor in endocytosis of crocidolite and its effect on intracellular glutathione levels in human lung epithelial (A549) cells

Our plain-English summary of Role of alphavbeta5 integrin receptor in endocytosis of crocidolite and its effect on intracellular glutathione levels in human lung epithelial (A549) cells, by P. Pande, T.A. Mosleh, A.E. Aust (Toxicology and Applied Pharmacology, 2006).

The study

• Authors: P. Pande, T.A. Mosleh, A.E. Aust
• Journal: Toxicology and Applied Pharmacology
• Published: 2006;210(1-2):70-7
• Cited by: 22 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Crocidolite, containing 27% iron by weight, is the most carcinogenic form of asbestos. Crocidolite fibers are endocytized by alphavbeta5 integrin receptors in rabbit pleural mesothelial cells. We show here that crocidolite fibers are endocytized in human lung epithelial (A549) cells and in primary small airway epithelial (SAEC) cells. Presence of the integrin alphavbeta5 blocking antibody, P1F6, significantly reduced the uptake of crocidolite fibers in A549 cells. Thus, the integrin alphavbeta5 receptor is involved in endocytosis of crocidolite fibers in A549 cells as well. Previously, it has been observed that asbestos fibers lead to changes in the intracellular redox environment, i.e. a marked decrease in intracellular glutathione concentrations and an increase in the extracellular glutathione in A549 cells. In addition, the decrease in intracellular glutathione was found to be largely independent of iron present on the surface of the fiber. A549 cells were treated with crocidolite in the presence of endocytosis inhibitor cytochalasin D. Our data indicate that, upon preventing endocytosis, we were able to reverse the decrease in total intracellular glutathione. The decrease in total intracellular glutathione could also be prevented in the presence of the monoclonal antibody P1F6. Thus, we observed that endocytosis of crocidolite fibers via integrin alphavbeta5 receptor is linked to the marked decrease in total intracellular glutathione in A549 cells.

In plain English

This laboratory study used human lung cells grown in culture. It examined how crocidolite asbestos fibers get inside cells and whether that entry is tied to a drop in the cells' glutathione levels. The authors exposed human lung epithelial (A549) cells, and in some experiments primary small airway epithelial (SAEC) cells, to crocidolite fibers. Using a fluorescent membrane dye and confocal microscopy, they saw fibers taken inside A549 cells, with the alpha-v-beta-5 integrin receptor found around the fibers. The same pattern appeared in SAEC cells. Coating fibers with serum increased the number taken in but not the number attached to the cell surface. An antibody that blocks the receptor (P1F6) significantly reduced fiber uptake, while a non-blocking antibody did not. Crocidolite caused a marked drop in total glutathione inside A549 cells after 6 hours, and the blocking antibody prevented this drop. Cytochalasin D, a drug that stops cells from taking in material, also prevented the drop, with significant differences at 12 and 24 hours. The authors concluded that fiber uptake appears linked to the glutathione decrease.

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 experiments using fluorescence confocal microscopy, receptor-blocking antibodies, an endocytosis inhibitor and glutathione measurement; each experiment repeated three times (n = 3)
• Who was studied: Human lung epithelial type II cells (A549 cell line) and, for the receptor colocalization experiment, primary small airway epithelial cells (SAEC); 100 cells counted per fiber-uptake experiment
• Exposure: Crocidolite asbestos fibers (mean length 10 micrometers, obtained from NIEHS/NTP), uncoated or coated with fetal bovine serum, at 4 micrograms per square centimeter for 2 hours (uptake experiments) or 6 micrograms per square centimeter for 6 to 24 hours (glutathione experiments)
• Main results:
  • Crocidolite fibers were seen inside A549 cells, surrounded by dye-labeled cell membrane, after 2 hours
  • In A549 cells, the alpha-v-beta-5 integrin receptor colocalized with the labeled membrane surrounding the fibers; an identical pattern was seen in SAEC cells
  • Serum-coated fibers were taken into A549 cells in significantly greater numbers than uncoated fibers (P < 0.01), with no difference in the number of fibers attached to the cells
  • The receptor-blocking antibody P1F6 at 50 micrograms per milliliter significantly reduced the number of serum-coated fibers taken into A549 cells (P < 0.01)
  • The non-blocking antibody H5P10 at the same concentration had no significant effect on fiber uptake
  • Crocidolite treatment for 6 hours caused a large decrease in total intracellular glutathione in A549 cells (exact values shown only in a figure)
  • In the presence of antibody P1F6, glutathione levels in crocidolite-treated A549 cells were significantly different from those with crocidolite alone (P < 0.05)
  • Cytochalasin D prevented the time-dependent glutathione decrease in crocidolite-treated A549 cells, with the difference significant at 12 and 24 hours (P < 0.05)
• The authors' conclusion: The authors concluded that crocidolite fibers are taken into A549 cells by binding to alpha-v-beta-5 integrin receptors, and that this uptake appears linked to the marked decrease in intracellular glutathione
• Limitations the authors state:
  • The authors state that how glutathione leaves the cells after crocidolite exposure is not understood and needs further experiments

Topics

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

Medical terms in this study, explained in our Lexicon: Crocidolite, Glutathione (GSH), Carcinogenic, Mesothelial Cells, A549 Cells, Monoclonal Antibody.

Related studies

• Efflux of reduced glutathione after exposure of human lung epithelial cells to crocidolite asbestos — S.A. Golladay, S.H. Park, et al. (1997)
• Vitronectin enhances internalization of crocidolite asbestos by rabbit pleural mesothelial cells via the integrin alpha v beta 5 — A.M. Boylan, D.A. Sanan, et al. (1995)
• Modulation of DNA single-strand breaks by intracellular glutathione in human lung cells exposed to asbestos fibers — A. Puhakka, T. Ollikainen, et al. (2002)
• Regulation of nitric oxide synthase induction by iron and glutathione in asbestos-treated human lung epithelial cells — S.H. Park, A.E. Aust (1998)
• Apoptosis induced by crocidolite asbestos in human lung epithelial cells involves inactivation of Akt and MAPK pathways — A. Baldys, P. Pande, et al. (2007)
• Receptor role of the annexin A2 in the mesothelial endocytosis of crocidolite fibers — K. Yamashita, H. Nagai, et al. (2015)

Browse more research in Toxicology and Applied Pharmacology, or return to medical research.