Tumorigenicity of human mesothelial cell line transfected with EJ-ras oncogene

Our plain-English summary of Tumorigenicity of human mesothelial cell line transfected with EJ-ras oncogene, by R.R. Reddel, L. Malan-Shibley, B.I. Gerwin, et al (Journal of the National Cancer Institute, 1989).

The study

• Authors: R.R. Reddel, L. Malan-Shibley, B.I. Gerwin, R.A. Metcalf, C.C. Harris
• Journal: Journal of the National Cancer Institute
• Published: 1989;81(12):945-8
• Cited by: 27 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

We performed this study to determine whether human mesothelial cells are capable of undergoing neoplastic change in vitro and to observe their interaction with the activated c-Ha-ras (HRAS1) oncogene EJ-ras, which has a role in the development of many malignant human tumors. Mesothelial cells are presumed to be the progenitor cells of malignant mesothelioma, a cancer strongly correlated with asbestos exposure. Previously, we established a non-tumorigenic cell line, MeT-5A, from normal human mesothelial cells after transfection with a plasmid containing the simian virus 40 (SV40) early-region genes. In the present study, we performed transfection of a plasmid containing the EJ-ras gene and the neomycin-resistance gene into these cells and selected a population resistant to G418, a neomycin analogue. Cells from this cell line formed rapidly growing sc tumors in NIH Swiss athymic nude mice, but untransfected with the vector DNA and selected for G418 resistance formed no tumors. The tumors formed by EJ-ras-transfected cells were established in vitro, and cells from these tumor cell lines exhibited a characteristic altered morphology. The cells had the same isoenzyme phenotype as the parent cells, and they expressed the mutant EJ-ras p21 protein. This first demonstration of malignant transformation of human mesothelial cells in vitro may permit molecular analysis of mesothelial carcinogenesis.

In plain English

This laboratory study asked whether human mesothelial cells, presumed to be the cells from which malignant mesothelioma arises, could become cancerous in the laboratory. The authors used MeT-5A, a cell line they had earlier made from normal human mesothelial cells using simian virus 40 (SV40) genes, and inserted the mutant cancer gene EJ-ras. No asbestos was used in this experiment. The altered cells were injected under the skin of immune-deficient (athymic nude) mice. In a first experiment, all 10 mice developed tumors 1.0 cm across, in a mean of 6 weeks. In a second, 7 of 10 did, in a mean of 9 weeks. Mice given MeT-5A cells without EJ-ras, either untransfected or carrying only the control vector, developed no tumors within 52 weeks. Tests indicated the tumor cells came from the injected human cells. The authors concluded that human mesothelial cells can become fully malignant in the laboratory. They noted the tumors were consistent with, but not diagnostic of, mesothelioma, and that whether ras genes act in naturally occurring mesothelioma was not yet known.

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 experiment: a human cell line was genetically altered in culture and its ability to form tumors was tested by injection into mice
• Who was studied: The MeT-5A human mesothelial cell line, which the authors had earlier made from normal human mesothelial cells using SV40 early-region genes. Tumor formation was tested in irradiated NIH Swiss athymic nude mice under 60 days old, each injected with 5 million cells (10 mice per group per experiment). The work was done at the National Cancer Institute, Bethesda, MD.
• Exposure: Transfection of MeT-5A cells with a plasmid carrying the activated c-Ha-ras (HRAS1) oncogene EJ-ras and a neomycin-resistance gene. Controls were cells given the vector DNA (pSV2neo) only, and untransfected cells. No asbestos exposure was part of this experiment.
• Main results:
  • Experiment 1: all 10 mice injected with EJ-ras-transfected cells developed tumors reaching 1.0 cm in diameter, in a mean time of 6 ± 1 (SD) weeks
  • Experiment 2: 7 of the 10 mice injected with EJ-ras-transfected cells developed tumors reaching 1.0 cm in diameter
  • In experiment 2, those tumors reached 1.0 cm in a mean of 9 ± 3 weeks. In the other three mice, nodules reached 3 to 8 mm and then regressed.
  • Mice injected with vector-only (MeT-5A/pSV2neo) cells or untransfected MeT-5A cells developed no tumors within 52 weeks
  • Fragments of three tumors from experiment 1 implanted into new mice all grew to 1.0 cm within 2 to 3 weeks (one later regressed completely)
  • Cells from tumor cell lines MEJ-T2 and MEJ-T10 formed 1.0-cm tumors in mice within 2 weeks of injection
  • The tumors consisted of pleomorphic, undifferentiated, clearly malignant cells
  • Isoenzyme analysis of two tumor cell lines matched the parent MeT-5A cells
  • The mutant (codon-12 valine) ras p21 protein was detected in EJ-ras-transfected cells and in cells from the tumor cell lines
• The authors' conclusion: The authors concluded that cells derived from human mesothelium can be transformed to a fully malignant type in the laboratory
• Limitations the authors state:
  • The appearance of the mouse tumors was consistent with mesothelioma but not diagnostic of it
  • The tumors grew faster than those typically formed by mesothelioma cell lines
  • The authors suggested the differences in tumor behavior and lack of differentiation may relate to the experimental protocol, including the long time the cells were kept in culture
  • It was not yet known whether ras oncogenes are active in naturally occurring mesothelioma

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, Malignant Mesothelioma, Asbestos Exposure, SV40, Malignant Transformation, Carcinogenesis.

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