Asbestos fibers mediate transformation of monkey cells by exogenous plasmid DNA

Our plain-English summary of Asbestos fibers mediate transformation of monkey cells by exogenous plasmid DNA, by J.D. Appel, T.M. Fasy, D.S. Kohtz, et al (Proceedings of the National Academy of Sciences of the United States of America, 1988).

The study

• Authors: J.D. Appel, T.M. Fasy, D.S. Kohtz, J.D. Kohtz, E.M. Johnson
• Journal: Proceedings of the National Academy of Sciences of the United States of America
• Published: 1988;85(20):7670-4
• Cited by: 56 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

We have tested the ability of chrysotile asbestos fibers to introduce plasmid DNA into monkey COS-7 cells and the ability of this DNA to function in both replication and gene expression. Chrysotile fibers are at least as effective as calcium phosphate in standard transfection assays at optimal ratios of asbestos to DNA. After transfection with chrysotile, a minor percentage of introduced plasmid DNA bearing a simian virus 40 origin of replication replicates after 24 hr. Fragmentation of entering DNA is more prominent with asbestos than with calcium phosphate, and after 72 hr most DNA introduced by asbestos is associated with chromosomal DNA. Cells transfected with plasmid p11-4, bearing the p53 protooncogene, express this gene. Cells transfected with pSV2-neo express a gene conferring resistance of antibiotic G418, allowing isolation of colonies of transformed cells after 18 days. The introduction of exogenous DNA into eukaryotic cells could cause mutations in several ways and thus contribute to asbestos-induced oncogenesis.

In plain English

This laboratory experiment used cultured monkey cells (COS-7), not people. The authors tested whether chrysotile asbestos fibers could carry plasmids (DNA rings) into the cells. They compared it with calcium phosphate, a standard method, and glass fibers. Electron microscopy showed plasmid DNA bound to chrysotile fibers. The plasmid carried a simian virus 40 origin of replication, letting it copy itself in COS-7 cells; 24 hours after chrysotile transfer, a minor percentage had replicated. Much of it was fragmented, and a high proportion joined the cells' chromosomes. A p53 gene plasmid was expressed; asbestos plates had about 1.4 times as many p53-staining cells as calcium phosphate plates. With an antibiotic-resistance plasmid, asbestos plates had 36 to 45 resistant colonies per one million transfected cells at 18 days in four experiments, against 10 to 14 with calcium phosphate. Glass-fiber and no-mineral plates had none. The authors concluded that chrysotile can promote DNA entry into cultured primate cells, consistent with the possibility that this is an aspect of asbestos carcinogenesis. They noted it does not fully account for features such as long latency and synergism with other carcinogens.

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, including electron microscopy of DNA bound to fibers and DNA transfection assays
• Who was studied: Cultured monkey COS-7 cells (for example, 10 to the 6th cells per 100-mm dish in the transfection experiments); no human subjects
• Exposure: UICC Canadian chrysotile sample B, used to carry plasmid DNA (pSV2-neo, or p11-4 carrying the p53 protooncogene) into cells. It was compared with calcium phosphate precipitate and with glass fibers.
• Main results:
  • Electron microscopy showed plasmid DNA bound to the surface of chrysotile fibers. Chrysotile filaments with no added DNA appeared uniformly smooth.
  • After transfection with chrysotile, a minor percentage of the introduced plasmid DNA, which carried a simian virus 40 origin of replication, had replicated at 24 hours. COS-7 cells carry part of the SV40 genome, which allows such plasmids to replicate.
  • Asbestos introduced highly fragmented plasmid DNA into the cells. DNA introduced by calcium phosphate did not show the same extensive fragmentation.
  • Some of the DNA introduced by asbestos could replicate, but a high proportion was integrated into chromosomes.
  • Simply incubating plasmid DNA with chrysotile in buffered saline for several hours did not fragment it. The authors concluded that other factors in the culture media or the cells are needed for the fragmentation.
  • Cells peroxidase-stained for p53 protein 24 hours after transfection with plasmid p11-4, in four experiments: asbestos 125, 130, 140 and 130; calcium phosphate 95, 85, 102 and 88; glass fibers 0, 10, 6 and 0; asbestos without added DNA 5, 3, 0 and 0. Counts were per 2.5 micrograms of DNA per 25 micrograms of mineral agent per 10 to the 5th transfected cells. Asbestos plates had about 1.4 times as many positive cells as calcium phosphate plates.
  • Colonies resistant to the antibiotic G418 18 days after transfection with pSV2-neo, in four experiments: asbestos 45, 36, 37 and 40; calcium phosphate 12, 13, 10 and 14. Counts were per 5 micrograms of DNA per 50 micrograms of mineral agent per 10 to the 6th (one million) transfected cells. Asbestos plates had about 3 times as many colonies.
  • Control plates had no colonies at 18 days. These were plates with DNA and glass fibers, plates with asbestos but no DNA, and plates with DNA but no mineral agent.
• The authors' conclusion: The authors concluded that chrysotile fibers can bind plasmid DNA and promote its entry into primate cells in culture. They found the transformation frequencies consistent with the possibility that transfection is an aspect of asbestos carcinogenesis.
• Limitations the authors state:
  • The authors stated that this mechanism does not fully account for some aspects of asbestos-related cancer, such as the long latency of onset and synergism with other carcinogens.
  • The colony results were not corrected for cell killing caused by asbestos.

Topics

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

Medical terms in this study, explained in our Lexicon: Chrysotile, Oncogenesis.

Related studies

• Chrysotile asbestos fibers mediate transformation of Escherichia coli by exogenous plasmid DNA — N. Yoshida, T. Ikeda, et al. (2001)
• Escherichia coli cells penetrated by chrysotile fibers are transformed to antibiotic resistance by incorporation of exogenous plasmid DNA — N. Yoshida, K. Kodama, et al. (2002)
• Plasmid DNA is released from nanosized acicular material surface by low molecular weight oligonucleotides: exogenous plasmid acquisition mechanism for penetration intermediates based on the Yoshida effect — N. Yoshida, K. Ide (2008)
• Detection of surface free radical activity of respirable industrial fibres using supercoiled phi X174 RF1 plasmid DNA — P.S. Gilmour, P.H. Beswick, et al. (1995)
• Supercoiled plasmid DNA as a model target for assessing the generation of free radicals at the surface of fibres — K. Donaldson, P.S. Gilmour, et al. (1995)
• Chestnut bur-shaped aggregates of chrysotile particles enable inoculation of Escherichia coli cells with plasmid DNA — N. Yoshida, Y. Saeki (2004)

Browse more research in Proceedings of the National Academy of Sciences of the United States of America, or return to medical research.