Human mesothelial cells are unusually susceptible to simian virus 40-mediated transformation and asbestos cocarcinogenicity

Our plain-English summary of Human mesothelial cells are unusually susceptible to simian virus 40-mediated transformation and asbestos cocarcinogenicity, by M. Bocchetta, I. Di Resta, A. Powers, et al (Proceedings of the National Academy of Sciences of the United States of America, 2000).

The study

• Authors: M. Bocchetta, I. Di Resta, A. Powers, R. Fresco, A. Tosolini, J.R. Testa, H.I. Pass, P. Rizzo, M. Carbone
• Journal: Proceedings of the National Academy of Sciences of the United States of America
• Published: 2000;97(18):10214-9
• Cited by: 184 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Mesothelioma, a malignancy associated with asbestos, has been recently linked to simian virus 40 (SV40). We found that infection of human mesothelial cells by SV40 is very different from the semipermissive infection thought to be characteristic of human cells. Mesothelial cells are uniformly infected but not lysed by SV40, a mechanism related to p53, and undergo cell transformation at an extremely high rate. Exposure of mesothelial cells to asbestos complemented SV40 mutants in transformation. Our data provide a mechanistic explanation for the ability of SV40 to transform mesothelial cells preferentially and indicate that asbestos and SV40 may be cocarcinogens.

In plain English

This was a laboratory study of cells, not people. The authors infected human mesothelial cells from patients with congestive heart failure or liver disease, and three fibroblast cultures for comparison, with simian virus 40 (SV40). About 95% of mesothelial cells made the viral protein Tag by 24 hours. About 20% were destroyed by day seven, while almost all Tag-positive fibroblasts were destroyed by then. Mesothelial cells had about 4 times more of the protein p53 than fibroblasts. Lowering p53 increased viral copying and led to destruction of about 50% of mesothelial cells. Infected mesothelial cells formed transformed (abnormally growing) cell clusters at an average of 2 × 10^-4 per cell. Two fibroblast cultures formed none, and the third formed six from 7.4 × 10^7 cells, which did not grow further. Crocidolite asbestos alone transformed no cells but killed mesothelial cells at every concentration tested. Fibroblasts given SV40 genes plus crocidolite formed more clusters than without it (p less than 0.05). A defective SV40 gene set formed clusters in mesothelial cells only together with crocidolite. The authors concluded that asbestos and SV40 may be cocarcinogens.

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 comparing human mesothelial cells with human fibroblasts as controls
• Who was studied: Three primary human mesothelial cell cultures were studied. HM1 and HM2 each came from one patient whose pleural fluid had accumulated because of congestive heart failure. HM3 was pooled from cells of five patients with congestive heart failure or liver disease, and the article does not state the source of those cells. Controls were three human fibroblast cultures: WI38 and MRC-5 (fetal lung) and CCD1069Sk (breast fibroblasts from a 70-year-old woman). The work was done at Loyola University Chicago and collaborating centers. No dates of cell collection are given.
• Exposure: Infection with SV40 strain 776 at a multiplicity of infection of 10. Transfection with plasmids carrying different combinations of the SV40 large and small tumor antigen genes. Crocidolite asbestos from the U.S. National Institute of Environmental Health Sciences at concentrations of 0.1, 0.5, 1.0, 2.5 and 5.0 (the units are garbled in the scanned text), alone or combined with the plasmids.
• Main results:
  • About 95% of mesothelial cells expressed the viral protein Tag as early as 24 hours after infection. In fibroblasts at 48 hours, about 20% of WI38 and 0.5–1% of MRC5 and CCD1069Sk expressed Tag.
  • Seven days after infection, about 20% of mesothelial cells were destroyed (lysed), while most other mesothelial cells expressed Tag with no visible changes. At the same time, almost all Tag-positive fibroblasts were lysed.
  • At 72 hours after infection, fibroblasts contained 10 times more SV40 DNA than mesothelial cells, and fibroblast culture medium contained 12 times more. The authors read this as lower viral replication and rare cell destruction in mesothelial cells.
  • Before infection, mesothelial cells expressed about 4 times more p53 than fibroblasts.
  • When p53 was lowered with an antisense treatment, mesothelial cells made on average about 4 times more SV40 DNA than control-treated cells. Cell destruction occurred in about 50% of the treated mesothelial cells.
  • After infection, the average transformation frequency in mesothelial cells was 2 × 10^-4 (foci per infected cell). No foci developed from 10^7 infected WI38 or 10^7 infected MRC-5 fibroblasts. Six foci developed from 7.4 × 10^7 CCD1069Sk fibroblasts, but these could not be grown in culture.
  • All 16 mesothelial foci that were cultured grew. Fourteen were immortal and were passed up to 76 times; two entered crisis after 30 passages and died.
  • Crocidolite alone caused death of mesothelial cells at all concentrations tested, and at 2.5 about 50% died within 7 days. Fibroblasts tolerated crocidolite well. No foci developed from either cell type exposed to crocidolite alone.
  • Fibroblasts transfected with both SV40 tumor antigen genes and then exposed to crocidolite developed more foci than fibroblasts transfected without crocidolite (9.3 × 10^-6 vs 6 × 10^-6 foci per treated cell; p less than 0.05).
  • Mesothelial cells transfected with a plasmid expressing only the large tumor antigen formed no foci without asbestos. With crocidolite they formed foci at 4 × 10^-4 per treated cell.
• The authors' conclusion: The authors concluded that their data explain why SV40 preferentially transforms mesothelial cells: these cells resist virus-induced cell destruction, which the authors linked to p53 levels. They also concluded that asbestos and SV40 may be cocarcinogens, and that mesothelioma may be an example of cocarcinogenesis between a virus and an environmental carcinogen.
• Limitations the authors state:
  • Electron microscopy suggested fewer viral particles in mesothelial cells, but the authors note it is not a quantitative test.
  • The apparent increase in transformation of mesothelial cells exposed to crocidolite plus both SV40 genes was difficult to quantify because asbestos killed many mesothelial cells.
  • The authors note that effects seen in cell culture may differ from effects in the body, where asbestos may have stronger effects.

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelial Cells, Mesothelioma, SV40.

Related studies

• Simian virus 40 infection down-regulates the expression of nitric oxide synthase in human mesothelial cells — E. Aldieri, S. Orecchia, et al. (2004)
• Simian virus 40 and the human mesothelium — G. Klein (2000)
• Crocidolite asbestos and SV40 are cocarcinogens in human mesothelial cells and in causing mesothelioma in hamsters — B. Kroczynska, R. Cutrone, et al. (2006)
• Progressive aberrant methylation of the RASSF1A gene in simian virus 40 infected human mesothelial cells — S. Toyooka, M. Carbone, et al. (2002)
• The presence of simian-virus 40 sequences in mesothelioma and mesothelial cells is associated with high levels of vascular endothelial growth factor — P. Cacciotti, L. Strizzi, et al. (2002)
• SV40 infection induces telomerase activity in human mesothelial cells — R. Foddis, A. De Rienzo, et al. (2002)

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