Asbestos promotes morphological transformation and elevates expression of a gene family invariably induced by tumor promoters in C3H/10T1/2 cells

Our plain-English summary of Asbestos promotes morphological transformation and elevates expression of a gene family invariably induced by tumor promoters in C3H/10T1/2 cells, by C.L. Parfett, R. Pilon, A.A. Caldeira (Carcinogenesis, 1996).

The study

• Authors: C.L. Parfett, R. Pilon, A.A. Caldeira
• Journal: Carcinogenesis
• Published: 1996;17(12):2719-26
• Cited by: 7 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The murine proliferin gene family, which has been shown to respond consistently to tumor promoters and other cellular pro-oxidant agents in C3H/10T1/2 cells, was used to monitor responses after treatment of these cell cultures with toxic, pro-oxidant asbestos fibres. Proliferin mRNA levels were increased by amosite, crocidolite or chrysotile asbestos fibres, especially in the presence of fresh serum and at low cell densities. Promotion of morphological transformation was confirmed in two-stage focus formation assays using crocidolite at a fibre density that induced proliferin expression. Asbestos-induced gene expression was inhibited by millimolar levels of N-acetylcysteine (NAC), supporting a linkage between: (i) induced oxidant stress that was sufficient to promote morphological transformation; (ii) induction of proliferin expression. Other anti-oxidant compounds (dithiothreitol and pyrrolidine dithiocarbamate) or enzymes (superoxide dismutase and catalase) did not inhibit induced expression. Non-fibrous powders (titanium dioxide, quartz or silica gel) were also effective inducers of proliferin mRNA accumulation. Latex beads and activated charcoal were effective at higher particle densities, implying that ubiquitous particle-induced surface membrane effects can lead to an NAC-reversible step necessary for proliferin induction. The results showed that asbestos resembled all other promoters of morphological transformation in C3H/10T1/2 cells in that an antioxidant-sensitive induction of the proliferin gene family occurred following treatment.

In plain English

This was a laboratory study in a mouse embryo cell line (C3H/10T1/2) grown in culture. The authors measured messages (mRNA) from the proliferin gene family, which they had previously found rise after tumor promoters in these cells. Amosite, crocidolite and chrysotile asbestos raised proliferin mRNA, especially with fresh serum added and at lower cell densities. The antioxidant N-acetylcysteine (NAC) blocked this rise: 4 mM fully repressed the crocidolite effect and 8 mM cut the chrysotile effect by nearly 80%. The enzymes superoxide dismutase and catalase increased it instead. In a two-stage test, crocidolite alone did not increase clusters of transformed cells (foci). Crocidolite added 2 days after removal of medium containing the chemical MCA raised Type II or III foci about 4.3-fold over the combined effects of each agent alone (36 foci on 24 dishes). Non-fibrous materials (charcoal, latex beads, titanium dioxide, silica gel and quartz) also raised proliferin mRNA. The authors concluded that asbestos resembled other promoters of transformation in these cells, with an antioxidant-sensitive rise in proliferin.

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 cell culture experiment (gene expression measurements and two-stage morphological transformation assays)
• Who was studied: the mouse embryo-derived C3H/10T1/2 cell line grown in culture dishes; no people or animals
• Exposure: UICC reference samples of amosite, crocidolite and chrysotile asbestos added to cell cultures. Non-fibrous powders (activated charcoal, latex/polystyrene beads, titanium dioxide, silica gel, quartz) were also tested. The chemical MCA was used as the initiator in transformation assays.
• Main results:
  • In confluent cells, metabolic capacity fell to about 50% of control values within 18 h at 2 micrograms per square centimetre of crocidolite and 8 micrograms per square centimetre of amosite.
  • Neither extra serum alone nor amosite alone (2.8 micrograms per square centimetre) changed proliferin mRNA. In combination, levels rose to about 50% of those seen with the tumor promoter TPA.
  • With crocidolite, and with combined serum and crocidolite, proliferin mRNA reached higher levels as culture density decreased.
  • NAC at 4 mM completely repressed crocidolite-induced expression. NAC at 8 mM reduced chrysotile-induced expression by nearly 80%.
  • Superoxide dismutase and catalase together increased, rather than reduced, asbestos-induced proliferin mRNA.
  • Crocidolite alone did not increase transformed foci above spontaneous numbers.
  • Crocidolite added 2 days after removal of the MCA-containing medium increased transformed foci (Types II and III) about 4.3-fold over the sum of the effects of MCA alone and asbestos alone.
  • In the group given MCA and then crocidolite after 2 days, there were 36 Type II or III foci on 24 dishes (mean 1.5 plus or minus 0.22 per dish).
  • When crocidolite was added 12 days after MCA removal, once cultures were confluent, no increase in transformed foci was seen.
  • All non-fibrous powders tested also increased proliferin mRNA.
  • Counted per cell, chrysotile was the most potent material, giving detectable increases at about 0.7 fibres per cell. Silica gel needed 1.3 particles per cell and latex beads 21 particles per cell.
  • The authors found no evidence that the iron content of the asbestos played a role in inducing proliferin mRNA.
• The authors' conclusion: The authors concluded that asbestos resembled all other promoters of morphological transformation in these cells, in that an antioxidant-sensitive induction of the proliferin gene family followed treatment.
• Limitations the authors state:
  • For particle types other than asbestos, the link between gene induction and promotion of transformation was not tested. For asbestos it was tested only with a single concentration of crocidolite.
  • The experiments were not designed to assess whether the size of the gene effect and the size of the promotion effect were closely correlated.
  • Iron in the culture medium could have coated the fibre surfaces and masked differences in iron content between fibre types.
  • The two toxicity assays (dye reduction and colony formation) were not compared side by side.

Topics

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

Medical terms in this study, explained in our Lexicon: Amosite, Crocidolite, Chrysotile, Superoxide.

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