Characterization of activated proto-oncogenes in chemically transformed Syrian hamster embryo cells

Our plain-English summary of Characterization of activated proto-oncogenes in chemically transformed Syrian hamster embryo cells, by T.M. Gilmer, L.A. Annab, J.C. Barrett (Molecular Carcinogenesis, 1988).

The study

• Authors: T.M. Gilmer, L.A. Annab, J.C. Barrett
• Journal: Molecular Carcinogenesis
• Published: 1988;1(3):180-8
• Cited by: 23 articles, as counted by NIH iCite
• Read it: PubMed · Publisher

Abstract

The Syrian hamster embryo (SHE) cell transformation model has been used by many investigators to study the multistep process of neoplastic transformation induced by chemical carcinogens. In this study we have attempted to determine if activated proto-oncogenes are present in the transformed cells induced by a variety of chemical carcinogens. Twelve carcinogen-induced hamster cell lines, established by treatment of normal SHE cells with benzo[a]pyrene, diethylstilbestrol, or asbestos, were examined. One spontaneously transformed cell line (BHK-A) was also studied. Some of the cell lines were also tested for oncogene activation at the preneoplastic stage, before they acquired tumorigenic potential. DNAs from normal, preneoplastic, and neoplastic cells were tested by transfection into mouse NIH 3T3 cells, and morphologically transformed foci were scored on the contact-inhibited monolayer of 3T3 cells. The frequency of focus formation for normal SHE cell DNA was less than 0.0008 foci/microgram DNA, while approximately 40% (5 of 12) of the DNAs from carcinogen-induced, tumorigenic hamster cell lines induced foci at a frequency of greater than or equal to 0.012 foci/microgram DNA. The other seven carcinogen-induced cell lines and the BHK-A cells were negative (less than 0.002 foci/microgram DNA). When the DNAs from transformed foci induced by the five positive cell lines were retransfected into NIH 3T3 cells, the frequency of secondary foci of 3T3 cells was as much as 50-fold higher (1.34 foci/microgram DNA) than with the primary transfectants. DNAs from transformed foci or tumors derived from transformed foci were screened by Southern blot analyses with known oncogenes and with a hamster repetitive DNA probe for the presence of transfected hamster oncogenes.(ABSTRACT TRUNCATED AT 250 WORDS)

In plain English

This was a laboratory study of hamster cells grown in culture, not of people. The authors examined twelve cell lines made by treating normal Syrian hamster embryo cells with benzo[a]pyrene, diethylstilbestrol or chrysotile asbestos, plus one spontaneously transformed line (BHK-A1). They transferred DNA from these cells into mouse NIH 3T3 cells to look for activated cancer genes (oncogenes). DNA from normal hamster cells gave fewer than 0.0008 transformed foci per microgram of DNA. DNA from 5 of the 12 carcinogen-induced, tumor-forming lines produced foci, including one of the two asbestos-transformed lines. BHK-A1 was negative. In four of the five positive lines, the transferred gene was a hamster Ha-ras gene, probably altered at codon 12. The fifth line (BP6T) appeared to carry a non-ras gene. DNA from five lines tested at the earlier, non-tumor-forming stage was negative. The authors concluded that about 40% of these lines had activated Ha-ras, although their own counts showed Ha-ras in 4 of the 12. They also concluded that this activation was a late step and that other test systems are needed.

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 (DNA transfection assay in NIH 3T3 mouse cells, with Southern blot and protein analyses)
• Who was studied: Twelve carcinogen-induced Syrian hamster embryo (SHE) cell lines and one spontaneously transformed hamster cell line (BHK-A1), plus normal SHE cells as a comparison; some lines were also tested at the preneoplastic stage
• Exposure: Hamster cells treated with chrysotile asbestos at 2 micrograms per square centimeter, diethylstilbestrol at 1 or 0.1 micrograms per mL, or benzo[a]pyrene at 1 microgram per mL; two of the twelve lines were asbestos-induced
• Main results:
  • DNA from normal SHE cells produced fewer than 0.0008 transformed foci per microgram of DNA. Positive tumor cell DNAs produced primary foci at a minimum of 0.012 foci per microgram of DNA.
  • 5 of 12 chemically transformed lines showed transforming activity: two of six diethylstilbestrol-transformed lines, two of four benzo[a]pyrene-transformed lines, and one of two asbestos-transformed lines
  • On a second round of transfection, transforming activity increased as much as 50-fold, up to 1.34 foci per microgram of DNA
  • Four of the five positive transformants contained newly acquired hamster Ha-ras sequences (not Ki-ras or N-ras). That is 4 of the 12 carcinogen-induced lines. The altered p21ras protein was consistent with a mutation at codon 12.
  • Activated Ha-ras was found in cell lines induced by each of the three carcinogens studied (benzo[a]pyrene, diethylstilbestrol and asbestos)
  • DNA from all five carcinogen-induced lines tested at the preneoplastic stage was negative. Tumor-forming cells derived from two of these lines were positive.
  • One benzo[a]pyrene-derived tumor line (BP6T) transferred hamster sequences but showed no new Ha-ras, Ki-ras or N-ras genes and no altered p21ras; its transforming gene appeared to be a non-ras oncogene
• The authors' conclusion: The authors concluded that about 40% of the chemically transformed Syrian hamster tumor cell lines had activated Ha-ras oncogenes. Their own reported counts were 5 of 12 lines with transforming activity and Ha-ras in 4 of those 5, which is 4 of 12. They concluded that Ha-ras activation was a late step, after immortalization. They suggested it was probably a spontaneous secondary event not directly caused by the carcinogen. They also stated that alternative assays are needed because about 60% of lines were inactive in this test.
• Limitations the authors state:
  • The authors could not rule out that a small subset of preneoplastic cells carried an activated Ha-ras gene that the assay could not detect
  • Most tumor-forming lines were inactive in the NIH 3T3 assay, so the authors stated that other assay systems are needed to detect transforming genes

Related studies

• Asbestos and benzo(a)pyrene synergism in the transformation of Syrian hamster embryo cells — J.A. DiPaolo, A.J. DeMarinis, et al. (1983)
• Morphological transformation of Syrian hamster embryo cells induced by mineral fibres and the alleged enhancement of benzo[a]pyrene — S.O. Mikalsen, E. Rivedal, et al. (1988)
• An early, nonrandom karyotypic change in immortal Syrian hamster cell lines transformed by asbestos: trisomy of chromosome 11 — M. Oshimura, T.W. Hesterberg, et al. (1986)
• Detection of aneuploidy-inducing carcinogens in the Syrian hamster embryo (SHE) cell transformation assay — D.P. Gibson, M.J. Aardema, et al. (1995)
• In vitro cytotoxicity and transforming potential of industrial carbon dust (fibers and particles) in syrian hamster embryo (SHE) cells — C. Darne, F. Terzetti, et al. (2010)
• 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)

Browse more research in Molecular Carcinogenesis, or return to medical research.