Chrysotile asbestos fibers mediate homologous recombination in Rat2 lambda fibroblasts: implications for carcinogenesis

Our plain-English summary of Chrysotile asbestos fibers mediate homologous recombination in Rat2 lambda fibroblasts: implications for carcinogenesis, by K. Lezon-Geyda, C.M. Jaime, J.H. Godbold, et al (Mutation Research, 1996).

The study

• Authors: K. Lezon-Geyda, C.M. Jaime, J.H. Godbold, E.F. Savransky, A. Hope, S.A. Kheiri, Z.M. Dzmura, H. Uehara, E.M. Johnson, T.M. Fasy
• Journal: Mutation Research
• Published: 1996;361(2-3):113-20
• Cited by: 17 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Asbestos fibers are widespread environmental carcinogens whose mutagenicity is now established. Nonetheless, the molecular nature of these mutations and the mechanisms by which they accelerate carcinogenesis remain poorly understood. We have assessed the ability of asbestos fibers to promote homologous recombination, a potent mechanism for generating intrachromosomal rearrangements, such as deletions, and mitotic recombination. For this, we have developed a new assay which determines the extent to which a marker gene present in DNA introduced by asbestos can recombine with homologous genes residing in a transfected cell. We have demonstrated that Calidria chrysotile fibers are mutagenic and are able to mediate transfection of molecularly marked mutant lacI genes in a manner that results in their preferential recombination with homologous wild-type genes in the transfected cell. Asbestos induced recombination events may play a significant role in asbestos mutagenesis and carcinogenesis, and promotion of recombination may underlie the well-recognized synergy of asbestos with other carcinogens.

In plain English

This was a laboratory cell-culture experiment testing whether chrysotile asbestos fibers can promote homologous recombination. The authors exposed Rat2 lambda fibroblasts (Big Blue rat cells, which carry multiple integrated copies of a lambda LIZ shuttle vector containing the lacI target gene) for 3 hours to Calidria chrysotile fibers together with CM3 plasmid DNA, a plasmid carrying a marker C to T point mutation at base pair 977 of lacI. Controls included media only, untreated cells, chrysotile alone, ethyl methanesulfonate (EMS), calcium phosphate transfection with untreated or gamma-irradiated CM3, and a packaging control. Cells given chrysotile plus CM3 had a mutant frequency of 12.87 per 100,000 plaque forming units versus 3.70 for the pooled media control (more than 3-fold); chrysotile alone gave a 2.5-fold increase (9.08), reported as significant at p less than 0.05; EMS gave a 6-fold increase. Calcium phosphate groups did not differ significantly. Seven of 13 sequenced mutants from the chrysotile plus CM3 group (53.8%) carried the CM3 marker mutation, seen in no other group. The authors concluded this reflected homologous recombination rather than chance.

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: in vitro experimental study in a cultured rat cell line, using a newly developed lacI mutagenesis/homologous recombination assay
• Who was studied: Rat2 lambda fibroblasts (Big Blue rat cell line, obtained from Stratagene) carrying integrated copies of a lambda LIZ shuttle vector with the lacI target gene; laboratory work at Mount Sinai School of Medicine, New York
• Exposure: Calidria chrysotile fibers, given with CM3 plasmid DNA or alone (50 micrograms per ml; 6.7 micrograms per square centimetre), for 3 hours; comparison agents were 4.7 mM ethyl methanesulfonate and calcium phosphate transfection with untreated or gamma-irradiated CM3 plasmid DNA (total dose, 999.7 Gy)
• Main results:
  • Cells treated with chrysotile plus CM3 plasmid DNA had a mutant frequency more than 3-fold higher than the media or untreated controls
  • Chrysotile plus CM3 group: 23 blue mutants among 178,635 plaque forming units, mutant frequency 12.87 per 100,000 PFU (Poissonian error 8.16; 18.65), p less than 0.01
  • Pooled media control: 25 blue mutants among 675,625 plaque forming units, mutant frequency 3.70 per 100,000 PFU (2.39; 5.29)
  • Chrysotile alone gave a 2.5-fold increase over the media control, described by the authors as significantly higher than the spontaneous mutant frequency
  • EMS-treated cells had a 6-fold increase in mutant frequency over the media control
  • No calcium phosphate transfection group differed significantly in mutant frequency, indicating transfection alone did not raise mutant frequency
  • In the chrysotile plus CM3 group, 7 of 13 sequenced mutants (53.8%) carried the CM3 marker mutation at base pair 977
  • The marker mutation was found in no other treatment group, and in none of the 14 mutant lacI genes sequenced from the packaging control
  • The authors calculated the probability that seven or more of thirteen spontaneously arising mutants would carry the same specific base change as 2.91 x 10 to the minus 20
• The authors' conclusion: The authors concluded that the seven marker mutations arose by homologous recombination rather than by chance, and that asbestos-induced recombination may contribute to asbestos mutagenesis and carcinogenesis and to the synergism of asbestos with other carcinogens
• Limitations the authors state:
  • The authors raised, and argued against, the possibility that the seven marker mutants came from expansion of a single mutant clone rather than independent events
  • The authors noted that asbestos-induced mitotic recombination events would generally have no consequence unless the chromosomes already carried prior mutations

Mines named here

Asbestos mines this study is about. Each mine's page says who ran it, when it worked, and what it produced.

• Santa Rita mine, Joaquin Ridge near Coalinga, California

All asbestos mines

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, Fibroblast, Carcinogenesis, Calidria.

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• Mutagenesis by asbestos in the lung of lambda-lacI transgenic rats — J. Topinka, P. Loli, et al. (2004)

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