Asbestos induction of extended lifespan in normal human mesothelial cells: interindividual susceptibility and SV40 T antigen

Our plain-English summary of Asbestos induction of extended lifespan in normal human mesothelial cells: interindividual susceptibility and SV40 T antigen, by L. Xu, B.J. Flynn, S. Ungar, et al (Carcinogenesis, 1999).

The study

• Authors: L. Xu, B.J. Flynn, S. Ungar, H.I. Pass, K. Linnainmaa, K. Mattson, B.I. Gerwin
• Journal: Carcinogenesis
• Published: 1999;20(5):773-83
• Cited by: 23 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

Normal human mesothelial cells from individual donors were studied for susceptibility to asbestos-induction of apoptosis and generation of an extended lifespan population. Such populations were generated after death of the majority of cells and arose from a subset of mesothelial cultures (4/16) whereas fibroblastic cells (5/5) did not develop extended lifespan populations after asbestos exposure. All mesothelial cultures were examined for the presence of SV40 T antigen to obtain information on (i) the presence of SV40 T antigen expression in normal human mesothelial cells and (ii) the relationship between generation of an extended lifespan population and expression of SV40 T antigen. Immunostaining for SV40 T antigen was positive in 2/38 normal human mesothelial cultures. These cultures also had elevated p53 expression. However, the two isolates expressing SV40 T antigen did not exhibit enhanced proliferative potential or develop an extended lifespan population. Asbestos-generated extended lifespan populations were specifically resistant to asbestos-mediated but not to alpha-Fas-induced apoptosis. Deletion of p16Ink4a was shown in 70% of tumor samples. All mesothelioma cell lines examined showed homozygous deletion of this locus which extended to exon 1beta. Extended lifespan cultures were examined for expression of p16Ink4a to establish whether deletion was an early response to asbestos exposure. During their rapid growth phase, extended lifespan cultures showed decreased expression of p16Ink4a relative to untreated cultures, but methylation was not observed, and p16Ink4a expression became elevated when cells entered culture crisis. These data extend the earlier observation that asbestos can generate extended lifespan populations, providing data on frequency and cell type specificity. In addition, this report shows that generation of such populations does not require expression of SV40 T antigen. Extended lifespan cells could represent a population expressing early changes critical for mesothelioma development. Further study of these populations could identify such changes.

In plain English

This was a laboratory cell study, not a study of people. The authors grew normal mesothelial cells from pleural fluid of donors without cancer. They exposed the cells to amosite asbestos at doses near those killing half the cells. Most cells died, but 4 of 16 mesothelial cultures yielded cells that kept dividing longer than controls. None of 5 fibroblast cultures did. These longer-lived cells eventually stopped dividing. They resisted death caused by asbestos but not by an anti-Fas antibody. A virus protein, SV40 T antigen, appeared in 2 of 38 mesothelial cultures. The only one treated with asbestos did not develop the longer lifespan; the authors called this evidence anecdotal given the small numbers. The p16Ink4a gene was lost, relative to a control gene, in 15 of 20 mesothelioma tumor samples and undetectable in 20 mesothelioma cell lines. In the long-lived cells, p16Ink4a protein fell during rapid growth and rose when growth stopped; no methylation was detected in the one region tested. The authors concluded that cells from some donors can gain an extended lifespan after direct laboratory asbestos treatment.

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) study of human cells in culture, with additional molecular analysis of mesothelioma tumor samples and cell lines
• Who was studied: Normal human mesothelial cell cultures grown from pleural effusions of non-cancerous donors (38 isolates tested for SV40 T antigen; 16 treated with asbestos), 5 normal human fibroblast isolates from the Coriell Institute, plus mesothelioma and matched normal lung DNA samples and 20 mesothelioma cell lines
• Exposure: Amosite asbestos of two types (UICC and NAIMA, the NAIMA sample having longer fibers). For the lifespan experiments, doses were close to the LD50 (2.4 or 4.8 micrograms per square centimetre) rather than LD90. Glass beads and mock treatment were used as controls, and an anti-Fas antibody was used as a comparison trigger of cell death.
• Main results:
  • Four of 16 asbestos-treated mesothelial strains generated a population with an extended proliferative lifespan
  • None of the 5 fibroblast isolates showed an increased lifespan after asbestos treatment
  • Mesothelial cells were more sensitive to NAIMA amosite than fibroblasts: LD50 of 2.4 micrograms per square centimetre for mesothelial cells versus 10.8 for fibroblasts
  • In normal mesothelial cells, NAIMA amosite induced more apoptosis than UICC amosite across the doses tested
  • All four extended-lifespan cultures eventually stopped dividing (culture crisis)
  • Extended-lifespan populations showed less asbestos-induced apoptosis than mock-treated cells, but responded to anti-Fas antibody the same way as mock-treated cells
  • SV40 T antigen staining was positive in 2 of 38 normal mesothelial cultures
  • Only one T antigen-positive isolate grew well enough to be treated with asbestos, and it did not develop an extended lifespan
  • In mesothelioma tumor samples compared with matched normal samples, loss of p16Ink4a relative to the control gene XPB was found in 15 of 20 samples (75%)
  • All mesothelioma cell lines tested were negative for the p15Ink4b, p16Ink4a and p14ARF gene regions, whereas normal mesothelial cells and MeT-5A were positive
  • In extended-lifespan cells, p16Ink4a expression decreased during rapid growth and increased again when growth stopped
  • No p16Ink4a methylation was detected in mock-treated or extended-lifespan cells at the one GC island analyzed (results shown for three of the four isolates)
  • p53 and p21 levels were similar in asbestos-treated extended-lifespan cells and in control cells
• The authors' conclusion: The authors concluded that cells from a subset of normal human mesothelial donors can develop an extended lifespan after direct asbestos treatment in vitro, while most cells die. They also concluded that SV40 T antigen expression was not required for this and was not shown to facilitate it.
• Limitations the authors state:
  • The SV40 T antigen findings rest on very few samples and the authors described them as anecdotal
  • The authors noted an alternative explanation: T antigen may in fact have extended the lifespan of the positive cells beyond what it would otherwise have been
  • The data do not identify the mechanism by which the extended-lifespan populations arise
  • The original number of cells in each culture could not be counted precisely
  • Tumor sample values are affected by contamination with stromal tissue
  • The absence of methylation applies only to the GC island the authors analyzed

Topics

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

Medical terms in this study, explained in our Lexicon: Mesothelial Cells, SV40, Apoptosis, Asbestos Exposure, Mesothelioma, Homozygous Deletion.

Related studies

• Effect of simian virus large T antigen expression on cell cycle control and apoptosis in rat pleural mesothelial cells exposed to DNA damaging agents — V. Levresse, S. Moritz, et al. (1998)
• In vitro sensitivity of normal human mesothelial and malignant mesothelioma cell lines to four new chemotherapeutic agents — T. Ollikainen, A. Knuuttila, et al. (2000)
• Human mesothelial cells are unusually susceptible to simian virus 40-mediated transformation and asbestos cocarcinogenicity — M. Bocchetta, I. Di Resta, et al. (2000)
• Expression of genes coding for proteoglycans and Wilms' tumour susceptibility gene 1 (WT1) by variously differentiated benign human mesothelial cells — M. Gulyás, K. Dobra, et al. (1999)
• Differential responses to growth factors by normal human mesothelial cultures from individual donors — J.F. Lechner, M.A. LaVeck, et al. (1989)
• Novel cell imaging techniques show induction of apoptosis and proliferation in mesothelial cells by asbestos — J.L. Goldberg, C.L. Zanella, et al. (1997)

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