Malignant transformation of immortalized human bronchial epithelial cells by asbestos fibers

Our plain-English summary of Malignant transformation of immortalized human bronchial epithelial cells by asbestos fibers, by T.K. Hei, L.J. Wu, C.Q. Piao (Environmental Health Perspectives, 1997).

The study

• Authors: T.K. Hei, L.J. Wu, C.Q. Piao
• Journal: Environmental Health Perspectives
• Published: 1997;105 Suppl 5(Suppl 5):1085-8
• Cited by: 28 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

Although asbestos is a well-established lung carcinogen, there currently is no suitable human cell model in which to examine the underlying cellular and molecular changes associated with fiber-mediated bronchial carcinogenesis. Using a recently established transformation model based on a human papillomavirus-immortalized human bronchial epithelial cell line, we successfully transformed these BEP2D cells after a single, 7-day treatment with a 20-microgram/ml (4 micrograms per cm2 area) dose of Union Internationale Contre le Cancer (UICC) Rhodesian chrysotile fibers. Asbestos treatment resulted in a surviving fraction of 0.18 compared to control cells. Transformed cells developed through a series of sequential steps, including altered growth kinetics, resistance to serum-induced terminal differentiation, and anchorage-independent growth, before becoming tumorigenic to form progressively growing tumors in nude mice. Seven tumorigenic cell lines were isolated and determined to be of human epithelial origin based on immunofluorescent staining of keratin and isozyme analysis. Analysis of tumor DNA revealed no mutations at either codon 12 or 13 in any the ras oncogenes. An independent role for K-ras mutation in fiber carcinogenesis, therefore, cannot be confirmed. This model provides a unique opportunity to study the cellular and molecular changes at the various stages in fiber-mediated neoplastic transformation of human bronchial epithelial cells.

In plain English

This was a laboratory study of BEP2D, a human bronchial (airway lining) cell line. The cells had been made to grow indefinitely with human papillomavirus but did not form tumors in mice. The authors treated the cells once, for 7 days, with UICC Rhodesian chrysotile asbestos fibers. At the higher dose, the surviving fraction was 0.18 compared with untreated cells. Treated cells injected into nude mice at an early stage formed no tumors (0 of 3 mice). With further culture, the cells changed step by step. They resisted serum-induced terminal differentiation, which normally stops these cells dividing, and grew in soft agar. Such colonies appeared after 11 weeks at frequencies of 0.25 to 0.8%. Later-stage cells formed tumors in mice, described as carcinomas: seven tumors in five mice. No mice given control cells formed tumors (0 of 37, including historical controls). None of the four tumor cell lines shown had a mutation at codon 13 of the K-ras gene. The authors reported similar negative results at other ras gene sites. The authors concluded that chrysotile-treated cells went through gradual, sequential changes before becoming tumorigenic in nude mice.

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 (in vitro) transformation experiment, with tumor-formation testing of the cells in nude mice
• Who was studied: BEP2D, a human papillomavirus (HPV18)-immortalized human bronchial epithelial cell line, at passages 21 and 22 (3 x 10^6 to 5 x 10^6 cells per treatment), studied at Columbia University, New York. Athymic nude mice were injected with the cells: 8 with asbestos-treated cells per Table 1, and 3 with control cells plus 34 historical controls.
• Exposure: UICC standard reference Rhodesian chrysotile fibers, given as a single 7-day treatment at two doses printed as 10 or 20 per milliliter (the unit symbol is garbled in the scanned text)
• Main results:
  • In the asbestos-treated BEP2D cells, the single treatment left a surviving fraction of 0.18 compared to control cells
  • Treated cells injected into nude mice at an early stage (cell line Asb7Fc, 2 weeks after treatment) formed no tumors (0 of 3 mice in Table 1)
  • After 11 weeks of continuous culture, agar-positive (anchorage-independent) colonies of the treated cells emerged at frequencies of 0.25 to 0.8%
  • In contrast to control cells, the tumorigenic clone AsbTL grew equally well with or without serum and TPA (resistance to terminal differentiation)
  • Later-stage treated cells produced tumors at the injection site after 8 to 10 weeks. Seven tumors were obtained from five nude mice (2 of 2 mice for line Asb7, 3 of 3 for AsbTL), and the tumors were carcinoma in nature.
  • No tumors formed in mice given control cells: 0 of 3 control animals plus 34 historical controls, followed up to 22 weeks
  • When AsbTL tumor cells were reinjected into nude mice, secondary tumors appeared after a shorter latency of 2 to 3 weeks
  • None of the four asbestos-induced tumorigenic cell lines examined had mutations at codon 13 of K-ras. Similar negative results were reported at codon 12 of K-ras and at codons 12 and 13 of H-ras and N-ras (data not shown).
• The authors' conclusion: The authors concluded that chrysotile-treated BEP2D cells undergo gradual, sequential changes of altered growth and anchorage-independent growth before becoming tumorigenic in nude mice

Topics

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

Medical terms in this study, explained in our Lexicon: Malignant Transformation, Carcinogenesis, UICC, Chrysotile.

Related studies

• Karyotype analysis of tumorigenic human bronchial epithelial cells transformed by chrysolite asbestos using chemically induced premature chromosome condensation technique — M. Suzuki, C.Q. Piao, et al. (2001)
• Differentially expressed genes in asbestos-induced tumorigenic human bronchial epithelial cells: implication for mechanism — Y.L. Zhao, C.Q. Piao, et al. (2000)
• Role of mesothelin in carbon nanotube-induced carcinogenic transformation of human bronchial epithelial cells — X. He, E. Despeaux, et al. (2016)
• Chrysotile Causes Human Bronchial Epithelial Cell Apoptosis in Response to the Fas-Mediated Apoptosis Pathway — M. Zhang, J. Chen, et al. (2017)
• Neoplastic-like transformation effect of single-walled and multi-walled carbon nanotubes compared to asbestos on human lung small airway epithelial cells — L. Wang, T.A. Stueckle, et al. (2014)
• Spontaneously immortalized mouse mesothelial cells display characteristics of malignant transformation — A.L. Sherwood, S.E. Mutsaers, et al. (2008)

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